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Oceans on Mars

2026-04-17T18:23:04Z

Suitupshowup: /* Was there enough water */ added new info and ref about shorelines

Article written by Jim Secosky. Jim is a retired science teacher who has used the Hubble Space Telescope, the Mars Global Surveyor, and HiRISE.

[[File:Marsoceanimage.jpg|600pxr| Drawing showing the extent of ocean on Mars]]

Today, much evidence supports at least one ocean in the past on Mars.<ref>https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4872529/</ref> <ref> Carr, M. & J. Head. 2010 Geologic history of Mars. Earth and Planetary Science Letters. 294. 185-203.</ref> <ref>Clifford, S. M.; Parker, T. J. (2001). "The Evolution of the Martian Hydrosphere: Implications for the Fate of a Primordial Ocean and the Current State of the Northern Plains". Icarus. 154 (1): 40–79. Bibcode:2001Icar..154...40C. doi:10.1006/icar.2001.6671</ref> <ref> Baker, V. R.; Strom, R. G.; Gulick, V. C.; Kargel, J. S.; Komatsu, G.; Kale, V. S. (1991). "Ancient oceans, ice sheets and the hydrological cycle on Mars". Nature. 352 (6336): 589–594. Bibcode:1991Natur.352..589B. doi:10.1038/352589a0. </ref> <ref>Lucchitta, B. et al. 1986. Sedimentary deposits in the northern lowland plains, Mars. Proc. Lunar planet. Conf. 17th, part 1, j. Geophys. Res., 91, suppl., E166-E174.</ref> Support for the idea of Martian oceans was boosted when it was concluded that Mars has [[Atmospheric loss |lost most of its atmosphere]] (and water).<ref>Villanueva G. L., Mumma M. J., Novak R. E., Käufl H. U., Hartogh P., Encrenaz T., Tokunaga A., Khayat A., and Smith M. D., Science, Published online 5 March 2015 [DOI:10.1126/science.aaa3630]</ref> <ref> Villanueva, G., et al. 2015. Strong water isotopic anomalies in the martian atmosphere: Probing current and ancient reservoirs. Science 10 Apr 2015: Vol. 348, Issue 6231, pp. 218-221. </ref> <ref> https://www.nasa.gov/press-release/nasas-maven-reveals-most-of-mars-atmosphere-was-lost-to-space </ref> <ref> B.M. Jakosky et al. 2017. Mars’ atmospheric history derived from upper-atmosphere measurements of 38Ar/36Ar. Science 355 (6332): 1408-1410; doi: 10.1126/science.aai7721 </ref> <ref> http://www.sci-news.com/space/maven-martian-atmosphere-lost-space-04750.html</ref> In addition, researchers in 2015 published a paper detailing two tsunamis that happened when asteroids struck a Martian ocean that existed at the time. <ref> http://astrobiology.com/2016/05/ancient-tsunami-evidence-on-mars-reveals-life-potential.html </ref> <ref>Rodriguez, J.; et al. 2016. "Tsunami waves extensively resurfaced the shorelines of an early Martian ocean. :" (PDF). Scientific Reports / 47th Lunar and Planetary Science Conference. 6: 25106. Bibcode:2016NatSR...625106R. doi:10.1038/srep25106. PMC 4872529 Freely accessible. PMID 27196957.version at Nature </ref>
A large team of researchers announced the discovery of beaches near Zhurong, the six-wheeled rover built by China. . Radar on the rover found beds that slope the same amount as beds on the Earth. These beaches support the idea of a large ocean on the north end of the planet.<ref>Penn State. "Gulf of Mars: Rover finds evidence of 'vacation-style' beaches on Mars." ScienceDaily. ScienceDaily, 24 February 2025. <www.sciencedaily.com/releases/2025/02/250224155110.htm>.</ref> <ref>Jianhui Li, Hai Liu, Xu Meng, Diwen Duan, Haijing Lu, Jinhai Zhang, Fengshou Zhang, Derek Elsworth, Benjamin T. Cardenas, Michael Manga, Bin Zhou, Guangyou Fang. Ancient ocean coastal deposits imaged on Mars. Proceedings of the National Academy of Sciences, 2025; 122 (9) DOI: 10.1073/pnas.2422213122</ref>
Most of the rest of this article will cover the long history of how evidence built up for one or more oceans on Mars. Nevertheless, it must be said that although there are decades of accumulated evidence for a Martian ocean, the idea remains controversial. <ref>Head, J., et al. 2018. TWO OCEANS ON MARS?: HISTORY, PROBLEMS AND PROSPECTS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2194.pdf</ref>

==Appearance==

When Mariner 9 pictures arrived in 1969, pictures revealed outflow channels that could carry water into the northern lowlands.<ref> Carr,M. 1996. Water on Mars. Oxford</ref> These lowlands, called Vastitas Borealis, were smooth and level, as if they were formed under an ocean. Moreover, the age of Vastitas Borealis and the channels were found to be similar.<ref>Head, J., et al. 2002. Northern lowlands of Mars: Evidence for widespread volcanic flooding and tectonic deformation in the Hesperian Period. J. Geophys. Res. 107(E1), 5003.</ref> Hence, it was logical to assume that huge outflow channels supplied water to form an ocean covering one third of the planet. The ground was smooth because it was an ocean floor.

<gallery class="center" widths="380px" heights="360px">
File:Kasei Valles topolabled.JPG|Labeled topo map of Kasei Valles and many other outflow channels that supplied water to a Mars Ocean

File:USGS-Mars-MC-11-OxiaPalusRegion-mola.png|Labeled topo map of outflow channels in the Oxia Palus region

File:Mgs orbiter.jpg|Mars Global Surveyor Its instrument, called MOLA, while measuring topography revealed a deep, smooth basin that could have contained an ocean.

Mars_MGS_colorhillshade_mola_1024.jpg|MOLA map of Mars The blue area in the north (top of image) is low and smooth as if it were under an ocean.

</gallery>

Further study by researchers seemed to show features common to shorelines on Earth.<ref> Parker, T.J., Saunders, R.S., and Schneeberger, D.M. 1989. Transitional morphology in the west Deuteronilus Mensae region of Mars: Implications for modification of the lowland/upland boundary: Icarus , v. 82, 111–145, doi:10.1016/0019-1035(89)90027-4.</ref> Still, other explanations for these features were advanced when higher resolution photos from Mars Global Surveyor (5-10 times better than Viking) were examined. Some could be identified as volcanic in origin. <ref>Carr, M. , J. Head. 2003. Oceans of Mars: An assessment of the observational evidence and possible fate. Journal of Geophysical Research. 108(E5). 5041. Doi:10.1029/2002JE001963, 2003.</ref> Also, many shoreline features were located at vastly different altitudes according to MOLA measurements from the Mars Global spacecraft, when in theory all should be of the same level. However, large sections of the shorelines did line up to be nearly on a level line on one of the two shorelines that were previously been proposed .<ref>Head et al. 1999. Possible Ancient Oceans on Mars: Evidence from Mars Orbiter Laser Altimeter Data. Science: 286, 2134.</ref> <ref>Malin, M. C., and Edgett, K. S. 1999. "Oceans or Seas in the Martian Northern Lowlands: High Resolution Imaging Tests of Proposed Coastlines". Geophys. Res. Lett. 26 (19): 3049–3052. Bibcode:1999GeoRL..26.3049M. doi:10.1029/1999GL002342.</ref>

[[File:Mars rampart crater.jpg|left|thumb|320px| Yuty Crater showing lobe and rampart morphology; it looks like mud was formed during the impact.]]

As researchers examined more and more data from orbiting spacecraft more hints that an ocean had existed become evident. The deepest parts of the supposed ocean basins displayed polygonal ground which could be formed from abundant water.<ref>Parker, T., et al. 1989. Transitional morphology in the west Deuteronilus Mensae region of Mars: Implications for modification of the lowland/upland boundary . Icarus. 82111–145, doi:10.1016/0019-1035(89)90027-4.</ref> <ref> Parker, T., et al. 1993. Coastal geomorphology of the Martian northern plains. Journal of Geophysical Research. 98. 11061.</ref> Furthermore, craters that would have been under the ocean had a different appearance. They looked like projectiles had landed in mud. Scientists described the shapes as having a “lobe and rampart morphology.” In these places, the ground may have been full of water and/or ice that could have been left by a previous ocean. <ref> Carr, M. , et al. 1977. Martian permafrost features. Journal of Geophysical Research. 82. 195. </ref> When a detailed analysis was performed, it was found that the deeper basins showed that lobe and rampart shapes appeared in smaller craters than in other regions. Consequently, the team concluded that the ice was shallower in the deeper basins. <ref>Kuzmin, R., et al. 1988. Structure inhomogeneities of the Martian cryosphere, Solar System Res. 22. 195-212. </ref> Many of the major channels that drained into the northern lowlands stopped at about the same elevation; just as if they were at the edge of a large body of water.<ref>Head et al. 1999. Possible Ancient oceans on Mars: Evidence from mars orbiter laser Altimeter Data. Science 286, 2134</ref> <ref> Carr,M. 1996. Water on Mars. Oxford</ref> Similarly, with access to high resolution photos from HiRISE, a 2010 study of deltas revealed that over a dozen stop at the shoreline of the possible ocean.<ref>cite journal | last1 = DiAchille | first1 = G | last2 = Hynek | first2 = B. | year = 2010 | title = Ancient ocean on Mars supported by global distribution of deltas and valleys. nat | url = | journal = Geosci | volume = 3 | issue = 7| pages = 459–463 | doi = 10.1038/ngeo891 | bibcode=2010NatGe...3..459D</ref> Initial observations showed deltas at near the same level and that can be explained if they were at the edge of an ocean.<ref>cite journal | last1 = DiBiasse | first1 = | last2 = Limaye | first2 = A. | last3 = Scheingross | first3 = J. | last4 = Fischer | first4 = W. | last5 = Lamb | first5 = M. | year = 2013 | title = Deltic deposits at Aeolis Dorsa: Sedimentary evidence for a standing body of water on the northern plains of Mars | url = | journal = Journal of Geophysical Research: Planets | volume = 118 | issue = | pages = 1285–1302</ref> <ref>Fawdon, P., et al. 2018. HYPANIS VALLES DELTA: THE LAST HIGH-STAND OF A SEA ON EARLY MARS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2839.pdf</ref> However, later studies showed that many of the deltas were in clusters as if they were in depressions like craters. If they were lined up along the proposed edge of ocean, it would be strong evidence for an ocean.<ref> Rivera-Hernbardez, F. 2019, From Grains to Landscapes: Reconstructing Martian Environments at Multiple Scales. From talk given to Schoumberger</ref>

== Theoretical and computational considerations==

===Was there enough water===

The northern lowlands, where the ocean was, appear to be covered by a material that has been called the Vastitas Borealis Formation. Many craters here were called "stealth" craters because they looked like they were hidden under some sort of covering--like a deposit on an ocean floor.<ref>Kreslavsky, M., J. Head. 2002. Fate of outflow channel effluents in the northern lowlands of Mars: The Vastitas Borealis Formation as a sublimation residue from frozen ponded bodies of water. Journal of Geophysical Research: 107, 5121</ref> This formation may represent the eroded materials from the outflow channels. Evidence for this relationship is that the volume of the Vastitas Borealis Formation is almost the same as the volume of the eroded material from the channels.<ref>Carr, M., et al. 1987. Volumes of channels, canyons, and chaos in the circum-Chryse region of mars. Lunar Planet. Sci. XVIII. 155-156</ref>
In addition, more water was required to develop valley networks, outflow channels, and delta deposits of Mars than was in a Martian ocean, according to research reported in 2017. This implies that there was plenty of water for an ocean.<ref>cite journal | url=https://www.hou.usra.edu/meetings/lpsc2017/pdf/1734.pdf | title=New Martian valley network volume estimate consistent with ancient ocean and warm and wet climate | author=Luo, W., et al. | journal=Lunar And Planetary Science | year=2017 | volume=XLVIII | pages=15766 | doi=10.1038/ncomms15766 | pmid=28580943 |pmc=5465386| bibcode=2017NatCo...815766L </ref>
In 2009 a team of researchers tried to find out exactly how many stream channels existed on Mars. They developed a computer program that examined topographical data. The program looked for U-shaped structures, since that would be the shape of channels carved by water. They found many more channels, and in some areas the valley density was similar to what is found on the Earth. Such a high density of channels supports rain on the planet. A large ocean may have been needed to provide enough moisture for rain. A northern ocean would explain the way that certain channels are distributed around the planet. For example, valleys tend to get shallower in the south, perhaps because they are farther from the ocean. Also, there seems to be a southern limit for valleys where less water could be carried from a northern ocean.<ref>cite news | author = Staff | title = Martian North Once Covered by Ocean | date = 26 November 2009 | url = http://www.astrobio.net/pressrelease/3322/martian-north-once-covered-by-ocean | work = Astrobiology Magazine | accessdate = 19 February 2014</ref> <ref>cite news | author = Staff | title = New Map Bolsters Case for Ancient Ocean on Mars | date = 23 November 2009 | url = http://www.space.com/7584-map-bolsters-case-ancient-ocean-mars.html | work = Space.com | accessdate = 2014-02-19</ref>

In 2026. researchers found that topographic shelves rather than shorelines may be better indicators of long-lived oceans on Mars. On Earth, the most prominent topographic sign of a global ocean is not a shoreline, but a band of low slope and curvature values that comprises coastal plains and the continental shelf, with an elevation range of −410 m to −15 m. Mars also a comparably flat zone between approximately –1,800 m and –3,800 m elevation, potentially marking a partially preserved Martian coastal shelf. <ref>Zaki, A.S., Lamb, M.P. Identifying the topographic signature of early Martian oceans. Nature (2026). https://doi.org/10.1038/s41586-026-10381-2 </ref>

===Size of ocean===

Different researchers have come up with different sizes for an ancient ocean on Mars. However, many of these estimates are reasonable in that the ocean volume is similar to the volume of water needed to carve the many channels on Mars. In fact, it is even less than the maximum amount that the ground could hold.<ref>Head et al. 1999. Possible Ancient oceans on Mars: Evidence from mars orbiter laser Altimeter Data. Science 286, 2134</ref> <ref> Carr,M. 1996. Water on Mars. Oxford</ref> So, the ground could contain all of the water that was in the ocean. There is a division of opinion as to the area of the ocean. Early on two different shorelines were proposed.<ref> Parker, T.J., Saunders, R.S., and Schneeberger, D.M., 1989, Transitional morphology in the west Deuteronilus Mensae region of Mars: Implications for modification of the lowland/upland boundary: Icarus , v. 82, 111–145, doi:10.1016/0019-1035(89)90027-4.</ref> <ref> Parker, T., et al. 1993. Coastal geomorphology of the Martian northern plains. Journal of Geophysical Research. 98. 11061.</ref> The shoreline for the smaller ocean is more plausible since there are far less elevation differences along the shoreline.<ref>Carr, M. , J. Head. 2003. Oceans of Mars: An assessment of the observational evidence and possible fate. Journal of Geophysical Research. 108(E5). 5041. Doi:10.1029/2002JE001963, 2003.</ref> One early estimate of the ocean volume was 19,000,000 Km cubed (1.9 X 107). This volume is equal to 130 meters of water covering the entire planet.(Global Equivalent level-GEL). Estimates would be 23,000,000 Km cubed (2.3 X 107) equal to 156 meters GEL for the high end for the ocean’s size. This larger number represents the ocean’s if we take of total size of the Vastitas Borealis Formation as the area for the ocean.<ref>Carr, M. , J. Head. 2003. Oceans of Mars: An assessment of the observational evidence and possible fate. Journal of Geophysical Research. 108(E5). 5041. Doi:10.1029/2002JE001963, 2003.</ref>

===What was the source of the water===

Many have wondered where did the water come from? Today Mars is cold and dry—very dry. Many believe that the atmosphere was once much thicker with a great deal of carbon dioxide that would have caused a global warming. But, models of long term climate change indicate that Mars may have always been cold and dry. <ref> Forget et al. 2013. 3D modelling of the early martian climate under a denser CO2 atmosphere: Temperatures and CO2 ice clouds. Icarus 222, 81-99.</ref> <ref> Wordsworth et al. 2013. Global modelling of the early martian climate under a denser CO atmosphere: Water cycle and ice evolution. Icarus 222, 1-19.</ref> One major consideration is that the early sun was not as strong. Perhaps, the average temperature was never above freezing. If that was the case, then the many channels on Mars may have formed during relatively short term, localized events like impacts or volcanic activity.<ref>https://www.hou.usra.edu/meetings/lpsc2019/pdf/2024.pdf</ref> <ref>Palumbo, A., J. Head. 2019. OCEANS ON MARS: THE POSSIBILITY OF A NOACHIAN GROUNDWATER-FED OCEAN IN A SUBFREEZING MARTIAN CLIMATE. A. SUB- FREEZING MARTIAN CLIMATE. 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132) 2024.pdf</ref> <ref>Head, J., et al. 2017. DECIPHERING THE NOACHIAN GEOLOGICAL AND CLIMATE HISTORY OF MARS: A STRATIGRAPHIC, GEOLOGIC PROCESS AND MINERALOGICAL PERSPECTIVE – PART 1: CURRENT KNOWNS AND UNKNOWNS. 4th Early Mars, 3046/3047.</ref> <ref> Head, J. et al. 2017. DECIPHERING THE NOACHIAN GEOLOGICAL AND CLIMATE HISTORY OF MARS: PART 2 – A NOACHIAN STRATIGRAPHIC VIEW OF MAJOR GEOLOGIC PROCESSES AND THEIR CLIMATIC CONSEQUENCES. 4th Early Mars, 3047</ref>
Today, we generally accept ideas that were put forth in a long paper by Steven Clifford in which he proposed that a thick layer of ice, called a cryosphere, circled the entire planet. This frozen cryosphere is estimated to contain hundreds meters of GEL.<ref> Clifford, S. 1993. A model for the hydrologic and climatic behavior of water on Mars. Geophys. Res. 98 (E6)</ref> As the planet cooled, water in the ground froze to the bottom of this ice layer, creating an aquifer under great pressure. Then the water in the aquifer was suddenly released, perhaps after an asteroid impact cracked the cryosphere. Huge, catastrophic floods came out of chaos regions and carved great outflow channels that carried the water to a northern ocean. <ref>Clifford, S. M.; Parker, T. J. (2001). "The Evolution of the Martian Hydrosphere: Implications for the Fate of a Primordial Ocean and the Current State of the Northern Plains". Icarus. 154 (1): 40–79. Bibcode:2001Icar..154...40C. doi:10.1006/icar.2001.6671</ref> <ref> Gulick, V., D. Tyler, C. McKay, and R. Haberle. 1997. Episodic ocean‐induced CO2 greenhouse on Mars: Implications for fluvial valley formation. Icarus: 130, 68–86.</ref> <ref> Andrews-Hanna, J., R. Phillips. 2007. Hydrological modeling of outflow channels and chaos regions on Mars. Journal of Geophysical Research: Planets Volume 112, Issue E8</ref> <ref> Clifford, S. 1993. A model for the hydrologic and climatic behavior of water on Mars. JGR, 98, 10973L</ref>

Evidence for a past aquifer at depth on Mars came out in February 2019, from a group of European scientists who published geological evidence of an ancient planet-wide groundwater system that was probably connected to a Martian ocean.<ref name="ESA-20190228">ESA Staff |title=First Evidence of "Planet-Wide Groundwater System" on Mars Found |url=https://www.esa.int/Our_Activities/Space_Science/Mars_Express/First_evidence_of_planet-wide_groundwater_system_on_Mars |date=28 February 2019 |work=[[European Space Agency]]</ref> <ref name="FTR-20190228">Houser |first=Kristin |title=First Evidence of "Planet-Wide Groundwater System" on Mars Found |url=https://futurism.com/the-byte/mars-groundwater-system-planet-wide |date=28 February 2019 |work=Futurism.com</ref> <ref>https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018JE005802</ref> <ref> https://www.leonarddavid.com/planet%E2%80%90wide-groundwater-system-on-mars-new-geological-evidence/</ref> The study was of 24 craters that did not display an inlet or outlet; hence, water for the lake must have come from the ground. All craters were located in the northern hemisphere of Mars. These craters had floors lying roughly 4000 m below Martian 'sea level' (a level that, given the planet's lack of seas, is defined based on elevation and atmospheric pressure). Features on the floors of these craters could only have formed in the presence of water.<ref>Salese, F., et al. 2019. A GEOLOGICAL MODEL FOR MARTIAN GROUNDWATER BASED ON WATER-FORMED
FEATURES WITHIN DEEP BASINS. 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132). 3240.pdf</ref> <ref>https://www.hou.usra.edu/meetings/lpsc2019/pdf/3240.pdf</ref> There are multiple features showing that the water level in the craters rose and fell over time. Deltas and terraces were present in many craters.<ref>http://astrobiology.com/2019/02/first-evidence-of-a-planet-wide-groundwater-system-on-mars.html</ref> Some crater floors contain minerals such as various clays and light-toned minerals that form in water. In addition, layers are found in some of these craters, and layers often form under water. Taken together, these observations strongly suggest that water was present in these places.<ref>https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018JE005802</ref> Some of the craters studied were Pettit, Sagan, Nicholson, Mclaughlin, du Martheray, Tombaugh, Mojave, Curie, Oyama, and Wahoo. It seems that if a crater was deep enough, water came out of the ground and produced a lake.<ref>https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018JE005802</ref> Water may have came out of the ground to contribute water to an ocean in the low-lying North.

<gallery class="center" widths="380px" heights="360px">

File:J03 045825 2081sappingcraterarrowslabeled.jpg|Crater showing valleys that formed from sapping--that is the water flowed out of the ground. Eventually, the water formed a lake.

File:J03 045825 2081sappingcraterdelta.jpg|Red arrows show deltas that formed from water that issued from the ground in sapping valleys. This is evidence that water came out of the ground and made a lake.

</gallery>

===Where did the water go===

Another consideration that needs to be explained is where did all the water go? At first the water would freeze. Then, in the thin, cold atmosphere of Mars, the ice would have slowly sublimated--that is turned directly into a gas. This water in the vapor state would have migrated to the poles, and then the base of the ice caps would melt with the liquid water freezing to the cryosphere. However, if dust covered the ice the ice may have been lasted for a very long time.<ref> Clifford, S., T. Parker, 2001. The evolution of the Martian hydrosphere: implications for the fate of a primordial ocean and the current state of the Northern Plains. Icarus 154, 40</ref>
The biggest present supply of water is the ice caps, also called the layered polar deposits. Scientists have said that they account for only 25 meter Global Equivalent level (GEL). More recent estimates are 17-22 meters of GEL.<ref>Lasue, J., et al. 2013. Quantitative Assessments of the Martian Hydrosphere. Space Sci. Rev. 174, 155-212.</ref> <ref> Carr, M., J. Head. 2015. Martian surface/near-surface water inventory: Sources, sinks, and changes with time. Geophys. Res. Lett. 42, 726-732.</ref> However, it could be less, as radar studies from orbit have measured the larger cap, the northern one, as having only 821,000 Km cubed which is less than 6 meters GEL. <ref>https://www.space.com/17048-water-on-mars.html </ref> <ref> Radar Map of Buried Mars Layers Matches Climate Cycles". Jet Propulsion Lab. 2009-09-22</ref> Remember, the ocean may have held more than 100 meters of GEL.

[[File:Mars NPArea-PIA00161.jpg |left|thumb|320px| The North Polar layered deposits are the largest reservoir of water . They contain enough water to cover Mars to a depth of 6-25 meters.]]

Some water is frozen in the ground and in glaciers. A team of researchers led by Jeremie Mauginot reasoned that there was 7 meters GEL in the ground between the polar deposits and 50 degrees latitude. <ref> Mauginot , J., et al. 2010. The 3-5 MHz-global ref map of Mars by MARSIS/Mars Express: implications for the current inventory of subsurface H2O. Icarus: 210, 612-625.</ref> In addition, a study, published in 2017, found evidence for ice sheets down to 38 degrees latitude in Utopia and Arcadia Planitiae.<ref> Bramson, A., et al. 2017. Preservation of mid-latitude ice-sheets on Mars. J. Geophys. Res. 122, 2250-2260.</ref> Glaciers that are covered with debris and pedestal craters can account for another 2.6 meters GEL in the 30-50 degree bands according to Joseph Levy and his team that were published in Icarus.<ref> Levey, J., et al. 2010. Concentric crater fill in the northern mid-latitudes of Mars: Formation. Icarus: 209, 390-404.</ref>

[[File:ESP 018857 2225alpineglacier.jpg |right|thumb|320px| Glacier moving down a valley Picture taken with HiRISE under HiWish program. ]]

The abundance of water in the upper surface of the ground was mapped by the gamma ray and neutron spectrometers from the orbiting Mars Odyssey.<ref>https://mars.nasa.gov/odyssey/mission/overview/</ref> <ref> Mitrofanov, I., Anfimov, D., Kozyrev, A., Litvak, M., Sanin, A., Tret'yakov, V., ... Saunders, R. S. (2002). Maps of subsurface hydrogen from the High Energy Neutron Detector, Mars Odyssey. Science, 297(5578), 78-81. DOI: 10.1126/science.1073616</ref> <ref> Wilson, J. et al. 2018. Equatorial locations of water on Mars: Improved resolution maps based on Mars Odyssey Neutron Spectrometer data. Icarus 299: 148-160; doi: 10.1016/j.icarus.2017.07.028</ref>

<gallery class="center" widths="380px" heights="360px">
File:Mars Odyssey spacecraft model.png|Mars Odyssey found water-ice in the ground on Mars.
</gallery>

It found much water ice just beneath the surface, just as predicted by mathematical models. In fact, ice was actually seen when the landing rockets of the Phoenix lander blow away a dust cover to reveal ice.<ref>Smith, P., et al. 2009. H2O at the Phoenix Landing Site. Science: 325, 58-61.</ref> <ref>https://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080530.html</ref> Powerful cameras have showed features that resemble glaciers on the Earth. Radar on satellites found ice just beneath the surface around mesas in features that were named lobate debris aprons (LDA). <ref>Holt, J. W.; Safaeinili, A.; Plaut, J. J.; Young, D. A.; Head, J. W.; Phillips, R. J.; Campbell, B. A.; Carter, L. M.; Gim, Y.; Seu, R.; Team, Sharad (2008). "Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars" (PDF). Lunar and Planetary Science. XXXIX: 2441. </ref> Measurements with MARSIS/Mars Express of something called a dielectric constant indicates that much ice is contained in the material that was under the ocean.<ref>Mouginot, J., et al. 2012. Dielectric map of the Martian northern hemisphere and the nature of plain filling materials. GEOPHYSICAL RESEARCH LETTERS, VOL. 39, L02202, doi:10.1029/2011GL050286, 2012</ref> <ref>Holt, J. W.; Safaeinili, A.; Plaut, J. J.; Young, D. A.; Head, J. W.; Phillips, R. J.; Campbell, B. A.; Carter, L. M.; Gim, Y.; Seu, R.; Team, Sharad (2008). "Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars" (PDF). Lunar and Planetary Science. XXXIX: 2441.</ref> All these observations support the notion that there is a great deal of water frozen under the Martian surface.<ref>https://www.jpl.nasa.gov/news/new-study-challenges-long-held-theory-of-fate-of-mars-water?utm_source=iContact&utm_medium=email&utm_campaign=nasajpl&utm_content=daily20210316-2</ref> <ref>E. L. Scheller, B. L. Ehlmann, Renyu Hu, D. J. Adams, Y. L. Yung. Long-term drying of Mars by sequestration of ocean-scale volumes of water in the crust. Science, 2021; eabc7717 DOI: 10.1126/science.abc7717</ref> <ref>https://www.sciencedaily.com/releases/2021/03/210316132106.htm</ref>

<gallery class="center" widths="380px" heights="360px">

File:PIA10741 Possible Ice Below Phoenix.jpg|Smooth areas under Phoenix may be top of an ice layer.
File:800px-Wideviewlda42n18e.jpg|Labeled picture showing mesa surrounded by lobate debris aprons which radar has shown contain water-ice under a thin debris covering
</gallery>

It was believed that Mars may have been much warmer in the past due to a thick carbon dioxide atmosphere that would have through a global warming effect raised the temperature above the freezing point of water. If that was so, where did all the Carbon dioxide go? Chemically it should have been deposited as carbonates and formed limestone type rocks. Despite searches with instruments aboard satellites, very little carbonates have been found. <ref>Bandfield, J. , et al. 2000. A global view of Martian surface composition from MGS-TES. Science: 287, 1626-1630.</ref> <ref>Christensen, P., et al. 2001. Mars Global Surveyor Thermal Emission Spectrometer experiment: Investigation description and surface science results. J. Geosphy. Res. 106, 23823-23871</ref> Better data that was obtained from the Curiosity Rover did find some iron carbonates. CheMin measurements of rocks found crystalline siderite (FeCO3). One rock contained over 10 % of the mineral. The rocks also were composed of the silicate mineral plagioclase with the elements sodium (Na)–, Ca-, and aluminum (Al)–, as well as Ca- and Mg-bearing silicate mineral pyroxene. Other minerals found were calcium sulfates, magnesium sulfates, different amounts of iron oxyhydroxides, and an unidentified x-ray amorphous material.<ref> https://www.science.org/doi/10.1126/science.ado9966</ref> On the other hand, there is strong evidence of acid conditions which would prevent carbonates from forming.<ref> Grotzinger, J. and R. Milliken (eds.) 2012. Sedimentary Geology of Mars. SEPM</ref> <ref> Catling, D. (1999-07-25). "A chemical model for evaporites on early Mars: Possible sedimentary tracers of the early climate and implications for exploration" (PDF). Journal of Geophysical Research. 104 (E7): 16453–16469. Bibcode:1999JGR...10416453C. doi:10.1029/1998JE001020</ref> <ref> Fairén, Alberto G.; Fernández-Remolar, David; Dohm, James M.; Baker, Victor R.; Amils, Ricardo (2004-09-23). "Inhibition of carbonate synthesis in acidic oceans on early Mars" (PDF). Nature. 431 (7007): 423–426. Bibcode:2004Natur.431..423F. doi:10.1038/nature02911. PMID 15386004</ref> Orbiting instruments, as well as instruments on landers have found sulfates that may have formed under acid conditions.<ref>https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160006674.pdf</ref> <ref>https://www.sciencedirect.com/science/article/pii/S0019103514003522</ref> <ref>Farrand, W., et al. 2014. Detection of copiapite in the northern Mawrth Vallis region of Mars: Evidence of acid sulfate alteration. Icarus: 241, 346-357.</ref>

Based on data from InSight, scientists used models to determine that liquid water exists deep underground. According to a paper published April 25, 2025 in the journal National Science Review, recordings of seismic waves from deep within the Red Planet indicate that a layer of liquid water may be lurking in the Martian rocks between 3.4 and 5 miles [5.4 to 8 kilometers] below the surface.

The total volume of hidden water could flood the whole of Mars' surface with an ocean 1,700 to 2,560 feet [520 to 780 metres] deep, around the same volume of liquid that is contained within Antarctica's ice sheet, the study authors estimated.<ref>https://www.livescience.com/space/mars/scientists-find-hint-of-hidden-liquid-water-ocean-deep-below-mars-surface?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=7A404C61-C432-438F-9414-F1C935EF3C79&utm_source=SmartBrief</ref> <ref> Sun, W., et al. 2025. Seismic evidence of liquid water at the base of Mars' upper crust. National Science Review. nwaf166, https://doi.org/10.1093/nsr/nwaf166 </ref>. Another group earilier found similar results and suggested the water would be in fractures in igneous rocks.Liquid water in the Martian mid-crust
<ref>Vashan Wright https://orcid.org/0000-0002-3238-4526 vwright@ucsd.edu, Matthias Morzfeld https://orcid.org/0000-0003-2257-8930, and Michael Manga https://orcid.org/0000-0003-3286-4682
121 (35) e2409983121
https://doi.org/10.1073/pnas.2409983121</ref> <ref>https://www.pnas.org/doi/10.1073/pnas.2409983121</ref> <ref> https://www.youtube.com/watch?v=6cPSA9_PrMg</ref> <ref>https://www.youtube.com/watch?v=KOTxzi_CqFU</ref>
They estimate that there is enough liquid water under the surface to produce water across the surface that would be more than half a mile deep. However, it would be hard to get to as it is 10-20km deep. The team of researchers used measurements from more than 1,319 quakes to come to their conclusions.<ref>https://www.bbc.com/news/articles/czxl849j77ko</ref> Calculations obtained from InSight lander's data suggest up to 2 km global equivalent layer (GEL) could be in the crust.<ref>https://www.pnas.org/doi/10.1073/pnas.2418978122</ref> <ref>Jakosky, B. 2025. Results from the inSight Mars mission do not require a water-saturated mid crust. Letter Earth, Atmospheric, and Planetary Sciences. 122 (11) e2418978122 https://doi.org/10.1073/pnas.2418978122</ref> <ref>https://www.space.com/the-universe/mars/what-happened-to-all-the-water-on-mars-the-debate-continues?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=58E4DE65-C57F-4CD3-9A5A-609994E2C5A9&utm_medium=email&utm_content=22609226-D300-4C70-9B8F-1139DC6030FA&utm_source=SmartBrief</ref>

===Water lost to space===

Of great significance in answering where the water went has come from advanced studies of the Martian atmosphere. In short, most of the atmosphere and water was lost into space by various processes.
As far back as 2001, NASA’s Far Ultraviolet Spectroscopic Explorer (FUSE) measurements of the ratio of molecular hydrogen to deuterium in the upper atmosphere of Mars suggested an abundant water supply on primordial Mars that has since been lost. Deuterium is a rare, heavy isotope of hydrogen. It has a neutron its nucleus. Since it is heavier, it tends to stick around longer. The ratio between the hydrogen and deuterium tells us how much has been lost in the past. <ref name=Krasnopolsky>cite journal | last1 = Krasnopolsky | first1 = Vladimir A. | last2 = Feldman | first2 = Paul D. | year = 2001 | title = Detection of Molecular Hydrogen in the Atmosphere of Mars | url = | journal = Science | volume = 294 | issue = 5548| pages = 1914–1917 | doi=10.1126/science.1065569 | pmid=11729314| bibcode = 2001Sci...294.1914K </ref>
Another later study, published in 2015, of water and deuterium came to the conclusion that Mars has lost the equivalent of an Arctic Ocean of water. <ref>Villanueva G. L., Mumma M. J., Novak R. E., Käufl H. U., Hartogh P., Encrenaz T., Tokunaga A., Khayat A., and Smith M. D., Science, Published online 5 March 2015 [DOI:10.1126/science.aaa3630]</ref> <ref>Villanueva, G., et al. 2015. Strong water isotopic anomalies in the martian atmosphere: Probing current and ancient reservoirs. Science 10 Apr 2015:Vol. 348, Issue 6231, pp. 218-221.</ref> This discovery was derived from the ratio of water and deuterium in the modern Martian atmosphere compared to the ratio found on Earth and derived from telescopic observations. Telescopic observations from the Earth found eight times the concentration of deuterium at the polar deposits of Mars than exists on Earth, signifying that Mars once had much greater levels of water. The telescopic values are within range that the ''Curiosity'' rover detected in Gale Crater.<ref>cite journal | last1 = Webster | first1 = C.R. | display-authors = 1 | last2 = et al | year = 2013 | title = Isotope Ratios of H, C, and O in CO2 and H2O of the Martian Atmosphere | url = | journal = Science | volume = 341 | issue = 6| pages = 260–263 | bibcode = 2013Sci...341..260W | doi = 10.1126/science.1237961 | pmid = 23869013 </ref> Dust storms also increase water loss.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JE006616</ref> <ref>Fedorova, A. et al. 2020. Multi‐Annual Monitoring of the Water Vapor Vertical Distribution on Mars by SPICAM on Mars Express. JGR Planets. Volume126, Issue1
January 2021. e2020JE006616</ref>
Ten percent of the water loss from Mars may have been caused by dust storms, according to a study of dust storms with the Mars Reconnaissance Orbiter. Dust storms carry water vapor to very high altitudes; there ultraviolet light from the Sun can then break the water apart in a process called photodissociation. Hydrogen from the water molecule then goes into space.<ref>https://www.sciencenews.org/article/mars-dust-storms-water?mode=topic&context=36</ref> <ref>N. Heavens et al. Hydrogen escape from Mars enhanced by deep convection in dust storms. ''Nature Astronomy''. Published online January 22, 2018. doi: 10.1038/s41550-017-0353-4.</ref> <ref>https://www.jpl.nasa.gov/news/news.php?release=2018-012&rn=news.xml&rst=7041</ref>

[[File:PIA03170 fig1duststroms.jpg |left|thumb|320px| Mars with and without a dust storm Dust storms may have caused 10% of the water loss from Mars into space. ]]

Further evidence that Mars once had a thicker atmosphere which would make an ocean more probable came from the MAVEN spacecraft that has been making measurements from Mars orbit. Bruce Jakosky, lead author of a paper published in Science, stated that "We've determined that most of the gas ever present in the Mars atmosphere has been lost to space."<ref>https://www.nasa.gov/press-release/nasas-maven-reveals-most-of-mars-atmosphere-was-lost-to-space</ref> This research was based upon two different isotopes of argon gas.<ref>B.M. Jakosky et al. 2017. Mars’ atmospheric history derived from upper-atmosphere measurements of 38Ar/36Ar. Science 355 (6332): 1408-1410; doi: 10.1126/science.aai7721</ref> <ref>http://www.sci-news.com/space/maven-martian-atmosphere-lost-space-04750.html</ref> Argon gas is inert, it does not react with anything; hence, the ratio of its isotopes gives an accurate reading of how much has been lost. Like deuterium, a heavy isotope of hydrogen, the heavy form of argon is not lost to space as easily as the lighter variety. A greater proportion of heavy isotope left on the planet means that more of the gas has disappeared. By studying the ratio of the heavier Ar38 to the lighter Ar36, scientists found that 65% of argon has left the planet. The main way that argon left the atmosphere was through a process called “sputtering.” Sputtering is a complex method in which the sun strips atmosphere from a planet. The sun is constantly shooting out particles at high speed. If one hits a gas particle in the atmosphere, it may directly knock it into space. Alternatively, it would cause an atom of atmosphere to lose an electron and thereby become an ion. Ions can interact with the sun’s magnetic field as it moves through space. In the such an exchange, the ion can then acquire energy and fly off into space or hit other atoms in the atmosphere, knocking them into space, as well.<ref> https://www.nasa.gov/press-release/nasas-maven-reveals-most-of-mars-atmosphere-was-lost-to-space</ref>

<gallery class="center" widths="380px" heights="360px">
File:1-Mars limb-1024x665maveninorbit.jpg|Artist’s conception of MAVEN orbiting Mars
File:Mars vs Earth Solar Wind-1024x576.png|Artist’s conception of how the solar wind strikes Mars, but does not reach the Earth’s surface because of the Earth’s magnetic field

File:Mavenargoninfographic2.jpg|Drawing showing how Mars lost argon and other gases into space

</gallery>

The shoreline of a Mars ocean is not even; also it is hard to account for where the all water came from and where it went. These big problems were potentially solved by a team of scientists, in 2018. They proposed that Martian oceans appeared very early--before or along with the growth of Tharsis. The great mass of the Tharsis volcanoes pulled the crust down making a deep basin. If the ocean was formed before the mass of Tharsis deepen the basins, much less water would be needed. Also, the shorelines would not be regular since Tharsis would still be growing and changing the position of the shoreline. As Tharsis volcanoes erupted they added huge amounts of gases (such as water, carbon dioxide, sulfur dioxide) into the atmosphere and created a global warming, thereby possibly allowing liquid water to exist.<ref>[https://www.sciencedaily.com/releases/2018/03/180319124255.htm Mars' oceans formed early, possibly aided by massive volcanic eruptions]. University of California - Berkeley. March 19, 2018.</ref> <ref>Citron, R., M. Manga, D. Hemingway. 2018. "Timing of oceans on Mars from shoreline deformation." ''Nature'' doi| 10.1038/nature26144</ref> <ref>Citro, R., et al. 2018. EVIDENCE OF EARLY MARTIAN OCEANS FROM SHORELINE DEFORMATION DUE TO THARSIS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1244.pdf</ref>

<gallery class="center" widths="380px" heights="360px">
File:Olympus Mons.jpg|Olympus Mons, the largest of the Tharsis volcanoes, pulled the crust down making a deep basin nearby. New research indicates that the ocean may have formed before Olympus Mons reached its final size; hence, the ocean may have been only half as deep as thought.
File:USGS-Mars-MC-9-TharsisRegion-mola.png|Most of the volcanoes of Tharsis These volcanoes and others may have released vast amounts of greenhouse gases.
</gallery>

However, it is hotly debated just how much of a global warming took place. Newest climate models show Mars to always have been too cold for much water to exist as a liquid. <ref> Forget et al. 2013 3D modelling of the early martian climate under a denser CO2 atmosphere: Temperatures and CO2 ice clouds. Icarus 222, 81-99.</ref> <ref> Wordsworth et al. 2013. Global modelling of the early martian climate under a denser CO2 atmosphere: Water cycle and ice evolution. Icarus 222, 1-19.</ref> <ref>http://astrobiology.com/2018/12/geologic-constraints-on-early-mars-climate.html</ref> One group of researchers have proposed that if an object 1000 km across were to strike Mars at certain angles that the large body would break up into small pieces and react with ice on the surface as well as the iron core of Mars. Such reactions could generate large amounts of hydrogen gas (3 times as thick as the Earth's atmosphere). This gas, being a greenhouse gas, could raise the temperature of the atmosphere.<ref>https://www.hou.usra.edu/meetings/lpsc2019/pdf/1067.pdf</ref> <ref>Woo, J., et al. 2019. MARS IN THE AFTERMATH OF COLOSSAL IMPACT. 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132). 1067.pdf)</ref> Even though research studies continue to support a Mars ocean, there have been other ideas put forth to explain observations.<ref>https://www.hou.usra.edu/meetings/lpsc2019/pdf/2024.pdf</ref> <ref>Palumbo, A., J. Head. OCEANS ON MARS: THE POSSIBILITY OF A NOACHIAN GROUNDWATER-FED OCEAN IN A SUBFREEZING MARTIAN CLIMATE. 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132). 2024.pdf</ref> Some have suggested a series of lakes rather than one large ocean. A recent study suggested a frozen ocean resulting from a succession of floods. Water from the outflow channels probably rushed out many times with long gaps between flooding events. Each time the water would have frozen. <ref>Carr, M., J. Head. 2019. Icarus Volume 319, February 2019, Pages 433-443. Mars: Formation and fate of a frozen Hesperian ocean. Icarus. https://doi.org/10.1016/j.icarus.2018.08.021</ref> <ref>Carr, M. 1996. Water on Mars. Oxford</ref> Circulation in an ocean may have warmed the surface up to 4.5°C, according to a study published in 2022. The research team noted that an ocean could be stable even if the average temperature of Mars was below 0°C.<ref>https://www.hou.usra.edu/meetings/lpsc2022/pdf/1467.pdf</ref> <ref>Schmidt, F. 2022. CIRCUMPOLAR OCEAN STABILITY ON MARS 3 GY AGO. 53rd Lunar and Planetary Science Conference (2022. 1467.pdf</ref>

===Tsunamis===

If Mars had an ocean for a time, there is a chance that sooner or later an asteroid would strike it and cause a great wave, called a tsunami. Evidence for two such events was published in May 2016. Parts of the surface in Ismenius Lacus quadrangle were altered by two tsunamis argue a large team of scientists. Both impacts which caused the tsunamis were powerful enough to leave behind 30 km diameter craters. The first picked up and transported boulders the size of small houses. The wave washed over the land, and then gravity pulled it back to lower ground and when it did, the backwash created channels by rearranging the boulders. The second came in when the ocean was 300 m lower. The second tsunami brought great deal of ice which was dropped in valleys. The average height of the waves would have been 50 m, but the heights would vary from 10 m to 120 m according to calculations. That means that some waves were tall enough to have gone way over the United States Capitol Building. Lobes of giant boulders went around obstacles and down low paths. Having such strikes are quite plausible, as simulations indicate that in this particular part of the ocean two impact craters of 30 km in diameter are expected every 30 million years. Two of these events imply that a huge ocean may have existed for millions of years. One persistent argument against an ocean has been the lack of shoreline features, but they may have been destroyed by these tsunamis. Chryse Planitia and northwestern Arabia Terra were studied in this research. <ref>http://astrobiology.com/2016/05/ancient-tsunami-evidence-on-mars-reveals-life-potential.html</ref> <ref>https://www.hou.usra.edu/meetings/lpsc2016/pdf/1680.pdf | title=Tsunami waves extensively resurfaced the shorelines of an early Martian ocean. : | author=Rodriguez, J., et al. | journal=Scientific Reports / 47th Lunar and Planetary Science Conference | year=2016 | volume=6 | pages=25106 | doi=10.1038/srep25106| pmid=27196957 | pmc=4872529 | [https://www.nature.com/articles/srep25106 version at ''Nature'']</ref> <ref> [https://www.sciencedaily.com/releases/2016/05/160519101756.htm "Ancient tsunami evidence on Mars reveals life potential."] ''ScienceDaily''. 19 May 2016.</ref> The crater Lomonosov has been identified as a likely source of tsunami waves.<ref name = "Rincon2017">cite web | url = https://www.bbc.com/news/science-environment-39394583 | title = Impact crater linked to Martian tsunamis | last = Rincon | first = P. | date = 2017-03-26 | website = BBC | access-date = 2017-03-26</ref> <ref>Costard | first2 = A. | last2 = Séjourné | first3 = K. | last3 = Kelfoun | first4 = S. | last4 = Clifford | first5 = F. | last5 = Lavigne | first6 = I. | last6 = Di Pietro | first7 = S. | last7 = Bouley | title = Modelling Investigation of Tsunamis on Mars | book-title = Lunar and Planetary Science Conference|Lunar and Planetary Science XLVIII | pages = 1171 | publisher = Lunar and Planetary Institute | date = 2017 | location = The Woodlands, Texas | url = http://www.lpi.usra.edu/meetings/lpsc2017/pdf/1171.pdf | access-date = 2017-03-26</ref> <ref>Costard, F., et al. 2018. FORMATION OF THE NORTHERN PLAINS LOMONOSOV CRATER DURING A TSUNAMI GENERATING MARINE IMPACT CRATER EVENT. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1928.pdf</ref> <ref>https://www.techtimes.com/articles/203105/20170326/impact-crater-linked-to-powerful-tsunamis-on-mars-another-proof-of-an-ancient-ocean.htm</ref> <ref>https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019JE006008</ref> Another possible crater for the origin was the crater Pohl. It's formation would have made the first tsunami, while the impact creating Lomonosov could have caused the second one.<ref>https://www.nature.com/articles/s41598-022-18082-2?utm_medium=affiliate&utm_source=commission_junction&utm_campaign=CONR_PF018_ECOM_GL_PHSS_ALWYS_DEEPLINK&utm_content=textlink&utm_term=PID100052172&CJEVENT=327985de727d11ed80c400a00a1c0e10</ref> <ref>Rodriguez, J.A.P., Robertson, D.K., Kargel, J.S. et al. Evidence of an oceanic impact and megatsunami sedimentation in Chryse Planitia, Mars. Sci Rep 12, 19589 (2022). https://doi.org/10.1038/s41598-022-18082-2</ref> <ref>https://www.livescience.com/mars-mega-tsunami-impact-point</ref> Pohl is 111 Km across and is located at 34.04 N and 323.01 E.<ref>https://planetarynames.wr.usgs.gov/Feature/Pohl</ref>

[[File:Pohloceancomposit.jpg|600pxr| Map showing location of Pohl Crater the source of the first tsunami]]

Map showing location of Pohl Crater the source of the first tsunami

<gallery class="center" widths="380px" heights="360px">

File:Mars Reconnaissance Orbiter spacecraft model.png|The Mars Reconnaissance Orbiter with its powerful HiRISE saw house-sized boulders that may have been carried and formed into channels by tsunamis.

