Planet-planet scattering in circumstellar gas disks

Context. 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. Aims: 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. Methods: The hydrodynamical code FARGO-2D-1D is used to model the evolution of the disk and planets, modified to properly handle close encounters between the massive bodies. Results: 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. Conclusions: This implies that the final fate of a multiplanet system under the action of the disk torques is not necessarily a packed resonant configuration.