Variation in exoplanetary structure and mineralogy from observed stellar metallicities, and related geophysical implications

Despite the detection of thousands of exoplanetary candidates, too few of these are known to resemble Earth in terms of volume and composition for many meaningful statistics on Earth-sized exoplanets to be obtained. Therefore, we instead estimate the bulk mineralogy of Earth-sized planet models, using the emission spectra of Sun-like stars. It is possible to convert the results of many stellar spectral observations into major oxides, thus allowing conversion of these oxides to silicate mantle mineralogies, similar to work done by Unterborn et al. (2017), as well as estimate the relative volume of a metallic core for cases where terrestrial worlds are near Earth’s size. This approach provides a way to anticipate how such exoplanets may differ from Earth structurally, compositionally, and perhaps in terms of geologic behavior. In order to isolate the effects on an otherwise Earth-analogue planet due only to initial variations in elemental composition, the volume, surface temperature, hydrosphere, and atmosphere are all considered equal to Earth, as differences in these aspects of a planet are not directly linked to the composition of the host star. The goal is to increase understanding of effects due solely to differences in initial bulk chemical composition and provide improved mineralogical and geophysical constraints of planets which may orbit roughly solar-analogue stars.