Stellar Abundances as Probes of Rocky Exoplanet Interiors: The Mantle Composition and Mineralogy of GJ 486b

Abstract

Over the past three decades, hundreds of rocky exoplanets have been discovered. Some of these show atmospheric signatures indicative of diverse chemical compositions. Interpreting these atmospheres requires a physically grounded understanding of planetary interiors, as interior composition and mineralogy govern the formation and evolution of secondary atmospheres. Rocky terrestrial exoplanets are expected to inherit the refractory composition of their host stars, providing a direct pathway to constrain their bulk composition and mineralogy. However, a large fraction of these planets orbit M-type stars, whose compositions remain poorly constrained because of limited and uncertain stellar abundance measurements. Here, we present a physically consistent framework that connects stellar abundances to the interior structure and mineralogy of rocky exoplanets by combining stellar abundance inference, devolatilization modeling to estimate bulk and mantle elemental abundances, interior structure calculations to derive pressure-temperature profiles, and thermodynamic equilibrium modeling of mantle mineralogy. We first benchmark the framework against Earth and then apply it to the super-Earth GJ 486b using chemically consistent abundances derived from ensembles of similar M-dwarf hosts. We find that GJ 486b likely hosts an iron-rich and silica-poor mantle relative to Earth while preserving the major mantle phase transitions. Sensitivity analyses show that the overall mineralogical structure is robust to variations in bulk composition and pressure-temperature profiles, with temperature primarily modulating phase proportions near key transitions. Finally, our results show that stellar-abundance inference combined with devolatilization models constrains the interior composition of rocky exoplanets and provides a foundation for linking planetary interiors to atmospheric characterization.