On the trail of the Martian wet: Researchers have confirmed previous indications of the existence of a liquid body of water under the South Pole ice cap of our neighboring planet and have also tracked down other smaller reservoirs in its vicinity. Presumably, the high salt content prevents the water from freezing at a depth of around 1500 meters. The researchers say that microbial life may even exist in the frosty liquid.
Today only the frozen remains on the poles can be seen, but it is now accepted that Mars was shaped by liquid water in its youth. It is assumed that in the course of time a large part of this water resource escaped into space, while the planet grew increasingly cold. The remains of the water now form the ice caps at the poles and there are presumably also various ice deposits under the surface. But maybe Mars also has liquid water reservoirs?
Salty liquid underground?
In 2018, the researchers led by Roberto Orosei from the National Institute for Astrophysics in Bologna presented evidence of such a reservoir under the South Pole ice cap of Mars. In radar data from the MARSIS instrument of ESA’s Mars Express spacecraft, they discovered a zone with conspicuous patterns of radar reflection under the ice. They interpreted it as a sign of a layer of liquid water. But questions remained unanswered and so Orosei and his colleagues have continued to investigate the trail in the meantime. As part of their current study, they evaluated new radar scans of the MARSIS instrument that were created between 2010 and 2019.
The focus was once again on the area in which the researchers had previously discovered the evidence of the water body – but now they have expanded the focus: They examined fluoroscopic data from an area 250 kilometers wide and 300 kilometers long, the one on the edge of the Martian South Pole Ice Cap and is covered by layers of ice and Martian dust. They also applied an additional analytical method to the data, based on a signal processing technique that was recently successfully applied to the detection of terrestrial water bodies beneath the polar ice sheets. The basic indication is the fact that liquid water reflects the radar rays differently than ice or rock – it appears as a particularly bright layer on the visualizations.
A “lake” surrounded by “ponds”
As the scientists report, they have now been able to further substantiate and expand their theory of the existence of the liquid water reservoir. The data show that the primary body of water is approximately 30 kilometers long and 20 kilometers wide at a depth of about 1,500 meters. The new data also confirmed the fluid consistency of the material. In addition, the team now presents new references to other smaller water reservoirs, which are apparently separated from the main body by strips of dry areas.
The authors suspect that the fluid reservoirs consist of so-called hypersaline solutions that do not freeze even at extremely low temperatures. In principle, this is the effect of road salt that is used for winter maintenance on the roads. In the case of Mars, high concentrations of so-called perchlorate salts, which are known to be common there, could provide protection against freezing. The bottom line is that the evidence now increasingly reinforces the assumption that there are various liquid or wet areas in the subsurface of Mars, the scientists summarize.
Finally, they also emphasize the importance of the results for astrobiology, because it seems conceivable that specially adapted Mars microbes could exist in the liquids. “The possibility of extensive hypersaline water bodies on Mars is particularly exciting because of the potential for extremophilic life forms to exist. The possible reservoirs under the strata at the South Pole therefore represent areas of particular interest. Future missions to Mars should target this region to obtain experimental data on the hydrological system, its chemistry and possible traces of astrobiological activity, ”the scientists write.