On stable H-C-N-O compounds at high pressure

TL;DR

This study systematically explores the stability and formation of H-C-N-O compounds under high-pressure conditions relevant to planetary interiors, revealing new potential compounds that influence planetary structure and evolution.

Contribution

The paper presents the first unbiased crystal structure search of H-C-N-O compounds at 5 Mbar, identifying stable compounds under extreme pressure.

Findings

Identification of stable H-C-N-O compounds at 5 Mbar

Insights into planetary interior composition and behavior

New compounds potentially relevant to planetary science

Abstract

The make-up of the outer planets, and many of their moons, are dominated by matter from the H-C-N-O chemical space, commonly assumed to originate from mixtures of hydrogen and the planetary ices H$_2$O, CH$_4$, and NH$_3$. In their interiors, these ices experience extreme pressure conditions, around 5 Mbar at the Neptune mantle-core boundary, and it is expected that they undergo phase transitions, decompose, and form entirely new compounds. In turn, this determines planets' interior structure, thermal history, magnetic field generation, etc. Despite its importance, the H-C-N-O space has not been surveyed systematically. Asked simply: at high-pressure conditions, what compounds emerge within this space, and what governs their stability? Here, we report on results from an unbiased crystal structure search amongst H-C-N-O compounds at 5 Mbar to answer this question.