  Giant planets in circumstellar disks can migrate inward from their initial
(formation) positions. Radial migration is caused by inward torques between the
planet and the disk; by outward torques between the planet and the spinning
star; and by outward torques due to Roche lobe overflow and consequent mass
loss from the planet. We present self-consistent numerical considerations of
the problem of migrating giant planets. Summing torques on planets for various
physical parameters, we find that Jupiter-mass planets can stably arrive and
survive at small heliocentric distances, thus reproducing observed properties
of some of the recently discovered extra-solar planets. Inward migration
timescales can be approximately equal to or less than disk lifetimes and star
spindown timescales. Therefore, the range of fates of massive planets is broad,
and generally comprises three classes: (I) planets which migrate inward too
rapidly and lose all their mass; (II) planets which migrate inward, lose some
but not all of their mass, and survive in very small orbits; and (III) planets
which 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.
