Giant impacts stochastically change the internal pressures of terrestrial planets

TL;DR

This paper reveals that giant impacts cause stochastic fluctuations in the internal pressures of terrestrial planets, challenging the previous assumption of monotonic pressure increase with planetary mass, and highlights the importance of impact-driven thermal and rotational evolution.

Contribution

It introduces a new paradigm showing that impact events can cause significant, non-monotonic changes in planetary internal pressures during formation.

Findings

Impact-produced bodies can have lower internal pressures than cooler, slower-rotating planets of the same mass.

Internal pressures increase over time due to thermal and rotational evolution.

Pressure profiles are established long after initial impacts, over tens of millions of years.

Abstract

Pressure is a key parameter in the physics and chemistry of planet formation and evolution. Previous studies have erroneously assumed that internal pressures monotonically increase with the mass of a body. Using smoothed particle hydrodynamics and potential field method calculations, we demonstrate that the hot, rapidly-rotating bodies produced by giant impacts can have much lower internal pressures than cool, slowly-rotating planets of the same mass. Pressures subsequently increase due to thermal and rotational evolution of the body. Using the Moon-forming impact as an example, we show that the internal pressures after the collision could have been less than half that in present-day Earth. The current pressure profile was not established until Earth cooled and the Moon receded, a process that may take up to 10s Myr after the last giant impact. Our work defines a new paradigm for pressure evolution during accretion of terrestrial planets: stochastic changes driven by impacts.