Latitude dependent mantle

Much of the Martian surface is covered with a thick ice-rich, mantle layer that has fallen from the sky a number of times in the past.^{[1] [2] [3]} In some places a number of layers are visible in the mantle.

• 

  Layers in mantle deposit, as seen by HiRISE, under the HiWish program. Mantle was probably formed from snow and dust falling during a different climate. Location is Thaumasia quadrangle

• 

  HiRISE image showing smooth mantle covering parts of a crater in the Phaethontis quadrangle. Along the outer rim of the crater, the mantle is displayed as layers. This suggests that the mantle was deposited multiple times in the past. Picture was taken with HiRISE under HiWish program. The layers are enlarged in the next image.

• 

  Enlargement of previous image of mantle layers. Four to five layers are visible. Location is the Phaethontis quadrangle.

• 

  Surface showing appearance with and without mantle covering, as seen by HiRISE, under the HiWish program. Location is Terra Sirenum in Phaethontis quadrangle.

• 

  Mantle layers, as seen by HiRISE under HiWish program. Location is Eridania quadrangle

• 

  Close view of places covered and not covered by mantle layer which falls from the sky when climate changes. Location is Eridania quadrangle. Picture taken with HiRISE under HiWish program.

• 

  Close up view of mantle, as seen by HiRISE under the HiWish program. Mantle may be composed of ice and dust that fell from the sky during past climatic conditions. Location is Cebrenia quadrangle.

• 

  Smooth mantle with layers in Hellas quadrangle, as seen by HiRISE under HiWish program

• 

  Close view of mantle, as seen by HiRISE under HiWish program Arrows show craters along edge which highlight the thickness of mantle. Location is Ismenius Lacus quadrangle.

• 

  Close view that displays the thickness of the mantle, as seen by HiRISE under HiWish program Location is Ismenius Lacus quadrangle.

• 

  Close view of mantle, as seen by HiRISE under HiWish program Location is Hellas quadrangle.

It fell as snow and ice-coated dust. There is good evidence that this mantle is ice-rich. The shapes of the polygons common on many surfaces suggest ice-rich soil. High levels of hydrogen (probably from water) have been found with Mars Odyssey.^{[4][5] [6] [7] [8]} Thermal measurements from orbit suggest ice. ^{[9] [10]} The Phoenix (spacecraft) discovered water ice with made direct observations since it landed in a field of polygons. ^{[11] [12]} In fact, its landing rockets exposed pure ice. Theory had predicted that ice would be found under a few cm of soil. This mantle layer is called "latitude dependent mantle" because its occurrence is related to the latitude. It is this mantle that cracks and then forms polygonal ground. This cracking of ice-rich ground is predicted based on physical processes.^{[13][14] [15] [16] [17] [18] [19]} Another type of surface is called "brain terrain" as it looks like the surface of a human brain. Brain terrain lies under polygonal ground when the two are both visible in a region.

• 

  Context picture showing origin of next picture. The location is a region of lineated valley fill. Image from HiRISE under HiWish program.

• 

  Open and closed-cell brain terrain, as seen by HiRISE, under HiWish program.

• 

  Brain terrain being formed from a thicker layer, as seen by HiRISE under HiWish program. Arrows show the thicker unit breaking up into small cells.

Since the top, polygon layer is fairly smooth although the underlying brain terrain is irregular; it is believed that the mantle layer that contains the polygons needs to be 10–20 meters thick to smooth out the irregularities. The mantle layer lasts for a very long time before all the ice is gone because a protective lag deposit forms on the top.^{[20] [21][22] [23]} The mantle contains ice and dust. After a certain amount of ice disappears from sublimation the dust stays on the top, forming the lag deposit. ^{[24] [25] [26] [27]}

The total amount of water locked up in the mantle has been calculated based on the total area of polygonal ground and an estimated depth of 10 meters. This volume is equal to a layer 2.5 meters deep spread over the entire planet. This compares to a 30-meter depth over the whole planet for the water locked up in the north and south polar caps.^[28]

Mantle forms when the Martian climate is different than the present climate.^{[29] [30] [31]} The tilt or obliquity of the axis of the planet changes a great deal.^{[32] [33] [34]} The Earth’s tilt changes little because our rather large moon stabilizes the Earth. Mars only has two very small moons that do not possess enough gravity to stabilize its tilt. When the tilt of Mars exceeds around 40 degrees (from today's 25 degrees), ice is deposited in certain latitude bands where much mantle exists today.^{[35] [36]}

