A detailed model to constrain the interior and bulk composition of terrestrial Exoplanets

Probing the internal structure and composition of exoplanets through models of planetary interiors remains limited by the precision on the fundamental parameters of studied bodies, and by the degeneracy on their composition. The first limitation will be greatly reduced with upcoming space missions like PLATO or CHEOPS. The second point, however, is bound to interior models, and cannot be solved by improving current detection methods. We present a model which overcomes this degeneracy by assuming the elemental abundances of a host star are retrieved in the planetary values. It accurately simulates the planet’s metallic core and silicate mantle, through a detailed description of the phase chemistry of both layers, coupled to an adapted equation of state. Using a Monte-Carlo approach, our model derives constraints on a planet’s internal structure and on its bulk elemental composition. It can thus be used to study a broad range of solid exoplanet interiors, from Mercury-like to ocean planets. Applied to a set of exoplanets whose compositions led to theories suggesting a strong post-formation alteration, our model shows that these processes are not necessary. This draws the characteristics of a new family of exoplanets strongly resembling one of our solar system’s bodies.

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