Liquid methane at extreme temperature and pressure: Implications for models of Uranus and Neptune

TL;DR

This study uses large-scale molecular dynamics simulations to investigate the state of liquid methane and carbon in planetary interiors, challenging the diamond formation hypothesis and suggesting metallic hydrogen presence.

Contribution

It provides new simulation evidence that liquid methane does not form diamonds under planetary conditions, but instead forms polymeric carbon, and predicts metallic hydrogen at high temperatures.

Findings

No evidence of diamond formation in simulations

Presence of sp2-bonded polymeric carbon

Hydrogen may exist as monoatomic and metallic at high temperatures

Abstract

We present large scale electronic structure based molecular dynamics simulations of liquid methane at planetary conditions. In particular, we address the controversy of whether or not the interior of Uranus and Neptune consists of diamond. In our simulations we find no evidence for the formation of diamond, but rather sp2-bonded polymeric carbon. Furthermore, we predict that at high tem- perature hydrogen may exist in its monoatomic and metallic state. The implications of our finding for the planetary models of Uranus and Neptune are in detail discussed.