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Maybe hold off on that Martian ice fishing trip. Two new studies splash cold water on the idea that potentially habitable lakes of liquid water exist deep under the Red Planet’s southern polar ice cap.

The possibility of a lake roughly 20 kilometers across was first raised in 2018, when the European Space Agency’s Mars Express spacecraft probed the planet’s southern polar cap with its Mars Advanced Radar for Subsurface and Ionosphere Sounding, or MARSIS, instrument. The orbiter detected bright spots on radar measurements, hinting at a large body of liquid water beneath 1.5 kilometers of solid ice that could be an abode to living organisms (SN: 7/25/18). Subsequent work found hints of additional pools surrounding the main lake basin (SN: 9/28/20).

But the planetary science community has always held some skepticism over the lakes’ existence, which would require some kind of continuous geothermal heating to maintain subglacial conditions (SN: 2/19/19). Below the ice, temperatures average –68° Celsius, far past the freezing point of water, even if the lakes are a brine containing a healthy amount of salt, which lowers water’s freezing point. An underground magma pool would be needed to keep the area liquid — an unlikely scenario given Mars’ lack of present-day volcanism.

“If it’s not liquid water, is there something else that could explain the bright radar reflections we’re seeing?” asks planetary scientist Carver Bierson of Arizona State University in Tempe.

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