ESP 028537 2270tsunamischannels.jpg|Channels made by the backwash from tsunamis, as seen by HiRISE The tsunami wave carried great boulders over the land, and then when the wave went back out to the sea channels like these were created.

28537 2270tsunamisboulders.jpg|Boulders that were picked up, carried, and dropped by tsunamis, as seen by HiRISE Tsunamis picked up and carried these boulders, the size of small houses.

Tsunamisstreamlinedp20008931.jpg|Streamlined island eroded by tsunami, as seen by HiRISE Tsunamis were probably caused by asteroids striking ocean.

File:MarsLomonosovCraterWinter.jpg|Lomonosov Crater in the winter with frost One of the two tsunamis may have been caused by the formation of this crater.
</gallery>

Evidence of other tsunami events was presented at the 50th Lunar and Planetary Science Conference (March 18–22, 2019) in The Woodlands, Texas.<ref>https://www.hou.usra.edu/meetings/lpsc2019/pdf/lpsc2019_program.htm</ref> Observations made by a large group of scientists showed that a large tsunami traveled up into the highlands at least ~1.2 km in
elevation over a distance of ~350 km. The paper's authors calculated that an impact ~150 km in diameter in a Martian northern ocean could have produced this tsunami. Deposits from the tsunami cover the lower reaches of Maumee Valles and most of the highland surfaces next to Kasei Valles, Maumee Valles, and Xanthe Montes. The [[Viking 1]] lander set down on a part of the deposit from the tsunami.<ref>https://www.hou.usra.edu/meetings/lpsc2019/pdf/2757.pdf</ref> <ref>Rodrignez, J., et al. 2019. A NASA SPACECRAFT MAY HAVE LANDED ON AN EARLY MARS MEGA-TSUNAMI DEPOSIT IN 1976. 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132). 2757.pdf</ref> Another tsunami may have occurred from a landside that slide down [[Olympus Mons]], the largest volcano on Mars. The deposit went much further than expected for just a landslide. However, the great distance covered by landslide would have been expected if the material sliding down Olympus Mons were mixed with water from an ocean or smaller ponds. If this tsunami did occur that means that an ocean lasted until the early Amazonia period, at least in the area of Amazonis Arcadia Planitiae. So, an ocean may have lasted longer than previously thought.<ref>https://www.hou.usra.edu/meetings/lpsc2019/pdf/1573.pdf</ref> <ref>DeBlasio, F. 2019. LANDSLIDE-GENERATED TSUNAMI ON MARS? 50th Lunar and Planetary Science Conference 2019 (LPI Contrib. No. 2132). 1573.pdf</ref> <ref> Costard, F., et al. 2019. The Lomonosov Crater Impact Event: A Possible Mega‐Tsunami Source on Mars. JGR. Volume124, Issue7. Pages 1840-1851,</ref>

== References ==
{{reflist}}

==See also==
* [[Geography of Mars]]
* [[Global warming]]

* [[Greenhouse effect]]
* [[High Resolution Imaging Science Experiment (HiRISE)]]
* [[Mars Global Surveyor ]]
* [[MAVEN]]
* [[Rivers on Mars]]
* [[Tharsis]]
* [[Water]]

[[Category: Climate]]

== External links ==

*Carr, M. and J. Head. 2019. Mars: Formation and fate of a frozen Hesperian ocean. Icarus. Volume 319. Pages 433-443.

*Head, J., et al. 2023. GEOLOGICAL AND CLIMATE HISTORY OF MARS: IDENTIFICATION OF POTENTIAL WARM AND
WET CLIMATE ‘FALSE POSITIVES’. 54th Lunar and Planetary Science Conference 2023 (LPI Contrib. No. 2806). 1731.pdf

* https://mail.google.com/mail/u/0/?tab=wm&pli=1#inbox/FMfcgzGrbHtSWzJjdRzftxgXCrbxXNnK Water on Mars - A Literature Review" by Mohammad Nazari-Sharabian

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]

* [https://www.youtube.com/watch?v=D-SCOHj8u-A Water on Mars - James Secosky - 2021 Mars Society Virtual Convention -- Tells where water was and where ice is today on Mars (34 minutes)]

* [https://www.youtube.com/watch?v=EoUy4lsgRo8 NASA | Mars Atmosphere Loss: Sputtering]

*[https://www.youtube.com/watch?v=Y4vVFetfSF8 MAVEN | Measuring Mars' Atmospheric Loss]

* [https://www.youtube.com/watch?v=m2ERsEXAq_s - Jeffrey Plaut - Subsurface Ice - 21st Annual International Mars Society Convention-2018]

*[https://en.wikipedia.org/wiki/Water_on_Mars Wikipedia page on water on Mars]

*[https://www.bing.com/videos/search?q=nasa+gsfc+mars+ocean&view=detail&mid=435F5E5E3D31FFF0D5AC435F5E5E3D31FFF0D5AC&FORM=VIRE NASA | Mars' Ancient Ocean]

* [https://www.youtube.com/watch?v=NiT02piO40c The Geological History of Water on Mars and Astrobiological Implications (Vic Baker)]

* [https://www.youtube.com/watch?v=RWNXJk0Y01k The Evolution of Water on Mars]

* [https://www.youtube.com/watch?v=1SRmXG6UnHY&t=1335s Dr. Geronimo Villanueva - Ancient Ocean on Mars - 18th Annual International Mars Society Convention]

* [https://www.youtube.com/watch?v=WH8kHncLZwM NASA | Measuring Mars' Ancient Ocean]

* [https://www.youtube.com/watch?v=GX9XzRyuYLc Oceans and Life on Mars]
* [https://www.youtube.com/watch?v=HyV4K7EeV3U Scientists Identify a Crater that Created Massive Tsunamis on Mars]
*[https://www.youtube.com/watch?v=b4hCWIQsyps Mars: Ancient Water, Present Day Ice]
* [https://www.youtube.com/watch?v=bs8wTdCJ-NA What Happened To All The Water On Mars?]
*[https://www.youtube.com/watch?v=EJk0hS4_gz4 Water on Mars and the Potential for Martian Life]
*[https://www.youtube.com/watch?v=gtcEdeezuYg Explore the Geology of Mars]

Geological processes that have shaped Mars: Why Mars looks like it does

2026-04-10T16:34:13Z

Suitupshowup: /* Ice in the ground */ added image

Article written by Jim Secosky. Jim is a retired science teacher who has used the Hubble Space Telescope, the Mars Global Surveyor, and HiRISE.

[[File:Mars, Earth size comparison.jpg|left|thumb|px|Earth and Mars Earth is much bigger, but both have the same land area. Mars has about one third the gravity of the Earth.]]

Mars looks like it does because of certain geological processes. Some of them are common to both the Earth and Mars. However, others are rare or nonexistent on the Earth. Mars shows an extremely old record of the past that is lacking on the Earth. Plate tectonics and vigorous air and water erosion has wiped out nearly all of the past geology of the Earth. In contrast, much of the Martian surface is billions of years old. Another factor that has affected the appearance of Mars is its extreme cold. The coldness of the planet makes carbon dioxide significant. It has influenced Mars both as a gas and as a solid. As a greenhouse gas, early in the history of the planet, it may have been thick enough in the atmosphere to help raise the temperature enough to permit water to flow, to carve rivers, to form lakes and an ocean. Indeed, it may have been warm enough from carbon dioxide for life to first originate on Mars and then travel to the Earth on meteorites. Today, as a solid, carbon dioxide (dry ice) produces the ubiquitous gullies found in numerous areas of the planet.

==Erosion Related==

As on the Earth material was laid down and then later eroded. Many spectacular scenes are present with places that were mostly eroded, but with remnants remaining in the form of buttes and mesas. Sometimes, sediments were put down in layers. As a result beautiful places were created. On the Earth we admire such layers in Monument Valley and many beautiful canyons. The same types of landscapes show up on Mars.
The top layer of buttes and mesas is hard and resistant to erosion. It protects the lower layers from being eroded away. On Mars that hard, cap rock could be made from a lava flow. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area.

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File:16 21 2117 monument valley.jpg|Spearhead Mesa in Monument Valley Note the flat top and steep walls that are characteristic of mesas.

Image:Glacier as seen by ctx.JPG|Mesa in Ismenius Lacus quadrangle, as seen by CTX. Mesa has several glaciers eroding it.

File:58563 2225mesa.jpg|Mesa

File:45016 2080mesas.jpg|Mesas, as seen by HiRISE under HiWish program These are like the ones in Monument Valley

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte: Buttes have a much smaller area than mesas, but both have a hard cap rock on the top. Box shows the size of a football field.

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As on the Earth, there are landslides. However, they could be a little different since Mars has only about a third of Earth’s gravity.

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File:ESP 043963 1550landslide.jpg|Landslide

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Common features in certain areas of the Earth’s surface are “Yardangs.” They are found in desert areas which contain much sand. The wind blows sand and shapes the relatively soft grained deposits into the long, boat shapes of yardangs. On Mars it is thought that these forms are the result of the weathering of huge ash deposits from volcanoes. Mars has the biggest known volcanoes in the solar system. Many probably threw out much fine-grained material which was easily eroded to make vast fields of yardangs. Regions called the “Medusa Fossae Formation and Electris deposits contain thousands of yardangs.

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File:61167 1735yardangs.jpg|Yardangs
File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.

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Unlike the Earth, Mars shows landscapes that are billions of years old. In that time material has been deposited and then eroded and/or greatly changed. Some features have been “inverted.” Low areas turned into high areas. Low areas like stream beds were filled with erosion-resistant materials like lava and large rocks. Later, the surrounding, softer ground became eroded. As a result, the old stream bed now appears raised. We can tell it was originally a stream bed since the overall shape from above still looks like a stream with curves and branches.

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Inverted streams Here a branched stream became filled with hard material and then the surrounding ground was eroded.]]

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File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.
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Another structure made with erosion is a “pedestal crater.” They are abundant in regions far from the equator. These craters seem to sit on little circular shelves or pedestals.<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> In the impacting process, ejecta fell about the crater and protected the underlying ground from erosion. These craters occur where we think there was a great deal of ice in the ground. So, much of the material that disappeared was just ice. With that being said, pedestal craters give us an indication of how much ice was in the region. In some places hundreds of meters of ice-rich ground were removed to make pedestal craters.<ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

[[File:ESP 037528 2350pedestal.jpg |thumb|left|px||Pedestal crater Surface close to crater was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

[[Image:Pedestal crater3.jpg |thumb|right|px||Pedestal craters form when the ejecta from impacts protect the underlying material from erosion. As a result of this process, craters appear perched above their surroundings]]

[[File:Pedestaldrawingcolor2.jpg|thumb|600px|center|Drawing shows a later idea of how some pedestal craters form. In this way of thinking, an impacting projectile goes into an ice-rich layer—but no further. Heat and wind from the impact hardens the surface against erosion. This hardening can be accomplished by the melting of ice which produces a salt/mineral solution thereby cementing the surface.]]

Some structures on Mars are being “exhumed.” Craters are observed that are being uncovered. In the past, impacts produced craters. Later, they were buried. Now they are in the process of being uncovered by erosion. When an asteroid strikes the surface it generates a hole and throws out ejecta all around it. A circular hole is the result. If we see a half of a crater, we know that that it is being exposed by erosion. Impacts do not produce half holes!

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File:57652 2215exhumed.jpg|Close view of exhumed crater This crater is and was under a set of dipping layers.
[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]
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==Craters==

Impact craters occur on both the Earth and Mars. Craters are still occuring on Mars. Between 2007 and 2021, 1,203 new impacts were discovered in orbital images on ther Martian surface.<ref>Daubar, I., McEwen, A., Byrne, S., Kennedy, M., & Ivanov, B. (2013). The current martian cratering rate. Icarus, 225(1), 506–516. https://doi.org/10.1016/j.icarus.2013.0</ref> <ref> Daubar, I., Dundas, C., McEwen, A., Gao, A., Wexler, D., Piquex, S., et al. (2022). New craters on Mars: An updated catalog. JGR Planets, 127(7). https://doi.org/10.1029/2021je007145</ref> <ref>Malin, M., Edgett, K., Posiolova, L., McColley, S., & Noe Dobrea, E. (2006). Present-day impact cratering rate and contemporary gully activity on Mars. Science, 314(5805), 1573–1577. https://doi.org/10.1126/science.113515</ref> However, due to the extreme age of the Martian surface, most of Mars shows a high density of impact craters especially in the southern hemisphere. Craters do not last long on the Earth. Remember, the Earth experiences a great deal more erosion due to its thick atmosphere and abundant water. And, at intervals, the crust is taken into the Earth at plate boundaries. We know a fair amount about impact craters because the Earth has impact craters like Meteor Crater in Arizona that we can study easily.

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File:Barringer Crater USGS.jpg|Meteor Crater in Arizona
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[[File:Craters from around Mars 01.jpg |600pxr| different kinds of impact craters on Mars.]]
Different kinds of impact craters on Mars.

[[File:Types of Martian craters.jpg|600pxr|Different types of Martian craters]]

Different types of Martian craters

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

We know that a new crater will have a rim and ejecta around it. Large ones may have a central uplift and maybe a ring around the middle of the floor. We know that the impact brings up material from deep underground.<ref>https://www.uahirise.org/hipod/PSP_007464_1985</ref> If we study the rocks in the central mound and in the ejecta, we can learn about what is deep underground. During an impact, the ground is pushed down. It then rebounds and brings up rocks from deep underground.<ref> https://www.uahirise.org/ESP_013514_1630</ref>

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File:ESP 013514 1630centralcolors.jpg|Central peak of an impact crater, as seen by HiRISE Colors show different minerals--some used to be deep underground.

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File:ESP 046046 2095craterejectarim.jpg|Young crater showing layers, rim, and ejecta. Ejecta was thrown out by the force of impact.

Wikisinton.jpg|West side of Sinton Crater, as seen by CTX camera (on [[Mars Reconnaissance Orbiter]]) A central peak is visible--it occurs in larger craters and is caused by a rebound from the force of the impact.
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The heat from an impact into ice-rich ground may produce channels emanating from the edge of the ejecta. These have been seen around a number of craters.

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File:ESP 057139 2140channels.jpg|Channels These channels are in the ejecta of a crater; hence, they may have formed from warm ejecta melting ground ice.

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Mars shows some interesting variations to the usual appearance of craters. At times the force of an impact reaches down to a different type of layer. The lower layer may be of a different color; therefore the ejecta that is spread on the landscape may be a different color.

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File:ESP 059649 1695craterpretty.jpg |Young crater with bright ejecta Impact reached down to a layer that is light-toned. That light-toned material was then deposited on a dark surface.

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File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
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File:29565 2075newcratercomposite.jpg|New, small crater Meteorite that hit here throw up dark material that was under a layer of bright, surface dust. We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref>

File:ESP 011425 1775newcrater.jpg|Dark ejecta of a new crater covers the bright surroundings.
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Sometimes it looks as if an impact caused rocks to melt and when the molted rocks landed on the crater floor steam explosions occurred with ice-rich ground. What results is ground with a high density of pits.

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File:ESP 012531 1435pits.jpg|Floor of Hale Crater showing pits from steam explosions when hot, melt from an impact landed.

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On occasion, an impact may go down to ice-rich ground or maybe to a layer of ice. Indeed, a number of craters expose ice on their floors which after a period of time disappears into the thin Martian atmosphere.

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File:Iceincraterscomparison.jpg|Exposed ice in small craters The fresh ice had almost disappeared when the second picture was taken. This set of images is good evidence that ice lies under a thin layer of debris.
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Then there is a type of crater which is common in locations we think contain much ice. Called “ring-mold” craters, they may be caused by a rebound of an ice layer. Experiments in labs confirm that this behavior can occur. Ring-mold craters are called that because they resemble ring-molds used in baking.

Another, later idea, for their formation suggests that the impacting body goes through mantle layers of different densities. Later, erosion made the ring mold shape. The center of the crater's mantle was not eroded as much because it was compressed more due to greater depth of mantle there. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

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File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.

26055ringmoldcrater.jpg|Close view of ring mold crater.

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[[File:Ringmolddiagramlabeled.jpg|600pxr|Ring-mold craters form when an impact goes through to an ice layer. The rebound forms the ring-mold shape, and then dust and debris settle on the top to insulate the ice.]]
Ring-mold craters form when an impact goes through to an ice layer. The rebound forms the ring-mold shape, and then dust and debris settle on the top to insulate the ice.

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File:Alternative way of forming ring-mold craters.jpg|In this other idea for ring mold crater formation, an impact crater and the area around it is covered with mantle layers. Next, erosion removes most of the mantle. In the crater, the central section was compressed more due to thick mantle. As a result, it became more resistant to erosion. Only the edges of the mantle were removed by erosion--a plateau results.

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Now, during the impact process much material is sent flying in the air. Some of it will come down and create new craters. These are called secondary craters. They can be identified by all being of the same age. In addition, sometimes molted rock is produced by the impact. If molten rock lands on ice-rich ground, an area with a high density of pits will form. The hot molten rocks cause ice in the ground to burst into steam and cause pits to form.

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File:Secondary craters ESP 081458 1425.jpg|Secondary craters These are formed from material that is blasted way up in the air from the impact. Evidence that they are secondary craters is that they are all of the same age.
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File:66873 2180doublecrater.jpg|Double crater These form when the impactor breaks up in the atmosphere right before it lands. the two craters have the same age and share a wall.

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We can only learn so much by the study of photogrphs For years now, Jezero Crater has bben studied with the Perseverance Rover. We have learned many details of its complex history. A paper published December 2025 in Science by over 70 authors details what Perseverance discovered in the “Margin Unit,” a geologic area at the margin, or inner edge, of Jezero Crater. With the information collected, the scientists were able to come up with an understanding of the history of the crater. Other craters on Mars may have undergone some of the same processes.
After a large impact created Jezero Crater hot magma moved and accumulated under the ground forming what are called intrusions. Some are called sills or lacoliths depending on their shapes. In these chambers, magma underwent a slow cooling. Scientists concluded that because the rocks they examined contained large crystals. Such crystals are produced by very slow cooling. Later erosion exposed these old chambers. Lava, then came into Jezero. The basalt that was formed was detected by Perseverance. It also found carbonate minerals. These minerals meant that water came in and formed a lake. Just looking at satellite pictures of Jezero, one might guess that only minerals derived from sedimentary rocks would be found on the surface. However, several classes of rocks were formed that indicated a complex history. <ref>https://www.jpl.nasa.gov/news/nasas-perseverance-mars-rover-ready-to-roll-for-miles-in-years-ahead/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20251218-3</ref> <ref>https://www.science.org/doi/10.1126/science.adu8264</ref> <ref>Kenneth H. Williford et al. ,Carbonated ultramafic igneous rocks in Jezero crater, Mars.Science0,eadu8264DOI:10.1126/science.adu8264</ref>

==Features in and around craters==
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File:Small group of dunes.jpg|Dunes on crater floor|Dunes often form on the floor of craters. The sand is too heavy to be carried out of crater, so it stays on the floor. And then it is shaped by the wind. The colors are due to small amounts of various minerals. Images are processed in false colors to bring out more detail and to help identify minerals.

File:ESP 082974 1685ridge and star shaped dunes 02.jpg|The winds inside of craters may come from different angles. If they blow in 2 different dirctions star shaped dunes may result. This picture is about 1 Km wide.
File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel
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File:Dark Streaks in crater 81668 1960.jpg|Dark streaks in crater Dark streaks are beleived to be avalances of bright dust that uncovers a dark underlying surface.
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File:Close view of gully in Phaethontis 01.jpg|Gullies in crater Many steep slopes, especially in craters, display gullies. Today, some of these are forming with the help of dry ice. In the past, liquid water may have been involved with their creation.

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File:Mantle and brain terrain ESP 056826 1445.jpg|Mantle and brain terrain Mantle is smooth material that covers many parts of Mars. It is ice-rich and falls from the sky. Some ice-rich surfaces develop cracks. Along the cracks the ground ice disappears. Where is disappears, hollowed spots are formed. The higher parts may still contain ice.

File:ESP 053524 2050hollows.jpg|Hollowed ground because ice has left the ground. When ice is exposed to the thin atmosphere of Mars it disapperas by a process called sublimation. With sublimation a solid goes directly into a gas--not melting first.
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File:Layers in Danielson Crater, as seen by HiRISE under HiWish program 09.jpg|Wide view of layers in Damielson Crater Layers often need water for their formation. It may come from the atmosphere or from the ground.

File:Close view of layers in Danielson Crater, as seen by HiRISE under HiWish program 07.jpg|Close up of layers in Damielson Crater Many layers are produced when the climate changes. The Martian climate changes quite a bit due to the major shifts in its rotational axis.

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File:ESP 055091 1405flow.jpg|Flow (Glacier) Glaciers on Mars consist of ice that is covered with a layer of dirt. The dirt insulates the ice from the atmosphere.
File:ESP 057806 2155ccf.jpg|Concentric Crater Fill (CCF) CCF is made as material moves off crater walls. Most of the material in the crater is ice that has a covering of dirt and rocks.
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File:ESP 056607 2170layers.jpg|Young crater showing layers, rim, and ejecta Old craters do not display these things.
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File:ESP 055146 1425ridges.jpg|Floor of Hellas Parts of the floor of Hellas, the giant imapact crater in the southern hemisphere, display many strange shapes. We currently do not have a total understand of them. Large glaciers moving from the walls may have been involved.
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File:ESP 055104 1385pyramid.jpg|Layered feature in crater These features are formed from an accumulation of ice-rich material that falls from the sky. The material will drop down at intervals as the climate changes. Its shape is made smooth by winds.
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==Glaciers==

Today, we recognize several types of features that contain ice that is covered with dirt and rocks that keep the ice from disappearing. These features behave like glaciers. Concentric crater fill (CCF), lobate debris aprons (LDA), and lineated valley fill (LVF) are their names.<ref>https://www.sciencedirect.com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103520304619#bb0190</ref> <ref>Jawin, E, and J. Head. 2021. Patterns of late Amazonian deglaciation from the distribution of martian paraglacial features. Icarus. Volume 355. 114117</ref> <ref> S.W. Squyres. 1979. The distribution of lobate debris aprons and similar flows on Mars. J. Geophys. Res. Solid Earth, 84. pp. 8087-8096, 10.1029/JB084iB14p08087</ref> <ref>J.W. Head, G. Neukum, R. Jaumann, H. Hiesinger, E. Hauber, M. Carr, P. Masson, B. Foing, H. Hoffmann, M. Kreslavsky, S. Werner, S. Milkovich, S. van Gasselt, Co-Investigator Team, T.H. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature, 434. pp. 346-351</ref> <ref>J.W. Head, D.R. Marchant, J.L. Dickson, A.M. Kress, D.M. Baker. 2010. Northern mid-latitude glaciation in the late Amazonian period of Mars: criteria for the recognition of debris-covered glacier and valley glacier landsystem deposits
Earth Planet. Sci. Lett., 294. pp. 306-320</ref> <ref> D.M.H. Baker, J.W. Head, D.R. Marchant. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae fossae, Mars: evidence for extensive mid-latitude glaciation in the late Amazonian. Icarus, 207 (2010), pp. 186-209, 10.1016/j.icarus.2009.11.017</ref> <ref>J.S. Levy, J.W. Head, D.R. Marchant. 2010. Concentric crater fill in the northern mid-latitudes of Mars: formation processes and relationships to similar landforms of glacial origin. Icarus. 209. pp. 390-404, 10.1016/j.icarus.2010.03.036</ref>

Mars may have had much water in past ages. Much of that water is now frozen in the ground and locked up in glacier-like forms. Many features have been found that are like glaciers—in that they are mostly made of ice and flow like glaciers. <ref name="SquyresCarr">cite journal | last1 = Squyres | first1 = S.W. | last2 = Carr | first2 = M.H. | year = 1986 | title = Geomorphic evidence for the distribution of ground ice on Mars | url = | journal = Science | volume = 213 | issue = | pages = 249–253 | doi = 10.1126/science.231.4735.249 | </ref> <ref name="Headetal2010">cite journal | last1 = Head | first1 = J.W. | last2 = Marchant | first2 = D.R. | last3 = Dickson | first3 = J.L. | last4 = Kress | first4 = A.M. | year = 2010 | title = Criteria for the recognition of debris-covered glacier and valley glacier landsystem deposits | url = | journal = Earth Planet. Sci. Lett. | volume = 294 | issue = | pages = 306–320 | doi=10.1016/j.epsl.2009.06.041 | </ref> <ref name="HoltetalSHARAD">cite journal | last1 = Holt | first1 = J.W. | display-authors = 1 | last2 = et al | year = 2008 | title = Radar sounding evidence for buried glaciers in the southern mid-latitudes of Mars | url = | journal = Science | volume = 322 | issue = | pages = 1235–1238 | doi=10.1126/science.1164246 | pmid=19023078|</ref> <ref name="MorganetalDeuteronilus">| last1 = Morgan | first1 = G.A. | last2 = Head | first2 = J.W. | last3 = Marchant | first3 = D.R. | year = 2009 | title = Lineated valley fill (LVF) and lobate debris aprons (LDA) in the Deuteronilus Mensae northern dichotomy boundary region, Mars: Constraints on the extent, age and episodicity of Amazonian glacial events | url = | journal = Icarus | volume = 202 | issue = | pages = 22–38 | doi=10.1016/j.icarus.2009.02.017 |</ref > <ref name="Plautetal">cite journal | last1 = Plaut | first1 = J.J. | last2 = Safaeinili | first2 = A. | last3 = Holt | first3 = J.W. | last4 = Phillips | first4 = R.J. | last5 = Head | first5 = J.W. | last6 = Sue | first6 = R. | last7 = Putzig | first7 = A. | year = 2009 | title = Frigeri Radar evidence for ice in lobate debris aprons in the mid-northern latitudes of Mars | doi = 10.1029/2008gl036379 | journal = Geophys. Res. Lett. | volume = 36 | issue = | page = L02203 | </ref> <ref name="Bakeretal2010">cite journal | last1 = Baker | first1 = D.M.H. | last2 = Head | first2 = J.W. | last3 = Marchant | first3 = D.R. | year = 2010 | title = Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian | url = | journal = Icarus | volume = 207 | issue = | pages = 186–209 | doi=10.1016/j.icarus.2009.11.017 | </ref> <ref name="ArfstromHartmann">cite journal | last1 = Arfstrom | first1 = J. | year = 2005 | title = Terrestrial analogs and interrelationships | url = | journal = Icarus | volume = 174 | issue = | pages = 321–335 | doi=10.1016/j.icarus.2004.05.026 |</ref> That means they move slowly and in a downhill direction. For ice to exist under today’s climate conditions, it must be covered with a layer of debris—dust, rocks, etc. A layer several meters or a few tens of meters thick will preserve ice for millions of years. <ref name="WilliamsSnowpack">cite journal | last1 = Williams | first1 = K. E. | display-authors = 1 | last2 = et al | year = 2008 | title = Stability of mid-latitude snowpacks on Mars | url = | journal = Icarus | volume = 196 | issue = 2| pages = 565–577 | doi=10.1016/j.icarus.2008.03.017 |</ref> Under today’s conditions any exposed ice would undergo [[sublimation]] and disappear into the thin Martian atmosphere. That is, it would go directly from a solid to a gas. But, the isulating effect of surface material prevents loss of ice.<ref name="Plautetal" /> <ref name="WilliamsSnowpack" /> <ref name="Head, J. 2005">cite journal | doi = 10.1038/nature03359 | last1 = Head | first1 = J. | date = 2005 | last2 = Neukum | first2 = G. | last3 = Jaumann | first3 = R. | last4 = Hiesinger | first4 = H. | last5 = Hauber | first5 = E. | last6 = Carr | first6 = M. | last7 = Masson | first7 = P. | last8 = Foing | first8 = B. | last9 = Hoffmann | first9 = H. | last10 = Kreslavsky | first10 = M. | last11 = Werner | first11 = S. | last12 = Milkovich | first12 = S. | last13 = Van Gasselt | first13 = S. | last14 = Co-Investigator Team | first14 = The Hrsc | title = Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars | url = | journal=Nature | volume = 434 | issue = 7031| pages = 346–350 | pmid=15772652|</ref> <ref> Head, J., et al. 2009. Northern mid-latitude glaciation in the Late Amazonian period of Mars: Criteria for the recognition of debris-covered glacier and valley glacier landsystem deposits. Earth and Planetary Science Letters. Doi:10.1016/j.epsl.2009.06.041</ref>
Martian glaciers show evidence of movement on their surfaces and in their shapes. The actual existence of water ice in some of them has been proven with radar studies from orbit. <ref>http://news.discovery.com/space/mars-ice-sheet-climate.html</ref>

Analysis of [[SHARAD]] data led researchers to conclude that martian glaciers are 80% pure ice. The paper authors examined five different sites and all showed high levels of pure water ice. <ref> Yuval Steinberg et al, "Physical properties of subsurface water ice deposits in Mars's Mid-Latitudes from the shallow radar.", Icarus (2025)</ref> <ref> https://www.space.com/astronomy/mars/good-news-for-mars-settlers-red-planet-glaciers-are-mostly-pure-water-ice-study-suggests</ref> <ref>https://www.youtube.com/watch?v=nzh2sirXfD8</ref> <ref> Steinberg, Y. et al. 2025. Physical properties of subsurface water ice deposits in Mars’s Mid-Latitudes from the shallow radar. Icarus. vol. 441 116716</ref>

Some of them look just like alpine glaciers on the Earth.<ref> https://www.uahirise.org/hipod/PSP_008809_2215</ref> Most show piles of debris called moraine. This was material that was removed from one place and moved along to another by ice. Also, shapes looking just like eskers of terrestrial glaciers are common in places. Eskers form from streams moving under glaciers. These streams deposit rocks in tunnels in the ice at the bottom of glaciers. When the ice goes away, curved ridges stay behind.

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File:R0502109dorsaargentea.jpg|Possible eskers indicated by arrows. Eskers form under glaciers.

Wikilau.jpg|Lau Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Curved ridges are probably eskers which formed under glaciers.
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File:ESP 018857 2225alpineglacier.jpg |Alpine glacier moving from a valley Lat: 42.2° N Long: 50.5° . Note how it spreads out when leaving the valley.

File: Wikielephantglacier.jpg|Glacier in Greenland Glacier spreads out when it leaves valley.
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For Mars, a number of names have been applied to these glacier-like forms. Some of them are tongue-shaped glaciers, lobate debris aprons (LDA’s), lineated valley fill (LVF), and concentric crater fill (CCF).<ref>Levy, J., J. Head, D. Marchant. 2010. Concentric Crater fill in the northern mid-latitudes of Mars: Formation process and relationships to similar landforms of glacial origin. Icarus 2009, 390-404.</ref> <ref>Levy, J., J. Head, J. Dickson, C. Fassett, G. Morgan, S. Schon. 2010. Identification of gully debris flow deposits in Protonilus Mensae, Mars: Characterization of a water-bearing, energetic gully-forming process. Earth Planet. Sci. Lett. 294, 368–377.</ref> <ref>http://hirise.lpl.arizona.edu/ESP_032569_2225</ref> <ref>Garvin, J., S. Sakimoto, J. Frawley. 2003. Craters on Mars: Geometric properties from gridded MOLA topography. In: Sixth International Conference on Mars. July 20–25, 2003, Pasadena, California. Abstract 3277.</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>http://hirise.lpl.arizona.edu/PSP_009535_2240</ref> <ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. ISBN|978-0-521-87201-0</ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> <ref>Levy,J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res. 112</ref> <ref>Garvin, J. et al. 2002. Lunar Planet. Sci: 33. Abstract # 1255.</ref>
<ref>http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185</ref>

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File:ESP 035327 2255tongues.jpg|Tongue-shaped glaciers These were made when a flow encountered an obstacle that made it split into two.
File:ESP 036619 2275ldalabeled.jpg|Lobate debris apron LDA) around a mound <ref>Baker, D., et al. 2009. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209.</ref> <ref>Marchant, D. and J. Head. 2007. Antarctic dry valleys: Microclimate zonation, variable geomorphic processes, and implications for assessing climatic change on Mars. Icarus: 192.187-222</ref> <ref>Dickson, J., et al. 2008. Late Amazonian glaciation at the dichotomy boundary on Mars: Evidence for glacial thickness maxima and multiple glacial phases. Geology: 36 (5) 411-415</ref> <ref>Kress, A., et al. 2006. The nature of the transition from lobate debris aprons to lineated valley fill: Mamers Valles, Northern Arabia Terra-Deuteronilus Mensae region on Mars. Lunar. Planet. Sci. 37. Abstract 1323</ref>
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File:30707946 10212010896087124 5214252926280663040 nccf.jpg|Concentric Crater Fill, as seen by CTX This crater was bowl shaped when formed; now it is full of ice and dust . <ref>Levy, J., J. Head, D. Marchant. 2010. Concentric Crater fill in the northern mid-latitudes of Mars: Formation process and relationships to similar landforms of glacial origin. Icarus 2009, 390-404.</ref> <ref>Levy, J., J. Head, J. Dickson, C. Fassett, G. Morgan, S. Schon. 2010. Identification of gully debris flow deposits in Protonilus Mensae, Mars: Characterization of a water-bearing, energetic gully-forming process. Earth Planet. Sci. Lett. 294, 368–377.</ref> <ref>http://hirise.lpl.arizona.edu/ESP_032569_2225</ref> <ref>Garvin, J., S. Sakimoto, J. Frawley. 2003. Craters on Mars: Geometric properties from gridded MOLA topography. In: Sixth International Conference on Mars. July 20–25, 2003, Pasadena, California. Abstract 3277.</ref>

File:Ccffigurecaptioned.jpg| The depth of craters can be predicted based upon the observed diameter. Many craters are now almost full, instead of having bowl shape; consequently, it is believed that they have added ice, dust, and other debris since they were formed. <ref>Dickson, J., et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>cite web|url=http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> <ref>Levy, J. et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial processes. Icarus: 202. 462-476.</ref>

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File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.

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[[File:ESP 052138 1435lvf.jpg|thumb|600px|center|Lineated valley fill, as seen by HiRISE under [[HiWish program]]]]

==Ice in the ground==

Mars has some unique landscapes and features that are common just to it. Since so much water is frozen in the ground and since the thin atmosphere of Mars allows ground ice to disappear when it became exposed, unreal scenes can develop. Under current conditions on Mars, ice sublimates when exposed to the air. In that process, ice goes directly to a gas instead of first melting. It often starts with small, narrow cracks that get larger and larger. Once ice leaves the ground there is not much left except dust. And winds will eventually carry the dust away. The end result is various shaped holes, pits, canyons, and hollows. Some of these forms are called brain terrain,<ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> ribbed terrain, hollows, scalloped terrain, and exposed ice sheets.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> <ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> All of these may be of use to future colonists who need to find supplies of water.

[[File:45917 2220brainsopenclosed.jpg|Open an closed brain terrain <ref >Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>]]

Open and closed brain terrain <ref >Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows.

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File:46916 2270scallopsmerging.jpg|Scalloped terrain <ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>Lefort, A.; Russell, P. S.; Thomas, N.; McEwen, A. S.; Dundas, C. M.; Kirk, R. L. 2009. "Observations of periglacial landforms in Utopia Planitia with the High Resolution Imaging Science Experiment (HiRISE)". Journal of Geophysical Research. 114 (E4). </ref> <ref> Morgenstern, A; Hauber, E; Reiss, D; van Gasselt, S; Grosse, G; Schirrmeister, L (2007). "Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars" (PDF). Journal of Geophysical Research: Planets. 112 (E6): E06010.</ref> <ref> Zanetti, M.; Hiesinger, H.; Reiss, D.; Hauber, E.; Neukum, G. 2009. "Scalloped Depression Development on Malea Planum and the Southern Wall of the Hellas Basin, Mars" (PDF). Lunar and Planetary Science. 40. p. 2178, abstract 2178. </ref> <ref>Lefort, A.; Russell, P.S.; Thomas, N. (2010). "Scalloped terrains in the Peneus and Amphitrites Paterae region of Mars as observed by HiRISE". Icarus. 205 (1): 259. </ref>
PIA22078 hireswideview.jpg|Wide view of triangular depression The colored strip shows the part of the image that can be seen in color. The wall at the top of the depression contains pure ice. This wall faces the south pole. <ref>Supplementary Materials Exposed subsurface ice sheets in the Martian mid-latitudes Colin M. Dundas, Ali M. Bramson, Lujendra Ojha, James J. Wray, Michael T. Mellon, Shane Byrne, Alfred S. McEwen, Nathaniel E. Putzig, Donna Viola, Sarah Sutton, Erin Clark, John W. Holt</ref>

PIA22077 hirescloseblue.jpg|Close, color view of wall containing ice from previous image <ref name='exposed ice 2018'>[https://www.jpl.nasa.gov/news/news.php?feature=7038 Steep Slopes on Mars Reveal Structure of Buried Ice]. NASA Press Release. 11 January 2018.</ref> <ref>[http://www.sciencemag.org/news/2018/01/ice-cliffs-spotted-mars Ice cliffs spotted on Mars]. ''Science News''. Paul Voosen. 11 January 2018.</ref> <ref>Dundas, E., et al. 2018. Exposed subsurface ice sheets in the martian mid-latitudes. Science. 359. 199.</ref> <ref> http://spaceref.com/mars/steep-slopes-on-mars-reveal-structure-of-buried-ice.html</ref>
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[[File: 46325 2225hollowsclose2.jpg|600pxr|Close view of hollowed terrain caused by ice leaving the ground Box shows size of football field.]]

Close view of terrain caused by ice leaving the ground Box shows size of football field.

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File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.
File:ESP 066765 2245 ribs labeledcropped.jpg|Enlarged diagram of how hollows form starting with cracks.

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Other signs of water ice in the ground are: lobed (rampart craters), patterned ground, and possible pingos. Pattered ground or polygonal ground is common in ice-rich areas on Earth. Most of these features on the surface of Mars are common on the Earth where ground ice is present. <ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

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File:56942 1075icepolygonslabeled2.jpg|Polygons Ice is in the low troughs that lie between the polygons.<ref>https://www.uahirise.org/ESP_047247_1150</ref>

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Pingos are mounds that contain a core of ice.<ref>http://www.uahirise.org/ESP_046359_1250</ref> <ref>Soare, E., et al. 2019.</ref> <ref> Possible (closed system) pingo and ice-wedge/thermokarst complexes at the mid latitudes of Utopia Planitia, Mars. Icarus. https://doi.org/10.1016/j.icarus.2019.03.010</ref> They often have cracks on their surfaces. Cracks form when water freezes and expands. Pingos would be useful as sources of water for future colonies on the planet.

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51230 2200pingos.jpg|Close view of possible pingos Pingos contain a core of pure ice; they would be useful for a source of water by future colonists.
ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program
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Craters with ejecta that look like they were made by an impact into mud are called lobed or rampart craters. They were discovered by early, orbital missions to Mars. They are most common where we expect ice in the ground.

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File:Mars rampart crater.jpg|Yuty Crater showing lobe and rampart morphology; it looks like mud was formed during the impact.

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Channels are sometimes found in a crater's ejecta or along the edges of the ejecta. Heat from the ejecta probably melted ice in the ground. Much heat is produced with an impact.

