Underground lakes on Mars? Researchers have put forward another explanation

The researchers suggest that the possible bodies of liquid water isolated under the surface of Mars a few months ago were in fact layers of mud. Divided into several studies, this work has been published in Geophysical Research Letters.

Liquid water on Mars?

Three years ago, a team of researchers surprised the scientific community by assuming the existence of a body of liquid water buried beneath the icy surface of Mars’ south pole. This body of water is twenty kilometers wide and not very deep ”It looks like one of the interconnected basins under several kilometers of ice in Greenland and Antarctica‘, was articulated at the time by Martin Siegert, of Imperial College London. Last year, these same researchers also described Discovering new bodies of water possible in the same area.

In these studies, the researchers relied on data from a radar installed on the Mars Express (ESA) probe called Mars. Radar signals, which can penetrate rock and ice, change when they are reflected from different materials. In this case, they would have produced particularly bright signals at about 1.5 km Below the surface, indicating that they cannot pass through liquid water.

If validated, this new discovery could be a real game-changer in the field of exobiology. In fact, similar subglacial lakes are known to harbor microbial life on our planet. However, re-examination of the collected data along with laboratory analyzes suggests another interpretation of the recorded signals.

Hypothesis testing

Shortly after the study was published in 2018, dozens of researchers gathered at the International Conference on Polar Science and Mars Exploration in Ushuaia. These meetings provide an opportunity to discuss the latest findings and test new theories. Naturally, many discussions revolved around these famous underground lakes. Then many scientists began to think of ways to test the underground lakes hypothesis.

A team from Arizona State University focused specifically on analyzing 44,000 radar echoes were recorded over fifteen years Using the MARSIS instrument at the south pole of Mars. The researchers revealed dozens of “bright highlights” like those in the 2018 study. In contrast, many of these signals were isolated in regions close to the surface. Now there Too cold for the water to stay liquid, even if you mix it with perchlorate, a brine commonly found on Mars that helps lower the freezing temperature of water.

mud, not water

Then two other teams analyzed these signals to determine if something other than liquid water could produce them. Soon all eyes turned to a group of mud called smectites formed by liquid water on Mars long ago.

Then the researchers tested their hypothesis in the lab. To do this, they placed smectite samples frozen at -50 degrees Celsius in a cylinder designed to measure how radar signals interact with them. The result is a response to this material Almost completely consistent with 2018 radar observations. Based on data from Mars reconnaissance vehicle (MRO), the researchers then confirmed the presence of these muds near the location of the radar observations.

These new articles offer a more reasonable interpretation of the recorded observations. Of course, the only way to be sure is to get there and dig deep under the ice. But at the moment, this is impossible.