New evidence of liquid water beneath Mars’ southern polar cap has been discovered by an international research team led by the University of Cambridge.
While this doesn’t necessarily mean life exists on the Red Planet, it does make it more likely that it may have existed in the past.
Mars has thick ice caps at both poles, like Earth, and these are roughly equivalent in their combined volume to the Greenland ice cap.
But unlike Earth’s ice caps, which have water-filled channels beneath them and even large subglacial lakes, Mars’ polar ice caps are believed to be frozen to their bed due to the cold climate.
Now, researchers have used spacecraft laser altimeter measurements of the shape of the ice sheet’s upper surface to identify subtle patterns in its height.
They showed that these models match computer model predictions of how a body of water below the ice sheet would affect the surface.
The results confirm 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 under the ice. This interpretation had been questioned, with other studies suggesting that the radar signal may not have been caused by liquid water but by other types of dry material that exist elsewhere on Mars, which could produce similar reflectance patterns if they were below the ice sheet.
The new results provide the first line of independent evidence using data other than radar that there is liquid water beneath Mars’ southern ice cap.
Professor Neil Arnold, from the Scott Polar Research Institute in Cambridge, who led the research, said: “The combination of new topographic evidence, results from our computer model and radar data makes it much more likely that at least one area Subglacial liquid water exists on Mars today, and that Mars must still be geothermally active in order to keep the water under the liquid ice cap.
Earth’s subglacial lakes affect the surface topography of the overlying ice sheet by reducing friction between the ice sheet and its bed. This changes the speed of ice flow under gravity, affecting the shape of the ice sheet surface over lakes, usually by creating a depression in the ice surface and a raised area further downstream.
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 the Mars Global satellite NASA surveyor.
They found a 10 to 15 km long surface undulation comprising a depression and a corresponding uplifted area. Both deviated from the surrounding ice surface by several meters, which is comparable to what is found on Earth.
Computer models of ice flow, fitted to conditions on Mars, generated ripples that matched those found in the data.
This, along with the radar evidence, implies that magmatic activity occurred relatively recently in Mars’ subsurface to power the enhanced geothermal heating needed to keep water in a liquid state.
Professor Arnold, Fellow of St John’s College, said: ‘The quality of data from Mars, orbiting satellites as well as landers, is such that we can use it to answer really difficult questions about conditions on, and even below the surface of the planet, using the same techniques that we also use on Earth. It’s exciting to use these techniques to discover things on 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, as it means that two of the main 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 that doesn’t necessarily mean life exists on Mars.
“To be liquid at such cold temperatures, the water under the South Pole might need to be really salty, which would make it difficult for any microbial life to inhabit it.
“However, it gives 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.