Melting and metallization of silica in the cores of gas giants, ice giants and super Earths

TL;DR

This study uses first-principles simulations to explore the behavior of silica under extreme pressures and temperatures relevant to planetary cores, revealing its state and composition in gas giants, ice giants, and super-Earths.

Contribution

It provides the first detailed theoretical predictions of silica's properties at ultra-high pressures and temperatures, informing planetary core composition models.

Findings

Silica remains poorly conductive up to 10 Mbar due to increased Si-O coordination.

MgSiO₃ dissociates into MgO and SiO₂ in giant planet cores.

Core differentiation likely results in liquid SiO₂ and solid Mg,Fe)O phases.

Abstract

The physical state and properties of silicates at conditions encountered in the cores of gas giants, ice giants and of Earth like exoplanets now discovered with masses up to several times the mass of the Earth remains mostly unknown. Here, we report on theoretical predictions of the properties of silica, SiO$_2$, up to 4 TPa and about 20,000K using first principle molecular dynamics simulations based on density functional theory. For conditions found in the Super-Earths and in ice giants, we show that silica remains a poor electrical conductor up to 10 Mbar due to an increase in the Si-O coordination with pressure. For Jupiter and Saturn cores, we find that MgSiO$_3$ silicate has not only dissociated into MgO and SiO$_2$, as shown in previous studies, but that these two phases have likely differentiated to lead to a core made of liquid SiO$_2$ and solid (Mg,Fe)O.