Dusty disc–planet interaction with dust-free simulations

Abstract

Protoplanets may be born into dust-rich environments if planetesimals formed through streaming or gravitational instabilities, or if the protoplanetary disc is undergoing mass loss due to disc winds or photoevaporation. Motivated by this possibility, we explore the interaction between low mass planets and dusty protoplanetary discs with focus on disc-planet torques. We implement Lin & Youdin's newly developed, purely hydrodynamic model of dusty gas into the Pluto code to simulate dusty protoplanetary discs with an embedded planet. We find that for imperfectly coupled dust and high metallicity, e.g. Stokes number 10 −3 and dust-to-gas ratio Σ d /Σ g = 0.5, a 'bubble' develops inside the planet's co-orbital region, which introduces unsteadiness in the flow. The resulting disc-planet torques sustain large amplitude oscillations that persists well beyond that in simulations with perfectly coupled dust or low dust-loading, where co-rotation torques are always damped. We show that the desaturation of the co-rotation torques by finite-sized particles is related to potential vorticity generation from the misalignment of dust and gas densities. We briefly discuss possible implications for the orbital evolution of protoplanets in dust-rich discs. We also demonstrate Lin & Youdin's dust-free framework reproduces previous results pertaining to dusty protoplanetary discs, including dust-trapping by pressure bumps, dust settling, and the streaming instability.

Vortex instabilities triggered by low-mass planets in pebble-rich, inviscid protoplanetary discs

“…Compared to the simulation with St = 0.1, the Time=400 panel of the pebble surface density reveals that only a few vortices are formed at the planet separatrix, but with a larger radial size. Extrapolating down to smaller values of the Stokes number, we would expect that a large, single vortex to be eventually formed in the limit of small dust grains with St → 0, which would be consistent with the results of Chen & Lin (2018). From the pebble surface density profile that is plotted for each model in the left panel of Fig.9, it appears that this arises because the width of the separatrix tends to increase as the Stokes number decreases, resulting in a weaker bump in the generalized PV profile (see right panel of Fig.…”

“…12. This is due to the fact that gradients at the separatrix are better resolved (Chen & Lin 2018), as can be observed in the lower right panel of Fig. 12 which displays the profiles of the generalized PV function at Time=50 and for both resolutions.…”

Asymptotically Stable Numerical Method for Multispecies Momentum Transfer: Gas and Multifluid Dust Test Suite and Implementation in FARGO3D

“…Dust can also concentrate due to torques exerted by low-mass planets (e.g. Chen & Lin 2018). It has also been shown that dust can concentrate because of vortices induced by the self-organization due to the Hall effect in magnetized disks (e.g.…”

Small dust grain dynamics on adaptive mesh refinement grids

“…More recently, Hutchison et al (2018) improved this method and adapted it to treat simultaneously several dust species. Lin & Youdin (2017) and Chen & Lin (2018) have applied the monofluid formalism on a cylindrical grid adapted to protoplanetary disk simulations with an Eulerian approach.…”