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File:ESP 055530 2180channels.jpg

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==Liquid water==

Mars used to have lots of water and maybe a much thicker atmosphere billions of years ago. With liquid water, life is possible. Indeed, life may have first appeared on Mars before it occurred on Earth. Martian organisms could have been knocked off Mars by low angle asteroid impacts and found their way to Earth. Perhaps, the DNA of all Earthly organisms, included us, still contains genes from early Martian life. When we have samples of Mars brought back to Earth, we may find traces of DNA that are like ours.
Data are still being gathered and ideas debated, but scientists think that once Mars cooled down and lost its magnetic field, the solar wind may have carried away much of its atmosphere. In addition, some researchers have suggested that some of the atmosphere was splashed out by impacts. After the planet cooled, water became frozen in the polar ice caps and in the ground. But, for some period there was liquid water.

[[File:Mars vs Earth Solar Wind-1024x576.png|Artist’s conception of how the solar wind strikes Mars, but does not reach the Earth’s surface because of the Earth’s magnetic field]]

Artist’s conception of how the solar wind strikes Mars, but does not reach the Earth’s surface because of the Earth’s magnetic field

[[File:Mavenargoninfographic2.jpg|This poster made by NASA shows the different ways that Mars lost most of its atmosphere after its magnetic field disappeared.]]

This poster made by NASA shows the different ways that Mars lost most of its atmosphere after its magnetic field disappeared.

Huge amounts of water had to be present to carve the many outflow channels and produce the valley networks. Many of the outflow channels begin in "Chaos Terrain." Such a landscape often is where the ground seems to have just collapsed into giant blocks.<ref>https://marsed.asu.edu/mep/ice/chaos-terrain</ref> <ref>https://link.springer.com/referenceworkentry/10.1007%2F978-1-4614-9213-9_46-2</ref> It is believed that a shell of ice was created when the planet's climate cooled. Perhaps, at times the shell was broken by asteroid impacts, movements of magma, or faults. Such events would allow pressurized water to rapidly escape from under the shell of ice (shell has been called a cryosphere).<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> Evidence is accumulating for the existence of an ocean. Lakes existed in low spots, especially craters. A large group of researchers modeled the effects of ice cover on a lake in Gale Crater. They found that
liquid water can remain in a lake for 100–125 years when the climate is cold (seasonally below 0°C), humid (70%), and gets ∼50–100 mm of water every month. The greater the concentration of salts, the more the freezing point is depressed. As a result the thickness of the ice and the amount of ice cover is lower than with pure water.
Ice contributes to lake durability by minimizing evaporation rates during times of partial or total ice cover.<ref>Moreland, E., et al. 2026. Seasonal Ice Cover Could Allow Liquid Lakes to Persist in a Cold Mars Paleoclimate. AGU Advances. e2025AV001891</ref>

[[File:ESP 056689 2210channelslowspotcropped.jpg |thumb|right|px||Channels that empty into a low area that could have been a lake Arrows show channels that lead to a low area that could have hosted a lake.]]

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel

These forms were shaped by running water.

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File:ESP 056800 1385channels.jpg|Crater with channels Arrows show channels that carried water into and out of crater.

File:Ravi Vallis.jpg|Ravi Vallis was formed when the ground released a great flood of water from Aromatum Chaos. Maybe it started when hot magma moved under the ground.

File:Ister Chaos.jpg|Ister Chaos Water may have come out of this landscape when the ground broke up into blocks.<ref>https://www.uahirise.org/hipod/PSP_008311_1835</ref>

File:Branched Channels from Viking.jpg|These valley networks look like they were made from precipitation.

File:Meanderingridgeswide ESP 079382 1735 01.jpg|Inverted streams Cutting across the scene are curvilinear ridges. These likely represent ancient, meandering river channels that flowed across the surface and buried themselves over time. The channels have subsequently been exposed to the surface by the wind, forming the cross-cutting ridges.

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At present, it is hotly debated just how long water stayed around. The sun was not as strong billions of years ago. Greenhouse gases like carbon dioxide, methane, and hydrogen may have made Mars warm enough for liquid water. Massive volcanoes would have given up many of these gases, along with water vapor.

[[File: Olympus Mons Side View.svg.png|thumb|left|300px|Height of Olympus Mons compared to tall mountains on Earth]]

[[File:ESP 077583 2255inverted.jpg|thumb|500px|center|Inverted stream, a stream bed has been filled with hard materials that did not erode away like the surroundings]]

Maybe the water just existed for short periods. Some studies have showed that large impacts into icy ground could release water and change the local climate for thousands of years. Also, impacts may have punctured an ice shell and allowed pressurized water to flow out for a time. Any water moving on the surface would quickly freeze at the top. But, it would continue to flow under the ice for a long time and make many of the channels we see today. Heat to allow water to flow may have been from underground flows of magma. On the other hand, many of the features created by liquid water could have formed under massive ice sheets where water was insulated from the Martian atmosphere.
 

==Layers==

Many locations display layered formations. Some are mostly just made of ice and dust. These types of layers are common in the polar ice caps, especially the northern ice cap.<ref>https://www.uahirise.org/hipod/PSP_008244_2645</ref> Other, rockier layers, are visible in the walls of impact craters and canyon walls.

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File:PSP 008244 2645northicecaplabeled.jpg|Layers in northern ice cap that are exposed along a cliff

File:ESP 054515 2595icecaplayers.jpg|Close view of many layers exposed in northern ice cap
File: 57080 1380layerscratercolor.jpg|Layers in crater wall in Phaethontis quadrangle, as seen by HiRISE under HiWish program
48980 1725layersclose2.jpg|Close view of layers in Louros Valles
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And then there are layers that may be more recent, they may be connected to repeated climate changes. Some have regularity to them. The climate of Mars changes drastically due to changes in the tilt of its rotational axis. At times, like now, it is close to the Earth’s 23.5 degrees. But, at times it may be as much as 70 degrees.<ref> Schorghofer, Norbert (2008). "Temperature response of Mars to Milankovitch cycles". Geophysical Research Letters. 35 (18): doi:10.1029/2008GL034954.</ref> <ref>ouma | first1 = J. | last2 = Wisdom | first2 = J. | year = 1993 | title = The Chaotic Obliquity of Mars | url = | journal = Science | volume = 259 | issue = 5099| pages = 1294–1297 |</ref> <ref>Laskar | first1 = J. | last2 = Correia | first2 = A. | last3 = Gastineau | first3 = M. | last4 = Joutel | first4 = F. | last5 = Levrard | first5 = B. | last6 = Robutel | first6 = P. | year = 2004 | title = Long term evolution and chaotic diffusion of the insolation quantities of Mars | url = | journal = Icarus | volume = 170 | issue = 2| pages = 343–364 |</ref> Tilt governs the seasons and where ice is distributed. Currently, the largest deposit of ice is at the poles. At other times could have been at mid-latitudes. Imagine how it would be to have Pittsburgh under an ice cap. Mars may have had ice caps at the latitude of Pittsburgh.

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File:Mars Ice Age PIA04933 modest.jpg|How Mars may have looked with a greater tilt of Mars' rotational axis caused increased solar heating at the poles. This larger tilt would make a surface deposit of ice and dust down to about 30 degrees latitude in both hemispheres.
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There is an ice-rich material that falls from the sky. It is called latitude dependent mantle.<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> <ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> It is thought to come from snow and ice-coated dust. At times, there is a lot of dust in the air. When that happens, moisture will freeze onto dust grains. When the ice-coated dust particle gets heavy enough, it will fall. Recent accumulations of this mantle look smooth. In some places the mantle is layered. Some formations, particularly in protected spots in craters and against mounds, suggest that these layered formations had many more layers. The wind sometimes shapes them into layered mounds.

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.
[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

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File:ESP 035801 2210dipping.jpg|Layers leaning against a mound The mound protected them from erosion.
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The older layers visible on crater and canyon walls may have different sources. Some are from lava flows or ash from volcanoes. Some may have formed under water like most layered sedimentary rocks on the Earth.<ref>https://www.uahirise.org/PSP_008391_1790</ref> Curiosity, our robotic explorer, has found that layers in Gale Crater were made from sediments at the bottom of a lake. Some may be just from dust and debris settling in low areas and then being cemented by rising groundwater carrying minerals like sulfates and silica.<ref> Rates and mechanisms of chemical weathering of ferromagnesian silicate minerals on Mars | date = 1993 | last1 = Burns | first1 = Roger G | journal = Geochimica et Cosmochimica Acta | volume = 57 | issue = 19 | pages = 4555–4574 |</ref> <ref>{{cite journal | doi = 10.1029/92JE02055 | title = Rates of Oxidative Weathering on the Surface of Mars | date = 1993 | last1 = Burns | first1 = Roger G. | last2 = Fisher | first2 = Duncan S. | journal = Journal of Geophysical Research | volume = 98 | issue = E2 | pages = 3365–3372 |</ref> <ref>Hurowitz | first1 = J. A. | last2 = Fischer | first2 = W. W. | last3 = Tosca | first3 = N. J. | last4 = Milliken | first4 = R. E. | year = 2010 | title = Origin of acidic surface waters and the evolution of atmospheric chemistry on early Mars | url = https://authors.library.caltech.edu/18444/2/ngeo831-s1.pdf| journal = Nat. Geosci. | volume = 3 | issue = 5| pages = 323–326 | doi = 10.1038/ngeo831 | </ref> Sometimes a crater may have been filled up with layered rocks and then the rocks may have been eroded by the wind in such a way to just leave a layered mound in the center of the crater. Gale crater, where Curiosity is exploring, was like that.

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Image:Topographic Map of Gale Crater.jpg|Gale Crater with Aeolis Mons rising from the center. The noted [[Curiosity]] landing area is near Peace Vallis in Aeolis Palus. Curiosity landed in the northern part of the crater. Colors indicate elevation.

File:Marscratermounds.jpg|Some layers form mounds in the center of craters. They could have been made by the erosion of layers that were deposited after the impact.

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[[File:8021 mars-curiosity-rover-msl-rock-layers-PIA21043-full2murray.jpg|600pxr|Rock layers in the Murray Buttes area in lower Mount Sharp They look like rocks formed at the bottom of lakes and their chemistry proves it.]]

Rock layers in the Murray Buttes area in lower Mount Sharp

==Igneous effects==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

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File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons

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Igneous refers to rock that is heated to a molten condition. On Mars, this is a major shaper of landscapes. Lava comes out of the ground at holes called vents. Flows of lava can be about as fluid as water and move long distances. Sometimes the top cools to a solid, but the liquid rock continues to flow underneath a hard crust. Giant pieces of this stiff crust can move around as “lava rafts.”

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File:ESP 054891 2040lavarafts.jpg|Lava rafts
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In other places, lava travels in channels. When they make a hard crust, lave tunnels are created. A picture below shows lava tunnels.<ref> https://www.uahirise.org/PSP_009501_1755</ref> After the liquid lava moves away, an empty tunnel can be formed. These are significant for future colonists as they may be where our first colonies will be built. There people would be protected from surface radiation. We have already found spots that might be openings to these tunnels in HiRISE images.

[[File:PSP 009501 1755lavatube.jpg |Lava tubes and lava tunnels Future colonists may live in lava tunnels.]]

[[File:Pavonis Mons lava tube skylight crop.jpg|thumb|left|Possible cave entrance to a lava tunnel Future colonies may live in caves for protection from weather and radiation.]]

[[File:Tharsis mons Viking.jpg |right|thumb|px|Some of the Martian volcanoes, as seen by Viking 1]]

There are huge volcanoes that were noticed by our first spacecraft to orbit the planet. The first satellite to orbit the planet was only able to see a few volcanoes peeking above a massive global dust storm. Since Mars has not had plate tectonics for nearly all of its history, volcanoes can grow very large.<ref>https://www.jpl.nasa.gov/edu/learn/video/mars-in-a-minute-how-did-mars-get-such-enormous-mountains/</ref> Lava and ash can erupt from the same spot for long periods of time. On the Earth, the plates move so volcanoes can only grow so big.

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File:Olympus Mons alt.jpg|Olympus Mons, tallest volcano in solar system The mass of volcanoes on mars stretches and cracks the crust causing faults.

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Volcanoes are only the surface manifestations of liquid rock. There is more molted rock moving under the surface than what we see above ground in volcanoes. Molted rock is called magma when underground. Stretching out around volcanoes underground are various structures. Vast linear walls, called dikes radiate out from volcanoes. On Mars they can be many miles in length. Many form by moving along cracks or weak parts of rocks. Some scientists have suggested that they from long troughs when they melt ground ice. Troughs are some of the longest features on Mars.

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File:ESP 045981 2100dike2.jpg|Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

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Besides the direct action of lava and magma, volcanoes affect Mars with just their weight. The mass of a volcano stretches the crust and makes cracks form. The large canyon system of Valles Marineris may have been started with some sort of stretching of the crust. But, its stretching may have been caused by rising mantle plumes or maybe the rise of Tharsis where so many volcanoes are located.<ref>https://astronomy.com/magazine/ask-astro/2013/08/valles-marineris</ref> Cracks in the crust are called faults. Faults on Mars are often double faults. A center section is lower than the sides. This arrangement is called a graben. On the Earth they can turn into lakes like Lake George in New York State. Graben on Mars can be thousands of miles long.

Researchers have discovered that there is a large plume under Cerberus Fossae. It is almost the area of the continental United States. The plume is warmer than its surroundings by 95 to 285 degrees Celsius (171 to 513 degrees Fahrenheit). Plumes like this are like the plume under Hawaii.

Evidence for the plume are (1) origin of nearly all Marsquakes, (2) a rise of a mile above the surroundings, (3) crater floors tilted away from the rise, and (4) slight variations in the gravity field showing that the uplift is supported from deep within the planet.
Cerberus Fossae is in Elysium Planitia, a site of the youngest known volcanic eruption on Mars. That eruption produced a small explosion of volcanic ash around 53,000 years ago--a short time in geology.

The discovery of a plume increases the chance of life. Heat from the plume could melt ground ice; consequently, allowing chemical reactions that could sustain life.<ref>A. Broquet, J. C. Andrews-Hanna. Geophysical evidence for an active mantle plume underneath Elysium Planitia on Mars. Nature Astronomy, 2022; DOI: 10.1038/s41550-022-01836-3</ref> <ref>https://www.sciencedaily.com/releases/2022/12/221205121545.htm</ref> <ref>https://www.nature.com/articles/s41550-022-01836-3</ref>

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File:Troughs in Elysium Planitia.jpg|Troughs showing layers The center section of the picture is in color. With HiRISE only a strip in the middle is in color. These troughs are in Cerberus Fossae, as seen by HiRISE under the HiWish program. Location is 15.819 N and 161.448 E. Cerberus Fossae is the source of most of the Marsqukes detected by the InSight mission.

ESP 046251 2165graben.jpg|Straight trough is a fossa that would be classified as a graben. Curved channels may have carried lava/water from the fossa. Picture taken with HiRISE under [[HiWish program]].

File:ESP 057834 2005troughmesa.jpg|Trough or graben cutting through mesa
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Sometimes lava moves over frozen ground. That results in steam explosions. Large fields of small cones can be produced when this happens. Those cones are called “rootless cones” since they do not go down very far.

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File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones
File:45384 2065cones2.jpg|Close view of rootless cones
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Volcanoes sometimes explode with great amounts of ash that travels long distances, covering everything. Some of the layers seen on Mars are probably from these ash deposits. These deposits do not contain boulders and are easily eroded by just the wind. Two areas on Mars have widespread and thick deposits made in this way; they are called the Medusae Fossae Formation and the Electris deposits. These relatively soft deposits often form shapes called yardangs. They are sort of boat shaped and show the direction of the prevailing wind when they were created.

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File:61167 1735yardangs3.jpg|Yardangs
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Much of the atmosphere of Mars came from volcanoes. Volcanoes give off large amounts of carbon dioxide and water, along with other chemicals. Some of these chemical compounds are “greenhouse gases” that served to heat up early Mars.
A few places are thought to be where volcanoes erupted under ice. The shapes that resulted look like those made on Earth when a volcano erupted under the ice.

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

==Bright dust==

A thin coating of bright-toned dust covers almost all parts of Mars. It has a rust brown color. It is not too noticeable until it is not here. Some things remove the dust and then reveal the dark underlying surface. The contrast between this thin coating and the underlying dark rock is striking. Much of the difference derives from how NASA pictures are processed.<ref> Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref> To bring out more detail, the brightest tone is considered white, while the darkest black. It only takes a very thin layer of dust to make a difference in the over-all appearance of a picture. Experiments on Earth found that the layer may be only as thick as the diameter of a human hair.<ref> https://en.wikipedia.org/wiki/Micrometre
</ref> Incidentally, the dust has the color of rust because it is rust—it is oxidized iron.

Dark slope streaks are generally believed to occur when bright dust avalanches down steep slopes like crater walls.
In a study of over 500,000 dark slope streaks, researchers found that streaks were more likey to form in dusty areas instead of moist places. The authors state: "We show that slope streaks modify less than 0.1% of the martian surface, but transport several global storm equivalents of dust per Mars year, potentially playing a major role in the martian dust cycle." <ref> Valentin, T. and A. Valantinas. 2025. Streaks on martian slopes are dry.
Nature Communications. </ref> <ref>https://www.space.com/astronomy/mars/dark-streaks-on-mars-may-not-come-from-water-after-all-scientists-say?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=58E4DE65-C57F-4CD3-9A5A-609994E2C5A9&utm_medium=email&utm_content=CC262A6E-5136-48F9-B124-6B5979B0DBA3&utm_source=SmartBrief</ref> However, some researchers suggest that water may be involved.<ref>A. Bhardwaj, L. Sam, F.J. Martín-Torres, M.P. Zorzano. 2019. Are slope streaks indicative of global-scale aqueous processes on contemporary Mars?
Rev. Geophys. 10.1029/2018RG000617</ref> Dust devils have been observed to start the formation of dark slope streaks.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103520303249#bb0020</ref> <ref>Heyer, T., et al. 2020. Dust devil triggering of slope streaks on Mars. Icarus. Icarus
Volume 351. 113951</ref> Streaks can be very long and elaborate. These movements are affected by obstacles like boulders. A streak may split into two when encountering a boulder. They may be initiated when an impact happens nearby.<ref>Kaylan J. Burleigh, Henry J. Melosh, Livio L. Tornabene, Boris Ivanov, Alfred S. McEwen, Ingrid J. Daubar. Impact air blast triggers dust avalanches on Mars" ''Icarus'' 2012; 217 (1) 194 </ref><ref>http://redplanet.asu.edu/</ref>
<ref>http://phys.org/news/2011-12-meteorite-shockwaves-trigger-avalanches-mars.html</ref>

[[File:ESP 043128 2005mesastreaks.jpg|600pxr|Dark slope streaks on layered mesa, as seen by HiRISE under [[HiWish program]]]]

Dark slope streaks on layered mesa

[[File:55107 1930streaksboulders2.jpg|thumb|500px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

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Another thing that causes light and dark patterns is a dust devil. These miniature tornadoes remove the bright dust and make straight and/or curved tracks. They are common especially in areas with much dust cover and at certain times of the day. They have been observed both from orbit and from the ground.<ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> <ref>https://www.uahirise.org/ESP_042201_1715</ref> We even have movies of them in action. They can form beautiful scenes. And, the arrangement of the tracks can be different in just a few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

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The atmosphere of Mars contains a great deal of fine dust. Large dust storms happen just about every Martian year. A year on Mars is about 23 of our months. Dust storms typically occur when it is spring or summer in the southern hemisphere. At that time, Mars is at its closest to the sun. Unlike the Earth, Mars has a very elliptical orbit which brings it much closer to the sun than at other times. This makes for differences in season both in intensity and length. For example the southern summer is much shorter than that of the north. However, the summer season in the southern hemisphere is much more intense.

[[File:Marsorbitsolarsystem.gif|Comparrsion of the orbits of Earth and Mars. The Earth’s orbit is almost a perfect circle.<ref> https://www.compadre.org/osp/items/detail.cfm?ID=9757</ref> <ref> https://www.compadre.org/osp/items/detail.cfm?ID=7305</ref>]]

Comparison of the orbits of Earth and Mars. The Earth’s orbit is almost a perfect circle. Mars changes its distances to sun a great deal--this changes makes drastic seasonal changes.

==Dry Ice==

Some of the strangest things on Mars involve dry ice—solid carbon dioxide. The cold conditions on Mars cause much of the carbon dioxide to freeze out of the atmosphere. Both ice caps contain some dry ice. Each year about 25% of the atmosphere freezes out onto the poles. This is so much that the gravity of the planet shifts. <ref>NASA/Goddard Space Flight Center. "New gravity map gives best view yet inside Mars." ScienceDaily. ScienceDaily, 21 March 2016. https://www.sciencedaily.com/releases/2016/03/160321154013.htm.</ref> <ref>Antonio Genova, Sander Goossens, Frank G. Lemoine, Erwan Mazarico, Gregory A. Neumann, David E. Smith, Maria T. Zuber. Seasonal and static gravity field of Mars from MGS, Mars Odyssey and MRO radio science. Icarus, 2016; 272: 228 DOI: 10.1016/j.icarus.2016.02.05</ref> Winds and weather systems that almost look like the Earth’s are produced by so much dry ice changing to a gas at these times.

[[File:PIA00190-MC-30-MareAustraleRegion-19980605.jpg |right|thumb|px| Region of South Pole with ice cap Southern ice cap is much smaller than the North’s.]]

[[File:Mars NPArea-PIA00161.jpg |left|thumb|px| Spiral troughs in the northern ice cap]]

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File:Marscyclone hst.jpg|Cyclone on Mars, as seen by HST
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In the winter dry ice accumulates. So, large areas appear white. When things warm up in the spring, the landscape gets many dark spots and areas. <ref>https://mars.jpl.nasa.gov/mgs/msss/camera/images/dune_defrost_6_2001/</ref><ref>SPRING DEFROSTING OF MARTIAN POLAR REGIONS: MARS GLOBAL SURVEYOR MOC AND TES MONITORING OF THE RICHARDSON CRATER DUNE FIELD, 1999–2000. K. S. Edgett, K. D. Supulver, and M. C. Malin, Malin Space Science Systems, P.O. Box 910148, San Diego, CA 92191-0148, USA.</ref> <ref>K.-Michael Aye, K., et al. PROBING THE MARTIAN SOUTH POLAR WINDS BY MAPPING CO2 JET DEPOSITS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2841.pdf</ref> In the past, observers thought that Mars was full of life. They saw the northern ice cap get smaller and smaller. At the same time, they watched the area get darker. They concluded that the darkening was vegetation growing from the water coming out of the ice caps. What was happening was the dry ice was disappearing. Today, we can watch this darkening occur in great detail. <ref>http://www.jpl.nasa.gov/news/news.php?release=2013-034</ref>

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43821 2555defrostingdune2.jpg|Defrosting surface Frost is disappearing in patches from a dune and from the surrounding surface. Note: the north side (side near top) has not defrosted because the sun is coming from the other side.

File:ESP 011605 1170defrosting.jpg|Defrosting The dark spots are where the ice has gone. We now can see the underlying dark surface.

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In some places, there are many geyser-like eruptions of gas and dark dust.<ref>https://www.uahirise.org/</ref> High pressure gas and dust explode out of the ground. Winds often blow these eruptions into dark plumes. After many observations, scientists concluded that what happens is that a transparent-translucent dry ice slab forms in the winter. With increased sun in the spring, pressure builds up under this slab as light heats cavities under the slab and causes dry ice to turn into a gas. At weak areas in the slab, the gas comes out along with dark dust.<ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> The channels may get dark from the dust and make a pattern that looks like a spider. These patterns are called “spiders.” <ref>http://mars.jpl.nasa.gov/multimedia/images/2016/possible-development-stages-of-martian-spiders</ref> <ref>http://spaceref.com/mars/growth-of-a-martian-trough-network.html</ref> <ref>Benson, M. 2012. Planetfall: New Solar System Visions</ref> <ref>http://www.astrobio.net/topic/solar-system/mars/spiders-invade-mars/</ref> <ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>Portyankina, G., et al. 2017. Present-day erosion of Martian polar terrain by the seasonal CO2 jets. Icarus: 282, 93-103.</ref> The official name for spiders is "araneiforms."<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref>

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File:Spiders2eruptionlabeled2.jpg|Drawing showing the cause of plumes and spiders. In the spring, sunlight goes through a clear slap of dry ice. It heats up the dark ground. Heat causes dry ice to turn into a gas and pressurize. When pressure is great enough a dark plume of carbon dioxide gas and dark dust erupt. Wind will form it into a fan shape plume.

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[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

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ESP 048845 1010spiders.jpg|Wide view of crater that contains examples of spiders
File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program
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Around the southern cap, dry ice makes round, low areas that look like Swiss cheese. <ref>Thomas,P., M. Malin, P. James, B. Cantor, R. Williams, P. Gierasch
South polar residual cap of Mars: features, stratigraphy, and changes
Icarus, 174 (2 SPEC. ISS.). 2005. pp. 535–559. http://doi.org/10.1016/j.icarus.2004.07.028</ref> <ref>Thomas, P., P. James, W. Calvin, R. Haberle, M. Malin. 2009. Residual south polar cap of Mars: stratigraphy, history, and implications of recent changes
Icarus: 203, 352–375 http://doi.org/10.1016/j.icarus.2009.05.014</ref> <ref>Thomas, P., W.Calvin, P. Gierasch, R. Haberle, P. James, S. Sholes. 2013. Time scales of erosion and deposition recorded in the residual south polar cap of mars
Icarus: 225: 923–932 http://doi.org/10.1016/j.icarus.2012.08.038</ref> <ref>Thomas, P., W. Calvin, B. Cantor, R. Haberle, P. James, S. Lee. 2016. Mass balance of Mars’ residual south polar cap from CTX images and other data
Icarus: 268, 118–130 http://doi.org/10.1016/j.icarus.2015.12.038</ref> So, it is called “Swiss cheese terrain.” The roundness of the pits is believed to be related to the low angle of the sun.<ref>Buhler, Peter, Andrew Ingersoll, Bethany Ehlmann, Caleb Fassett, James Head. 2017. How the martian residual south polar cap develops quasi-circular and heart-shaped pits, troughs, and moats. Icarus: 286, 69-9.</ref>

[[File:South Pole Terrain.jpg|600pxr|HiRISE view of South Pole Terrain.]]
HiRISE view of South Pole Terrain.

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The ice caps contain a great deal of water ice. The northern cap has a covering of dry ice only 1 meter thick in the winter, but the southern cap always has a coating of dry ice up to 8 meters thick. Large deposits of dry ice are also buried in the water ice of the cap at some locations.

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==Gullies==

Since 2000, researchers have been studying gullies that are common in the mid-latitudes on steep slopes. They look like they were carved by liquid water. After many years of observations, it has been concluded that today they are being made by chunks of dry ice sliding down slopes.<ref>Vincendon, M. 2015. JGR:120, 1859–1879.</ref> <ref> Pilorget | first1 = C. | last2 = Forget | first2 = F. | year = 2016 | title = Formation of gullies on Mars by debris flows triggered by CO2 sublimation | url = | journal = Nature Geoscience | volume = 9 | issue = | pages = 65–69 | doi = 10.1038/ngeo2619 | </ref> <ref>Schorghofer, N., K. Edgett. 2005. Seasonal surface frost at low latitudes on Mars. Icarus: 180, 321-334.</ref> However, some scientists concede that water may have been involved in their formation in the past.<ref>Harrington |first=J.D. |last2=Webster |first2=Guy |title=RELEASE 14-191 – NASA Spacecraft Observes Further Evidence of Dry Ice Gullies on Mars |url=http://www.nasa.gov/press/2014/july/nasa-spacecraft-observes-further-evidence-of-dry-ice-gullies-on-mars |</ref> <ref>CNRS. "Gullies on Mars sculpted by dry ice rather than liquid water." ScienceDaily. ScienceDaily, 22 December 2015. www.sciencedaily.com/releases/2015/12/151222082255.htm</ref> <ref>http://www.skyandtelescope.com/astronomy-news/martian-gullies-triggered-by-exploding-dry-ice-122320158</ref>

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File:Channels on Southern Sand Dunes with ice blocks visible ESP 079809 1325.jpg|Channels on sand dunes, as seen by HiRISE. Arrows show chunks of ice that moved down to enlarge gullies.

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ESP 047956 1420gullies.jpg|Crater with gullies, as seen by HiRISE under HiWish program
File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
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File:Close view of gullies ESP 080430 2310 01.jpg|Gullies on crater wall The bright apron is a bit unusual.
File:Close view of gullies ESP 080430 2310 02.jpg|Gully on crater wall The bright apron is a bit unusual.

File:ESP 084896 1355 small gullies 02.jpg|Gullies, as seen by HiRISE. The gullies range from very samll to large, as such they may represent different stages in the formation of gullies. The colored strip is about 1 km wide.
File:ESP 084896 1355 small gullies 03.jpg|Small gully This gully may be in its initial state of formation.
File:ESP 084896 1355 small gullies 04.jpg|Gully, as seen by HiRISE
</gallery>

[[File:Gullies near Newton Crater.jpg|600pxr|Gullies near Newton Crater]]
Gullies near Newton Crater

==Other features==

The surface of Mars is very old—billions of years. This is plenty of time for rocks to have broken down into sand. In low places, like crater floors, sand accumulates and makes dunes. Some are quite pretty. And the colors used by NASA make them even more pretty—they can appear blue, purple, green, or turquoise.

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:61974 1710dunesrgb2.jpg|Dunes
File:ESP 046378 1415dunefield.jpg|Black and white, wide view of dunes
File:ESP 55095 2170dunes.jpg|Dunes near Sklodowski Crater in North Arabia Terra
</gallery>

Related to dunes are something called transverse aeolian ridges (TAR’s). They look like small dunes. They are often parallel to each other. They generally are in low areas and one of the most common landforms on Mars.<ref>http://www.lpi.usra.edu/meetings/lpsc2012/pdf/1598.pdf|format=PDF|type=conference paper|title=Investigations of transverse aeolian ridges on Mars|first1=Daniel C.|last1=Berman|first2=Matthew R.|last2=Balme|year=2012|publisher=Lunar and Planetary Science Conference</ref> They are mid-way in height between dunes and ripples; they are not well understood.<ref>http://www.uahirise.org/ESP_042625_1655</ref> <ref>Berman, D., et al. 2018. High-resolution investigations of Transverse Aeolian Ridges on Mars: Icarus: 312, 247-266.</ref>

<gallery class="center" widths="380px" heights="360px">

File:64038 2155tarslabeled.jpg|Transverse Aeolian Ridges, as seen by HiRISE under HiWish program

File:ESP 039563 1730tars.jpg|Transverse Aeolian Ridges (TAR’s) between yardangs We do not totally understand these.
File:ESP 042625 1655tars.jpg|Wide view of Transverse Aeolian Ridges (TAR’s) near a channel
</gallery>

Some landscape expressions are mysteries.<ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref> <ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref>

In rocks of certain ages, often at the bottom of low spots are complex arrangements of ridges.
These are walls of rock.<ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref>

There are different ideas for what caused them.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> Over 14,000 people from around the world helped map them, so that scientists could better understand them. The team of volunteers found 952 polygonal ridge networks in an area that measures about a fifth of Mars’ total surface area. Some ridges contain clays, so water may have been involved in their formation because clays need water to be formed.<ref>https://news.asu.edu/20220405-citizen-scientists-help-map-ridge-networks-may-hold-records-ancient-groundwater-mars</ref> <ref>Khuller, A., et al. 2022. Irregular polygonal ridge networks in ancient Noachian terrain on Mars. Icarus. 374. 114833</ref>

[[File:ESP 036745 1905top.jpg|600pxr|Linear ridge networks]]
Linear ridge networks

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.
</gallery>

[[File:Ridgesmappedbycitizens.jpg|600pxr|Map of Linear ridge networks]]

Map of Linear ridge networks

Of eerie beauty are odd arrangements visible on the bottom of the Hellas Impact basin. We are not sure exactly what caused them.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref> They have been called honeycomb terrain or banded terrain.

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

[[File: ESP 033995 1410bands.jpg|600pxr|Close-up of banded terrain on the floor of the Hellas basin, as seen by HiRISE]]
Close-up of banded terrain on the floor of the Hellas basin, as seen by HiRISE

[[File:ESP 055067 1420ridgenetwork.jpg|600pxr|Floor features in Hellas Planitia]]

Honeycomb terrain on floor of Hellas Basin The exact origin of these shapes is unknown at present.

<gallery class="center" widths="380px" heights="360px">

</gallery>

Mars is one planet that we can see the surface clearly. Its super thin atmosphere (about 1% of the Earth’s) makes it easy to observe. Early telescopes revealed many markings and patterns. As we sent better and better cameras to examine it, more mysteries and more beautiful scenes emerged. We were able to answer many questions, but always more questions arose concerning what we were seeing.

<gallery class="center" widths="380px" heights="360px">

</gallery>

==References==

{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=D-SCOHj8u-A Water on Mars - James Secosky - 2021 Mars Society Virtual Convention -- Tells where water was and where ice is today on Mars (34 minutes)]

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* https://mail.google.com/mail/u/0/?tab=wm&pli=1#inbox/FMfcgzGrbHtSWzJjdRzftxgXCrbxXNnK Water on Mars - A Literature Review" by Mohammad Nazari-Sharabian

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]

*[https://www.youtube.com/watch?v=jcaawA7d0ro Sublimation of Dry Ice]

* [https://www.youtube.com/watch?v=NiT02piO40c The Geological History of Water on Mars and Astrobiological Implications (Vic Baker)]

* [https://www.youtube.com/watch?v=z6B742f8yPs Mars Bunker: Martian Ice Revealed]

* [https://www.youtube.com/watch?v=RWNXJk0Y01k The Evolution of Water on Mars]

*Jawin, E.,et al. 2018. Transient post-glacial processes on Mars: Geomorphologic evidence for a paraglacial period. Icarus. Volume 309. Pages 187-206

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]

==Recommended reading==

*Head, J., et al. 2023. GEOLOGICAL AND CLIMATE HISTORY OF MARS: IDENTIFICATION OF POTENTIAL WARM AND
WET CLIMATE ‘FALSE POSITIVES’. 54th Lunar and Planetary Science Conference 2023 (LPI Contrib. No. 2806). 1731.pdf
*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-10T16:29:56Z

Suitupshowup: /* Cracks/fractures */

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

File:ESP 066765 2245ribslabeled.jpg|How hollows are formed from cracks. Cracks expose more ground ice to the air; hence, more sublimation can take place, making the cracks larger and larger.

File:ESP 066765 2245 ribs labeledcropped.jpg|Enlarged diagram of how hollows form starting with cracks.
</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygons==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.</ref>

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==Cracks/fractures==

Various features like hollows and ribbed terrain begin with cracks. As time goes by the cracks enlarge becasue the extra surface area exposing more ground ice to go into the air by sublimation. Sublimation is when a solid goes directly to a gas without melting.

<gallery class="center" widths="380px" heights="360px">

44322 2215fractures.jpg|Fractures These fractures are believed to eventually turn into canyons because the cracks will get much larger when ice in the ground disappears into the thin Martian atmosphere and the remaining dust blows away.

File:56968 2140cracks.jpg|Close view of cracks on crater floor, as seen by HiRISE under [[HiWish program]]

File:ESP 057311 2125crackscraters.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger. Note that small craters do not have very big rims; they may be just pits.

File:57311 2155crackssmallarge.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger.

File:57311 2155crackscrater.jpg|Cracks around crater, as seen by HiRISE under [[HiWish program]]

</gallery>

==High center pologons==
The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A high-centered polygon features a raised central dome and deeply depressed troughs or margins. <ref>Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724. https://doi.org/10.1029/2024JE008724</ref> These typically evolve from low-centered polygons through a process of degradation. If climate conditions change and the ice wedges in the cracks begin to sublimate (turn from solid to gas) or melt, the support for the raised margins is lost. The edges of the polygon collapse into the widening troughs, leaving the center of the polygon at a higher relative elevation than its crumbling boundaries. The presence of high-centered polygons often suggests a drying or warming trend where subsurface ice is being depleted.<ref> https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

<gallery class="center" widths="380px" heights="360px">

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
43899 2265highcenterpolygonsclose.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Troughs between polygons are easily visible in this view. Location is [[Ismenius Lacus quadrangle]].

45070 1440polygonscloseshadows.jpg|Close view of high center polygons near the glacier, as seen by HiRISE under the HiWish program Box shows size of the football field.

43899 2265highcenterpolygonsclose2.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Note: the black box is the size of a football field.
</gallery>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-10T16:19:59Z

Suitupshowup: /* Hollows */ added image

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

File:ESP 066765 2245ribslabeled.jpg|How hollows are formed from cracks. Cracks expose more ground ice to the air; hence, more sublimation can take place, making the cracks larger and larger.

File:ESP 066765 2245 ribs labeledcropped.jpg|Enlarged diagram of how hollows form starting with cracks.
</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygons==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.</ref>

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==Cracks/fractures==

Various features like hollows and ribbed terrain begin wih cracks. As time goes by the cracks enlarge becasue the extra surface area exposing more ground ice to go into the air by sublimation. Sublimation is when a solid goes directly to a gas without melting.

<gallery class="center" widths="380px" heights="360px">

44322 2215fractures.jpg|Fractures These fractures are believed to eventually turn into canyons because the cracks will get much larger when ice in the ground disappears into the thin Martian atmosphere and the remaining dust blows away.

File:56968 2140cracks.jpg|Close view of cracks on crater floor, as seen by HiRISE under [[HiWish program]]

File:ESP 057311 2125crackscraters.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger. Note that small craters do not have very big rims; they may be just pits.

File:57311 2155crackssmallarge.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger.

File:57311 2155crackscrater.jpg|Cracks around crater, as seen by HiRISE under [[HiWish program]]

</gallery>

==High center pologons==
The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A high-centered polygon features a raised central dome and deeply depressed troughs or margins. <ref>Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724. https://doi.org/10.1029/2024JE008724</ref> These typically evolve from low-centered polygons through a process of degradation. If climate conditions change and the ice wedges in the cracks begin to sublimate (turn from solid to gas) or melt, the support for the raised margins is lost. The edges of the polygon collapse into the widening troughs, leaving the center of the polygon at a higher relative elevation than its crumbling boundaries. The presence of high-centered polygons often suggests a drying or warming trend where subsurface ice is being depleted.<ref> https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

<gallery class="center" widths="380px" heights="360px">

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
43899 2265highcenterpolygonsclose.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Troughs between polygons are easily visible in this view. Location is [[Ismenius Lacus quadrangle]].

45070 1440polygonscloseshadows.jpg|Close view of high center polygons near the glacier, as seen by HiRISE under the HiWish program Box shows size of the football field.

43899 2265highcenterpolygonsclose2.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Note: the black box is the size of a football field.
</gallery>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-10T16:10:46Z

Suitupshowup: /* Hollows */

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

File:ESP 066765 2245ribslabeled.jpg|How hollows are formed from cracks. Cracks expose more ground ice to the air; hence, more sublimation can take place, making the cracks larger and larger.
</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygons==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.</ref>

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==Cracks/fractures==

Various features like hollows and ribbed terrain begin wih cracks. As time goes by the cracks enlarge becasue the extra surface area exposing more ground ice to go into the air by sublimation. Sublimation is when a solid goes directly to a gas without melting.

<gallery class="center" widths="380px" heights="360px">

44322 2215fractures.jpg|Fractures These fractures are believed to eventually turn into canyons because the cracks will get much larger when ice in the ground disappears into the thin Martian atmosphere and the remaining dust blows away.

File:56968 2140cracks.jpg|Close view of cracks on crater floor, as seen by HiRISE under [[HiWish program]]

File:ESP 057311 2125crackscraters.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger. Note that small craters do not have very big rims; they may be just pits.

File:57311 2155crackssmallarge.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger.

File:57311 2155crackscrater.jpg|Cracks around crater, as seen by HiRISE under [[HiWish program]]

</gallery>

==High center pologons==
The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A high-centered polygon features a raised central dome and deeply depressed troughs or margins. <ref>Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724. https://doi.org/10.1029/2024JE008724</ref> These typically evolve from low-centered polygons through a process of degradation. If climate conditions change and the ice wedges in the cracks begin to sublimate (turn from solid to gas) or melt, the support for the raised margins is lost. The edges of the polygon collapse into the widening troughs, leaving the center of the polygon at a higher relative elevation than its crumbling boundaries. The presence of high-centered polygons often suggests a drying or warming trend where subsurface ice is being depleted.<ref> https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

<gallery class="center" widths="380px" heights="360px">

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
43899 2265highcenterpolygonsclose.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Troughs between polygons are easily visible in this view. Location is [[Ismenius Lacus quadrangle]].

45070 1440polygonscloseshadows.jpg|Close view of high center polygons near the glacier, as seen by HiRISE under the HiWish program Box shows size of the football field.

43899 2265highcenterpolygonsclose2.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Note: the black box is the size of a football field.
</gallery>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-10T16:05:46Z

Suitupshowup: /* Hollows */ added image

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

File:ESP 066765 2245ribslabeled.jpg|How hollows are formed from cracks. Cracks expose more groung ice to the air; hence, more sublimation can take place, making the cracks larger and larger.
</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygons==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.</ref>

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==Cracks/fractures==

Various features like hollows and ribbed terrain begin wih cracks. As time goes by the cracks enlarge becasue the extra surface area exposing more ground ice to go into the air by sublimation. Sublimation is when a solid goes directly to a gas without melting.

<gallery class="center" widths="380px" heights="360px">

44322 2215fractures.jpg|Fractures These fractures are believed to eventually turn into canyons because the cracks will get much larger when ice in the ground disappears into the thin Martian atmosphere and the remaining dust blows away.

File:56968 2140cracks.jpg|Close view of cracks on crater floor, as seen by HiRISE under [[HiWish program]]

File:ESP 057311 2125crackscraters.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger. Note that small craters do not have very big rims; they may be just pits.

File:57311 2155crackssmallarge.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger.

File:57311 2155crackscrater.jpg|Cracks around crater, as seen by HiRISE under [[HiWish program]]

</gallery>

==High center pologons==
The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A high-centered polygon features a raised central dome and deeply depressed troughs or margins. <ref>Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724. https://doi.org/10.1029/2024JE008724</ref> These typically evolve from low-centered polygons through a process of degradation. If climate conditions change and the ice wedges in the cracks begin to sublimate (turn from solid to gas) or melt, the support for the raised margins is lost. The edges of the polygon collapse into the widening troughs, leaving the center of the polygon at a higher relative elevation than its crumbling boundaries. The presence of high-centered polygons often suggests a drying or warming trend where subsurface ice is being depleted.<ref> https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

<gallery class="center" widths="380px" heights="360px">

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
43899 2265highcenterpolygonsclose.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Troughs between polygons are easily visible in this view. Location is [[Ismenius Lacus quadrangle]].

45070 1440polygonscloseshadows.jpg|Close view of high center polygons near the glacier, as seen by HiRISE under the HiWish program Box shows size of the football field.

43899 2265highcenterpolygonsclose2.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Note: the black box is the size of a football field.
</gallery>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-10T14:57:42Z

Suitupshowup: /* Cracks/fractures */

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygons==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.</ref>

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==Cracks/fractures==

Various features like hollows and ribbed terrain begin wih cracks. As time goes by the cracks enlarge becasue the extra surface area exposing more ground ice to go into the air by sublimation. Sublimation is when a solid goes directly to a gas without melting.

