The Shock Physics of Giant Impacts: Key Requirements for the Equations of State

TL;DR

This paper addresses the challenges in modeling giant impacts by improving the equations of state, specifically updating the ANEOS model for forsterite to better match experimental data relevant to planetary formation.

Contribution

An updated ANEOS model for forsterite with a user-defined heat capacity limit, enhancing the accuracy of thermodynamic property predictions during giant impacts.

Findings

Revised ANEOS model fits experimental data better across impact phase space.

Identifies limitations of the Tillotson EOS in modeling planetary impacts.

Provides insights into EOS requirements for planetary formation simulations.

Abstract

We discuss major challenges in modeling giant impacts between planetary bodies, focusing on the equations of state (EOS). During the giant impact stage of planet formation, rocky planets are melted and partially vaporized. However, most EOS models fail to reproduce experimental constraints on the thermodynamic properties of the major minerals over the required phase space. Here, we present an updated version of the widely-used ANEOS model that includes a user-defined heat capacity limit in the thermal free energy term. Our revised model for forsterite (Mg$_2$SiO$_4$), a common proxy for the mantles of rocky planets, provides a better fit to material data over most of the phase space of giant impacts. We discuss the limitations of this model and the Tillotson equation of state, a commonly used alternative model.