intriguing discoveries about the past of the crater where Perseverance landed

intriguing discoveries about the past of the crater where Perseverance landed

intriguing discoveries about the past of the crater where Perseverance landed

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

The arrival of the rover Perseverance on Mars, which integrated instruments already on site such as the Curiosity rover or the InSight Seismic Stationmade it possible to explore a new Martian environment: the Jezero crater.

The first observations immediately made it possible to establish that this crater was once occupied by a vast lake, fed by a river that forms a delta. The site is therefore particularly suitable for studying the history of the water of the Red Planet and looking for potential traces of life. However, these issues require detailed study of the geology of the place: nature of the rocks, mineralogy, sedimentary architecture as evidence of the episodes and conditions the needle, volcanism

Waiting for the return of the champions to Earth, an operation that is only scheduled for 2033, the analyzes are still doing well from the data transmitted by the rover. Four new studies have just been published together and detail the nature of the soil and subsoil of the Jezero crater.

The bottom of the Jezero crater is composed of igneous rocks of deep origin

During its journey into the heart of the old lake, the Perseverance rover carried out several analyzes of the rocks that form the bottom of the crater. When everyone expected to find sedimentary rocks deposited on the bottom of the lake or volcanic rockslike the old streams of to washthe data revealed that the bottom of the crater actually is often formed by magma heaps. Find this type of rocksurfacing it is surprising, because these are called rocks plutonicthat is to say that they usually form deep, generally in the heart of magma chambers or at the bottom of the lava lakes. In fact, they derive from a slow cooling of the magma. The crystals that form as the temperature decreases 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 at the outcrop at the bottom of the crater can only mean one thing: all the material that covered them has been removed by the slow process of erosion over the years, billions of years. We are still talking about a rock thickness of several hundred meters! These results were published in the journal Science under the title A heap of olivine outcropping on the bottom of the Jezero craterMarch as well as in the article Igneous terrain stratified by composition and density in the Jezero crater, Mars appeared in Science advances.

This layering of the base of the Jezero crater was confirmed by radar images made by Perseverance. The instrument carried by the rover made it possible to film the subsoil at a depth of about 15 meters, revealing a highly stratified architecture, explained by the magmatic origin of the rocks, but also by the presence of lake sedimentary deposits. These results are presented in the article Ground penetrating radar observations of underground structures at the bottom of the Jezero crater, Marspublished in the journal Science advances.

One thing is certain, the rocks analyzed by the rover testify to a magmatic episode prior to the formation of the Jezero delta. They could therefore make it possible to give a lower age limit to this sedimentary formation.

Several traces of atmospheric agents by the water

Their discovery is doubly interesting since these rocks also bear traces of atmospheric agents from the water. The igneous rocks Being particularly easy to date, the samples taken by Perseverance could therefore allow to establish a precise chronology of the various water events of 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 climate Martian. The study of these rocks could therefore allow us to know precisely when the planet’s climate allowed the establishment of a water system on the surface and when the situation has drastically changed towards the cold and arid conditions we observe today.

Perseverance, however, is unable to fulfill such dates. We will therefore have to wait patiently for the samples to return to Earth. Thanks to the instruments on board the rover, it is however possible to study the mounds on the bottom of the crater in detail. Their mineralogical analysis shows that they are composed of small intricate crystals ofolivine and pyroxene, indicating slow crystallization. But what interests specialists most are the traces of atmospheric agents caused by water. The different samples taken by Perseverance in different points of the crater seem in fact to have been altered in different ways.

The rocks of the Máaz site contain in their pores minerals which would be formed by a brackish water, very salty. In contrast, the rocks at the Seitah site show traces of reaction with carbonate-rich water. The two samples therefore testify to a change in the conditions of the lake over time, to which it could be related climate change. Once again, we will have to await the return of the samples to Earth in order to accurately date these different phases and establish their chronology. The detail of the analysis is available in the article Aqueous weathered igneous rocks sampled from the bottom of the Jezero crater, MarsPosted in Science.

The scarce abundance of minerals resulting from erosion of igneous rocks, however, suggests that the lake’s existence period was relatively short.

Precious samples

Aside from the very local case of Jezero, a more detailed study of olivine-rich mounds could help better understand Mars’ magmatic activity. Combined with satellite imagery, the data reported by Perseverance could therefore help paint a larger picture of the planet’s magma 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 backup and their arrival on Earth in 11 years. On each of the four sites studied, the collected samples were duplicated. These duplicates will be stored in a backup site near the delta in case the samples held by Perseverance cannot be recovered, for example due to mechanical failure. This site will also store sedimentary rock samples recently collected by the rover at the delta level. New samples that should also provide us with valuable information about the past of Mars.

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