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南極高原 (火星)

坐标：83°54′S 160°00′E / 83.9°S 160.0°E / -83.9; 160.0
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南極高原
Planum Australe
火星全球探勘者號拍攝的南極高原
经纬83°54′S 160°00′E / 83.9°S 160.0°E / -83.9; 160.0

南極高原(拉丁語：Planum Australe，南方的平原；Planum 是指高海拔的平原或高原)是火星南極的一個高原。延伸範圍大約到 75°S，中心位置在 83°54′S 160°00′E / 83.9°S 160.0°E / -83.9; 160.0。NASA原定以火星極地著陸者號研究當地地質，但在降落過程中在火星大氣層內失去聯絡，任務失敗。

冰帽

Planum Australe is partially covered by a permanent polar ice cap composed of frozen water and carbon dioxide about 3 km thick. A seasonal ice cap forms on top of the permanent one during the Martian winter, extending from 60°S southwards. It is, at the height of winter, approximately 1 metre thick.[1] It is possible that the area of this ice cap may be shrinking due to localized climate change or more widespread global warming.[2]

Elevation map of the south pole. Note how Planum Australe rises above the surrounding cratered terrain. Click to enlarge and for more info.

In 1966, Leighton and Murray proposed that the Martian polar caps provided a store of CO2 much larger than the atmospheric reservoir. However it is now thought that both poles are made mostly of water ice. Both poles have a thin seasonal covering of CO2, while in addition the southern pole has a permanent residual CO2 cap, about 8 to 10 metres thick, that lies on top of the water ice. Perhaps the key argument that the bulk of the ice is water is that CO2 ice isn't mechanically strong enough to make a 3 km thick ice cap stable over long periods of time.[3].

Data from ESA's Mars Express indicates that there are three main parts to the ice cap. The most reflective part of the ice cap is approximately 85% dry ice and 15% water ice. The second part, where the ice cap forms steep slopes at the boundary with the surrounding plain, is almost exclusively water ice. Finally, the ice cap is surrounded by permafrost fields that extend for tens of kilometres north away from the scarps.[4]

The centre of the permanent ice cap is not located at 90°S but rather approximately 150 kilometres north of the geographical south pole. The presence of two massive impact basins in the western hemisphere - Hellas Planitia and Argyre Planitia - creates an immobile area of low pressure over the permanent ice cap. The resulting weather patterns produce fluffy white snow which has a high albedo. This is in contrast to the black ice that forms in the eastern part of the polar region, which receives little snow.[5]

地表特徵

There are two distinct subregions in Planum Australe - Australe Lingula and Promethei Lingula. It is dissected by canyons Promethei Chasma, Ultimum Chasma, Chasma Australe and Australe Sulci. It is theorised that these canyons were created by katabatic wind.[6] The largest crater in Planum Australe is McMurdo Crater.

火星上的噴泉

Artist concept showing sand-laden jets erupt from geysers on Mars. (published by NASA; artist: Ron Miller.
Close up of "dark dune spots" created by geyser-like systems.
主条目：火星上的噴泉

The seasonal frosting and defrosting of the southern ice cap results in the formation of spider-like radial channels carved on 1 meter thick ice by sunlight. Then, sublimed CO2 -and probably water- increase pressure in their interior producing geyser-like eruptions of cold fluids often mixed with dark basaltic sand or mud.[7][8][9][10] This process is rapid, observed happening in the space of a few days, weeks or months, a growth rate rather unusual in geology - especially for Mars. No lander is presently planned to visit the dark dune spots and spider areas.

參見

维基新闻中的相关報導：Massive ice deposits found on Mars

參考資料

  1. ^ Phillips, Tony. Mars is Melting. Science @ NASA. [2006-10-20]. 
  2. ^ Sigurdsson, Steinn. Global warming on Mars?. RealClimate.org. [2006-10-20]. 
  3. ^ Byrne, Shane; Ingersoll, AP. A Sublimation Model for Martian South Polar Ice Features. Science. 14 February 2003, 299 (5609): 1051–1053. PMID 12586939. doi:10.1126/science.1080148. 
  4. ^ Water at Martian south pole. European Space Agency. [2006-10-22]. 
  5. ^ Mars' South Pole mystery. Spaceflight Now. [2006-10-26]. 
  6. ^ Kolb, Eric J.; Kenneth L. Tanaka. Accumulation and erosion of south polar layered deposits in the Promethei Lingula region, Planum Australe, Mars. The Mars Journal (Mars Informatics Inc.). 2006, 2: 1–9. doi:10.1555/mars.2006.0001. 
  7. ^ NASA Findings Suggest Jets Bursting From Martian Ice Cap. Jet Propulsion Laboratory (NASA). August 16, 2006 [2009-08-11]. 
  8. ^ Kieffer, H. H. Mars Polar Science 2000 (PDF). 2000.  |contribution=被忽略 (帮助);
  9. ^ Fourth Mars Polar Science Conference (PDF). 2006.  |contribution=被忽略 (帮助); Editors list列表中的|first1=缺少|last1= (帮助);
  10. ^ Kieffer, Hugh H.; Philip R. Christensen and Timothy N. Titus. CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap. Nature. 30 May 2006, 442 (7104): 793–796 [2009-09-02]. PMID 16915284. doi:10.1038/nature04945. 

外部連結

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