A mixture of swirling gas and dust
About 4.5 billion years ago, the Solar System gradually adopted this arrangement that we know today. At this time, an interstellar molecular cloud collapsed, composing the Sun at its center. Around, a disk of gas and dust appeared. » The Earth formed when gravity attracted swirling gases and dust to become the third planet from the Sun, » observes NASA on its website. Each planet in the Solar System has formed with a mixture of its own. But where does this dust come from which finally condensed to give our planet?
According to a study published at the end of 2019 in the journal Nature Astronomy and relayed on the Sciences et Avenir website, it would come in part from red giants, old stars which have already burned their hydrogen, as will be the case for our star within 4 to 5 billion years. To achieve this result, the researchers performed measurements of the abundance of palladium. This element, which is formed during the process of « slow neutron capture » taking place in the hearts of red giants, was remarkably present in our planet. The latter therefore inherited, in « its mixture », dust from one of these old stars. In general, stars disperse throughout their life or at the end, thanks to stellar winds, by exploding, or even by merging, chemical elements which are the building blocks of matter.
And the Moon in all of this?
According to the theory most accepted by the scientific community, that of the « giant impact », the Moon was created around 4.5 billion years ago when the primitive Earth was violently struck by a celestial body named Théia (mother of the Moon, Selene, in Greek mythology). The proto-planet was as massive as the planet Mars and the shock was tremendously violent. It vaporized Théia and a large part of the earth’s crust and mantle, poor in metals. Part of the cloud of vaporized rocks would have aggregated to Earth again, while the other part would have solidified not far away, giving rise to our satellite.
Problem: the lunar subsoil is richer in metals than the portions of Earth excavated by Théia. This fact has long been known to scientists who are looking for an explanation. But a new study relayed by Sciences et Avenir in 2020indicates that there are still more metals than imagined which makes it even more difficult to interpret this shift while preserving the hypothesis of the giant impact. The study’s authors suggest that the collision between Theia and Terra was more violent and devastating than expected, and propelled deeper sections of the planet into orbit, including chunks of cores much richer in metals. Unless the collision happened much earlier when the Earth was still a ball covered in molten magma. Other theories exist to explain the formation of the Moon, some call for a series of impacts and others even believe that our satellite is older than the Earth. ! Further investigations will still be necessary to settle this thorny debate.
With Sciences et Avenir