Arrival on Mars in February 2021, the rover Perseverance has so far explored the Jezero Crater in detail and collected rock and soil samples from this area where life could presumably have thrived. Separately, NASA and the European Space Agency are planning the mission Mars Sample Return which will aim to fetch these samples and bring them back to Earth.
When it landed on Mars, the rover Perseverance carried on board a drill and 43 titanium tubes intended to collect cores of Martian rock and soil that we hope to be able to analyze more thoroughly one day in the advanced laboratories of our planet.
Currently, 18 of the 43 tubes are already filled and sealed: among these 18 tubes, one contains air from the Martian atmosphere, two others contain samples of sand taken from the ground, and 15 include cores of rock extracted from the Martian atmosphere. Jezero crater.
The huge crater, 49 kilometers in diameter, which was created by the impact of a meteorite, was, 3.5 billion years ago, filled with water and formed a lake like that found here, in Canada, in ancient meteorite craters. Manicouagan, in Quebec, is a typical example. “There was a lake in the crater with a river coming from the west flowing into it and creating a large delta. As a delta is formed very slowly by the deposition of successive layers of sediment, it is therefore obvious that the lake has been present for a very long time, “says Canadian Raymond Francis, deputy director of scientific operations for the mission. Perseverance.
What was the lifespan of this lake? What were the environmental conditions at the time of the lake? Was the lake permanent, intermittent, or even seasonal? “The geological and geochemical details of our samples will allow us to understand all of this,” says Francis, who holds a doctorate in planetary geology and computer engineering from the University of Western Ontario.
The analysis of the samples taken from the bottom of the crater by the instruments on board Perseverance revealed last year that they are made of igneous (or magmatic) rocks that have been altered by lake water, which has changed the geochemistry and mineralogy of these rocks, says the specialist.
“In 2022, we have completed the exploration of the crater floor. Then, we reached the front of the delta towards the end of April, after a very fast crossing of the crater, the fastest ever achieved by a rover. Perseverance traveled hundreds of meters a day using new automatic navigation software that can analyze stereo photos of the environment, find safe routes for the Rover, plan the route to follow, and do that planning itself while the wheels of the Rover are turning. All this is possible thanks to the fact that Perseverance is equipped with a more powerful computer than the one with which the two previous rovers were equipped. This automatic navigation system, called AUTONAV, is the most advanced ever used on another planet,” says Francis from NASA’s Jet Propulsion Laboratory in Pasadena, California.
In search of traces of life
Perseverance therefore began exploration of the delta in 2022 and took some samples from the portion that ends in the crater. In a few weeks, the rover will begin a new campaign of exploration and sampling on the surface of the delta, which is “a very complicated terrain created by the river which has dug a multitude of different furrows. This will be very interesting for scientists because we will see what materials the delta is made of, and we will thus be able to determine whether its formation took place in a single long event or in several successive phases,” points out Mr. Francis.
“The delta is a good place to look for traces of ancient life on Mars, because the deposition of thin layers of sediment during its formation allows the physical and chemical traces of life to be well preserved,” he says.
Scientists don’t expect to find mollusk shells as fossils, but rather layers of stromatolites that are formed by bacteria. The chemical traces of life should in turn take the form of an enrichment of certain isotopes of carbon, potassium and oxygen in particular, which are abundantly used by living beings.
the helicopter Ingenuitywhich was developed and piloted at the start of the mission March 2020 by engineer Farah Alibay, is now employed to survey the terrain before driving the rover there. “This allows us to determine the places in the delta that would be the most interesting to explore with Perseverance “says Mr. Francis.
“Currently, it is winter in the northern hemisphere of Mars, where the Jezero crater and its delta are located. However, the helicopter was not designed to be in operation during this season, so it was necessary to change the software and also to turn the propellers faster because the atmosphere is even thinner in winter. Additionally, all of its navigation algorithms assume that the ground is flat. It will therefore be a challenge to climb the delta, which also has a lot of relief,” underlines Mr. Francis.
The samples
Before taking a soil or rock sample, the instruments on board the rover carry out analyzes of the terrain that will help to choose the ideal place to drill and extract Martian material. Perseverance is indeed equipped with multispectral cameras, spectrometers in remote sensing mode and spectrometers mounted on its robotic arm which allow measurements very close to the target using X, ultraviolet and infrared rays.
In 2021 and 2022, almost all samples were taken in duplicate. “We took two samples of the same rock a few centimeters apart. This duplicate sample represents a backup in case Perseverance would no longer work when we go to get the samples to bring them back to Earth, ”says Mr. Francis.
NASA and the European Space Agency are currently preparing the mission Mars Sample Return (MSR), which predicts that a lander will land on the Red Planet in 2031 to retrieve the samples. As this lander will not be mobile, Perseverance will come to meet her and send her the sample tubes that she has kept inside her, using her robotic arm.
“But since this maneuver will not take place for nearly a decade, the mechanical and robotic systems of the rover may have become defective and unable to deliver the scales. MSR says Mr. Francis. Two alternative plans have therefore been provided if such technical problems arise.
“If, in a few years, we realize that the system of Perseverance who makes the mechanical transfer begins to have problems, we can take the decision to drop all the tubes it contains on the Martian soil so that they are picked up during the MSR mission by two small robotic helicopters that the lander will bring with him,” says Francis.
If, even worse, Perseverance suffers a major failure that prevents it from releasing the samples it contains on the ground, they will be lost forever. It is therefore in anticipation of such an eventuality that certain samples were collected in duplicate, which are deposited on the Martian soil, where they would be recovered by the two helicopters of the MSR.
Since last December 16, the robot has dropped on the surface of Mars 5 the 18 tubes that it had filled and inserted into its carcass. Five other tubes will also be abandoned on the ground by February, each in a location that is clearly documented and archived. When the rover releases a tube, a camera located at the end of its robotic arm looks under the machine to check that the tube has indeed fallen on the ground and that it has not rolled in the ruts of the wheels of the vehicle. Perseverancewhere it could be overwritten.
It is planned to leave on the surface of Mars 10 tubes containing a copy of 10 different samples. The rover will keep the 33 other tubes inside it, 5 of which will be witnesses that will make it possible to check the level of cleanliness and contamination of the mechanical sampling system, until 2031, when, if all goes well, it will will transmit to the lander MSR to be sent to Earth.