Because it looked like Earth in its early days, Mars is the only place in the universe where humans are likely to find traces of ancient alien life. And never before has the exploration of the Red Planet been so promising.
Three missions (United Arab Emirates, China, United States) will take advantage this summer of a favorable celestial positioning to send a new flight of robots, in orbit or on the ground of our close neighbor, the most coveted of the solar system.
“Mars is the priority of space exploration because we know that billions of years ago, it was habitable”, explained during a press conference Jean-Yves Le Gall, the president of CNES, the French space agency that designed one of the main instruments of the NASA “Mars 2020” mission.
While the Moon is “desperately empty of life”, Mars seemed “promising in terms of habitability from the 17th century”, the first observations showing the possibility of the presence of frozen water at the South Pole, traces the astrophysicist Francis Rocard in his book “Latest news from Mars”.
In 1976, two American landers from the Viking program provided, for the first time, in situ data on the atmosphere, the ground … showing that there was no life present on the surface of this large frozen desert. “It was a blow to the bamboo”, which slowed down Martian exploration for 20 years, said this specialist in the solar system, interviewed by AFP.
“We had to change the strategy, with a new doctrine, which has become + follow water, follow carbon, follow light +” – the presuppositions for the formation of the living, he continues.
In the early 2000s, the proof that liquid water had flowed in quantity rekindled passions, and since then, each mission brings “more and more evidence that Mars is not as dead as it is believes “, explains Michel Viso, exobiologist.
– “History of water” –
The work of NASA’s Perseverance rover, scheduled to land in February 2021, is eagerly awaited. Complementing the Curiosity robot, working in a Martian crater since 2012, Perseverance will take up residence in an as yet unexplored environment: the Jezero crater, from which it must take samples to bring them back to Earth in the long term – this will be a first.
This 45 km diameter basin is an ideal candidate for having been able to preserve traces of a past life on its surface. It is rich in sedimentary rocks (clays and carbonates, life traps), and, above all, its delta relief is attributed to the mouth of an ancient river.
By studying the geology of Jezero, the rover will be able to characterize the geochemical environment which saw the birth of the lake, making it possible to understand “the history of water”, hopes Francis Rocard.
“Because yes, water has flowed on Mars, but the question that tarnishes us is: for how long? The longer will be the best for the living to be able to form,” said the astrophysicist.
It is not known, however, for our own planet, how long water has allowed life to flow. Or even when exactly it appeared.
Deciphering the history of Mars therefore also sheds light on that of Earth. And try to understand why, when four billion years ago, the two planets met the same favorable conditions, life remained on one, and would have disappeared on the other.
– Decisive fragments –
On Earth, the first traces of life date back 3.5 billion years – a billion years after its formation – but “it is certain that the living goes back further”, according to Jorge Vago, scientific expert at the European Space Agency (ESA), whose own ExoMars mission will leave in 2022 to drill on Martian soil.
Earth plate tectonics, which regularly renews the earth’s crust in depth, prevents any preservation of this ancestral life. Mars is free of tectonics and therefore likely to have retained in its entrails the mark of an “original” life of more than 4 billion years ago.
What if there had never been a life? The return of Martian fragments to Earth, hoped for decades, will be decisive in order to finally rule, because they can be analyzed in depth by ultra-efficient instruments, such as synchrotrons.
“If there is something, it is through these samples that we will be sure of the response we provide,” summarizes Michel Viso.
But such fragments are not expected before ten years, as this return is a complex mission. And the answer will also be difficult to interpret: “It will be a set of beams of presumptions which would lead us to say + yes, these molecules are undoubtedly the remains of metabolic activity, microbial for example”, according to l ‘expert.
There are other potential candidates for extraterrestrial life, such as Enceladus and Europe, two moons of Saturn and Jupiter. But bringing back samples or drilling their thick layer of ice is science fiction at the moment.
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