For 15 years, methane emissions detected in the Martian atmosphere have puzzled exobiologists because they could betray the existence of micro-organisms. The Curiosity rover recently measured its highest rate in the atmosphere.
The saga of methane (CH 4) in the atmosphere of Mars has been going on since the beginning of the 2000s, notably with a resounding publication in 2004 of the planetologist Thérèse Encrenaz and her colleagues who had spotted traces of this gas with the help of instruments of the European Mars Express probe. It was later found that there was seasonal methane seepage which only increased the excitement of the exobiologists. It must be known that the photochemical models of the Martian atmosphere predict that this gas would have a lifespan of about 300 years.
Among the possible origins of these injections, there is one that fascinates since it could be micro-organisms that would be cousins of terrestrial methanogens, archaea that can thrive in extreme environments such as deserts, ice in Greenland and even geysers and hydrothermal vents. To develop, they need only carbon dioxide and hydrogen as a source of energy because they are not photoautotrophic (photosynthetic) but chemotropic.
In 2015, a scientific article published in the American magazine Science showed that methane would have been detected on the Red Planet by the robot Curiosity. Where would it come from? Several hypotheses, still valid, were presented by Francis Rocard, a planetary scientist at CNES.
At the beginning of its history, everything indicates that Mars was much more welcoming, with vast expanses of liquid water and active volcanism, like the young Earth. Life could very well have appeared and taken the time to adapt to conditions. Some descendants of the first Martian microorganisms similar to terrestrial methanogens may still exist, perhaps in pockets of water maintained liquid by the heat of the residual volcanic activity of Mars. It would, therefore, be their methane generating activity that would be detected today by the Martian probes.
But as Francis Rocard explained, caution is necessary because other explanations of these seasonal seeps of methane are equally credible. They could come from fossil clathrates , well-known methane-rich ice at the bottom of the Earth’s oceans, just below the surface of Mars. During the spring and especially the Martian summer, the rise in temperature would vaporize ice in surface cracks allowing this methane to be released.