Nearly 15 years af­ter ar­riv­ing at the Red Planet, ESA’s Mars Ex­press mis­sion makes a break­through dis­cov­ery

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At the end of July, sci­en­tists from the Euro­pean Space Agency (ESA) an­nounced what’s ar­guably one of the big­gest sci­en­tific break­throughs of 2018 so far: there is liq­uid water on Mars. The dis­cov­ery of an un­der­wa­ter lake be­low a glacier in Mars’s south po­lar re­gion was made us­ing the MARSIS (Mars Ad­vanced Radar for Sub­sur­face and Iono­sphere Sound­ing) in­stru­ment on ESA’s Mars Ex­press probe, which has been in or­bit around the Red Planet since De­cem­ber 2003.

While the sur­face of Mars is far too cold for water to ex­ist in liq­uid form, the cov­er­ing of ice at the poles, which can be up to 2km thick, acts like an igloo, trap­ping what lit­tle heat Mars emits due to the de­cay of ra­dioac­tive el­e­ments within its core. If the water in ques­tion is also highly salty, as it’s be­lieved to be, it could there­fore per­sist in liq­uid form, as salty water has a lower freez­ing point.

Mars Ex­press project sci­en­tist Dmitri Ti­tov, who’s been in­volved in the mis­sion since its ear­li­est days, was up­beat about the dis­cov­ery. “MARSIS has told us lots of other in­ter­est­ing things,” he said. “Its sub­sur­face sound­ing of the en­tire planet has re­vealed the many layers be­low the sur­face, and its radar is also very ef­fi­cient at


sound­ing the iono­sphere [up­per at­mos­phere], so it’s re­ally a very mul­ti­dis­ci­plinary op­er­a­tion. But one of the pri­mary goals of the mis­sion, like a torch on the far hori­zon, was al­ways to dis­cover water.”

Sci­en­tists have known for a long time that there was water on the Mar­tian sur­face in the dis­tant past, due to the ero­sion pat­terns in the rock and the ex­is­tence of hy­drated ma­te­ri­als. The pres­ence of water ice to­day was con­firmed for sure 10 years ago by NASA’s Phoenix lan­der, but this is the first time that liq­uid water has been dis­cov­ered there.

The dis­cov­ery was made pos­si­ble by what was ef­fec­tively a firmware up­grade to MARSIS, so that in­stead of study­ing the whole plan­e­tary sur­face in stan­dard res­o­lu­tion, it sent back high-res­o­lu­tion data from a spe­cific area. To do this, the team had to by­pass some of the on­board data pro­cess­ing, which as Ti­tov ex­plains “was do­ing some kind of av­er­ag­ing and cal­cu­la­tions on­board. But now they said no, let’s just download all of the data and do all the pro­cess­ing here on the ground.”


The un­der­wa­ter lake found by MARSIS is sim­i­lar in many ways to Lake Vos­tok, the lake that in 1973 was dis­cov­ered ly­ing un­der four kilo­me­tres of Antarc­tic ice here on Earth. Given that there are widely be­lieved to be unknown mi­crobes dwelling in Lake Vos­tok, what does the MARSIS dis­cov­ery say about the prospects for find­ing life on Mars?

“I think that yes, now we have some po­ten­tial for Mar­tian life,” said Ti­tov. “Simply be­cause water is there and water is one of the ma­jor in­gre­di­ents. It’s also im­por­tant that this water is hid­den un­der a 1.5 to 2km layer of ice, which pro­tects it from the in­ten­sive UV ra­di­a­tion from the Sun. But get­ting there and drilling through the ice is a huge challenge, so it will be some time, pos­si­bly decades, be­fore we know for sure.”

In the mean­time, the MARSIS in­stru­ment will con­tinue to look for more sub­sur­face pock­ets of water. But the dis­cov­ery of just one has clearly made Ti­tov and his team ex­tremely happy.

“For us, this dis­cov­ery demon­strates that de­spite the mis­sion be­ing quite old now, de­spite there be­ing new mis­sions there, it still it has the po­ten­tial for new dis­cov­er­ies, for col­lect­ing new data,” he told us. “So it’s very good news for the Mars Ex­press team.”

Radar sig­nals sent out by the MARSIS in­stru­ment can be used to build an im­age of the Red Planet’s in­te­rior. Here, the bright­est re­gions sug­gest the pres­ence of water Sur­face South po­lar lay­ered de­posits (ice and dust layers) Bright­est radar echoes sug­gest water

NASA’s Mars In­Sight lan­der is due to ar­rive at the Red Planet later this year, and should tell us even more about the planet’s in­te­rior

ESA’s Mars Ex­press probe

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