Dead Zones and the Diversity of Exoplanetary Systems
Abstract
Planetary migration provides a theoretical basis for the observed diversity
of exoplanetary systems. We demonstrate that dust settling - an inescapable
feature of disk evolution - gives even more rapid type I migration by up to a
factor of about 2 than occurs in disks with fully mixed dust. On the other
hand, type II migration becomes slower by a factor of 2 due to dust settling.
This even more problematic type I migration can be resolved by the presence of
a dead zone; the inner, high density region of a disk which features a low
level of turbulence. We show that enhanced dust settling in the dead zone
leaves a dusty wall at its outer edge. Back-heating of the dead zone by this
wall produces a positive radial gradient for the disk temperature, which acts
as a barrier for type I migration.