Scientists just discovered curious details concerning the formation of the planet Mars. After carrying out a new analysis of the meteorite Chassigny, which originates from the Red Planet, researchers have found that the way the planet obtained its volatile gases contradicts what is known about planet formation. The gases in question include carbon, oxygen, hydrogen, nitrogen, as well as noble gases.
According to current models, planets form from the rest of the materials that form stars. The latter are born from the cloud of dust and gas of a nebula which collapses due to gravity. As it spins, the star’s base material forms a disc where dust and gas clump together to form a baby planet.
So far, there are still a few issues to be cleared up regarding the inclusion of certain elements in the new planets. According to current models, volatile gases are absorbed by a planet still in fusion from the solar nebula. These gases end up in the global magma ocean to later be released into the atmosphere when the mantle cools.
Later, other volatile gases arrive on the planet in formation through meteor bombardment. These volatile gases are present in carbonaceous meteorites called chondrites and are released when space rocks break apart upon arriving on the planet.
Thereby, the interior of a planet should reflect the composition of the solar nebula while its atmosphere mainly reflects volatile gases from meteorites. It is possible to tell the difference between the two gas sources by analyzing the ratio of noble gas isotopes, especially krypton.
The case of Mars
According to scientists, the planet Mars was formed and solidified from relatively fast way. The process lasted 4 million years, compared to 100 million for the Earth. Mars thus represents a very good record of the first stages of the formation of a planet.
According to Sandrine Péron, geochemist at ETH Zurich, it is possible to reconstruct the history of the “delivery” of volatile gases from the first million years of the Solar System. But it is necessary to have access to certain information, and it is there that the Chassigny meteorite comes into play who fell to Earth in 1815.
The analyzes showed that the composition of the meteorite in noble gases is different from that of the Martian atmosphere. This suggests that the piece of rock that arrived on Earth came from the mantle of Mars, and thus represents the interior of the planet and the solar nebula.
It was difficult to precisely measure the ratio of krypton in the meteorite. But Péron and his colleagues used a new technique using the UC Davis Noble Gas Laboratory to measure the ratio of krypton in Martian rock. What they found, however, was not planned at all. In effect, krypton isotope ratios in the meteorite were close to ratios associated with chondrites.
According to Péron, the composition of the interior of Mars is almost purely chondritic, while the atmosphere is solar. This suggests that meteorites brought volatile gases to Mars much earlier than expected, long before the solar nebula was dissipated by solar radiation.
In this case, Mars has obtained its atmosphere from the solar nebula after its global magma ocean has cooled. If this is not the case, the chondritic gases and the nebulous gases would be more mixed than what the analyzes have shown.
According to the scientists, this conclusion leads to another mystery. When the solar radiation finally dissipated the nebula, the atmosphere of Mars coming from the nebula should also have been dissipated. This means that the atmospheric krypton present later had to be preserved elsewhere, for example in the polar ice caps. But again, for this to be the case, Mars would have had to become cold immediately after its accretion.
According to the researchers, their study highlights the fact that there are chondritic gases inside Mars. But the results also raise questions about the origin and composition of the primary atmosphere of Mars.