THE CURIOSITY MISSION

AFTER TEN YEARS ON MARS

On Mars, days are called sols, numbered from landing (Sol 0); August 6, 2022 therefore corresponds to Sol 3555, or 3652 Earth days.

This anniversary gives us the opportunity to draw up a technical and scientific assessment of this mission and to discuss the discoveries made with the instruments on board Curiosity.

Curiosity: an international adventure that began long before landing

Curiosity took ten instruments on board, two of which were Franco-American: ChemCam and SAM.

ChemCam is the result of the work of more than 300 people in France (CNRS, universities, CNES and industries) under the technical and scientific responsibility of the Institute for Research in Astrophysics and Planetology (IRAP) in cooperation with the Los Alamos National Laboratory ( LANL – USA) and under the project management of the National Center for Space Studies (CNES), which finances the French contribution to the project.

The ChemCam instrument was selected to analyze the chemical composition of the Martian rocks around the rover, by firing lasers at them and collecting the returned light (this is called laser-induced plasma spectrometry or LIBS). The principle is to heat the rock very strongly (>10,000°C) on a small surface (less than a square millimeter) so that a very small fragment is sublimated (passes from the solid state to the gaseous state) then ionized in the plasma state.

It is with the spectral analysis of the light from this spark that the atomic composition of the rock is determined and that the scientists deduce the nature of the rock.

SAM meanwhile is a large analytical chemistry laboratory, weighing nearly 40kg, or half of all the rover's instruments. It allows the rover's environment to be analyzed at the molecular level. It is also a Franco-American contribution to the mission, and results from the work of nearly 100 people in France (CNRS, universities, CNES and industry) under the responsibility of the Laboratoire Atmosphères Observations Spatiales (LATMOS) and under the supervision work of CNES. It was developed in collaboration with NASA Goddard Space Flight Center and NASA Jet Propulsion Laboratory (JPL). The latter also designed, developed and assembled Curiosity.

SAM makes it possible to heat the samples taken by the rover up to more than 850°C, and to finely analyze the chemical nature of the gases produced with the three additional instruments it contains. This makes it possible to provide information on the nature of the minerals and organic compounds present in the samples analyzed. SAM also has the ability to analyze the composition of the atmosphere to understand the present and past climate of the planet.

SAM is made up of three different instruments that search for and measure the organic compounds often associated with the presence of life on a planet. NASA

For 10 years, at CNES in Toulouse, the Martian Operations Center, named FOCSE (French Operation Center for Science and Exploration), has been welcoming French teams working directly with NASA (American Space Agency) every other week. Every evening, the engineers and scientists who operate the ChemCam and SAM instruments meet at CNES to ensure the monitoring and programming of the instruments, the recovery and processing of scientific data.

Mars: A once habitable planet

During the first soils following its landing, a phase of verification of the good health of the scientific instruments (ChemCam, SAM, etc.) was carried out. Then Curiosity began exploring the crater. We thought we would find there alluvium (sedimentary deposits) transported by one or more rivers, one of which flowed from the surrounding plateau. The rover was then looking for traces of these past flows.

Stupor: a sample, taken from the Cumberland drilling site, revealed that Mars had met, at one point in its history, all the conditions required for its habitability: liquid water, organic matter and a source of energy. A simple life form could have existed there, but we cannot say whether or not Gale Crater ever hosted a life form.

The various on-board tools have also made it possible to discover the presence of organic matter that has been sought for nearly 40 years. The teams are also studying the origin of the sediments present and their transformation into rocks when the water flowed on the Red Planet...

Observing all the conditions of habitability exhaustively is not common. To date, this has only been possible on Earth and Mars.

Confronting “ground truth” with orbital data

The Mars adventure nominally took place during the first Martian year (almost 2 Earth years). NASA then decided to extend the mission to explore other geological formations.

In the middle of the Gale crater, rises the central peak which culminates at more than 5500 meters above the floor. It is called Aeolis Mons, more familiarly called Mont Sharp. It exposes on its sides many geological layers whose stacking constitutes an open book on the history of the planet. Within 10 km of Curiosity's landing site, there are access routes to Mount Sharp that the rover takes around Sol 750.

