Constraints on Super-Earths Interiors from Stellar Abundances

TL;DR

This paper develops a model to better constrain the interior compositions of Super-Earths using stellar abundances, reducing degeneracies in density-based models and applying it to known exoplanets.

Contribution

It introduces a new internal structure model for Super-Earths that incorporates stellar Fe/Si ratios to improve composition estimates from mass and radius data.

Findings

Core mass fractions of CoRoT-7b and Kepler-10b are within 10-37% and 10-33%.

Proxima Centauri b's radius could reach 1.94 Earth radii for a 5 Earth mass planet.

The model refines mass-radius relationships for Super-Earths.

Abstract

Modeling the interior of exoplanets is essential to go further than the conclusions provided by mean density measurements. In addition to the still limited precision on the planets' fundamental parameters, models are limited by the existence of degeneracies on their compositions. Here we present a model of internal structure dedicated to the study of solid planets up to ~10 Earth masses, i.e. Super-Earths. When the measurement is available, the assumption that the bulk Fe/Si ratio of a planet is similar to that of its host star allows us to significantly reduce the existing degeneracy and more precisely constrain the planet's composition. Based on our model, we provide an update of the mass-radius relationships used to provide a first estimate of a planet's composition from density measurements. Our model is also applied to the cases of two well-known exoplanets, CoRoT-7b and Kepler-10b, using their recently updated parameters. The core mass fractions of CoRoT-7b and Kepler-10b are found to lie within the 10-37% and 10-33% ranges, respectively, allowing both planets to be compatible with an Earth-like composition. We also extend the recent study of Proxima Centauri b, and show that its radius may reach 1.94 Earth radii in the case of a 5 Earth masses planet, as there is a 96.7% probability that the real mass of Proxima Centauri b is below this value.