Dust settling against hydrodynamic turbulence in protoplanetary discs

Abstract

Enhancing the local dust-to-gas ratio in protoplanetary discs is a necessary first step to planetesimal formation. In laminar discs, dust settling is an efficient mechanism to raise the dust-to-gas ratio at the disc midplane. However, turbulence, if present, can stir and lift dust particles, which ultimately hinders planetesimal formation. In this work, we study dust settling in protoplanetary discs with hydrodynamic turbulence sustained by the vertical shear instability. We perform axisymmetric numerical simulations to investigate the effect of turbulence, particle size, and solid abundance or metallicity on dust settling. We highlight the positive role of drag forces exerted onto the gas by the dust for settling to overcome the vertical shear instability. In typical disc models we find particles with a Stokes number $\sim 10^{-3}$ can sediment to $\lesssim 10\%$ of the gas scale-height, provided that ${\Sigma }_{\mathrm{d}}/{\Sigma }_{\mathrm{g}}\gtrsim 0.02$-$0.05$, where ${\Sigma }_{\mathrm{d},\mathrm{g}}$ are the surface densities in dust and gas, respectively. This coincides with the metallicity condition for small particles to undergo clumping via the streaming instability. Super-solar metallicities, at least locally, are thus required for a self-consistent picture of planetesimal formation. Our results also imply that dust rings observed in protoplanetary discs should have smaller scale-heights than dust gaps, provided that the metallicity contrast between rings and gaps exceed the corresponding contrast in gas density.

Accepted by MNRAS; see https://minkailin.wixsite.com/minkailin/blog/dust-settling-in-turbulent-discs for a summary

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Cited by in corpus (19)

• Streaming Instability for Particle-Size Distributions
• Gas and dust dynamics in starlight-heated protoplanetary disks
• Formation of Giant Planet Satellites
• Protostellar collapse: the conditions to form dust rich protoplanetary disks
• Radial variations in grain sizes and dust scale heights in the protoplanetary disk around HD 163296 revealed by ALMA polarization observation
• High Resolution Parameter Study of the Vertical Shear Instability
• Hydrodynamical turbulence in eccentric circumbinary discs and its impact on the in situ formation of circumbinary planets
• Stratified and vertically-shearing streaming instabilities in protoplanetary disks
• Turbulence in outer protoplanetary disks: MRI or VSI?
• The coexistence of the streaming instability and the vertical shear instability in protoplanetary disks: Planetesimal formation thresholds explored in two-dimensional global models
• Impact of Local Pressure Enhancements on Dust Concentration inTurbulent Protoplanetary Discs
• The saturation of the VSI in protoplanetary disks via parametric instability
• On the Vertical Shear Instability in Magnetized Protoplanetary Disks
• Vertical settling of pebbles in turbulent circumbinary discs and the in situ formation of circumbinary planets
• Migrating Low-Mass Planets in Inviscid Dusty Protoplanetary Discs
• Instabilities in dusty non-isothermal proto-planetary discs
• Three-Dimensional Dust Stirring by a Giant Planet Embedded in a Protoplanetary Disk
• On the settling of small grains in dusty discs: analysis and formulas
• Nonlinear Outcome of Coagulation Instability in Protoplanetary Disks II: Dust Ring Formation Mediated by Backreaction and Fragmentation