The effects of the stellar C/O ratio on planet compositions around solar-like stars

The elemental ratios in the cooling solar nebula are fundamental in determining the chemistry of the rocky planets that formed in the solar system. Partial condensation of dust in the solar nebula is one of the major contributors to the chemical composition of the chondrites and planetesimals that would ultimately form the solar system’s rocky planets. Current partial condensation models are able to reproduce the chemical compositions of most chondrites as well as the bulk compositions of the rocky planets. We use a leading partial condensation model to predict the chemical composition of dust that will form around stars with different elemental abundances than the Sun. The carbon-to-oxygen ratio (C/O) is often cited as one of the most important elemental ratios in determining the chemistry of rocky planets. The silicate chemistry that we observe in the solar system’s bodies is the result of the Sun’s initial C/O ratio falling below a threshold value. Stellar C/O ratios above this threshold are common in exoplanet systems and these high C/O ratios are likely to cause carbide-dominant planet composition – a composition so different from the Earth’s that significant differences in planet geology and habitability are almost certain. We explore how and where the threshold C/O ratio occurs and finely examine the exact impacts of this important chemical ratio on planet formation. Our study is the first to specifically examine the threshold C/O ratio, without extraneous factors, and its impacts using a modern partial condensation model.