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The first solar system solids created in less than a week

A team of researchers from the Centre de recherches pétrographiques et géochimiques (CRPG/CNRS/Université de Lorraine), the Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC/CNRS/MNHN) and the Institut de physique du globe de Paris (IPGP/Université de Paris/CNRS) reveal in a study published in the journal Proceedings of the National Academy of Sciences that the first solids in the Solar System probably formed in less than six days.

The first solar system solids created in less than a week

Publication date: 12/11/2019

Press, Research

Related themes : Origins

Primitive meteorites, or chondrites, are evidence of the first millions of years of our Solar System, when the young Sun was surrounded by a disc of gas and dust, the protoplanetary disc. Chondrites are the debris of asteroids that escaped during the formation of telluric planets. They contain the oldest solids in the Solar System, refractory inclusions, which are millimetre-sized objects of irregular shape. They are so named because, according to thermodynamic models, they will form at very high temperatures (> 1300°C) during the cooling of the protoplanetary disc. Their age determines the age of our Sun, i.e. 4,567 billion years.

However, the time taken for the refractory inclusions to condense was not known precisely until now. Dating based on radioactive isotopes (uranium 235, uranium 238, aluminium 26) suggested a limited formation time of a few hundred thousand years. This duration could support the idea of very slow condensation during the cooling of the protoplanetary disc, but did not really give any information about the formation time of an individual solid. In addition, for most refractory inclusions, the information was blurred by later melting episodes, making it impossible to determine the condensation times of the first solids in the Solar System.

This new study focuses on little-studied condensates, the Amoeboid Olivine Aggregates (AOA). These are evidence of the condensation of olivine, the most abundant mineral in chondrites, and have largely escaped the melting processes undergone by other refractory inclusions. Determination of their silicon isotopic composition using the CRPG ion probe in Nancy shows enrichments in light isotopes of up to 5 ‰/u. Such isotopic fractionation is only possible when the cooling time of AOAs is shorter than the condensation time: a duration estimated at between one day and one week. The AOAs, and probably the other refractory inclusions, each condensed extremely rapidly in just a few days.

This is a very short time compared with the overall cooling time of the protoplanetary disc (a few hundred thousand or even millions of years), but also taking into account the transport times of individual solids from the hot regions to the cold regions of the disc. We therefore need to consider localised increases and decreases in temperature, as suggested by certain models of turbulence in the disc. The primordial matter of the protoplanetary disc would thus have undergone evaporation/recondensation cycles, from which condensates would have emerged, rapidly forming aggregates that would have been incorporated into asteroids within a few million years. Thus, 4,567 billion years ago, the oldest solids in the solar system formed almost instantaneously.

Ref:

Y. Marrocchia, J. Villeneuvea, E. Jacquetb, M. Pirallaa & M. Chaussidon, Rapid condensation of the first Solar System solids, Proceedings of the National Academy of Sciences, Nov. 2019, 116 (47) 23461-23466, doi : 10.1073/pnas.1912479116

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