There are two fundamentally different processes in the formation of rocky planets, but it is not known which one built the Earth and the other planets in the Earth’s solar system. They were formed either by collisions between planetary embryos of the inner solar system, or by the accumulation of tiny “pebbles” drifting towards the sun of the outer solar system. New research shows that the isotopic compositions of Earth and Mars are governed by a two-component mixture of materials in the inner solar system, including the innermost disc material unsampled by meteorites, while the contribution of the material from the outer solar system is limited to a few percent by mass.
“Our data refute an origin of pebble accretion from terrestrial planets, but are consistent with the collisional growth of inner solar system embryos,” said Dr. Jan Render, researcher in the Division of Nuclear and Chemical Sciences at Lawrence Livermore National. Laboratory.
“This small fraction of material from the outer solar system on Earth and on Mars suggests the presence of a persistent barrier to dust drift in the disk and highlights the specific pathway for the formation of rocky planets in the solar system. . “
Determining which of the two processes governed the formation of the terrestrial planets in our solar system is crucial for understanding the architecture and dynamic evolution of the solar system, and for placing the formation of the planets in the solar system in the context of the general processes of formation of planets, such as those observed in exoplanetary systems.
The amount of matter from the outer solar system accumulated by terrestrial planets can be determined using nucleosynthetic isotopic anomalies.
These arise from the heterogeneous distribution of presolar matter within the solar protoplanetary disk and provide a record of the inheritance of a planet’s building material.
These isotopic anomalies help distinguish between non-carbon (NC) and carbon (CC) meteorites, which are generally believed to represent planetary bodies that have accreted in the inner and outer solar system, respectively.
Dr Render and his colleagues used the recent observation of correlated isotopic variations among NC meteorites to show that Earth and Mars incorporated unsampled material among meteorites, determined the provenance and isotopic composition of this building material. planetary loss and used this information to estimate the amount of CC Material accreted by Earth and Mars.
“The isotopic composition of this type of building material as deduced from our computer simulations implies that it must originate from the innermost region of the solar system,” said Dr Christoph Burkhardt, researcher at the Institute. für Planetology of the University of Münster.
“Because bodies so close to the Sun have hardly ever been dispersed in the asteroid belt, this material has been almost completely absorbed into the inner planets and therefore does not occur in meteorites.”
“It is, so to speak, a ‘lost building material’ to which we no longer have direct access today,” said Dr Thorsten Kleine, researcher at the Institute for Planetology at the University of Münster and the Max Planck Institute for the Solar System. To research.
“The surprising finding does not change the consequences of the study for the theory of planetary formation.”
“The fact that Earth and Mars apparently contain mostly material from the inner solar system fits well with the formation of planets from collisions of large bodies in the inner solar system,” said Dr Burkhardt.
the results were published in the journal Scientists progress.
Christoph burkhardt et al. 2021. Formation of terrestrial planets from lost material from the inner solar system. Scientists progress 7 (52); doi: 10.1126 / sciadv.abj7601