“For the first time, we can trace the evolution of the Martian climate over several million years”

When it landed on Mars last February, Perseverance kinda stole the show from another rover: Curiosity. It has been nearly ten years now that the latter has been surveying Gale crater. And it is thanks to the telescope of its ChemCam that a Franco-American team has just discovered that in the past, the climate of Mars has known an alternation of dry periods and wetter periods. William Rapin, researcher at the CNRS, explains.

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In 2012, the rover Curiosity landed on Mars. A heavy machine, of nearly 900 kilograms. Intended to explore a gigantic impact crater, 150 kilometers in diameter, the Gale crater. “In the center of this crater, we find vestiges of its filling by sediment. Of sedimentary rocks partially eroded that form a mountain five kilometers high – Mount Sharp or Aeolis Monsand who recorded part of the history of Mars ”, explains William Rapin, researcher at the CNRS, in the introduction.

“Since theorbit, we already had an idea of ​​the mineral composition of the slopes of Mount Sharp. But to learn more, we had to go there. It is now done. And we were able to produce images revealing in detail the organization of the sedimentary layers and the conditions under which they were formed. “ And these change radically over the several hundred meters of depth of relief explored. Betraying climatic changes occurred in the past.

William Rapin is part of the Franco-American team that operates with the rover Curiosity. He is more exactly a specialist ininstrument ChemCam — for Chemistry Camera complet. “The particularity of this instrument – beyond the fact that it was made in France – is that it is equipped with a telescope. In principle, this is used to focus a laser to analyze rocks near the rover. But this time, we have diverted the use of this telescope to record images and analyze the outcrops in the landscape as Curiosity neared Mount Sharp. “

Climate change on Mars

Thanks to high-resolution images, the telescope of the ChemCam therefore gave to researchers a first glimpse of this region. “We observed new structures there. Above the clay formation, at least in the lower part of the formation with sulphates, we discovered sediments which were not deposited by lakes. These are arid deposits likely formed during a long dry period in the past of Mars. Long-awaited evidence that sulphates from Gale crater are correlated with environmental change, a change in weather », explains William Rapin.

Several hundred meters higher, the ChemCam telescope still shows different structures. Which this time seem to correspond to a humid environment. “For the first time, we can trace the evolution of the Martian climate over several million years. But the reason behind the climatic changes recorded in Mount Sharp still eludes us. “

This is where the Curiosity rover comes into the picture again. “We kind of gave him a road map. Now it’s up to him to take a closer look. To look for clues that will allow us to understand what happened on Mars to allow such climate changes ”, says William Rapin. By carrying out chemical analyzes that will allow researchers to finally establish with precision the composition of these sediments. ” The Curiosity drill rig is a precious instrument for us. The powder it produces is analyzed by diffraction to the X-rays. » Enough to unravel the secrets that Mars still keeps hidden in these outcrops.

“Curiosity has just arrived at the sulphate transition”, William Rapin tells us. “The outcrops that we present in our study are a few meters higher. The excitement builds as the rover climbs the foothills of mont Sharp. We will be able to begin our stratigraphic analysis. We are talking about a thickness of strates about 500 meters. It will take us years to cover this thickness. We don’t know if Curiosity will survive this. But our goal is to collect as much data as possible to understand what was at the origin of the climate changes that occurred on Mars more than three billion years ago ”, concludes the CNRS researcher.

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