The silicate model and carbon rich model of CoRoT-7b, Kepler-9d and Kepler-10b

TL;DR

This paper investigates the possible internal compositions of three super-Earth exoplanets using silicate and carbon models, providing insights into their structure, formation, and likelihood of Earth-like or Mercury-like compositions.

Contribution

It introduces a comparative analysis of silicate and carbon models for CoRoT-7b, Kepler-9d, and Kepler-10b, addressing composition degeneracy and implications for planetary formation.

Findings

CoRoT-7b's iron core is likely less than 27% of its mass.

Kepler-10b probably has a Mercury-like composition.

Constraints on Kepler-9d's mass and composition are proposed.

Abstract

Possible bulk compositions of the super-Earth exoplanets, CoRoT-7b, Kepler-9d, and Kepler-10b are investigated by applying a commonly used silicate and a non-standard carbon model. Their internal structures are deduced using the suitable equation of state of the materials. The degeneracy problems of their compositions can be partly overcome, based on the fact that all three planets are extremely close to their host stars. By analyzing the numerical results, we conclude: 1) The iron core of CoRoT-7b is not more than 27% of its total mass within 1 $\sigma$ mass-radius error bars, so an Earth-like composition is less likely, but its carbon rich model can be compatible with an Earth-like core/mantle mass fraction; 2) Kepler-10b is more likely with a Mercury-like composition, its old age implies that its high iron content may be a result of strong solar wind or giant impact; 3) the transiting-only super-Earth Kepler-9d is also discussed. Combining its possible composition with the formation theory, we can place some constraints on its mass and bulk composition.