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Hidden Lakes of Liquid Water on Mars? Scientists Unveil New Evidence

New research suggests it might be warm enough under Mars' polar cap for salty water.

White swirls of ice look like cappuccino foam with dark red and brown surroundings on the Mars south pole.
ESA's Mars Express captured a swirling view of Mars' frigid south pole.
ESA/DLR/FU Berlin/Bill Dunford

This story is part of Welcome to Mars, our series exploring the red planet.

If we found a stash of liquid water on Mars, it would boost hopes of one day spotting signs of extraterrestrial life on the inhospitable red planet. This explains why there's an intriguing science dialogue underway about whether a reservoir of salty water lurks beneath Mars' south polar ice cap -- and a pair of new studies backs the watery side of the debate.

The two studies came out in Nature Communications and the Journal of Geophysical Research Planets within the last couple of months. Combined, they build a case for the area beneath the ice cap being warm enough for subsurface lakes to exist.

But let's rewind and review both sides of the story so far.

Water or no?

The liquid-water-under-the-ice-cap debate started with the European Space Agency's Mars Express spacecraft. 

Mars Express had gathered radar data showing mysterious reflections coming from below the cap. In 2018, a team of researchers said the data indicates a salt water lake hiding out 1 mile (1.5 kilometers) below the icy surface, and a 2019 study suggested brackish ponds were more widespread in the region than initially thought.

But not everyone agreed on the water-forward interpretation. 

NASA questioned the conclusion in a 2021 study, doubting that the subsurface area is indeed warm enough to support liquid water, even if a potential lake was extremely salty. Since then, science teams have suggested alternative explanations for those Mars Express radar reflections, ranging from volcanic rock to frozen clay.

A new argument for lakes

The new research used a combination of computer models and laboratory experiments to dissect the situation. "We decided to study the physical properties of the deposits themselves, by modeling the propagation of the radar waves through water ice and dust," said geoscientist Graziella Caprarelli in a University of Southern Queensland statement on Thursday. Caprarelli is a co-author of both papers.  

The work found that temperatures under the polar cap may reach -100 Fahrenheit (-73 Celsius), within range for briny water. Previous research had pegged the temperature as being colder, closer to -137 Fahrenheit (-93 Celsius). According to Caprarelli, "the physical properties of brines at these revised temperatures are entirely consistent with the strength of the radar signals acquired from the base of the Martian south polar deposits." 

The Journal of Geophysical Research Planets study also specifically suggests that the unique geologic and geographic conditions at the south pole could play into the existence of liquid water. Insulation from layers of carbon dioxide ice, it explains, might help maintain warmer temperatures down below.

What's next

Chances are slim humanity will get around to sending a massive drill to Mars' south pole, so expect the lakes debate to continue as scientists revisit and work through the existing data while creating new models and experiments to test their ideas.

While Mars has been slowly revealing its secrets to scientists through the work of our robotic explorers on the ground and in orbit, there's still a lot we don't know. Thus, the back-and-forth on the water question promises to remain peppy.