Researchers believe they’ve found some more evidence that confirms the presence of a massive reservoir of liquid water beneath the surface of Mars that was first discovered in 2018. They estimate they’ve found three additional subsurface saltwater lakes surrounding the main one.
This is a remarkable discovery, as those lakes are potential habitats for life. As Nature notes in its post detailing the researchers’ paper, the first breakthrough was met with high-level skepticism because it was only based on 29 observations between 2012 and 2015. This new research and the findings were based on 134 observations collected from 2012 to 2019.
Liquid Water Under the Martian Surface
Liquid water is crucial for biology, so the discovery will be important to experts studying the potential for life elsewhere in the Solar System. But the water bodies on Mars are also believed to be incredibly salty, making it rather challenging for any microbial life to survive in them.
Mars’ fine atmosphere means that the presence of liquid water on the surface is an almost impossibility. However, water could remain liquid underneath the ground. The most recent discovery was made using data collected by a radar instrument attached to the European Space Agency‘s (ESA) Mars Express probe, which has been rotating around the Red Planet since December 2003.
Back in 2018, scientists used data from the Marsis radar to announce the finding of a 20 kilometer-wide (12.42 miles wide) surface lake located about 1.5 km (0.92 miles) beneath Mars’ south polar deposits.
“Not only did we confirm the position, extent, and strength of the reflector from our 2018 study, but we found three new bright areas,” said co-author Elena Pettinelli from Roma Tre University in Italy. “The main lake is surrounded by smaller bodies of liquid water, but because of the technical characteristics of the radar, and of its distance from the Martian surface, we cannot conclusively determine whether they are interconnected.”
The team used a method commonly employed in radar sounder examinations of sub-glacial lakes in Antarctica, Canada, and Greenland, but slightly changed the technique so it would be able to analyze the data collected by Marsis.
“The interpretation that best reconciles all the available evidence is that the high-intensity reflections (from Mars) are coming from extended pools of liquid water,” said co-author Sebastian Lauro, also from Roma Tre University.
Salty Water Bodies Unlikely to Host Life
There is not sufficient heat at these depths to melt the ice, so researchers believe the liquid water must have high concentrations of dissolved salts. These chemical salts can lower water’s freezing point in a rather significant manner.
Recent experiments have actually shown that water with dissolved salts of magnesium and calcium perchlorate – a chemical element that contains chlorine bound to four oxygens – can remain liquid at temperatures of -123 C (-189 Fahrenheit).
“These experiments have demonstrated that brines can persist for geologically significant periods of time even at the temperatures typical of the Martian polar regions (considerably below the freezing temperature of pure water),” said co-author Graziella Caprarelli, from the University of Southern Queensland, Australia. “Therefore, we think that any process of formation and persistence of sub-ice water beneath the polar ice caps requires the liquid to have high salinity.”
Whether life could survive in such settings depends on how salty these Martian lakes are. On Earth, only very particular types of microbes, called halophiles, are able to survive in the saltiest bodies of water.
Roberto Orosei, the chief scientist on the Marsis experiment, explained: “While the existence of a single sub-glacial lake could be attributed to exceptional conditions such as the presence of a volcano under the ice sheet, the discovery of an entire system of lakes implies that their formation process is relatively simple and common and that these lakes have probably existed for much of Mars’ history.”
He added: “For this reason, they could still retain traces of any life forms that could have evolved when Mars had a dense atmosphere, a milder climate, and the presence of liquid water on the surface, similar to the early Earth.”