Warm Jupiters — giant planets orbiting between 0.1 and 1 AU — show a pattern that cold Jupiters don't: the more massive ones have more eccentric orbits. Dong, Lee, Kokubo, Murray-Clay, and Gupta explain this correlation through a single mechanism: planet-planet scattering, where the outcome depends on mass.
When two low-mass giant planets in a compact system destabilize and encounter each other, they collide. The merged planet inherits a relatively circular orbit. When two high-mass giants scatter, they don't merge — one ejects the other from the system entirely. The survivor retains a highly eccentric orbit, carrying the memory of the violent encounter in its orbital shape.
The transition from collision-dominated to ejection-dominated outcomes is what creates the mass-eccentricity correlation. Below a threshold mass, scattering ends in merger and circularization. Above it, scattering ends in ejection and eccentricity. The relationship between mass and orbital shape isn't set during formation — it's carved by the dynamics of destruction.
The same mechanism explains several other observations simultaneously. Stellar obliquities — the misalignment between the star's spin axis and the planet's orbit — increase with eccentricity, as expected if violent scattering events tilt orbits relative to the original disk plane. The model also predicts that warm Jupiters should have unseen companion planets at wider orbits, detectable through radial velocity surveys, because scattering from a compact multi-planet system doesn't always eject all the neighbors.
The mass doesn't cause the eccentricity. The mass determines whether the collision sticks or the competitor flies away. The orbit remembers which happened.