Dynamical Outcomes of Planet‐Planet Scattering

TLDR

Observations reveal a wide range of exoplanet orbits, and core‑accretion theory predicts closely packed giants whose eccentricities grow after gas disk dissipation, leading to close encounters that can scatter planets into high‑eccentricity or short‑period orbits. The study investigates planet‑planet scattering by integrating three‑giant‑planet systems with and without residual gas disks. Initial planetary masses and orbits are assigned realistically following the core‑accretion model, and the systems are integrated dynamically. Scattering with realistic initial conditions reproduces the observed eccentricity distribution and predicts orbital inclinations for short‑period giants.

Abstract

Observations in the past decade have revealed extrasolar planets with a wide range of orbital semimajor axes and eccentricities. Based on the present understanding of planet formation via core accretion and oligarchic growth, we expect that giant planets often form in closely packed configurations. While the protoplanets are embedded in a protoplanetary gas disk, dissipation can prevent eccentricity growth and suppress instabilities from becoming manifest. However, once the disk dissipates, eccentricities can grow rapidly, leading to close encounters between planets. Strong planet-planet gravitational scattering could produce both high eccentricities and, after tidal circularization, very short period planets, as observed in the exoplanet population. We present new results for this scenario based on extensive dynamical integrations of systems containing three giant planets, both with and without residual gas disks. We assign the initial planetary masses and orbits in a realistic manner following the core accretion model of planet formation. We show that, with realistic initial conditions, planet-planet scattering can reproduce quite well the observed eccentricity distribution. Our results also make testable predictions for the orbital inclinations of short-period giant planets formed via strong planet scattering followed by tidal circularization.