Halting planet migration in the evacuated centers of protoplanetary disks

Precise Doppler searches for extrasolar planets find a surfeit of planets with orbital periods of 3-4 days and no planets with orbital periods less than 3 days. The circumstellar distance R-0, where small grains in a proto- planetary disk reach sublimation temperatures (similar to1500 K), corresponds to a period of 6 days. Interior to, R-0 turbulent accretion due to magnetorotational instability may evacuate the disk center. We suggest that planets with orbital periods of 3-4 days are so common because migrating planets halt once this evacuated region contains the sites of their exterior 2 : 1 Lindblad resonances.