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Ponds under the ice: On Mars, there could still be stable occurrences of liquid water – hidden under the ice of the South Pole of Mars. At a depth of about 1.5 kilometers, the radar measurements show a glossy layer indicating the presence of liquid water. It can be badumed that these are subglacial basins of laundry, which do not freeze due to their high salt content, as reported by the researchers in the journal "Science". If confirmed, it would be the first stable water resource on the red planet
Radar measurements suggest the presence of liquid water (blue) under the ice cover of the south pole of Mars.
© ESA / INAF, Davide Borga Coher 
Is there still liquid water on Mars today? Until now, this question is disputed. Although the red planet has a lot of ice water – both in the ice caps of its poles, as well as in the form of glaciers and ice deposits beneath the surface. However, the cold and low gaseous pressure of its atmosphere freezes or evaporates the liquid water.
The liquid water, according to common badumptions, could therefore exist only for a short time as alkali containing perchlorate in the subsoil and possibly in the craters of Mars. The fact that there are still larger and older liquid water tanks on the red planet was considered improbable.
South Pole Ice Radiated
But now Roberto Orosei of the National Institute of Astrophysics of Bologna and his colleagues could join such a reservoir of water – under the ice cap of the South Pole of Mars . "The presence of liquid water under Martian ice caps was suspected more than 30 years ago," the researchers say. Because even on Earth – for example, in the Antarctic, in northern Canada or in Greenland – radar data has detected lakes and water resources under ice caps. The pressure of ice and dissolved salts maintains this subglacial fluid.
For their study, the researchers badyzed radar data from the MARSIS instrument aboard the Mars Express spacecraft of ESA. In the period from 20012 to 29015, this radar had repeatedly illuminated an area in the Planum Austral – a flat area on the edge of the South Pole ice. In this plane, the ground is covered with alternating layers of ice and ice-mixed ice
Radar cross-section of the study area of the Austral Planum.
© ESA / INAF, Davide Borga Coher
Glossy Treacherous Radar Signal
And indeed: In part of the study area, the ice base reflected radar radiation in a striking way – that's an indication of the presence of liquid water. The thin area of radar brightness increase was located about 1.5 kilometers below the ice cap and extended over an area of 20 kilometers wide, researchers report.
According to Orosei and his colleagues, these radar signatures suggest that there is liquid water under the surface of Planum Austral. "The high conductivity data of this bright area under the South Pole ice cap indicate that there must be a saturated material in water or layers of liquid water," say the scientists. However, alternative explanations such as CO2 ice or a particularly cold water ice could not explain this signature. "So we must conclude that there is still water on Mars today," says Orosei.
Leach Pools Under Ice
If confirmed, this would be the first stable occurrence of liquid water on the red planet. Similar to subglacial water resources on Earth, this water of the Virgin Mary could also be prevented from freezing by dissolved salts, as the researchers explain. Their estimates suggest that sufficiently high concentrations of perchlorate salts could lower the freezing point of this water to around minus 60 degrees.
The study area of Planum Australia is located north of the south pole visible cap at 81 GRAD SOUTH and 193 EST.
© USGS / State University of Arizona, ESA / INAF
"We find it plausible that there is a layer of liquid perchlorate at the base of this ice," say Orosei and his colleagues. "This leaching can be mixed with the subsoil to form mud or form local leach ponds on the surface of the underground rock."
Can there be life there?
"This is certainly not a pleasant environment for life," Orosei says. But even on Earth there are subglacial, salty waters, in which there is at least one unicellular life. "These organisms survive because of salts – they use them for their metabolism," says the researcher.
He and his colleagues do not consider it impossible for life to exist in Mars's subglacial basins. However, confirming the existence of these ponds and looking for a possible life may not be easy. (Science, 2018, doi: 10.1126 / science.aar7268)
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