  The recent discovery of Jupiter-mass planets orbiting at a few AU from their
stars compliments earlier detections of massive planets on very small orbits.
The short period orbits strongly suggest that planet migration has occurred,
with the likely mechanism being tidal interactions between the planets and the
gas disks out of which they formed. The newly discovered long period planets,
together with the gas giant planets in our solar system, show that migration is
either absent or rapidly halted in at least some systems. We propose a
mechanism for halting type-II migration at several AU in a gas disk.
Photoevaporation of the disk by irradiation from the central star can produce a
gap in the disk at a few AU, preventing planets outside the gap from migrating
down to the star. This would result in an excess of systems with planets at or
just outside the photoevaporation radius.
