Formation of the solar system in two stages

An international team of researchers from the University of Oxford, LMU Munich, ETH Zurich, BGI Bayreuth and the University of Zurich have found that a two-step formation process of the first solar system can explain the chronology and division into volatile and isotopic content of the inner and outer solar system.

Their results will be published in Science.

The article presents a new theoretical framework for the formation and structure of the solar system that can explain several key characteristics of the terrestrial planets (like Earth, Venus and Mars), the outer solar system (like Jupiter) and the composition of asteroids and meteorites. families. The team’s work builds on and connects recent advances in astronomy (i.e. observations of other solar systems during their formation) and meteorite – laboratory experiments and analyzes on isotope content , iron and water from meteorites.

The suggested combination of astrophysical and geophysical phenomena during the early formation phase of the Sun and the solar system itself may explain why the inner planets of the solar system are small and dry with little water in mass, while the planets external areas of the solar system are larger and humid with a lot of water. He explains the meteorite record by forming planets in two distinct stages. The internal terrestrial protoplanets accreted early and were heated inside by strong radioactive decay; it dried them up and separated the inner, dry planetary population from the outer wet planetary population. This has several implications for the distribution and necessary formation conditions of planets like Earth in extrasolar planetary systems.

Numerical experiments performed by the interdisciplinary team showed that the relative chronologies of early onset and prolonged end of accretion in the inner solar system, and later onset and faster accretion of the outer planets of the solar system can be explained by two distinct eras of formation of planetesimals, the building blocks of the planets. Recent observations of discs forming planets have shown that the mid-planes of discs, where planets form, can have relatively low levels of turbulence. Under such conditions, interactions between the dust grains embedded in the gaseous disk and the water around the orbital location where it changes from the gas phase to the glacial phase (the snow line) can trigger an early explosion of formation of planetesimals in the inner solar system and another later. and further.

The two distinct formation episodes of the planetesimal populations, which further increase the material of the surrounding disc and through mutual collisions, result in different geophysical modes of internal evolution for the forming protoplanets. Dr Tim Lichtenberg of the Department of Atmospheric, Oceanic and Planetary Physics at the University of Oxford and lead author of the study notes: “The different time intervals in which these planetesimal populations form means that their internal heat engine of decay radioactive differed considerably. The planetesimals of the inner solar system got very hot, developed internal magmatic oceans, quickly formed iron nuclei, and degassed their initial volatile contents, which ultimately resulted in dry planetary compositions. therefore limited formation of iron nucleus and volatile release.

“The dry, early-formed inner solar system and the later, wet-formed outer solar system were therefore placed on two different evolutionary paths very early in their history. This opens up new avenues for understanding the origins of Earth’s earliest atmospheres. like the planets and the place of the solar system in the context of the exoplanetary census across the galaxy. “

This research was supported by funding from the Simons Collaboration on the Origins of Life, the Swiss National Science Foundation and the European Research Council.

The full study, “Bifurcation of the planetary building blocks during the formation of the solar system”, will be published on January 22, 2021 in Science, 371, 6527.