See also

• Climate of Mars

References

1. Hecht, M. 2002. Metastability of water on Mars. Icarus 156, 373–386
2. Mustard, J., et al. 2001. Evidence for recent climate change on Mars from the identification of youthful near-surface ground ice. Nature 412 (6845), 411–414.
3. 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.
4. Boynton, W., and 24 colleagues. 2002. Distribution of hydrogen in the nearsurface of Mars: Evidence for sub-surface ice deposits. Science 297, 81–85
5. Kuzmin, R, et al. 2004. Regions of potential existence of free water (ice) in the near-surface martian ground: Results from the Mars Odyssey High-Energy Neutron Detector (HEND). Solar System Research 38 (1), 1–11.
6. Mitrofanov, I. et al. 2007a. Burial depth of water ice in Mars permafrost subsurface. In: LPSC 38, Abstract #3108. Houston, TX.
7. Mitrofanov, I., and 11 colleagues. 2007b. Water ice permafrost on Mars: Layering structure and subsurface distribution according to HEND/Odyssey and MOLA/ MGS data. Geophys. Res. Lett. 34 (18). doi:10.1029/2007GL030030.
8. Mangold, N., et al. 2004. Spatial relationships between patterned ground and ground ice detected by the neutron spectrometer on Mars. J. Geophys. Res. 109 (E8). doi:10.1029/ 2004JE002235.
9. Feldman, W., and 12 colleagues. 2002. Global distribution of neutrons from Mars: Results from Mars Odyssey. Science 297, 75–78.
10. Feldman, W., et al. 2008. North to south asymmetries in the water-equivalent hydrogen distribution at high latitudes on Mars. J. Geophys. Res. 113. doi:10.1029/2007JE003020.
11. Bright Chunks at Phoenix Lander's Mars Site Must Have Been Ice – Official NASA press release (19.06.2008)
12. "Confirmation of Water on Mars". Nasa.gov. 2008-06-20. Retrieved 2012-07-13.
13. Mutch, T.A., and 24 colleagues, 1976. The surface of Mars: The view from the Viking2 lander. Science 194 (4271), 1277–1283.
14. Mutch, T., et al. 1977. The geology of the Viking Lander 2 site. J. Geophys. Res. 82, 4452–4467.
15. Levy, J., et al. 2009. Thermal contraction crack polygons on Mars: Classification, distribution, and climate implications from HiRISE observations. J. Geophys. Res. 114. doi:10.1029/2008JE003273.
16. Washburn, A. 1973. Periglacial Processes and Environments. St. Martin’s Press, New York, pp. 1–2, 100–147.
17. Mellon, M. 1997. Small-scale polygonal features on Mars: Seasonal thermal contraction cracks in permafrost. J. Geophys. Res. 102, 25,617-625,628.
18. Mangold, N. 2005. High latitude patterned grounds on Mars: Classification, distribution and climatic control. Icarus 174, 336–359.
19. Marchant, D., J. Head. 2007. Antarctic dry valleys: Microclimate zonation, variable geomorphic processes, and implications for assessing climate change on Mars. Icarus 192, 187–222
20. Marchant, D., et al. 2002. Formation of patterned ground and sublimation till over Miocene glacier ice in Beacon valley, southern Victoria land, Antarctica. Geol. Soc. Am. Bull. 114, 718–730.
21. Mellon, M., B. Jakosky. 1995. The distribution and behavior of Martian ground ice during past and present epochs. J. Geophys. Res. 100, 11781–11799.
22. Mellon, M., B. Jakosky. 1995. The distribution and behavior of Martian ground ice during past and present epochs. J. Geophys. Res. 100, 11781–11799.
23. Schorghofer, N., 2007. Dynamics of ice ages on Mars. Nature 449, 192–194.
24. 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.
25. Schorghofer, N., O. Aharonson. 2005. Stability and exchange of subsurface ice on Mars. J. Geophys. Res. 110 (E05). doi:10.1029/2004JE002350.
26. Schorghofer, N., 2007. Dynamics of ice ages on Mars. Nature 449 (7159), 192–194
27. Head, J., J. Mustard, M. Kreslavsky, R. Milliken, D. Marchant. 2003. Recent ice ages on Mars. Nature 426 (6968), 797–802.
28. Levy, J. et al. 2010. Thermal contraction crack polygons on Mars: A synthesis from HiRISE, Phoenix, and terrestrial analog studies. Icarus: 206, 229-252.
29. Mustard, J., et al. 2001. Evidence for recent climate change on Mars from the identification of youthful near-surface ground ice. Nature 412 (6845), 411–414.
30. Kreslavsky, M.A., Head, J.W., 2002. High-latitude Recent Surface Mantle on Mars: New Results from MOLA and MOC. European Geophysical Society XXVII, Nice.
31. Head, J.W., Mustard, J.F., Kreslavsky, M.A., Milliken, R.E., Marchant, D.R., 2003. Recent ice ages on Mars. Nature 426 (6968), 797–802.
32. name= Touma J. and J. Wisdom. 1993. The Chaotic Obliquity of Mars. Science 259, 1294-1297.
33. Laskar, J., A. Correia, M. Gastineau, F. Joutel, B. Levrard, and P. Robutel. 2004. Long term evolution and chaotic diffusion of the insolation quantities of Mars. Icarus 170, 343-364.
34. Levy, J., J. Head, D. Marchant, D. Kowalewski. 2008. Identification of sublimation-type thermal contraction crack polygons at the proposed NASA Phoenix landing site: Implications for substrate properties and climate-driven morphological evolution. Geophys. Res. Lett. 35. doi:10.1029/2007GL032813.
35. 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.
36. Kreslavsky, M., J. Head. 2006. Modification of impact craters in the northern plains of Mars: Implications for the Amazonian climate history. Meteorit. Planet. Sci. 41, 1633–1646.