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Mars: Life had everything it needed to develop

Since 2012, the rover Curiosity is conducting investigations on the surface of Mars with the aim of better constraining the climate evolution of the Red Planet and the presence of water liquid in its past, but also to determine whether or not Mars was ever able to support life.

If we now know that many lakes and rivers have shaped the Martian landscape and that its climate was a day favorable to life, no direct biological trace has yet been found. Never mind, scientists continue to search, in particular by looking into the presence of the elementary chemical bricks necessary for theemergence of life.

An amount of organic carbon comparable to certain terrestrial regions

In 2014, Curiosity thus carried out a series of experiments to measure the fraction of carbon total organic matter contained in Martian rocks. After eight years of data analysis, the results are finally available in the journal PNAS and reveal that Martian rocks are relatively rich in organic carbon, which is one of the key components for the initiation of chemical reactions prebiotics and potentially the construction of molecules biological.

It has been some time since scientists found traces of organic carbon on the red planet. But the evaluation of its available quantity is a major parameter, which determines the development potential of life. And the results are rather surprising, since they show that Martian rocks contain a significant fraction of organic carbon, comparable to certain terrestrial regions. Admittedly, the values ​​are rather similar to those of harsh environments depleted in organic carbon (for the repository terrestrial), as the Atacama desert, but these are encouraging results as far as Mars is concerned. Because it shows that the carbon was available in sufficient quantity for the construction (hypothetical) organic moleculeswhich are the basis of all life forms known to date.

Water, carbon, sources of energy… all the ingredients of life together

Total organic carbon is defined as the amount ofatoms of carbon bound in organic molecules (generally composed of atoms ofhydrogenofoxygen and nitrogen). If on Earth a large part of the organic carbon has a biological origin, it can have non-biological origins, in particular meteorites, volcanic activity, or certain chemical reactions on the surface of the planet. The presence of organic carbon on Mars therefore in no way proves that life ever developed on this planet.

With liquid water, the presence of organic carbon in significant quantities is on the other hand a new element which indicates that the basic ingredients necessary for life were indeed present on Mars a few billion years ago. The Gale crater in which Curiosity evolves would have been a place favorable enough for the appearance of lifesince in addition to water and carbon, the environment had the other essential elements: sources ofenergylow acidity, oxygen, nitrogen and sulfur.

Curiosity could therefore be in the right place to discover the first traces of Martian life so sought after. However, if they exist, they could be more difficult to access than we thought.

Review the search strategy for organic molecules such as amino acids

A new experiment carried out by the Nasa indeed suggests that to have a chance of finding organic molecules, the rover should drill to a depth of two meters in the Martian subsoil. This concerns in particular the search foramino acidswhich may or may not be of biological origin, but which in all cases are considered to be building blocks for the construction of protein. However, the acids amino acids are fragile and easily destroyed by cosmic rays reaching the surface of Mars whose thin atmosphere does not provide effective protection. Currently, rovers are drilling to a depth of five centimeters. Scientists estimate that at this depth, amino acids are destroyed in just 20 million years. Knowing that potential Martian life could have developed several billion years ago, investigating this very superficial level therefore appears totally useless.

These results, published in Astrobiology, show the need to implement a new search strategy for the rovers currently in operation, which are unfortunately not equipped to drill to the required depth. One solution would be to look for outcrops having recently exposed deep parts of the subsoil, such as in small impact craters less than 10 million years old or in material ejected from such craters.

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