David F. Coppedge has the story:
The paper in Geophysical Research Letters by I.B. Smith et al., “A Solid Interpretation of Bright Radar Reflectors Under the Mars South Polar Ice” (GRL, 15 July 2021, DOI: 10.1029/2021GL093618) says that clay is a sufficient material to account for the observations. The water interpretation is problematic, because “the amount of dissolved salt and heat required to maintain liquid water at this location is difficult to reconcile with what we know about Mars.”
Clays, not water, are likely source of Mars ‘lakes’ (NASA). This press release from NASA points to another time when hydrobioscopy led planetary scientists astray. Remember the streaks on some crater slopes that were interpreted as flows of water leaking out from the subsurface? Notice the tendency to jump to biological conclusions; the first sentence in the article is, “Where there’s water, there’s life.”
David F. Coppedge, “Water on the Planetary Science Brain” at Creation-Evolution Headlines (July 30, 2021)
Credits: ESA/NASA/JPL-Caltech
Disappointing, of course. The paper is closed access but Coppedge points to this NASA story for more info:
Three studies published in the past month have cast doubt on the premise of subsurface lakes below the Martian south pole. Where there’s water, there’s life. That’s the case on Earth, at least, and also why scientists remain tantalized by any evidence suggesting there’s liquid water on cold, dry Mars. The Red Planet is a difficult place to look for liquid water: While water ice is plentiful, any water warm enough to be liquid on the surface would last for only a few moments before turning into vapor in Mars’ wispy air.
Hence the interest generated in 2018, when a team led by Roberto Orosei of Italy’s Istituto Nazionale di Astrofisica announced they had found evidence of subsurface lakes deep below the ice cap at Mars’ south pole. The evidence they cited came from a radar instrument aboard the ESA (European Space Agency) Mars Express orbiter.
Isaac Smith of Toronto’s York University bundled up while working in a lab, freezing smectite clays with liquid nitrogen to test how they respond to radar signals. The results have challenged the hypothesis that subsurface lakes can be found at Mars’ south pole. Credits: York University/Craig Rezza Radar signals, which can penetrate rock and ice, change as they’re reflected off different materials. In this case, they produced especially bright signals beneath the polar cap that could be interpreted as liquid water. The possibility of a potentially habitable environment for microbes was exciting.
But after taking a closer look at the data, along with experiments in a cold laboratory here on Earth, some scientists now think clays, not water, might be creating the signals. In the past month, a trio of new papers have unraveled the mystery – and may have dried up the lakes hypothesis.
Andrew Good and Karen Fox, “Clays, Not Water, Are Likely Source of Mars ‘Lakes’” at Mars Reconnaissance Orbiter (July 29, 2021)