Radar data collected by ESA’s Mars Express probe – which detected a reflective surface – reveals a large lake of liquid water hidden beneath the southern ice sheets of the planet Mars. There have been hotly debated hints of small amounts of water on Mars before, but if confirmed, this finding would represent a before and after in the chances of our neighboring red planet.
The lake is about 20 kilometers in diameter, but the water is buried under 1.5 kilometers of solid ice.
“This is potentially a big problem,” says planetary scientist Briony Horgan of Purdue University in West Lafayette, USA. “It is another type of habitat in which life could be living on Mars today,” the authors explain to the journal Science that publishes the work.
The researchers detected the lake by combining more than three years of observations from the Mars Express spacecraft operated by the European Space Agency. The spacecraft’s MARSIS instrument pointed radar waves at the planet to probe below its surface.
As those waves broke through the ice, they bounced off different materials embedded in the glaciers. The brightness of the reflection tells scientists which material is reflecting: liquid water produces a brighter echo than ice or rock.
Combining 29 radar observations taken from May 2012 to December 2015, MARSIS revealed a bright spot in the ice sheets near the south pole of Mars, surrounded by much less reflective areas. The experts considered other explanations for that bright spot, such as the radar bouncing off a hypothetical layer of carbon dioxide ice on top of the sheet, but decided that that option would either not produce the same radar signal or be too artificial to be physically probable.
That left only one option: it is a lake of liquid water.
In fact, similar lakes have been discovered under the ice in Antarctica and Greenland.
“On Earth, no one would have been surprised to conclude that this was water, but proving the same on Mars was much more complicated, ” clarifies Roberto Orosei from the Istituto Nazionale di Astrofisica, in Bologna and leader of the study.
A brine
The lake is probably not pure water: temperatures at the bottom of the ice sheet are around -68 ° C, so pure water would be frozen, even under the pressure of so much ice. But too much salt dissolved in the water could lower the freezing point. Salts of sodium, magnesium and calcium have already been found elsewhere on Mars, and they could be helping to keep this lake liquid. It could also be that the lake was more mud than water, but it could still be a livable environment, Horgan says.
“If this lake is confirmed, it is a substantial change in our understanding of the current habitability of Mars,” says Lisa Pratt, NASA planetary protection officer.
Although the depth of the newly discovered lake is unclear, its volume still overshadows any previous signs of liquid water on Mars. It must be at least 10 centimeters deep for MARSIS to have detected it, that means it could contain at least 10 billion liters of liquid water.
Finally, discovering the lake is “a testament to perseverance and longevity,” says planetary scientist Isaac Smith of the Lakewood, Colorado-based Planetary Science Institute. “Long after the others stopped searching, this team kept searching.”
Referencia: R. Orosei et al. “Radar evidence of subglacial liquid water on Mars”. Science, 25 de julio de 2018. doi:10.1126/science.aar7268.
