Ritchey Crater

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Mars topography (MOLA dataset) HiRes (1).jpg


Ritchey Crater is located in the Coprates quadrangle at 28.8° South and 51° West. It measures 79 kilometers across and was named after the American astronomer George W. Ritchey. [1] Ritchey lies south of Valles Marineris and north of Argyre Planitia, a large impact crater.[2]

  • Topography of Ritchey Crater


Importance

There is strong evidence that it was once a lake.[3] [4] Ritchey Crater has been suggested as a landing site for a Mars Rover.[5] A thick sequence of sedimentary deposits that include clay is found in the crater; these deposits are strong evidence that a lake once existed here.[6] [7] Finding clay is significant because it forms in water with a pH close to neutral. This type of environment would support life, and clay can form well-preserved fossils. The presence of fluvial features along crater wall and rim, as well as alluvial/fluvial deposits is additional evidence of abundant past water.

Ritchey Crater layers, as seen by HiRISE. The dark cap layer seems to be resistant to erosion, while the white middle layer is weak. Scale bar is 500 meters long.
Western side of Ritchey Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter).
Fan along western wall of Ritchey Crater, as seen by CTX camera (on Mars Reconnaissance Orbiter). Note: this is an enlargement of previous image.

Description

It formed later than the Noachian period. Pictures from HiRISE show that the central peak has massive bedrock and megabreccia with large clasts.[8] Ritchey Crater holds several different layers. A dark layer at the top forms a cap rock that protects the underlying layers from erosion. Under this hard, dark layer is a softer, light-toned rock that breaks into small boulders. The layers might be formed of volcanic ash, lake or stream deposits, or sand dunes.[9] Fluvial channels and fan deposit are common on and along the walls.[10] Clay minerals have been found in Ritchy.[11] [12] [13] These minerals indicate that water was present for a time. Evidence of smectite clay was found around the central uplift of the crater. The clay was probably formed as a result of the impact. The heat from the impact allowed liquid water to be around long enough to turn minerals into clay. Researchers at Brown University discovered impact melt deposits containing clay minerals in Ritchey Crater. Impact melt is created when rock melted during an impact cools and hardens. [14] Smectite clays can absorb water, as a result they shrink and swell depending on how much water they contain. [15] Because Ritchey is Hesperian or younger in age this means that liquid water could have existed at various times in Martian history, including more recently than when many of the channels were made. Clay minerals were also found in the crater wall, crater floor, and fan deposits but it is not known for certain when they might have been produced. They could have formed in place, transported from another location, or have been come from erosion of preexisting clays. However, spectra show that at least some of the clays in the crater floor and fan deposits came from the crater wall.[16] In addition, other minerals have been found in the crater. The central peak contains hydrated opaline silica. Since it is hydrated water was needed to make it.[17] Also, Olivine, Low calcium pyroxene and plagioclase have been detected there.[18]

See also

References

  1. ↑ https://planetarynames.wr.usgs.gov/Feature/5156
  2. ↑ Moore, P. et al. 1990. The Atlas of the Solar System. Crescent Books. NY
  3. ↑ Sun, V., R. Milliken. 2014. The geology and mineralogy of Ritchey crater, Mars: Evidence for post-Noachian clay formation. Journal of Geophysical Research:119(4), 810–836
  4. ↑ http://marsoweb.nas.nasa.gov/landingsites/msl/workshops/2nd_workshop/talks/Milliken_Ritchey.pdf
  5. ↑ http://marsoweb.nas.nasa.gov/landingsites/msl/workshops/2nd_workshop/talks/Milliken_Ritchey.pdf
  6. ↑ Sun, V., R. Milliken. 2014. The geology and mineralogy of Ritchey crater, Mars: Evidence for post-Noachian clay formation. Journal of Geophysical Research:119(4), 810–836
  7. ↑ Murchie, S. et al. 2009. A synthesis of Martian aqueous mineralogy after 1 Mars year of observations from the Mars Reconnaissance Orbiter. Journal of Geophysical Research: 114.
  8. ↑ Ding, N., V. Brayb, A. McEwen, S. Mattson, C. Okubo, M. Chojnacki, L. Tornabene, 2015. The central uplift of Ritchey crater, Mars. Icarus: 252, 255-270.
  9. ↑ http://hirise.lpl.arizona.edu/PSP_003249_1510
  10. ↑ Sun, V., and R. Milliken. 2014. The geology and mineralogy of Ritchey crater, Mars: Evidence for post-Noachian clay formation, J. Geophys. Res.:119, 810-836, doi: 10.1002/2013JE004602.
  11. ↑ Milliken, R., et al. 2010. The case for mixed-layered clays on Mars, Lunar Planet. Sci. XLI, Abstract 2030
  12. ↑ https://www.sciencedaily.com/releases/2015/12/151214150129.htm
  13. ↑ Sun, V., R. Milliken. Ancient and recent clay formation on Mars as revealed from a global survey of hydrous minerals in crater central peaks. Journal of Geophysical Research: Planets, 2015; DOI: 10.1002/2015JE004918
  14. ↑ Sun, V., and R. Milliken. 2014. The geology and mineralogy of Ritchey crater, Mars: Evidence for post-Noachian clay formation, J. Geophys. Res.:119, 810-836, doi: 10.1002/2013JE004602.
  15. ↑ https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/smectite
  16. ↑ Sun, V., and R. Milliken. 2014. The geology and mineralogy of Ritchey crater, Mars: Evidence for post-Noachian clay formation, J. Geophys. Res.:119, 810-836, doi: 10.1002/2013JE004602.
  17. ↑ Milliken, R., et al. 2008. Opaline silica in young deposits on Mars, Geology, 36(11), 847–850, doi:10.1130/G24967A.1.
  18. ↑ Ding, N., V. Brayb, A. McEwen, S. Mattson, C. Okubo, M. Chojnacki, L. Tornabene, 2015. The central uplift of Ritchey crater, Mars. Icarus: 252, 255-270.

External links

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