page_title: Water on Mars
section_title: Subglacial liquid water
hierarchical_section_title: Water on Mars / Present water / Polar ice caps / Subglacial liquid water
caption_attribution_description: English: 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.&#91;1&#93;&#91;2&#93; The New York Times &amp; Science - July 25, 2018 https://www.nytimes.com/2018/07/25/science/mars-liquid-alien-life.html A view of the southern polar plain of Mars, with the Mars Express’s color-coded findings superimposed at the site where they were detected. The 12-mile-wide lake is believed to be about a mile deep. References ↑ Chang, Kenneth; Overbye, Dennis&#32;(25 July 2018).&#32;"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. Retrieved on 25 July 2018. ↑ Orosei, R. et al.&#32;(25 July 2018).&#32;"Radar evidence of subglacial liquid water on Mars". Science. DOI:10.1126/science.aar7268. Retrieved on 25 July 2018.
context_page_description: Almost all water on Mars today exists as ice, though it also exists in small quantities as vapor in the atmosphere. What was thought to be low-volume liquid brines in shallow Martian soil, also called recurrent slope lineae, may be grains of flowing sand and dust slipping downhill to make dark streaks. The only place where water ice is visible at the surface is at the north polar ice cap. Abundant water ice is also present beneath the permanent carbon dioxide ice cap at the Martian south pole and in the shallow subsurface at more temperate conditions. More than 21 million km³ of ice have been detected at or near the surface of Mars, enough to cover the whole planet to a depth of 35 meters. Even more ice is likely to be locked away in the deep subsurface.
  Some liquid water may occur transiently on the Martian surface today, but limited to traces of dissolved moisture from the atmosphere and thin films, which are challenging environments for known life.
context_section_description: The existence of subglacial lakes on Mars was hypothesised when modelling of Lake Vostok in Antarctica showed that this lake could have existed before the Antarctic glaciation, and that a similar scenario could potentially have occurred on Mars. In July 2018, scientists from the Italian Space Agency reported the detection of such a subglacial lake on Mars, 1.5 kilometres (1 mi) below the southern polar ice cap, and spanning 20 kilometres (10 mi) horizontally, the first evidence for a stable body of liquid water on the planet. The evidence for this Martian lake was deduced from a bright spot in the radar echo sounding data of the MARSIS radar on board the European Mars Express orbiter, collected between May 2012 and December 2015.  The detected lake is centred at 193°E, 81°S, a flat area that does not exhibit any peculiar topographic characteristics but is surrounded by higher ground, except on its eastern side where there is a depression. The SHARAD radar on board NASA's Mars Reconnaissance Orbiter has seen no sign of the lake. The operating frequencies of SHARAD are designed for higher resolution, but lower penetration depth, so if the overlying ice contains a significant amount of silicates, it is unlikely that SHARAD will be able to detect the putative lake.
  Because the temperature at the base of the polar cap is estimated to be 205 K (−68 °C; −91 °F), scientists assume that the water may remain liquid through the antifreeze effect of magnesium and calcium perchlorates. The 1.5-kilometre (0.93 mi) ice layer covering the lake is composed of water ice with 10 to 20% admixed dust, and seasonally covered by a 1-metre (3 ft 3 in)-thick layer of CO
  2 ice. Since the raw-data coverage of the south polar ice cap is limited, the discoverers stated that "there is no reason to conclude that the presence of subsurface water on Mars is limited to a single location."
  In 2019, a study was published that explored the physical conditions necessary for such a lake to exist. The study calculated the amount of geothermal heat necessary to reach temperatures under which a liquid water and perchlorate mix would be stable under the ice. The authors concluded that "even if there are local concentrations of large amounts of perchlorate salts at the base of the south polar ice, typical Martian conditions are too cold to melt the ice...a local heat source within the crust is needed to increase the temperatures, and a magma chamber within 10 km of the ice could provide such a heat source. This result suggests that if the liquid water interpretation of the observations is correct, magmatism on Mars may have been active extremely recently."
  If a liquid lake does indeed exist, its salty water may also be mixed with soil to form a sludge. The lake's high levels of salt would present difficulties for most lifeforms. On Earth, organisms called halophiles exist that thrive in extremely salty conditions, though not in dark, cold, concentrated perchlorate solutions.
caption: Site of south polar subglacial water body (reported July 2018).
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