Chemical Abundances Shape History (CASH). I. A Link between Giant Planets Orbital Periods and Host Stellar C/O Ratios

Abstract

The chemical abundance of host stars plays a pivotal role in shaping the formation history of planetary systems, yet the influence of elements beyond iron remains poorly understood. Here, we investigate the relationship between the carbon-to-oxygen (C/O) ratio of host stars and the orbital periods of giant planets. By analyzing high-resolution spectroscopic data from 598 planet-hosting stars (hosting 929 planets) across SDSS, Keck, and HARPS surveys, we identify a correlation: stars with higher C/O ratios are more likely to host longer-period giant planets. Theoretical models of pebble-driven planet formation and migration further support this observation, demonstrating that elevated C/O ratios enhance solid material availability at outer disk regions, promoting giant planet formation at larger distances and subsequent moderate inward migration. Our findings establish stellar C/O as a critical factor in shaping the orbital architecture of giant planets, bridging disk chemistry to planetary system evolution.