A Two-Fluid Analysis of the Kelvin-Helmholtz Instability in the Dusty Layer of a Protoplanetary Disk: A Possible Path toward Planetesimal Formation through Gravitational Instability
We analyze the stability of the dust layer in protoplanetary disks to understand the effect of relative motion between gas and dust. Previous analyses not including the effect of the relative motion between gas and dust show that shear-induced turbulence may prevent the dust grains from settling sufficiently to be gravitationally unstable. We determine the growth rate of the Kelvin-Helmholtz instability in a wide range of parameter space and propose a possible path toward planetesimal formation through gravitational instability. We expect the density of the dust layer to become ρd/ρg~100 if the dust grains can grow up to 10 m.