Are there lakes on Mars? Scientists find evidence of multiple water bodies under Red Planet's icy surface
Besides confirming the presence of a lake first detected in 2018, the study says that three more have been detected under the Martian surface
In 2018, scientists said that they have spotted a large reservoir of what could be liquid water beneath the South Pole of Mars. Taking this intriguing discovery forward, researchers now say they have not only confirmed the presence of the first lake, but they have also found evidence of a patchwork of three salty lakes below the surface of Mars.
The current study involves a 13-member team comprising physicists, geologists and engineers from the University of Southern Queensland (Australia), Roma Tre University (Italy), Jacobs University (Germany), Italy's National Institute for Astrophysics (INAF) and Italy's Consiglio Nazionale delle Ricerche (National Research Council). Their findings point to the existence of "multiple ponds of hypersaline water" under the Red Planet's icy surface.
The results add significantly to the long-studied and long-debated question of how much surface water was once on Mars, a subject that has major implications for the question of whether life ever existed on the planet. The breakthrough was made by examining radar data from MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding), a scientific instrument onboard the European Space Agency's Mars Express spacecraft.
According to the international team, it is the first "alien" water found there since 2018. “Not only did we confirm the position, extent and strength of the reflector from our 2018 study, but we found three new bright areas. The main lake is surrounded by smaller bodies of liquid water, but because of the technical characteristics of the radar, and its distance from the Martian surface, we cannot conclusively determine whether they are interconnected," explains co-lead author Elena Pettinell from Roma Tre University, in the analysis published in Nature Astronomy.
Roma Tre University along with INAF was involved in the 2018 study, which detected an area of strong reflectivity, approximately 1.5 km beneath the South Polar layered deposits, a thick polar cap formed by layers of ice and dust. Data originally indicated that a large, salty lake might be buried beneath a region called Ultimi Scopuli. The subterranean lake was described as being about 20 kilometers in diameter.
Back then, the team had said that the detection of signs of liquid water below the Martian surface suggests that there are other underground lakes and streams below the surface of Mars. The latest results "strengthen the claim of the detection of a liquid water body at Ultimi Scopuli and indicate the presence of other wet areas nearby."
"The biggest unanswered question from our earlier paper was: is this the only evidence of sub-ice liquid water? At the time we did not have enough evidence to address this question, but this new research demonstrates that the 2018 discovery was only the first piece of evidence of a widespread system of liquid water bodies in the Martian subsurface," explains Enrico Flamini, president of the International Research School of Planetary Sciences at the University of Chieti-Pescara (Italy), formerly science mission programs manager with the Italian Space Agency.
Principal Investigator of the MARSIS experiment, Roberto Orosei, says that while the existence of a single subglacial 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. "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," he adds.
The investigators borrowed a methodology commonly used in radar sounder investigations of subglacial lakes in Antarctica, Canada, and Greenland, adapting the method to analyze old and new MARSIS data. MARSIS sends radar pulses that penetrate the surface and ice caps of the planet, then measures how the radio waves propagate and reflect back to the spacecraft.
Reflections off sub-surface features provide scientists with information about what lies beneath the surface. The team confirms that thick ice sheets, far from being uniformly structured wastelands, should be viewed as "stratigraphically and physically complex geological formations," deserving to be fully explored in detail. "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," writes co-lead author Sebastian Lauro from Roma Tre University.
Laboratory experiments that studied the stability of "hypersaline aqueous solutions" or brines helped explain the presence of liquid water. According to co-author Graziella Caprarelli, an adjunct research fellow with the University of Southern Queensland’s Centre for Astrophysics, these experiments "have demonstrated that brines can persist for geologically significant periods even at the temperatures typical of the Martian polar regions (considerably below the freezing temperature of pure water). Therefore, we think that any process of formation and persistence of sub-ice water beneath the ice polar caps requires the liquid to have high salinity."
Since brines had been shown to have the potential to sustain microbial life in extreme conditions, the scientists recommend that renewed efforts should be made to explore the polar regions of Mars, with the specific purpose of finding reservoirs of subglacial water and of determining their composition.