<gallery class="center" widths="380px" heights="360px">

44322 2215fractures.jpg|Fractures These fractures are believed to eventually turn into canyons because the cracks will get much larger when ice in the ground disappears into the thin Martian atmosphere and the remaining dust blows away.

File:56968 2140cracks.jpg|Close view of cracks on crater floor, as seen by HiRISE under [[HiWish program]]

File:ESP 057311 2125crackscraters.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger. Note that small craters do not have very big rims; they may be just pits.

File:57311 2155crackssmallarge.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger.

File:57311 2155crackscrater.jpg|Cracks around crater, as seen by HiRISE under [[HiWish program]]

</gallery>

==High center pologons==
The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A high-centered polygon features a raised central dome and deeply depressed troughs or margins. <ref>Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724. https://doi.org/10.1029/2024JE008724</ref> These typically evolve from low-centered polygons through a process of degradation. If climate conditions change and the ice wedges in the cracks begin to sublimate (turn from solid to gas) or melt, the support for the raised margins is lost. The edges of the polygon collapse into the widening troughs, leaving the center of the polygon at a higher relative elevation than its crumbling boundaries. The presence of high-centered polygons often suggests a drying or warming trend where subsurface ice is being depleted.<ref> https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

<gallery class="center" widths="380px" heights="360px">

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
43899 2265highcenterpolygonsclose.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Troughs between polygons are easily visible in this view. Location is [[Ismenius Lacus quadrangle]].

45070 1440polygonscloseshadows.jpg|Close view of high center polygons near the glacier, as seen by HiRISE under the HiWish program Box shows size of the football field.

43899 2265highcenterpolygonsclose2.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Note: the black box is the size of a football field.
</gallery>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-10T14:56:37Z

Suitupshowup: /* Cracks/fractures */

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygons==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.</ref>

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==Cracks/fractures==

Various features like hollows and ribbed terrain begin wih cracks. As time goes by the cracks enlarge becasue the extra surface area exposed more ground ice to go into the air by sublimation. Sublimation is when a solid goes directly to a gas without melting.

<gallery class="center" widths="380px" heights="360px">

44322 2215fractures.jpg|Fractures These fractures are believed to eventually turn into canyons because the cracks will get much larger when ice in the ground disappears into the thin Martian atmosphere and the remaining dust blows away.

46366 2215fractures.jpg|Close view of fractures from the previous image

File:56968 2140cracks.jpg|Close view of cracks on crater floor, as seen by HiRISE under [[HiWish program]]

File:ESP 057311 2125crackscraters.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger. Note that small craters do not have very big rims; they may be just pits.

File:57311 2155crackssmallarge.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger.

File:57311 2155crackscrater.jpg|Cracks around crater, as seen by HiRISE under [[HiWish program]]

</gallery>

==High center pologons==
The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A high-centered polygon features a raised central dome and deeply depressed troughs or margins. <ref>Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724. https://doi.org/10.1029/2024JE008724</ref> These typically evolve from low-centered polygons through a process of degradation. If climate conditions change and the ice wedges in the cracks begin to sublimate (turn from solid to gas) or melt, the support for the raised margins is lost. The edges of the polygon collapse into the widening troughs, leaving the center of the polygon at a higher relative elevation than its crumbling boundaries. The presence of high-centered polygons often suggests a drying or warming trend where subsurface ice is being depleted.<ref> https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

<gallery class="center" widths="380px" heights="360px">

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
43899 2265highcenterpolygonsclose.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Troughs between polygons are easily visible in this view. Location is [[Ismenius Lacus quadrangle]].

45070 1440polygonscloseshadows.jpg|Close view of high center polygons near the glacier, as seen by HiRISE under the HiWish program Box shows size of the football field.

43899 2265highcenterpolygonsclose2.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Note: the black box is the size of a football field.
</gallery>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-10T14:52:33Z

Suitupshowup: /* High center pologons */ created a new section about cracks

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygons==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.</ref>

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==Cracks/fractures==

Various features like hollows and ribbed terrain begin wih cracks. As time goes by the cracks enlarge becasue the extra surface area exposed more ground ice to go into the air by sublimation. Sublimation is when a solid goes directly to a gas without melting.

<gallery class="center" widths="380px" heights="360px">

44322 2215fractures.jpg|Fractures These fractures are believed to eventually turn into canyons because the cracks will get much larger when ice in the ground disappears into the thin Martian atmosphere and the remaining dust blows away.

ESP 046366 2215fractures.jpg|Wide view of fractured ground, as seen by HiRISE under HiWish program Cracks form on the Martian surface, and then they turn into large fractures.

46366 2215fractures.jpg|Close view of fractures from the previous image

File:ESP 056968 2140cracks.jpg|Cracks on crater floor

File:56968 2140cracks.jpg|Close view of cracks on crater floor, as seen by HiRISE under [[HiWish program]]

File:ESP 057311 2125crackscraters.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger. Note that small craters do not have very big rims; they may be just pits.

File:57311 2155crackssmallarge.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger.

File:57311 2155crackscrater.jpg|Cracks around crater, as seen by HiRISE under [[HiWish program]]

</gallery>

==High center pologons==
The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A high-centered polygon features a raised central dome and deeply depressed troughs or margins. <ref>Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724. https://doi.org/10.1029/2024JE008724</ref> These typically evolve from low-centered polygons through a process of degradation. If climate conditions change and the ice wedges in the cracks begin to sublimate (turn from solid to gas) or melt, the support for the raised margins is lost. The edges of the polygon collapse into the widening troughs, leaving the center of the polygon at a higher relative elevation than its crumbling boundaries. The presence of high-centered polygons often suggests a drying or warming trend where subsurface ice is being depleted.<ref> https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

<gallery class="center" widths="380px" heights="360px">

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
43899 2265highcenterpolygonsclose.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Troughs between polygons are easily visible in this view. Location is [[Ismenius Lacus quadrangle]].

45070 1440polygonscloseshadows.jpg|Close view of high center polygons near the glacier, as seen by HiRISE under the HiWish program Box shows size of the football field.

43899 2265highcenterpolygonsclose2.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Note: the black box is the size of a football field.
</gallery>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-10T12:25:20Z

Suitupshowup: /* High center pologon craters */

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygons==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.</ref>

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==High center pologons==
The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A high-centered polygon features a raised central dome and deeply depressed troughs or margins. <ref>Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724. https://doi.org/10.1029/2024JE008724</ref> These typically evolve from low-centered polygons through a process of degradation. If climate conditions change and the ice wedges in the cracks begin to sublimate (turn from solid to gas) or melt, the support for the raised margins is lost. The edges of the polygon collapse into the widening troughs, leaving the center of the polygon at a higher relative elevation than its crumbling boundaries. The presence of high-centered polygons often suggests a drying or warming trend where subsurface ice is being depleted.<ref> https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

<gallery class="center" widths="380px" heights="360px">

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
43899 2265highcenterpolygonsclose.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Troughs between polygons are easily visible in this view. Location is [[Ismenius Lacus quadrangle]].

45070 1440polygonscloseshadows.jpg|Close view of high center polygons near the glacier, as seen by HiRISE under the HiWish program Box shows size of the football field.

43899 2265highcenterpolygonsclose2.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Note: the black box is the size of a football field.
</gallery>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-10T12:24:20Z

Suitupshowup: /* Low center polygon craters */

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygons==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.</ref>

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==High center pologon craters==
The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A high-centered polygon features a raised central dome and deeply depressed troughs or margins. <ref>Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724. https://doi.org/10.1029/2024JE008724</ref> These typically evolve from low-centered polygons through a process of degradation. If climate conditions change and the ice wedges in the cracks begin to sublimate (turn from solid to gas) or melt, the support for the raised margins is lost. The edges of the polygon collapse into the widening troughs, leaving the center of the polygon at a higher relative elevation than its crumbling boundaries. The presence of high-centered polygons often suggests a drying or warming trend where subsurface ice is being depleted.<ref> https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

<gallery class="center" widths="380px" heights="360px">

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
43899 2265highcenterpolygonsclose.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Troughs between polygons are easily visible in this view. Location is [[Ismenius Lacus quadrangle]].

45070 1440polygonscloseshadows.jpg|Close view of high center polygons near the glacier, as seen by HiRISE under the HiWish program Box shows size of the football field.

43899 2265highcenterpolygonsclose2.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Note: the black box is the size of a football field.
</gallery>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-09T15:49:56Z

Suitupshowup: /* High center pologon craters */

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygon craters==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.</ref>

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==High center pologon craters==
The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A high-centered polygon features a raised central dome and deeply depressed troughs or margins. <ref>Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724. https://doi.org/10.1029/2024JE008724</ref> These typically evolve from low-centered polygons through a process of degradation. If climate conditions change and the ice wedges in the cracks begin to sublimate (turn from solid to gas) or melt, the support for the raised margins is lost. The edges of the polygon collapse into the widening troughs, leaving the center of the polygon at a higher relative elevation than its crumbling boundaries. The presence of high-centered polygons often suggests a drying or warming trend where subsurface ice is being depleted.<ref> https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

<gallery class="center" widths="380px" heights="360px">

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
43899 2265highcenterpolygonsclose.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Troughs between polygons are easily visible in this view. Location is [[Ismenius Lacus quadrangle]].

45070 1440polygonscloseshadows.jpg|Close view of high center polygons near the glacier, as seen by HiRISE under the HiWish program Box shows size of the football field.

43899 2265highcenterpolygonsclose2.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Note: the black box is the size of a football field.
</gallery>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-09T15:48:49Z

Suitupshowup: /* Scalloped Terrain */ creater section on high center pologon craters

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygon craters==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.</ref>

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==High center pologon craters==
The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.

A high-centered polygon features a raised central dome and deeply depressed troughs or margins. <ref>Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724. https://doi.org/10.1029/2024JE008724</ref> These typically evolve from low-centered polygons through a process of degradation. If climate conditions change and the ice wedges in the cracks begin to sublimate (turn from solid to gas) or melt, the support for the raised margins is lost. The edges of the polygon collapse into the widening troughs, leaving the center of the polygon at a higher relative elevation than its crumbling boundaries. The presence of high-centered polygons often suggests a drying or warming trend where subsurface ice is being depleted.<ref> https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

<gallery class="center" widths="380px" heights="360px">

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
43899 2265highcenterpolygonsclose.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Troughs between polygons are easily visible in this view. Location is [[Ismenius Lacus quadrangle]].

45070 1440polygonscloseshadows.jpg|Close view of high center polygons near the glacier, as seen by HiRISE under the HiWish program Box shows size of the football field.

43899 2265highcenterpolygonsclose2.jpg|Close-up of high center polygons seen by HiRISE under HiWish program Note: the black box is the size of a football field.
</gallery>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-09T15:46:39Z

Suitupshowup: /* Low center polygon craters */

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygon craters==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.</ref>

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-09T15:45:29Z

Suitupshowup: /* Low center polygon craters */

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygon craters==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.</ref>

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-09T15:44:30Z

Suitupshowup: /* Polygons */ creater new section on low center pologon craters

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Low center polygon craters==

The polygonal areas of Mars are geometric patterns found in the planet's mid-to-high latitudes. They give us clues of past and present climate conditions. These features are similar to patterned ground in Earth's Arctic and Antarctic regions The sometimes strange shapes mostly form through a cycle of thermal contraction and subsequent cracking of ice-rich soil. <ref>Sako, T., Hasegawa, H., Ruj, T., Komatsu, G., & Sekine, Y. (2025). The periglacial landforms and estimated subsurface ice distribution in the northern mid-latitude of Mars. Journal of Geophysical Research: Planets, 130, e2023JE008232. https://doi.org/10.1029/2023JE008232</ref>

The initial formation of these polygons begins when sharp drops in temperature cause the permanently frozen ground (permafrost) to contract and fracture. Over time, these individual fractures connect into a vast network of hexagonal or pentagonal shapes. Once these cracks form, they can be filled by windblown sand, ice, or a combination of both, creating "wedges" that physically pry the ground apart. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref> <ref>Roeloff, L., et al. Thermal-contraction polygons on Earth and Mars.

A low-centered polygon is characterized by a central basin surrounded by raised margins or "shoulders".<ref> Luzzi, E., Heldmann, J. L., Williams, K. E., Nodjoumi, G., Deutsch, A., & Sehlke, A. (2025). Geomorphological evidence of near-surface ice at candidate landing sites in northern Amazonis Planitia, Mars. Journal of Geophysical Research: Planets, 130, e2024JE008724.

<gallery class="center" widths="380px" heights="360px">
44042 2240lowcenter.jpg|Low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.

44042 2240highlowcenters.jpg|High and low center polygons, as seen by HiRISE under HiWish program Location is [[Casius quadrangle]]. Image enlarged with HiView.
49369 2250low center polygons.jpg|Low-centered polygons in a region of scalloped terrain, as seen by HiRISE under HiWish program
</gallery>

As ice or sand seasonally accumulates in the cracks (aggradation), the expanding wedges exert lateral pressure on the surrounding soil. This pressure forces the sediment upward along the edges of the polygon, creating elevated rims while the center remains relatively depressed. On Mars, these are often considered "young" or "active" features, indicating that ground ice is currently stable or accumulating. <ref>https://planetarygeomorphology.wordpress.com/2022/01/01/thermal-contraction-polygons-on-earth-and-mars/#:~:text=D%20student%2C%20Laboratoire%20de%20Plan%C3%A9tologie,Mars%20in%20the%20mid%2Dlatitudes.</ref>

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-06T19:20:49Z

Suitupshowup: /* Brain Terrain */

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

HiWish program

2026-04-06T19:17:00Z

Suitupshowup: /* Layers in Craters */ added new section on crater lakes

HiWish is a NASA program in which anyone can suggest a place for the [[High Resolution Imaging Science Experiment (HiRISE)]] camera on the [[Mars Reconnaissance Orbiter]] to image.<ref>http://www.marsdaily.com/reports/Public_Invited_To_Pick_Pixels_On_Mars_999.html |title=Public Invited To Pick Pixels On Mars |date=January 22, 2010 |publisher=Mars Daily</ref> <ref>http://www.astronomy.com/magazine/2018/08/take-control-of-a-mars-orbiter</ref> <ref>http://www.planetary.org/blogs/guest-blogs/hiwishing-for-3d-mars-images-1.html</ref> It started in January 2010. Three thousand people signed up in the first few months of the program.<ref>Interview with Alfred McEwen on Planetary Radio, 3/15/2010</ref> <ref>http://www.planetary.org/multimedia/planetary-radio/show/2010/384.html|title=Your Personal Photoshoot on Mars?|website=www.planetary.org|</ref> By February 2020, 9,726 had signed up and 24,059 suggestions had been submitted for targets in each of the 30 quadrangles of Mars. A that point 10,318 images had been taken.<ref> https://www.jpl.nasa.gov/missions/viking-1/</ref> <ref> OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE</ref> The first images were released in April 2010.<ref>http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |title=NASA releases first eight "HiWish" selections of people's choice Mars images |date=April 2, 2010 |publisher=TopNews |accessdate=January 10, 2011 |archive-url=https://www.webcitation.org/6Gop7RR0c?url=http://topnews.net.nz/content/23052-nasa-releases-first-eight-hiwish-selections-people-s-choice-mars-images |</ref> Some of the images from HiWish were used for three talks at the 16th Annual International Mars Society Convention. Below are some of the over 4,224 images that have been released from the HiWish program as of March 2016.<ref>McEwen, A. et al. 2016. THE FIRST DECADE OF HIRISE AT MARS. 47th Lunar and Planetary Science Conference (2016) 1372.pdf</ref>

==Landslides==

[[File:ESP 057191 2150landslidecropped.jpg|Landslide]]

Landslides have been observed on Mars. They may be a little different since the gravity of Mars is only about one third as that of the Earth.
<gallery class="center" widths="380px" heights="360px">
File:ESP 045981 1585landslide.jpg|Landslide
File:ESP 043963 1550landslide.jpg|Landslide
</gallery>

==Hollows==

[[File:28207 2250hollowsarrows.jpg|Hollows]]

Hollows make strange, beautiful landscapes. The hollows are believed to be produced when ice leaves the ground and the remaining dust is blown away. There is much water frozen in the ground. Water is carried around the planet frozen on dust grains that fall to the ground and make up what is called “mantle.” Mantle is produced when the climate is such that there is a lot of dust and moisture in the atmosphere. During those times, water will freeze onto the dust particles. Eventually, the particles will be too heavy and fall to the surface. In addition, it may snow on Mars.
The mantle covers wide expanses. It has a smooth appearance. It covers the irregular, created surface of the planet.

<gallery class="center" widths="380px" heights="360px">

File:46325 2225hollows4.jpg|Hollows

File:ESP 046325 2225hollowsmiddlelabeled.jpg|Hollows
File:Close view of hollows created when ice left the ground. 03.jpg|Close view of hollows. Narrow ridges were made when hollows kept expanding.

File:Close view of hollows created when ice left the ground.jpg|Close, color view of hollows. The HiView program was used in the rgb color scheme.

</gallery>

==Mud Volcanoes==
[[File:Mud volcanoes from around Mars 11.jpg|600pxr|Mud volcanoes from around Mars]]

Mud volcanoes from around Mars

[[File:53381 2265mud.jpg|Mud volcanoes]]

Mud volcanoes They may have come through a zone of weakness in the rock here

Mud volcanoes are very common in a place on Mars called the Mare Acidalium quadrangle. Because they bring up mud from underground, they may hold evidence of life.<ref>Wheatley, D., et al., 2019. Clastic pipes and mud volcanism across Mars: Terrestrial analog evidence of past Martian groundwater and subsurface fluid mobilization. Icarus. In Press</ref> Mud that formed the volcanoes comes from a depth underground that is deep enough to be protected from radiation. The radiation level at the surface would kill most organisms over time. Methane has been detected on Mars; methane may be produced by certain bacteria. Some scientists speculate that methane may come from mud volcanoes.<ref>https://hirise.lpl.arizona.edu/ESP_055307_2215</ref>

<gallery class="center" widths="380px" heights="360px">
File:570770 2100coneslabeled.jpg|Mud volcanoes

File:52050 2200mudvolcanoes.jpg|Mud volcanoes
File:ESP 043580 2120mud.jpg|Wide view of field of mud volcanoes
File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

==Volcanic vents==

[[File:30348 1925vent2.jpg|Volcanic vent with lava channel]]

Volcanic vent with lava channel

[[File:ESP 030440 1945ventcropped.jpg|Volcanic vent]]

Volcanic vent

==Lava Flows==

[[File:ESP 056023 1965lavaolympus.jpg|Lava flow on Olympus Mons]]

Lava flow on Olympus Mons

Large areas of Mars are covered with lava flows.<ref>https://en.wikipedia.org/wiki/Volcanology_of_Mars</ref> <ref>Head, J.W. 2007. The Geology of Mars: New Insights and Outstanding Questions in The Geology of Mars: Evidence from Earth-Based Analogs, Chapman, M., Ed; Cambridge University Press: Cambridge UK</ref> <ref>Carr, Michael H. (1973). "Volcanism on Mars". Journal of Geophysical Research. 78 (20): 4049–4062.</ref> <ref>Barlow, N.G. 2008. Mars: An Introduction to Its Interior, Surface, and Atmosphere; Cambridge University Press: Cambridge, UK</ref> Large volcanoes in the [[Tharsis]] region show many overlapping lava flows. Lava flows can also move around and create what appear to be layers, especially if it behaves like water. Basalt flows are very fluid.<ref>https://www.uahirise.org/ESP_057978_1875</ref>

<gallery class="center" widths="380px" heights="360px">
File:44828 2030lavaflow.jpg|Lava flows These are common in large sections of Mars.

File:ESP 044840 1620lavaflow.jpg|Lava flow

File:WikiESP 035095 1975lavalobestharsiswide.jpg|Old and young lava flows

File:68460 1945laveolympus.jpg|Lava flowing down a slope from [[Olympus Mons]]

File:68460 1945lavechannel.jpg|Lava channel from Olympus Mons

</gallery>

==Rootless Cones==

[[File:40162 2065conesarrows2.jpg|Rootless cones ]]

Rootless cones

Rootless Cones are thought to be caused by lava flowing over ice or ground containing ice.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103523000507</ref> <ref> Czechowski, L., et al. 2023. The formation of cone chains in the Chryse Planitia region on Mars and the thermodynamic aspects of this process. Icarus: Volume 396, 15 May 2023, 115473</ref> Heat from the lava causes the ice to quickly change to steam. The resulting steam explosion produces a ring or cone. Such features are common in certain locations on the Earth. Some of the forms do not have the shape of rings or cones because maybe the lava moved too quickly; thereby not allowing a complete cone shape to form. Sometimes a wake is made as the lava moves along the surface.

<gallery class="center" widths="380px" heights="360px">

File:45384 2065cones2.jpg|Rootless cones
File:45384 2065cones.jpg|Rootless cones Here, lava has moved over ice-rich ground from the upper right to the lower left of the picture.
File:58610 2100coneswakeslabeled.jpg|Close view of wake of a rootless cone
File:ESP 045384 2065lavaice.jpg|Wide view of large field of rootless cones

</gallery>

==Dikes==

[[File:ESP 045981 2100dike2.jpg|Dike]]

Dike Notice how straight it is. Magma moved along underground and then rose up along a fault. Afterwards, softer material eroded and left the harder dike behind.

Dikes show as mostly straight ridges. They are made when magma flows along cracks or faults in the ground. This part of the process happens under the ground. Later erosion will remove the weaker materials around the dike. What is left is a narrow wall of rock.<ref> "Characteristics and Origin of Giant Radiating Dyke Swarms". MantlePlumes.org.</ref> On Mars many faults are due to stretching of the crust. The mass of huge volcanoes pull at the crust until it cracks.

[[File:ESP 046403 2095dikecropped.jpg|thumb|400px|center|Dike in [[Syrtis Major quadrangle]]]]

==Troughs==

[[File:ESP 051781 2035troughs.jpg |Troughs]]

Troughs are common on Mars. They are due to the great weight of several huge volcanoes on Mars. The mass of these structures has caused the crust to stretch. That tension made the crust break into cracks called, “troughs” or “fossae.” Some of them show evidence that lava and/or water have come out of them in the past. They can be very long.<ref>https://en.wikipedia.org/wiki/Fossa_(geology)</ref> <ref>James W. Head; Lionel Wilson; Karl L. Mitchell (2003). "Generation of recent massive water floods at Cerberus Fossae, Mars by dike emplacement, cryospheric cracking, and confined aquifer groundwater release". Geophysical Research Letters. 30 (11): 2265. Bibcode:2003GeoRL..30k..31H. doi:10.1029/2003GL017135</ref> <ref>Burr, D. et al. 2002. Repeated aqueous flooding from the Cerberus Fossae: evidence for very recently extant deep groundwater on Mars. Icarus. 159: 53-73.</ref>

<gallery class="center" widths="380px" heights="360px">

File:56910 2100trough.jpg|Group of troughs

File:Troughs in Elysium Planitia.jpg|Troughs showing layers Hard cap rock is at the surface. The center section is in color. With HiRISE only a strip in the middle is in color.

File:ESP 057834 2005troughmesa.jpg|Troughs cutting through mesa, as seen by HiRISE under HiWish program
</gallery>

==Faults==

Faults are visible in some parts of Mars.<ref> https://www.uahirise.org/ESP_052893_1835</ref> They are most noticeable in places where many layers exist. Sometimes their presence is known because they can change the direction of stream channels.

[[File:Wikiesp 039404 1820landingfir.jpg|Layers and fault in Firsoff Crater|600pxr|Layers and fault in Firsoff Crater]]

Layers and fault in Firsoff Crater

[[File:60331 1880faultslabeled2.jpg|thumb|300px|left|Faults in layered terrain]]

[[File:27615 1880faults.jpg|thumb|300px|center|Faults in layered terrain]]

[[File:71634 1880layersfaultslabeled.jpg|thumb|300px|Faults in layers in Danielson Crater]]

<gallery class="center" widths="380px" heights="360px">
File:26086 1800fault.jpg|Fault that changed direction of stream. CTX image is included for context.

</gallery>

==Mesas and layers==

[[File:Layered hills around Mars 21.jpg|600pxr|File:Layered hills around Mars]]

Layered hills around Mars

[[File:58788 1890layerscolorlabeled2.jpg|Mesa with layers]]

Mesa with layers

On Mars much layered terrain is visible. Layered rock is formed from separate events. For example, a layer may be formed at the bottom of a lake. Later, lava may cover that layer, thus making a new layer—one that is harder. In times erosion may remove nearly all the layers. But, sometimes remnants are left behind, especially if they are topped off by a hard cap rock. Lave flows can make cap rock. The cap rock will protect the underlying rocks from erosion. Cap rock often breaks up into large boulders. Sometimes the boulders are in the shape of cube-shaped blocks. Many, large areas of Mars have eroded in such a fashion. The remaining structures are called mesas or buttes—if they are small in area. Some mesas and buttes show layers. Mesas show the kind of material that covered a wide area. Mesas are what are left after the ground is mostly eroded.

<gallery class="center" widths="380px" heights="360px">
File:58563 2225mesa.jpg|Mesa

File:58524 1820layerscolor4labeled.jpg|Mesa with layers

File:58919 1935mesalayers.jpg|Mesa with layers Box is the size of a football field.

File:55119 2080ridgesmesafootballlabeled3.jpg|Butte The box shows the size of a football field.

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Layers in Craters==

[[File:61161 2210pyramidcraterlabeled.jpg|Mesa in crater with layers]]

Layers in crater They were protected from erosion by being in the crater.

Craters can contain mesas that show layers. It is believed that these layers are the remnants of material that once covered a wide area, but is now only in protected places like inside craters. The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Wind, acting over millions of years, will shape the material in craters into smooth mesas.

<gallery class="center" widths="380px" heights="360px">

File:48024 2195pyramid.jpg|Layered mound in crater Layers represent material that once covered a wide area. Mound was shaped by winds.<ref>https://www.uahirise.org/hipod/ESP_054486_2210</ref>

File:ESP 049884 2125pyramid.jpg|Layered feature in crater in Casius quadrangle These layered features are quite common in some regions of Mars.

File:28207 2250cratermesa.jpg|Color view of layers in a mesa in a crater
</gallery>

==Dipping Layers==

[[File:46180 2225dippinglayers.jpg|Dipping layers and brain terrain (right side of picture)]]

Dipping layers and brain terrain (right side of picture)

A common feature on Mars is “dipping layers.” They are groups or stacks of layers that seem to be leaning against something steep like a crater wall or the wall of a mesa. It is believed that they represent material that once covered a wide area, but is now only in protected places.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> The layers mean that different events laid down the layers. These layers are probably due to latitude dependent mantle that falls from the sky at different times. Mantle is mostly from ice-coated dust falling from the sky under certain climate conditions. These dipping layers are often smooth from the action of the wind over millions of years. Another idea for their origin was presented at 55th LPSC (2024) by an international team of researchers. They suggest that the layers are from past ice sheets.<ref>Blanc, E., et al. 2024. ORIGIN OF WIDESPREAD LAYERED DEPOSITS ASSOCIATED WITH MARTIAN DEBRIS COVERED GLACIERS. 55th LPSC (2024). 1466.pdf</ref>

[[File:ESP 038002 1375dipping.jpg|thumb|300px|left|Wide view of dipping layers against slopes]]

[[File:ESP 062082 2175dippingcropped.jpg|thumb|300px|right|Dipping layers These may be the remains of past layers of mantle that covered the whole area.]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 035801 2210pyramidsismenius.jpg|Dipping layers against a mesa wall.

</gallery>

[[File:ESP 019778 1385pyramid.jpg|Set of dipping layers in crater]]

Set of dipping layers in crater

<gallery class="center" widths="380px" heights="360px">

File:Dipping layers in HiRISE image ESP 080402 2240 01.jpg| Wide view of dipping layers, as seen by HiRISE under the HiWish program. The dark strip is where a computer problem is preventing the gathering of data.

File:Dipping layers in HiRISE image ESP 080402 2240 02.jpg|Group of dipping layers. Each layer represents a change in the Martian climate.

File:Dipping layers in HiRISE image ESP 080402 2240 03.jpg|Remaining parts of a group of dipping layers. Erosion has removed most of the material.

File:Dipping layers in HiRISE image ESP 080402 2240 05.jpg|Close view of dipping layers that show the thin nature of the layers.

</gallery>

==Boulders==

[[File:28497 2250boulderslabeled.jpg|Boulders near hollows]]

Boulders near hollows

Large, house-sized boulders are widespread on the Red Planet. Mars has an old surface—billions of years old. In that time, erosion has broken down many hard rocks. Most of Mars is covered with hard volcanic rock. The dark volcanic rock basalt covers most of the Martian surface. When it breaks, it first forms large boulders.

<gallery class="center" widths="380px" heights="360px">
File:Boulder track down crater wall ESP 081601 1615.jpg|Boulder rolled down crater wall and left a track

File:55119 2080mesasinglelabeled.jpg|Mesa The top has a hard cap rock that protects the underlying rocks from erosion. Boulders are visible in the image.
File:58904 2240brainsboulders.jpg|Boulders and brain terrain
File:48878 2095fracturesboulders.jpg| Fractures with boulders in low areas Box shows size of football field.
49950 2125ridgesboulders.jpg|Close view of ridge networks, as seen by HiRISE under HiWish program Many boulders are visible.

File:ESP 045415 2220boulders.jpg|Color view of boulders

45575 2535dunebouldertracks.jpg|Boulders and tracks, as seen by HiRISE under HiWish program The arrows show a boulders that have produced a track by rolling down dune.

</gallery>

[[File: 47157 1850boulders.jpg|Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.]]

Boulders and their tracks from rolling down a slope Arrows show two boulders at the end of their tracks.

[[File:59458 2145boulders.jpg|Color view of boulders]]

Boulders formed from break up of a mesa

==Yardangs==

[[File:61167 1735yardangs.jpg|Yardangs]]

Yardangs

Yardangs develop from fine-grained material.<ref>https://www.uahirise.org/hipod/ESP_046504_1785</ref> They are shaped by the wind and show the direction of the dominant winds.<ref> Bridges, Nathan T.; Muhs, Daniel R. (2012). "Duststones on Mars: Source, Transport, Deposition, and Erosion". Sedimentary Geology of Mars. pp. 169–182. doi:10.2110/pec.12.102.0169. ISBN 978-1-56576-312-8.</ref> <ref> https://www.uahirise.org/ESP_039563_1730</ref> Volcanoes supply much of this fine-grained material. Yardangs are especially widespread in what's called the "Medusae Fossae Formation." This formation is found in the Amazonis quadrangle and near the equator.<ref>http://adsabs.harvard.edu/abs/1979JGR....84.8147W SAO/NASA ADS Astronomy Abstract Service: Yardangs on Mars</ref> Because yardangs exhibit very few impact craters they are believed to be relatively young.<ref>http://themis.asu.edu/zoom-20020416a</ref> The largest single source of dust in the air on Mars comes from the Medusae Fossae Formation.<ref> Ojha, Lujendra; Lewis, Kevin; Karunatillake, Suniti; Schmidt, Mariek (2018). "The Medusae Fossae Formation as the single largest source of dust on Mars". Nature Communications. 9 (1): 2867.</ref>

<gallery class="center" widths="380px" heights="360px">

File:61167 1735yardangs3.jpg|Yardangs
File:ESP 045831 1750yardangswide.jpg|Wide view of yardangs in Amazonis quadrangle
File:ESP 047915 1815yardangs.jpg|Wide view of yardangs
File:ESP 045831 1750yardangscolor.jpg|Close, color view of yardangs

File:Wide view of field of yardings.jpg|Wide view of yardangs in Arabia quadrangle
File:ESP 061610 1895yardangsclose.jpg|Close view of yardangs, these features are shaped by the wind.
</gallery>

==Ring-Mold Craters==

[[File:52260 2165ringmoldcraters2.jpg|Ring mold craters They may contain ice.]]

Ring mold craters They may contain ice.

Ring-mold craters are a type of small impact crater that looks like the ring molds used in baking.<ref>https://link.springer.com/referenceworkentry/10.1007/978-1-4614-9213-9_318-1</ref> <ref>kress, A., J. Head. 2008. Ring‐mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophysical Research Letters Volume 35, Issue 23</ref> One popular idea for their formation is an impact into ice--Ice that is covered by a layer of debris.<ref>https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008GL035501</ref> They are found in parts of Mars that contain buried ice. Laboratory experiments confirm that impacts into ice end in a "ring mold shape." Other evidence for this contention is that they are bigger than other craters in which an asteroid impacted solid rock implying that the material entered by the impact was softer than rock (as ice is). Impacts into ice warm the ice and cause it to flow into the ring mold shape. These craters are common in lobate debris aprons and lineated valley fill—both thought to have buried ice under a thin layer of rocky debris<ref>Kress, A., J. Head. 2008. Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys.Res. Lett: 35. L23206-8</ref> <ref>Baker, D. et al. 2010. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus: 207. 186-209</ref> <ref>Kress., A. and J. Head. 2009. Ring-mold craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci: 40. abstract 1379</ref> Ring-mold craters may be an easy way for future colonists of Mars to find water ice because some may contain ice that is relatively pure. And, since it was generated during a rebound, ice may have been brought up from below the surface; hence, less digging or drilling may be required to gather ice.

Another, later idea, for their formation suggests that the crater was buried with mantle. Since the center of the crater is deeper, the mantle will get compacted more. The weight of the sediment would make it more resistant to later erosion. Later, will be greater along the edge; a plateau will be left in the middle, which is what we see with some right mold craters. It was thought that ring-mold craters could only exist in areas with large amounts of ground ice. However, with more extensive analysis of larger areas, it was found the ring mold craters are sometimes formed where there is not as much ice underground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103518301532</ref> <ref>Baker, D. and L. Carter. 2019. Probing supraglacial debris on Mars 2: Crater morphology. Icarus. Volume 319. Pages 264-280</ref>

<gallery class="center" widths="380px" heights="360px">

26055ringmoldcrater.jpg|Close view of ring mold crater.
File:60858 2160ring.jpg|Ring-mold crater from the Picture of the Day 11/18/19
</gallery>

==Dark Slope Streaks==

[[File:Dark slope streaks on Mars 24.jpg|600pxr|Dark slope streaks]]

Dark slope streaks

[[File:55480 2060streaksobstacles.jpg|Some of the streaks here were affected by boulders.]]

Streaks around a mound. Some of the streaks here were affected by boulders.

[[File:55107 1930streaksboulders2.jpg|thumb|300px|right|Dark slope streaks As these streaks moved down, boulders changed their appearance.]]

[[Dark slope streaks]] are avalanche-like features common on dust-covered slopes.<ref>Chuang, F.C.; Beyer, R.A.; Bridges, N.T. 2010. Modification of Martian Slope Streaks by Eolian Processes. ''Icarus,'' '''205''' 154–164.</ref> These streaks have never been observed on the Earth.<ref>Heyer, T., et al. 2019. Seasonal formation rates of martian slope streaks. Icarus </ref>
They form in relatively steep terrain, such as along cliffs and crater walls.<ref name= Schorghofer02>Schorghofer, N.; Aharonson, O.; Khatiwala, S. 2002. Slope Streaks on Mars: Correlations with Surface Properties and the Potential Role of Water. ''Geophys. Res. Lett.,'' '''29'''(23), 2126.</ref> Although they appear much darker than their surroundings, the darkest streaks are only about 10% darker than their backgrounds. Streaks seem much darker because of contrast enhancement in the image processing.<ref>Sullivan, R. et al. 2001. Mass Movement Slope Streaks Imaged by the Mars Orbiter Camera. J. Geophys. Res., 106(E10), 23,607–23,633.</ref>

[[File:ESP 046188 1855streakslabeled2.jpg|600 pxr|Streaks along a mesa]]

Streaks along a mesa

<gallery class="center" widths="380px" heights="360px">
File:ESP 045435 2055troughlayers.jpg|Dark slope streaks in a trough

</gallery>

[[File:23677streakslabeled.jpg|Streaks often start at a small point and then expand down slope.]]

Streaks often start at a small point and then expand down slope. Many streaks may be caused by the action of solid carbon dioxide (dry ice). Under conditions on Mars, during the night dry ice forms under the surface. When the ground warms in the morning, the dry ice turns into a gas and creates a wind that disturbs the dust grains. If situated on a steep slope, an avalanche of bright dust moves down and uncovers the dark undersurface.<ref>https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JE006988</ref> <ref>Lange, S., et al. 2022. Gardening of the Martian Regolith by Diurnal CO2 Frost and the Formation of Slope Streaks. JGR Planets. Volume127, Issue4. e2021JE006988</ref>

==Dust Devil Tracks==

Dust devil tracks can be very beautiful. They are made by giant [[dust devils]] removing bright colored dust from the Martian surface. As a result, dark underlying material is exposed.<ref>https://www.uahirise.org/ESP_058427_1080</ref> <ref>https://www.jpl.nasa.gov/news/perseverance-rover-witnesses-one-martian-dust-devil-eating-another/?utm_source=iContact&utm_medium=email&utm_campaign=1-nasajpl&utm_content=daily20250403</ref> Dust devils on Mars have been photographed both from the ground and from orbit.<ref>https://www.uahirise.org/ESP_042201_1715</ref> They helped scientists by blowing dust off the solar panels of two Rovers on Mars, thereby greatly extending their useful lifetime.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html Mars Exploration Rover Mission: Press Release Images: Spirit. Marsrovers.jpl.nasa.gov</ref> Dust devils can be 650 meters high and 50 meters across.<ref> https://www.uahirise.org/ESP_061787_2140</ref> The pattern of the tracks has been shown to change every few months.<ref>http://hirise.lpl.arizona.edu/PSP_005383_1255</ref> They have been seen from the surface by the Perseverance Rover.<ref>https://www.jpl.nasa.gov/images/pia26074-martian-whirlwind-takes-the-thorofare</ref> Dust devils are common.<ref>https://www.uahirise.org/ESP_042201_1715</ref> One team of researchers have calculated that on average 1 dust devil happens every sol (day on Mars) for each square kilometer.<ref> https://scholarworks.boisestate.edu/cgi/viewcontent.cgi?article=1207&context=physics_facpubs</ref> <ref>Jackson, Brian; Lorenz, Ralph; and Davis, Karan. (2018). "A Framework for Relating the Structures and Recovery Statistics in Pressure Time-Series Surveys for Dust Devils". Icarus, 299, 166-174. http://dx.doi.org/10.1016/j.icarus.2017.07.027</ref>

Researchers V. Bickel and others, studied over a thousand dust devils and published their results in 2025. The study found that the diameters of dust devils range from an estimated ~18 to ~578 m, with a average diameter of 82 m.<ref> https://www.science.org/doi/10.1126/sciadv.adw5170?adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927070&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927073&adobe_mc=MCMID%3D68227027333727904592434133527388632768%7CMCORGID%3D242B6472541199F70A4C98A6%2540AdobeOrg%7CTS%3D1759927544%27</ref> <ref>Valentin T. Bickel et al. ,Dust devil migration patterns reveal strong near-surface winds across Mars.Sci. Adv.11,eadw5170(2025).DOI:10.1126/sciadv.adw5170</ref>

[[File:ESP 057581 1340devils.jpg |Dust devil tracks near crater|600pxr|Dust devil tracks near crater]]

<gallery class="center" widths="380px" heights="360px">

File:ESP 036297 2370devils.jpg|Dust Devil Tracks

File:ESP 036631 2335devilsbottom.jpg|Dust devil tracks in Casius quadrangle

</gallery>

[[File:ESP 048078 1160devils.jpg|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.|500pxr|Dust devil tracks in Hellas quadrangle Dark material is visible in the troughs of polygons.]]

Dust devil tracks in Casius quadrangle

==Dunes==

[[File:ESP 034745 1665blue dunes.jpg|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>|600pxr|Colorful dunes in the Mare Tyrrhenum quadrangle<ref>https://www.uahirise.org/ESP_057071_1890</ref>]]

Some places on Mars have many beautiful dark dunes. Rovers on the Martian surface confirmed earlier ideas that the dunes are composed of sand made from the volcanic rock basalt..<ref>Lorenz, R. and J. Zimbelman. 2014. Dune Worlds How Windblown Sand Shapes Planetary Landscapes. Springer. NY.</ref> Dunes are often covered by a seasonal carbon dioxide frost that forms in early autumn and remains until late spring. As the frost disappears, different patterns can emerge on the dunes. Dunes can take on different colors because of slight chemical variations in the sand grains.

The presence of dunes on Mars and the observations that they do change is clear proof that there is air on Mars. However, we must remember that its atmosphere is only about 1 % as dense as the Earth's. Hence, a wind speed of a 60-mph storm on Mars would feel more like 6 mph (9.6 km/hr).<ref> https://www.space.com/30663-the-martian-dust-storms-a-breeze.html</ref> Since we have imaged Mars for many years, we have been able to detect some movement in dunes.<ref>https://www.uahirise.org/hipod/ESP_043617_1885</ref>

[[File:ESP 046378 1415dunescolor.jpg|thumb|300px|right|Dunes]]

[[File:33272 1400dunes.jpg|thumb|300px|left|Dunes]]

<gallery class="center" widths="380px" heights="360px">

File:59628 1275dunes.jpg|Dunes in Hellas quadrangle

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes.
File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across.

File:ESP 082974 1685ridge and star shaped dunes 04.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.

File:ESP 082974 1685 star shaped dunes 03.jpg|Close view of various shaped dunes Picture is about 1 km across. Some dunes would be called star dunes. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
File:ESP 082974 1685star shaped dunes 05.jpg|Close view of various shaped dunes Picture is about 1 km across. Image is from Sinus Sabaeus quadrangle and was taken with HiRISE.
</gallery>

==Glaciers==

[[File:ESP 018857 2225alpineglacier.jpg|Glacier moving out of a valley This is similar to glaciers on the Earth]]

Glacier moving out of a valley This is similar to glaciers on the Earth

Glaciers have been described as “rivers of ice.” With glaciers there is a downward movement that can be noticed by examining patterns on their surface. There are large areas on Mars that contain what is thought to be ice moving under a cover of debris. Exposed ice will not last long under present climate conditions on Mars, but just a few meters of debris can preserve ice for long periods of time.<ref>Head, J. W.; et al. (2006). "Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for Late Amazonian obliquity-driven climate change". Earth and Planetary Science Letters. 241 (3): 663–671.</ref> Researchers noticed decades ago that many forms on Mars resembled glaciers on the Earth. As scientists received pictures with greater resolution, the shapes and patterns visible on their surfaces looked like the flows visible in the Earth’s glaciers.

