Английская Википедия:Deuteronilus Mensae

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Шаблон:Short description Шаблон:Use dmy dates Шаблон:Infobox feature on celestial object Deuteronilus Mensae is a region on Mars 937 km across and centered at Шаблон:Coord. It covers 344°–325° West and 40°–48° North.[1] Deuteronilus region lies just to the north of Arabia Terra and is included in the Ismenius Lacus quadrangle. It is along the dichotomy boundary, that is between the old, heavily cratered southern highlands and the low plains of the northern hemisphere. The region contains flat-topped knobby terrain that may have been formed by glaciers at some time in the past. Deuteronilus Mensae is to the immediate west of Protonilus Mensae and Ismeniae Fossae.[2][3] Glaciers persist in the region in modern times, with at least one glacier estimated to have formed as recently as 100,000 to 10,000 years ago.[4] Recent evidence from the radar on the Mars Reconnaissance Orbiter has shown that parts of Deuteronilus Mensae do indeed contain ice.[5][6][7]

Source of ice

It is now widely believed that ice accumulated in many areas of Mars, including Deuteronilus Mensae, when the planet's orbital tilt was very different from now (the axis of Mars has considerable "wobble", meaning its angle changes over time).[8][9][10] A few million years ago, the tilt of the axis of Mars was 45 degrees instead of its present 25 degrees. Its tilt, also called obliquity, varies greatly because its two tiny moons cannot stabilize it, like our relatively large moon does the Earth.

Many features on Mars, including Deuteronilus Mensae, are believed to contain large amounts of ice. The most popular model for the origin of the ice is climate change from large changes in the tilt of the planet's rotational axis. At times the tilt has even been greater than 80 degrees[11][12] Large changes in the tilt explains many ice-rich features on Mars.

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.[13] 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. 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.[14][15] General circulation models of the Martian atmosphere predict accumulations of ice-rich dust in the same areas where ice-rich features are found.[12] When the tilt begins to return to lower values, the ice sublimates (turns directly to a gas) and leaves behind a lag of dust.[16][17] The lag deposit caps the underlying material so with each cycle of high tilt levels, some ice-rich mantle remains behind.[18] Note, that the smooth surface mantle layer probably represents only relative recent material.

Polygonal patterned ground

Шаблон:Main Polygonal, patterned ground is quite common in some regions of Mars.[19][20][21][22][23][24][25] It is commonly believed to be caused by the sublimation of ice from the ground. Sublimation is the direct change of solid ice to a gas. This is similar to what happens to dry ice on the Earth. Places on Mars that display polygonal ground may indicate where future colonists can find water ice. Patterned ground forms in a mantle layer, called latitude dependent mantle, that fell from the sky when the climate was different.[26][27][28][29]

Upper plains unit

Remnants of a 50–100 meter thick mantling, called the upper plains unit, has been discovered in the mid-latitudes of Mars. First investigated in the Deuteronilus Mensae region, but it occurs in other places as well. The remnants consist of sets of dipping layers in craters and along mesas.[30] Sets of dipping layers may be of various sizes and shapes—some look like Aztec pyramids from Central America.

This unit also degrades into brain terrain. Brain terrain is a region of maze-like ridges 3–5 meters high. Some ridges may consist of an ice core, so they may be sources of water for future colonists.

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 exposed more surfaces, and consequently more ice in the material sublimates into the planet's thin atmosphere. Eventually, small cracks become large canyons or troughs.

Small cracks often contain small pits and chains of pits; these are thought to be from sublimation (phase transition) of ice in the ground.[31][32] Large areas of the Martian surface are loaded with ice that is protected by a meters thick layer of dust and other material. However, if cracks appear, a fresh surface will expose ice to the thin atmosphere.[33][34] In a short time, the ice will disappear into the cold, thin atmosphere in a process called sublimation (phase transition) . Dry ice behaves in a similar fashion on the Earth. On Mars sublimation has been observed when the Phoenix lander uncovered chunks of ice that disappeared in a few days.[35][36] In addition, HiRISE has seen fresh craters with ice at the bottom. After a time, HiRISE saw the ice deposit disappear.[37]

The upper plains unit is thought to have fallen from the sky. It drapes various surfaces, as if it fell evenly. As is the case for other mantle deposits, the upper plains unit 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. It is a major cause of the surface appearance of lobate debris aprons.[32] The layering of the upper plains mantling unit and other mantling units are believed to be caused by major changes in the planet's climate. Models predict that the obliquity or tilt of the rotational axis has varied from its present 25 degrees to maybe over 80 degrees over geological time. Periods of high tilt will cause the ice in the polar caps to be redistributed and change the amount of dust in the atmosphere.[38][39][40]

