Abstract
We have studied the dust evolution in a quiescent or turbulent protoplanetary disk by numerically solving coagulation equation for settling dust particles. As a result, in a quiescent disk the dust particles settle towards the disk midplane to form a gravitationally unstable layer within 2x103 - 5x104 yr at 1 - 30 AU, which is in good agreement with an analytical calculation by Nakagawa et al. (1986). In a turbulent disk, on the other hand, the dust particles vertically oscillate and most particles become large enough to move inward very rapidly within ~102 - 105 yr at 1 - 30 AU, depending on the strength of turbulence. Our result suggests that global turbulent motion should cease for the planetesimal formation in protoplanetary disks.