<gallery class="center" widths="380px" heights="360px">

File:ESP 050176 2245glacier.jpg|Glacier moving out of a valley
File:ESP 045085 2205flowlabeled.jpg|Alpine Glacier moving out of a valley and then moving onto Lineated valley fill (LVF) The LVF contains ice under a layer of insulating debris. Lineated Valley Fill is considered to be a glacier.
File:47193 1440glacier.jpg|Glaciers
File:35934 2215brainsglacier.jpg|End of an old glacier. Most of the ice is gone, but the material moved by the glacier is formed into an arc.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

</gallery>

==Lobate Debris Aprons (LDA’s) ==

Lobate debris aprons (LDAs), first seen by the Viking Orbiters, look like piles of rock debris below cliffs.<ref>Carr, M. 2006. The Surface of Mars. Cambridge University Press. </ref> <ref>Squyres, S. 1978. Martian fretted terrain: Flow of erosional debris. Icarus: 34. 600-613.</ref> They slope away from mesas and buttes.
The Mars Reconnaissance Orbiter's Shallow Radar found pure ice in LDA’s around many mesas.<ref>http://www.planetary.brown.edu/pdfs/3733.pdf</ref> Based on this data, LDA’s are considered to be glaciers covered with a thin layer of rocks.<ref>Head, J. et al. 2005. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature: 434. 346-350</ref><ref>http://www.marstoday.com/news/viewpr.html?pid=18050</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut, J. et al. 2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2290.pdf</ref> <ref>Holt, J. et al. 2008. Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars. Lunar and Planetary Science XXXIX. 2441.pdf</ref> <ref>Petersen, E., et al. 2018. ALL OUR APRONS ARE ICY: NO EVIDENCE FOR DEBRIS-RICH “LOBATE DEBRIS APRONS” IN DEUTERONILUS MENSAE 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 2354.</ref>

[[File:ESP 057389 2195ldacropped.jpg|thumb|300px|right|Lobate Debris Aprons (LDA) around a mound]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 036580 2260ldacropped.jpg|Lobate debris apron
File:ESP 036619 2275ldacropped.jpg|Lobate debris apron
</gallery>

==Lineated Valley Fill (LVF) ==

Lineated valley floor consists of many mostly parallel ridges and grooves on the floors of many channels. The ridges and grooves look like they moved around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features.<ref> https://www.uahirise.org/ESP_026414_2205</ref>
[[File:ESP 052138 1435lvf.jpg|600pxr|Image of gullies with main parts labeled. The main parts of a Martian gully are alcove, channel, and apron. Since there are no craters on this gully, it is thought to be rather young. Picture was taken by HiRISE under HiWish program.]]

[[File:ESP 046061 2190lvf.jpg|thumb|300px|right|Wide view of Lineated Valley Fill (LVF) Lat: 38.7° N Long: 45.7°E (314.3 W)]]
[[File:46061 2190closelvf..jpg|thumb|400px|center|Close view of Lineated Valley Fill (LVF)]]

<gallery class="center" widths="380px" heights="360px">
File:ESP 055408 1375lvf2.jpg|Lineated Valley Fill
File:ESP 046840 2130lvf.jpg|Lineated Valley Fill in valley
File:53630 2195lvf.jpg|Lineated Valley Fill
File:56544 2200lvfbrains.jpg|Lineated Valley Fill
File:56544 2200lvflabeled.jpg|Lineated Valley Fill

File:ESP 084607 2210lvf 01.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 02.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 03.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 04.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 05.jpg|Lineated valley fill in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
File:ESP 084607 2210lvf 06.jpg|Close view of lineated valley fill (LVF) in valley, as seen by HiRISE under HiWish program. Linear valley flow is ice covered by debris. Picture is about 1 km wide. Lineated valley fill is generally considered to be and example of a glacier, as it involves the movement of ice.
</gallery>

==Concentric Crater Fill (CCF) ==

[[Image: ESP_046622_1365ccf.jpg |Concentric Crater Fill Lat: 43.1° S Long: 219.8°E (140.2 W]]

Concentric Crater Fill Located at Lat: 43.1° S Long: 219.8°E (140.2 W

Concentric crater fill is believed to be an ice-rich feature on the floors of many Martian craters. The floor of craters exhibiting CCF is almost totally covered with many parallel ridges.<ref>https://web.archive.org/web/20161001224229/http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_111926_2185 </ref> It is common in the mid-latitudes of Mars,<ref>Dickson, J. et al. 2009. Kilometer-thick ice accumulation and glaciation in the northern mid-latitudes of Mars: Evidence for crater-filling events in the Late Amazonian at the Phlegra Montes. Earth and Planetary Science Letters.</ref> <ref>http://hirise.lpl.arizona.edu/PSP_001926_2185|title=HiRISE - Concentric Crater Fill in the Northern Plains (PSP_001926_2185)|author=|date=|website=hirise.lpl.arizona.edu</ref> and is widely accepted as caused by glacial movement.<ref>Head, J. et al. 2006. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci Lett: 241. 663-671.</ref> <ref>Levy, J. et al. 2007. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacial modification of the dichotomy boundary. J. Geophys. Res.: 112.</ref> The [[Ismenius Lacus quadrangle]] contains examples of concentric crater fill.

<gallery class="center" widths="380px" heights="360px">
Image: ESP_046622_1365ccfclosecolor.jpg|Close, color view of Concentric Crater Fill

File:46688 1365ccf2.jpg|Close view of Concentric Crater Fill (CCF)
</gallery>

==Brain Terrain==

[[File:45917 2220brainsopenclosed.jpg|Open and closed brain terrain]]

Open and closed brain terrain The closed cell brain terrain may still hold an ice core, so they may be sources of water for future colonists.<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref>

Brain terrain is an area of maze-like ridges 3–5 meters high. A person could wander between these ridges like a rat in a maze. Brain terrain is one of the unsolved mysteries on Mars because we do not totally understand it.<ref>https://www.uahirise.org/ESP_058008_2225</ref> <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists. There are two kinds—open and closed. One hypothesis is that it begins with cracks that get larger and larger as ice leaves the ground. When ice is exposed on Mars under its present climate conditions, ice goes directly into the air. That process of going from a solid to a gas—instead of first to a liquid—is called sublimation. With this process, the cracks get wider and wider until a complex of high and low areas remains. <ref> Levy, J., J. Head, D. Marchant. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial “brain terrain” and periglacial mantle processes. Icarus 202, 462–476.</ref>

<gallery class="center" widths="380px" heights="360px">
File:25246brainseroding.jpg|Brain terrain
File:45917 2220openclosedbrains.jpg|Labeled picture of open and closed brain terrain in the Ismenius Lacus quadrangle The closed cell brain terrain may still hold an ice core,<ref>Levy, J., et al. 2009. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial mantle processes. Icarus: 202, 462-476.</ref> so it may a source of water for future colonists.
File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle

File:53630 2195brainslvf.jpg|Brains on surface of leaneted valley fill
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>

==Ice Cap Layers==

[[File:ESP 054515 2595layersicecap.jpg|Layers in northern ice cap This photo was named picture of the day for January 21, 2019. ]]

Layers in northern ice cap This photo was named picture of the day for January 21, 2019.

The northern ice cap of layers displays many layers. These layers are visible when a valley cuts through the cap. Layers in the ice cap, as with other exposures of layers across the planet, are formed from frequent dramatic changes in the climate. These changes are the result of great changes in the rotational axis or tilt of the planet. Mars does not have a large moon to stabilize its' tilt; hence the planet has huge variations in its tilt (maybe from its present Earth-like tilt to over twice the Earth’s).

<gallery class="center" widths="380px" heights="360px">

File:ESP 061636 2620nicecaplayerscroppedlabeled.jpg|Northern ice cap layers
File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle

File:ESP 044934 2670icecaplayers.jpg|Layers exposed in ice cap in Mare Boreum quadrangle
File:ESP 036863 2670icecaplayers.jpg| Layers exposed in ice cap in Mare Boreum quadrangle
ESP_052405_2595icelayers.jpg|Layers in northern ice cap Some of the layers are at different angles because erosion took away some layers to the right.

</gallery>

==Spiders==

[[File:Spiders on Mars 23.jpg|600pxr|Spiders and plumes]]

Spiders and plumes

[[File:56839 1000spiderslabeled.jpg |Close view of spiders]]

Close view of spiders

Some features have been called spiders because they can resemble spiders. The official name for spiders is "araneiforms."As the temperature goes up in the spring, pressurized carbon dioxide gas and dark dust are released from under slabs of ice.<ref>Portyankina, G., et al. 2019. How Martian araneiforms get their shapes: morphological analysis and diffusion-limited aggregation model for polar surface erosion Icarus. https://doi.org/10.1016/j.icarus.2019.02.032</ref> <ref>https://www.uahirise.org/</ref> This process results in the appearance of dark plumes that are often blown in one direction by local winds. Besides producing plumes, dust darkens channels under the ice and forms dark shapes that resemble spiders.<ref>Kieffer H, Christensen P, Titus T. 2006 Aug 17. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature: 442(7104):793-6.</ref> <ref>https://mars.nasa.gov/resources/possible-development-stages-of-martian-spiders/</ref> <ref>http://themis.asu.edu/news/gas-jets-spawn-dark-spiders-and-spots-mars-icecap</ref> <ref>http://spaceref.com/mars/how-gas-carves-channels-on-mars.html</ref> <ref>https://www.livescience.com/space/mars/spiders-on-mars-fully-awakened-on-earth-for-1st-time-and-scientists-are-shrieking-with-joy?utm_term=CABA215D-3D47-4C9A-92FE-9ECF8D4C7909&lrh=e62336263a3610a07ef7c8af2080c758f2ecd0661aab1a8e6234cf31f0d0fdff&utm_campaign=368B3745-DDE0-4A69-A2E8-62503D85375D&utm_medium=email&utm_content=542DE80B-08E0-4FC1-B871-90E60036945E&utm_source=SmartBrief</ref>
The process of making spiders was demonstrated in laboratory simulations involving slabs of dry ice and glass spheres of different sizes.<ref>https://www.nature.com/articles/s41598-021-82763-7.pdf</ref> <ref>McKeown, L., et al. 2021. The formation of araneiforms by carbon dioxide venting and vigorous sublimation dynamics under martian atmospheric
pressure. Scientific Reports.</ref> <ref>https://www.livescience.com/spiders-on-mars-explained-dry-ice.html?utm_source=Selligent&utm_medium=email&utm_campaign=LVS_newsletter&utm_content=LVS_newsletter+&utm_term=2946561</ref>

<gallery class="center" widths="380px" heights="360px">

File:47609 0985spiders.jpg|Spiders and plumes, as seen by HiRISE under HiWish program

</gallery>

==Mantle==

[[File:37167 1445mantlelabeled.jpg|Mantle Mantle covers the surface irregularities on Mars]]

Mantle Mantle covers the surface irregularities on Mars

Mantle on Mars appears as a smooth surface. It covers the normal irregular surface of the planet. It is often called “Latitude Dependent Mantle” because it occurs at certain distances from the equator (certain latitudes).<ref>Kreslavsky, M., J. Head, J. 2002. Mars: Nature and evolution of young, latitude-dependent water-ice-rich mantle. Geophys. Res. Lett. 29, doi:10.1029/ 2002GL015392.</ref> This latitude dependent mantle is believed to fall from the sky. During certain climatic conditions, moisture from the air will freeze onto dust particles. When they become too heavy, these particles fall to the ground.<ref>Head, J., et al. 2003, Recent ice ages on Mars. Nature. 426.797-802</ref> Snow may also fall on to the mantle. So, mantle consists of ice with dust. Since Mantle has a widespread distribution, it may be a major source of water for future colonists. Sometimes mantle displays layers because it was deposited at different times. The climate of Mars has changed many times due to a lack of a large moon. Our Earth’s moon is very massive and that helps to control the tilt of the rotational axis of our Earth. In other words, our moon keeps our planet’s tilt from changing much. Changes in the tilt of a planet will cause major changes in climate.

<gallery class="center" widths="380px" heights="360px">

File:46294 1395mantle.jpg|Comparison of terrain with and without a covering of mantle
46444 2225mantle.jpg|Mantle, as seen by HiRISE under HiWish program
45917 2220gulliesmantle.jpg|Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program

</gallery>

[[File:54742 1485mantle.jpg|Mantle in a crater The mantle here has made everything look smooth on one side of the crater.]]

Mantle in a crater The mantle here has made everything look smooth on one side of the crater.

==Polygons==

[[File:56942 1075icepolygonslabeled2.jpg|Polygons]]

Polygons

Many surfaces on Mars have polygon shapes. These areas are sometimes called “polygonal patterned ground.” The polygons can be of different shapes and sizes—often very beautiful. They are believed to be caused by ice in the ground because they occur on the Earth where there is ice in the ground.<ref>https://www-sciencedirect-com.wikipedialibrary.idm.oclc.org/science/article/pii/S0019103525002751</ref> <ref>Soare, R., et al. 2025. “Icy” scarp exposures, “ice-rich” overburdens and ephemeral climate-warming at Mars' mid-latitudes in the very late Amazonian epoch. Icarus. Volume 441, 15 November 2025, 116727</ref>

With the changing seasons, alternate cooling and warming causes the ice-cemented soil to contract and expand. With the right conditions, cracks are made into the hard frozen ground releasing the stresses caused by contraction.<ref>https://www.uahirise.org/ESP_066782_1110</ref> <ref>https://www.uahirise.org/ESP_047247_1150</ref>

In the future they may help point us to supplies of ice for colonists. The locations of polygons will provide evidence for us to make detailed maps for locations of water before we send crews to live there.

<gallery class="center" widths="380px" heights="360px">

File:56148 1145polygonsveryclose.jpg|Enlarged view of polygons that shows polygons of varying sizes. Dark lines are defects in processing.
File:56148 1145polygons.jpg|Close view of polygons

File:ESP 043821 2555dryice.jpg|Field of dunes defrosting Black areas are free of frost, so the dark of the dunes shows up. White portions of dunes are still covered with frost.

File:ESP 043821 2555dryicecolor.jpg|Close view of parts of two dunes showing white parts with frost. The polygon surface they sit on still has frost in the low areas.

</gallery>

[[File:43821 2555dunesdefrosting2.jpg|Defrosting dune--white areas still contain frost]]

Defrosting dune--white areas still contain frost. Frost is in low parts of polygons.

==Scalloped Terrain==

[[File:37461 2255scallopslabeled2.jpg|Scalloped terrain This feature is important it may point future colonists to water supplies.]]

Scalloped terrain This feature is important it may point future colonists to water supplies.

Scalloped topography or terrain is common in the mid-latitudes of Mars, between 45° and 60° north and south. It is especially prominent in the region called “Utopia Planitia.”<ref>last1 = Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | last4 = McEwen | first4 = A.S. | last5 = Dundas | first5 = C.M. | last6 = Kirk | first6 = R.L. | year = 2009 | title = HiRISE observations of periglacial landforms in Utopia Planitia | url = http://www.agu.org/pubs/crossref/2009/2008JE003264.shtml | journal = Journal of Geophysical Research | volume = 114 | issue = | page = E04005 | doi = 10.1029/2008JE003264 |</ref> <ref>Morgenstern A, Hauber E, Reiss D, van Gasselt S, Grosse G, Schirrmeister L (2007): Deposition and degradation of a volatile-rich layer in Utopia Planitia, and implications for climate history on Mars. Journal of Geophysical Research: Planets 112, E06010.</ref> This terrain displays shallow, rimless depressions with scalloped edges--commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. The usual scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>https://www.uahirise.org/hipod/PSP_001938_2265</ref> <ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped topography may be of great importance for future colonization of Mars because radar studies reveal it is ice-rich.<ref>"Dundas, C. 2015" Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 </ref> <ref>Stuurman, C., et al. 2016. SHARAD reflectors in Utopia Planitia, SHARAD detection and characterization of subsurface water ice deposits in Utopia Planitia, Mars. Geophysical Research Letters, Volume 43, Issue 18, 28 September 2016, Pages 9484–9491.</ref> <ref>Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

<gallery class="center" widths="380px" heights="360px">

File:46916 2270scallopsmerging.jpg|Scalloped terrain
File:37461 2255scallopedscale.jpg|Scalloped terrain in Utopia Planitia
File:37461 2255scallopedclose.jpg|Scalloped terrain
</gallery>

==Pingos==

[[File: ESP 046359 1250-2pingoscale.jpg|Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)]]

Close view of possible pingo with scale, as seen by HiRISE under HiWish program Lat: 54.7° S Long: 202.7°E (157.3 W)

For many years, Pingos were believed to be present on Mars. Since they contain pure water ice, they would be a great source of water for future colonists on Mars. One picture from HiRISE under the HiWish program was thought to be a pingo.

<gallery class="center" widths="380px" heights="360px">

File:76854 2220pingo.jpg|Possible pingos. Pingos should look like mounds. Some will have cracks that formed when the water inside expanded as it froze.

</gallery>

==Gullies==

[[File:50858 1435gullylabeled.jpg|Gullies with parts labeled--Alcove, Channel, Apron]]

Gullies with parts labeled--Alcove, Channel, Apron

[[Martian gullies]] are narrow channels and their associated downslope deposits. They are found on steep slopes. Most are seen on the walls of craters. Many are visible near 40 degrees north and south of the equator. Usually, each gully has an ''alcove'' at its head, a fan-shaped ''apron'' at its base, and a ''channel'' linking the two.<ref >Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. For many years, gullies were thought to be caused by recent running water.<ref>https://www.uahirise.org/hipod/ESP_014074_1445</ref> But since some are being formed today, even when the climate of Mars is too cold for running water to exist on the surface, there must be another cause. After more observations, it was shown that pieces of dry ice moving down slopes could cause them. Nevertheless, some scientists think that in the past, water may have been involved in their formation.

<gallery class="center" widths="380px" heights="360px">
File:ESP 046386 1420gullies.jpg|Gullies

File:47395 1415gullycurvedchannels.jpg|Gullies Curved channels were thought to need running water to form.
File:57707 1410gullycolorwide.jpg|Color view of Gullies, as seen by HiRISE under HiWish program Only part of the picture appears in color because the camera only produces color in a center strip.

</gallery>

[[File:Gullies near Newton Crater2185.jpg|Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>]]

Gullies in Phaethontis quadrangle Ridges at the end of the gullies may be the remains of old glaciers.<ref>https://www.uahirise.org/ESP_057450_1410</ref>

==Craters==

[[File:ESP 046046 2095craterandejecta.jpg|This is a fairly young crater as it still shows ejecta, layers, and a rim.]]

This is a fairly young crater as it still shows ejecta, layers, and a rim.

[[File:Features in and around Martian craters.jpg|600pxr|Features in and around Martian craters]]

Features in and around Martian craters

Craters cover nearly all parts of Mars. Most of the surface of Mars is over a billion years old. Because Mars has not had active plate tectonics for a very long time (if it ever had active plate tectonics), impact craters stay for a long time. There are many kinds of craters on the planet.<ref>https://en.wikipedia.org/wiki/List_of_craters_on_Mars</ref> <ref>Carr, M.H. (2006) The surface of Mars; Cambridge University Press: Cambridge, UK</ref>

<gallery class="center" widths="380px" heights="360px">

File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.

File:55252 1385craterfloorbrains.jpg|Crater floor with brain terrain

File:ESP 055252 1385brainscolorclose.jpg|Edge of crater with brain terrain on its floor

File:52030 1560crater.jpg|Average crater showing layers

File:54774 1700colorcraterejecta.jpg|Crater and part of its ejecta

File:ESP 048062 1425gulliesridges.jpg|Crater containing gullies and depressions The curved depressions are formed when the ground loses ice. Gullies may be due to water or dry ice moving down the walls.
File:ESP 048131 2055crater.jpg|Crater with pits and holes on floor The shapes on the floor occurred when ice left the ground.

File:ESP 046548 2355pedestalbutterfly.jpg|Pedestal crater with a butterfly shape. this may have formed from a low angle impact.
File:ESP 053576 1990lightstreak.jpg|Crater with light streak Streaks associated with craters are quite common on Mars because there is a great deal of fine dust that can be blown around.

File:61167 1735crater.jpg|Crater with thin ejecta The color strip for HiRISE images is only in the center of images.

</gallery>
<gallery class="center" widths="380px" heights="360px">
File:75431 1665ejecta2.jpg|Crater with colorful ejecta, as seen by HiRISE under the HiWish program The ejecta represents samples of material from underground. Craters allow us to study underlying material.

File:75431 1665ejecta3.jpg|Crater with colorful ejecta, as seen by HiRISE The ejecta represents samples of material from underground. Craters allow us to study underlying material.
</gallery>

[[File:29565 2075newcratercomposite.jpg|New, small crater We have detected many new craters on Mars that have impacted the planet since good cameras have orbited the planet.]]

New, small crater We have found that Mars is hit by 200 impacts/year.<ref>https://www.space.com/21198-mars-asteroid-strikes-common.html</ref> <ref>https://www.sciencedirect.com/science/article/abs/pii/S0019103513001693?via%3Dihub</ref> <ref>Daubar, I., et al. 2013. The current martian cratering rate. Icarus. Volume 225. 506-516. </ref>

==Hellas Floor Features==

[[File:Shapes on the floor of Hellas 17.jpg|600pxr|Hellas floor shapes]]

Hellas floor features

[[File:55146 1425hellisfloor.jpg|Wide view of features on floor of Hellas impact basin. The exact origin of these shapes is unknown at present.]]

Wide view of features on floor of Hellas impact basin.
The exact origin of these shapes is unknown at present.

The Hellas floor contains strange-looking features that look like some sort of abstract art. One such feature is called "banded terrain." <ref>Diot, X., et al. 2014. The geomorphology and morphometry of the banded terrain in Hellas basin, Mars. Planetary and Space Science: 101, 118-134.</ref> <ref>http://www.nasa.gov/mission_pages/MRO/multimedia/20070717-2.html | title=NASA - Banded Terrain in Hellas</ref> <ref>http://hirise.lpl.arizona.edu/ESP_016154_1420 | title=HiRISE | Complex Banded Terrain in Hellas Planitia (ESP_016154_1420)</ref> This terrain has also been called "taffy pull" terrain, and it lies near honeycomb terrain, another strange surface.<ref>Bernhardt, H., et al. 2018. THE BANDED TERRAIN ON THE HELLAS BASIN FLOOR, MARS: GRAVITY-DRIVEN FLOW NOT SUPPORTED BY NEW OBSERVATIONS. 49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083). 1143.pdf</ref> Banded terrain is found in the north-western part of the Hellas basin, the deepest section. The bands can be classified as linear, concentric, or lobate. Bands are typically 3–15km long and 3km wide. Narrow inter-band depressions are 65 m wide and 10 m deep.<ref>doi=10.1016/j.pss.2015.12.003 |title=Complex geomorphologic assemblage of terrains in association with the banded terrain in Hellas basin, Mars |journal=Planetary and Space Science |volume=121 |pages=36–52 |year=2016 |last1=Diot |first1=X. |last2=El-Maarry |first2=M.R. |last3=Schlunegger |first3=F. |last4=Norton |first4=K.P. |last5=Thomas |first5=N. |last6=Grindrod |first6=P.M. |last7=Chojnacki |first7=M. |121...36D |url=https://boris.unibe.ch/74530/1/Diot_Schlunegger.pdf </ref> How these shapes were made is still a mystery, although some explanations have been advanced.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref>

[[File:55146 1425hellisfloorcropped.jpg|thumb|400px|center|Features on floor of Hellas impact basin.]]

[[File:55146 1425hellascenter.jpg|Close view of center of a Hellas floor feature]]

Close view of center of a Hellas floor feature

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

[[File:90251 1380hellascropped.jpg|600pxr|Twisted bands on Hellas floor]]

Twisted bands on Hellas floor

==Oxbow lakes and meanders==

An oxbow lake is a U-shaped lake that forms when a wide meander of a river is a cut off that makes a lake. This landform is so named for its distinctive curved shape, which resembles the bow pin of an oxbow.<ref>https://en.wikipedia.org/wiki/Oxbow_lake</ref> Finding them on Mars means that water probably flowed for a long time.

<gallery class="center" widths="380px" heights="360px">
File:WikiESP 039594 1365oxbow.jpg|An oxbow means that water flowed long enough to make a meander before the stream made a shortcut across the meanders.

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
</gallery>

[[File: ESP 045779 1730meander.jpg|600pxr|Channel showing an old oxbow and a cutoff, as seen by HiRISE under HiWish program]]

Channel showing an old oxbow and a cutoff

[[File: ESP 045868 2245channel.jpg|600pxr|Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.]]
Channel, with meanders These meanders may have meandered a little more and then made oxbow lakes. Arrow points to a crater that was probably eroded by flowing water.

[[File:ESP 043623 2160meander.jpg|600pxr|Meanders Meanders are commonly formed in old river systems when the water is moving slowly.]]
Meanders They are formed in old river systems when the water is moving slowly.

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Channels==

[[File:ESP 056917 2170channels3.jpg|Old river channel with branches]]

Old river channel with branches and meanders

There are thousands of channels that were caused by running water in the past on Mars. Some are large; some are tiny.<ref>https://en.wikipedia.org/wiki/Outflow_channels</ref> <ref>Carr, M.H. (2006), The Surface of Mars. Cambridge Planetary Science Series, Cambridge University Press.</ref> <ref>Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R. & Marley, M.S. "Channels and Valley Networks". In Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W. & Matthews, M.S. Mars. Tucson, AZ: University of Arizona Press.</ref> <ref>Burr, D.M., McEwan, A.S., and Sakimoto, S.E. (2002). "Recent aqueous floods from the Cerberus Fossae, Mars". Geophys. Res. Lett., 29(1), 10.1029/2001G1013345.</ref> <ref>^ Baker, V.R. (1982). The Channels of Mars. Austin: Texas University Press.</ref> These channels have been seen in pictures from spacecraft for nearly 50 years. Current climate models do not support a warm climate on Mars; consequently, various ideas have been advanced to explain the existence of so many channels when it may have always been too cold for liquid water to exist on the surface. Some say they could be formed under ice sheets. Other scientists maintain that they could be produced in short periods after an asteroid impact warms the planet for thousands of years.

<gallery class="center" widths="380px" heights="360px">
File:41974 1740channellabeled.jpg|Old river valley in the Sinus Sabaeus quadrangle

WikiESP 033729 1410stream.jpg|Small branched channel

File:13882282 10207143921535802 7740003704272946655 nchannelinvalley.jpg|Channel in valley The valley was formed early on and then at a later time a small channel appeared. This arrangement means that water flowed here twice--once for the valley, another time for the small channel.

</gallery>

==Streamlined Shapes==

[[File:ESP 045860 2085streamlinedcroppedlabeled.jpg|Streamlined shapes made by running water]]

Streamlined shapes made by running water

Some locations on Mars show clear evidence of massive flows of water in the past. During these floods, the ground was carved into streamlined shapes. There are several ideas for how all this happened.<ref> Carr, M. 1979. Formation of Martian Flood Features by Release of Water From Confined Aquifers. Journal of Geophysical Research. 84. 2995-3007</ref> <ref>https://www.uahirise.org/ESP_045833_1845</ref> It may have resulted from asteroid impacts into frozen ground. Under a cap of frozen ground there may have been vast buildups of water that were suddenly released.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057728 2090streamlined.jpg|Streamlined forms

File:58137 2090streamlined.jpg|Streamlined features These were created by the erosion of running water that flowed from the bottom of the image to the top. This direction can be determined by the way the erosion tails are pointed. The location is the Amenthes quadrangle

</gallery>

[[File:ESP 052677 2075streamlined.jpg |Streamlined forms in wide channel These forms were shaped by running water.]]

Streamlined forms in wide channel
These forms were shaped by running water.

==Inverted Terrain==

[[File:ESP 057453 2050ridges.jpg|thumb|500px|center|Possible inverted streams, as seen by HiRISE under HiWish program]]

Often low areas can become high areas. This frequently happens with streams. An old stream channel may become filled with a hard, erosion resistant material like lava or large boulders. Later, erosion of the whole area may remove all the surrounding soft materials. But, the stream channel will be preserved because of the hard materials that were deposited in it. In the end, you are left with a feature which is elevated above the landscape, but has the shape of the original stream. Geologists will then call the stream “inverted.”

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024997ridges.jpg|Possible inverted stream channels, as seen by HiRISE under HiWish program. The ridges were probably once stream valleys that have become full of sediment and cemented. So, they became hardened against erosion which removed surrounding material.

ESP 036362 2195inverted.jpg|Inverted stream channels on crater slope, as seen by HiRISE under HiWish program Location is [[Diacria quadrangle]].

<gallery class="center" widths="380px" heights="360px">
File:87429 1580invertedstreams2.jpg|Curved ridge was once a stream, now it is a ridge becasuse it become filled with erosion-resistant materials. Later, the surrounding, softer ground became eroded. Image obtained through NASA's [[HiWish program]].

File:87429 1580invertedstreams3.jpg|Curved ridges were once streams, now they are ridges becasuse they become filled with erosion-resistant materials. Later, the surrounding, softer ground was eroded away.

</gallery>

==Exhumed Craters==

[[File:ESP 055550 1660exhumed.jpg|Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."]]

Exhumed crater This crater was covered over and now it is being uncovered or "exhumed."

Exhumed terrain appears to be in the process of being uncovered.<ref>https://archive.org/details/PLAN-PIA06808</ref> <ref> https://www.uahirise.org/PSP_001374_1805</ref> The surface of Mars is very old. Places have been covered, uncovered, and covered again by sediments. The pictures below show a crater that is being exposed by erosion. When a crater forms, it will destroy what's under and around it. In the example below, only part of the crater is visible. Had the crater been created after the layered feature, it would have removed part of the feature and we would see the entire crater.

[[File:57652 2215exhumed.marspedaijpg.jpg|thumb|400px|left|This crater had been buried and now is being uncovered by erosion. Had it just been formed, it would have destroyed part of the layered formation that is on top of its right side (just to the left of the crater).]]

[[File:48057 1560craterlayersclose.jpg|thumb|400px|center|The small crater that sits in layers is being exhumed. If it had been made after the layers that it is sitting in, it would have destroyed some of the layered material.]]

==Pedestal Craters==

[[File:ESP 037528 2350pedestal.jpg |Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice."]]

Pedestal crater The surface was protected from erosion by the ejecta. In the past all the surrounding ground was at the level of the pedestal. Most of the loss is thought to be from the loss of ice.

A Pedestal crater is a crater with its ejecta sitting above the surrounding terrain. Its ejecta form a raised platform (like a pedestal).<ref>https://www.uahirise.org/hipod/PSP_008508_1870</ref> They are produced when an impact ejects material that forms an erosion-resistant layer. Consequently, the immediate area erodes more slowly than the rest of the region. Some pedestals are hundreds of meters above the surroundings. This means that hundreds of meters of material were eroded away. What remains is a crater and its ejecta blanket sitting above the surrounding ground. <ref> Bleacher, J. and S. Sakimoto. ''Pedestal Craters, A Tool For Interpreting Geological Histories and Estimating Erosion Rates''. LPSC</ref> <ref> https://web.archive.org/web/20100118173819/http://themis.asu.edu/feature_utopiacraters</ref> <ref> = McCauley, John F. 1972. Mariner 9 Evidence for Wind Erosion in the Equatorial and Mid-Latitude Regions of Mars. Journal of Geophysical Research: 78, 4123–4137(JGRHomepage). |doi = 10.1029/JB078i020p04123</ref>

<gallery class="center" widths="380px" heights="360px">
File:ESP 048021 2130pedestal2.jpg|Pedestal Crater with an odd ejecta pattern

Image: ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program Top layer has protected the lower material from being eroded. Location is Hellas quadrangle, at 52.014° S and 110.651° E (249.349 W).

File:62242 2265pedestal.jpg|Pedestal crater
</gallery>

==Ridges==

[[File:36745 1905ridgesv2.jpg |Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.]]

Close view of ridges We are sure how these were formed, but we have come up with a few possibilities.

Ridge fields are another feature that we do not yet fully understand.<ref>Kerber, L., et al.
2017. Polygonal ridge networks on Mars: Diversity of morphologies and the special case of the Eastern Medusae Fossae Formation. Icarus. Volume 281. Pages 200-219</ref> <ref>https://www.uahirise.org/hipod/PSP_008189_2080</ref> <ref>Pascuzzo, A., et al. 2019. The formation of irregular polygonal ridge networks, Nili Fossae, Mars:
Implications for extensive subsurface channelized fluid flow in the Noachian. Icarus: 319, 852-868</ref>
Hard ridges standing above the surroundings often meet at close to right angles. They may have something to do with cracks caused by impacts. Mineral laden water may then migrate up the cracks and harden.<ref> https://www.uahirise.org/hipod/ESP_077982_1920</ref> These fields can be quite complex and beautiful.

<gallery class="center" widths="380px" heights="360px">

File:ESP 048236 2105ridgeswide.jpg|Wide view of linear ridge network Location is Casius quadrangle.
File:48236 2105ridges2.jpg|Close view of linear ridge network Location is Casius quadrangle.

File:ESP 046269 1770ridegenetworkmiddle.jpg|Ridge network in Mare Tyrrhenum quadrangle
File:Ridges in ESP 074906 2160.jpg|Ridges, this picture was named HiRISE picture of the day on March 29, 2024.

File:ESP 074906 2160-2ridgesclose.jpg|Close view of ridges This picture was named HiRISE picture of the day on March 29, 2024.

</gallery>

[[File:ESP 036745 1905top.jpg|Ridge network in Amazonis quadrangle ]]

Ridge network in Amazonis quadrangle

==Layers==

[[File:44507 1880longlayersdanielson.jpg|600pxr|Layers in Dannielson Crater, as seen by HiRISE under HiWish program]]

Layers of rocks and other materials are very common on Mars.<ref>https://www.uahirise.org/PSP_007820_1505 Layered Sediments in Hellas Planitia</ref> They are found in many low places like craters.<ref>https://www.uahirise.org/hipod/PSP_008930_1880</ref> The widespread occurrence of layering on the Red Planet has great significance. On Earth, much layering originates in bodies of water.<ref>Namowitz, S., Stone, D. 1975. Earth science The World We Live in. American Book Company. N.Y. </ref> If this is true, at least to some extent on Mars, then traces of past life might be found in layered formations. Indeed, much evidence has been gathered for the existence of lakes in craters and some canyons.
Whether layers were created under water or through ground water, water is still being debated. Probably ground water is at least partial responsible for many of the layers we observe on the planet. The existence of water in the ground is important for life on Mars. Most of the organic mass on the Earth is found under the surface. Likewise, Mars may have a great deal of life living under the surface. <ref>https://microbewiki.kenyon.edu/index.php/Deep_subsurface_microbes</ref> <ref>Amend, J.. A. Teske. 2005. Expanding frontiers in deep subsurface microbiology. Palaeogeography, Palaeoclimatology, Palaeoecology: Volume 219, Issues 1–2, 131-155.</ref> Many microbes live deep underground.<ref>Pedersen, K. 1993. The deep subterranean biosphere. Earth Science Reviews: 34, 243-260.</ref> <ref> Stevens, T., J. McKiney. 1995. Lithoautotrophic Microbial Ecosystems in Deep Basalt Acquifers. Science: 270, 450-454.</ref> <ref>Fredrickson, J. , T. Onstott. 1996. Microbes Deep inside the Earth. Scientific American. October, 1996.</ref> Life under the Martian surface might find it easier since it would be protected from high levels of radiation.<ref>Boston, P., et al. 1992. On the Possibility of Chemosynthetic Ecosystems in Subsurface Habitats on Mars. Icarus: 95, 300-308.</ref> One recent study found that radiation from certain elements in the crust of Mars could have reacted with water in the ground to produce hydrogen. Hydrogen can supply chemical energy for life.<ref>http://astrobiology.com/2018/09/ancient-mars-had-right-conditions-for-underground-life.html</ref> <ref> Tarnas, J., et al. 2018 Radiolytic H2 Production on Noachian Mars: Implications for Habitability and Atmospheric Warming. Earth and Planetary Science Letters [https://doi.org/10.1016/j.epsl.2018.09.001</ref>

<gallery class="center" widths="380px" heights="360px">

File: 54763_1500layers2.jpg
File: 54763_1500layerscolor.jpg

File:59619 1845layers3.jpg|Close view of layers

File:59619 1845layers2labeled.jpg|Layers Different colors of the rocks means they contain different minerals.

ESP 048980 1725layers.jpg|Wide view of layers in Louros Valles, as seen by HiRISE under HiWish program Louros Valles is part of the Ius Chasma.
48980 1725layersclose2.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

48980 1725layersclose.jpg|Close view of layers in Louros VallesNote this is an enlargement of a previous image.
ESP 048980 1725layersclosecolor.jpg|Close view of layers in Louros Valles Note this is an enlargement of a previous image.

File: 47421 1890bigbutte.jpg|Close view of layers, as seen by HiRISE under HiWish program. Box shows the size of a football field.

File:Layers some with overhang ESP 26270 1820.jpg|Layers some with overhang. This image was named HiRISE picture of the day.
File:Layers and layered mounds ESP 26270 1820.jpg|Layers and layered mounds. Each layer records some sort of change and water may have been involved. This image was named HiRISE picture of the day.
File:Layered area with faults ESP 26270 1820.jpg|Layers Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

File:Color view of layers 26270 1820.jpg|Close, color view of layers. Light brown is from dust falling from sky. Dark parts are basalt sand that has settled on horizonal surfaces. This image was named HiRISE picture of the day.

</gallery>

[[File:Wide view of layers ESP 27747 1820.jpg|600pxr|Layers and faults in Arabia quadrangle]]

Layers and faults in Arabia quadrangle--HiRISE Picture of the Day (September 25, 2021)

[[File:544858 1885topcloselayers5.jpg|thumb|400px|center|Close view of layers, as seen by HiRISE under HiWish program Location is Danielson Crater.]]

==Ribbed terrain==

Ribbed terrain consists of mostly elongated canyon-like forms. Some portions turn into mesas. It is created when small cracks become larger and larger. A crack in the surface of an ice-rich area will permit more of the ice to go into the thin Martian air because of increased surface area. This process of going directly form a solid to a gas phase is called sublimation. On Earth it is easily observed in the behavior of dry ice (solid carbon dioxide).

[[File:ESP 047499 2245ribslabeled.jpg|500pxr|Ribbed terrain begins with cracks that eventually widen to produce hollows]]

Ribbed terrain begins with cracks that eventually widen to produce hollows

[[File:28339 2245ribbbed.jpg|thumb|400px|center|Wide view of ribbed terrain.]]

[[File:ESP 025174 2245ribs.jpg|500pxr|Wide view of ribbed terrain.]]

Wide view of ribbed terrain.

[[File:25174 2245ribscolor.jpg|thumb|400px|center|Close, color view of ribbed terrain.]]

==Blocks and boulders forming==

Some places on Mars show rocks breaking into boulders or cube-shaped blocks.

[[File:26557joints.jpg|500pxr|Crossing joints, as seen by HiRISE under HiWish program]]

Crossing joints, as seen by HiRISE under HiWish program
<gallery class="center" widths="380px" heights="360px">
48144 1475layerscubes.jpg|Close view of layers, as seen by HiRISE under HiWish program Some of the layers are breaking up into large blocks
48144 1475cubes.jpg|Close view of layers Some layers are breaking up
</gallery>

[[File:26557rocksforming.jpg|Rocks forming|thumb|300px|left|Rocks forming]]

[[File:44757 2185fracturesblocks.jpg|thumb|300px|center|Blocks forming]]

[[File: 47577 1515blocks.jpg|thumb|400px|right|Surface breaking up into cube-shaped blocks]]

[[File: 46684 1280breaking.jpg|thumb|500px|center|Layers breaking up into boulders in Galle Crater, as seen by HiRISE under HiWish program]]

[[File:45377 2170blocks2.jpg|500pxr|Fractures forming large blocks Box shows size of a football field]]

Fractures forming large blocks Box shows size of a football field

<gallery class="center" widths="380px" heights="360px">
File:Tilted blocks 82243 1765 01.jpg|Tilted blocks as seen by HiRISE under HiWish program These blockls were formed horizonality, but have been tilted. Perhaps ice left the ground on one side.
</gallery>

<gallery class="center" widths="190px" heights="180px">
File:Tilted blocks 82360 1925.jpg|Tilted blocks It is as if something pushed up from under the ground.
</gallery>

==Volcanoes under ice==

[[Image:25755concentriccracks.jpg|500pxr|Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.]]

Large group of concentric cracks Location is [[Ismenius Lacus quadrangle]]. Cracks were formed by a volcano under ice.

Researchers believe they have found evidence that volcanoes erupt under ice on Mars.<ref>https://www.uahirise.org/ESP_071541_2200</ref> <ref>Levy, J. et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus. Volume 285. Pages 185-194</ref> Candidate volcanic and impact-induced ice depressions on Mars Such eruptions have been observed on the Earth. What seems to happen is that ice melts, the water escapes, and then the surface cracks and collapses. The resulting formation shows concentric fractures and large pieces of ground that seemed to have been pulled apart.<ref>Smellie, J., B. Edwards. 2016. Glaciovolcanism on Earth and Mars. Cambridge University Press.</ref> Sites like this may have recently had held liquid water; therefore, they may be good places to search for evidence of life.<ref name="Levy, J. 2017">Levy, J., et al. 2017. Candidate volcanic and impact-induced ice depressions on Mars. Icarus: 285, 185-194.</ref><ref>University of Texas at Austin. "A funnel on Mars could be a place to look for life." ScienceDaily. ScienceDaily, 10 November 2016. <www.sciencedaily.com/releases/2016/11/161110125408.htm>.</ref>

[[File:25755 2200collapse.jpg|thumb|400px|left|Close view of fractures from volcano under ice.]]

[[File:25755 2200tiltedlayers.jpg|thumb|400px|center|Close view of fractures from volcano under ice.]]

==Recurrent slope lineae==

Recurrent slope lineae are small, narrow, dark streaks on slopes that get longer in warm seasons. They may be evidence of liquid water.<ref>McEwen, A., et al. 2014. Recurring slope lineae in equatorial regions of Mars. Nature Geoscience 7, 53-58. doi:10.1038/ngeo2014</ref> <ref>McEwen, A., et al. 2011. Seasonal Flows on Warm Martian Slopes. Science. 05 Aug 2011. 333, 6043,740-743. DOI: 10.1126/science.1204816</ref> <ref>http://redplanet.asu.edu/?tag=recurring-slope-lineae|title=recurring slope lineae - Red Planet Report|website=redplanet.asu.edu|</ref> Evidence is still being gathered on this feature.

[[File:49955 1665rslcolorarrows (1).jpg|500pxr|Recurrent slope lineae (RSL) They form in warm seasons.]]

Recurrent slope lineae (RSL) They form in warm seasons.

==Notes about pictures==

Most pictures from spacecraft are enhanced. The surface of Mars shows little contrast. Consequently, in order to see more detail, contrast is enhanced by a process known as stretching. In that process the darkest parts are set to black while the lightest parts are set to be white. This process makes a huge difference for some features like dark slope streaks. The colors for HiRISE images are different than the human eye would see. HiRISE only sees in only 3 colors and sometimes infrared is used rather than red. Displaying colors in this way allows us to better identify rocks and minerals. Usually, color images are constructed in one of two ways. An IRB image assigns the output from the infrared channel to the color red, the wide red channel to the color green, and the blue-green channel to the color blue. On the other hand, a RGB image has the output of the broad red channel displayed as red, the blue-green channel as green, and a synthetic blue channel (blue-green minus part of the red) as blue. The wavelengths of these channels are: RED: 570-830 nanometers BG: <580 nanometers IR: >790 nanometers. One nanometer is equal to one billionth of a meter (0.000 000 001 m). HiRISE images are about 5 km wide with a 1 km wide band in the center that is in color.[12]

HiRISE images are about 5 km wide, but only have a 1 km wide band in the center that is in color.<ref>McEwen, A., et al. 2017. Mars The Prestine Beauty of the Red Planet. University of Arizona Press. Tucson</ref>

==How to suggest image==

To suggest a location for HiRISE to image visit the site at http://www.uahirise.org/hiwish

In the sign up process you will need to come up with an ID and a password. When you choose a target to be imaged, you have to pick and exact location on a map and write about why the image should be taken. If your suggestion is accepted, it may take 3 months or more to see your image. You will be sent an email telling you about your images. The emails usually arrive on the first Wednesday of the month in the late afternoon.

