Dust ring and gap formation by gas flow induced by low-mass planets embedded in protoplanetary disks $\rm II$. Time-dependent model

TL;DR

This study models the time-dependent formation of dust rings and gaps in protoplanetary disks caused by low-mass planets, highlighting how gas flow and dust dynamics can produce observable structures.

Contribution

It introduces a time-dependent model of dust evolution influenced by low-mass planets, extending previous steady-state models to better match observations.

Findings

Planets > 0.05 thermal mass generate dust rings and gaps.

Dust gap depths vary with planet mass and diffusion levels.

Up to 65% of wide-orbit gaps could be caused by low-mass planets.

Abstract

The observed dust rings and gaps in protoplanetary disks could be imprints of forming planets. Even low-mass planets in the one-to-ten Earth-mass regime, that do not yet carve deep gas gaps, can generate such dust rings and gaps by driving a radially-outwards gas flow, as shown in previous work. However, understanding the creation and evolution of these dust structures is challenging due to dust drift and diffusion, requiring an approach beyond previous steady state models. Here we investigate the time evolution of the dust surface density influenced by the planet-induced gas flow, based on post-processing three-dimensional hydrodynamical simulations. We find that planets larger than a dimensionless thermal mass of $m=0.05$, corresponding to 0.3 Earth mass at 1 au or 1.7 Earth masses at 10 au, generate dust rings and gaps, provided that solids have small Stokes numbers} (${\rm St}\lesssim10^{-2}$) and that the disk midplane is weakly turbulent ($\alpha_{\rm diff}\lesssim10^{-4}$). As dust particles pile up outside the orbit of the planet, the interior gap expands with time, when the advective flux dominates over diffusion. Dust gap depths range from a factor a few, to several orders of magnitude, depending on planet mass and the level of midplane particle diffusion. We construct a semi-analytic model describing the width of the dust ring and gap, and then compare it with the observational data. We find that up to 65\% of the observed wide-orbit gaps could be explained as resulting from the presence of a low-mass planet, assuming $\alpha_{\rm diff}=10^{-5}$ and ${\rm St}=10^{-3}$. However, it is more challenging to explain the observed wide rings, which in our model would require the presence of a population of small particles (${\rm St=10^{-4}}$). Further work is needed to explore the role of pebble fragmentation, planet migration, and the effect of multiple planets.