Leading planetary scientists propose that the potential subsurface liquid water bodies on Mars, identified months ago, are in fact clay layers. Detailed across multiple peer-reviewed studies in Geophysical Research Letters, this research draws on radar data and lab experiments.
Three years ago, researchers stunned the scientific community with evidence of a subglacial lake beneath Mars' south polar ice cap—about 20 kilometers wide and relatively shallow. As Martin Siegert of Imperial College London noted at the time, it "resembles interconnected subglacial basins under kilometers-thick ice in Greenland and Antarctica." Last year, the same team reported additional potential water bodies in the region.
These findings stemmed from MARSIS radar data aboard ESA's Mars Express orbiter. Radar signals penetrate ice and rock but reflect distinctly from various materials. The signals showed bright spots at approximately 1.5 km depth, initially interpreted as liquid water interfaces.
Such a discovery would revolutionize exobiology, as Earth's subglacial lakes host microbial life. Yet, a rigorous reanalysis of the data, bolstered by laboratory tests, points to an alternative explanation.
Following the 2018 publication, experts convened at the International Conference on Mars Polar Science and Exploration in Ushuaia, Argentina, to scrutinize the lake hypothesis and explore alternatives.
A team from Arizona State University examined 44,000 radar echoes collected over fifteen years by MARSIS at Mars' south pole. They identified dozens of similar bright spots, many near the surface—where temperatures are far too cold for liquid water, even with perchlorates, Mars' brines that depress freezing points.
Two additional teams investigated non-water explanations, focusing on smectite clays—formed by ancient Martian water.
In lab tests, they froze smectite samples at -50°C and measured radar interactions in a specialized cylinder. The results matched the 2018 observations almost perfectly. Data from NASA's Mars Reconnaissance Orbiter (MRO) confirmed smectites near the radar sites.
These studies provide a compelling, evidence-based alternative. Definitive proof would require on-site drilling, but current technology falls short.
