A meteorite upsets the theory of the formation of Mars

The study of meteorites found on Earth makes it possible to better understand the formation of our planet and its sisters Mercury, Venus and Mars. True relics of the origin of Solar systemmeteorites help scientists to define in particular the original composition of rocky planets and in particular the nature and the origin of volatile elements which enter into the composition of rocks and which participated in the formation of our atmosphere.

Formation of rocky planets: nebula or chondrites?

Currently, the hypothesis in force concerning the formation of rocky planets suggests that these volatile elements were early punctured in the solar nebula by the young planets in formation. At this point, the Earth but the others rocky planets also were just balls of rock in merger. Volatile elements, such ashydrogenthe carbonI’oxygenI’nitrogen and many gas rare, were thus absorbed, dissolving within the ocean of magma occupying their surface. Then, through the volcanism intensive that followed, these gases came to form an atmosphere. The young planets were then subjected to a long and intense bombardment by meteorites which are called ” chondrites », which, too, participated in the contribution of volatile elements. The idea is also that it is the volatile elements of meteorites that have contributed the most to the formation of the atmosphere, terrestrial at least.

It follows from this hypothesis that the composition of the primitive solar nebula, or that of the nebula-meteorite mixture, would mainly be found at the level of the innermost layers of the Earth. The deep parts of the mantle are indeed more likely to have preserved this chemical signature. than the more superficial layers, subjected for billions of years to an intense process of melting and degassing. A new study, however, disrupts this pattern of thinking.

A meteorite testifying to the internal composition of Mars

Meteorites that fall to Earth can come from many sources, including the surfaces of other rocky planets in the world. Solar system. The powerful impacts which affected the various planets at the beginning of their life indeed threw planetary fragments into space, which still regularly collide with neighboring planets. This is how fragments of Martian rocks were found on Earth. One of these meteorites, however, has a particular value for scientists, since it would come not from the surface, but from the interior of Mars, an extremely rare fact. it’s about the meteorite de Chassigny, discovered in France in 1815.

A team of researchers has studied the composition of this meteorite and in particular the origin of its volatile elements. The analysis of the isotopic ratios of krypton usually makes it possible to differentiate the solar or chondritic origin of the volatile elements. And the results of the study of the Chassigny meteorite are surprising to say the least.

Indeed, the isotopic analysis shows that the volatile elements that it contains would not come from an assimilation of components of the solar nebula as we thought, but would come from an integration of chondritic material. This implies that the chondrites would have participated much earlier than we thought in the contribution of volatile material, that is to say at the time of the formation of the planet from the solar nebula.

It could even be that the situation is completely reversed, the internal composition of the planet being associated with the chondrites, and that of the atmosphere with the solar nebula.

The atmosphere of Mars would have formed very quickly

The article, which has just appeared in the journal Sciencesuggests in any case that the atmosphere of Mars could not have been formed solely by the degassing of the coat, which should then have had a chondritic composition. It is possible that the planet acquired its atmosphere very early, by integrating the elements of the solar nebula, and that before the ocean of magma cooled. It should be noted that Mars solidified very quickly, in only 4 million years, even if this duration is discussedunlike the Earth, which took between 50 and 100 million years to cool.

These new results suggest that Mars would have finished growing before the solar nebula dissipated under the effect of radiation from the young Sun.