Capturing the oxidation of silicon carbide in rocky exoplanetary interiors

TL;DR

This study investigates the stability of silicon carbide in the interiors of carbon-rich rocky exoplanets, revealing that oxidation processes convert it into other minerals unless specific conditions are met.

Contribution

It provides experimental evidence of silicon carbide oxidation in exoplanet interiors and identifies conditions necessary for its stability, advancing understanding of planetary composition.

Findings

Silicon carbide reacts to form quartz, graphite, and molten iron silicide.

Complete reduction of Fe$^{2+}$ to Fe$^{0}$ is needed to stabilize silicon carbide.

Detection of Fe$^{2+}$ or Fe$^{3+}$ on exoplanet surfaces suggests absence of silicon carbide.

Abstract

Theoretical models predict the condensation of silicon carbide around host stars with C/O ratios higher than 0.65 (cf. C/O$_{\mathrm{Sun}}$ = 0.54), in addition to its observations in meteorites, interstellar medium and protoplanetary disks. Consequently, the interiors of rocky exoplanets born from carbon-enriched refractory material are often assumed to contain large amounts of silicon carbide. Here we aim to investigate the stability of silicon carbide in the interior of carbon-enriched rocky exoplanets and to derive the reaction leading to its transformation. We performed a high-pressure high-temperature experiment to investigate the reaction between a silicon carbide layer and a layer representative of the bulk composition of a carbon-enriched rocky exoplanet. We report the reaction leading to oxidation of silicon carbide producing quartz, graphite, and molten iron silicide. Combined with previous studies, we show that in order to stabilize silicon carbide, carbon saturation is not sufficient, and a complete reduction of Fe$^{2+}$ to Fe$^{0}$ in a planetary mantle is required, suggesting that future spectroscopic detection of Fe$^{2+}$ or Fe$^{3+}$ on the surface of rocky exoplanets would imply the absence of silicon carbide in their interiors.