(Paris) Why is Mars deserted and uninhabitable, when life has flourished on a fairly similar planet Earth? The discovery of a NASA vehicle, presented in a study on Wednesday, suggests that if rivers have flowed well sporadically on the red planet, it was condemned to remain desert.
Mars is considered to have had all the ingredients necessary for the appearance of life, including the most essential: water. The surface of the nearest neighbor of the Earth is marked by the imprints of ancient lakes and rivers.
Several robotic vehicles are looking for traces of a life that could have been there ago millions of years ago.
Earlier this year, the vehicle Curiosity discovered a missing piece in this puzzle: rocks rich in carbon minerals. Of the same type as the limestone found on earth, they have been formed like sponges with carbon dioxide, captured in the atmosphere.
A new study, published in the scientific journal Naturehas accurately modeled how these rocks can modify our understanding of the past in March.
Ephemeral “oasis”
She would have recorded “brief episodes of habitability at certain times and places”, explained to AFP the first author of the study, Edwin Kite, planetologist at the University of Chicago. But these “oasis” were the exception rather than the rule.
On the earth, carbon dioxide present in the atmosphere warms the planet. And on long time scales, it is incorporated into carbonated rocks. Before volcanic eruptions refer gas to the atmosphere, creating a climate cycle which allows to maintain that of water.
Only Mars experienced a “low” rate of volcanic gas rejection, rich in carbon, compared to that of the land, explained Edwin Kite. With the consequence of an imbalance which left the planet much colder and less hospital.
According to the modeling of researchers, the brief periods of presence of liquid water on Mars were followed by 100 million years of a desert episode, far too long for anything to survive.
However, the researcher does not exclude the presence of deeply buried liquid water pockets below the surface.
Another NASA vehicle, Perseverancewhich arose in 2021 in another former planet delta, also found traces of carbonated rocks on the fringe of a dry lake.
But to have the end of the story, you should be able to study samples of these rocks on earth. American-European and Chinese space programs have that in their box.
“The origin of life”
In the end, scientists seek the answer to one of the great questions asked to man: is the land the only planet to shelter life?
To date, astronomers have discovered around 6000 planets outside the solar system. But they are all far too distant to hope to report samples one day.
A point raised by Mr. Kite to defend a mission reporting samples in March. It would determine if the planet could contain it would be only microorganisms during the period when water was present. Otherwise, this would be an indication of the difficulty in seeing life appear elsewhere.
Conversely, finding such traces of life spent in samples, “we would tell us that the appearance of life is easy on a planetary scale”, according to Mr. Kite.
