Life on Mars ? Between myths and scientific realities

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The Egyptians, Greeks and Romans already had their eye on Mars even before the invention of the telescope, which only arrived in the 17th century. Each people has attributed its own characteristics and symbolism, often linked to blood and war because of its unique reddish color. It is from this planet that Mars, Roman god of violence, war and youth, took its name. This fascination was subsequently largely amplified in the 19th and 20th centuries by cinema and literature. Works like The War of the Worlds (1898) by H. G. Wells or The Martian Chronicles (1950 ) by Ray Bradbury have largely contributed to the democratization of Mars in popular culture.

If speculation on the existence of Martian life actually dates back to the 17th century, the first real explorations of the planet with the aim of look for signs of lifeon the planet only began in the 1970s. NASA's Viking program was the first to land American spacecraft for this purpose. In 2011, the Curiosity mission provided new evidence that Mars could have supported life. The past presence of organic compounds and liquid water have revived hopes for the potential for Martian life. More recently, the Rover Perseverance marked a further step in the search for any trace of life. What stage have we reached and what does science say about it currently ?

In search of life beneath the Martian surface

On February 18, 2021, Perseverance landed on Mars. One of its missions is to collect samples of Martian rocks and soil from places on the planet that could have been habitable. These could be sent back to Earth for researchers to analyze in more detail. The Jezero crater (place of his arrival), according to preliminary observations, would have once contained liquid water in the form of a lake, which is excellent news.

However, the presence of water is not sufficient to determine whether Mars was once inhabited; this is why Perseverance is also looking for specific compounds: carbon, hydrocarbons, amino acids or lipids. The search for these organic compounds is essential, because they are the basic building blocks of life as we know it. In July 2023, Perseverance detected organic molecules in the Jezero crater, dating back to at least 2.3 to 2.6 billion years ago. ;years » according to this publication published in Nature.

Parallel to this, the mission Curiosity (another NASA rover) pursues a goal equivalent to Perseverance, and also carries out various analyzes and environmental measurements. At the end of 2021, he “  observed a mixture of carbon isotopes in the rocks of Gale crater which, on Earth, would be a sign of life ” we can read in this article from National Geographic. Here too, there is nothing to indicate that these isotopic variations originate from biological activity.

Clues and interpretations: the challenge of proof

The analysis of data from these two missions, as well as others (ExoMars, Insight, etc.) puts forward the hypothesis that microbial life forms could persist in the subsoil. Martian. These microbial communities would be the result of contact between rocks from meteorites and water. But this still remains to be proven and the hypothesis is currently being studied.

Jesse Tarnas, researcher at the Jet Propulsion Laboratory, (USA) explained in a press release from Brown University: “ We still don't know if there was life beneath the surface of Mars. We are only saying that if that were the case, we think that there would also be enough energy there to maintain it until today < /em>”. Nothing explicitly yet indicates today that Mars was once populated by a form of life.