Rocky Planet Compositions Do Not Strongly Depend on Stellar Abundances

Planets and the stars they orbit are born from the same cloud of nebular material, and it has long been suggested that chemical abundances of rocky exoplanets should follow those of their host star, just as we see for the Earth, Venus, and Mars in our solar system. Previous results found not only a significant correlation between rocky planet and host star Iron/Magnesium ratios, but also a slope much steeper than unity. In addition, it has been suggested that there is a distinct population of iron-enriched super-Mercuries orbiting iron-rich hosts, all of which suggests that planets do not simply inherit their primordial nebular composition, but that iron-enhancing planet formation mechanisms occur more frequently around iron-rich stars and iron-depleting mechanisms occur more frequently around iron-poor stars. We revisit the relationship using new, homogeneously measured stellar elemental abundances, along with updated masses and radii for both rocky exoplanets and host stars. Our results show that (1) we do not conclusively recover the steep and statistically significant dependence of planet iron enrichment on stellar iron enrichment, and (2) we find no distinct population of super-Mercuries. Our findings suggest that stars spanning a wide range in Fe/Mg form planets depleted in iron relative to stellar abundances, and do not preferentially happen around iron-poor host stars. Additionally, we find that stochastic processes such as giant impacts can be responsible for enriching planetary cores in iron, but we do not see evidence that this process occurs at a higher frequency around iron-rich host stars.