Refractory element abundances in rocky planets and their host stars: Revisiting the compositional link

¹ Institute of Science and Technology for Deep Space Exploration, Nanjing University, Suzhou 215163, PR China
² State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau 999078, PR China

^★ Corresponding author: ddni@nju.edu.cn

Received: 22 July 2025
Accepted: 14 October 2025

Abstract

Context. Stars and planets form within the same protoplanetary disk, and hence their refractory element abundances are expected to share compositional links. Recent studies have revealed a pronounced non-1:1 relationship between the refractory element abundances of rocky exoplanets and their host stars. This finding is challenged by other works using updated stellar and planetary parameters.

Aims. We reanalyze the interior structure of rocky exoplanets by incorporating the updated observational constraints. Through a systematic assessment of model assumptions and statistical methods, we aim to resolve the existing discrepancies and advance our understanding of the compositional link between rocky exoplanets and their host stars.

Methods. We modeled the interior structure of 60 close-orbiting rocky exoplanets and derived their possible compositions using Bayesian statistical methods. Their bulk iron-to-silicate ratios were systematically compared with the refractory elemental abundances in their host stars, together with the core mass fraction as a first-order proxy for planetary bulk composition.

Results. Despite incorporating the updated measurements, we find that the planet-star compositional link maintains a non-1:1 relationship. It is demonstrated that both interior composition priors and uncertainty propagation methods significantly influence the derived planetary bulk compositions, thereby affecting the inferred star-planet compositional link. Moreover, a positive correlation between planetary iron content and stellar age is also identified, with younger stars hosting planets that are richer in iron. This is because the bulk compositions of rocky exoplanets show a clear correlation with the refractory abundances of their host stars, while the stellar chemical abundances serve as powerful proxies for ages.