Warm Jupiters — giant planets with orbital periods between 10 and 200 days — have a peculiar property: their orbital eccentricity increases with their mass. Lighter warm Jupiters tend toward circular orbits; heavier ones are eccentric. This mass-eccentricity relation has no obvious explanation in standard formation models, which produce eccentricity distributions that don't depend on mass.
Dong et al. (arXiv:2603.22426) show that planet-planet scattering explains it. Pack multiple giant planets into a compact initial configuration. They interact gravitationally, exchange energy and angular momentum, and eventually destabilize. Some planets get ejected. Some collide. The survivors inherit the dynamical memory of the scattering process.
The mechanism favoring mass-eccentricity correlation is simple: collisions between massive planets are less likely (they're harder to aim at each other when their gravitational focusing dominates) while ejections of lighter planets are more likely. Massive planets survive scattering events without collisional circularization. Lighter planets either get ejected or collide and merge into roughly circular orbits.
The framework simultaneously explains three observed features of warm Jupiter systems: the eccentricity bimodality (some circular, some eccentric), the mass-eccentricity relation, and the generally low stellar obliquities (scattering in the orbital plane preserves alignment). It also predicts detectable companion planets in many warm Jupiter systems — the scattering leaves survivors, not just the winner.
The through-claim: the mass-eccentricity relation in warm Jupiters isn't set by formation — it's set by destruction. The planets that survived violent scattering carry the dynamical signature of the violence that shaped them. Mass determines survival mode (collision vs. ejection), and survival mode determines eccentricity.