Drying up a claim — maybe — of liquid water under the south pole of Mars

In 2018, planetary scientists made a startling announcement: They had found evidence for a large lake of liquid water under the south pole of Mars.

This was surprising for many reasons. For one, while we know there's a lot of frozen water on Mars — the polar ice caps are mostly water ice, and it's been seen just under the surface down to mid-latitudes — evidence of liquid water was scarce. Also, the south polar cap of Mars is cold, so this water would have to be extremely salty to withstand the...