A gigantic meteorite impact could have compromised the habitability of Mars

Researchers have found evidence in Martian meteorites that the Red Planet suffered a major meteor impact no more than 4.45 billion years ago. This discovery calls into question the hypothesis of the establishment of conditions favorable to life relatively early in the history of the planet.

Among all the meteorites that have fallen to Earth over time, some come from Mars. These pieces of Red Planet are extremely rare, however, and bear witness to the intense meteoritic bombardment that the planet suffered.

Martian meteorites have been found in northwestern Africa. Their study shows that they are pieces of Martian regolith, which forms the surface crust of the Red Planet. This discovery is therefore exceptional since it could in particular make it possible to better understand the geological history of Mars. One of the questions that most interests scientists is that concerning the habitability of Mars. From when did the planet present potentially favorable conditions for the appearance of life?

To clear up this mystery, a team of researchers focused on the study of small mineralszircons, found in three Martian meteorites.

Zircons, witnesses to the evolution of the Earth… and Mars

Zircons are well known to geologists. Silicate minerals emblematic of the Earth’s crust primitive, they were formed 4.3 to 4.4 billion years ago. So these are markers of the conditions that prevailed on Earth in its early youth. Particularly resistant, zircons are not easily altered by cycles of erosion, transport or by most cataclysms (such as a meteorite fall) and are therefore today found almost everywhere, in a large number of sedimentary rocks of all ages. It is also the only mineral to be able to survive over several billion years, which makes it a particularly valuable witness to the different geological stages that the Earth has known. With apatites, they are often used as thermochronological markers.

It should be known that at the time of their crystallization, the zircons enclose in their crystal lattice a number of radioactive elements. By studying the quantity of child elements produced by the disintegration of the parent element (uranium), it is therefore possible to date the age of the crystal. If this method was of course developed for the terrestrial environment, it is also applicable to the Martian environment.

Zircons deformed by a titanic shock

The team of scientists thus observed that one of the Martian zircons showed traces of an atomic rearrangement that led to a growth slightly deviated from the crystal. This observation indicates that this zircon would have undergone the passage of an intense shock wave. However, such a pressure wave can only have been created by a major event, such as a major meteorite impact. On Earth, this kind of mark is observed only for the zircons present in the rocks of the central zone of the major impact sites, where the pressure is maximum. Such zircons have been found in particular in the crater of the Chicxulubwhich is associated with a meteorite that caused the disappearance of the dinosaurs.

The finding of a similar signature in fragments of the Martian crust suggests that the planet suffered a particularly violent impact. But when ? The zircon in question would be 4.45 billion years old, but the deformation of its crystal system is difficult to date. It could have occurred at any time after the formation of the crystal. As for its original location on the surface of Mars, it will certainly always remain a mystery.

A late impact that would have compromised the establishment of habitable conditions?

However, this discovery must be placed in the context of current knowledge. Previous studies suggest that Mars would have been intensely bombarded about 4.48 billion years ago and that the surface of the planet would then have benefited from a lull allowing the development of conditions favorable to the potential development of life. , around 4.2 billion years ago. However, these new results, published in Science, suggest that a cataclysmic event would have occurred later, at the most 4.45 billion years ago, calling into question this hypothesis of habitability from 4.2 billion years. The researchers consider that such an impact could certainly have postponed or at least hindered the establishment of conditions conducive to the development of life on March.