A scaling relation for core heating by giant impacts and implications for dynamo onset

TL;DR

This study develops a scaling relation for core heating from giant impacts, revealing significant heat deposition that influences the timing of Earth's geodynamo onset.

Contribution

It introduces a systematic SPH simulation approach to quantify impact-induced core heating and derives a new scaling relation for core temperature profiles.

Findings

Impact impacts can raise core temperature by about 3000 K.

Heat distribution causes strong thermal stratification in the core.

Core can cool to an adiabatic state within 290 million years after impact.

Abstract

Accretional heating of Earth's interior during formation is pivotal to its subsequent thermal and chemical evolution. In particular, impact heating of Earth's core is expected, but its amplitude and radial distribution within the core is unknown and could influence the onset of the geodynamo. The uncertainty is due, in part, to the lack of constraints on the temperature of the interior following formation due to the difficulty of preserving a record of such a high energy environment, and the assertion that super-heating during formation would be rapidly lost through magma ocean cooling. Here we systematically investigate core heating due to giant impacts using a Smoothed Particle Hydrodynamics (SPH) code with simulations spanning a range of impact angles, velocities, and masses. From these simulations we derive a scaling relation for core heating that depends on the impact parameters and predicts the radial core temperature profile following the impact. Our findings show that a significant amount of heat is deposited into the core, with a canonical impact scenario resulting in an average core temperature increase of about 3000 K, approximately 500 K higher than that of the overlying mantle. In this case the heat distribution within the the core produces a strong thermal stratification. We use a parameterized cooling model to estimate that the core could have cooled to an adiabatic state 290 Myr after a canonical impact, which is consistent with the observed time span between the age of the Moon and evidence for an active geodynamo.