Dusty substructures induced by planets in ALMA discs: how dust growth and dynamics changes the picture

ABSTRACT Protoplanetary discs exhibit a rich variety of substructure in millimeter continuum emission, often attributed to unseen planets. As these planets carve gaps in the gas, dust particles can accumulate in the resulting pressure bumps, forming bright features in the dust continuum. We investigate the role of dust dynamics in the gap-opening process with 2D radiation hydrodynamics simulations of planet–disc interaction and a two-population dust component modelled as a pressureless fluid. We consider the opacity feedback and backreaction due to drag forces as mm grains accumulate in pressure bumps at different stages of dust growth. We find that dust dynamics can significantly affect the resulting substructure driven by the quasi-thermal-mass planet with Mₚ/M_ =10^-4. Opacity feedback causes non-axisymmetric features to become more compact in azimuth, whereas the drag-induced backreaction tends to dissolve non-axisymmetries. For our fiducial model, this results in multiple concentric rings of dust rather than the expected vortices and corotating dust clumps found in models without dust feedback. A higher coagulation fraction disproportionately enhances the effect of dust opacity feedback, favouring the formation of crescents rather than rings. Our results suggest that turbulent diffusion is not always necessary to explain the rarity of observed non-axisymmetric features, and that incorporating dust dynamics is vital for interpreting the observed substructure in protoplanetary discs. We also describe and test the implementation of the publicly available dust fluid module in the pluto code.