Like the Earth, Marte It has thick ice caps at both poles. But it was thought that, unlike these masses on our planet, which are underlain by channels of liquid water in even large subglacial lakes (‘hidden’ under a thick layer of ice), the Red Planet’s polar ice caps were completely frozen to bedrock due to the cold Martian climate.
However, this theory took a radical turn when in 2018 the probe Mars Expressof the European Space Agency (ESA), collected unexpected data: with its instrument MARSISan ice-penetrating radar that can ‘peek’ under the ice cap, captured what looked like liquid water at the south pole, as the signal was reflected like a mirror, just like subglacial lakes here in the earth.
And that’s where the controversy began, because for there to be liquid water under the ice cap, there should be an additional source of heat, such as geothermal heat from the core, although the levels should be higher than those recorded. Later studies indicated that other materials or substances, whose existence has been proven in other places on Mars, such as the famous brines (a mixture of water and mineral salts more resistant to boiling, freezing and evaporation than pure water), could explain that reflection. It could even be nothing more than the reflection in ancient rocks, according to a study published just a few days ago in ‘Nature Astronomy’. Still, none of these investigations has provided irrefutable evidence about the existence (or not) of liquid water under the poles of Mars.
Now a new paper, published precisely in the same journal, supports the yes hypothesis. Researchers, led by the University of Cambridge, have used laser measurements from orbiters on Mars to identify subtle patterns on the surface of the poles. With this they wanted to observe if there are small depressions in the icy surface that, as happens with subglacial lakes on Earth, indicate masses of liquid water in depth. They then made computer models to check that the movement of the ice, which is different if it has a mass of water under it than if it is on top of bedrock, corresponded to what is seen over the Martian south pole.
Their results are consistent with previous ice-penetrating radar measurements made by the European spacecraft and provide the first evidence to support the theory that there is liquid water there, albeit using tools other than radar measurements. “The combination of the new topographical evidence, the results of our computer model, and the radar data make it much more likely that at least one area of subglacial liquid water exists on Mars today; as well as that Mars must still be geothermally active so that there can be water in a liquid state under the ice cap“, affirms Neil Arnoldof the Scott Polar Research Institute in Cambridge, who led the research.
The water of the depths is reflected on the surface
On Earth, subglacial lakes affect the shape of the ice sheet above them: it reduces the friction between the ice sheet and its bed, which affects the speed of ice flow by gravity. This, in turn, affects the shape of the ice sheet surface above the lake, often creating a depression in the ice surface.
Using satellite data Mars Global Surveyor, from NASA, the team observed a surface ripple about 10 to 15 kilometers long on the ice in the area where the radar places the subglacial lake. The researchers then tested whether this observed depression on the ice surface could be explained by liquid water in the bed. They ran computer model simulations of ice flow, tailored to specific conditions on Mars, and tested with the possible existence of the lake and how it would affect the rate of ice sheet slippage. They also varied the amount of geothermal heat coming from the planet’s interior. These experiments generated ripples on the simulated ice surface that were similar in size and shape to those the team observed on the surface of the real ice sheet.
The similarity between the topographic undulation produced by the model and the actual spacecraft observations, along with previous radar work, suggest that there is an accumulation of liquid water under the south polar cap of Mars. On the other hand, the authors also point out that there was volcanic activity that, relatively recently, heated the planet, maintaining in this area the necessary heat to house a lake of liquid water under the entrails of the ice.
“The quality of the data coming back from Mars, both from orbiting satellites and landers, is such that we can use it to answer really hard questions about conditions on, and even below, the surface of the planet, using the same data. techniques that we also use on Earth”, says Arnold. “It’s exciting to use these techniques to discover things about planets other than our own.”