{{Short description|Map of Mars}} {{Infobox feature on celestial object |name = Mare Australe [[quadrangle (geography)|quadrangle]] |image = [[File:USGS-Mars-MC-30-MareAustraleRegion-mola.png|300px]] |caption = Map of Mare Australe quadrangle from [[Mars Orbiter Laser Altimeter]] (MOLA) data. The highest elevations are red and the lowest are blue. |coordinates = {{coord|75|S|0|E|globe:mars_type:landmark|display=inline,title}} }} [[File:PIA00190-MC-30-MareAustraleRegion-19980605.jpg|thumb|300px|Image of the Mare Australe Quadrangle (MC-30). The region includes the [[Martian polar ice caps|South Polar ice cap]]. The central part is mainly a permanent residual ice cap surrounded by layered and troughed terrain which is, in turn, encircled by heavily cratered terrain.]] The '''Mare Australe quadrangle''' is one of a series of [[list of quadrangles on Mars|30 quadrangle maps of Mars]] used by the [[United States Geological Survey]] (USGS) [[Astrogeology Research Program]]. The Mare Australe [[quadrangle (geography)|quadrangle]] is also referred to as MC-30 (Mars Chart-30).<ref>{{cite book |last1= Davies |first1= M.E. |last2= Batson |first2= R.M. |last3= Wu |first3= S.S.C. |chapter= Geodesy and Cartography |editor1-last= Kieffer |editor1-first= H.H. |editor2-last= Jakosky |editor2-first= B.M. |editor3-last= Snyder |editor3-first= C.W. |display-editors= 3 |editor4-last= Matthews |editor4-first= M.S. |title= Mars |publisher= University of Arizona Press |location= Tucson |date= 1992 |isbn= 978-0-8165-1257-7 |url-access= registration |url= https://archive.org/details/mars0000unse }}</ref> The quadrangle covers all the area of Mars south of 65°, including the [[Martian polar ice caps|South polar ice cap]], and its surrounding area. The quadrangle's name derives from an older name for a feature that is now called [[Planum Australe]], a large plain surrounding the polar cap.<ref>Patrick Moore and Robin Rees, ed. ''Patrick Moore's Data Book of Astronomy'' (Cambridge University Press, 2011), p. 130.</ref> The [[Mars polar lander]] crash landed in this region.<ref>{{Cite web|url=https://science.nasa.gov/mission/mars-polar-lander-deep-space-2/|title=Mars Polar Lander / Deep Space 2 - NASA Science|website=science.nasa.gov|date=17 January 2019 }}</ref><ref>{{Cite web|url=http://www.spaceref.com/news/viewnews.html?id=105|archive-url=https://archive.today/20160901155525/http://www.spaceref.com/news/viewnews.html?id=105|url-status=dead|archive-date=September 1, 2016|title=NASA Reveals Probable Cause of Mars Polar Lander and Deep Space-2 Mission Failures. | SpaceRef - Your Space Reference|date=28 March 2000}}</ref>
==Notable features==
Around the southern ice cap is a surface, called the ''Dorsa Argentea Formation'' that may be an old ice-rich deposit. It contains a group of sinuous, branched ridges that resembles eskers that form when streams are under glaciers.<ref>{{cite journal | last1=Kargel |first1= J. |first2= R. |last2=Strom |date= 1991 |title= Terrestrial glacial eskers: analogs for martian sinuous ridges | journal= LPSC | volume=XXII | pages= 683–684 | bibcode = 1991LPI....22..683K |url=http://www.lpi.usra.edu/meetings/lpsc1991/pdf/1340.pdf }}</ref> The formation often contains pits: two major locations are named ''Cavi Angusti'' and ''Cavi Sisyphi''. The pits have steep sides and an irregular shape. They are up to 50 km across and 1 km deep.<ref>{{cite book | last=Carr | first=Michael H. | publisher=Cambridge University Press | isbn= 978-0-521-87201-0 | title= The Surface of Mars |date=2006 | page={{page needed|date=January 2011}} }}</ref>
The quadrangle also contains [[Angustus Labyrinthus]], a formation of intersecting valley or ridges, nicknamed the "Inca City".<ref name="Hartmann, W 2003">Hartmann, W. 2003. A Traveler's Guide to Mars. Workman Publishing. NY NY.</ref> Researchers were surprised to see parts of the surface having a Swiss-cheese appearance. Also, some areas showed strange spider-shaped forms, which were determined to be caused by carbon dioxide gas blowing dust around at certain times of the year.
