Nasa computer generated image simulating the arrival on Mars of the Mars 2020 mission and its Perseverance rover.

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Handout / NASA / AFP

  • After focusing on the search for liquid water and the question of the habitability of Mars, Martian exploration has now reached another stage: the search for traces of past life.

  • This is the heart of the mission entrusted to Perseverance, which arrives Thursday evening on the red planet.

    The rover will not only do this on site, but will also prepare for the return of Martian rock samples to Earth.

  • Other missions, starting with the European ExoMars2020 and its rover Rosalind Franklin, will also set out in search of traces of Martian life.

    And what these rover will find will depend on whether or not humans are sent to Mars.

Sojourner, Spirit, Opportunity… Perseverance will not be the first rover to land on Mars this Thursday evening.

Four have surveyed the surface of the Red Planet before him, including Curiosity, still active more than eight years after his arrival.

And we are only talking about rovers here, these space vehicles capable of moving on the surface of a star.

Sylvestre Maurice, astrophysicist at the Institute for Research in Astrophysics and Planetology (Irap - Univ Toulouse, Cnrs, Cnes), has also added, since the end of the 1990s, seven orbiters (space probes placed in orbit around Mars) and two " landers ”(machines that have landed on Mars but have no mobility).

That is to say a total of thirteen vehicles that have left to explore our neighboring planet in twenty years.

Still missions to come?

Enough to make Sylvestre Maurice say that "we are living in a great time".

And it's not over.

If we come back to the rovers, another should land on Mars very soon.

The Chinese probe Tianwen-1, in orbit since February 10 around the red planet, is to land its own at the end of April-beginning of May.

A 240 kg robot which, for three months, will study the soil and the atmosphere of the planet, take photos, do cartography ... And then, there is Rosalind Franklin in the boxes.

It is the rover of the European ExoMars mission, which was due to leave last summer but was finally postponed to 2022. "We will then probably arrive at the end of a cycle," says Sylvestre Maurice.

In any case, the major space powers will have shown what they were capable of doing on Mars.

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But space exploration isn't all about a cock fight, either.

“Even if these different missions have not always been coordinated, there are scientific directions that emerge clearly,” continues the astrophysicist from Irap.

The first questions revolved around the search for liquid water on Mars and the characterization of past habitability.

In other words, did this liquid water allow life?

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The search for traces of past life

To these two questions, the various Martian missions made it possible to answer in the affirmative.

We have now moved on to another stage: the search for traces of past life.

This is the common thread of the mission entrusted to Perseverance.

“This quest, he will do it on site with the various instruments that he takes on board with him,” explains Sylvestre Maurice.

But the mission is even more ambitious.

Perseverance must also collect around forty samples of Martian rocks, which it will condition in sealed tubes and sow in its path.

It is then up to another rover, which should be launched around 2026, to recover these tubes, deposit them in a small rocket so that they are sent into orbit around Mars.

There, a probe will come to recover them and will take care of bringing them back to Earth.

With the promise, if all goes as planned, to be able to sift through these Martian rocks in our most modern laboratories and with analytical capacities far superior to what can be done on Mars.

But the challenge is great: "We have never yet succeeded in making a rocket take off from the surface of Mars", recalls Sylvestre Maurice.

The return of these samples is not expected before 2032 in any case.

In depth quest

For her part, if he does not aim for a return to Earth of Martian samples, Rosalind Franklin could allow a great leap in this quest for traces of past life.

Thanks in particular to its drill, capable of digging Martian soil up to two meters deep.

A first, again, which raises many hopes.

"The atmosphere of Mars is very thin and there is no magnetic field that protects against radiation, so we know that organic matter is quickly degraded on the surface," explains Jessica Flahaut, Martian geologist. and lunar from the Center for Petrographic and Geochemical Research (CNRS, Nancy).

If there is or if there has been life on Mars, it is undoubtedly in the basement that it was able to take refuge, and it is therefore there that we have the most luck. to find traces of it.

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The continuation of Martian exploration in the hands of Perseverance?

But imagine that Perseverance or Rosalind Franklin do not find any trace of past life on the red planet… “However, we will not be able to conclude that there was no or no life on Mars, explains Jessica Flahaut.

The whole problem today is that we can only land on small parts of Mars for technical reasons.

Where it is flat, where it is sufficiently illuminated *.

Above all, where the altitude is low enough to allow space probes to have time to decelerate from their entry into the atmosphere **.

In other words, many potentially very interesting sites for looking for traces of past life are inaccessible to us today.

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Conversely, if the Perseverance or Rosalind Franklin missions provide proof of current or past life on Mars, “then our view of the Universe will change.

Life will potentially be everywhere and interest in the red planet will increase further, says Sylvestre Maurice.

We would move on to the last stage of Martian exploration: the dispatch of the first manned missions.

NASA does not rule out the idea of ​​such missions for 2033.

Very optimistic, agree in saying Jessica Flahaut as Sylvestre Maurice.

"We will never risk sending men to Mars until we are sure we know how to launch a rocket from there and be able to bring samples from the red planet back to Earth", they say. both.

That's a little more pressure on Perseverance's shoulders.

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* For rovers that work with solar panels, which is not the case with Perseverance.

** “60% of the planet Mars is made up of highlands,” explains Jessica Flahaut.

In particular the entire southern hemisphere.

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