Dust Settling and Clumping in MRI-turbulent Outer Protoplanetary Disks

Planetesimal formation is a crucial yet poorly understood process in planet formation. It widely believed that planetesimal the outcome of dust clumping by streaming instability (SI). However, recent analytical and numerical studies have shown SI can be damped or suppressed external turbulence, at least outer regions protoplanetary disks are likely weakly turbulent due to magneto-rotational (MRI). We conduct high-resolution local shearing-box simulations hybrid particle-gas magnetohydrodynamics (MHD), incorporating ambipolar diffusion as dominant non-ideal MHD effect, applicable disk regions. first show backreaction enhances settling towards midplane reducing turbulence correlation time. Under modest level MRI we find fact easier than conventional case, sense threshold solid abundance for lower. The key includes presence pressure maxima, which our work formed zonal flows overcoming background gradient. Overall, results support MRI-turbulent disks, especially ring-like substructures.