Abstract
Planets may complete their accretion when they become massive enough to open gaps in the face of disk viscosity. The prediction that gap-opening mass is related to disk viscosity implies that planetary masses are sensitive to the degree of ionization of the disk in the expected situation that viscosity is driven by magneto-turbulence by the well-known MRI instability. We show that in dead zones - poorly ionized regions wherein the MRI instability is unable to develop - only planets of terrestrial mass can form while Jovian planets form outside such regions. Dead zones extend out to 5-20 AU depending upon the disk column density.