Some craters in Mare Australe show gullies. [[Gullies on Mars|Martian gullies]] are small, incised networks of narrow channels and their associated downslope [[sediment]] deposits, found on the planet of [[Mars]]. They are named for their resemblance to terrestrial [[gully|gullies]]. First discovered on images from [[Mars Global Surveyor]], they occur on steep slopes, especially on the walls of craters. Usually, each gully has a [[Dendritic drainage#Drainage patterns|dendritic]] ''alcove'' at its head, a [[Alluvial fan|fan-shaped]] ''apron'' at its base, and a single thread of incised ''channel'' linking the two, giving the whole gully an hourglass shape.<ref name="Malin, M. 2000">Malin, M., Edgett, K. 2000. Evidence for recent groundwater seepage and surface runoff on Mars. Science 288, 2330–2335.</ref> They are believed to be relatively young because they have few, if any craters. A subclass of gullies is also found cut into the faces of sand dunes which themselves considered to be quite young. On the basis of their form, aspects, positions, and location amongst and apparent interaction with features thought to be rich in water ice, many researchers believed that the processes carving the gullies involve liquid water. However, this remains a topic of active research. As soon as gullies were discovered,<ref name="Malin, M. 2000"/> researchers began to image many gullies over and over, looking for possible changes. By 2006, some changes were found.<ref>Malin, M., K. Edgett, L. Posiolova, S. McColley, E. Dobrea. 2006. Present-day impact cratering rate and contemporary gully activity on Mars. Science 314, 1573_1577.</ref> Later, with further analysis it was determined that the changes could have occurred by dry granular flows rather than being driven by flowing water.<ref>Kolb, et al. 2010. Investigating gully flow emplacement mechanisms using apex slopes. Icarus 2008, 132-142.</ref><ref>McEwen, A. et al. 2007. A closer look at water-related geological activity on Mars. Science 317, 1706-1708.</ref><ref>Pelletier, J., et al. 2008. Recent bright gully deposits on Mars wet or dry flow? Geology 36, 211-214.</ref> With continued observations many more changes were found in Gasa Crater and others.<ref>NASA/Jet Propulsion Laboratory. "NASA orbiter finds new gully channel on Mars." ScienceDaily. ScienceDaily, 22 March 2014. www.sciencedaily.com/releases/2014/03/140322094409.htm</ref> With more repeated observations, more and more changes have been found; since the changes occur in the winter and spring, experts are tending to believe that gullies were formed from dry ice. Before-and-after images demonstrated the timing of this activity coincided with seasonal carbon-dioxide frost and temperatures that would not have allowed for liquid water. When dry ice frost changes to a gas, it may lubricate dry material to flow especially on steep slopes.<ref>{{Cite web|url=https://www.jpl.nasa.gov/news/nasa-spacecraft-observes-further-evidence-of-dry-ice-gullies-on-mars|title=NASA Spacecraft Observes Further Evidence of Dry Ice Gullies on Mars|website=NASA Jet Propulsion Laboratory (JPL)}}</ref><ref>{{Cite web|url=https://hirise.lpl.arizona.edu/ESP_032078_1420|title=HiRISE | Activity in Martian Gullies (ESP_032078_1420)|website=hirise.lpl.arizona.edu}}</ref><ref>{{Cite web|url=http://www.space.com/26534-mars-gullies-dry-ice.html|title = Gullies on Mars Carved by Dry Ice, Not Water|website = [[Space.com]]|date = 16 July 2014}}</ref> In some years frost, perhaps as thick as 1 meter.
