  Gravitational scattering between massive planets has been invoked to explain
the eccentricity distribution of extrasolar planets. For scattering to occur,
the planets must either form in -- or migrate into -- an unstable
configuration. In either case, it is likely that a residual gas disk, with a
mass comparable to that of the planets, will be present when scattering occurs.
Using explicit hydrodynamic simulations, we study the impact of gas disks on
the outcome of two-planet scattering. We assume a specific model in which the
planets are driven toward instability by gravitational torques from an outer
low mass disk. We find that the accretion of mass and angular momentum that
occurs when a scattered planet impacts the disk can strongly influence the
subsequent dynamics by reducing the number of close encounters. The
eccentricity of the innermost surviving planet at the epoch when the system
becomes Hill stable is not substantially altered from the gas-free case, but
the outer planet is circularized by its interaction with the disk. The
signature of scattering initiated by gas disk migration is thus a high fraction
of low eccentricity planets at larger radii accompanying known eccentric
planets. Subsequent secular evolution of the two planets in the presence of
damping can further damp both eccentricities, and tends to push systems away
from apsidal alignment and toward anti-alignment. We note that the late burst
of accretion when the outer planet impacts the disk is in principle observable,
probably via detection of a strong near-IR excess in systems with otherwise
weak disk and stellar accretion signatures.
