Dynamical Outcomes of Planet‐Planet Scattering

Observations in the past decade have revealed extrasolar planets with a widerange of orbital semimajor axes and eccentricities. Based on the presentunderstanding of planet formation via core accretion and oligarchic growth, weexpect that giant planets often form in closely packed configurations. Whilethe protoplanets are embedded in a protoplanetary gas disk, dissipation canprevent eccentricity growth and suppress instabilities from becoming manifest.However, once the disk dissipates, eccentricities can grow rapidly, leading toclose encounters between planets. Strong planet--planet gravitationalscattering could produce both high eccentricities and, after tidalcircularization, very short-period planets, as observed in the exoplanetpopulation. We present new results for this scenario based on extensivedynamical integrations of systems containing three giant planets, both with andwithout residual gas disks. We assign the initial planetary masses and orbitsin a realistic manner following the core accretion model of planet formation.We show that, with realistic initial conditions, planet--planet scattering canreproduce quite well the observed eccentricity distribution. Our results alsomake testable predictions for the orbital inclinations of short-period giantplanets formed via strong planet scattering followed by tidal circularization.