Morphological signatures induced by dust back reaction in discs with an embedded planet

Abstract

Recent observations have revealed a gallery of substructures in the dust component of nearby protoplanetary discs, including rings, gaps, spiral arms, and lopsided concentrations. One interpretation of these substructures is the existence of embedded planets. Not until recently, however, most of the modelling effort to interpret these observations ignored the dust back reaction to the gas. In this work, we conduct local-shearing-sheet simulations for an isothermal, inviscid, non-self-gravitating, razor-thin dusty disc with a planet on a fixed circular orbit. We systematically examine the parameter space spanned by planet mass ($0.1M_\text{th} \le M_\text{p} \le 1M_\text{th}$, where $M_\text{th}$ is the thermal mass), dimensionless stopping time ($10^{-3} \le τ_\text{s} \le 1$), and solid abundance ($0 < Z \le 1$). We find that when the dust particles are tightly coupled to the gas ($τ_\text{s} < 0.1$), the spiral arms are less open and the gap driven by the planet becomes deeper with increasing $Z$, consistent with a reduced speed of sound in the approximation of a single dust-gas mixture. By contrast, when the dust particles are marginally coupled ($0.1 \lesssim τ_\text{s} \lesssim 1$), the spiral structure is insensitive to $Z$ and the gap structure in the gas can become significantly skewed and unidentifiable. When the latter occurs, the pressure maximum radially outside of the planet is weakened or even extinguished, and hence dust filtration by a low-mass ($M_\text{p} < M_\text{th}$) planet could be reduced or eliminated. Finally, we find that the gap edges where the dust particles are accumulated as well as the lopsided large-scale vortices driven by a massive planet, if any, are unstable, and they are broken into numerous small-scale dust-gas vortices.