Science

Mars: What has Curiosity taught us since it arrived on the red planet 10 years ago?

Six wheels, ultra-precise instruments and hundreds of successful experiments. The Curiosity rover mission (“astromobile” in Molière’s parlance) celebrates on Saturday, August 6, a decade of activity since it was deployed to Mars by NASA in 2012. pictures and explored the Martian soil with one question: was the red planet ever habitable? “Affirmative,” the scientists answer, who, however, have made many other discoveries at a distance of 78 million kilometers from Earth.

Mars was habitable… about 3.5 billion years ago

This is the main lesson of the Mars Science Laboratory (MSL) mission, the project that surrounds Curiosity: the red planet has (very) long offered conditions favorable for the emergence of life. To reach this conclusion, the science teams piloted the robot remotely to clean, scan, and drill into the Martian soil. “Little holes, holes…” laughed the National Center for Space Research (Cnes) in early 2020, referring to Serge Gainsbourg’s song “Le poinçonneur des Lilas”. Small holes, of course, but rich in discoveries. Indeed, these wells have made it possible to detect the presence of sulfur, oxygen, phosphorus, or even carbon – “necessary for life,” NASA explains on its website*.

Drilling a few centimeters deep by Curiosity on Mars. (NASAJPL-CaltechMSSS)

“This is the most important discovery because it touches on the great question of life,” astrophysicist Sylvestre Maurice, who helped develop ChemCam, a tool developed in part by teams from astrophysics and planetary science, explains to franceinfo. Research Institute (IRAP) and Cnes in Toulouse (Haute-Garonne).

Introduced by Curiosity, this system makes it possible to analyze the chemical composition of the rock without moving the robot thanks to a pulsed laser. “For ten years, we have carried out 900,000 shots (laser), – the scientist proudly sums up, – all this from Toulouse and Los Alamos (USA)”. Because to control the Curiosity robot, the MSL mission scientists are constantly communicating.

“You have to give a warning when you want to order a laser shot, a shovel… It’s like driving a car with 60 people, all from a distance.”

Sylvester Maurice, astrophysicist

on Franceinfo

Another important find: Curiosity discovered a large number of organic molecules thanks to the SAM mini-lab, also operating from Toulouse. But be careful, these molecules do not prove that there were or still are living things on Mars. They simply show that “the basic ingredients were there to support a simple form of life 3 billion years ago,” notes Valerie Mousse, MSL project leader at Cnes, adding that “all the chemical compounds found in our DNA are also present.” on Mars”. However, this study of traces of Martian life is not the work of Curiosity, but its little sister Perseverance, a rover that has been traveling the surface of Mars since February 2021.

Liquid water has long flowed on the red planet

An integral component of life as we know it on Earth, water was at the center of all concerns during the launch of Curiosity. Since then, several clues have suggested that streams or even freshwater rivers were once part of the Martian landscape. A pebble discovered by the rover, whose rounded shape could thus be due to the long journey along the riverbed, is being promoted by NASA*.

Also deposits of hardened mud found at the bottom of what looks like a dry river bed. “This is what justified the choice of landing site (Curiosity),” Olivier Gasnot, current ChemCam instrument manager at Cnes, explains to franceinfo. The rover was sent to a more or less closed lake (…) in order to confirm the hypotheses formulated for several decades.”

3D stereo image of a rounded pebble (in the center of the image) taken by the Curiosity rover on Mars on May 20, 2013 (NASA/JPL-Caltech/MSSS)

A 3D stereo image of a rounded pebble (in the center of the image) taken by the Curiosity rover on Mars on May 20, 2013. (NASA/JPL-Caltech/MCSS)

Curiosity also made it possible to learn more about the characteristics of Martian water, which was “neither too acidic nor too alkaline,” explains Valerie Mousset, and its temperature was also defined as “neutral.” The presence of clay and relatively low levels of salt even leads NASA* to say that this water “was fresh and potentially drinkable.” More or less 2 billion years pass before changing shape.

Unprecedented visualization of the surface of Mars

All of these discoveries were made possible by careful observation of the Martian environment, including grace up to 17 cameras aboard the rover, providing visibility in all directions. Since arriving on Mars, Curiosity has traveled just over 28km, averaging 7.6m each day. Yellowknife Bay, the Pahrump Hills, the Butte de Murray, or the foothills of Mount Sharp: these are the mysterious places that the rover traveled through. A science walk immortalized with over 500,000 photographs, including several selfies against unusual rocks.

On the rover’s mast, often referred to as the head of the vehicle, MastCam, for example, is capable of capturing color photos and videos, as well as 3D stereo images. Thanks to special filters, this sensor can even determine the composition of certain rocks. Curiosity also has a Mars Hand Lens Imager (MAHLI), the equivalent of a magnifying glass attached to the end of a robotic arm, capable of observing things as fine as a human hair. From landscape photos to the details of a meteorite on the way*, Curiosity continues to offer breathtaking panoramas of the red planet.

We know more about how the planet becomes uninhabitable

Able to both explore the ground and scan the sky, Curiosity has provided a better understanding of the extreme harshness of the Martian environment. “This planet, the same age as the Earth, has undergone tremendous climatic and geological changes,” emphasizes Sylvester Maurice. Gravity, three times weaker than Earth, and constant cold (average -63 ° C) turn Mars into an icy and inhospitable desert. But it was not always so. Thanks to Curiosity, MSL mission scientists realized that Mars had a much denser atmosphere in the past before seeing gas masses, as well as water reserves, evaporate in the vacuum of space.

“This is exactly what we are starting to study now and over the next three years,” points out Olivier Gasneau, “that is, the transition from a wetter period to a drier period of Mars, which, apparently, was done in the form of long cycles.” Designed to last between two and six years, the Curiosity rover far exceeded the expectations of the engineers who designed it. “Everything that we have discovered in recent years is just a bonus,” says Sylvester Maurice. And even if the robot is in poor condition, in particular with very damaged wheels, NASA and its partners (including Cnes) would like to be able to pilot it until at least 2025.

The wheel of the Curiosity rover on Mars on January 27, 2022. (NASA/JPL-CALTECH/MSSS)

The wheel of the Curiosity rover on Mars on January 27, 2022. (NASA/JPL-CALTECH/MSSS)

Collected the necessary information for future manned flights

Among Curiosity’s great discoveries in the Martian environment, explorer Olivier Gasnot is saving the latest, capital for future exploration missions. “Now we know that the level of radiation on Mars is higher than on Earth, which is dangerous for humans,” the scientist emphasizes. “A mission to Mars corresponds to the maximum dose of radiation that NASA sets for the entire career of an astronaut.”

But shields are being prepared, and by placing Curiosity “under certain hills”, scientists have already noted a small drop in this radiation. Enough to fuel the dream of a manned mission after the successful deployment of satellites, several rovers and even a mini-helicopter around the planet Mars, which has not yet finished revealing its secrets.

*Links marked with an asterisk refer to publications in English

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