Evidence of 1:1 slope between rocky Super-Earths and their host stars

TL;DR

This study investigates the compositional relationship between rocky exoplanets and their host stars, finding a tentative 1:1 correlation in iron-mass fraction that could inform planetary formation theories, but requires larger datasets for confirmation.

Contribution

It provides a self-consistent analysis of 21 exoplanets and their stars, suggesting a potential 1:1 compositional relationship and highlighting the need for larger samples to confirm primordial origins.

Findings

Potential 1:1 slope between planetary and stellar iron-mass fractions

Reduces super-Mercuries from four to one in the sample

High-density planets may have non-primordial origins

Abstract

The relationship between the composition of rocky exoplanets and their host stars is fundamental to understanding planetary formation and evolution. However, previous studies have been limited by inconsistent datasets, observational biases and methodological differences. This study investigates the compositional relationship between rocky exoplanets and their host stars, utilizing a self-consistent and homogeneous dataset of 21 exoplanets and their 20 host stars. By applying sophisticated interior structure modeling and comprehensive chemical analysis, we identify a potential 1:1 best-fit line between the iron-mass fraction of planets and their host stars equivalent with a slope of $m = 0.94^{+1.02}_{-1.07}$ and intercept of $c = -0.02^{+0.31}_{-0.29}$. This results are consistent at the 1$\sigma$ level with other homogeneous studies, but not with heterogeneous samples that suggest much steeper best-fit lines. Although, our results remain tentative due to sample size and data uncertainties, the updated dataset significantly reduces the number of super-Mercuries from four to one, but it remains that several high-density planets are beyond what a primordial origin would suggest. The planets in our sample have a wider range of compositions compared to stellar equivalent values, that could indicate formation pathways away from primordial or be the result of random scattering owing to current mass-radius uncertainties as we recover the observed outliers in mock population analysis $\sim15\%$ of the time. To truly determine whether the origin is primordial with a 1:1 true relation, we find that sample of at least 150 planets is needed and that stars that are iron enrich or depleted are high value targets.