Author: Lisa Grossman / Source: Science News
A Mars orbiter has detected a wide lake of liquid water hidden below the planet’s southern ice sheets.
There have been much-debated hints of tiny, ephemeral amounts of water on Mars before. But if confirmed, this lake marks the first discovery of a long-lasting cache of the liquid.“This is potentially a really big deal,” says planetary scientist Briony Horgan of Purdue University in West Lafayette, Ind. “It’s another type of habitat in which life could be living on Mars today.”
The lake is about 20 kilometers across, planetary scientist Roberto Orosei of the National Institute of Astrophysics in Bologna, Italy and his colleagues report online July 25 in Science — but the water is buried beneath 1.5 kilometers of solid ice.
Orosei and colleagues spotted the lake by combining more than three years of observations from the European Space Agency’s orbiting Mars Express spacecraft. The craft’s MARSIS instrument, which stands for Mars Advanced Radar for Subsurface and Ionosphere Sounding, aimed radar waves at the planet to probe beneath its surface.
As those waves passed through the ice, they bounced off different materials embedded in the glaciers. The brightness of the reflection tells scientists about the material doing the reflecting — liquid water makes a brighter echo than either ice or rock.
Combining 29 radar observations taken from May 2012 to December 2015, MARSIS revealed a bright spot in the ice layers near Mars’ south pole, surrounded by much less reflective areas. Orosei and colleagues considered other explanations for the bright spot, such as radar bouncing off a hypothetical layer of carbon dioxide ice at the top of the sheet, but decided those options either wouldn’t produce the same radar signal or were too contrived to be physically likely.
That left one option: A lake of liquid water. Similar lakes beneath the ice in Antarctica and Greenland have been discovered in the same way (SN: 9/7/13, p. 26).
“On Earth, nobody would have been surprised to conclude that this was water,” Orosei says. “But to demonstrate the same on Mars…
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