What has curiosity taught us since we arrived on the red planet 10 years ago?

Six wheels, ultra-precise instruments and hundreds of successful experiments. The mission of the Curiosity rover (an “astromobile” in Molière’s language) celebrates on Saturday, August 6, its ten years of activity since it was deployed on Mars by NASA in 2012. Along the way, the 900 kg machine took thousands of snapshots and studied the Martian earth with one question in mind: was the red planet ever habitable? “Affirmative”answer the researchers, who have made many other discoveries, 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 around Curiosity: the Red Planet offered (very) long ago conditions conducive to the appearance of life. To reach this conclusion, the scientific teams remotely controlled the robot to scrape, scan, but also drill the Martian soil. “Little holes, little holes…”amused the National Center for Space Studies (Cnes) in early 2020, referring to the song The puncher of the lilacs, by Serge Gainsbourg. Small gaps, certainly, but rich in discoveries. Indeed, these drillings made it possible to detect the presence of sulphur, oxygen, phosphorus or even carbon – “essential to life”explains NASA on its website*.

A drilling a few centimeters deep carried out by Curiosity on Mars.  (NASAJPL-CaltechMSSS)

“It is the most significant discovery because it touches the big question of life”explains to franceinfo the astrophysicist Sylvestre Maurice, who participated in the development of “ChemCam”, an instrument designed in part by the teams from the Institute for Research in Astrophysics and Planetology (IRAP) and CNES in Toulouse (Haute-Garonne).

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

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

Sylvestre Maurice, astrophysicist

at france info

Another significant discovery: a large number of organic molecules were detected by Curiosity thanks to the SAM mini-laboratory, also operated from Toulouse. But beware, these molecules do not prove that there was or still is living beings on Mars. They just show that “the basic ingredients were there to support a simple life form 3 billion years ago”, points out Valérie Mousset, MSL project manager at Cnes, who adds that “all the chemical compounds found in our DNA are also present on Mars”. However, this investigation of the traces of Martian life is not the work of Curiosity, but of by its little sister, Perseverance, a rover that has been traveling on the Martian surface since February 2021.

Water in liquid form has long flowed over the red planet

An essential part of life as we know it on Earth, water was at the center of all concerns during the launch of Curiosity. Several clues have since suggested that streams, or even freshwater rivers, were once part of the Martian landscape. Pebbles, spotted by the rover, whose rounded shape could thus be due to a long journey at the bottom of a river advances NASA *.

But also deposits of solidified mud, discovered at the bottom of what look like dried up river beds. “That is what justified the choice of the landing site (from Curiosity), explains to franceinfo Olivier Gasnault, the current head of the ChemCam instrument at CNES. The rover was sent to what was a more or less closed lake (…) to confirm hypotheses that had already been formulated for several decades.

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

Curiosity also made it possible to learn more about the properties of Martian water, which were “neither too acidic nor too basic”, explains Valérie Mousset, with a temperature qualified as “neutral” her too. The presence of clay and a relatively low level of salt even makes NASA* say that this water “was fresh and potentially drinkable”. Before changing form, there are more or less 2 billion years.

An unprecedented visualization of the surface of Mars

All these discoveries were made possible by careful observation of the Martian environment, including mercy to 17 cameras on board the rover that provide views in all directions. Since arriving at Mars, Curiosity has traveled just over 28 km, an average distance of 7.6 m traveled each day. Yellowknife Bay, the hills of Pahrump, the Buttes de Murray or the foot of Mount Sharp: it is these mysterious places that the rover traveled. A scientific walk immortalized by more than 500,000 photos – including a few selfies in front of unusual rocks.

For example, on the rover’s mast, often described as the head of the machine, the MastCam is capable of taking color photos and videos as well as 3D stereo images. Thanks to special filters, this sensor can even bring out the composition of certain stones. Curiosity also has the Mars Hand Lens Imager (MAHLI), which is the equivalent of a magnifying glass attached to the end of a robotic arm capable of observing elements as fine as a human hair. From landscape images to details about a meteorite you encounter along the way*, Curiosity continues to offer a striking panorama of the Red Planet.

We know more about how a planet becomes uninhabitable

Capable of both probing the ground and scanning the sky, Curiosity has made it possible to better understand the extreme harshness of the Martian environment. “This planet, which is the same age as Earth, has undergone colossal climatic and geological changes”, emphasizes Sylvestre Maurice. Gravity three times weaker than Earth’s and persistent cold (-63°C on average) make the red planet an icy and inhospitable desert. But it was not always so. Thanks to Curiosity, scientists from the MSL mission realized that Mars’ atmosphere was much thicker in the past, before they saw gas masses as well as its water reserves evaporate in the vacuum of space.

“This is exactly what we are starting to study now and over the next three years, point Olivier Gasnault, that is, the transition from the wetter period to the drier period on Mars, which appears to have taken place in the form of long cycles.” Planned to last between two and six years, the Curiosity rover far exceeded the expectations of the engineers who designed it. “Everything we discover in recent years is just a bonus”, rejoices Sylvestre Maurice. And although the robot is in poor condition, with particularly badly damaged wheels, NASA and its partners (including Cnes) would like to be able to pilot it until at least 2025.

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

Important information has been gathered for future manned missions

Among the major discoveries of Curiosity on the Martian environment, researcher Olivier Gasnault keeps one last, capital for future exploration missions. “We now know that radiation levels on Mars are higher than on Earth, which is dangerous for humans.stresses the scientist. A mission to Mars corresponds to the maximum radiation dose that NASA sets for an astronaut’s entire career.

But shields are being prepared, and by placing Curiosity “under certain hills”, researchers have already noticed a slight decrease in these radiations. Enough to reinforce the dream of a manned mission, after the successful launch of satellites, several rovers and even a mini-helicopter around a planet Mars, which is definitely not done revealing its secrets.

*Links marked with an asterisk refer to publications in English

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