ORBITAL EVOLUTION AND MIGRATION OF GIANT PLANETS - MODELING EXTRASOLAR PLANETS

Giant planets in circumstellar disks can migrate inward from their ini tial (formation) positions. Radial migration is caused by inward torqu es between the planet and the disk, by outward torques between the pla net and the spinning star, and by outward torques due to Roche lobe ov erflow and consequent mass loss from the planet. We present self-consi stent numerical considerations of the problem of migrating giant plane ts. Summing torques on planets for various physical parameters, we fin d that Jupiter-mass planets can stably arrive and survive at small hel iocentric distances, thus reproducing observed properties of some of t he recently discovered extrasolar planets. Inward migration timescales can be approximately equal to or less than disk lifetimes and star sp indown timescales. Therefore, the range of fates of massive planets is broad and generally comprises three classes: (I) planets that migrate inward too rapidly and lose all their mass; (II) planets that migrate inward, lose some but not all of their mass, and survive in very smal l orbits; and (III) planets that do not lose any mass. Some planets in class III do not migrate very far from their formation locations. Our results show that there is a wide range of possible fates for Jupiter -mass planets for both final heliocentric distance and final mass.