Composition of super-Earths, super-Mercuries, and their host stars

TL;DR

This study confirms a correlation between rocky exoplanet composition and host star chemistry, highlighting the influence of disk chemistry and formation processes on super-Earths and super-Mercuries.

Contribution

It extends previous research by adding new exoplanet data, reaffirming the link between stellar and planetary compositions, and emphasizing the role of disk chemistry in planet formation.

Findings

Iron-mass fraction correlates with host star composition.

Planet iron-mass fraction is higher than primordial disk iron.

Super-Mercuries form in high-iron disks.

Abstract

Because of their common origin, it was assumed that the composition of planet building blocks should, to a first order, correlate with stellar atmospheric composition, especially for refractory elements. In fact, information on the relative abundance of refractory and major rock-forming elements such as Fe, Mg, Si has been commonly used to improve interior estimates for terrestrial planets. Recently Adibekyan et al. (2021) presented evidence of a tight chemical link between rocky planets and their host stars. In this study we add six recently discovered exoplanets to the sample of Adibekyan et al and re-evaluate their findings in light of these new data. We confirm that i) iron-mass fraction of rocky exoplanets correlates (but not a 1:1 relationship) with the composition of their host stars, ii) on average the iron-mass fraction of planets is higher than that of the primordial iron-mass fraction of the protoplanetary disk, iii) super-Mercuries are formed in disks with high iron content. Based on these results we conclude that disk-chemistry and planet formation processes play an important role in the composition, formation, and evolution of super-Earths and super-Mercuries.