  We present three-dimensional self-gravitating smoothed-particle hydrodynamics
(SPH) simulations of an isothermal gaseous disc interacting with an embedded
planet. Discs of varying stability are simulated with planets ranging from 10
Earth-masses to 2 Jupiter-masses. The SPH technique provides the large dynamic
range needed to accurately capture the large scale behavior of the disc as well
as the small scale interaction of the planet with surrounding material. Most
runs used 10^5 gas particles, giving us the spatial resolution required to
observe the formation of planets. We find four regions in parameter space:
low-mass planets undergo Type I migration; higher-mass planets can form a gap;
the gravitational instability mode of planet formation in marginally stable
discs can be triggered by embedded planets; discs that are completely unstable
can fragment to form many planets. The disc stability is the most important
factor in determing which interaction a system will exhibit. For the stable
disc cases, our migration and accretion time-scales are shorter and scale
differently than previously suggested.
