Preferred Locations for Planet Formation in MRI Active Disks
First Author:
Katherine Kretke
Email: kretke AT ucolick.org
University of California, Santa Cruz
Astronomy Dept
Santa Cruz, CA 95064 USA
Abstract
The first challenge in the formation of both terrestrial planets and the cores of gas giants is the retention of grains in protoplanetary disks. In most regions of these disks, gas attains sub-Keplerian speeds as a consequence of a negative pressure gradient. Hydrodynamic drag leads to orbital decay and depletion of the solid material in the disk. However, at local pressure maximums solids and gas will move at the same velocity allowing solids to accumulate. If the viscous evolution of the disk is due to turbulence driven by the magneto-rotational instability (MRI) then radial changes in viscosity in an incompletely ionized disk, will create local pressure maxima as the disk approaches a quasi-steady state. Two locations where these pressure maximums should occur are (1) the outer boundary of the thermally ionized region (the inner edge of the dead zone) and (2) at sublimation fronts (such as the snow line) where the grain-to-gas ratio changes significantly over a short distance. These changes in viscosity will produce pressure maximums which alter the disk structure and may seed the formation of planets.
