Low Mg/Si planetary host stars and their Mg-depleted terrestrial planets

TL;DR

This study explores the composition of terrestrial planets around stars with low Mg/Si ratios, predicting Mg-depleted planets with specific mineralogy and variable carbon content, supported by white dwarf observations.

Contribution

It introduces a focus on Mg/Si ratios below 1 in host stars and predicts resulting planetary compositions, filling a gap in previous planetary formation models.

Findings

Mg-depleted planets with pyroxene and feldspar mineralogy

Planetary carbon varies with host star C/O ratio

Predicted compositions align with polluted white dwarf observations

Abstract

Simulations have shown that a diverse range of extrasolar terrestrial planet bulk compositions are likely to exist, based on the observed variations in host star elemental abundances. Based on recent studies, it is expected that a significant proportion of host stars may have Mg/Si ratios below 1. Here we examine this previously neglected group of systems. Planets simulated as forming within these systems are found to be Mg-depleted (compared to the Earth), consisting of silicate species such as pyroxene and various feldspars. Planetary carbon abundances also vary in accordance with the host stars C/O ratio. The predicted abundances are in keeping with observations of polluted white dwarfs, lending validity to this approach. Further studies are required to determine the full planetary impacts of the bulk compositions predicted here.