Various forms of organic matter, the basic element of life on Earth, have been detected on Mars, in the Jezero crater, which the robot Perseverance explores since he landed on the red planet. The presence of these organic molecules increases the possibility that life could have existed on Mars, but it will be necessary to wait for the arrival on Earth of soil samples to confirm their origin by further analysis, warn the experts.
In an article which appeared on Wednesday in Natureresearchers from NASA and various American universities describe the various forms of organic matter and the minerals with which they are associated that the SHERLOC instrument (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals), with which the robot is equipped Perseverancedetected in two different geological formations present at the bottom of the crater.
“Each of these geological formations does not seem to have the same variety of organic molecules. Moreover, with the data collected by SHERLOC, it is quite difficult to know exactly the process that led to the formation of this organic matter. There could be several,” summarizes Richard Léveillé, geologist in the Department of Earth and Planetary Sciences at the McGill University Space Institute.
It is very encouraging to detect organic molecules in such ancient rocks, because if there was life [sur Mars]this means that traces of this life may have persisted in the rocks
Remember that organic molecules necessarily contain carbon atoms having bonds with hydrogen, nitrogen, oxygen, phosphorus or sulfur atoms. These organic molecules are the building blocks of all life on Earth, which consists of sugars, lipids and proteins, hence the mission of Perseverance to search for their presence on the planet Mars.
Where do these molecules come from?
Several hypotheses are advanced by the authors of the article of Nature to explain the origin of this organic matter. According to some of them, these organic molecules result from an interaction between rocks and water, called serpentinization. It is “a reaction that takes place on Earth with rocks of mafic composition, i.e. rich in magnesium and iron, which, when mixed with water at a certain temperature above 60°C, gives hydrogen and fairly simple organic molecules,” explains Mr. Léveillé. “This reaction is possible on Mars,” he adds. Organic molecules could also arise from a reduction of CO2 by electrochemistry.
They could also come from meteorites and interstellar dust that would have fallen on Mars. And it is not excluded that they derive from a biological source.
“It is possible that there was life on Mars and that the organic molecules quite simple in terms of the complexity of carbon chains and aromatic rings that we have detected are traces of these forms. of life, including molecules such as DNA and RNA [qu’elles contenaient] degraded into molecules similar to those found. We cannot rule out this possibility, but there is nothing to indicate that these molecules come from a biological form”, emphasizes Richard Léveillé, who is a member of the scientific team of Perseverance.
The article of Nature tells us that the carbon cycle on Mars is more complex than we imagined, says the geologist. “Observations do not confirm that there was life on Mars, but it is very encouraging to detect organic molecules in such ancient rocks [de 2,3 à 2,6 milliards d’années], because if there was life, it means that traces of this life may have persisted in the rocks. »
“When samples of these rocks arrive on Earth, we will be able to carry out further analyzes and probably determine whether these molecules are abiotic in nature or whether they come from a form of life. We have more efficient instrumentation on Earth that will allow us to confirm the identity of these molecules and better understand their origin,” explains the researcher. Indeed, NASA and the European Space Agency are currently preparing the Mars Sample Return (MSR) mission, which foresees that a lander will land on the red planet in 2028 to collect the samples and bring them to Earth in 2033.
“The detection of traces of organic matter on Mars is not a big surprise, because we knew that this kind of molecules existed in the Martian meteorites which fell on Earth as well as in the Gale crater explored by the robot. Curiositybut the article reveals to us the diversity of the assemblies between organic matter and minerals”, points out Mr. Léveillé.
“But maybe we have a bias towards life on Earth and we need to take a broader look. Perhaps we should look for carbon-free biosignatures, complex molecules, regardless of their composition”, says Richard Léveillé, contacted in the Arctic where he studies gossans, geological formations rich in iron oxides which are also present on Mars and which represent targets for the search for ancient traces of life.
