Water on Mars: Huge Lake Detected Below Red Planet's Surface in 'Major Milestone' Discovery

Researchers have detected a 12.5 mile-wide body of liquid water below the surface of Mars using a radar zipping around the red planet.

Buried a mile beneath Mars's southern polar ice caps, the team think they've found a salty lake that might be able to harbor life, a discovery hailed as a "major milestone" for our understanding of the planet. Their research was published in the journal Science.

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An artist superimposes Mars and the Mars Express spacecraft on radar data depicting the planet’s surface (solid white line at the top) and the subglacial lake (blue patches). USGS Astrogeology Science Center/Arizona State University/ESA/INAF/Davide Coero Borga

Roberto Orosei from Italy's National Institute for Astrophysics and his team probed radar data from an instrument on the European Space Agency's Mars Express spacecraft. Launched in 2003, it's been exploring the red planet for almost 15 years.

The craft's "Mars Advanced Radar for Subsurface and Ionosphere Sounding" (MARSIS) came across strange echoes that most likely indicate a large body of water about a mile below the planet's southern polar ice cap, Orosei said in a video explaining the discovery.

These weird echoes were stronger than those from the surface. On Earth, this only happens when radars probe subglacial bodies of water like Lake Vostok in Antarctica. "We found, in fact, that any other explanation for these very strong echoes was not really tenable in light of [our] evidence," Orosei said.

The team thinks the lake is at least 3 feet deep but can't say for sure because the radar signal is absorbed by liquid very quickly.

Because the ice above the lake is incredibly clear, scientists think the water must be very cold. Liquid touching the ice, Orosei said, is probably between -14 and -22 degrees Fahrenheit. Although this is well below freezing, high concentrations of salt can keep water liquid at incredibly low temperatures, he explained. It's why trucks sprinkle salt on icy roads in winter.

"The underground water might exist as a lake trapped beneath rock layers or mixed in with Martian soil to create a salty sludge," Swinburne University astronomer Alan Duffy told the Australian Science Media Centre (ASMC). "Either way at [12.5 miles] across there is a lot of it."

Penguins explore Antarctica. Scientists think the subglacial lakes of Antarctica are a good analog for the newly detected Martian reservoir. Getty Images

"If confirmed, this is a major milestone in the understanding of the current subsurface conditions," Nicolas Mangold, a planetary geologist at the University of Nantes, France, told Newsweek in an email.

But he warned the radar data doesn't necessarily prove the lake exists. It's worth considering what other options might explain the results, he said. "I doubt that the whole community will be convinced at first look," Mangold said. "But it is a unique data set, so it [deserves] strong interest."

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"There are good reasons for caution," Michael Brown, an astronomer and professor at Monash University in Melbourne, Australia, told the ASMC. "This result relies on the interpretation of radar images.... I'm sure the scientific community will debate alternative explanations."

If the results are confirmed, they open up the possibility that other pockets of water exist on Mars, Mangold said. MARSIS—which can penetrate ice this deeply, but not rock—might miss these underground pools of liquid.

If humans one day probe this particular subglacial lake in person, it's unlikely they'll actually use its water to survive, he added. "This is deeply buried water below caps. Astronauts could [melt] the water ice at the surface...much more easily."

But—if we're very lucky—this salty, sludgy lake might just be home to some very basic alien life.

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Although it's hardly pleasant, life in such an environment is possible. Scientists believe single-cell organisms can survive in the subglacial lakes of Antarctica, Orosei explained. But given the depth of this particular pool, it will be a long time before rovers and other technology can explore the site directly.

For now, scientists will carry on using Earth as a stand-in for the red planet. "Mars has many striking similarities with our own planet. Its axial tilt and day length produce a climate that is a chilly analog of Earth's, with polar caps that mimic those of our own world's," the Australian Astronomical Observatory's Fred Watson told the ASMC.

If life is possible in the deepest, darkest, coldest parts of our planet, it might just be possible on Mars.