The Influence of Equation of State on the Giant Impact Simulations

Abstract

We explore the role of various equations of state (EoS) in controlling the composition of the Moon formed by a giant impact (GI) using a density‐independent SPH code. A limitation in our previous model Hosono et al. (2019), https://doi.org/10.1038/s41561-019-0354-2 is improved by replacing the EoS of the solid from Tillotson EoS to M‐ANEOS, and we also explored two recently proposed EoSs by Stewart et al. (2020), https://doi.org/10.1063/12.0000946 and Wissing and Hobbs (2020a), https://doi.org/10.1051/0004-6361/201935814; Wissing and Hobbs (2020b), https://doi.org/10.1051/0004-6361/201936227. The goal is to investigate to what extent we can explain the observed composition of the Moon including the similarity in the isotopic composition and the dissimilarity in the FeO/(FeO + MgO) ratio as compared to that of Earth by the different types of EoS assuming the conventional collision conditions. We found that changing the EoS for solids from Tillotson to M‐ANEOS EoS resolves the issues of latent heat, but its effect on the composition of the disk is small compared to the influence of the hard‐sphere EoS of magma ocean in controlling the composition of the disk. Similarly, two recently proposed EoSs have small effects on the composition of the disk in comparison to the model where the hard‐sphere EoS is used for preexisting magma ocean. We attribute this difference to a fundamental difference in thermodynamic behavior of silicate melts captured by the hard‐sphere EoS and by newly proposed EoSs; in the hard‐sphere model of silicate melts, configurational entropy dominates in free energy, whereas in the newly proposed model, entropy is dominated by vibrational entropy similar to entropy of solids.

First-principles equation of state of CHON resin for inertial confinement fusion applications

“…We also note that the Grüneisen parameter is important in constructing empirical EOS and planetary impact models [64,65]. Our ndings about the existence of a basin structure in the Grüneisen parameter of CHON before it reaches the limit of 2/3 is consistent with previous calculations for MgSiO 3 [66].…”

Effect of Equation of State and Cutoff Density in Smoothed Particle Hydrodynamics Simulations of the Moon-forming Giant Impact

“…N-SPH M-ANEOS does not include the heat capacity correction found in Stewart M-ANEOS and has erroneous relationships between particle velocity and temperature extrapolated above its sub-200 GPa experimental Hugoniot (Root et al 2018), both contributing to systematically higher disk temperatures and VMF than Stewart M-ANEOS. Recently, Hosono & Karato (2022) provided the first SPH implementation of Stewart M-ANEOS for a preexisting magma ocean and underlying solid rock during the giant impact while assessing its ability to reproduce the refractory isotopic similarities between the Moon and the Earth. While their study found that Stewart M-ANEOS placed too much impactor material into the disk to explain the Moon's composition, they did not assess specific dynamical differences or vapor production.…”