Dusty, Magnetized Disks During the Birth of Planets

 Planets form in thin, rotating disks of dust and gas.  The discovery of hundreds of exoplanets in compact and sometimes tightly spaced orbits has exposed major gaps in our understanding of how gas, dust, and angular momentum are redistributed in the natal disk.  This talk will review some fundamental problems that must be tackled to obtain a deterministic model of disk evolution and the conditions for planet formation. I will then describe a relatively constrained approach, based on the idea that the magnetic field that drives angular momentum transport is derived from the protostar.  We find that the disk mass profile quickly evolves to a configuration that differs radically from the minimal-mass Solar nebula, or a standard `alpha' disk.  The depletion of gas from the disk is buffered by fragmentation of a settled layer of solid particles into small grains. The disk profile that results is consistent with massive planets in small orbits; and a relatively small planet can feed back on the neighboring gas in interesting ways.  Shocks driven into a dense particle layer by   asteroid-sized objects offer a promising mechanism for generating high temperatures during the assembly of primitive chondritic material.