Perseverance, a sophisticated scientific laboratory: interview with planetologist Erwin Dehouck





In addition to the 23 (!) Cameras on board the Mars2020 mission and the small Ingenuity helicopter, Perseverance is carrying eight scientific instruments and enough to take soil samples. A real laboratory to discover in detail the Jezero crater!

To discuss the scientific aspect of this mission, we spoke with teacher-researcher Erwin Dehouck, from the Lyon Geology Laboratory (Earth, Planets, Environment), who works daily with data from the Curiosity rover, and soon to Perseverance.



On the team side, a lot of enthusiasm!

“It's a fantastic opportunity”, explains Erwin Dehouck. Part of the scientific team working today with the Curiosity rover will be in charge of the first operations with its cousin, Perseverance. “There is an obvious continuity between the two missions, at the technical level as well as at the human level. We will discover a new place on Mars, and we will help choose the first Martian samples that will return to Earth! At the same time, it's also a challenge: as Curiosity continues to function well, many of us are going to have to 'juggle' between the two projects ”.

However in France as in the United States, the whole team is in the excitement of the departure… And this even if the rovers are piloted from the JPL in California (Pasadena), which implies to work in the evening, even until 2:00 am, Toulouse time!




NASA already organizes regular training sessions, so that all concerned are ready by next February. 'I am a teacher-researcher, so I share my time between teaching at the university and scientific research,' explains Dehouck. My role will be quite similar, with Perseverance, to what it is today with Curiosity: I will participate in the planning of the rover's activities on Mars (which we call 'operations') in particular with the SuperCam instrument, but also to scientific discussions on data ”.

However, with a different organization, details the planetologist, because the American agency has decided to reduce the time between the moment when the data of the past day will be received on Earth, and that or a new list of orders will be transmitted to Mars. While perfect for optimizing the rover's activities, this will require even greater interaction between colleagues!

Having two missions such as Curiosity and Perseverance active at the same time is a chance. Eight years apart, the two robots have a lot in common. “But there are some analyzes possible with Curiosity that won't be possible with Perseverance, and vice versa. Importantly, the two missions are on two different sites. It would not occur to an Egyptologist to study only one piece in a pyramid, and to abandon all the others. On Mars, it's a bit the same thing: we need to have an overview of the planet in order to accurately reconstruct its geological and climatic evolution, ”explains Erwin Dehouck.




What tools for Perseverance?

NASA has set itself four very long-term objectives for the planet Mars: to determine whether life has existed there, to precisely characterize its climate and geology, and to prepare for future human exploration missions. We have to admit that the instruments on board Perseverance correspond very well to these objectives! On the body of the rover first, there is a very interesting ground-penetrating radar at the rear, named RIMFAX (delivered by Norway) and an experimental MOXIE box which will test the production of oxygen and methane from atmospheric CO2. This is a very first test of the so-called 'ISRU' technology for In-Situ Resource Utilization, that is to say the production of useful resources for a future inhabited adventure with the elements in place.

Placed both on the body and on the Perseverance mast, we find the Spanish MEDA experience, which consists in a way of a 'weather station' and measures wind speed, atmospheric pressure, temperature, humidity and solar radiation. Also on the mast, just under the “head” of the rover are the two Mastcam-Z stereoscopic cameras, capable of zooming and capturing native color images of the planet Mars, in 2D and 3D.




Perseverance also has, like its predecessor, a robotic arm 2 meters long, at the end of which there is a scientific 'toolbox' with the PIXL X-ray spectrometer and the SHERLOCK instrument which will attempt to determine the nature of the minerals with very high resolution.

Above all, we will also find the rotary drill of the rover, more impressive than that of Curiosity. It should be able to take several grams of material, then delicately deposit them in one of the 43 tubes carried by the mission in front of the “caching system”. This device alone represents an almost independent robot that operates in and under the Perseverance sill. It collects, stores, sorts, seals the soil samples, with its own robotic arm that remains inside the rover.



France is on board!

The big white case, the 'head of the rover' which culminates at almost 2 meters high, is SuperCam, a multiple instrument that brings French expertise into play. There is a laser capable of pulverizing the rock to study it with the LIBS (Laser Induced Breakdown Spectroscopy) technique and Raman spectrometry, a microphone capable of listening to impacts (but also the mechanical noises of Perseverance), a camera high resolution color for the background, and a passive visible-infrared spectrometer (VISIR) which will analyze the light reflected from the ground of Mars. It should be noted that the box is only the visible facade of SuperCam, whose analysis instruments are located inside the rover and connected by optical fiber.





“Supercam takes over the functionality of ChemCam, which uses an infrared laser to remotely measure the chemical composition of rocks,” confirms Erwin Dehouck. But he adds several more! The mission of infrared and Raman techniques is to identify the minerals that make up the rock, and possibly the organic molecules it contains. In other words, in addition to the amount of the different chemical elements present, we will now be able to know how these elements are assembled with each other, which is crucial to understand the conditions under which the rock was formed, if it encountered 'a lot of liquid water since its formation, etc. '.

