Dust Dynamics and Implications for Planetesimal Formation in Turbulent Protoplanetary Disks

Planetesimal formation from dust grains has long been one of the least understood processes in planet formation. Recent observations of ring-like substructures in protoplanetary disks indicate dust concentration in axisymmetric gas pressure bumps, but it is unclear whether such dust rings can be precursors to planetesimal formation. In laminar environments, planetesimal formation is widely believed to be the outcome of dust clumping by the streaming instability, triggered by the dust feedback to the gas drag force in a background pressure gradient. However, forming planetesimals generally requires super-solar solid abundances, as expected in dust rings, and the streaming instability is unlikely to operate in pressure bumps. In addition, the bulk disk is believed to be weakly turbulent.

We conduct 3D non-ideal MHD simulations with Athena code to study dust dynamics in weakly turbulent disks, focusing on the role of dust feedback. We find that in a smooth disk, dust feedback modifies turbulence properties, enhances dust settling, and reduces dust layer thickness. Dust clumping is seen in the simulations, likely related to magnetic zonal flows. Introducing a gas pressure bump in our simulations leads to dust trapping in a ring. Dust feedback further affects turbulence properties and promotes dust trapping by making the dust ring narrower. We find evidence of dust clumping in the ring for near-solar global solid abundance of mm-sized dust. These results suggest that dust rings are preferable locations for planetesimal formation, with implications for the observed ring structures.