Evolution of Dust In Protoplanetary Disks With Magnetized Winds

Abstract

Observations and theory increasingly indicate that protoplanetary disks are weakly turbulent, implying that magnetized disk winds may dominate their angular momentum transport and long-term evolution. Yet dust evolution in wind-dominated disks remains poorly understood, despite its importance for planet formation. In particular, whether wind-dominated disk evolution can create regions with enhanced dust-to-gas mass ratios that enable planetesimal formation via the streaming instability is unclear. We build a parametric hybrid disk evolution model that includes turbulent accretion, wind-driven accretion, and wind-driven mass loss to investigate dust evolution in magnetized protoplanetary disks. We employ this model to carry out a parameter study in which the initial total accretion rate, the wind-driven mass loss rate, and the turbulence strength are varied. We find that although wind-dominated disks are more favorable to dust growth and concentration than turbulence-dominated disks, conditions suitable for the streaming instability arise only within the inner few au and only under the most extreme conditions: very weak turbulence ($α_\text{turb} = 10^{-5}$) where magnetized winds drive most of the accretion ($\dot{M}_\text{acc,tot} \simeq \dot{M}_\text{wind,acc}$), and wind-driven mass loss comparable to the accretion rate ($\dot{M}_\text{wind,outflow} \simeq \dot{M}_\text{acc,wind}$). Our results therefore imply that, beyond the inner few au, the parametric wind-driven evolution models considered in the literature do not by themselves produce conditions suitable for planetesimal formation via the streaming instability, motivating more physically complete models in which spontaneous, long-lived dust traps can arise.