==Notes to teachers==

This article goes along with the video Features of Mars with HiRISE under HiWish program at https://www.youtube.com/watch?v=b7q1Xyz_LBc

==References==
{{reflist|colwidth=30em}}

== External links ==

* [https://www.youtube.com/watch?v=uopweFSovUM&t=4s Seeing the wonders of Mars with HiRISE under the HiWish program]

* [https://www.youtube.com/watch?v=4dIktDIUTr4 The strange beauty of Mars with HiRISE and HiWish]

* [https://www.youtube.com/watch?v=PAwtP23EHGc 0:25 / 0:48 Zooming in on Mars with HiRISE images from HiWish program]

*[https://www.youtube.com/watch?v=b7q1Xyz_LBc Features of Mars with HiRISE under HiWish program] Shows nearly all major features discovered on Mars. This would be good for teachers covering Mars.

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]

*[https://www.youtube.com/watch?v=EtyLFJGV9nw Mars through HiRISE under the HiWish program]

*[https://www.youtube.com/watch?v=_g8QcVvaHrk Beautiful Mars as seen by HiRISE under HiWish program]

* [https://www.youtube.com/watch?v=nhYQEzK-MYE&t=17s HiRISE images from HiWish Program]

* [https://www.youtube.com/watch?v=_sUUKcZaTgA Martian Ice - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=RYG-HLr33CM Martian Geology - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.youtube.com/watch?v=ZNTNzQy1_UA Walks on Mars - Jim Secosky - 16th Annual International Mars Society Convention]
*[https://www.jpl.nasa.gov/missions/viking-1/ OP Lunch Talk #10: HiWish, public suggestion targeting web tool for Mars imaging with MRO/HIRISE]

*[https://www.youtube.com/watch?v=0fQHEay-Yas&list=PLn0lnGc1Saik-yyWpeec3AWz9NgdtxDAF&index=122 How to Explore Mars without Leaving Your Chair - Jim Secosky - 23rd Annual Mars Society Convention]

* McEwen, A., et al. 2024. The high-resolution imaging science experiment (HiRISE) in the MRO extended science phases (2009–2023). Icarus. Available online 16 September 2023, 115795. In Press.

==See Also==

*[[Geography of Mars]]
*[[Glaciers on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[Layers on Mars]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]
*[[Sublimation]]
*[[Sublimation landscapes on Mars]]
*[[Viking 2]]

==Recommended reading==

*Grotzinger, J., R. Milliken (eds.). 2012. Sedimentary Geology of Mars. Tulsa: Society for Sedimentary Geology.
*Kieffer, H., et al. (eds) 1992. Mars. The University of Arizona Press. Tucson
*[https://history.nasa.gov/SP-4212/ch11.html history.nasa.gov/SP-4212/ch11]
* Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14
* Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer Praxis Books / Geophysical Sciences.

Mare Acidalium quadrangle

2026-04-06T17:13:29Z

Suitupshowup: /* Mud volcanoes */ added section about crater lakes

{{Mars atlas}}

{| class="wikitable sortable"
|MC-04
|Mare Acidalium
|30–65° N
|0–60° W
|[[Mars Quadrangles|Quadrangles]]
|[[Mars Atlas|Atlas]]
|}

<gallery widths="400" heights="300">
File:USGS-Mars-MC-4-MareAcidaliumRegion-mola.png
File:PIA00164-MC-4-MareAcidaliumRegion-19980604.jpg
</gallery>

The [[The Face on Mars|face on Mars]] is found in the lower right corner or the Mare Acidalium quadrangle, between the craters Aranda and Bamberg in the [[Cydonia]] Labyrinthus region.

The Mare Acidalium quadrangle contains many interesting features, but is most famous for an eroded mesa that looked like a face when originally seen in Viking images in the 70’s. Outstanding views of polygonal ground, mud volcanoes, gullies, and channels are here. In this article, some of the best pictures from a number of spacecraft will show what the landscape looks like in this region. The origins and significance of all features will be explained as they are currently understood.

The Mare Acidalium quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS). The quadrangle is located in the northern hemisphere and covers 30° to 65° north latitude and 0° to 60° west longitude (300° to 360° east longitude). The Mare Acidalium quadrangle is also referred to as MC-4 (Mars Chart-4).<ref>Davies, M.E.; Batson, R.M.; Wu, S.S.C. "Geodesy and Cartography" in Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W.; Matthews, M.S., Eds. ''Mars.'' University of Arizona Press: Tucson, 1992.</ref>
The southern and northern borders of the quadrangle are approximately 3,065 km and 1,500 km wide, respectively. The north to south distance is about 2,050 km (slightly less than the length of Greenland).<ref>Distances calculated using NASA World Wind measuring tool. http://worldwind.arc.nasa.gov/.</ref> The quadrangle covers a little over 3% of Mars’ surface.

Many regions with classical names are located here. Most of the region called Acidalia Planitia is found in Acidalium quadrangle. Parts of Tempe Terra, Arabia Terra, and Chryse Planitia are also in this quadrangle. This area contains many bright spots on a dark background that may be mud volcanoes. Lomonosov Crater and Kunowsky Crater are easily seen. The famous "face" on Mars is located in the [[Cydonia]] Mensae area--the southeastern part of quadrangle.

In this article, some of the best pictures from a number of spacecraft will show what the landscape looks like in this region. The origins and significance of all features will be explained as they are currently understood.

The quadrangle contains many interesting features, including gullies and possible shorelines of an ancient northern ocean. Some areas are densely layered. The boundary between the southern highlands and the northern lowlands lies in Mare Acidalium.<ref>http://hirise.lpl.arizona.edu/PSP_010354_2165</ref> The Cydonia Region includes the Face on Mars (located near 40.8 degrees north and 9.6 degrees west). When Mars Global Surveyor examined it with high resolution, the face turned out to just be an eroded mesa.<ref>http://mars.jpl.nasa.gov/mgs/msss/camera/images/moc_5_24_01/face/index.html</ref> Mare Acidalium contains the Kasei Valles system of canyons. This huge system is 300 miles wide in some places—Earth's Grand Canyon is only 18 miles wide.<ref>http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_001640_2125</ref>

[[File:Collage mare acidalium02.jpg|Typical features of Mare Acidalium quadrangle, as seen by HiRISE under under HiWish program|600pxr| Typical features of Mare Acidalium quadrangle]]

Typical features of Mare Acidalium quadrangle

==Origin of name==

Mare Acidalium (Acidalian Sea) is the name of a classical albedo features on Mars located at 45° N and 330° E on Mars. The feature was named for a well or fountain in Boeotia, Greece. According to classical tradition, it is a location where Venus and the Graces bathed.<ref>Blunck, J. 1982. Mars and its Satellites. Exposition Press. Smithtown, N.Y.</ref> The name was approved by the International Astronomical Union (IAU) in 1958.<ref>USGS Gazetteer of Planetary Nomenclature. Mars. http://planetarynames.wr.usgs.gov/.</ref>

== Gullies ==

[[File:Acidalia Colles Gullies.JPG|600pxr|Acidalia Colles Gullies and other features, as seen by HiRISE The scale bar is 1,000 meters long.]]

Acidalia Colles Gullies and other features, as seen by HiRISE The scale bar is 1,000 meters long.

The HiRISE image above of Acidalia Colles shows gullies in the northern hemisphere. Gullies occur on steep slopes, especially craters. Gullies are believed to be relatively young because they have few, if any craters, and they lie on top of sand dunes which are themselves young. Usually, each gully has an alcove, channel, and apron. Many researchers believed that the processes carving the gullies involved liquid water. However, with more observations and research this idea was changed.
As soon as gullies were discovered, researchers began to image many gullies over and over, looking for possible changes. By 2006, some changes were found.<ref>Malin, M., K. Edgett, L. Posiolova, S. McColley, E. Dobrea. 2006. Present-day impact cratering rate and contemporary gully activity on Mars. Science 314, 1573_1577.</ref> Later, with further analysis it was determined that the changes could have occurred with dry granular flows rather than being driven by flowing water.<ref>Kolb, et al. 2010. Investigating gully flow emplacement mechanisms using apex slopes. Icarus 2008, 132-142.</ref> <ref>McEwen, A. et al. 2007. A closer look at water-related geological activity on Mars. Science 317, 1706-1708.</ref> <ref>Pelletier, J., et al. 2008. Recent bright gully deposits on Mars wet or dry flow? Geology 36, 211-214.</ref> With continued observations many more changes were found in Gasa Crater and other craters.<ref>NASA/Jet Propulsion Laboratory. "NASA orbiter finds new gully channel on Mars." ScienceDaily. ScienceDaily, 22 March 2014. www.sciencedaily.com/releases/2014/03/140322094409.htm</ref>
With more repeated observations, more and more changes were found; since the changes occur in the winter and spring, experts are tending to believe that gullies were formed from dry ice. Before-and-after images demonstrated the timing of this activity coincided with seasonal carbon-dioxide frost changes, and at temperatures that would not have allowed for liquid water. The conditions during gully formation are just about right to allow chunks of dry ice to slide down slopes. In addition, when dry ice frost changes to a gas, it may lubricate dry material to flow especially on steep slopes.<ref>http://www.jpl.nasa.gov/news/news.php?release=2014-226</ref> <ref>http://hirise.lpl.arizona.edu/ESP_032078_1420</ref><ref>http://www.space.com/26534-mars-gullies-dry-ice.html</ref> In some years frost build up may be-as thick as 1 meter.

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Image:24951bambergwidectx.jpg|Context for next image of Bamberg crater. Box shows where the next image came from. This is a CTX image from [[Mars Reconnaissance Orbiter]].

Image:ESP 024951gulliesandflow.jpg|Gullies and massive flow of material, as seen by HiRISE under [[HiWish program]]. Gullies are enlarged in next two images.

Image:24951gulliesclose.jpg|Close up view of some gullies

Image:24951gullyclose.jpg|Close up view of another gully in same HiRISE picture. Picture taken under HiWish program.

Image:27707gulliesclose.jpg|Close-up of gullies in a crater Image taken by HiRISE under HiWish program.

ESP 037506 2285gullychannels.jpg|Gullies on wall of crater

ESP 037506 2285gullychannelsclose.jpg|Close-up of gully channels This image shows many streamlined forms and some benches along a channel. These features suggest formation by running water. Benches are usually formed when the water level goes down a bit and stays at that level for a time.

File:ESP 053751 2150gullies.jpg|Gullies

File:55122 2225gulliesclosecolor.jpg|Gullies, as seen by HiRISE under [[HiWish program]]

File:Close view of gullies ESP 080430 2310 01.jpg|Gullies on crater wall The bright apron is a bit unusual.
File:Close view of gullies ESP 080430 2310 02.jpg|Gully on crater wall The bright apron is a bit unusual.

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==Polygonal patterned ground==

[[File:27707 2195gullygonsclose2.jpg|600pxr|Close-up of gully alcove showing "gullygons" (polygonal patterned ground near gullies), as seen by HiRISE under HiWish program]]
Close-up of gully alcove showing "gullygons" (polygonal patterned ground near gullies), as seen by HiRISE

Polygonal, patterned ground is quite common in some regions of Mars.<ref>http://www.diss.fu-berlin.de/diss/servlets/MCRFileNodeServlet/FUDISS_derivate_000000003198/16_ColdClimateLandforms-13-utopia.pdf?hosts=</ref> <ref>Kostama, V.-P., M. Kreslavsky, Head, J. 2006. Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement. Geophys. Res. Lett. 33 (L11201). doi:10.1029/2006GL025946.</ref> <ref>Malin, M., Edgett, K. 2001. Mars Global Surveyor Mars Orbiter Camera: Interplanetary cruise through primary mission. J. Geophys. Res. 106 (E10), 23429–23540.</ref> <ref>Milliken, R., et al. 2003. Viscous flow features on the surface of Mars: Observations from high-resolution Mars Orbiter Camera (MOC) images. J. Geophys. Res. 108 (E6). doi:10.1029/2002JE002005.</ref> <ref>Mangold | first1 = N | year = 2005 | title = High latitude patterned grounds on Mars: Classification, distribution and climatic control | url = | journal = Icarus | volume = 174 | issue = | pages = 336–359 | doi = 10.1016/j.icarus.2004.07.030 | </ref> <ref>Kreslavsky, M., Head, J. 2000. Kilometer-scale roughness on Mars: Results from MOLA data analysis. J. Geophys. Res. 105 (E11), 26695–26712.</ref> <ref>Seibert | first1 = N. | last2 = Kargel | first2 = J. | year = 2001 | title = Small-scale martian polygonal terrain: Implications for liquid surface water | url = | journal = Geophys. Res. Lett. | volume = 28 | issue = 5| pages = 899–902 | doi = 10.1029/2000gl012093 | </ref> It is commonly believed that the shapes we see here are related to ground frozen with water ice.

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27707 2195gullygonsclose.jpg|Close-up of gully alcove showing "gullygons" (polygonal patterned ground near gullies)

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==Craters==

Impact craters generally have a rim with ejecta around them, in contrast volcanic craters usually do not have a rim or ejecta deposits.<ref>Hugh H. Kieffer|title=Mars|url=https://books.google.com/books?id=NoDvAAAAMAAJ|accessdate=7 March 2011|year=1992|publisher=University of Arizona Press|isbn=978-0-8165-1257-7 </ref> Sometimes craters display layers. Since the collision that produces a crater is like a powerful explosion, rocks from deep underground are tossed unto the surface. Hence, craters can show us what lies deep under the surface.

Craters usually get a bowl shape when first formed, but with age, debris and ice fall in it and make it more flat. If one measures the diameter of a crater, the original depth can be estimated with various ratios. Because of this relationship, researchers have found that many Martian craters contain a great deal of material; much of it is believed to be ice deposited when the climate was different.<ref>Garvin, J., et al. 2002. Global geometric properities of martian impact craters. Lunar Planet Sci. 33. Abstract @1255.</ref> Some of these flat floored craters display numberous concentric lines--they are called concentric crater fill craters. Craters like these may be used by future colonists for water. Before we land, we will have a map of where these water sources are. Eventually, we will probably develop robotic machines to extract the water.

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Image:Arandas Crater.JPG|Arandas Crater, as seen by HiRISE. Scale bar is 1000 meters long.

Image:Exhumedburied Craterin Coprates.jpg|Exhumed Crater in Mare Acidalium, as seen by [[Mars Global Surveyor]] This crater was buried and now it is being uncovered.
Image:ESP 026594 1470closecraters.jpg|Craters that formed at the same time. If the craters were formed at different times, they would have wiped away parts of the others. These craters may been made when an asteroid broke up in the atmosphere. Picture was taken by HiRISE, under HiWish program. Image located in Terra Cimmeria.

Image:ESP 027538 2265.jpg|Crater wall covered with a smooth mantle

ESP 052749 2285pits.jpg|Concentric crater fill crater with pits on floor, as seen by HiRISE under [[HiWish program]]

</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.

</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Mud volcanoes==

[[File:ESP 047053 2165cones.jpg|600pxr|Line of possible mud volcanoes]]
Line of possible mud volcanoes

Large areas of Mare Acidalium display bright spots on a dark background. It has been suggested that these spots are mud volcanoes.<ref>Farrand | first1 = W. | display-authors = etal | year = 2005 | title = Pitted cones and domes on Mars: observations in Acidalia Planitia and Cydonia Mensae using MOC, THEMIS, and TES data | url = | journal = J. Geophys. Res. | volume = 110 | issue = | page = 14 | doi = 10.1029/2004JE002297 </ref> <ref>Tanaka, K. et al. 2003 Resurfacing history of the northern plains of Mars based on geologic mapping of Mars Global Surveyor data. J. Geophys. Res. 108 (E4), doi:10.1029/2002JE001908.</ref><ref>Grotzinger, J. and R. Milliken (eds.) 2012. Sedimentary Geology of Mars. SEPM</ref> More than 18,000 of these features, which have an average diameter of about 800 meters, have been mapped.<ref>Oehler, D. and C. Allen. 2010. Evidence for pervasive mud volcanism in Acidalia Planitia, Mars. Icarus: 208. 636-657.</ref> As more observations poured in over the years, more evidence supported the notion that these abundant bright marks are mud volcanoes. Mare Acidalium would have received large quantities of mud and fluids form outflow channels, so much mud may have accumulated there. The bright mounds have been found to contain crystalline ferric oxides. Mud volcanism may be highly significant because long lived conduits for upwelling groundwater could have been produced. These could have been habitats for micro organisms.<ref>Komatsu, G., et al. 2014. ASTROBIOLOGICAL POTENTIAL OF MUD VOLCANISM ON MARS. 45th Lunar and Planetary Science Conference (2014). 1085.pdf</ref> Mud volcanoes could have brought up samples from deep zones that could be gathered by robots.<ref>Oehler | first1 = D | last2 = Allen | first2 = C. | year = 2011 | title = Evidence for pervasive mud volcanism in Acidalia Planitia, Mars | url = | journal = Icarus | volume = 208 | issue = | pages = 636–657 | doi = 10.1016/j.icarus.2010.03.031 }}</ref> The authors of an article in Icarus compare these Martian features to mud volcanoes found on the Earth. Their study using HiRISE images and CRISM data support the idea that these features are indeed mud volcanoes. Nanophase ferric minerals and hydrated minerals found with Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show that water was involved with the formation of these possible Martian mud volcanoes.<ref>Komatsu, G., et al. 2016. Small edifice features in Chryse Planitia, Mars: Assessment of a mud volcano hypothesis. Icarus: 268, 56-75.</ref> Scientists are excited that Mars may have mud volcanoes because these small volcanoes may have brought up samples of dirt that were not affected by the high radiation on the Martian surface. We may find evidence of past life in these volcanoes.

<gallery class="center" widths="380px" heights="360px">

Image:White craters in Mare Acidalium.JPG|Craters with white centers in Mare Acidalium. Sand dunes are visible in low areas in image. Some of the features may be mud volcanoes. Picture taken by [[Mars Global Surveyor]] under the MOC Public Targeting Program.

ESP 040775 2235cones.jpg|Large field of cones that may be mud volcanoes
040775 2235conesclose.jpg|Close-up of possible mud volcanoes Note: this is an enlargement of the previous image.

ESP 044665 2240cone.jpg|Possible mud volcano, as seen by HiRISE under [[HiWish program]]

ESP 046617 2210mudvolcanoes.jpg|Mud volcanoes

File:Mud volcanoes In Mare Acidalium, Mars 01.jpg|Wide view of mud volcanoes, as seen by HiRISE under HiWish program
File:Mud volcanoes In Mare Acidalium, Mars 02.jpg|Close view of mud volcanoes, as seen by HiRISE
File:Mud volcanoes In Mare Acidalium, Mars 03.jpg|Close view of mud volcanoes Low area around the volcanoes contains transverse aeolian ridges (TAR's). Only part of picture is in color because HiRISE only takes a color strip in middle of image.
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<gallery class="center" widths="190px" heights="180px" >
ESP 052050 2200mudvolcanoes.jpg|Wide view of field of mud volcanoes

File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

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Gobustan State Reserve 04.png|Close view of mud volcanoes on Earth Location is Gobustan Azerbaijan.
</gallery>

==Channels in Idaeus Fossae region==

There is a 300 km long ancient river system in Idaeus Fossae. It is carved into the highlands of Idaeus Fossae, and it originated from the melting of ice in the ground after asteroid impacts. There is evidence that it was formed relatively recently. Dating has determined that the water activity came after most of the water activity ended at the boundary between the Noachian and Hesperian periods. Lakes and fan-shaped deposits were formed by running water in this system as it drained eastward into Liberta Crater and formed a delta deposit. Part of the drainage path is the Moa Valley.<ref>Salese, F., G. Di Achille, F., et al. 2016. Hydrological and sedimentary analyses of well-preserved paleo fluvial-paleolacustrine systems at Moa Valles, Mars. J. Geophys. Res. Planets. 121, 194–232, doi:10.1002/2015JE004891.</ref> <ref>Salese, F., G. Di Achille, G. Ori. 2015. SEDIMENTOLOGY OF A RIVER SYSTEM WITH A SERIES OF DAM-BREACH PALEOLAKES AT IDAEUS FOSSAE, MARS. 46th Lunar and Planetary Science Conference 2296.pdf</ref>

<gallery class="center" widths="380px" heights="360px">

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
ESP 045590 2170hanging.jpg|Hanging valley, as seen by HiRISE under HiWish program This may have been a waterfall at one time.
ESP 045946 2170channel.jpg|Hanging valley that once may have been a waterfall, as seen by HiRISE under HiWish program
</gallery>

==Channels==

[[File:ESP 045867 2150channels.jpg|600pxr|Channels]]
Channels

There is much evidence that water once flowed in river valleys on Mars.<ref>Baker | first1 = V. | display-authors = etal | year = 2015 | title = Fluvial geomorphology on Earth-like planetary surfaces: a review | journal = Geomorphology | volume = 245 | issue = | pages = 149–182 |</ref> <ref>Carr, M. 1996. in Water on Mars. Oxford Univ. Press.</ref> Images of curved channels have been seen in images from Mars spacecraft dating back to the early seventies with the [[Mariner 9]] orbiter.<ref>Baker, V. 1982. The Channels of Mars. Univ. of Tex. Press, Austin, TX</ref> <ref>Baker | first1 = V. | last2 = Strom | first2 = R. | last3 = Gulick | first3 = V. | last4 = Kargel | first4 = J. | last5 = Komatsu | first5 = G. | last6 = Kale | first6 = V. | year = 1991 | title = Ancient oceans, ice sheets and the hydrological cycle on Mars | url = | journal = Nature | volume = 352 | issue = | pages = 589–594 | doi = 10.1038/352589a0 | </ref> <ref> Carr | first1 = M | year = 1979 | title = Formation of Martian flood features by release of water from confined aquifers | url = | journal = J. Geophys. Res. | volume = 84 | issue = | pages = 2995–300 | doi = 10.1029/jb084ib06p02995 | </ref> <ref>Komar | first1 = P | year = 1979 | title = Comparisons of the hydraulics of water flows in Martian outflow channels with flows of similar scale on Earth | url = | journal = Icarus | volume = 37 | issue = | pages = 156–181 | doi = 10.1016/0019-1035(79)90123-4 | </ref> We have seen more and more channels with each orbiter mission to the Red Planet. Indeed, a study published in June 2017, calculated that the volume of water needed to carve all the channels on Mars was even larger than the proposed ocean that the planet may have had.<ref>http://spaceref.com/mars/how-much-water-was-needed-to-carve-valleys-on-mars.html</ref><ref>Luo, W., et al. 2017. New Martian valley network volume estimate consistent with ancient ocean and warm and wet climate. Nature Communications 8. Article number: 15766 (2017). doi:10.1038/ncomms15766</ref>

<gallery class="center" widths="380px" heights="360px">

Wikisklodowskachannels.jpg|Channels in Sklodowska Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter)
WikisklodowskaESP 035500 2130.jpg|Channels in Sklodowska Crater

ESP 048003 2165channels.jpg|Channels, as seen by HiRISE under HiWish program

File:Labeled meander showing early and later channels ESP 59515 2160.jpg|Meander with parts labeled Features like this show that water stayed around for a while. Meanmders start with small loops that get progressively larger.

File:6438 2155meander.jpg

</gallery>

[[File:ESP 055374 2175channelnetwork.jpg|600pxr|Channel network]]
Channel network

[[File:ESP 077583 2255inverted.jpg|thumb|500px|center|Inverted stream, a stream bed has been filled with hard materials that did not erode away like the surroundings]]

==Ocean==

Many researchers have suggested that Mars once had a great ocean in the north.<ref>Parker | first1 = T. J. | last2 = Gorsline | first2 = D. S. | last3 = Saunders | first3 = R. S. | last4 = Pieri | first4 = D. C. | last5 = Schneeberger | first5 = D. M. | year = 1993 | title = Coastal geomorphology of the Martian northern plains | url = | journal = J. Geophys. Res. | volume = 98 | issue = E6| pages = 11061–11078 | doi=10.1029/93je00618 |</ref> <ref>Fairén | first1 = A. G. |display-authors=etal | year = 2003 | title = Episodic flood inundations of the northern plains of Mars | url = http://eprints.ucm.es/10431/1/9-Marte_3.pdf| journal = Icarus | volume = 165 | issue = 1| pages = 53–67 | </ref> <ref> Head | first1 = J. W. |display-authors=etal | year = 1999 | title = Possible ancient oceans on Mars: Evidence from Mars Orbiter Laser Altimeter data | url = | journal = Science | volume = 286 | issue = 5447| pages = 2134–2137 | doi=10.1126/science.286.5447.2134| pmid = 10591640 |</ref> <ref>Parker, T. J., Saunders, R. S. & Schneeberger, D. M. Transitional morphology in west Deuteronilus Mensae, Mars: Implications for modification of the lowland/upland boundary" ''Icarus'' 1989; 82, 111–145</ref> <ref>Carr | first1 = M. H. | last2 = Head | first2 = J. W. | year = 2003 | title = Oceans on Mars: An assessment of the observational evidence and possible fate | url = | journal = J. Geophys. Res. | volume = 108 | issue = E5| page = 5042 |</ref> <ref>Kreslavsky | first1 = M. A. | last2 = Head | first2 = J. W. | year = 2002| title = Fate of outflow channel effluent in the northern lowlands of Mars: The Vastitas Borealis Formation as a sublimation residue from frozen ponded bodies of water | url = | journal = J. Geophys. Res. | volume = 107 | issue = E12| page = 5121 |</ref> <ref>Clifford, S. M. & Parker, T. J. The evolution of the martian hydrosphere: Implications for the fate of a primordial ocean and the current state of the northern plains" ''Icarus'' 2001; 154, 40–79</ref> Much evidence for this ocean has been gathered over several decades. New evidence was published in May 2016. A large team of scientists described how some of the surface in Ismenius Lacus quadrangle was altered by two tsunamis. The tsunamis were caused by asteroids striking into an ocean. Both were thought to have been strong enough to create 30 km diameter craters. The first tsunami picked up and carried boulders the size of cars or small houses. The backwash from the wave formed channels by rearranging the boulders. The second came in when the ocean was 300 m lower. The second carried a great deal of ice which was dropped in valleys. Calculations show that the average height of the waves would have been 50 m, but the heights would vary from 10 m to 120 m. So, some large waves would have gone over a 36 story building.<ref>https://www.convertunits.com/from/metre/to/story</ref> Asteroids hitting an ocean on Mars are quite possible. Numerical simulations show that in this particular part of the ocean two 30 km in diameter would form every 30 million years. The implication here is that a great northern ocean may have existed for millions of years. One argument against an ocean has been the lack of shoreline features. But shoreline features may have been washed away by these tsunami events. The parts of Mars studied in this research are Chryse Planitia and northwestern Arabia Terra. These tsunamis affected some surfaces in the [[Ismenius Lacus quadrangle]] and in the Mare Acidalium quadrangle.<ref>Ancient Tsunami Evidence on Mars Reveals Life Potential |date=May 20, 2016 |url=http://astrobiology.com/2016/05/ancient-tsunami-evidence-on-mars-reveals-life-potential.html</ref> <ref>Rodriguez | first1 = J. |display-authors=etal | year = 2016 | title = Tsunami waves extensively resurfaced the shorelines of an early Martian ocean | url = | journal = Scientific Reports | volume = 6 | issue = | page = 25106 | doi=10.1038/srep25106| pmid = 27196957 | pmc = 4872529 |</ref> <ref>| doi=10.1038/srep25106| pmid=27196957| pmc=4872529| title=Tsunami waves extensively resurfaced the shorelines of an early Martian ocean| journal=Scientific Reports| volume=6| pages=25106| year=2016| last1=Rodriguez| first1=J. Alexis P.| last2=Fairén| first2=Alberto G.| last3=Tanaka| first3=Kenneth L.| last4=Zarroca| first4=Mario| last5=Linares| first5=Rogelio| last6=Platz| first6=Thomas| last7=Komatsu| first7=Goro| last8=Miyamoto| first8=Hideaki| last9=Kargel| first9=Jeffrey S.| last10=Yan| first10=Jianguo| last11=Gulick| first11=Virginia| last12=Higuchi| first12=Kana| last13=Baker| first13=Victor R.| last14=Glines| first14=Natalie</ref> <ref>Cornell University. "Ancient tsunami evidence on Mars reveals life potential." ScienceDaily. ScienceDaily, 19 May 2016. https://www.sciencedaily.com/releases/2016/05/160519101756.htm.</ref>

==Pingos==

Pingos are believed to be present on Mars. They are mounds that contain cracks. These particular fractures were evidently produced by something emerging from below the brittle surface of Mars. Ice lenses, resulting from the accumulation of ice beneath the surface, possibly created these mounds with fractures. Ice is less dense than rock, so the buried ice rose and pushed upwards on the surface and generated these cracks. An analogous process creates similar sized mounds in arctic tundra on Earth. The name ''pingos'' is an Inuit word.<ref>http://www.uahirise.org/ESP_046359_1250</ref> They contain pure water ice, so they would be a great source of water for future colonists on Mars.

[[File:44322 2215pingos.jpg|600pxr|Arrows point to possible pingos, as seen by HiRISE under HiWish program Pingos contain a core of pure ice.]]
Arrows point to possible pingos, as seen by HiRISE under HiWish program Pingos contain a core of pure ice.

==Fractured ground==

<gallery class="center" widths="380px" heights="360px">

44322 2215fractures.jpg|Fractures These fractures are believed to eventually turn into canyons because the cracks will get much larger when ice in the ground disappears into the thin Martian atmosphere and the remaining dust blows away.

ESP 046366 2215fractures.jpg|Wide view of fractured ground, as seen by HiRISE under HiWish program Cracks form on the Martian surface, and then they turn into large fractures.

46366 2215fractures.jpg|Close view of fractures from the previous image

File:ESP 056968 2140cracks.jpg|Cracks on crater floor

File:56968 2140cracks.jpg|Close view of cracks on crater floor, as seen by HiRISE under [[HiWish program]]

File:ESP 057311 2125cracks.jpg|Group of cracks

File:ESP 057311 2125crackscraters.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger. Note that small craters do not have very big rims; they may be just pits.

File:57311 2155crackssmallarge.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger.

File:57311 2155crackscrater.jpg|Cracks around crater, as seen by HiRISE under [[HiWish program]]

</gallery>

==Layers==

Layered terrain is common on the Earth and on Mars. Water is usually involved with the formation of layers. Hence, when we see layers, there is the possibility of a lake or sea in the past.

[[File:ESP 047080 2120layered mesa.jpg|600pxr|Layers in mesa, as seen by HiRISE under [[HiWish program]]]]
Layers in mesa, as seen by HiRISE under [[HiWish program]]

Rock can be formed into layers in a variety of ways. Volcanoes, wind, or water can produce layers<ref>http://hirise.lpl.arizona.edu?PSP_008437_1750</ref> Layers can be hardened by the action of groundwater. Martian ground water probably moved hundreds of kilometers, and in the process it dissolved many minerals from the rock it passed through. When ground water surfaces in low areas containing sediments, water evaporates in the thin atmosphere and leaves behind minerals as deposits and/or cementing agents.

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File:53490 2230layers.jpg|Close view of layers in a trough

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==Features close to Face on Mars==

Here are some CTX images of area near the Face. These pictures show natural formations on Mars. In the area around the face are mesas, mud volcanoes, pedestal craters, and brain terrain. Many of the mesas are sitting on what looks like platforms. They may be from a change in sea level. There is strong evidence building that an ocean was once all through the northern lowlands. All of the features seen here are common on Mars, especially in this latitude. For more pictures and information about the face go to The [[The Face on Mars]].

<gallery class="center" widths="380px" heights="360px">

File:FaceG22 026771 2213 XI 41N009W.jpg|Terrain to the west of Face Face is visible in upper right.

File:FacectxT01 00807 2205glaciers.jpg|Terrain near Face showing possible glacier erosion Curved portions of the mounds look like the start of what are called cirques that form as snow accumulates on mountains.<ref>http://www.landforms.eu/cairngorms/corrie%20formation.htm</ref>

File:FacectxD02 027892 2219pyramid.jpg|Mud volcanoes in terrain near Face

File:Faceg22 026771 2213pedestal.jpg|Mesa, mud volcano, and pedestal crater in area near Face.

</gallery>
[[File:FacectxF23 044929 2199 XI 39N010Wlabeled.jpg|600pxr|Mesa, ridges, possible cirques near Face]]
Mesa, ridges, possible cirques near Face.

== Other landscape features in Mare Acidalium quadrangle ==

<gallery class="center" widths="380px" heights="360px">

Image:Cliff in Mare Acidalium.JPG|Cliff in Kasei Valles system, as seen by HiRISE

</gallery>

[[File:Rolling boulders in kasei.JPG|600pxr|Boulders that are about 2.2 yards acoss (smaller than a bedroom) and their tracks after rolling down a cliff in Kasei Valles system, as seen by HiRISE]]

Boulders that are about 2.2 yards across (smaller than a bedroom) and their tracks after rolling down a cliff in Kasei Valles system, as seen by HiRISE

<gallery class="center" widths="380px" heights="360px">

Image:Context for fault.JPG|CTX image showing the context for the next image of a fault The area in the black rectangle is enlarged in next photo.

Image:Fault in Mare Acidalium.JPG|Close-up of a possible fault in Mare Acidalium, as seen by HiRISE under the [[HiWish program]]. A circle is drawn around crater to show that it may be off round because of movement of the fault. Many other faults are in the region.

ESP 045524 2120fan.jpg|Fan with channels on its surface

48924 2150ovalpits.jpg|Sample of oval pits in this location of unknown origin, as seen by HiRISE under HiWish program
File:Fan along crater wall. ESP 055110 2265.jpg|Fan This fan is formed on the edge of a crater. Dirt and rocks mixed with water, flowed down a slope and were deposited in crater. The fan has layers which means that this was done at different intervals, not all at once. This image was named picture of the day for January 14, 2024. Image credit is NASA/JPL/University of Arizona/Secosky.

</gallery>

== See also ==

*[[The Face on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[HiWish program]]
*[[How are features on Mars Named?]]

*[[Layers on Mars]]
*[[Mars Global Surveyor]]

*[[Martian gullies]]
*[[Oceans on Mars]]

*[[Rivers on Mars]]

== References ==

[[Category:Mars Atlas]]

Mare Acidalium quadrangle

2026-04-06T17:09:02Z

Suitupshowup: /* Craters */

{{Mars atlas}}

{| class="wikitable sortable"
|MC-04
|Mare Acidalium
|30–65° N
|0–60° W
|[[Mars Quadrangles|Quadrangles]]
|[[Mars Atlas|Atlas]]
|}

<gallery widths="400" heights="300">
File:USGS-Mars-MC-4-MareAcidaliumRegion-mola.png
File:PIA00164-MC-4-MareAcidaliumRegion-19980604.jpg
</gallery>

The [[The Face on Mars|face on Mars]] is found in the lower right corner or the Mare Acidalium quadrangle, between the craters Aranda and Bamberg in the [[Cydonia]] Labyrinthus region.

The Mare Acidalium quadrangle contains many interesting features, but is most famous for an eroded mesa that looked like a face when originally seen in Viking images in the 70’s. Outstanding views of polygonal ground, mud volcanoes, gullies, and channels are here. In this article, some of the best pictures from a number of spacecraft will show what the landscape looks like in this region. The origins and significance of all features will be explained as they are currently understood.

The Mare Acidalium quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS). The quadrangle is located in the northern hemisphere and covers 30° to 65° north latitude and 0° to 60° west longitude (300° to 360° east longitude). The Mare Acidalium quadrangle is also referred to as MC-4 (Mars Chart-4).<ref>Davies, M.E.; Batson, R.M.; Wu, S.S.C. "Geodesy and Cartography" in Kieffer, H.H.; Jakosky, B.M.; Snyder, C.W.; Matthews, M.S., Eds. ''Mars.'' University of Arizona Press: Tucson, 1992.</ref>
The southern and northern borders of the quadrangle are approximately 3,065 km and 1,500 km wide, respectively. The north to south distance is about 2,050 km (slightly less than the length of Greenland).<ref>Distances calculated using NASA World Wind measuring tool. http://worldwind.arc.nasa.gov/.</ref> The quadrangle covers a little over 3% of Mars’ surface.

Many regions with classical names are located here. Most of the region called Acidalia Planitia is found in Acidalium quadrangle. Parts of Tempe Terra, Arabia Terra, and Chryse Planitia are also in this quadrangle. This area contains many bright spots on a dark background that may be mud volcanoes. Lomonosov Crater and Kunowsky Crater are easily seen. The famous "face" on Mars is located in the [[Cydonia]] Mensae area--the southeastern part of quadrangle.

In this article, some of the best pictures from a number of spacecraft will show what the landscape looks like in this region. The origins and significance of all features will be explained as they are currently understood.

The quadrangle contains many interesting features, including gullies and possible shorelines of an ancient northern ocean. Some areas are densely layered. The boundary between the southern highlands and the northern lowlands lies in Mare Acidalium.<ref>http://hirise.lpl.arizona.edu/PSP_010354_2165</ref> The Cydonia Region includes the Face on Mars (located near 40.8 degrees north and 9.6 degrees west). When Mars Global Surveyor examined it with high resolution, the face turned out to just be an eroded mesa.<ref>http://mars.jpl.nasa.gov/mgs/msss/camera/images/moc_5_24_01/face/index.html</ref> Mare Acidalium contains the Kasei Valles system of canyons. This huge system is 300 miles wide in some places—Earth's Grand Canyon is only 18 miles wide.<ref>http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_001640_2125</ref>

[[File:Collage mare acidalium02.jpg|Typical features of Mare Acidalium quadrangle, as seen by HiRISE under under HiWish program|600pxr| Typical features of Mare Acidalium quadrangle]]

Typical features of Mare Acidalium quadrangle

==Origin of name==

Mare Acidalium (Acidalian Sea) is the name of a classical albedo features on Mars located at 45° N and 330° E on Mars. The feature was named for a well or fountain in Boeotia, Greece. According to classical tradition, it is a location where Venus and the Graces bathed.<ref>Blunck, J. 1982. Mars and its Satellites. Exposition Press. Smithtown, N.Y.</ref> The name was approved by the International Astronomical Union (IAU) in 1958.<ref>USGS Gazetteer of Planetary Nomenclature. Mars. http://planetarynames.wr.usgs.gov/.</ref>

== Gullies ==

[[File:Acidalia Colles Gullies.JPG|600pxr|Acidalia Colles Gullies and other features, as seen by HiRISE The scale bar is 1,000 meters long.]]

Acidalia Colles Gullies and other features, as seen by HiRISE The scale bar is 1,000 meters long.

The HiRISE image above of Acidalia Colles shows gullies in the northern hemisphere. Gullies occur on steep slopes, especially craters. Gullies are believed to be relatively young because they have few, if any craters, and they lie on top of sand dunes which are themselves young. Usually, each gully has an alcove, channel, and apron. Many researchers believed that the processes carving the gullies involved liquid water. However, with more observations and research this idea was changed.
As soon as gullies were discovered, researchers began to image many gullies over and over, looking for possible changes. By 2006, some changes were found.<ref>Malin, M., K. Edgett, L. Posiolova, S. McColley, E. Dobrea. 2006. Present-day impact cratering rate and contemporary gully activity on Mars. Science 314, 1573_1577.</ref> Later, with further analysis it was determined that the changes could have occurred with dry granular flows rather than being driven by flowing water.<ref>Kolb, et al. 2010. Investigating gully flow emplacement mechanisms using apex slopes. Icarus 2008, 132-142.</ref> <ref>McEwen, A. et al. 2007. A closer look at water-related geological activity on Mars. Science 317, 1706-1708.</ref> <ref>Pelletier, J., et al. 2008. Recent bright gully deposits on Mars wet or dry flow? Geology 36, 211-214.</ref> With continued observations many more changes were found in Gasa Crater and other craters.<ref>NASA/Jet Propulsion Laboratory. "NASA orbiter finds new gully channel on Mars." ScienceDaily. ScienceDaily, 22 March 2014. www.sciencedaily.com/releases/2014/03/140322094409.htm</ref>
With more repeated observations, more and more changes were found; since the changes occur in the winter and spring, experts are tending to believe that gullies were formed from dry ice. Before-and-after images demonstrated the timing of this activity coincided with seasonal carbon-dioxide frost changes, and at temperatures that would not have allowed for liquid water. The conditions during gully formation are just about right to allow chunks of dry ice to slide down slopes. In addition, when dry ice frost changes to a gas, it may lubricate dry material to flow especially on steep slopes.<ref>http://www.jpl.nasa.gov/news/news.php?release=2014-226</ref> <ref>http://hirise.lpl.arizona.edu/ESP_032078_1420</ref><ref>http://www.space.com/26534-mars-gullies-dry-ice.html</ref> In some years frost build up may be-as thick as 1 meter.

<gallery class="center" widths="380px" heights="360px">

Image:24951bambergwidectx.jpg|Context for next image of Bamberg crater. Box shows where the next image came from. This is a CTX image from [[Mars Reconnaissance Orbiter]].

Image:ESP 024951gulliesandflow.jpg|Gullies and massive flow of material, as seen by HiRISE under [[HiWish program]]. Gullies are enlarged in next two images.

Image:24951gulliesclose.jpg|Close up view of some gullies

Image:24951gullyclose.jpg|Close up view of another gully in same HiRISE picture. Picture taken under HiWish program.

Image:27707gulliesclose.jpg|Close-up of gullies in a crater Image taken by HiRISE under HiWish program.

ESP 037506 2285gullychannels.jpg|Gullies on wall of crater

ESP 037506 2285gullychannelsclose.jpg|Close-up of gully channels This image shows many streamlined forms and some benches along a channel. These features suggest formation by running water. Benches are usually formed when the water level goes down a bit and stays at that level for a time.

File:ESP 053751 2150gullies.jpg|Gullies

File:55122 2225gulliesclosecolor.jpg|Gullies, as seen by HiRISE under [[HiWish program]]

File:Close view of gullies ESP 080430 2310 01.jpg|Gullies on crater wall The bright apron is a bit unusual.
File:Close view of gullies ESP 080430 2310 02.jpg|Gully on crater wall The bright apron is a bit unusual.

</gallery>

==Polygonal patterned ground==

[[File:27707 2195gullygonsclose2.jpg|600pxr|Close-up of gully alcove showing "gullygons" (polygonal patterned ground near gullies), as seen by HiRISE under HiWish program]]
Close-up of gully alcove showing "gullygons" (polygonal patterned ground near gullies), as seen by HiRISE

Polygonal, patterned ground is quite common in some regions of Mars.<ref>http://www.diss.fu-berlin.de/diss/servlets/MCRFileNodeServlet/FUDISS_derivate_000000003198/16_ColdClimateLandforms-13-utopia.pdf?hosts=</ref> <ref>Kostama, V.-P., M. Kreslavsky, Head, J. 2006. Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement. Geophys. Res. Lett. 33 (L11201). doi:10.1029/2006GL025946.</ref> <ref>Malin, M., Edgett, K. 2001. Mars Global Surveyor Mars Orbiter Camera: Interplanetary cruise through primary mission. J. Geophys. Res. 106 (E10), 23429–23540.</ref> <ref>Milliken, R., et al. 2003. Viscous flow features on the surface of Mars: Observations from high-resolution Mars Orbiter Camera (MOC) images. J. Geophys. Res. 108 (E6). doi:10.1029/2002JE002005.</ref> <ref>Mangold | first1 = N | year = 2005 | title = High latitude patterned grounds on Mars: Classification, distribution and climatic control | url = | journal = Icarus | volume = 174 | issue = | pages = 336–359 | doi = 10.1016/j.icarus.2004.07.030 | </ref> <ref>Kreslavsky, M., Head, J. 2000. Kilometer-scale roughness on Mars: Results from MOLA data analysis. J. Geophys. Res. 105 (E11), 26695–26712.</ref> <ref>Seibert | first1 = N. | last2 = Kargel | first2 = J. | year = 2001 | title = Small-scale martian polygonal terrain: Implications for liquid surface water | url = | journal = Geophys. Res. Lett. | volume = 28 | issue = 5| pages = 899–902 | doi = 10.1029/2000gl012093 | </ref> It is commonly believed that the shapes we see here are related to ground frozen with water ice.

