Distinct e – λ Trends in Three Gas-giant Mass Regimes

Stellar obliquity ( λ ) and orbital eccentricity ( e ) trace the dynamical histories of close-in giant planets, but the current observational picture is assembled from heterogeneous analyses that have obscured population-level trends. In this work, we homogeneously refit systems with Rossiter–McLaughlin (RM) measurements by performing a joint global fit to spectral energy distributions, transit light curves, mid-transit times, and out-of-transit and in-transit radial velocities, yielding self-consistent posterior distributions for the physical and orbital parameters of both stars and planets across 256 systems. Restricting to 146 single-star systems with reliable planet-mass measurements, we uncover pronounced structure in the e – λ plane that depends on planet mass: (i) sub-Saturns ( M p ≤ ∼0.3 M J ) can be both eccentric and misaligned; (ii) Jupiters (∼0.3 M J < M p ≤ ∼3 M J ) are misaligned only on circular orbits; and (iii) super Jupiters and brown dwarfs ( M p > ∼3 M J ) are aligned across the full eccentricity range. A two-dimensional Kolmogorov–Smirnov test shows that the joint ( e , λ ) distributions differ significantly among these three mass regimes. These trends demonstrate that λ depends jointly on eccentricity and planet mass, implying that obliquity alone is not a unique tracer of evolutionary history and underscoring the need for a unified framework for the origins of spin–orbit misalignment.