In 2020, the Perseverance rover was transported to Mars as part of NASA’s “MARS 2020” mission in collaboration with an international team. This mission has two objectives. On the one hand, understand the ancient climate as well as the geology of the red planet. On the other hand, trying to find traces of “past lives that could still be preserved” explains Nicolas Mangold, author of the article on the results of research and director of research at the CNRS at the Laboratory of planetology and geodynamics (LPG).
To do this, the rover must take rock samples for observation and analysis. A joint mission between the United States and Europe to bring some 40 samples back to Earth is being prepared and scheduled for the early 2030s. These will be the first Martian samples ever brought back to our planet.
The choice of Jezero is the result of field studies carried out over several years by scientists at NASA’s Jet Propulsion Laboratory. Its geological richness and its liquid past made it the ideal candidate to host the Perseverance rover. A meteorite formed Jezero about 4 billion years ago. The impact caused a depression 45 km in diameter in the ocean that once covered the North Pole of Mars.
A LAKE 3.6 BILLION YEARS AGO
Scientists once doubted the presence of an ancient lake within Jezero Crater. As Nicolas Mangold explains, the first images sent by Perseverance, which had landed two kilometers from its initial target, revealed large boulders, which made it possible to understand that the old watercourse had experienced “extremely turbulent” episodes. “. However, these rocks should not be there, at the bottom of a delta. “This first observation completely heckled us. This called into question the presence of a lake “confides Nicolas Mangold.
The search continued until Kodiak Hill was sighted. “It’s a mound that was part of that delta, but that has been cut off by erosion. She shows us some hard-hitting deposits. There, [it was] really, what you expected: the place where river water comes to the bottom of the lake and deposits its sediment. There, the stratigraphy is unique on Mars. We have never seen this type of stratigraphy, which leaves no room for interpretation “.
“We are about 100 meters below the end of the river,” explains the scientist. The lake is 100 meters lower than predicted by scientists, for a depth of several tens of meters. The Jezero Crater Lake would have measured 35 kilometers in diameter, instead of the 40 kilometers announced. “These aren’t huge differences, but it still had consequences [on our research]. The lake as seen today has no reason to have been opened to the outside. A closed lake, that has implications for what we will observe next with the rover “.
The lake would have disappeared following a very violent planetary hydrological change. Experts do not yet know the cause, but do know that it marked the end of hydrological activity within the Jezero crater.
The presence of the famous boulders present at the bottom of the delta, which had sown doubt, is explained by episodes of heavy rains that took place after the disappearance of the lake. “After the activity of the lake, there were high energy rains with a strong flow which washed away these boulders,” confirms Nicolas Mangold.
OBSERVE THE SMALLEST DETAILS
Perseverance will look for organic matter in the sediments to then sample them and be able to bring them back to Earth for future missions. “Finding the life that may have formed in the lake is a degree of complexity that is far greater than that of finding the organic matter preserved in the sediments”. Despite its seven on-board instruments and twenty cameras, it is very difficult to determine whether there was life in this lake, according to Nicolas Mangold.
After this discovery, the rover will explore further the bottom of the Jezero crater “You have to understand these rocks, […] before going further on the delta” explains the scientist.
When the rocks have been studied, the rover will be able to conquer the crater from the bottom up “to explore all the strata of the delta”.
SUPERCAM WAS DESIGNED BY A FRENCH TEAM
Why did you install so many cameras? “Cameras are our eyes. We need to be able to see at different scales, “says Nicolas Mangold.
Certain instruments are positioned at the end of the Perseverance arm “they really go into contact, they will observe with resolutions of 10, 15, 20 [micrometers]” explains Sylvester Maurice, astrophysicist at the University of Toulouse (CNES, CNRS).
Sometimes, they are more cameras that allow observation from a distance, like the MasCam and SuperCam “they look very far, at the edge of the crater or at 2 or 3 meters, down to a centimeter, even a millimeter”. There is also an environmental camera that serves as a relay for weather data, and another that serves as a radar to estimate what is happening around the rover.
The SuperCam camera was designed and conceptualized by a French team of 300 people. It consists of five different techniques allowing it to have a very varied field of action. “It’s an instrument that is based on lasers. Red lasers, green lasers, he does many things and is a bit like the French Swiss Army Knife of the mission! »Explains the scientific co-manager of the camera.
One of the innovative elements of SuperCam is the microphone, which picks up the sounds of the red planet. This is the first to have been installed; it allows Terrans to hear what is happening on the Red Planet and imagine how their own voices might resonate there.
“The mission is built around the return of samples. We have done three so far. [We have] samples of about ten grams in a tube. We are going to do about forty of them, and then they will be brought back to Earth one day”. In order to determine which samples will be selected, SuperCam itself does the selection and context work to understand where this stone comes from and what its environment is.
SuperCam is in fact the modern version of the camera installed on the Curiosity rover, which has been on Mars since 2012. “In 2000, there are two of us; we draw on a piece of paper. Afterwards, we try to convince the agencies, the labs, etc… Then in the end, it worked rather well, even very well! Therefore, in 2014, we drew another one that was SuperCam, “remembers Sylvester Maurice. The camera is reproduced identically, but modernized, “adding another laser to vibrate the molecules. Then we added infrared, which is a kind of thermal signature, as well as the microphone.
