The Hot Jupiter Period–Mass Distribution as a Signature of in situ Formation

Abstract

More than two decades after the widespread detection of Jovian-class planets on short-period orbits around other stars, their dynamical origins remain imperfectly understood. In the traditional narrative, these highly irradiated giant planets, like Jupiter and Saturn, are envisioned to have formed at large stello-centric distances and to have subsequently undergone large-scale orbital decay. Conversely, more recent models propose that a large fraction of hot Jupiters could have formed via rapid gas accretion in their current orbital neighborhood. In this study, we examine the period–mass distribution of close-in giant planets, and demonstrate that the inner boundary of this population conforms to the expectations of the in situ formation scenario. Specifically, we show that if conglomeration unfolds close to the disk's inner edge, the semimajor axis–mass relation of the emergent planets should follow a power law a ∝ M^(−2/7)—a trend clearly reflected in the data. We further discuss corrections to this relationship due to tidal decay of planetary orbits. Although our findings do not discount orbital migration as an active physical process, they suggest that the characteristic range of orbital migration experienced by giant planets is limited.