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Formation of the solar system’s first small bodies in two separate rings

The formation of small solar system bodies, such as asteroids and planetesimals, remains a mystery. While there's general agreement that their formation is the result of dust clusters in the protoplanetary disk collapsing under their own weight, there's still a great deal of uncertainty as to where and when they formed.

Formation of the solar system’s first small bodies in two separate rings

Publication date: 12/01/2022

Press, Research

Related themes : Origins

To date, numerical simulations show that the most favourable location for the rapid formation of small bodies is the “ice line”, i.e. the part of the disk where water vapour condenses into ice, at a temperature of around 160K (about -110°C). But this result conflicts with the analysis of iron meteorites from the cores of the solar system’s first small bodies. They are divided into two groups with different isotopic and chemical properties, arguing in favor of two, rather than one, formation sites of distinct compositions, at different distances from the Sun.

A team of researchers from Observatoire de la Côte d’Azur, Observatoire de Paris and Institut de Physique du Globe de Paris has shown, for the first time, in an article published on the Nature Astronomy website on December 22nd, 2021, that the first small bodies in the solar system could have formed in two distinct rings, one near the silicate condensation line (around 1000K) , the other near the ice line (around 160K).

The study shows that a first reservoir of small ice-rich bodies (with a mass around 30 times that of the Earth) would have formed near the current orbit of Jupiter, enabling the cores of the giant planets to be formed, while a second reservoir of small ice-free but silicate-rich bodies (containing only 2 to 3 times the mass of the Earth) would have formed near the current orbit of the Earth, enabling the telluric planets to be formed.

A diagram of the model devised by the authors to explain the formation of the two families of iron meteorite parent bodies, rocky on the one hand and ice-rich on the other. The key point is that a disk fuelled near the Sun spreads out radially. The gas cools and condenses the more refractory chemical species, such as silicates, and then the more volatile ones, such as water vapour. Once condensed into dust, these elements drift towards the sun under the effect of friction with the gas. Matter thus accumulates at the condensation lines of water and silicates, enabling the first planetesimals to form in two distinct rings at these points.

The contemporary formation of these two populations of small bodies with different chemical characteristics is in very good agreement with the observational constraints provided by the iron meteorites.  It also shows that the process of planetary formation began very early in the solar nebula, at the same time as the formation of the Sun, when our Solar System was still being supplied with material by the interstellar medium.

 

Ref :  Morbidelli, A., Baillié, K., Batygin, K. et al. Contemporary formation of early Solar System planetesimals at two distinct radial locations. Nat Astron (2021). https://doi.org/10.1038/s41550-021-01517-7

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