A Dead Zone within a
Circumstellar Disk is an area of low gas viscosity.
Planetary Migration, which has been much studied since Extra-Solar Planets
have been found that must have migrated, has proved "too efficient",
i.e., models suggest planets in circumstellar disks, where they
would be when they first formed, would migrate into the star.
Some models attempting to solve this dilemma provide a means of creating
dead zones within the disk, places where the causes of migration are absent.
They are areas with low gas viscosity.