  Migration of protoplanets in their gaseous host disks may be largely
responsible for the observed orbital distribution of extrasolar planets. Recent
simulations have shown that the magnetorotational turbulence thought to drive
accretion in protoplanetary disks can affect migration by turning it into an
orbital random walk. However, these simulations neglected the disk's ionization
structure. Low ionization fraction near the midplane of the disk can decouple
the magnetic field from the gas, forming a dead zone with reduced or no
turbulence. Here, to understand the effect of dead zones on protoplanetary
migration, we perform numerical simulations of a small region of a stratified
disk with magnetorotational turbulence confined to thin active layers above and
below the midplane. Turbulence in the active layers exerts decreased, but still
measurable, gravitational torques on a protoplanet located at the disk
midplane. We find a decrease of two orders of magnitude in the diffusion
coefficient for dead zones with dead-to-active surface density ratios
approaching realistic values in protoplanetary disks. This torque arises
primarily from density fluctuations within a distance of one scale height of
the protoplanet. Turbulent torques have correlation times of only $\sim 0.3$
orbital periods and apparently time-stationary distributions. These properties
are encouraging signs that stochastic methods can be used to determine the
orbital evolution of populations of protoplanets under turbulent migration. Our
results indicate that dead zones may be dynamically distinct regions for
protoplanetary migration.
