Depuis 18 mois, le rover Perseverance analyse sans relâche la géologie du cratère martien Jezero. © Nasa, JPL-Caltech, ASU, MSSS

Mars: the past of the crater where Perseverance landed intrigues scientists

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[EN VIDÉO] Perseverance, in search of life on Mars
Perseverance, this is how NASA has decided to name the rover that it will send to Mars in the summer of 2020. A rover that researchers expect a lot from. He will be the first to collect rock samples to bring back to Earth. Objective: find traces of microbial life.

The arrival of the rover Perseverance on Mars, which complemented instruments already on site, such as Curiosity rover or the InSight seismic stationallowed to explore a new Martian environment: the Jezero crater.

The first observations quickly established that this crater was once occupied by a large lake, fed by a river that forms a delta. Therefore, the site is particularly well suited to studying the Red Planet’s water history and searching for possible traces of life. However, these topics require a detailed study of Geology, Earth Sciences
Geology is a scientific discipline that focuses on the outer layers of the Earth, in particular its structure…” data-image=” / d /7/3d738ba741_45745_def-geologie-bonacherajf-flickr.jpg” data-url=”” data-more=”Read more “>geology of the place: nature of the rocks, mineralogy, sedimentary architecture attesting to the episodes and conditions lakeVolcano: what is the difference between lava and magma?
The morphologies created…” data-image=”” data-url=”https://news” data-more=”Read more”>volcanism

While waiting for the samples to return to Earth, an operation that is only planned for 2033analyses, however, are progressing well from the data transmitted by the homeless. Four new studies detailing the nature of the floor and subsurface of Jezero Crater have just been published together.

The Jezero Crater floor is composed of igneous rocks of deep origin.

During its journey into the heart of the ancient lake, the Perseverance rover has carried out various analyzes of the rocks that form the bottom of the crater. When everyone expected to find sedimentary rocks deposited at the bottom of the lake o Classification of volcanic rocks
Volcanic rocks are subject to classification based on various…” data-image=” pierre-thomas-ens-lyon.jpg” data-url=”” data-more=”Read more”>volcanic rockslike old streams washthe data revealed that the crater floor is actually often formed by magmatic accumulations. Find this type of rockoutcrop surprising, because these are rocks called plutonicthat is to say that they usually form in depth, generally within magma chambers and volcanoes
Coming from the Earth’s mantle through one or more conduits, the accumulated molten rock can…” data-image=” dd921d8236_45733_def -semhur-volcano-magmatic-chamber-wikimediacommons.jpg” data-url=”” data-more=”Read more “>magma chambers or at the bottom of lava lakes. They are the result in fact of a slow cooling of the magma formation
It forms at high temperature and under high pressure…” data-image=” jpg” data-url=”” data-more=”Read more”>magma. The crystals that form as the temperature decreases will gradually settle to the bottom of the magma reservoir and accumulate to form a layered rock.

In both cases, the presence of this type of rock in the outcrop at the bottom of the crater can only mean one thing: all the material that covered it has been removed by the slow process of erosion over billions of years. We are still talking about a thickness of rock several hundred meters thick! These results were published in the journal Sciences under the title An accumulated outcrop of olivine on the floor of Jezero CraterMarch as well as in the article Layered igneous terrain of composition and density in Jezero Crater, Mars appeared in Progress of science.

East stratification from the basement of Jezero Crater was confirmed by radar images made by Perseverance. In fact, the instrument carried by the rover has made it possible to obtain images of the subsoil at a depth of about 15 meters, revealing a highly stratified architecture, which can be explained by the magmatic origin of the rocks, but also by the presence of lacustrine sedimentary deposits. . These results are presented in the article Ground Penetrating Radar Observations of Subterranean Structures on the Floor of Jezero Crater, Marspublished in the magazine Progress of science.

One thing is certain, the rocks analyzed by the rover testify to a magmatic episode prior to the formation of the Jezero delta. Therefore, they could allow a lower age limit to be established for this sedimentary formation.

Different traces of weathering by water.

Their discovery is doubly interesting as these rocks also show traces of weathering by water. the igneous rocks Being particularly easy to date, the samples taken by Perseverance could make it possible to establish a precise chronology of the various hydrological events at the site and, in particular, to date the formation of the lake. These data are one of the key elements that allow a better understanding of the evolution of the heated Martian. Therefore, the study of these rocks could allow us to know precisely when the planet’s climate allowed the establishment of a water system on the surface and when the situation changed drastically towards the cold and arid conditions that we observe today.

Perseverance is not, however, in a position to carry out such dates. Therefore, we will have to wait patiently for the samples to return to Earth. However, thanks to the instruments on board the rover, a detailed study of the cumulus clouds present at the bottom of the crater is possible. Their mineralogical analysis shows that they are composed of small intricate crystals ofolivine and pyroxene, indicating slow crystallization. But what most interests specialists are the traces of weathering by water. In fact, the different samples taken by Perseverance at different points in the crater appear to have been altered in different ways.

The rocks of the Máaz site contain in their pores minerals that would have formed from an Apparation of brackish water
Brackish water may appear as a result of…” data-image=” ” data-url=”” data-more=”Read more”>Brackish water, Very salty. In contrast, rocks from the Seitah site show traces of reaction with carbonate-rich water. The two samples testify to a change in the conditions of the lake over time, which may be related to climate change. Once again, we will have to wait for the samples to return to Earth in order to accurately date these different stages and establish their chronology. The detail of the analysis is available in the article. Aqueous altered igneous rocks sampled on the floor of Jezero Crater, Marspublished in Sciences.

However, the low abundance of minerals resulting from the weathering of igneous rocks suggests that the lake’s period of existence was relatively short.

valuable samples

Apart from the very local case of Jezero, further study of olivine-rich accumulates could help to better understand Mars’ magmatic activity. Combined with satellite imagery, the data reported by Perseverance could help paint a larger-scale picture of the planet’s magmatic history.

We better understand the value of the samples taken by Perseverance and the precautions taken by the scientists in charge of the mission to ensure their back and his arrival on Earth in 11 years. In each of the four sites studied, the samples taken were duplicated. These duplicates will be stored at a backup site near the delta in case the samples held by Perseverance cannot be retrieved, due to mechanical failure, for example. Sedimentary rock samples recently collected by the rover at the delta level will also be stored at this site. New samples that should also provide us with valuable information about the past of Mars.

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