<gallery class="center" widths="380px" heights="360px">

27707 2195gullygonsclose.jpg|Close-up of gully alcove showing "gullygons" (polygonal patterned ground near gullies)

</gallery>

==Craters==

Impact craters generally have a rim with ejecta around them, in contrast volcanic craters usually do not have a rim or ejecta deposits.<ref>Hugh H. Kieffer|title=Mars|url=https://books.google.com/books?id=NoDvAAAAMAAJ|accessdate=7 March 2011|year=1992|publisher=University of Arizona Press|isbn=978-0-8165-1257-7 </ref> Sometimes craters display layers. Since the collision that produces a crater is like a powerful explosion, rocks from deep underground are tossed unto the surface. Hence, craters can show us what lies deep under the surface.

Craters usually get a bowl shape when first formed, but with age, debris and ice fall in it and make it more flat. If one measures the diameter of a crater, the original depth can be estimated with various ratios. Because of this relationship, researchers have found that many Martian craters contain a great deal of material; much of it is believed to be ice deposited when the climate was different.<ref>Garvin, J., et al. 2002. Global geometric properities of martian impact craters. Lunar Planet Sci. 33. Abstract @1255.</ref> Some of these flat floored craters display numberous concentric lines--they are called concentric crater fill craters. Craters like these may be used by future colonists for water. Before we land, we will have a map of where these water sources are. Eventually, we will probably develop robotic machines to extract the water.

<gallery class="center" widths="380px" heights="360px">

Image:Arandas Crater.JPG|Arandas Crater, as seen by HiRISE. Scale bar is 1000 meters long.

Image:Exhumedburied Craterin Coprates.jpg|Exhumed Crater in Mare Acidalium, as seen by [[Mars Global Surveyor]] This crater was buried and now it is being uncovered.
Image:ESP 026594 1470closecraters.jpg|Craters that formed at the same time. If the craters were formed at different times, they would have wiped away parts of the others. These craters may been made when an asteroid broke up in the atmosphere. Picture was taken by HiRISE, under HiWish program. Image located in Terra Cimmeria.

Image:ESP 027538 2265.jpg|Crater wall covered with a smooth mantle

ESP 052749 2285pits.jpg|Concentric crater fill crater with pits on floor, as seen by HiRISE under [[HiWish program]]

</gallery>

==Mud volcanoes==

[[File:ESP 047053 2165cones.jpg|600pxr|Line of possible mud volcanoes]]
Line of possible mud volcanoes

Large areas of Mare Acidalium display bright spots on a dark background. It has been suggested that these spots are mud volcanoes.<ref>Farrand | first1 = W. | display-authors = etal | year = 2005 | title = Pitted cones and domes on Mars: observations in Acidalia Planitia and Cydonia Mensae using MOC, THEMIS, and TES data | url = | journal = J. Geophys. Res. | volume = 110 | issue = | page = 14 | doi = 10.1029/2004JE002297 </ref> <ref>Tanaka, K. et al. 2003 Resurfacing history of the northern plains of Mars based on geologic mapping of Mars Global Surveyor data. J. Geophys. Res. 108 (E4), doi:10.1029/2002JE001908.</ref><ref>Grotzinger, J. and R. Milliken (eds.) 2012. Sedimentary Geology of Mars. SEPM</ref> More than 18,000 of these features, which have an average diameter of about 800 meters, have been mapped.<ref>Oehler, D. and C. Allen. 2010. Evidence for pervasive mud volcanism in Acidalia Planitia, Mars. Icarus: 208. 636-657.</ref> As more observations poured in over the years, more evidence supported the notion that these abundant bright marks are mud volcanoes. Mare Acidalium would have received large quantities of mud and fluids form outflow channels, so much mud may have accumulated there. The bright mounds have been found to contain crystalline ferric oxides. Mud volcanism may be highly significant because long lived conduits for upwelling groundwater could have been produced. These could have been habitats for micro organisms.<ref>Komatsu, G., et al. 2014. ASTROBIOLOGICAL POTENTIAL OF MUD VOLCANISM ON MARS. 45th Lunar and Planetary Science Conference (2014). 1085.pdf</ref> Mud volcanoes could have brought up samples from deep zones that could be gathered by robots.<ref>Oehler | first1 = D | last2 = Allen | first2 = C. | year = 2011 | title = Evidence for pervasive mud volcanism in Acidalia Planitia, Mars | url = | journal = Icarus | volume = 208 | issue = | pages = 636–657 | doi = 10.1016/j.icarus.2010.03.031 }}</ref> The authors of an article in Icarus compare these Martian features to mud volcanoes found on the Earth. Their study using HiRISE images and CRISM data support the idea that these features are indeed mud volcanoes. Nanophase ferric minerals and hydrated minerals found with Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show that water was involved with the formation of these possible Martian mud volcanoes.<ref>Komatsu, G., et al. 2016. Small edifice features in Chryse Planitia, Mars: Assessment of a mud volcano hypothesis. Icarus: 268, 56-75.</ref> Scientists are excited that Mars may have mud volcanoes because these small volcanoes may have brought up samples of dirt that were not affected by the high radiation on the Martian surface. We may find evidence of past life in these volcanoes.

<gallery class="center" widths="380px" heights="360px">

Image:White craters in Mare Acidalium.JPG|Craters with white centers in Mare Acidalium. Sand dunes are visible in low areas in image. Some of the features may be mud volcanoes. Picture taken by [[Mars Global Surveyor]] under the MOC Public Targeting Program.

ESP 040775 2235cones.jpg|Large field of cones that may be mud volcanoes
040775 2235conesclose.jpg|Close-up of possible mud volcanoes Note: this is an enlargement of the previous image.

ESP 044665 2240cone.jpg|Possible mud volcano, as seen by HiRISE under [[HiWish program]]

ESP 046617 2210mudvolcanoes.jpg|Mud volcanoes

File:Mud volcanoes In Mare Acidalium, Mars 01.jpg|Wide view of mud volcanoes, as seen by HiRISE under HiWish program
File:Mud volcanoes In Mare Acidalium, Mars 02.jpg|Close view of mud volcanoes, as seen by HiRISE
File:Mud volcanoes In Mare Acidalium, Mars 03.jpg|Close view of mud volcanoes Low area around the volcanoes contains transverse aeolian ridges (TAR's). Only part of picture is in color because HiRISE only takes a color strip in middle of image.
</gallery>

<gallery class="center" widths="190px" heights="180px" >
ESP 052050 2200mudvolcanoes.jpg|Wide view of field of mud volcanoes

File:84807 2225conecolor 01.jpg|Close view of mud volcano, as seen by HiRISE. Picture is about 1 km across. This mud volcano has a different color than the surroundings because it consists of material brought up from depth. These structures may be useful to explore for reamins of past life since they contain samples that would have been protected from the strong radiation at the surface.
</gallery>

<gallery class="center" widths="380px" heights="360px">
Gobustan State Reserve 04.png|Close view of mud volcanoes on Earth Location is Gobustan Azerbaijan.
</gallery>

==Channels in Idaeus Fossae region==

There is a 300 km long ancient river system in Idaeus Fossae. It is carved into the highlands of Idaeus Fossae, and it originated from the melting of ice in the ground after asteroid impacts. There is evidence that it was formed relatively recently. Dating has determined that the water activity came after most of the water activity ended at the boundary between the Noachian and Hesperian periods. Lakes and fan-shaped deposits were formed by running water in this system as it drained eastward into Liberta Crater and formed a delta deposit. Part of the drainage path is the Moa Valley.<ref>Salese, F., G. Di Achille, F., et al. 2016. Hydrological and sedimentary analyses of well-preserved paleo fluvial-paleolacustrine systems at Moa Valles, Mars. J. Geophys. Res. Planets. 121, 194–232, doi:10.1002/2015JE004891.</ref> <ref>Salese, F., G. Di Achille, G. Ori. 2015. SEDIMENTOLOGY OF A RIVER SYSTEM WITH A SERIES OF DAM-BREACH PALEOLAKES AT IDAEUS FOSSAE, MARS. 46th Lunar and Planetary Science Conference 2296.pdf</ref>

<gallery class="center" widths="380px" heights="360px">

File:29054cutoff.jpg|Stream meander and cutoff, as seen by HiRISE under HiWish program. This is part of a major drainage system in the Idaeus Fossae region.
ESP 045590 2170hanging.jpg|Hanging valley, as seen by HiRISE under HiWish program This may have been a waterfall at one time.
ESP 045946 2170channel.jpg|Hanging valley that once may have been a waterfall, as seen by HiRISE under HiWish program
</gallery>

==Channels==

[[File:ESP 045867 2150channels.jpg|600pxr|Channels]]
Channels

There is much evidence that water once flowed in river valleys on Mars.<ref>Baker | first1 = V. | display-authors = etal | year = 2015 | title = Fluvial geomorphology on Earth-like planetary surfaces: a review | journal = Geomorphology | volume = 245 | issue = | pages = 149–182 |</ref> <ref>Carr, M. 1996. in Water on Mars. Oxford Univ. Press.</ref> Images of curved channels have been seen in images from Mars spacecraft dating back to the early seventies with the [[Mariner 9]] orbiter.<ref>Baker, V. 1982. The Channels of Mars. Univ. of Tex. Press, Austin, TX</ref> <ref>Baker | first1 = V. | last2 = Strom | first2 = R. | last3 = Gulick | first3 = V. | last4 = Kargel | first4 = J. | last5 = Komatsu | first5 = G. | last6 = Kale | first6 = V. | year = 1991 | title = Ancient oceans, ice sheets and the hydrological cycle on Mars | url = | journal = Nature | volume = 352 | issue = | pages = 589–594 | doi = 10.1038/352589a0 | </ref> <ref> Carr | first1 = M | year = 1979 | title = Formation of Martian flood features by release of water from confined aquifers | url = | journal = J. Geophys. Res. | volume = 84 | issue = | pages = 2995–300 | doi = 10.1029/jb084ib06p02995 | </ref> <ref>Komar | first1 = P | year = 1979 | title = Comparisons of the hydraulics of water flows in Martian outflow channels with flows of similar scale on Earth | url = | journal = Icarus | volume = 37 | issue = | pages = 156–181 | doi = 10.1016/0019-1035(79)90123-4 | </ref> We have seen more and more channels with each orbiter mission to the Red Planet. Indeed, a study published in June 2017, calculated that the volume of water needed to carve all the channels on Mars was even larger than the proposed ocean that the planet may have had.<ref>http://spaceref.com/mars/how-much-water-was-needed-to-carve-valleys-on-mars.html</ref><ref>Luo, W., et al. 2017. New Martian valley network volume estimate consistent with ancient ocean and warm and wet climate. Nature Communications 8. Article number: 15766 (2017). doi:10.1038/ncomms15766</ref>

<gallery class="center" widths="380px" heights="360px">

Wikisklodowskachannels.jpg|Channels in Sklodowska Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter)
WikisklodowskaESP 035500 2130.jpg|Channels in Sklodowska Crater

ESP 048003 2165channels.jpg|Channels, as seen by HiRISE under HiWish program

File:Labeled meander showing early and later channels ESP 59515 2160.jpg|Meander with parts labeled Features like this show that water stayed around for a while. Meanmders start with small loops that get progressively larger.

File:6438 2155meander.jpg

</gallery>

[[File:ESP 055374 2175channelnetwork.jpg|600pxr|Channel network]]
Channel network

[[File:ESP 077583 2255inverted.jpg|thumb|500px|center|Inverted stream, a stream bed has been filled with hard materials that did not erode away like the surroundings]]

==Ocean==

Many researchers have suggested that Mars once had a great ocean in the north.<ref>Parker | first1 = T. J. | last2 = Gorsline | first2 = D. S. | last3 = Saunders | first3 = R. S. | last4 = Pieri | first4 = D. C. | last5 = Schneeberger | first5 = D. M. | year = 1993 | title = Coastal geomorphology of the Martian northern plains | url = | journal = J. Geophys. Res. | volume = 98 | issue = E6| pages = 11061–11078 | doi=10.1029/93je00618 |</ref> <ref>Fairén | first1 = A. G. |display-authors=etal | year = 2003 | title = Episodic flood inundations of the northern plains of Mars | url = http://eprints.ucm.es/10431/1/9-Marte_3.pdf| journal = Icarus | volume = 165 | issue = 1| pages = 53–67 | </ref> <ref> Head | first1 = J. W. |display-authors=etal | year = 1999 | title = Possible ancient oceans on Mars: Evidence from Mars Orbiter Laser Altimeter data | url = | journal = Science | volume = 286 | issue = 5447| pages = 2134–2137 | doi=10.1126/science.286.5447.2134| pmid = 10591640 |</ref> <ref>Parker, T. J., Saunders, R. S. & Schneeberger, D. M. Transitional morphology in west Deuteronilus Mensae, Mars: Implications for modification of the lowland/upland boundary" ''Icarus'' 1989; 82, 111–145</ref> <ref>Carr | first1 = M. H. | last2 = Head | first2 = J. W. | year = 2003 | title = Oceans on Mars: An assessment of the observational evidence and possible fate | url = | journal = J. Geophys. Res. | volume = 108 | issue = E5| page = 5042 |</ref> <ref>Kreslavsky | first1 = M. A. | last2 = Head | first2 = J. W. | year = 2002| title = Fate of outflow channel effluent in the northern lowlands of Mars: The Vastitas Borealis Formation as a sublimation residue from frozen ponded bodies of water | url = | journal = J. Geophys. Res. | volume = 107 | issue = E12| page = 5121 |</ref> <ref>Clifford, S. M. & Parker, T. J. The evolution of the martian hydrosphere: Implications for the fate of a primordial ocean and the current state of the northern plains" ''Icarus'' 2001; 154, 40–79</ref> Much evidence for this ocean has been gathered over several decades. New evidence was published in May 2016. A large team of scientists described how some of the surface in Ismenius Lacus quadrangle was altered by two tsunamis. The tsunamis were caused by asteroids striking into an ocean. Both were thought to have been strong enough to create 30 km diameter craters. The first tsunami picked up and carried boulders the size of cars or small houses. The backwash from the wave formed channels by rearranging the boulders. The second came in when the ocean was 300 m lower. The second carried a great deal of ice which was dropped in valleys. Calculations show that the average height of the waves would have been 50 m, but the heights would vary from 10 m to 120 m. So, some large waves would have gone over a 36 story building.<ref>https://www.convertunits.com/from/metre/to/story</ref> Asteroids hitting an ocean on Mars are quite possible. Numerical simulations show that in this particular part of the ocean two 30 km in diameter would form every 30 million years. The implication here is that a great northern ocean may have existed for millions of years. One argument against an ocean has been the lack of shoreline features. But shoreline features may have been washed away by these tsunami events. The parts of Mars studied in this research are Chryse Planitia and northwestern Arabia Terra. These tsunamis affected some surfaces in the [[Ismenius Lacus quadrangle]] and in the Mare Acidalium quadrangle.<ref>Ancient Tsunami Evidence on Mars Reveals Life Potential |date=May 20, 2016 |url=http://astrobiology.com/2016/05/ancient-tsunami-evidence-on-mars-reveals-life-potential.html</ref> <ref>Rodriguez | first1 = J. |display-authors=etal | year = 2016 | title = Tsunami waves extensively resurfaced the shorelines of an early Martian ocean | url = | journal = Scientific Reports | volume = 6 | issue = | page = 25106 | doi=10.1038/srep25106| pmid = 27196957 | pmc = 4872529 |</ref> <ref>| doi=10.1038/srep25106| pmid=27196957| pmc=4872529| title=Tsunami waves extensively resurfaced the shorelines of an early Martian ocean| journal=Scientific Reports| volume=6| pages=25106| year=2016| last1=Rodriguez| first1=J. Alexis P.| last2=Fairén| first2=Alberto G.| last3=Tanaka| first3=Kenneth L.| last4=Zarroca| first4=Mario| last5=Linares| first5=Rogelio| last6=Platz| first6=Thomas| last7=Komatsu| first7=Goro| last8=Miyamoto| first8=Hideaki| last9=Kargel| first9=Jeffrey S.| last10=Yan| first10=Jianguo| last11=Gulick| first11=Virginia| last12=Higuchi| first12=Kana| last13=Baker| first13=Victor R.| last14=Glines| first14=Natalie</ref> <ref>Cornell University. "Ancient tsunami evidence on Mars reveals life potential." ScienceDaily. ScienceDaily, 19 May 2016. https://www.sciencedaily.com/releases/2016/05/160519101756.htm.</ref>

==Pingos==

Pingos are believed to be present on Mars. They are mounds that contain cracks. These particular fractures were evidently produced by something emerging from below the brittle surface of Mars. Ice lenses, resulting from the accumulation of ice beneath the surface, possibly created these mounds with fractures. Ice is less dense than rock, so the buried ice rose and pushed upwards on the surface and generated these cracks. An analogous process creates similar sized mounds in arctic tundra on Earth. The name ''pingos'' is an Inuit word.<ref>http://www.uahirise.org/ESP_046359_1250</ref> They contain pure water ice, so they would be a great source of water for future colonists on Mars.

[[File:44322 2215pingos.jpg|600pxr|Arrows point to possible pingos, as seen by HiRISE under HiWish program Pingos contain a core of pure ice.]]
Arrows point to possible pingos, as seen by HiRISE under HiWish program Pingos contain a core of pure ice.

==Fractured ground==

<gallery class="center" widths="380px" heights="360px">

44322 2215fractures.jpg|Fractures These fractures are believed to eventually turn into canyons because the cracks will get much larger when ice in the ground disappears into the thin Martian atmosphere and the remaining dust blows away.

ESP 046366 2215fractures.jpg|Wide view of fractured ground, as seen by HiRISE under HiWish program Cracks form on the Martian surface, and then they turn into large fractures.

46366 2215fractures.jpg|Close view of fractures from the previous image

File:ESP 056968 2140cracks.jpg|Cracks on crater floor

File:56968 2140cracks.jpg|Close view of cracks on crater floor, as seen by HiRISE under [[HiWish program]]

File:ESP 057311 2125cracks.jpg|Group of cracks

File:ESP 057311 2125crackscraters.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger. Note that small craters do not have very big rims; they may be just pits.

File:57311 2155crackssmallarge.jpg|Close view of cracks of various sizes Ice disappears along crack surfaces and makes crack larger.

File:57311 2155crackscrater.jpg|Cracks around crater, as seen by HiRISE under [[HiWish program]]

</gallery>

==Layers==

Layered terrain is common on the Earth and on Mars. Water is usually involved with the formation of layers. Hence, when we see layers, there is the possibility of a lake or sea in the past.

[[File:ESP 047080 2120layered mesa.jpg|600pxr|Layers in mesa, as seen by HiRISE under [[HiWish program]]]]
Layers in mesa, as seen by HiRISE under [[HiWish program]]

Rock can be formed into layers in a variety of ways. Volcanoes, wind, or water can produce layers<ref>http://hirise.lpl.arizona.edu?PSP_008437_1750</ref> Layers can be hardened by the action of groundwater. Martian ground water probably moved hundreds of kilometers, and in the process it dissolved many minerals from the rock it passed through. When ground water surfaces in low areas containing sediments, water evaporates in the thin atmosphere and leaves behind minerals as deposits and/or cementing agents.

<gallery class="center" widths="380px" heights="360px">

File:53490 2230layers.jpg|Close view of layers in a trough

</gallery>

==Features close to Face on Mars==

Here are some CTX images of area near the Face. These pictures show natural formations on Mars. In the area around the face are mesas, mud volcanoes, pedestal craters, and brain terrain. Many of the mesas are sitting on what looks like platforms. They may be from a change in sea level. There is strong evidence building that an ocean was once all through the northern lowlands. All of the features seen here are common on Mars, especially in this latitude. For more pictures and information about the face go to The [[The Face on Mars]].

<gallery class="center" widths="380px" heights="360px">

File:FaceG22 026771 2213 XI 41N009W.jpg|Terrain to the west of Face Face is visible in upper right.

File:FacectxT01 00807 2205glaciers.jpg|Terrain near Face showing possible glacier erosion Curved portions of the mounds look like the start of what are called cirques that form as snow accumulates on mountains.<ref>http://www.landforms.eu/cairngorms/corrie%20formation.htm</ref>

File:FacectxD02 027892 2219pyramid.jpg|Mud volcanoes in terrain near Face

File:Faceg22 026771 2213pedestal.jpg|Mesa, mud volcano, and pedestal crater in area near Face.

</gallery>
[[File:FacectxF23 044929 2199 XI 39N010Wlabeled.jpg|600pxr|Mesa, ridges, possible cirques near Face]]
Mesa, ridges, possible cirques near Face.

== Other landscape features in Mare Acidalium quadrangle ==

<gallery class="center" widths="380px" heights="360px">

Image:Cliff in Mare Acidalium.JPG|Cliff in Kasei Valles system, as seen by HiRISE

</gallery>

[[File:Rolling boulders in kasei.JPG|600pxr|Boulders that are about 2.2 yards acoss (smaller than a bedroom) and their tracks after rolling down a cliff in Kasei Valles system, as seen by HiRISE]]

Boulders that are about 2.2 yards across (smaller than a bedroom) and their tracks after rolling down a cliff in Kasei Valles system, as seen by HiRISE

<gallery class="center" widths="380px" heights="360px">

Image:Context for fault.JPG|CTX image showing the context for the next image of a fault The area in the black rectangle is enlarged in next photo.

Image:Fault in Mare Acidalium.JPG|Close-up of a possible fault in Mare Acidalium, as seen by HiRISE under the [[HiWish program]]. A circle is drawn around crater to show that it may be off round because of movement of the fault. Many other faults are in the region.

ESP 045524 2120fan.jpg|Fan with channels on its surface

48924 2150ovalpits.jpg|Sample of oval pits in this location of unknown origin, as seen by HiRISE under HiWish program
File:Fan along crater wall. ESP 055110 2265.jpg|Fan This fan is formed on the edge of a crater. Dirt and rocks mixed with water, flowed down a slope and were deposited in crater. The fan has layers which means that this was done at different intervals, not all at once. This image was named picture of the day for January 14, 2024. Image credit is NASA/JPL/University of Arizona/Secosky.

</gallery>

== See also ==

*[[The Face on Mars]]
*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[HiWish program]]
*[[How are features on Mars Named?]]

*[[Layers on Mars]]
*[[Mars Global Surveyor]]

*[[Martian gullies]]
*[[Oceans on Mars]]

*[[Rivers on Mars]]

== References ==

[[Category:Mars Atlas]]

Hellas quadrangle

2026-04-06T13:03:27Z

Suitupshowup: /* Crater Lakes */

{{Mars atlas}}
{| class="wikitable sortable"
|MC-28
|Hellas
|30–65° S
|60–120° E
|[[Mars Quadrangles|Quadrangles]]
|[[Mars Atlas|Atlas]]
|}
<gallery widths="400" heights="300">
File:USGS-Mars-MC-28-HellasRegion-mola.png
File:PIA00188-MC-28-HellasRegion-19980605.jpg
</gallery>

[[File:Collage Hellas 04.jpg|Features of Features of Hellas quadrangle, as seen by HiRISE under under HiWish program|600pxr| Features of Hellas quadrangle]]

Scenes of the Hellas quadrangle

The most famous feature of this area is the [[Hellas Basin|Hellas]] basin, a impact crater 2300 km in diameter.

The Hellas quadrangle covers the area from 30° to 65° south latitude and 240° to 300° west longitude (120-60 E ). When an asteroid slammed into Mars to create a big hole that makes up some of this quadrange, many unbelievable events happened—it was worse than any science fiction movie. Within the Hellas quadrangle lies the classic features Hellas Planitia and Promethei Terra. Giovanni Schiaparelli came up with the name Hellas (which in Greek means 'Greece').<ref>https://en.wikipedia.org/wiki/Hellas_Planitia#:~:text=Before%20Giovanni%20Schiaparelli%20gave%20it,produced%20%22the%20first%20really%20truthful</ref> The name was approved in 1973.<ref>https://planetarynames.wr.usgs.gov/</ref> Many interesting and mysterious features have been discovered in the Hellas quadrangle, including the giant river valleys Dao Vallis, Niger Vallis, Harmakhis, and Reull Vallis—all of which may have contributed water to a lake in the Hellas basin in the distant past.<ref>Carr | first=Michael H. | publisher=Cambridge University Press | isbn= 978-0-521-87201-0 | title= The Surface of Mars |date=2006 |</ref> <ref>Moore | first1= J | last2= Wilhelms | first2= Don E. | title= Hellas as a possible site of ancient ice-covered lakes on Mars | journal= Icarus | volume= 154 | issue= 2 |pages= 258–276 | date= 2001 | doi = 10.1006/icar.2001.6736 | </ref> <ref>Cabrol, N. and E. Grim (eds). 2010. Lakes on Mars</ref> Many places in the Hellas quadrangle show signs that the ground is full of ice, especially with glacier-like flow features.

In this article, some of the best pictures from a number of spacecraft will show what the landscape looks like in this region. The origins and significance of all features will be explained as they are currently understood.

==Hellas Basin==

The Hellas quadrangle contains part of the Hellas Basin, the largest known impact crater on the surface of Mars and the second largest in the solar system. The depth of the crater is 7152 m<ref>http://www-star.stanford.edu/projects/mgs/sum/s0403210230.html Martian Weather Observation] https://web.archive.org/web/20080531235046</ref> (23,000ft) below the standard topographic datum of Mars. As of 2001, based on measurements of the Mars Orbiter Laser zero elevation on Mars (standard topographic dataum) was defined as the average radius of the planet at the equator.<ref>Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars |journal=Journal of Geophysical Research: Planets |first1=D. |last1=Smith |first2=M. |last2=Zuber |first3=H. |last3=Frey |first4=J. |last4=Garvin |first5=J. |last5=Head |first6=D. |last6=Muhleman |first7=D. |last7=Pettengill |first8=R. |last8=Phillips |display-authors=5 |volume=106 |issue=E10 |pages=23689–23722 |date=25 October 2001 |doi=10.1029/2000JE001364|</ref> This type of agreement was necessary since Mars does not have a sea level like the Earth. Before this data came in from the Mars Orbiter, zero altitude was defined as a specific atmospheric pressure of 610.5 Pascals, about six millibars--it is a special number, it's where water can exist as gas, liquid or solid, called "the triple point of water."<ref>https://www.abc.net.au/science/articles/2013/08/12/3820057.htm</ref>

The basin is located in the southern highlands of Mars and is thought to have been formed about 3.9 billion years ago, during a period that geologists call the Late Heavy Bombardment. This was a period of much greater asteroid impacts.

Hellas stood out even from observations from Earth-based telecopes. Due to frost covering in the winter, it showed up as a white, round shape.<ref>Tanaka, K., et al. 1992. III. Global Stratigraphy. In: Kieffer, et al. 1992. Mars. pp. 345</ref>

==Results of asteroid collision==

The physics of this great event boggles the mind. Much of the atmosphere may have been removed by the impact.<ref> Melosh H.J., Vickery
A.M. (1989) Nature 338</ref> Also, torrential rains may have fallen all over the planet.<ref>Palumbo A.M., Head J.W. (2018)
MAPS 53; [9] Moore J.M., Wilhelms D.E. (2001) Icarus 154</ref> Studies suggest that when an impact created the Hellas Basin, the entire surface of Mars was heated hundreds of degrees, 70 meters of molted rock fell on the planet, and an atmosphere of gaseous rock was formed. Think about hot, molten rock falling to a depth of a 21 story building. On Earth that would cover all homes and most buildings. This rock atmosphere was 10 times as thick as the Earth's atmosphere. In a few days, the rock would have condensed out and covered the whole planet with an additional 10 m of molten rock.<ref>Carr | first=Michael H. | publisher=Cambridge University Press | isbn= 978-0-521-87201-0 | title= The Surface of Mars |date=2006 |</ref> When all this rock cooled all the planet would be covered with rock that was as deep as a 24 story building is tall. And this is not made up folks—the proof is the big hole called the Hellas Basin. Imagine if such a thing happened on the Earth.

Some speculate that the impact weakened the crust in such a way as to permit volcanoes to form. In the places near Hellas are the volcanoes Tyrrhena Patera, Hadriaca, Amphitrites Paterra, Malea Patera, Peneus Patera, and Pityusa Patera. There is even the possibility that the shock wave was focused on the exact oppostite of the planet to weaken the crust to pruduce Alba Mons, the largest volcano by volume on Mars.<ref>Morden, S. 2022. The Red Planet. Pegasus Books. New York.</ref>

On the opposite side of the planet is the [[Tharsis]] bulge. The vulcanism there may have been formed as part of the [[Chaotic Terrain]] formed from massive impacts.

==Strange surfaces—Origin Unknown==

In the Northwest portion of Hellas Planitia is a strange type of surface called complex banded terrain or taffy-pull terrain. Its process of formation is still largely unknown, although it appears to be due to erosion of hard and soft sediment along with ductile deformation. Ductile deformation results from layers undergoing strain.<ref>http://hirise.lpl.arizonai.edu/P/sP_008559_1405</ref>
<gallery class="center" widths="380px" heights="360px">
File:ESP 084001 1375twisted surfaces on floor of Hellas.jpg|Strange floor features in Hellas
</gallery>
==Giant Lake==

Early in the planet's history, it is believed that a giant lake existed in the Hellas Basin.<ref>Voelker, M., et al. 2016. DISTRIBUTION AND EVOLUTION OF LACUSTRINE AND FLUVIAL FEATURES IN HELLASPLANITIA, MARS, BASED ON PRELIMINARY RESULTS OF GRID-MAPPING. 47th Lunar and Planetary Science Conference (2016) 1228.pdf.</ref> Parts of the Hellas Basin are in three different quadrangles: Hellas, Noachis, and Iapygia. Possible shorelines have been discovered. These are evident in alternating benches and scarps visible in Mars orbiting camera narrow-angle images. In addition, Mars orbiting laser altimeter (MOLA) data show that the contacts of these sedimentary units mark contours of constant elevation for thousands of km, and in one case all around the basin. Channels, believed to be formed by water, enter into the basin. The Hellas drainage basin may be almost one-fifth that of the entire northern plains. A lake in Hellas in today's Martian climate would form a thick ice at the top that would eventually [[Sublimation|Sublimate]]. That is the ice would turn directly from a solid to a gas.<ref>Moore, J; Wilhelms, Don E. (2001). "Hellas as a possible site of ancient ice-covered lakes on Mars". Icarus. 154 (2): 258–276.</ref> Glacial features ( moraines, drumlins, and eskers) have been found that may have been formed when the water froze.<ref>Carr, Michael H. (2006). The Surface of Mars. Cambridge University Press.</ref> <ref>Kargel |first1= J. |first2= R. |last2=Strom |date= 1991 |title= Terrestrial glacial eskers: analogs for martian sinuous ridges | journal= LPSC | volume=XXII | pages= 683–684 |</ref>

<gallery class="center" widths="380px" heights="360px">
Image:Hellas basin topo.jpg|Hellas Basin Area topography. Crater depth is 7152 m<ref>Martian Weather Observation Archived 2008-05-31 at the Wayback Machine MGS radio science measured 11.50 mbar at 34.4° S 59.6° E -7152 meters.</ref> (23,000 ft) below the standard topographic datum of Mars.
Image:False color of Hellas Planitia.jpeg|Hellas Basin with graph showing the great depth of the crater. It is the deepest crater on Mars and has the highest surface pressure: 1155 pascal (Pa)<ref>Martian Weather Observation Archived 2008-05-31 at the Wayback Machine MGS radio science measured 11.50 mbar at 34.4° S 59.6° E -7152 meters.</ref> (11.55 millibar, 0.17 psi, or 0.01 atm).

</gallery>

[[File:Twisted Ground in Hellas.jpg|thumb|500px|center|Twisted Ground in Hellas This is a good example of how difficult it would be to walk on Mars.]]

==How climate change caused ice-rich features==

Many features on Mars, including ones in Hellas quadrangle, are believed to contain large amounts of ice. The Hellas region displays many strange and beautiful landscapes. Most do not have their counterparts on the Earth. Researchers have struggled to explain these features and others. Mars holds many mysteries. However, after so much coverage by satellites with increasing better cameras, we have made major strides in understanding the mysteries of the Red Planet. Some aspects of the planet are still debated. We do understand much of the nature of Mars, but some details have yet to be worked out.

Most of the strangeness of the Hellas region relates to climate change. Indeed, most of the whole planet’s surface appearance is driven by drastic and frequent climate changes. These changes are due to basic physics. Seasons on the planets, including the Earth, are caused by the tilt of a planet's rotational axis. Because the Earth has a moon of considerable mass, the Earth’s axis does not change much from its usual 23.5 degrees. However, Mars lacks a large moon; consequently its tilt has even been greater than 80 degrees. Note that its tilt at 25 degrees is almost the same as ours. <ref>Touma | first1 = J. | last2 = Wisdom | first2 = J. | year = 1993 | title = The Chaotic Obliquity of Mars | url = | journal = Science | volume = 259 | issue = 5099| pages = 1294–1297 | doi=10.1126/science.259.5099.1294 | pmid=17732249|</ref> <ref>Laskar | first1 = J. | last2 = Correia | first2 = A. | last3 = Gastineau | first3 = M. | last4 = Joutel | first4 = F. | last5 = Levrard | first5 = B. | last6 = Robutel | first6 = P. | year = 2004 | title = Long term evolution and chaotic diffusion of the insolation quantities of Mars | url =https://hal.archives-ouvertes.fr/hal-00000860/file/Ma_2004.laskar_prep.pdf | journal = Icarus | volume = 170 | issue = 2| pages = 343–364 | doi=10.1016/j.icarus.2004.04.005 | </ref>
Studies have shown that when the tilt of Mars reaches 45 degrees from its current 25 degrees, ice is no longer stable at the poles. As a result, it will disappear.<ref>Head | first2 = J. | last3 = Marchant | first3 = D. | last4 = Kowalewski | first4 = D. | year = 2008 | title = Identification of sublimation-type thermal contraction crack polygons at the proposed NASA Phoenix landing site: Implications for substrate properties and climate-driven morphological evolution | url = | journal = Geophys. Res. Lett. | volume = 35| issue = 4| pages = L04202 | doi = 10.1029/2007GL032813 | </ref> Furthermore, at this high tilt, stores of solid carbon dioxide (dry ice) sublimate, thereby increasing the atmospheric pressure. This increased pressure allows more dust to be held in the atmosphere. With more dust, more ice will freeze onto the dust. Eventually, moisture in the atmosphere will fall as snow or as ice frozen onto dust grains. Calculations suggest this material will concentrate in the mid-latitudes. And Hellas is in the mid-latitudes of the southern hemisphere.<ref>Levy | first1 = J. | last2 = Head | first2 = J. | last3 = Marchant | first3 = D. | year = 2009 | title = Thermal contraction crack polygons on Mars: Classification, distribution, and climate implications from HiRISE observations | url = | journal = J. Geophys. Res. | volume = 114| issue = E1| pages = E01007 |</ref> <ref>Hauber, E., D. Reiss, M. Ulrich, F. Preusker, F. Trauthan, M. Zanetti, H. Hiesinger, R. Jaumann, L. Johansson, A. Johnsson, S. Van Gaselt, M. Olvmo. 2011. Landscape evolution in Martian mid-latitude regions: insights from analogous periglacial landforms in Svalbard. In: Balme, M., A. Bargery, C. Gallagher, S. Guta (eds). Martian Geomorphology. Geological Society, London. Special Publications: 356. 111-131</ref>

Using decades of data from orbiting satellites together with general principles about weather and climate, researchers have developed theories or models that explain why Mars looks like it does. They call these models or theories general circulation models. These theories predict accumulations of ice-rich dust (which becomes permafrost, also called 'mantle') in the same areas where ice-rich features are found.<ref>Laskar, J.; Correia, A.; Gastineau, M.; Joutel, F.; Levrard, B.; Robutel, P. (2004). "Long term evolution and chaotic diffusion of the insolation quantities of Mars" (PDF). Icarus. 170 (2): 343–364.</ref>
When the tilt begins to return to lower values, the ice sublimates (turns directly to a gas) and leaves behind a lag of dust.<ref>Mellon | first1 = M. | last2 = Jakosky | first2 = B. | year = 1995 | title = The distribution and behavior of Martian ground ice during past and present epochs | url = https://semanticscholar.org/paper/815bfd93bdb19325e03e08556d145fa470112e4e| journal = J. Geophys. Res. | volume = 100 | issue = E6| pages = 11781–11799 |</ref> <ref>Schorghofer | first1 = N | year = 2007 | title = Dynamics of ice ages on Mars | url = | journal = Nature | volume = 449 | issue = 7159| pages = 192–194 |</ref> This lag deposit caps the underlying material so with each cycle of high tilt levels, some ice-rich mantle remains behind.<ref>Madeleine, J., F. Forget, J. Head, B. Levrard, F. Montmessin. 2007. Exploring the northern mid-latitude glaciation with a general circulation model. In: Seventh International Conference on Mars. Abstract 3096.</ref>
After many, many cycles of mantle accumulation some places, especially the Hellas region, accumulate very thick deposits of mantle, technically called latitude dependent mantle (because its occurrence depends on the latitude). Some parts of the mantle may have changed into solid ice in a manner analogous to how snow turns into ice in our Earth’s glaciers. The following pictures show expressions of this mantle in the Hellas region.

[[File:Niger Vallis hirise.JPG|thumb|Niger Vallis with features typical of this latitude, as seen by HiRISE. Chevron patterns result from movement of ice-rich material. Click on image to enlarge in order to see chevron pattern and mantle]]

The image at the right shows a good view of this smooth mantle around Niger Vallis, as observed with HiRISE.

<gallery class="center" widths="380px" heights="360px">
45070 1440mantlelayers.jpg|Smooth mantle with layers

46270 1445mantle.jpg|Close view of mantle

48063 1395mantle.jpg|Close view of the edge of mantle, as seen by HiRISE under the HiWish program
</gallery>

What happens next is that cracks appear in the surface. Stress is suggested to initiate a fracture process that produces cracks. Cracks expose more surfaces, and consequently more ice can escape into the planet's thin atmosphere. Conditions on Mars are such that the process called [[Sublimation]] dominates. On Mars sublimation has been observed when the Phoenix lander uncovered chunks of ice that disappeared in a few days.<ref>http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080619.html Bright Chunks at ''Phoenix'' Lander's Mars Site Must Have Been Ice – Official NASA press release (19.06.2008)</ref> <ref>http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080619.html</ref>

<gallery class="center" widths="380px" heights="360px">

Image:Ice sublimating in the Dodo-Goldilocks trench.gif|Die-sized clumps of bright material in the enlarged "Dodo-Goldilocks" trench vanished over the course of four days, implying that they were composed of ice which sublimated following exposure. those chunks are in the lower left of the trench.<ref>Smith, P., et al. 2009. H2O at the Phoenix Landing Site. Science: 325, 58-61.</ref>

Image:Evaporating ice on Mars Phoenix lander image.jpg|Color versions of the trench showing ice sublimation The lower left corner of the trench is enlarged in the insets in the upper right of the images. The chunks disappeared in the 4 days.

</gallery>

[[File:Evaporatingicephoenix.jpg|thumb|600px|center|Close up showing chunks of ice disappearing in trench called Dodo-Goldlocks]]

In addition, HiRISE has seen fresh craters with ice at the bottom. HiRISE, a powerful telescope in orbit around the planet, observed these ice deposit disappear over time.<ref>Byrne, S. et al. 2009. Distribution of Mid-Latitude Ground Ice on Mars from New Impact Craters: 329.1674-1676</ref>
Eventually, small cracks become large canyons or troughs in the mantle. Small cracks often contain small pits and chains of pits.<ref>Morgenstern, A., et al. 2007</ref> <ref name="Baker, D. 2015">Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref> When parts of this many meters deep mantle start to have cracks, sublimation takes over and many strange landscapes are created. HiRISE has imaged many of these scenes. Pictures in this article show many of these exotically beautiful forms.
Changes in Mars's orbit and tilt cause significant changes in the distribution of water ice from Polar Regions down to latitudes equivalent to Texas. During certain climate period’s, water vapor leaves polar ice and enters the atmosphere. The water returns to the ground at lower latitudes as deposits of frost or snow mixed generously with dust. The atmosphere of Mars contains a great deal of fine dust particles. Water vapor condenses on the particles; consequently, they fall down to the ground due to the additional weight of the water coating. This material that falls, along with snow lands in certain places on Mars. A great deal lands in the Hellas region. It appears as a smooth covering. Due to its great age, the Martian surface is very irregular, but where mantle has accumulated it is smooth. When ice at the top of the mantling layer goes back into the atmosphere, it leaves behind dust, which insulates the remaining ice.<ref>author=MLA NASA/Jet Propulsion Laboratory |date=December 18, 2003 | title= Mars May Be Emerging From An Ice Age |work= ScienceDaily |accessdate=February 19, 2009 |url= https://www.sciencedaily.com/releases/2003</ref>

==Lobate debris aprons (LDA)==

One very important feature common in east Hellas are piles of material surrounding cliffs. This formation is called a lobate debris apron (LDA). Recently, research with the Shallow Radar on the [[Mars Reconnaissance Orbiter]] has provided strong evidence that the LDAs are glaciers that are covered with a thin layer of rocks.<ref>Head | first1= JW | last2= Neukum | first2= G | last3= Jaumann | first3= R | last4= Hiesinger | first4= H | last5= Hauber | first5= E | last6= Carr | first6= M | last7= Masson | first7= P | last8= Foing | first8= B | last9= Hoffmann | first9= H | last10= Kreslavsky | first10= M. | last11= Werner | first11= S. | last12= Milkovich | first12= S. | last13= Van Gasselt | first13= S. | last14= Co-Investigator Team | first14= The Hrsc | title= Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars | journal= Nature | volume= 434 | issue= 7031 |pages= 346–350 | date= 2005 | pmid = 15772652 | doi= 10.1038/nature03359 |</ref> <ref>http://news.brown.edu/pressreleases/2008/04/martian-glaciers</ref> <ref>Plaut | first1= Jeffrey J. | last2= Safaeinili | first2= Ali | last3= Holt | first3= John W. | last4= Phillips | first4= Roger J. | last5= Head | first5= James W. | last6= Seu | first6= Roberto | last7= Putzig | first7= Nathaniel E. | last8= Frigeri | first8= Alessandro | title= Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars | journal=Geophysical Research Letters | volume= 36 | issue= 2 | pages= n/a | date= 2009 |</ref> <ref>http://www.lpi.usra.edu/meetings/lpsc2008/pdf/2290.pdf | </ref> <ref>Radar Sounding Evidence for Ice within Lobate Debris Aprons near Hellas Basin, Mid-Southern Latitudes of Mars |http://www.lpi.usra.edu/meetings/lpsc2008/pdf/2441.pdf | journal = Lunar and Planetary Science |volume=XXXIX | issue = 1391 | pages = 2441 |date=2008 |last1= Holt | first=J.W.| last2 = Safaeinili | first2 = A. | last3 = Plaut | first3 = J. J. | last4 = Young | first4 = D. A. | last5 = Head | first5 = J. W. | last6 = Phillips | first6 = R. J. | last7 = Campbell | first7 = B. A. | last8 = Carter | first8 = L. M. | last9 = Gim | first9 = Y. | last10 = Seu | </ref> Large amounts of water ice are believed to be in the LDAs. Available evidence strongly suggests that the eastern part of Hellas accumulated snow in the past. When the tilt (obliquity) of Mars increases the southern ice cap releases large amounts of water vapor. Climate models predict that when this occurs, water vapor condenses and falls where LDAs are located. The tilt of the earth changes little because our relatively large moon keeps it stable. The two tiny Martian moons do not stabilize their planet, so the rotational axis of Mars undergoes large variations.<ref>Holt | first1 = J. W. | last2 = Safaeinili | first2 = A. | last3 = Plaut | first3 = J. J. | last4 = Head | first4 = J. W. | last5 = Phillips | first5 = R. J. | last6 = Seu | first6 = R. | last7 = Kempf | first7 = S. D. | last8 = Choudhary | first8 = P. | last9 = Young | first9 = D. A. | last10 = Putzig | first10 = N. E. | last11 = Biccari | first11 = D. | last12 = Gim | first12 = Y. | title = Radar Sounding Evidence for Buried Glaciers in the Southern Mid-Latitudes of Mars | journal = Science | volume = 322 | issue = 5905 | pages = 1235–8 | date = 2008 | pmid = 19023078 | doi = 10.1126/science.1164246 | </ref> Lobate debris aprons may be a major source of water for future Mars colonists. Their major advantages over other sources of Martian water are that they can easily mapped from orbit and they are closer to the equator, where manned missions are more likely to land.