South polar layered deposits (SPLD) are the permanent, underlying geological structure, primarily made of water ice with dust.<ref>{{cite web | title=HiRISE | Informative Layers (ESP_066762_1050) | url=https://www.uahirise.org/ESP_066762_1050 }}</ref> In contrast, the Mars ice cap is a seasonal layer of carbon dioxide (CO2) frost that forms on top of the SPLD in the winter. The SPLD is much thicker, contains layered deposits that have accumulated over millions of years, and includes buried CO2 ice. The ice cap is a thin, transient CO2 coating that sublimates in the summer.<ref> Isaac B. Smith. 2022. A Retrospective on Mars Polar Ice and Climatelocked. https://doi.org/10.1093/acrefore/9780190647926.013.242</ref><ref>https://oxfordre.com/planetaryscience/display/10.1093/acrefore/9780190647926.001.0001/acrefore-9780190647926-e-242?p=emailAesRSwLeHBYKc&d=/10.1093/acrefore/9780190647926.001.0001/acrefore-9780190647926-e-242#:~:text=Summary,in%20spring%20and%20early%20summer.</ref>
==Liquid water== Scientists reported in July 2018, the discovery of a lake of liquid water under the southern ice cap. The measurements were gathered with the Mars Advanced Radar for Subsurface and Ionosphere Sounding ([[MARSIS]]) on board the European Space Agency's orbiting Mars Express spacecraft. Radar reflections showed a bright spot in the ice layers that analysis later showed that it had to be a lake of liquid water. It is believed that the water remains liquid, even at the temperature of -68 degrees Celsius because there is likely much dissolved salt that lowers the freezing point. The lake is about 20 kilometers across and at least 10 centimeters deep It could contain 10 billion liters of liquid water.<ref>{{Cite web|url=https://www.sciencenews.org/article/mars-may-have-lake-liquid-water-search-life|title = Mars (Probably) has a lake of liquid water|date = 25 July 2018}}</ref><ref name="R. Orosei 2018">R. Orosei et al. Radar evidence of subglacial liquid water on Mars. Science. Published online July 25, 2018. doi:10.1126/science.aar7268.</ref> There could very well be many small bodies of water under the ice cap; however, they are difficult to detect with MARSIS. Also, the raw date coverage needed for these detections is limited—only a few percent of the area has a full set of data.<ref name="R. Orosei 2018" />
==Dorsa Argentea Formation==
The [[Dorsa Argentea Formation]] (DAF) is thought to be a large system of [[eskers]] that were under an ancient ice cap in the south polar region of Mars.<ref>Allen, C. 1979. Volcano-ice interactions on Mars. J. Geophys. Res.: Solid Earth (1978–2012), 84 (B14), 8048-8059.</ref><ref>Howard, 1981</ref><ref>Kargel, J., R. Strom. 1992. Ancient glaciation on mars. Geology, 20 (1), 3-7.</ref><ref name="Head, J 2001">Head, J, S. Pratt. 2001. Extensive Hesperian-aged south polar ice sheet on Mars: Evidence for massive melting and retreat, and lateral flow and pending of meltwater. J. Geophys. Res.-Planet, 106 (E6), 12275-12299.</ref> This large polar ice sheet is believed to have covered about 1.5 million square kilometers. That area is twice the area of the state of [[Texas]].<ref>[[List of U.S. states and territories by area]]</ref>{{Circular reference|date=February 2018}}<ref>Scanlon, K., et al. 2018. Icarus: 299, 339-363.</ref> The ice sheet formed near the boundary of the [[Noachian]]-Hesperian era and receded in the early [[Hesperian]] era.<ref name="Head, J 2001" /><ref>Fastook, J., et al. 2012. Early Mars climate near the Noachian-Hesperian boundary: Independent evidence for cold conditions from basal melting of the south polar ice sheet (Dorsa Argentea Formation) and implications for valley network formation Icarus: 219,. 25-40.</ref> A thick ice sheet was able to be formed more easily in the south polar region than in the North pole because the south pole is higher in altitude.<ref>Wordsworth, R. et al. 2013. Global modelling of the early martian climate under a denser CO2 atmosphere: Water cycle and ice evolution Icarus, 222 (1), 1-19</ref><ref>Forget, F. et al. 2013. 3D modelling of the early martian climate under a denser CO2 atmosphere: Temperatures and CO2 ice clouds Icarus, 222 (1), 81-99</ref><ref>Mischna, M, et al. 2013. Effects of obliquity and water vapor/trace gas greenhouses in the early martian climate J. Geophys. Res.-Planet, 118 (3), 560-576</ref><ref>Urata, R. O. Toon. 2013. Simulations of the Martian hydrologic cycle with a general circulation model: Implications for the ancient martian climate Icarus, 226 (1), 229-250</ref><ref>Wordsworth, R. 2016. The Climate of Early Mars Annu. Rev. Earth Planet. Sci. 44, 381-408.</ref> There may have been much more water available in the Martian atmosphere when the ice sheet developed.<ref>Carr, M., J. Head. 2015. Martian surface/near-surface water inventory: Sources, sinks, and changes with time Geophys. Res. Lett., 42, pp. 1-7 10.1002/2014GL062464.</ref>
This group of ridges extends from 270–100 E and 70–90 S, around the south pole of Mars. It sits under the Late Amazonian South Polar Layered Deposits (SPLD). The amount of these ridges is huge, one study studied seven different ridge systems which contained almost 4,000 ridges that had a total length 51,000 km.<ref>Kress, A., J. Head. 2015. Late Noachian and early Hesperian ridge systems in the south circumpolar Dorsa Argentea Formation, Mars: Evidence for two stages of melting of an extensive late Noachian ice sheet. Planetary and Space Science: 109-110, 1-20</ref>
Most eskers are thought to be formed inside ice-walled tunnels by streams which flowed within and under glaciers. After the retaining ice walls melted away, stream deposits remained as long winding ridges.
