New evidence of liquid water under the south polar cap of Mars

The researchers, led by the University of Cambridge, used the spacecraft’s laser altimeter measurements of the shape of the ice sheet’s upper surface to determine precise patterns in its elevation. Then they showed that these models matched a computer model’s predictions of how a body of water beneath the ice sheet would affect the surface.

Their results are consistent with previous ice-penetrating radar measurements that were originally interpreted to show a possible region of liquid water under the ice. There has been some controversy over the interpretation of liquid water from radar data alone, with some studies suggesting that the radar signal is not due to liquid water.

The results reported in the journal natural astronomyIt provides the first line of independent evidence, using non-radar data, that liquid water exists under Mars’ south polar ice cap.

“Combining new topographic evidence, and results from our computer model and radar data, makes it likely that at least one region of subglacial liquid water exists on Mars today, and that Mars is still geothermally active. “Water is under the liquid ice sheet,” said Professor Neil Arnold of the Scott Polar Research Institute in Cambridge, who led the research.

Like Earth, Mars has thick ice sheets at both poles, roughly equal in common volume to the Greenland ice sheet. Unlike Earth’s ice caps, which rest on water-filled channels and even large glacial lakes, until recently the polar ice caps on Mars were thought to have froze in their beds due to the cold, Martian climate.

In 2018, evidence from the European Space Agency’s Mars Express satellite challenged this assumption. The satellite contains an ice-penetrating radar called MARSIS, which can see through Mars’ southern ice cap. It revealed a region at the base of the ice that strongly reflects the radar signal, which has been interpreted as a region of liquid water under the ice sheet.

However, later studies have suggested that other types of dry matter, found elsewhere on Mars, can produce similar reflection patterns if they are under the ice sheet. Given the cold weather conditions, liquid water under the ice cap would require an additional heat source, such as geothermal heat from the planet’s interior, at levels higher than expected for Mars today. This left confirmation of the existence of this lake is pending from another independent source of evidence.

On Earth, subglacial lakes affect the shape of the ice sheet – the topography of its surface. The water in subglacial lakes reduces the friction between the ice sheet and its bottom, which affects the flow rate of the ice under the influence of gravity. This in turn affects the shape of the surface of the ice sheet above the lake, often resulting in a depression of the ice surface followed by an upstream area.

The team – which also included researchers from the University of Sheffield, the University of Nantes, University College Dublin and the Open University – used a range of techniques to examine data from the NASA Global Surveyor Mars satellite on the surface topography of the part of Mars’ southern polar cap where the radar signal was identified.

Their analysis revealed a surface ripple of 10 to 15 km in length that includes a depression and a corresponding uplift area, both deviating from the surrounding ice surface by several metres. This is similar in size to the ripples on subglacial lakes here on Earth.

The team then tested whether the observed ripple on the ice surface could be explained by liquid water in the layer. They ran a computer simulation of ice flow, tailored to specific conditions on Mars. They then inserted a low friction patch into the bottom of the simulated ice sheet where water, if present, would allow the ice to slide and accelerate. They also changed the amount of geothermal heat coming from the planet’s interior. These experiments produced ripples on the simulated ice surface that were similar in size and shape to those the team observed on the surface of the actual ice sheet.

The similarity between the model-generated topographic undulation and actual spacecraft observations, as well as previous ice-penetrating radar evidence, suggests that there is an accumulation of liquid water under Mars’ south polar ice cap, and that magmatic activity occurred relatively recently in the interior of Mars to allow the necessary enhanced thermal heating. To keep the water in a liquid state.

“The quality of the data from Mars, the satellites orbiting the planet as well as the landers, makes us able to use it to answer really tough questions about conditions on the planet’s surface, and even below, using the same technologies we also use on Earth,” Arnold said. Exciting use of these technologies to discover things on planets other than our own. »

The research was partially funded by the European Research Council.

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Materials offered by Cambridge University. Original by Sarah Collins. The text of this work is licensed under a Creative Commons Attribution 4.0 International License. Note: Content can be modified according to style and length.