Martian mountain landscape

One of the first notable layers encountered on this climb is called Vera Rubin Ridge, after astronomer Vera Rubin.

According to data collected in Martian orbit, this area is rich in a mineral called “hematite”. It is an iron oxide frequently formed in aqueous medium. Observing this layer from the ground thanks to the rover allows us to acquire what in geology we call the ground truth.

Orbital data remains important because it allows global coverage of the planet, but will never be as accurate as data acquired directly on the ground. However, contrary to what the orbital data suggested, this area is not much more enriched in hematite than the surrounding terrain. This highlights the complementarity of the two types of data, in orbit and on the ground, to analyze the history of the planet.

The second area of ​​interest for the Curiosity mission is what has been called the clays unit. Clays are of great interest for exobiology, which is interested in pre-biotic (before the appearance of living things) and biological processes in the universe. They protect the organic matter because they preserve it between the layers that constitute them.

We could see clays a little like the mille-feuille of minerals because they are made up of a stack of sheets, between which slips organic matter. The data acquired in this clay zone are still being analyzed and the scientific articles concerning them are gradually being published in various specialized journals. This area therefore characterizes the humid period of the history of Mars with remains of lakes and rivers.

Finally, the third area of ​​interest that constitutes Mount Sharp is the sulphate layer. They are potentially the witnesses of an environmental transition: the passage from an era rich in liquid water towards an increasingly arid era. The rover is currently heading to this area to test this hypothesis, and the results are yet to come.

All of these discoveries show that Mars has a complex and rich geological history dating back more than 3 billion years.

After ten years, despite the many challenges (significant diurnal thermal changes, dust and radiation), Curiosity and its instruments are still working. Precautions are taken to preserve the material so that the scientific mission can continue.

Today, at the entrance to the impressive Gediz Valley, Curiosity finds itself in a breathtaking landscape and the mission has just been renewed for three years.

martian landscape

To date, Curiosity is no longer alone in surveying the surface of Mars since the Perseverance rover joined it on February 18, 2021 with the mission of searching for prebiotic traces and collecting samples that will be brought back to Earth.

The Insight lander also landed on Mars in November 2018 to "listen" to the planet's tremors, thanks to the French seismometer SEIS, and thus study the heart of Mars. Knowledge of the structure of Mars is important to understand its evolution, for example to know the reasons for the disappearance of the magnetic field which once surrounded Mars and is closely related to the habitability of the planet.

Should have been added to this Rosalind Franklin, the first European rover which also includes French participation, as part of the Exomars mission. It was supposed to take off in September 2022 with a Russian launcher, but its launch has been delayed until further notice following the outbreak of the war in Ukraine, the political consequences of which impact scientific cooperation.

This rover should dig up to two meters deep to analyze rocks better protected from the harsh conditions prevailing on the surface. They are therefore supposed to contain more information about the pre-biotic chemistry of Mars than the samples analyzed so far.

All these extremely complementary space missions for the study of Mars are designed with this in mind, and are the result of international cooperation. But if they allow us to better understand the history of the planet Mars, they also inform us about the history of the young Earth.

Indeed on Earth, the very old rocks, witnesses of the appearance of life, have been obliterated by plate tectonics. On the other hand, this tectonics did not exist on the planet Mars or was very limited: we therefore have access to rocks that have been preserved for billions of years, and which were probably formed in an environment close to that of our Earth. at the time.

In view of the similarities of the two planets, better understanding the geological history of Mars will allow us to understand our genesis as well as our possible evolution.

Cyril Szopa, University Professor, Exobiologist at the Atmospheres Modeling and Spatial Observations Laboratory (LATMOS), University of Versailles Saint-Quentin-en-Yvelines (UVSQ) – University of Paris-Saclay

Éric Lorigny, Head of MSL/ Curiosity and Perseverance Operations at CNES, National Center for Space Studies (CNES)

Olivier Gasnault, Researcher at the CNRS, Institute for Research in Astrophysics and Planetology, National Center for Space Studies (CNES)

Valérie Mousset, Project Manager for the French participation in the Mars Science Laboratory project, National Center for Space Studies (CNES) NASA

Article published in The Conversation