Gap Opening by Extremely Low Mass Planets in a Viscous Disk

Understand

By numerically integrating the compressible Navier-Stokes equations in two dimensions, we calculate the criterion for gap formation by a very low mass (q ~10^{-4}) protoplanet on a fixed orbit in a thin viscous disk.

• In contrast with some previously proposed gap-opening criteria, we find that a planet can open a gap even if the Hill radius is smaller than the disk scale height.
• Moreover, in the low-viscosity limit, we find no minimum mass necessary to open a gap for a planet held on a fixed orbit.
• In particular, a Neptune-mass planet will open a gap in a minimum mass solar nebula with suitably low viscosity (\alpha <10^{-4}).