Ross Crater

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Ross Crater
Ross Crater MOLA.JPG
Ross Crater as seen by MOLA which shows the elevations.
Planet Mars
Coordinates 57°42′S 107°50′W / 57.7°S 107.84°W / -57.7; -107.84Coordinates: 57°42′S 107°50′W / 57.7°S 107.84°W / -57.7; -107.84
Diameter 82.51 km
Eponym Frank E. Ross, an American astronomer (1874-1966)

Ross Crater is an impact crater in the Thaumasia quadrangle of Mars located at 57.7 S and 107.84 W. It is 82.51 km in diameter. It was named after Frank E. Ross, an American astronomer (1874-1966). The crater's name was approved in 1973.[1]

Martian Gullies[edit]

Gullies are common in some parts of Mars. 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. Some studies have found that gullies occur on slopes that face all directions,[2] others have found that the greater number of gullies are found on poleward facing slopes, especially from 30-44 S.[3][4]

Although many ideas have been put forward to explain them,[5] the most popular involve liquid water coming from an aquifer, from melting at the base of old glaciers, or from the melting of ice in the ground when the climate was warmer.[6][7] Because of the good possibility that liquid water was involved with their formation and that they could be very young, scientists are excited. Maybe the gullies are where we should go to find life.

There is evidence for all three theories. Most of the gully alcove heads occur at the same level, just as one would expect of an aquifer. Various measurements and calculations show that liquid water could exist in aquifers at the usual depths where gullies begin.[8] One variation of this model is that rising hot magma could have melted ice in the ground and caused water to flow in aquifers. Aquifers are layer that allow water to flow. They may consist of porous sandstone. The aquifer layer would be perched on top of another layer that prevents water from going down (in geological terms it would be called impermeable). Because water in an aquifer is prevented from going down, the only direction the trapped water can flow is horizontally. Eventually, water could flow out onto the surface when the aquifer reaches a break—like a crater wall. The resulting flow of water could erode the wall to create gullies.[9] Aquifers are quite common on Earth. A good example is "Weeping Rock" in Zion National Park Utah.[10]

As for the next theory, much of the surface of Mars is covered by a thick smooth mantle that is thought to be a mixture of ice and dust.[11][12][13] This ice-rich mantle, a few yards thick, smoothes the land, but in places it has a bumpy texture, resembling the surface of a basketball. The mantle may be like a glacier and under certain conditions the ice that is mixed in the mantle could melt and flow down the slopes and make gullies.[14][15][16] Because there are few craters on this mantle, the mantle is relatively young. An excellent view of this mantle is shown below in the picture of the Ptolemaeus Crater Rim, as seen by HiRISE.[17] The ice-rich mantle may be the result of climate changes.[18] 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 periods water vapor leaves polar ice and enters the atmosphere. The water comes back to 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 will condense on the particles, then fall down to the ground due to the additional weight of the water coating. When Mars is at its greatest tilt or obliquity, up to 2 cm of ice could be removed from the summer ice cap and deposited at midlatitudes. This movement of water could last for several thousand years and create a snow layer of up to around 10 meters thick.[19][20] When ice at the top of the mantling layer goes back into the atmosphere, it leaves behind dust, which insulating the remaining ice.[21] Measurements of altitudes and slopes of gullies support the idea that snowpacks or glaciers are associated with gullies. Steeper slopes have more shade which would preserve snow.[22][23] Higher elevations have far fewer gullies because ice would tend to sublimate more in the thin air of the higher altitude.[24] Very few gullies are found in the Thaumasia region; however, a few are present in the lower elevations like the one pictured below in Ross Crater.

See also[edit]

References[edit]

  1. ^ http://planetarynames.wr.usgs.gov/SearchResults
  2. ^ Edgett, K. et al. 2003. Polar-and middle-latitude martian gullies: A view from MGS MOC after 2 Mars years in the mapping orbit. Lunar Planet. Sci. 34. Abstract 1038.
  3. ^ http://www.planetary.brown.edu/pdfs/3138.pdf
  4. ^ Dickson, J. et al. 2007. Martian gullies in the southern mid-latitudes of Mars Evidence for climate-controlled formation of young fluvial features based upon local and global topography. Icarus: 188. 315-323
  5. ^ http://www.psrd.hawaii.edu/Aug03/MartianGullies.html
  6. ^ Heldmann, J. and M. Mellon. Observations of martian gullies and constraints on potential formation mechanisms. 2004. Icarus. 168: 285-304.
  7. ^ Forget, F. et al. 2006. Planet Mars Story of Another World. Praxis Publishing. Chichester, UK.
  8. ^ Heldmann, J. and M. Mellon. 2004. Observations of martian gullies and constraints on potential formation mechanisms. Icarus. 168:285-304
  9. ^ http://www.space.com/scienceastronomy/mars_aquifer_041112.html
  10. ^ Harris, A and E. Tuttle. 1990. Geology of National Parks. Kendall/Hunt Publishing Company. Dubuque, Iowa
  11. ^ Malin, M. and K. Edgett. 2001. Mars Global Surveyor Mars Orbiter Camera: Interplanetary cruse through primary mission. J. Geophys. Res: 106> 23429-23570
  12. ^ Mustard, J. et al. 2001. Evidence for recent climate change on Mars from the identification of youthful near-surface ground ice. Nature: 412. 411-414.
  13. ^ Carr, M. 2001. Mars Global Surveyor observations of fretted terrain. J. Geophys. Res: 106. 23571-23595.
  14. ^ http://www.msnbc.msn.com/id/15702457?
  15. ^ http://www.pnas.org/content/105/36/13258.full
  16. ^ Head, J. et al. 2008. Formation of gullies on Mars: Link to recent climate history and insolation microenvironments implicate surface water flow origin. PNAS: 105. 13258-13263.
  17. ^ Christensen, P. 2003. Formation of recent martian gullies through melting of extensive water-rich snow deposits. Nature: 422. 45-48.
  18. ^ http://news.nationalgeographic.com/news/2008/03/080319-mars-gullies_2.html
  19. ^ Jakosky B. and M. Carr. 1985. Possible precipitation of ice at low latitudes of Mars during periods of high obliquity. Nature: 315. 559-561.
  20. ^ Jakosky, B. et al. 1995. Chaotic obliquity and the nature of the Martian climate. J. Geophys. Res: 100. 1579-1584.
  21. ^ MLA NASA/Jet Propulsion Laboratory (2003, December 18). Mars May Be Emerging From An Ice Age. ScienceDaily. Retrieved February 19, 2009, from http://www.sciencedaily.com /releases/2003/12/031218075443.htmAds by GoogleAdvertise
  22. ^ http://www.planetary.brown.edu/pdfs/3138.pdf
  23. ^ Dickson, J. et al. 2007. Martian gullies in the southern mid-latitudes of Mars Evidence for climate-controlled formation of young fluvial features based upon local and global topography. Icarus: 188. 315-323.
  24. ^ Hecht, M. 2002. Metastability of liquid water on Mars. Icarus: 156. 373-386.