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The Perseverance rover has detected potential biosignatures on Mars

The Perseverance rover has reached a major milestone in its search for traces of ancient life on Mars with the collection of the “most valuable” samples so far, containing potential biosignatures whose nature will have to be confirmed once on Earth, announced the NASA Thursday.

If this is not yet proof that life once existed on the red planet, these samples represent the best chance so far of being able to one day be able to detect with certainty possible ancient microbial life.

A potential biosignature may have been produced by the presence of life, but also by some other mechanism not involving life. To consider this biosignature as definitive, these samples will therefore have to be analyzed by powerful laboratory instruments on Earth. NASA plans to bring them back with another mission by 2033.

“I think it’s safe to say that these are going to be, and are already, the most valuable rock samples ever collected,” David Shuster, of the University of California at Berkeley.

Two carrots the size of a little finger, and kept in sealed tubes on board the rover, were taken by drilling into a rock called “Wildcat ridge”. About a meter tall, it is located in a delta that formed about 3.5 billion years ago, where a river and an ancient lake meet.

This rock is particularly interesting because it is a sedimentary rock, which seems to have formed when the water in the lake evaporated.

“Wildcat ridge” thus has “a high potential for the conservation of a biosignature”, declared David Shuster.

Analyzed separately by an instrument at the end of Perseverance’s robotic arm, the rock revealed the most abundant presence of organic compounds detected in a year and a half of mission.

These compounds – made in particular of carbon, and which can also contain hydrogen – “are the basic elements of life”, declared Ken Farley, in charge of the scientific part of the mission.

They were detected in less quantity by the rover during previous analyzes in the crater of Jezero, which contained the lake, but “as we progress in the delta, the clues become stronger and stronger”, summed up Sunanda. Sharma, a scientist at NASA’s Jet Propulsion Laboratory.

“I personally find these results very moving, because it seems that we are in the right place, with the right instruments, at a pivotal moment,” she said.

“These rocks are exactly what we came for,” said Ken Farley.

– “Lava lake” –

Other analyzes of the rover have also surprised scientists. At the bottom of the crater, they “found igneous rocks, that is, rocks that crystallized after melting,” Mr Farley said.

This discovery indicates “active volcanism”, and that before receiving water, the crater may have been filled with “a lava lake”, he said.

Samples of these magmatic rocks have been collected, and their analysis on Earth should make it possible to determine for the first time directly the age of the surface of Mars. “It’s something that we’re only indirectly inferring today,” explained Ken Farley.

But getting those samples won’t be easy.

In 2028, a mission will take off in the direction of Mars. It will carry a lander, with a mini-rocket on its back. The Perseverance rover will roll up to it, and the samples will be placed into the mini-rocket by a robotic arm.

Then it will take off, and the precious cargo will be transferred to a vessel previously placed in orbit around Mars. Once the samples have been collected, this orbiter will return to Earth, for a landing in the Utah desert in 2033.

If Perseverance fails, the lander will send two small helicopters to collect the samples, either going to the rover itself or to a backup reserve.

Indeed, Perseverance has been collecting two samples of each rock since the beginning of its mission. About ten of them (half the number collected) will soon be deposited in a very flat area, where it will be easy to land if necessary. They represent the fallback samples if it became impossible to access the rover.

After leaving this treasure on the Martian surface, in the coming weeks, Perseverance will continue its exploration to fill the twenty or so tubes that are still empty.

The next goal will be to reach the shore overlooking the old lake, which will take about a year.