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New evidence of liquid water beneath Mars’ south polar ice cap uncovered by University of Cambridge-led research team




New evidence of liquid water beneath the south polar ice cap of Mars has been uncovered by an international research team led by the University of Cambridge.

While this does not necessarily mean life exists on the red planet, it does make it more likely that it could have existed in the past.

Mars has thick water ice caps at both poles, like Earth, and these are roughly equivalent in their combined volume to the Greenland Ice Sheet.

The south polar region of Mars. Picture: NASA/JPL/Malin Space Science Systems
The south polar region of Mars. Picture: NASA/JPL/Malin Space Science Systems

But unlike Earth’s ice sheets, which have water-filled channels beneath them and even large subglacial lakes, it has been thought that Mars’ polar ice caps are frozen solid to their beds due to the cold climate.

Now, researchers have used spacecraft laser-altimeter measurements of the shape of the upper surface of the ice cap to identify subtle patterns in its height.

They showed these patterns match computer model predictions for how a body of water beneath the ice cap would affect the surface.

The findings back up ice-penetrating radar measurements from the European Space Agency’s Mars Express satellite in 2018 that were originally interpreted as potential evidence of liquid water beneath the ice. That interpretation had been questioned, with other studies suggesting the radar signal may not have been caused by liquid water but by other types of dry materials that exist elsewhere on Mars, which could produce similar patterns of reflectance if they lie beneath the ice cap.

The new results provide the first independent line of evidence using data other than radar that there is liquid water beneath Mars’ southern ice cap.

Prof Neil Arnold, from Cambridge’s Scott Polar Research Institute, who led the research, said: “The combination of the new topographic evidence, our computer model results, and the radar data make it much more likely that at least one area of subglacial liquid water exists on Mars today, and that Mars must still be geothermally active in order to keep the water beneath the ice cap liquid.”

Earth’s subglacial lakes affect the surface topography of the overlying ice sheet by lowering the friction between the ice sheet and its bed. This alters the velocity of ice flow under gravity, impacting the shape of the ice sheet surface above the lakes, typically by creating a depression in the ice surface and a raised area further down-flow.

Using a range of techniques, the team – including researchers from the University of Sheffield, the University of Nantes, University College, Dublin, and the Open University – examined data from NASA’s Mars Global Surveyor satellite.

They found a 10 to 15km-long surface undulation comprising a depression and a corresponding raised area. Both deviated from the surrounding ice surface by several metres, which is comparable to what is found on Earth.

Computer models of ice flow, adapted to conditions on Mars, generated undulations that matched those found in the data.

This, along with the radar evidence, implies magmatic activity occurred relatively recently in the subsurface of Mars to power the enhanced geothermal heating required to keep the water in a liquid state.

Prof Arnold, a fellow of St John’s College, said: “The quality of data coming back from Mars, from orbital satellites as well as from the landers, is such that we can use it answer really difficult questions about conditions on, and even under the planet’s surface, using the same techniques we also use on Earth. It’s exciting to use these techniques to find out things about planets other than our own.”

Dr Frances Butcher, second author of the study, from the University of Sheffield, said: “This study gives the best indication yet that there is liquid water on Mars today because it means that two of the key pieces of evidence we would look for when searching for subglacial lakes on Earth have now been found on Mars.

“Liquid water is an essential ingredient for life, although it does not necessarily mean that life exists on Mars.

“In order to be liquid at such cold temperatures, the water beneath the south pole might need to be really salty, which would make it difficult for any microbial life to inhabit it.

“However, it does give hope that there were more habitable environments in the past when the climate was less unforgiving.”

The research, published in Nature Astronomy, was supported in part by the European Research Council.



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