A team of researchers of the Institut de physique du globe de Paris, Université de Paris, CNRS and the Muséum national d’Histoire naturelle, published in the last months, a series of three papers that contribute to explain the formation of the first minerals of our Solar System. In order to better convey the relevance of this study, they publish today a video illustrating their work.
The primitive meteorites, or chondrites, are the relics of the first million years of the Solar System. They contain different solids formed in a disk of gas and dust, called a protoplanetary disk, which surrounded the young Sun before the planets formed. Among these solids, the oldest are white inclusions (also known as Calcium-Aluminum-rich Inclusions or CAIs) dated 4567 million years. This age establishes, by convention, the “Time-Zero” of the Solar System.
CAIs are thought to have formed at temperatures above 1500 ° C by condensation of a gas of the same composition as our Sun. Such temperatures are expected near the young Sun. However, CAIs are most abundant in a class of meteorites, called carbonaceous chondrites, assembled far from the Sun and even incorporating ice. This meteoritic hot/cold paradox of has been a stumbling block for most of the Solar System's theoretical models.
"Classic" models generally consider an isolated protoplanetary disk. However, CAIs were formed in such a short time (~ 200 000 years) that the protoplanetary disk was likely still being formed by a collapsing interstellar cloud. In this primordial phase, the forming disk was anything but isolated: cold material coming from the cloud was continuously raining onto all its surface.
In this series of articles, the authors modeled this phase, and followed the fate and transport of different components in the early Solar System. In this way, they were able to derive the traces which the Solar System keeps of its first hundreds of millennia of existence. In these simulations, CAIs are indeed produced near the young Sun (inside the current Earth orbit) by vaporization of the infalling interstellar material. But the building disk, initially compact, spreads rapidly, transporting part of the CAIs towards the cold exterior of the primitive Solar System. CAIs that have not been able to "ride the wave" are quickly swallowed by the young Sun. It is thus possible to explain the overabundance of CAI in carbonaceous chondrites (far away) compared to their counterparts formed in the inner Solar System.
The authors also sought to understand the isotopic variations in the Solar System. Most chemical elements exist in several variants of different masses: isotopes. The oxygen atoms, for example, can be oxygen-16 or oxygen-17 or oxygen-18 (the number being proportional to their mass). The proportions of different isotopes are roughly constant on Earth. But they are not the same in the other bodies of the Solar System, as evidenced by meteorites. The origin of these "isotopic signatures" is not well understood. These variations are most pronounced in CAIs. Hence the idea that they have been inherited from the original cloud. Indeed, as the parent cloud received contributions from various stars, whose isotopic proportions differed, it is reasonable to assume that they were only imperfectly mixed. The authors have shown that the CAI could have "fossilized" this isotopic heterogeneity of the cloud, as it fed the protoplanetary disk. Once the disc was completed, these variations would have been attenuated, especially as a result of mixing, in accordance with the observations.
Chondrites are amazing time capsules, filled with encrypted stories that are billions of years old. These studies help to decipher them and place their mysterious components in their astrophysical context, opening new perspectives in the study of the origin of the compositional diversity of meteorites.
> Scientific references
1) Francesco C. Pignatale, Sébastien Charnoz, Marc Chaussidon, Emmanuel Jacquet "Making the Planetary Material Diversity During the Early Assembling of the Solar System" 2018, The Astrophysical Journal Letters, 867, L23
2) Francesco C. Pignatale, Emmanuel Jacquet, Marc Chaussidon, and Sébastien Charnoz "Fingerprints of the Protosolar Cloud Collapse in the Solar System I: Distribution of presolar short-lived 26Al" 2019, The Astrophysical Journal, 844 (1), 31
3) Emmanuel Jacquet, Francesco C. Pignatale, Marc Chaussidon, and Sébastien Charnoz "Fingerprints of the protosolar cloud collapse in the Solar System II: Nucleosynthetic anomalies in meteorites" 2019, The Astrophysical Journal, 844 (1), 32
> Download the french presse release