==Lineated Valley Fill (LVF)==

[[File:Reull Vallis lineated deposits.jpg|thumb|500px|center|Reull Vallis with lineated floor deposits, as seen by THEMIS. Click on image to enlarge to see relationship to other features.]]

On the floors of some channels are features called lineated floor deposits or lineated valley fill. They are ridged and grooved materials that seem to deflect around obstacles. They are believed to be ice-rich. Some glaciers on the Earth show such features. Lineated floor deposits may be related to lobate debris aprons, which have been proven to contain large amounts of ice. Reull Vallis, as pictured below, displays these deposits.<ref>https://web.archive.org/web/20100617191548/http://themis.asu.edu/zoom-20021022a |</ref> After years of observations, researchers consider lobate debris aprons (LDA's) and lineated valley fill (LVF) to be basically the same--mostly ice with a covering of debris, their shapes (and names) are dependent on their locations. If confined within a valley, LVF is present; in contrast when not confined, this flowing debris covered ice spreads out to form LDA's.<ref>Wueller, L., et al. 2025. Relationships between lobate debris aprons and lineated valley fill on Mars: Evidence for an extensive Amazonian valley glacial landsystem in Mamers Valles. Icarus. Volume 426, 15 116373</ref>

<gallery class="center" widths="380px" heights="360px">

File:ESP 055421 1395reullvallis.jpg|Reull Vallis floor showing lineated valley fill at the top and hollows near bottom,
File:55421 1395lvfclose.jpg|Close, color view of lineated valley fill

</gallery>

[[File:ESP 052138 1435lvf.jpg|thumb|500px|center|Lineated valley fill, as seen by HiRISE under [[HiWish program]]]]

==Upper Plains Unit==

[[File:48011 1370upperunit.jpg|600pxr|Close view of upper plains unit breaking down into brain terrain, as seen by HiRISE under HiWish program As ice leaves the ground, the ground collapses and winds blow the remaining dust away.]]

Close view of upper plains unit breaking down into brain terrain As ice leaves the ground, the ground collapses and winds blow the remaining dust away.

<gallery class="center" widths="380px" heights="360px">

File: ESP 019778 1385pyramid.jpg|Layered structure in crater that is probably what is left of a layered unit that once covered a much larger area. Material for this unit fell from the sky as ice-coated dust.

</gallery>

Some places the mantle has piled up quite deeply. The remains of a 50-100 meter thick mantling, called the upper plains unit, has been discovered in the mid-latitudes of Mars. It was first investigated in the Deuteronilus Mensae region (in the North), but it occurs in other places as well. The remnants sometimes consist of sets of dipping or tilted layers in craters and along mesas.<ref>Carr, M. 2001. Mars Global Surveyor observations of Martian fretted terrain. Journal of Geophysical Research: Planets. 106. Issue E10</ref> Sets of dipping layers may be of various sizes and shapes—some look like stepped Aztec pyramids from Central America. The Upper plains unit can have several different appearances.

<gallery class="center" widths="380px" heights="360px">

ESP 050793 1365pyramids.jpg|Tilted layers
50793 1365layers.jpg|Tilted layers
50793 1365layers2.jpg|Tilted layers, as seen by HiRISE under [[HiWish program]]
</gallery>

<gallery class="center" widths="380px" heights="360px">

Image:ESP_024868pyramid.jpg|Layered feature probably formed by the erosion of the upper plains unit

P1010377redrocksfall.jpg|Layered feature in Red Rocks Park, Colorado. This has a different origin than ones on Mars, but it has a similar shape. Features in Red Rocks region were caused by uplift of mountains.

ESP 034509 1450pyramidshellas.jpg|Layered feature

File:ESP 054485 1430craterpyramid.jpg|Layered feature in crater

</gallery>

<gallery class="center" widths="380px" heights="360px">

ESP 054775 1400craterpyramid.jpg|Layered feature in crater, as seen by HiRISE under HiWish program

</gallery>

Some regions of the upper plains unit display large fractures and troughs with raised rims; such regions are called ribbed upper plains. Fractures are believed to have started with small cracks from stresses. Stress is suggested to initiate the fracture process since ribbed upper plains are common when debris aprons come together or near the edge of debris aprons—such sites would generate compressional stresses. Cracks expose more surfaces, and consequently more ice in the material sublimates into the planet's thin atmosphere. Eventually, small cracks become large canyons or troughs.<ref>Morgenstern, A., et al. 2007</ref> <ref name="Baker, D. 2015">Baker, D., J. Head. 2015. Extensive Middle Amazonian mantling of debris aprons and plains in Deuteronilus Mensae, Mars: Implication for the record of mid-latitude glaciation. Icarus: 260, 269-288.</ref>

The upper plains unit is probably just a very thick pile of mantle that has dropped from the sky. It drapes various surfaces and as is the case for other mantle deposits, it has layers, is fine-grained, and is ice-rich. It is widespread; it does not seem to have a point source. The surface appearance of some regions of Mars is due to how this unit has degraded. This unit also degrades into a feature named brain terrain; it looks like the human brain. Brain terrain is a region of maze-like ridges 3–5 meters high. <ref> https://www.hou.usra.edu/meetings/lpsc2026/pdf/1626.pdf</ref> <ref>Dundas, C., et al. 2026. STRATIGRAPHIC OBSERVATIONS OF MARTIAN “BRAIN TERRAIN” AND IMPLICATIONS FOR
ORIGIN PROCESSES. 57th LPSC (2026). 1626.pdf</ref> Some ridges may consist of an ice core, so they may be sources of water for future colonists.

==Origin of Dao Vallis==

[[File:Dao Vallis.JPG|thumb|500px|Dao Vallis, as seen by THEMIS. Click on image to see relationship of Dao Vallis to other nearby features]]

Dao Vallis begins near a large volcano, called Hadriaca Patera, so it is thought to have received water when hot magma melted huge amounts of ice in the frozen ground.<ref>Carr, Michael H. (2006). The Surface of Mars. Cambridge University Press. ISBN 978-0-521-87201-0.</ref> The partially circular depressions on the left side of the channel in the adjacent image suggests that groundwater sapping also contributed water.<ref>http://themis.asu.edu/zoom-20020807a</ref>

==Dust devil tracks==

[[File:Secchi Crater Floor.JPG|thumb|Secchi Crater Floor, as seen by HiRISE. Click on image to see dust devil tracks and a pedestal crater.]]

Many areas on Mars, including the Hellas quadrangle, experience the passage of giant dust devils. A thin coating of fine bright dust covers most of the Martian surface. When a dust devil goes by it blows away the coating and exposes the underlying dark surface. Dust devils have been seen from the ground and from orbiting spacecraft. They have even blown the dust off of the solar panels of the two Mars Exploration Rovers (Spirit and Opportunity), thereby greatly extending their lives.<ref>http://marsrovers.jpl.nasa.gov/gallery/press/spirit/20070412a.html</ref> The twin Rovers were designed to last for 3 months, instead they have lasted far longer; Opportunity lasted more than 14 years. The pattern of dust devil tracks have been shown to change every few months.<ref name="mars.jpl.nasa.gov">https://web.archive.org/web/20111028015730/http://mars.jpl.nasa.gov/spotlight/kenEdgett.html |</ref> A study that combined data from the High Resolution Stereo Camera (HRSC) and the Mars Orbiter Camera (MOC) found that some large dust devils on Mars have a diameter of 700 meters and last at least 26 minutes.<ref>Reiss | first1 = D. |display-authors=etal | year = 2011 | title = Multitemporal observations of identical active dust devils on Mars with High Resolution Stereo Camera (HRSC) and Mars Orbiter Camera (MOC) | url = | journal = Icarus | volume = 215 | issue = 1| pages = 358–369 |</ref>

<gallery class="center" widths="380px" heights="360px">
Wikiwallacedevils.jpg|Dust devil tracks on floor of Wallace Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter)

File:ESP 057533 1445devilscolor.jpg|Close color view of dust devil tracks
File:57533 1445widedevil.jpg|Close color view of dust devil tracks
</gallery>

==Pedestal Craters==

Pedestal craters form when the ejecta from impacts protect the underlying material from erosion. As a result of this process, craters appear perched above their surroundings.

<gallery class="center" widths="380px" heights="360px">
ESP 047615 1275pedestal.jpg|Pedestal crater, as seen by HiRISE under HiWish program
Image:Pedestal crater3.jpg|Pedestal craters form when the ejecta from impacts protect the underlying material from erosion. As a result of this process, craters appear perched above their surroundings.

Image:Pedestaldrawingcolor2.jpg|Drawing shows a later idea of how some pedestal craters form. In this way of thinking, an impacting projectile goes into an ice-rich layer—but no further. Heat and wind from the impact hardens the surface against erosion. This hardening can be accomplished by the melting of ice which produces a salt/mineral solution thereby cementing the surface.

File:ESP 055449 1175pedestals.jpg|More pedestal craters
</gallery>

==Glacial Features==

Glaciers, loosely defined as patches of currently or recently flowing ice, are thought to be present across large but restricted areas of the modern Martian surface, and are inferred to have been more widely distributed at times in the past.<ref>"Carr">"The Surface of Mars" Series: Cambridge Planetary Science (No. 6) Michael H. Carr, United States Geological Survey, Menlo Park</ref> <ref>"Kieffer, Hugh H. Mars|url=https://books.google.com/books?id=NoDvAAAAMAAJ|accessdate=March 7, 2011|date=1992|publisher=University of Arizona Press|isbn=978-0-8165-1257-7</ref> Lobate convex features on the surface known as viscous flow features and lobate debris aprons are now almost unanimously regarded as true glaciers.<ref>Milliken | first1 = R. E. | last2 = Mustard | first2 = J. F. | last3 = Goldsby | first3 = D. L. | year = 2003 | title = Viscous flow features on the surface of Mars: Observations from high-resolution Mars Orbiter Camera (MOC) images | url = https://semanticscholar.org/paper/a822f14644d2294b948e101be2f294ac33b57ec3| journal = Journal of Geophysical Research | volume = 108 | issue = E6| page = 5057 | doi=10.1029/2002je002005 |</ref> <ref>Squyres | first1 = S.W. | last2 = Carr | first2 = M.H. | year = 1986 | title = Geomorphic evidence for the distribution of ground ice on Mars | url = | journal = Science | volume = 213 | issue = 4735| pages = 249–253 | doi = 10.1126/science.231.4735.249 | pmid = 17769645 |</ref> <ref>Head | first1 = J.W. | last2 = Marchant | first2 = D.R. | last3 = Dickson | first3 = J.L. | last4 = Kress | first4 = A.M. | year = 2010 | title = Criteria for the recognition of debris-covered glacier and valley glacier landsystem deposits | url = | journal = Earth Planet. Sci. Lett. | volume = 294 | issue = | pages = 306–320 | doi=10.1016/j.epsl.2009.06.041 | </ref> <ref>Holt | first1 = J.W. |display-authors=etal | year = 2008 | title = Radar sounding evidence for buried glaciers in the southern mid-latitudes of Mars | url = | journal = Science | volume = 322 | issue = 5905| pages = 1235–1238 |</ref> <ref>Morgan | first1 = G.A. | last2 = Head | first2 = J.W. | last3 = Marchant | first3 = D.R. | year = 2009 | title = Lineated valley fill (LVF) and lobate debris aprons (LDA) in the Deuteronilus Mensae northern dichotomy boundary region, Mars: Constraints on the extent, age and episodicity of Amazonian glacial events | url = | journal = Icarus | volume = 202 | issue = 1| pages = 22–38 | </ref> <ref>Plaut | first1 = J.J. | last2 = Safaeinili | first2 = A. | last3 = Holt | first3 = J.W. | last4 = Phillips | first4 = R.J. | last5 = Head | first5 = J.W. | last6 = Sue | first6 = R. | last7 = Putzig | first7 = A. | year = 2009 | title = Frigeri Radar evidence for ice in lobate debris aprons in the mid-northern latitudes of Mars | url = https://semanticscholar.org/paper/f6b94761e6a276ce6894374ae9bea88fdc3e5e19| journal = Geophys. Res. Lett. | volume = 36 | issue = 2| page = L02203 | </ref> <ref>Baker | first1 = D.M.H. | last2 = Head | first2 = J.W. | last3 = Marchant | first3 = D.R. | year = 2010 | title = Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian | url = | journal = Icarus | volume = 207 | issue = 1| pages = 186–209 | doi=10.1016/j.icarus.2009.11.017 | </ref> <ref>Arfstrom | first1 = J. | year = 2005 | title = Terrestrial analogs and interrelationships | url = | journal = Icarus | volume = 174 | issue = 2| pages = 321–335 | doi=10.1016/j.icarus.2004.05.026 | </ref>
A climate model, reported in the journal Science in 2006, found that large amounts of ice should accumulate in the Hellas region, in the same places where glaciers are observed. Water is transported from the south polar area to northern Hellas and falls as precipitation.<ref>Forget, F., et al. 2006. Formation of Glaciers on Mars by Atmospheric Precipitation at High Obliquity. Science: 311, 368-371.</ref>
The following pictures show many features that are probably glaciers—that is they are mostly ice and move downhill—like rivers—but much slower. Researchers started to call these things flows, but later came to understand that they are probably glaciers with a covering of debris.

<gallery class="center" widths="380px" heights="360px">
ESP 051151 1445flow.jpg|Flows, as seen by HiRISE

ESP 051162 1460flows.jpg|Flows

File:ESP 055065 1405flow.jpg|Flow
File:ESP 055091 1405flow.jpg|Flow

ESP 049527 1420tongue.jpg|Flow, as seen by HiRISE under HiWish program
49527 1420tongueclose.jpg|Close view of snout of flow, as seen by HiRISE under [[HiWish program]] Polygonal patterned ground is visible.

Wikielephantglacier.jpg|Romer Lake's Elephant Foot Glacier in the Earth's Arctic, as seen by Landsat 8. This picture shows several glaciers that have the same shape as many features on Mars that are believed to also be glaciers.

ESP 045505 1400flow.jpg|Flow feature that was probably a glacier

Image:ESP_020319flowcontext.jpg|Context for the next image of the end of a flow feature or glacier.

Image:ESP_020319flowsclose-up.jpg|Close-up of the area in the box in the previous image. This may be called by some the terminal moraine of a glacier. For scale, the box shows the approximate size of a football field.

Image:Tongue23141.jpg|Tongue-shaped glacier, Ice may exist in the glacier, even today, beneath an insulating layer of dirt.

Image:Tongue23141close.jpg|Close-up of tongue-shaped glacier Resolution is about 1 meter, so one can see objects a few meters across in this image.

45070 1440polygonscloseshadows.jpg|Close view of high center polygons near glacier Box shows size of football field.

ESP 047193 1440tongues.jpg|Wide view of tongue-shaped flows
47193 1440tonguesclose.jpg|Close view of tongue-shaped flows

47193 1440polygonsclose2.jpg|Close view of polygonal terrain near tongue-shaped flows, as seen by HiRISE under the HiWish program

File:Ice rich flows near Hellas ESP 025646 1440.jpg|Tongue-shaped flows going down crater wall, as seen by HiRISE

</gallery>

[[File: 45070 1440glacialsnout.jpg|600pxr|High center polygons are visible. Box shows size of football field.]]

High center polygons are visible. Box shows size of football field.

Picture below shows material moving through a crater rim Lateral moraines are labeled.

[[File:20543 gap in crater rim.jpg|300pxr|Material Flowing through a crater rim Lateral moraines are labeled.]]

==Channels==

[[File:48196 1460channels.jpg|600pxr|Channels,as seen by HiRISE under the HiWish program]]

Channels,as seen by HiRISE under the [[HiWish program]]

Today, it is generally accepted that water once flowed in river valleys on Mars.<ref>Baker | first1 = V. |display-authors=etal | year = 2015 | title = Fluvial geomorphology on Earth-like planetary surfaces: a review | url = | journal = Geomorphology | volume = 245 | issue = | pages = 149–182 | doi=10.1016/j.geomorph.2015.05.002|</ref> <ref>Carr, M. 1996. in Water on Mars. Oxford Univ. Press.</ref> Images of curved channels have been seen in images from Mars spacecraft dating back to the early seventies with the [[Mariner 9]] orbiter.<ref>Baker, V. 1982. The Channels of Mars. Univ. of Tex. Press, Austin, TX</ref> <ref>Baker | first1 = V. | last2 = Strom | first2 = R. | last3 = Gulick | first3 = V. | last4 = Kargel | first4 = J. | last5 = Komatsu | first5 = G. | last6 = Kale | first6 = V. | year = 1991 | title = Ancient oceans, ice sheets and the hydrological cycle on Mars | url = | journal = Nature | volume = 352 | issue = 6336| pages = 589–594 | doi=10.1038/352589a0 | </ref> <ref>Carr | first1 = M | year = 1979 | title = Formation of Martian flood features by release of water from confined aquifers | url = | journal = J. Geophys. Res. | volume = 84 | issue = | pages = 2995–300 | doi=10.1029/jb084ib06p02995 |</ref> <ref>Komar | first1 = P | year = 1979 | title = Comparisons of the hydraulics of water flows in Martian outflow channels with flows of similar scale on Earth | url = | journal = Icarus | volume = 37 | issue = 1| pages = 156–181 | doi=10.1016/0019-1035(79)90123-4 |</ref> Indeed, a study published in June 2017, calculated that the volume of water needed to carve all the channels on Mars was even larger than the proposed ocean that the planet may have had. <ref>http://spaceref.com/mars/how-much-water-was-needed-to-carve-valleys-on-mars.html</ref> <ref>Luo, W., et al. 2017. New Martian valley network volume estimate consistent with ancient ocean and warm and wet climate. Nature Communications 8. Article number: 15766 (2017). </ref>

<gallery class="center" widths="380px" heights="360px">

ESP 041972 1490channel.jpg|Streamlined shape in old river valley The streamlined shape is evidence of running water.

ESP 045492 1430channel.jpg|Channel, as seen by HiRISE under [[HiWish program]]

ESP 045492 1430channeltop.jpg|Channel

</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 048855 1450channels.jpg|Channel network

ESP 050964 1410channel.jpg|Channels

File:Small channels 82746 1395.jpg|Wide view of channel network, as seen by HiRISE under HiWish program Colored strip in center is about 1 km across.

</gallery>

[[File: ESP 052494 1395meanders.jpg|600pxr|Channel Arrows indicate evidence of a meander.]]

Channel Arrows indicate evidence of a meander.

==Layers==

[[File:48144 1475cubes.jpg|thumb|500px|center|Close view of layers Some layers are breaking up.]]

Many places on Mars show rocks arranged in layers. Rock can form layers in a variety of ways. Volcanoes, wind, or water can produce layers.<ref>http://hirise.lpl.arizona.edu?PSP_008437_1750 |title=HiRISE | High Resolution Imaging Science Experiment |publisher=Hirise.lpl.arizona.edu?psp_008437_1750 |</ref> A detailed discussion of layering with many Martian examples can be found in Sedimentary Geology of Mars.<ref>Grotzinger, J. and R. Milliken (eds.). 2012. Sedimentary Geology of Mars. SEPM.</ref>

<gallery class="center" widths="380px" heights="360px">

ESP 045507 1470layeredcrater.jpg|Close view of layered deposit in crater

45507 1470layerswhite.jpg|Layered formation
45507 1470layerswhiteclose.jpg|Close view of layers from previous image, as seen by HiRISE under [[HiWish program]]

47154 1410layersclose.jpg|Close view of layers

File:47154 1410layerscolor.jpg|Close, color view of layers Different colors mean different minerals.
</gallery>

<gallery class="center" widths="380px" heights="360px">

48144 1475layers.jpg|Close view of layers
48144 1475layerscubes.jpg|Close view of layers Some of the layers are breaking up into large blocks

</gallery>

<gallery class="center" widths="380px" heights="360px">
File:54763 1500layers.jpg|Close view of light and dark toned layers Some layers are light-toned which means that they may have been associated with water.
File:54763 1500layers2.jpg|Close view of light and dark toned layers
File:54763 1500layerscolor.jpg|Close, color view of layers The different colors represent different minerals.
</gallery>
<gallery class="center" widths="380px" heights="360px">

File:55053 1485layersclosecolor.jpg|Close, color view of layers The different colors represent different minerals.
File:55053 1485layersclosecolor2.jpg|Close, color view of layers Note: this image is only partial in color because HiRISE only has color ability in a center strip.
</gallery>

<gallery class="center" widths="380px" heights="360px">

File:55581 1470layered mounds.jpg|Close view of layers in mound
</gallery>

==Honeycomb terrain==

Honeycomb terrain is strangely beautiful. It presents with relatively flat-lying “cells” that appear to have concentric layers or bands, similar to a honeycomb. This "honeycomb" terrain was first discovered in the northwestern part of Hellas.<ref>Bernhardt | first1 = H. |display-authors=etal | year = 2016 | title = The honeycomb terrain on the Hellas basin floor, mars: a case for salt or ice diapirism: hellas honeycombs as salt/ice diapirs | url = | journal = J. Geophys. Res. | volume = 121 | issue = 4| pages = 714–738 | doi=10.1002/2016je005007| </ref> Although several ideas have been put forth, the exact geologic process responsible for creating these features remains unresolved.<ref>https://www.uahirise.org/hipod/ESP_085926_1410</ref> <ref>https://www.hou.usra.edu/meetings/lpsc2022/pdf/1588.pdf</ref> <ref>Cook, C., et al. 2022. FORMATION OF THE BANDED TERRAIN OF HELLAS PLANITIA, MARS. 53rd Lunar and Planetary Science Conference (2022). 1588.pdf</ref> <ref>http://www.uahirise.org/ESP_049330_1425</ref> Some calculations indicate that this formation may have been caused by ice moving up through the ground in this region. The ice layer would have been between 100 m and 1 km thick.<ref>Weiss, D., J. Head. 2017. HYDROLOGY OF THE HELLAS BASIN AND THE EARLY MARS CLIMATE: WAS THE HONEYCOMB TERRAIN FORMED BY SALT OR ICE DIAPIRISM? Lunar and Planetary Science XLVIII. 1060.pdf</ref> <ref>Weiss | first1 = D. | last2 = Head | first2 = J. | year = 2017 | title = Salt or ice diapirism origin for the honeycomb terrain in Hellas basin, Mars?: Implications for the early martian climate | url = | journal = Icarus | volume = 284 | issue = | pages = 249–263 | doi=10.1016/j.icarus.2016.11.016 | </ref> <ref>Bernhardt | first1 = H. |display-authors=etal | year = 2016 | title = The honeycomb terrain on the Hellas basin floor, mars: a case for salt or ice diapirism: hellas honeycombs as salt/ice diapirs | url = | journal = J. Geophys. Res. | volume = 121 | issue = 4| pages = 714–738 | doi=10.1002/2016je005007| </ref> When one substance moves up through another denser substance, it is called a “diapir.” In this idea, large masses of ice pushed up layers of rock into domes that were subsequently eroded. After erosion cut off the top of the layered domes, circular features remained.
Diapirs are thought to be responsible for features on Neptune's moon Triton, Jupiter's moon Europa, Saturn's moon Enceladus, and Uranus's moon Miranda.<ref>Cassini Imaging Central Laboratory for Operations, [http://ciclops.org/view/5156/Enceladus_Rev_80_Flyby Enceladus Rev 80 Flyby: Aug 11 '08]. Retrieved 2008-08-15.</ref>

<gallery class="center" widths="380px" heights="360px">

ESP 046139 1375ridgeslayers.jpg|Layers and ridges that form strange patterns

</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 049330 1425honeycomb.jpg|Honeycomb terrain

File:68704 1455honeycomb terrain.jpg|Honeycomb terrain, as seen by HiRISE under HiWish program
File:ESP 057110 1365ridges.jpg|Ridges

File:ESP 057110 1365ridgescircles.jpg|Close view of concentric and parallel ridges, as seen by HiRISE under [[HiWish program]]

</gallery>

==Ridge networks==

Networks of ridges sometimes show up in low areas like crater floors. There origin is not completely understood.

<gallery class="center" widths="380px" heights="360px">

File:ESP 057111 1455ridges.jpg|Wide view of ridge network

File:ESP 057111 1455ridges3.jpg|Close view of ridge network, as seen by HiRISE under [[HiWish program]]

File:57111 1455ridgenetwork.jpg|Close view of ridge network
</gallery>

==Gullies==

[[File:57044 1325curvedgullies.jpg|thumb|500px|center|Close view of gullies, as seen by HiRISE under HiWish program Curves in channels are evidence that these gullies were not created by landslides.]]

Gullies occur on steep slopes, especially on the walls of craters. Gullies are believed to be relatively young because they have few, if any craters. Moreover, they lie on top of sand dunes which themselves are considered to be quite young. Usually, each gully has an alcove, channel, and apron.<ref>Edgett |first1= K. |last2= Malin |first2= M. C. |last3= Williams |first3= R. M. E. |last4= Davis |first4= S. D. |date= 2003 |title= Polar-and middle-latitude martian gullies: A view from MGS MOC after 2 Mars years in the mapping orbit |journal= Lunar Planet. Sci. |volume=34 |at=p. 1038, Abstract 1038 | url=http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1038.pdf |</ref> <ref>Dickson | first1 = J | last2 = Head | first2 = J | last3 = Kreslavsky | first3 = M | title = Martian gullies in the southern mid-latitudes of Mars: Evidence for climate-controlled formation of young fluvial features based upon local and global topography | doi = 10.1016/j.icarus.2006.11.020 | </ref> <ref>http://www.planetary.brown.edu/pdfs/3138.pdf | date = 2007 | pages = 315–323 | volume = 188 | issue = 2 | journal = Icarus | </ref>
For years, many believed that gullies were formed by running water, but further observations demonstrate that they may be formed by dry ice. Recent studies, using the High Resolution Imaging Science Experiment (HiRISE) camera on the [[Mars Reconnaissance Orbiter]] (MRO), examined gullies at 356 sites, starting in 2006. Thirty-eight of the sites showed active gully formation. Before-and-after images demonstrated the timing of this activity coincided with seasonal carbon dioxide frost and temperatures that would not have allowed for liquid water. When dry ice frost changes to a gas, it may lubricate dry material to flow especially on steep slopes.<ref>http://www.jpl.nasa.gov/news/news.php?release=2014-226</ref> <ref>http://hirise.lpl.arizona.edu/ESP_032078_1420</ref><ref>http://www.space.com/26534-mars-gullies-dry-ice.html</ref> In some years frost, perhaps as thick as 1 meter, triggers avalanches. This frost contains mostly dry ice, but also has tiny amounts of water ice.<ref>http://spaceref.com/mars/frosty-gullies-on-mars.html</ref>

<gallery class="center" widths="380px" heights="360px">
49185 1350gully.jpg|Close view of small gully

File:ESP 084659 1355 gullies cropped 01.jpg|Wide view of gullies
File:ESP 084659 1355 gullies cropped 02.jpg|Close view of gully alcoves Picture is about 1 km across.
File:ESP 084659 1355 gullies cropped 03.jpg|Close view of gully alcoves Picture is about 1 km across.
File:ESP 084659 1355 gullies cropped 04.jpg|Close view of gully channels Picture is about 1 km across.
File:57044 1325colorgullies.jpg|Close, color view of gullies
File:ESP 084896 1355 small gullies 02.jpg|Gullies, as seen by HiRISE. The gullies range from very samll to large, as such they may represent different stages in the formation of gullies. The colored strip is about 1 km wide.
File:ESP 084896 1355 small gullies 03.jpg|Small gully This gully may be in its initial state of formation.
File:ESP 084896 1355 small gullies 04.jpg|Gully, as seen by HiRISE
</gallery>

[[File:ESP 048881 1415gullies.jpg|thumb|500px|center|Gullies in crater]]

[[File:48881 1415polygons.jpg|600pxr|Close view of gullies in crater Polygons are visible in this close view.]]

Close view of gullies in crater Polygons are visible in this close view.

==Polygons==

Some surfaces on Mars display polygons. These may be of different sizes. Polygons are an example of patterned ground. Polygonal, patterned ground is quite common in some regions of Mars.<ref>Kostama | first1 = V.-P. | last2 = Kreslavsky | first2 = M. | last3 = Head | first3 = J. | year = 2006 | title = Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement | url = | journal = Geophys. Res. Lett. | volume = 33 | issue = 11| page = L11201 | doi = 10.1029/2006GL025946 |</ref> <ref>Malin | first1 = M. | last2 = Edgett | first2 = K. | year = 2001 | title = Mars Global Surveyor Mars Orbiter Camera: Interplanetary cruise through primary mission | url = | journal = J. Geophys. Res. | volume = 106 | issue = E10| pages = 23429–23540 | doi=10.1029/2000je001455 | </ref> <ref>Milliken | first1 = R. |display-authors=etal | year = 2003 | title = Viscous flow features on the surface of Mars: Observations from high-resolution Mars Orbiter Camera (MOC) images | url = https://semanticscholar.org/paper/a822f14644d2294b948e101be2f294ac33b57ec3| journal = J. Geophys. Res. | volume = 108 | issue = | page = |</ref> <ref>Mangold | first1 = N | year = 2005 | title = High latitude patterned grounds on Mars: Classification, distribution and climatic control | url = | journal = Icarus | volume = 174 | issue = 2| pages = 336–359 | doi=10.1016/j.icarus.2004.07.030 |</ref> <ref>Kreslavsky | first1 = M. | last2 = Head | first2 = J. | year = 2000 | title = Kilometer-scale roughness on Mars: Results from MOLA data analysis | url = | journal = J. Geophys. Res. | volume = 105 | issue = E11| pages = 26695–26712 | doi=10.1029/2000je001259 |</ref> <ref>Seibert | first1 = N. | last2 = Kargel | first2 = J. | year = 2001 | title = Small-scale martian polygonal terrain: Implications for liquid surface water | url = | journal = Geophys. Res. Lett. | volume = 28 | issue = 5| pages = 899–902 | doi=10.1029/2000gl012093 |</ref>

<gallery class="center" widths="380px" heights="360px">
49185 1350polygons.jpg|Group of polygons
File:040310 1475flagstones.jpg|Patterned ground in Hellas The rectangle shows the size of a football field.
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 049660 1200polygons.jpg|Wide view of polygons Parts of this image are enlarged in following images.
49660 1200polygonswide.jpg|Polygons
49660 1200polygonsrockscraters.jpg|Close view of polygons Arrow point to boulders that sit inside of small craters.

49660 1200polygonspits.jpg|Close view of polygons

49660 1200polygonsrockscratersclose.jpg|Close view of polygons, as seen by HiRISE under [[HiWish program]]
</gallery>

==Exposed ice sheets==

Thick deposits of ice were found by a team of researchers using instruments on board the [[Mars Reconnaissance Orbiter]] (MRO).<ref>Dundas, E., et al. 2018. Exposed subsurface ice sheets in the martian mid-latitudes. Science. 359. 199.</ref> The team of scientists found eight eroding slopes that showed exposed water ice sheets as thick as 100 meters. Seven of the locations were in the southern hemisphere. Much evidence of buried ice under the ground on vast regions of Mars has already been found by past studies, but this study found that the ice was only covered by a layer of about 1 or 2 meters thick of Martian soil.<ref>https://www.jpl.nasa.gov/news/news.php?feature=7038 Steep Slopes on Mars Reveal Structure of Buried Ice]. NASA Press Release. 11 January 2018.</ref> <ref>http://www.sciencemag.org/news/2018/01/ice-cliffs-spotted-mars Ice cliffs spotted on Mars. ''Science News''. Paul Voosen. 11 January 2018.</ref> <ref>https://www.slideshare.net/sacani/exposed-subsurface-ice-sheets-in-the-martian-midlatitudes</ref> Shane Byrne of the University of Arizona Lunar and Planetary Laboratory, Tucson, one of the co-authors remarked that future colonists of the Red Planet would be able to gather up ice with just a bucket and shovel.<ref>http://spaceref.com/mars/steep-slopes-on-mars-reveal-structure-of-buried-ice.html</ref>
The layered ice is exposed in triangular shaped depressions. They are unique in that one wall is very steep and faces the pole. Confirmation that water-ice makes up the layers came from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the [[Mars Reconnaissance Orbiter]] (MRO). Spectra gathered by CRISM showed strong signals of water.<ref>Colin M. Dundas, et al. ''Science'', 12 January 2018. Vol. 359, Issue 6372, pp. 199-201. </ref> These layers are especially prominent in depressions in Hellas quadrangle as shown in the enlarged views below.

<gallery class="center" widths="380px" heights="360px">
PIA22078 hireswideview.jpg|Wide view of triangular depression The colored strip shows the part of the image that can be seen in color. The wall at the top of the depression contains pure ice. This wall faces the south pole. <ref>Supplementary Materials Exposed subsurface ice sheets in the Martian mid-latitudes Colin M. Dundas, Ali M. Bramson, Lujendra Ojha, James J. Wray, Michael T. Mellon, Shane Byrne, Alfred S. McEwen, Nathaniel E. Putzig, Donna Viola, Sarah Sutton, Erin Clark, John W. Holt</ref>

PIA22077 hirescloseblue.jpg|Close, color view of wall containing ice from previous image
</gallery>

<gallery class="center" widths="380px" heights="360px">
ESP 050345 1230icelayersangles.jpg|Wide view of triangular depression The wall which faces the south pole contains ice in distinct layers that are visible in next image. <ref>Supplementary Materials Exposed subsurface ice sheets in the Martian mid-latitudes Colin M. Dundas, Ali M. Bramson, Lujendra Ojha, James J. Wray, Michael T. Mellon, Shane Byrne, Alfred S. McEwen, Nathaniel E. Putzig, Donna Viola, Sarah Sutton, Erin Clark, John W. Holt</ref>

50477 1230icelayersangular.jpg|Close view of wall of triangular depression, as seen by HiRISE layers are visible in the wall. The lower layers are tilted, while layers near the surface are more or less horizontal. Such an arrangement of layers is called an "angular unconformity."
</gallery>

Besides being of great value to future explorers, these ice layers could help us better understand the climate history of Mars. They provide a record of the past. The large variations in the tilt of the planet cause dramatic climate variations. Mars does not possess a large moon to keep its tilt stable. Today, ice is concentrated at the poles, with a greater tilt, more ice will exist at mid-latitudes.
These climate changes may be able to be measured with study of these layers.

These triangular depressions are similar to those in scalloped terrain. However scalloped terrain, displays a gentle equator-facing slope and is rounded. Scalloped terrain lacks the sharp vertical wall of these depressions.

==Scalloped topography==

Scalloped topography is common in the mid-latitudes of Mars, between 45° and 60° north and south. In the region around Hellas it is found in locations called Peneus Patera and Amphitrites Paterae<ref>Lefort | first1 = A. | last2 = Russell | first2 = P. | last3 = Thomas | first3 = N. | year = 2009 | title = Scalloped terrains in the Peneus and Amphitrites Paterae region of Mars as observed by HiRISE | journal = Icarus | volume = 205| issue = 1 | pages = 259–268| doi = 10.1016/j.icarus.2009.06.005 |</ref> <ref>Zanetti, M., Hiesinger,H., Reiss, D., Hauber, E. and Neukum, G. 2009. http://www.lpi.usra.edu/meetings/lpsc2009/pdf/2178.pdf "Scalloped Depression Development on Malea Planum and the Southern Wall of the Hellas Basin, Mars", 40th Lunar and Planetary Science Conference, abstract 2178</ref> in the southern hemisphere. It consists of shallow, rimless depressions with scalloped edges, commonly referred to as "scalloped depressions" or simply "scallops". Scalloped depressions can be isolated or clustered and sometimes seem to coalesce. A typical scalloped depression displays a gentle equator-facing slope and a steeper pole-facing scarp.<ref>http://www.uahirise.org/ESP_038821_1235</ref> <ref>Dundas, C., et al. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref> Scalloped depressions are believed to form from the removal of subsurface material, possibly interstitial ice, by sublimation (direct transition of a material from the solid to the gas phase with no intermediate liquid stage). This process may still be happening at present.<ref>http://hiroc.lpl.arizona.edu/images/PSP/diafotizo.php?ID=PSP_002296_1215|title=Scalloped<nowiki> Topography in Peneus Patera Crater|publisher=HiRISE Operations Center|date=2007-02-28|accessdate=2014-11-24}}</nowiki></ref> This topography may be of great importance for future colonization of Mars because it may point to deposits of pure ice.<ref>Dundas | first1 = C. | last2 = Bryrne | first2 = S. | last3 = McEwen | first3 = A. | year = 2015 | title = Modeling the development of martian sublimation thermokarst landforms | url = | journal = Icarus | volume = 262 | issue = | pages = 154–169 | doi=10.1016/j.icarus.2015.07.033 |</ref>

<gallery class="center" widths="380px" heights="360px">
Image:Scalop formation.jpg|Stages in scalop formation, as seen by HiRISE. These formations probably form from the sublimation of ground rich in pure water ice many meters in depth.<ref name="ReferenceC">Dundas, C., S. Bryrne, A. McEwen. 2015. Modeling the development of martian sublimation thermokarst landforms. Icarus: 262, 154-169.</ref>
ESP 049304 1215scallops.jpg|Scalloped terrain, as seen by HiRISE under HIWish program Dust devil tracks are also visible.
</gallery>

==Crater Lakes==

Many craters on Mars probably became lakes. <ref> Fassett C. I. and Head J. W. 2008. Icarus. 195 61</ref> <ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346</ref> There could have been several sources for the water. Like:
(1) Runoff and River Inlets: Many craters show evidence of channels eroded into their rims, indicating that water flowed across the landscape and broke through the crater walls. Dense, branching valley networks across the southern highlands suggest that ancient rain or snowmelt carved channels that eventually breached crater rims. <ref>Bamber, E. R., Goudge, T. A., Fassett, C. I., Osinski, G. R., & Stucky de Quay, G. (2022). Paleolake inlet valley formation: Factors controlling which craters breached on early Mars. Geophysical Research Letters, 49, e2022GL101097. https://doi.org/10.1029/2022GL101097</ref>
(2) Glacial Melting: Researchers have found evidence that some lakes were fed by runoff from glaciers. In this scenario, glaciers occupying the area, or sitting on the crater walls, melted and transported water to the center of the crater.
(3) Groundwater Sapping: In some cases, water may have broken through the ground surface, known as groundwater sapping, feeding the lake from below or through the crater walls.<ref> Goudge T. A., Aureli K. L., Head J. W., Fassett C. I. and Mustard J. F. 2015 Icarus. 260 346
</ref> <ref>Salese F., Pondrelli M., Neeseman A., Schmidt G. and Ori G. G. 2019. JGRE. Vol. 124. P. 374</ref> Some craters, like McLaughlin Crater, lack large surface inflow channels. Instead, they feature layered rocks containing carbonate and clay minerals, suggesting that groundwater from underground aquifers came up through fractures in the crater floor.<ref>https://www.jpl.nasa.gov/news/martian-crater-may-once-have-held-groundwater-fed-lake/</ref>

Once water accumulated in a crater, it behaved in ways similar to terrestrial lakes.
Delta Formation: As water entered the crater via an inlet channel, it slowed down and dropped its sediment load, creating fan-shaped structures known as deltas. The Perseverance Rover has documented these, along with sloping layers known as foreset beds, which are characteristic of deltas building into a lake. At times, water input was so significant that the lakes filled to the brim and overflowed the crater rim, creating outlet canyons and changing the surrounding landscape.

<gallery class="center" widths="380px" heights="360px">
File:ESP 078227 2195lake.jpg|Channels that filled crater to make a crater lake, as seen by HiRISE under HiWish program.
File:91766 1455 open crater lake.jpg|Open crater lake--it has both an inlet and and outflow channel.
</gallery>

Martian crater lakes may have lasted from a million years down to just a century.<ref>https://www.nhm.ac.uk/discover/news/2022/september/ancient-crater-lakes-mars-could-have-hosted-life.html</ref>

==Additional Images in Hellas quadrangle==

[[File:ESP 043554 1440dike.jpg|600pxr|Possible dike and troughs The arrows point to the possible dike along the left edge of picture. Straight features are rare in nature; they are often due to dikes and joints.]]

Possible dike and troughs The arrows point to the possible dike along the left edge of picture. Straight features are rare in nature; they are often due to dikes and joints.

<gallery class="center" widths="380px" heights="360px">

File:55421 1395ribbed.jpg|Hollows on floor of Reull Vallis, as seen by HiRISE under HiWish program

Image:Banded terrain in Hellas.JPG|Banded or taffy-pull terrain in Hellas, as seen by [[Mars Global Surveyor]]. Origin is unknown at present.

</gallery>

[[File:45571 1375cracks.jpg|600pxr|Ridges forming from cracks Box in upper left shows size of football field. Just imagine trying to hike across such a landscape.]]

Ridges forming from cracks Box in upper left shows size of football field. Just imagine trying to hike across such a landscape.

<gallery class="center" widths="380px" heights="360px">
48196 1460meteoriteclose.jpg|Out of place rock The arrow points to a large rock that is definitely out of place. It may be a meteorite or it may have been tossed here by a nearby impact.

48196 1460meteoriteclosest.jpg|Close view of out of place rock, as seen by HiRISE under [[HiWish program]] It may be a meteorite or it may have been tossed here by a nearby impact.
</gallery>

==External links==

*[https://www.youtube.com/watch?v=Rws1mj1mnIc A trip to Mars with Hubble, Viking, and HiRISE]
*https://www.hou.usra.edu/meetings/lpsc2022/pdf/2069.pdf HELLAS BASIN: WITNESS PLATE FOR DECONVOLVING THE GEOLOGIC AND CLIMATIC
HISTORY OF MARS. Shows map of water related features.

==See also==

*[[Dark slope streaks]]
*[[Geography of Mars]]
*[[Glaciers on Mars]]

*[[High Resolution Imaging Science Experiment (HiRISE)]]
*[[HiWish program]]
*[[How are features on Mars Named?]]
*[[Layers on Mars]]
*[[Mars Global Surveyor]]
*[[Martian features that are signs of water ice]]
*[[Martian gullies]]
*[[Rivers on Mars]]

==References:==
{{Reflist|2}}

[[Category:Mars Atlas]]