[[MARSIS]] radar data suggest that significant areas of layered, potentially ice-rich parts of the Dorsa Argentea Formation remain today.<ref>Plaut, J., Ivanov, A., Safaeinili, A., Milkovich, S., Picardi, G., Seu, R., Phillips, R. 2007a. Radar sounding of subsurface layers in the South Polar plains of Mars: correlation with the Dorsa Argentea formation. Lunar Planet. Sci. XXXVIII (abstract 2144).</ref><ref>Head, J., Marchant, D. 2006. Regional polar glaciation in the hesperian period of the history of Mars. The South Circumpolar Dorsa Argentea Formation as an Ancient Ice Sheet Remnant. Fourth Mars Polar Science Conference. Davos, Switzerland.</ref><ref>Head, J., Marchant, D., Forget, F. 2007. Regional polar glaciation in the hesperian period of the history of Mars: the south circumpolar Dorsa Argentea formation as an ancient ice sheet remnant. Seventh International Conference on Mars. Pasadena, CA (abstract 3115).</ref>
A team of researchers used an early Mars global climate model together with the University of Maine Ice Sheet Model to determine how the eskers formed. They concluded that to get enough a high enough temperature in the Martian atmosphere to form the ice sheet, a greenhouse gas in addition to a thicker carbon dioxide atmosphere was needed to warm the surface near the poles by at least 20 degrees C. Also, to produce the shape of the ice sheet, at least part of the Tharsis volcanoes needed to be present.<ref>Scanlon, K., et al. 2018. The Dorsa Argentea Formation and the Noachian-Hesperian climate transition. Icarus: 299, 339-363.</ref>
==Potential ocean== Strong evidence for a one time ancient ocean was found from data gathered from the north and south poles. In March 2015, a team of scientists published results showing that this region was highly enriched with deuterium, heavy hydrogen, by seven times as much as the Earth. This means that Mars has lost a volume of water 6.5 times what is stored in today's polar caps. The water for a time would have formed an ocean in the low-lying Mare Boreum. The amount of water could have covered the planet about 140 meters, but was probably in an ocean that in places would be almost 1 mile deep.{{Citation needed|date=February 2026}}
This international team used [[European Southern Observatory|ESO]]’s [[Very Large Telescope]], along with instruments at the [[W. M. Keck Observatory]] and the [[NASA Infrared Telescope Facility]], to map out different forms of water in Mars’s atmosphere over a six-year period.<ref>{{Cite web|url=https://www.sciencedaily.com/releases/2015/03/150305140447.htm|title = Mars: The planet that lost an ocean's worth of water}}</ref><ref>. Villanueva, L., Mumma, R. Novak, H. Käufl, P. Hartogh, [[Thérèse Encrenaz|T. Encrenaz]], A. Tokunaga, A. Khayat, M. Smith. Strong water isotopic anomalies in the martian atmosphere: Probing current and ancient reservoirs. Science, 2015 DOI: 10.1126/science.aaa3630 </ref>{{div col|colwidth=30em}} * [[Climate of Mars]] * [[Dust Devil Tracks]] * [[HiRISE]] * [[Impact crater]] * [[List of quadrangles on Mars]] * [[Martian polar ice caps]] * [[Swiss cheese features]] * [[Geyser (Mars)]] * [[Water on Mars]] * [[Martian Gullies]] {{div col end}}
== References == {{reflist|colwidth=30em}}
{{commons category|Mare Australe quadrangle}} {{Mars quadrangle layout}} {{Mars}}
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