Tantalizing evidence of a salty water lake under the surface of Mars

Mars was warmer and wetter billions of years ago than it is today. Credit: NASA

There seems to be a salty lake lurking under the ice near the South Pole of Mars, if this is confirmed, this lake would be the first body of liquid water ever detected on the red planet, making this discovery a significant milestone in the quest to determine whether life exists there. 

The discovery has been reported by a team of Italian researchers, led by Roberto Orosei, and make public on 25 July in Science. They employed the European Space Agency’s Mars Express spacecraft to carry out this finding. Orosei, a planetary scientist at the National Institute of Astrophysics in Bologna, Italy. He said, “It’s a very promising place to look for life on Mars, but we do not know for sure if it is inhabited.” On our planet, similar ‘subglacial’ lakes are home to microbial life. 

There is mix feelings about this discovery, some say that the work is tantalizing but the hunt for water on Mars is a controversial theme. Here on earth, the researchers had drilled into subglacial lakes to sampled the water for signs of microbes while others are developing technologies to reach a buried ocean on Jupiter’s moon Europa. Currently, there are no ice-drilling missions to Mars, however this could change everything. “It begins a new line of inquiry that’s very exciting,” says Jim Green, NASA’s chief scientist. 

Today, we find water on Mars in various forms, a left over from when the planet was warmer and wetter. The orbiting missions spotted ice, including buried glaciers, in many locations. We have taken pictures of steep slopes whose appearance changes seasonally, as if liquid water is running downhill and leaving dark marks, and also NASA’s Curiosity rover has taken measurements of water vapour in the planet’s atmosphere. 

To find this salty lake, Orosei and his team used the radar instrument called MARSIS aboard Mars Express, focusing their search on the layers of ice and dust that cover the planet’s south pole. However, the observations were frustratingly inconsistent. But in 2012, the scientists decided to have MARSIS send back raw data, instead of performing automated processing before beaming the data to Earth. “This changed everything, and it was much more obvious to spot the bright reflectors,” says Orosei. 

Radar tracks on Mars's Planum Australe show the location of a potential buried lake (in blue). Credit: USGS Astrogeology Science Center, Arizona State University, INAF

Readings from the instrument, in a zone of 20 kilometre-long, known as Planum Australe, and after ruling out other possible explanations, such as carbon dioxide ice, make the scientists conclude that the reflections were coming from subsurface water. This would be at a depth of 1.5 kilometres beneath Mars’s surface and for at least 1 metre deep. For this water to keep from freezing it must be salty, Orosei says, and may be similar to the super-salty subglacial lakes reported in the Canadian Arctic earlier this year in Nature. Interestingly, on Mars, salts known as perchlorates might be what’s making the brine. Back in2008, NASA’s Phoenix spacecraft found perchlorates in soils near the planet’s northern polar ice. 

May be, Mars had many similar lakes in the past and with the right chemical elements available to supply energy, a buried martian lake would have the ingredients needed to sustain life — as long as it's not too salty, says John Priscu, a biogeochemist at Montana State University in Bozeman. He is drilling into Antarctica's subglacial Lake Mercer later this year, lots of equipment is needed for this, something that it might seem impossible for Mars. 

However, with the arrival of NASA’s InSight probe this November landing on the Martian equator, a new window opens up. Since, it will measure heat flow in the top 5 metres of the surface there, and Scientists can use that data to extrapolate how much heat might be rising from beneath the south polar cap, melting the ice and creating more potential lakes. The team of Orosei has glimpsed other bright reflections, however, they aren’t ready to say whether or not they are lakes. More work will be needed for this endeavour. 

Sources: Nature, Wikipedia,