The teams will be able to take advantage of the experience acquired with ChemCam to be more quickly operational and efficient on Mars with the use of the new instrument.



No SAM on Perseverance ...

Finally, you may remember that France and its laboratories contributed to the Curiosity mission with the SAM instrument, which analyzes the samples dug by the rover's arm. A system that has not been retained for Perseverance, which will leave its tubes behind to be brought back to Earth. A disappointment for French scientists?

“I imagine my colleagues on the SAM team would have liked to have had a second copy on Mars! But this is not really the philosophy of this mission, and there are two elements to remember, says Erwin Dehouck. First of all, the work with Curiosity is far from over: the teams are just about to collect a new sample for SAM! And above all, there will be the mission of the European rover Rosalind Franklin with its MOMA instrument, which will carry out certain analyzes similar to those of SAM on the soil of Mars ”. However, it will be necessary to wait until 2023 for the latter ...




Searching for 'traces of life', a scientific challenge

If all goes well on takeoff this Thursday, July 30 and the arrival of the rover on Mars on February 18 (and between the two), Perseverance will be able to begin its exploration of the Jezero site, chosen after several years of study, according to proposals from a scientific consortium. However, for the public, it is not always easy to understand why Jezero (which, on the visible level, will be just as deserted as the other Martian places visited before him) is of major interest.

After all, Curiosity also evolves within a crater (Gale) and there was a great deal of evidence found there for the presence of water… “It's true, like Gale, Jezero is an impact crater, but his diameter is about three times smaller. Like Gale, the interior of Jezero was occupied by a lake at one time - this can be seen by the very beautiful delta in its western part (near which Perseverance will land), which resembles those found in the mouths of rivers on Earth. One of the differences between the two sites is that Jezero has an outlet, that is, a valley through which water could exit the crater, while Gale was a hydrological 'terminus'. Another important difference is the presence of areas rich in carbonates in Jezero: these minerals are very common on Earth, but rare on Mars (Curiosity found only a few traces in Gale); However, carbonates are good indicators of past environmental conditions, and can preserve possible biosignatures. These areas are priority targets for Perseverance ”, explains Erwin Dehouck.

The planet Mars is often described as being 'frozen in the past', because the conditions on its surface have changed very little since it deserted more than 3 billion years ago. In a way, it is an extraordinary chance to be able to observe this preserved environment (the Earth having a geology and a much more active climate, the primary conditions on its surface are long gone).




But we do not necessarily realize the difficulty in finding traces of life. “The period in the history of Mars during which we believe that its surface environment may have been 'habitable', that is to say conducive to the emergence and development of life, is at a time when , on Earth, there were only single-celled and microscopic organisms. We are therefore not looking for fossilized skeletons on Mars, ”Erwin Dehouck recalls.

The answer lies in chemistry and geology. It is therefore rather a matter of looking for elements which, by being together one day, could allow the emergence of conditions favorable to the development of life.

“These are much more discreet markers,” says the planetologist. This can be mineral structures that cannot be explained by purely abiotic processes, or even anomalies in the abundance of certain organic molecules. Highlighting such markers, and demonstrating that they are indeed linked to life, requires very in-depth analyzes, which are difficult to carry out with a rover. Hence the idea of ​​bringing Martian samples to Earth! '.

We therefore understand that it is not easy to find a consensus on the results of the sensors sent to Mars, because what they observe is more akin to a treasure hunt, to a bundle of presumptions that we then shapes with our earthly knowledge of the living.

A treasure hunt that should not leave room for speculation, so the return of samples should allow very thorough analyzes, over long periods, by laboratories at the forefront of research throughout the world. The advantage of a platform such as Perseverance is that it is designed to travel several tens of kilometers, and that it is sent to an area rich for its geological diversity.

If all goes well, researchers may have an impressive variety of soil samples from Mars within a decade. And when we know that only a few grains of matter can reveal a lot about the past of the planets, we better understand the impatience for the upcoming Mars Sample Return mission!




This orientation for future collection and study is reflected in the very conception of Perseverance's mission. “The rover is indeed very well equipped for in situ analyzes, but the 'philosophy' of its payload is different from that of Curiosity. Where the latter was designed as an autonomous laboratory (hence the name of the mission: Mars Science Laboratory), capable of carrying out long and complex analyzes on site (X-ray diffraction, gas chromatography), Perseverance s' part of the perspective of returning samples: like a field geologist, his priority will not be to immediately resolve all the major questions that we ask ourselves, but rather to identify, document and take the best rock samples to be able to answer these questions after more in-depth analyzes on Earth. That said, even if the samples were never to return, we will learn a lot about Jezero and Mars thanks to the data from Perseverance, ”concludes Erwin Dehouck.

Now, we must cross our fingers for the landing of Perseverance on February 18, and hope that the rover can deploy all its capabilities on Mars for a successful mission, both now and in the long term!

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