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Artistic impression of the Mars Express spacecraft probing the southern hemisphere of Mars, along with the radar cross section of the deposits in that region. Credit: ESA, INAF, David Coero Borga

A body of liquid water stretching at least 20 kilometers, or 12.4 miles, across may exist under the icy surface of Mars' southern pole, according to new research published Wednesday in the journal Science.

Why it matters: The findings could put to rest the long-running question of whether liquid water still exists on the red planet, or if it all disappeared long ago. This question has major ramifications for the planet's habitability. For more than 30 years, the presence of water has been one of Mars' deepest mysteries, since it is a key building block for life.

Past studies concluded that while there are still small amounts of gaseous liquid, water ice and other liquid forms on Mars, water doesn't stick around for a long time on the planet.

Now, Roberto Orosei of the Institute of Radioastronomy of Bologna, along with nearly a dozen other researchers, found evidence there is a stable body of water underneath Mars' southern ice cap.

The details: The team used an instrument known as the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) to study a portion of the planet's Southern Ice Cap, known as Planum Australe, from 2012 to 2015. MARSIS, which is part of the European Space Agency's Mars Express spacecraft that is orbiting the red planet, sends radar pulses that can penetrate below the surface of the ice cap.

To determine what material lurks beneath the surface, researchers then measured how the signals propagated beneath the surface and reflected back to the spacecraft.

What they found:

  • The varying brightness of the reflections from the radar profile showed scientists what lurks beneath the surface, which in this case is likely water ice and dust.
  • The area studied was topographically flat, about 20 kilometers, or 12 miles, wide and seasonally covered by a relatively thin layer of carbon dioxide ice that's no more than 1.5 kilometers, or 0.9 miles, deep.
  • Previous work in 2009 by the Phoenix Lander's Wet Chemistry Lab detected large amounts of magnesium, calcium and sodium perchlorate in the soil of the northern plains of Mars that also support the evidence of liquid water.

The report rules out a number of alternative explanations for this bright reflector, leaving the existence of liquid water, either as a distinct water layer or as saturated sediments, as the only explanation.

"This subsurface anomaly on Mars has radar properties matching water or water-rich sediments," said Roberto Orosei, lead author of the new study, in a press release.

"This is just one small study area; it is an exciting prospect to think there could be more of these underground pockets of water elsewhere, yet to be discovered."
— Roberto Orosei, lead author of the new study
  • The study finds that the radar profile of the area resembles those of liquid water located beneath Earth's ice sheets, such as Lake Vostok within Antarctica. Though temperatures at this depth would probably be below freezing, other factors may lower the melting point, including chemicals present in the liquid as well as the pressure of the ice lying on top of it.
  • The findings could shed light on Mars' history, just as Earth's ice sheets contain data on the composition of our atmosphere.
  • "Like Earth’s ice sheets, the martian ice caps are important climate archives," writes Anja Diez, a glaciologist at the Norwegian Polar Institute who was not involved in the study, in an accompanying paper.

It's unclear if any forms of life exist in Mars' subsurface lake. On Earth, lakes located underneath ice sheets are known to contain some types of microbial life forms.

The findings are not a surprise, National Environment Research Council fellow Jon Wade tells Axios. Scientists are doing what they have been for the past 30 years, he said, following the water.

  • Yes, but the raw data is limited, the researchers note. A large surface area is required for the radar, which limits the possibility of identifying smaller bodies of liquid water or if any connections exist between them. "Because of this, there is no reason to conclude that the presence of subsurface water on Mars is limited to a single location," the study states.

The bottom line: The research can show big picture concepts to several parties involved. As more is discovered about the evolution of the once water planet, scientists may learn how Earth will evolve just as Mars did, and business ventures can understand if Mars can sustain life for humans, Wade tells Axios.

"If you don’t have to take water to Mars, then that’s one thing you don’t have to worry about."
— Jon Wade, National Environment Research Council

What's next: Searching for more water. In the future, higher-resolution data could show smaller liquid water bodies on Mars that influence the ice flow and might be detectable below martian ice caps, Anja Diez wrote in an accompanying paper.

  • By analyzing Mars' glaciers and taking into account the new findings of liquid water below the south polar ice cap, scientists can "help unravel the climate history of Mars," Diez said.

Go deeper: Where in the world is Mars' water? (Axios)

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