Other images

See also

References

Шаблон:Reflist Шаблон:Commons category

External links

Шаблон:Geography of Mars Шаблон:Portal bar

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  1. ↑ Шаблон:Cite book
  2. ↑ Baker, M. 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.
  3. ↑ Шаблон:Cite web
  4. ↑ Шаблон:Cite news
  5. ↑ Шаблон:Cite web
  6. ↑ http://news.discovery.com/space/mars-ice-sheet-climate.html Шаблон:Dead link
  7. ↑ Plaut, J., A. Safaeinili,, J. Holt, R. Phillips, J. Head, J., R. Seu, N. Putzig, A. Frigeri. 2009. Radar evidence for ice in lobate debris aprons in the midnorthern latitudes of Mars. Geophys. Res. Lett. 36. doi:10.1029/2008GL036379.
  8. ↑ Madeleine, J. et al. 2007. Mars: A proposed climatic scenario for northern mid-latitude glaciation. Lunar Planet. Sci. 38. Abstract 1778.
  9. ↑ Madeleine, J. et al. 2009. Amazonian northern mid-latitude glaciation on Mars: A proposed climate scenario. Icarus: 203. 300–405.
  10. ↑ Mischna, M. et al. 2003. On the orbital forcing of martian water and CO2 cycles: A general circulation model study with simplified volatile schemes. J. Geophys. Res. 108. (E6). 5062.
  11. ↑ Touma J. and J. Wisdom. 1993. The Chaotic Obliquity of Mars. Science 259, 1294–1297.
  12. ↑ 12,0 12,1 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.
  13. ↑ 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.
  14. ↑ Levy, J., J. Head, D. Marchant. 2009a. Thermal contraction crack polygons on Mars: Classification, distribution, and climate implications from HiRISE observations. J. Geophys. Res. 114. doi:10.1029/2008JE003273.
  15. ↑ 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
  16. ↑ Mellon, M., B. Jakosky. 1995. The distribution and behavior of Martian ground ice during past and present epochs. J. Geophys. Res. 100, 11781–11799.
  17. ↑ Schorghofer, N., 2007. Dynamics of ice ages on Mars. Nature 449, 192–194.
  18. ↑ 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.
  19. ↑ Шаблон:Cite web
  20. ↑ 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. K>
  21. ↑ Malin, M., Edgett, K. 2001. Mars Global Surveyor Mars Orbiter Camera: Interplanetary cruise through primary mission. J. Geophys. Res. 106 (E10), 23429–23540.
  22. ↑ 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.
  23. ↑ Mangold, N. 2005. High latitude patterned grounds on Mars: Classification, distribution and climatic control. Icarus 174, 336–359.
  24. ↑ Kreslavsky, M., Head, J. 2000. Kilometer-scale roughness on Mars: Results from MOLA data analysis. J. Geophys. Res. 105 (E11), 26695–26712.
  25. ↑ Seibert, N., J. Kargel. 2001. Small-scale martian polygonal terrain: Implications for liquid surface water. Geophys. Res. Lett. 28 (5), 899–902. S
  26. ↑ Hecht, M. 2002. Metastability of water on Mars. Icarus 156, 373–386
  27. ↑ 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.
  28. ↑ 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.
  29. ↑ 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.
  30. ↑ Carr, M. 2001. Mars Global Surveyor observations of martian fretted terrain. J. Geophys. Res. 106, 23571-23593.
  31. ↑ Morgenstern, A., et al. 2007
  32. ↑ 32,0 32,1 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.
  33. ↑ Mangold, N. 2003. Geomorphic analysis of lobate debris aprons on Mars at Mars Orbiter Camera scale: Evidence for ice sublimation initiated by fractures. J. Geophys. Res. 108, 8021.
  34. ↑ Levy, J. et al. 2009. Concentric
  35. ↑ Bright Chunks at Phoenix Lander's Mars Site Must Have Been Ice Шаблон:Webarchive – Official NASA press release (19.06.2008)
  36. ↑ 36,0 36,1 Шаблон:Cite web
  37. ↑ Byrne, S. et al. 2009. Distribution of Mid-Latitude Ground Ice on Mars from New Impact Craters: 329.1674–1676
  38. ↑ Head, J. et al. 2003.
  39. ↑ Madeleine, et al. 2014.
  40. ↑ Schon, et al. 2009. A recent ice age on Mars: Evidence for climate oscillations from regional layering in mid-latitude mantling deposits. Geophys. Res. Lett. 36, L15202.
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