The energy budget and figure of Earth during recovery from the Moon-forming giant impact

Abstract

Quantifying the energy budget of Earth in the first few million years following the Moon-forming giant impact is vital to understanding Earth's initial thermal state and the dynamics of lunar tidal evolution. After the impact, the body was substantially vaporized and rotating rapidly, very different from the planet we know today. The subsequent evolution of Earth's energy budget, as the body cooled and angular momentum was transferred during lunar tidal recession, has not been accurately calculated with all relevant energy components included. Here, we use giant impact simulations and planetary structure models to calculate the energy budget at stages in Earth's evolution. We show that the figure and internal structure of Earth changed substantially during its post-impact evolution and that changes in kinetic, potential, and internal energy were all significant. These changes have important implications for the dynamics of tidal recession and the thermal structure of early Earth.

The Energy Budgets of Giant Impacts

“…The distribution of energy after a giant impact is crucial for understanding the amount of melting and vaporization and the thermal state of the final planet. The variation in the degree of thermal inflation and spin rate induced by an impact will cause differences in the later evolution of the planet (Chau et al, ; Lock et al, ). The variation in energy budgets between giant impacts also has important implications for metal‐silicate equilibration and core evolution.…”

“…The thermal structure affects the composition of the Moon formed after an impact, as discussed by Lock et al (). The evolution of the energy budgets include changes in internal energy as the shape of the planet changes during cooling and tidal recession of the Moon (Lock et al, ).…”

“…The evolution of the energy budget and the relative magnitude of its components during giant impacts differ greatly across the range of possible impacts. The amount of energy that giant impacts deposit into growing bodies, and where this energy is deposited, has important consequences for the thermal and dynamical states of young planets and is a key factor in determining the composition of any satellites that are formed (e.g., Lock et al, , ; Nakajima & Stevenson, ). It is therefore important to examine how the energy budgets of different impacts affect growing planets.…”

Vertically Resolved Magma Ocean–Protoatmosphere Evolution: H2, H2O, CO2, CH4, CO, O2, and N2as Primary Absorbers

“…Furthermore, the solidification time influences the onset of solid‐state convection (Ballmer et al., 2017; Maurice et al., 2017) and the intrusion efficiency of upwelling magma columns, thereby regulating the post‐magma ocean cooling regime of the planet (Lourenço et al., 2018). Tidal effects due to rapid rotation following giant impacts, however, can alter the energetic balance and magmatic evolution of planetary bodies (Lock et al., 2020; Zahnle et al., 2015). From a long‐term geodynamical perspective, mineralogical stratification and potential mantle overturn may result in different styles of mantle convection, separating whole‐mantle convection from double‐layered convection regimes with consequences for long‐term outgassing behavior (Schaefer & Elkins‐Tanton, 2018; Spaargaren et al., 2020).…”

“…Tidal effects due to rapid rotation following giant impacts, however, can alter the energetic balance and magmatic evolution of planetary bodies (Zahnle et al, 2015;Lock et al, 2020). From a long-term geodynamical perspective, mineralogical stratification and potential mantle overturn may result in different styles of mantle convection, separating whole-mantle convection from double-layered convection regimes with consequences for long-term outgassing behavior (Schaefer & Elkins-Tanton, 2018;Spaargaren et al, 2020).…”