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Planum Australe

Coordinates:83°54′S160°00′E/ 83.9°S 160.0°E/-83.9; 160.0
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Planum Australe
Planum Australe, taken byMars Global Surveyor.
Feature typePartially glaciated plains
Coordinates83°54′S160°00′E/ 83.9°S 160.0°E/-83.9; 160.0

Planum Australe(Latin:"the southern plain" ) is the southern polar plain onMars.It extends southward of roughly 75°S and is centered at83°54′S160°00′E/ 83.9°S 160.0°E/-83.9; 160.0.The geology of this region was to be explored by the failedNASAmissionMars Polar Lander,which lost contact on entry into theMartian atmosphere.

In July 2018, scientists reported the discovery, based onMARSISradarstudies, of asubglacial lake on Mars,1.5 km (0.93 mi) below thesouthern polar ice cap,and extending sideways about 20 km (12 mi), the first known stable body of water on the planet.[1][2][3][4]

Ice cap[edit]

Site of south polarsubglacial water body(reported July 2018)
Elevation map of the south pole. Note how Planum Australe rises above the surrounding cratered terrain. Click to enlarge and for more info.

Planum Australe is partially covered by a permanentpolar ice capcomposed of frozenwaterandcarbon dioxideabout 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 meter thick.[5]It is possible that the area of this ice cap may be shrinking due to localizedclimate change.[6]Claims of more planetwideglobal warmingbased on imagery, however, ignore temperature data and global datasets. Spacecraft and microwave data indicate global average temperature is, at most, stable,[7][8]and possibly cooling.[9][10][11]

In 1966, Leighton and Murray proposed that the Martian polar caps provided a store of CO2much larger than the atmospheric reservoir. However it is now thought that both polar caps 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 CO2cap, 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 CO2ice isn't mechanically strong enough to make a 3 km thick ice cap stable over long periods of time.[12]Recent evidence fromSHARADice penetrating radar has revealed a massive subsurface CO2ice deposit approximately equal to 80% of the current atmosphere, or 4–5 mbar, stored in Planum Australe.[13]

Depiction of erupting south polar sand-laden jets (Ron Miller)

Data fromESA'sMars Expressindicates that there are three main parts to the ice cap. The most reflective part of the ice cap is approximately 85%dry iceand 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 bypermafrostfields that extend for tens of kilometres north away from the scarps.[14]

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 massiveimpact basinsin the western hemisphere –Hellas PlanitiaandArgyre Planitia– creates an immobilearea of low pressureover the permanent ice cap. The resulting weather patterns produce fluffy whitesnowwhich has a highalbedo.This is in contrast to theblack icethat forms in the eastern part of the polar region, which receives little snow.[15]

Features[edit]

There are two distinct subregions in Planum Australe –Australe LingulaandPromethei Lingula.It is dissected by canyonsPromethei Chasma,Ultimum Chasma,Chasma AustraleandAustrale Sulci.It is theorised that these canyons were created bykatabatic wind.[16]The largest crater in Planum Australe isMcMurdo Crater.

Geysers on Mars[edit]

Close up of "dark dune spots" created by geyser-like systems
Main article:Geysers on Mars

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.[17]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.[18][19][20][21]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. TheMars Geyser Hopperlander is a concept mission that would investigate the geysers of Mars.[22][23]

Saltwater lakes[edit]

In September 2020, scientists confirmed the existence of several largesaltwater lakesunder theicein the south polar region of the planetMars.According to one of the researchers, “We identified the same body of water [as suggested earlier in a preliminary initial detection], but we also found three other bodies of water around the main one... It’s a complex system.”[24][25]

See also[edit]

References[edit]

