No magma ocean surface after giant impacts between rocky planets

Vaporization is a major outcome of giant impacts during planet formation. The last giant impact marked a major stage in the early history of our planet, with the formation of a highly vaporized protolunar disk, that condenses onto the final Earth and Moon. The thermodynamic state of the disk and its condensation path are still uncertain, as most impact simulations have not used accurate material models. In this study, we compute the critical point and liquid spinodal of the bulk silicate Earth composition. We find that the thermal profiles through portions of the protolunar disk and the post-impact Earth exceeded the mantle critical point of 80-130 MPa kbars and 6500-7000 K. We find that Earth, and most rocky planets, will traverse a temporary state that lacks a surface defined by a magma ocean-atmosphere boundary. Furthermore, the atomic structure of the silicate fluid varies with the radius within the disk due to strong pressure and temperature gradients. Fluffy short-lived chemical species dominate the outer parts of the disk, and long-lasting dense polymers abound in the deeper parts. During cooling, the silicate vapor condenses and the composition of the post-impact atmosphere is dominated by species along the mantle vapor curve.(c) 2023 Published by Elsevier B.V.

Automated summary

Vaporization is a significant consequence of giant impacts in planet formation. The last giant impact during the early history of our planet resulted in the formation of a highly vaporized disk that condensed onto the Earth and Moon. This study investigated the thermodynamic state of the disk and its condensation process, finding that the mantle and post-impact Earth reached critical temperatures and pressures. The atomic structure of the silicate fluid within the disk varied with radius, leading to the presence of short-lived chemical species in the outer parts and long-lasting dense polymers in the deeper parts. The condensation of silicate vapor during cooling resulted in the dominance of species along the mantle vapor curve in the post-impact atmosphere.