View source for Periodic climate changes on Mars

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

Many features on Mars  contain large amounts of ice.  Many of these have formed beautiful forms.  The most popular model for the origin of the ice is climate changes caused by  large changes in the tilt of the planet's rotational axis.  At times the tilt has even been greater than 80 degrees.
<ref> last1 = Touma | first1 = J. | last2 = Wisdom | first2 = J. | year = 1993 | title = The Chaotic Obliquity of Mars | url = | journal = Science | volume = 259 | issue = | pages = 1294–1297 | doi=10.1126/science.259.5099.1294| </ref> <ref > | last1 = 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 = | pages = 343–364 | doi=10.1016/j.icarus.2004.04.005 | </ref>  
Large changes in the tilt explains how some places on Mars accumulated ice .  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.
<ref>| last1 = Levy | first1 = J. | last2 = 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 = | page =  | doi = 10.1029/2007GL032813 | </ref>  
Furthermore, at high degrees of tilt, stores of solid carbon dioxide (dry ice) sublimate, thereby increasing the atmospheric pressure.  Under current Martian atmospheric conditions both water ice and dry ice sublimate, that is they change directly from a solid phase to a gas phase.  Increased pressure  from higher carbon dioxide levels allows more dust to be held in the atmosphere.  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.
<ref> | last1 = Levy | first1 = J. | last2 = Head | first2 = J. | last3 = Marchant | first3 = D. | year = 2009a | title = Thermal contraction crack polygons on Mars: Classification, distribution, and climate implications from HiRISE observations | url = | journal = J. Geophys. Res. | volume =  114| issue = | page =  | doi = 10.1029/2008JE003273 | </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>  
General circulation models of the Martian atmosphere predict accumulations of ice-rich dust in the same areas where ice-rich features are found.
<ref name="ReferenceC"/> 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 name="Mellon, M. 1995">| last1 = Mellon | first1 = M. | last2 = Jakosky | first2 = B. | year = 1995 | title = The distribution and behavior of Martian ground ice during past and present epochs | url = | journal = J. Geophys. Res. | volume = 100 | issue = | pages = 11781–11799 | doi=10.1029/95je01027 | </ref> <ref name="Mellon, M. 1995"/><ref> | last1 = Schorghofer | first1 = N | year = 2007 | title = Dynamics of ice ages on Mars | url = | journal = Nature | volume = 449 | issue = | pages = 192–194 | doi=10.1038/nature06082| </ref>   
The lag deposit caps the underlying material so with each cycle of high tilt levels, some ice-rich mantle remains behind thereby insulating and preserving ice.
<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>  
Note, that the smooth surface mantle layer probably represents only relative recent material.

==Latitude Dependent Mantle==

With the increasing resolution of cameras orbiting Mars, we have discovered that many parts of the planet are covered by a smooth coating that in some cases is layered and quite thick. <ref>Mustard, J., C. Cooper, M. Rifkin.   2001.  Evidence for recent climate change on Mars from the identification of youthful near-surface ground ice. Nature 412, 411–414 .</ref>  Some parts are eroded, revealing rough surfaces.  Some parts possess layers.  It’s generally accepted that mantle is ice-rich dust that fell from the sky as snow and ice-coated dust grains during a different climate <ref> Pollack, J., D. Colburn, F. Flaser, R. Kahn, C. Carson, and D. Pidek.   1979.  Properties and effects of dust suspended in the martian atmosphere.  J. Geophys. Res.  84, 2929-2945. </ref>  Latitude Dependent Mantle and many other supposed ice-rich features occur in two rather wide  latitude bands in the mid-latitudes; 30-60 degrees North and 30-60 degrees South latitudes.    
There are many features with layers that may have been deposited as latitude dependent mantle in past times.  Later they were sculptured by winds into strange, beautiful shapes.  Some are in craters; others are leaning against steep walls.
<gallery class="center" widths="190px" heights="180px">
File:54996 2155mantle.jpg|Close view of latitude dependent mantle
File:55198 2170mantleclose.jpg| Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program
File:54742 1485mantle.jpg |Surface showing appearance with and without mantle covering, as seen by HiRISE, under the HiWish program 
</gallery>

