In what seems to have become somewhat of an annual event researchers have announced the discovery of water on Mars yet again—although this time it’s more of a confirmation of a previous announcement (with a bit extra for good measure) but not everyone is agreeing on the interpretation of the evidence… then again, that’s how science is supposed to work!

The most recent announcement of water on Mars was made today by ESA following a paper published in Nature Astronomy in which a team of researchers used radar data gathered by the Mars Express spacecraft to bolster previous claims made in 2018 of a wide, shallow lake of super-salty liquid water nearly a mile below layered ice and dust deposits at Mars’ south pole.

The team’s reanalysis of the radar data appears to not only confirm the earlier discovery, which itself was the result of a decade of painstaking research, but also identifies three more possible smaller lakes in the same “Ultimi Scopuli” region.

“We identified the same body of water, but we also found three other bodies of water around the main one. It’s a complex system.”
— Elena Pettinelli, University of Rome, research co-author

Based on the radar observations, the largest of these subglacial lakes is 12 to 18 miles (20-30 km) across and 0.9 miles (1.5 km) below the surface.

Because the atmospheric pressure on Mars is so low—just 1% of what’s found at sea level on Earth—water can’t exist on the surface in a liquid state. It would just quickly boil away, and what didn’t would instantly freeze in the average -81ºF/-60ºC temperatures. But a mile below the surface, if the water contains enough salts (that is, a lot) it could keep from freezing solid just enough to remain a liquid brine.

Here on Earth liquid brines can support life…if they’re not too salty. It is possible that a hypersaline subglacial lake on Mars might be somewhere life could exist on Mars today, but it’s also quite possible that such an environment would just be too extreme for any type of life as we know it—even if the water is there.

Remember the recurring slope lineae (RSL) news from September 2015? That was a watery discovery too.

Not all scientists agree on these findings, though. Some feel that the temperatures would have to be higher than they are at that depth to maintain water in an actual liquid state (as opposed to a thick briny slush or sludge) and others speculate that even if the lakes are liquid, they may be just too salty for any sort of life. And that’s based on what’s been found here on Earth which we already know is quite hospitable for many kinds of extreme organisms.

(Then there was the time Curiosity found traces of water in its scooped samples from “Rocknest…”in 2012.)

Lakes with a salt content about five times that of seawater can support life, but as you approach 20 times that of seawater life is no longer present, says John Priscu, an environmental scientist at Montana State University. “There’s not much active life in these briny pools in Antarctica,” says Priscu, whose group studies microbiology in icy environments. “They’re just pickled. And that might be the case [on Mars].” (Source: Nature)

Still, “not much life” isn’t zero life, and if relatively-shallowly buried lakes can be found on Mars today at the poles then perhaps they could be ubiquitous across the planet, with different kinds of environments….some of which are friendlier to life than others. If Mars did once have a thick atmosphere like Earth’s with oceans, lakes, and rivers on its surface like scientists think it once did billions of years ago (and the geologic evidence is there today) perhaps life may have arisen there and now resides in lakes like these, hidden (but also protected) below thick layers of ice and sediment.

Read more about this news from Nature here and from ESA here.