  1. ^Orosei, R.; et al. (25 July 2018)."Radar evidence of subglacial liquid water on Mars".Science.361(6401): 490–493.arXiv:2004.04587.Bibcode:2018Sci...361..490O.doi:10.1126/science.aar7268.hdl:11573/1148029.PMID30045881.
  2. ^Chang, Kenneth;Overbye, Dennis(25 July 2018)."A Watery Lake Is Detected on Mars, Raising the Potential for Alien Life – The discovery suggests that watery conditions beneath the icy southern polar cap may have provided one of the critical building blocks for life on the red planet".The New York Times.Retrieved25 July2018.
  3. ^"Huge reservoir of liquid water detected under the surface of Mars".EurekAlert.25 July 2018.Retrieved25 July2018.
  4. ^"Liquid water 'lake' revealed on Mars".BBC News.25 July 2018.Retrieved25 July2018.
  5. ^Phillips, Tony."Mars is Melting".Retrieved2021-04-22.
  6. ^Sigurdsson, Steinn."Global warming on Mars?".RealClimate.org.Retrieved2006-10-20.
  7. ^Wilson, R.; Richardson, M. (2000). "The Martian Atmosphere During the Viking I Mission, I: Infrared Measurements of Atmospheric Temperatures Revisited".Icarus.145(2): 555–579.Bibcode:2000Icar..145..555W.CiteSeerX10.1.1.352.9114.doi:10.1006/icar.2000.6378.
  8. ^Liu, J.; Richardson, M. (August 2003)."An assessment of the global, seasonal, and interannual spacecraft record of Martian climate in the thermal infrared".Journal of Geophysical Research.108(8): 5089.Bibcode:2003JGRE..108.5089L.doi:10.1029/2002je001921.S2CID7433260.
  9. ^Clancy, R.; et al. (2000)."An intercomparison of ground-based millimeter, MGS TES, and Viking atmospheric temperature measurements: Seasonal and interannual variability of temperatures and dust loading in the global Mars atmosphere".Journal of Geophysical Research.105(4): 9553–9571.Bibcode:2000JGR...105.9553C.doi:10.1029/1999je001089.
  10. ^Bell, J.; et al. (2009)."Mars Reconnaissance Orbiter Mars Color Imager (MARCI): Instrument Description, Calibration, and Performance".Journal of Geophysical Research.114(8): E08S92.Bibcode:2009JGRE..114.8S92B.doi:10.1029/2008je003315.S2CID140643009.
  11. ^Bandfield, J.; et al. (2013)."Radiometric Comparison of Mars Climate Sounder and Thermal Emission Spectrometer Measurements".Icarus.225(1): 28–39.Bibcode:2013Icar..225...28B.doi:10.1016/j.icarus.2013.03.007.
  12. ^ Byrne, Shane; Ingersoll, AP (14 February 2003). "A Sublimation Model for Martian South Polar Ice Features".Science.299(5609): 1051–1053.Bibcode:2003Sci...299.1051B.doi:10.1126/science.1080148.PMID12586939.S2CID7819614.
  13. ^Philips, R. J.; et al. (2011). "Onset and migration of spiral troughs on Mars revealed by orbital radar".Science.332(13): 838–841.Bibcode:2011Sci...332..838P.doi:10.1126/science.1203091.hdl:11573/496472.PMID21512003.S2CID1300107.
  14. ^"Water at Martian south pole".European Space Agency.Retrieved2006-10-22.
  15. ^"Mars' South Pole mystery".Spaceflight Now.Retrieved2006-10-26.
  16. ^ Kolb, Eric J.; Tanaka, Kenneth L. (2006). "Accumulation and erosion of south polar layered deposits in the Promethei Lingula region, Planum Australe, Mars".The Mars Journal.2:1–9.Bibcode:2006IJMSE...2....1K.doi:10.1555/mars.2006.0001.S2CID53400765.
  17. ^Mangold, N (2011). "Ice sublimation as a geomorphic process: A planetary perspective".Geomorphology.126(1–2): 1–17.doi:10.1016/j.geomorph.2010.11.009.
  18. ^"NASA Findings Suggest Jets Bursting From Martian Ice Cap".Jet Propulsion Laboratory.NASA. August 16, 2006. Archived fromthe originalon 2009-10-10.Retrieved2009-08-11.
  19. ^Kieffer, H. H. (2000).ANNUAL PUNCTUATED CO2 SLAB-ICE AND JETS ON MARS(PDF).Mars Polar Science 2000.Retrieved2009-09-06.
  20. ^Portyankina, G., ed. (2006).SIMULATIONS OF GEYSER-TYPE ERUPTIONS IN CRYPTIC REGION OF MARTIAN SOUTH(PDF).Fourth Mars Polar Science Conference.Retrieved2009-08-11.
  21. ^Kieffer, Hugh H.; Christensen, Philip R.; Titus, Timothy N. (30 May 2006). "CO2 jets formed by sublimation beneath translucent slab ice in Mars' seasonal south polar ice cap".Nature.442(7104): 793–796.Bibcode:2006Natur.442..793K.doi:10.1038/nature04945.PMID16915284.S2CID4418194.
  22. ^Landis, Geoffrey A.; Oleson, Steven J.; McGuire, Melissa (9 January 2012)."Design Study for a Mars Geyser Hopper".NASA.Retrieved2012-07-01.
  23. ^Landis, Geoffrey A.; Oleson, Steven J.; McGuire, Melissa (9 January 2012).Design Study for a Mars Geyser Hopper(PDF).50th AIAA Aerospace Sciences Conference. Glenn Research Center, NASA. AIAA-2012-0631.Retrieved2012-07-01.
  24. ^Lauro, Sebastian Emanuel; et al. (28 September 2020)."Multiple subglacial water bodies below the south pole of Mars unveiled by new MARSIS data".Nature Astronomy.5:63–70.arXiv:2010.00870.doi:10.1038/s41550-020-1200-6.S2CID222125007.Retrieved29 September2020.
  25. ^O'Callaghan, Jonathan (28 September 2020)."Water on Mars: discovery of three buried lakes intrigues scientists – Researchers have detected a group of lakes hidden under the red planet's icy surface".Nature.doi:10.1038/d41586-020-02751-1.PMID32989309.S2CID222155190.Retrieved29 September2020.

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