Equation of state of SiC at extreme conditions: new insight into the interior of carbon rich exoplanets

TL;DR

This study investigates the high-pressure and high-temperature properties of silicon carbide (SiC) to better understand the interior composition of carbon-rich exoplanets, providing new experimental data and modeling insights.

Contribution

It presents the first in situ X-ray diffraction data of SiC up to 200 GPa and 3500 K, refining the phase diagram and equation of state for high-pressure phases.

Findings

Refined phase diagram and transition line for SiC at extreme conditions

Provided pressure-volume-temperature equation of state for high-pressure SiC phases

Modeled mass-radius relations and convection onset in carbon-rich exoplanets

Abstract

There is a direct relation between the composition of a host star and that of the planets orbiting around it. As such, the recent discovery of stars with unusual chemical composition, notably enriched in carbon instead of oxygen, support the existence of exoplanets with a chemistry dominated by carbides instead of oxides. Accordingly several studies have been recently conducted on the Si C binary system at high pressure and temperature. Nonetheless, the properties of carbides at the P T conditions of exoplanets interiors are still inadequately constrained, effectively hampering reliable planetary modeling. Here we present an in situ X ray diffraction study of the Si C binary system up to 200 GPa and 3500 K, significantly enlarging the pressure range explored by previous experimental studies. The large amount of collected data allows us to properly investigate the phase diagram and to refine the Clapeyron slope of the transition line from the zinc blende to the rock salt structure. Furthermore the pressure volume temperature equation of state are provided for the high pressure phase, characterized by low compressibility and thermal expansion. Our results are used to model idealized C rich exoplanets of end members composition. In particular, we derived mass radius relations and performed numerical simulations defining rheological parameters and initial conditions which lead to onset of convection in such SiC planets. We demonstrate that if restrained to silicate rich mantle compositions, the interpretation of mass radius relations may underestimate the interior diversity of exoplanets.