Insights into Planet Formation from the Ages, Masses, and Elemental Abundances of Host Stars

Abstract How planetary systems form and evolve is a key question in astronomy. Revealing how host star properties—such as elemental abundances, age, and mass—differ from those of nonhost stars, and how they correlate with planetary characteristics such as radius, provides new insights into the formation and evolutionary pathways of planetary systems. We determine precise ages for 18,890 dwarfs and subgiants from the LAMOST–Kepler–Gaia sample with a mean age uncertainty ∼15% (median ∼10%). Within the framework of Galactic chemical evolution, we find that ∼86% of planet-hosting stars younger than 8 Gyr occupy the upper branch ([Fe/H] > −0.2) of the characteristic “V-shape” age–metallicity relation of the Galactic disk. Based on guiding radii ( R g ), we further infer that ∼19% of these young hosts likely originated in the inner disk and subsequently migrated to the solar neighborhood. Among stars older than 10 Gyr, host stars tend to be more metal-rich, with nearly 59% having [Fe/H] > −0.2. This suggests that both young and old planet-hosting stars preferentially form in relatively metal-rich environments. However, for host stars with [Fe/H] < −0.2, we find that their [Fe/H] is on average lower by ∼0.16 dex compared to nonhost stars of similar age and mass, indicating that [Fe/H] is unlikely to be the dominant factor governing planet formation in metal-poor environments. We also identify systematic depletion of volatile elements—especially carbon—in planet hosts. Moreover, host star [Fe/H] exhibits a weak correlation with planet radius, while [ α /Fe] primarily supports the formation of small planets.