Terrestrial planet formation from lost inner solar system material

TL;DR

This study demonstrates that Earth's and Mars's isotopic compositions primarily result from inner solar system material mixing, refuting the pebble accretion model and supporting collisional growth from planetary embryos.

Contribution

It provides evidence that terrestrial planets formed mainly from inner solar system material, challenging the pebble accretion hypothesis.

Findings

Outer solar system material contribution is limited to a few percent.

Isotopic compositions are governed by two-component mixing.

Supports collisional growth from inner solar system embryos.

Abstract

Two fundamentally different processes of rocky planet formation exist, but it is unclear which one built the terrestrial planets of the solar system. Either they formed by collisions among planetary embryos from the inner solar system, or by accreting sunward-drifting millimeter-sized 'pebbles' from the outer solar system. We show that the isotopic compositions of Earth and Mars are governed by two-component mixing among inner solar system materials, including material from the innermost disk unsampled by meteorites, whereas the contribution of outer solar system material is limited to a few percent by mass. This refutes a pebble accretion origin of the terrestrial planets, but is consistent with collisional growth from inner solar system embryos. The low fraction of outer solar system material in Earth and Mars indicates the presence of a persistent dust-drift barrier in the disk, highlighting the specific pathway of rocky planet formation in the solar system.