Hydrogen-Water Mixtures in Giant Planet Interiors Studied with Ab Initio Simulations

TL;DR

This study uses ab initio molecular dynamics to analyze water-hydrogen mixtures under planetary interior conditions, revealing phase behavior, structural properties, and transport characteristics relevant for modeling ice giant planets.

Contribution

It provides new thermodynamic, structural, and transport data for water-hydrogen mixtures at high pressures and temperatures relevant to planetary interiors.

Findings

Mixture is molecular at 2000 K and dissociates at 6000 K.

Viscosity estimates are around a few tenths of mPa.s.

Structural analysis via radial distribution functions.

Abstract

We study water-hydrogen mixtures under planetary interior conditions using ab initio molecular dynamics simulations. We determine the thermodynamic properties of various water-hydrogen mixing ratios at temperatures of 2000 and 6000 K for pressures of a few tens of GPa. These conditions are relevant for ice giant planets and for the outer envelope of the gas giants. We find that at 2000 K the mixture is in a molecular regime, while at 6000 K the dissociation of hydrogen and water is important and affects the thermodynamic properties. We study the structure of the liquid and analyze the radial distribution function. We provide estimates for the transport properties, diffusion and viscosity, based on autocorrelation functions. We obtained viscosity estimates of the order of a few tenths of mPa.s for the conditions under consideration. These results are relevant for dynamo simulations of ice giant planets.