Planet--planet scattering in circumstellar gas disks

TL;DR

This study demonstrates that three giant planets can undergo scattering events within a gaseous disk, challenging the idea that such dynamical instability only occurs after the gas dissipates.

Contribution

It shows that planet-planet scattering can happen during the presence of a gaseous disk, using hydrodynamical simulations with a modified FARGO code.

Findings

Multiple scattering outcomes including orbital exchange, merging, and hyperbolic ejections.

Scattering can occur while the disk still interacts with the planets, not only after gas dissipation.

Final planetary configurations are not necessarily resonant or tightly packed.

Abstract

Hydrodynamical simulations of two giant planets embedded in a gaseous disk have shown that in case of a smooth convergent migration they end up trapped into a mean motion resonance. These findings have led to the conviction that the onset of dynamical instability causing close encounters between the planets can occur only after the dissipation of the gas when the eccentricity damping is over. We show that a system of three giant planets may undergo planet-planet scattering when the gaseous disk, with density values comparable to that of the Minimum Mass Solar Nebula, is still interacting with the planets. The hydrodynamical code FARGO--2D--1D is used to model the evolution ofthe disk and planets, modified to properly handle close encounters between the massive bodies. Our simulations predict a variety of different outcomes of the scattering phase which includes orbital exchange, planet merging and scattering of a planet in a hyperbolic orbit. This implies thatthe final fate of a multiplanet system under the action of the disk torques is not necessarily a packed resonant configuration.