Mars' south polar ice cap may contain liquid water, according to new evidence from an international team of researchers.
Mars’ south polar ice cap may contain liquid water, according to new evidence from an international team of researchers. Spacecraft laser-altimeter measurements were used by a team of researchers at Cambridge University to identify subtle patterns in the height of the ice cap’s upper surface. Using computer models, they showed that these patterns matched those predicted by computer models.
These results confirm those obtained from earlier ice-penetrating radar measurements that showed liquid water beneath the ice. Some studies have suggested the radar signal is not a result of liquid water, based solely on the radar data. This study, published in the journal Nature Astronomy, provides the first independent evidence that liquid water exists beneath Mars’ south polar ice cap other than through radar.
It appears more likely that there is at least one area of subglacial liquid water on Mars today based on the new topographic evidence, our computer model, and radar data, which suggest that Mars is still geothermally active in order to maintain liquid water under its ice cap, according to Professor Neil Arnold, the author of the study. Mars also has thick ice caps at both poles, about as large as the Greenland Ice Sheet combined. The cold Martian climate, however, has until recently meant that the polar ice caps on Mars are frozen solid all the way to their beds, unlike Earth’s ice sheets that are underlain by water-filled channels.
As evidence from the Mars Express satellite was gathered by the European Space Agency in 2018, this assumption was contested. Through MARSIS, the satellite’s ice-penetrating radar, it can see through Mars’ southern ice cap. The radar signal was strongly reflected by an area at the base of the ice, indicating liquid water beneath the ice cap. The findings of subsequent studies, however, suggest that other types of dry materials exist beneath the ice cap of Mars, which could cause similar patterns of reflectance. It would be necessary to provide additional heat to liquid water beneath the ice cap, such as geothermal heat from within Mars, at a level far beyond that which is expected in the present day. An independent line of evidence was needed to confirm the existence of the water.
Overlying ice sheets are shaped by subglacial lakes, which affect the surface topography. As a result of subglacial lakes’ water content, the friction between the ice sheet and its bed is reduced, which affects the velocity of ice flow. Ice sheet surface shape changes in response to this, often creating a depression in the upper surface of the sheet followed by a raised area lower down. A range of techniques was used to analyze data from Mars Global Surveyor’s observations of the topography of Mars’ south polar ice cap, where the radar signal was observed.
An undulation of 10-15 kilometers long deviates by several meters from the surrounding ice surface and is composed of depression and a raised area. The scales of these undulations are similar to those over subglacial lakes on Earth.
Afterward, the team investigated whether liquid water beneath the ice could explain the observed undulations. Computer models were run that simulated ice flow under Mars’ specific conditions. In the simulated ice sheet bed, they inserted patches with reduced friction that would allow water to slide and speed up the ice if present. As well as varying the amount of solar heat that came from inside the planet, they varied the amount of geothermal heat. Simulated ice surfaces generated undulations similar to those seen on real ice caps.
Based on the similarities between the topographic undulation produced by the model and observations made by the spacecraft, combined with earlier ice-penetrating radar evidence, it seems likely that liquid water exists beneath Mars’ south polar ice cap and that magmatic activity recently occurred in the subsurface of Mars to ensure the water was kept liquid through enhanced geothermal heating. Using the same techniques as we do on Earth to answer difficult questions about conditions on, and even beneath, the planet, Arnold said, we can use data from Mars, both from orbital satellites and from the landers. “It’s exciting to use these techniques to find out things about planets other than our own.”