<gallery class="center" widths="190px" heights="180px">

File:ESP 054934 2160pyramid.jpg|Mantle layers eroded and shaped by winds
File:ESP 055104 1385pyramid.jpg|Mantle layers eroded and shaped by winds
File:55198 2170dipping.jpg|Dipping layers against wall  These are probably the remains of mantle layers from past climate changes.
</gallery>

==Glacial Features==

Satellite observations show  features that  look like glaciers.  It is believed that ice is flowing under a thin cover of debris.  Although ice is not stable at many latitudes of Mars, ice could survive for long periods under a few meters of dirt and rock.  Many of these supposed regions of underground ice generally begin around 30 degrees of latitude on both sides of the equator.  In other words latitudes greater than 30 degrees may have glaciers.<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>
Some bare an uncanny resemblance to alpine or mountain glaciers of the Earth.  These, supposed alpine glaciers, have been called glacier-like forms (GLF) or glacier-like flows (GLF). <ref> Arfstrom, J and W. Hartmann.  2005.  Martian flow features, moraine-like ridges, and gullies:  Terrestrial analogs and interrelationships.  Icarus 174, 321-335.</ref>   <ref> Hubbard B., R. Milliken, J. Kargel , A. Limaye, C. Souness .  2011.  Geomorphological characterization and interpretation of a mid-latitude glacier-like form: Hellas Planitia, Mars Icarus 211, 330–346 </ref>  Another, more general term sometimes seen in the literature is viscous flow features (VFF). <ref> Hubbard B., R. Milliken, J. Kargel , A. Limaye, C. Souness .  2011.  Geomorphological characterization and interpretation of a mid-latitude glacier-like form: Hellas Planitia, Mars Icarus 211, 330–346 </ref> 

<gallery class="center" widths="190px" heights="180px" >
File:ESP 018857 2225alpineglacier.jpg |Alpine glacier moving from a valley  Lat: 42.2° N Long: 50.5° E
File:  Wikielephantglacier.jpg|Glacier in Greenland Notice how is resembles the glacier on Mars.
File:ESP 047193 1440tongues.jpg|Tongue-shaped glaciers  Lat: 35.6° S Long: 109.7° E

File:ESP 054973 1405tongue.jpg|Old glacier that has lost most of its ice
</gallery>

==Ice Cap Layers==
A sign that the Martian climate has changed was  discovered early on  in the northern ice cap of Mars. It displays many layers of ice that accumulated when the climate changed.  These are visible in the walls of canyons.
<gallery class="center" widths="190px" heights="180px" >
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 removed some layers at the right.
</gallery>

==Brain Terrain==

Brain terrain is a region of maze-like ridges 3–5 meters high.  Brain terrain probably stars when cracks form in ice-rich ground—ground that was produced when the climate was different.  Along the cracks there is increased sublimation of ice.  As more and more ice disappears by sublimation, the cracks widen.   Some ridges may consist of an ice core, so they may be sources of water for future colonists.<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="190px" heights="180px" >
File:54526 2220brainscracks.jpg|Brain terrain and a field of cracks that will develop into brain terrain, as sublimation takes place along the crack surfaces
File:54996 2155brains.jpg|Close, color view of brain terrain
File:55027 2250hollows.jpg|Color view of some hollows and some brain terrain

File:ESP 035208 2215brainslabeledmarspedia.jpg|Wide view of brain terrain in the Ismenius Lacus quadrangle
File:45917 2220brainsforming.jpg|Brain terrain forming in Ismenius Lacus quadrangle
</gallery>
==Ribbed terrain==
Ribbed terrain forms as ice leaves the ground along cracks in a process called "
[[sublimation]]."  So much of the ground is ice that when the ice disappears the ground collapses.  The ice goes into the atmosphere.  Dust left behind is eventually just blown away, leaving wide valleys and hallows.<ref>https://en.wikipedia.org/wiki/Upper_Plains_Unit</ref>
<gallery class="center" widths="190px" heights="180px" >
File:ESP 047499 2245ribswide.jpg|Wide view of ribbed terrain in Ismenius Lacus quadrangle
File:ESP 028339 2245headarticle.jpg|Ribbed terrain in Ismenius Lacus quadrangle

File:54896 2240hollow.jpg|Hollowed terrain  Some of the cracks visible in image may eventually turn into ribbed or hollowed terrain, as sublimation progresses
File:ESP 054896 2240hollowsrelease.jpg|Close, color view of hollowed terrain  
</gallery>

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

==See Also==

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