Modeling the Interior Structure and Mineralogy of Terrestrial Exoplanets

Abstract

The interior structure and mineralogy of an exoplanet have strong effects on its structural properties such as mass and radius, as well as its dynamic processes which can influence its potential habitability (Noack and Breuer, 2014; Zhang and Rogers, 2022; Baumeister et al., 2023). In this paper, we describe the underlying physics behind our exoplanet model and use it to analyze the structural properties and mineralogies of terrestrial exoplanets ranging from 1 ME to 10 ME. This exoplanet model is the first ever to simultaneously implement iron (Fe) content in the exoplanet mantle, newly researched high pressure mineral phases, and the continuous phase transition between the B1 (NaCl-type) and B2 (CsCl-type) phases of ferropericlase with a phase diagram and equation of state (EOS) parameters that are entirely user-inputted. This paper is also the first to use three different phase diagrams that span across a large portion of the expected compositions of detected terrestrial exoplanets (Hinkel and Unterborn, 2018; Putirka et al., 2021). We begin by modeling Earth and find that the model calculates a structural profile and mineralogy that is nearly identical to previously published results (Dziewonski and Anderson, 1981). Next, we describe the model outputs for exoplanets between 1 ME and 10 ME using different phase diagrams, core mass fractions (CMFs), mantle Fe contents. We find that using different phase diagrams substantially alters predicted exoplanet mineralogies. Moreover, increasing CMF produces smaller, denser exoplanets, and larger mantle Fe contents increase mantle densities and lead to the continuous B1-B2 phase transition occurring over a larger range of radii. We also analyze how the mineralogies of exoplanets vary with mass. Finally, we report scaling law exponents for structural properties such as radius when fit to power laws with respect to exoplanet mass. We find that our model exhibits stronger compressional effects than existing models within the literature, which is likely due to our unique implementation of mantle Fe content and high pressure mineral phases.