Dust ring and gap formation by gas flow induced by low-mass planets embedded in protoplanetary disks

II. Time-dependent model

¹ Center for Star and Planet Formation, GLOBE Institute, University of Copenhagen, Øster Voldgade 5–7, 1350 Copenhagen, Denmark
² Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
³ Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan
⁴ Department of Earth Science and Astronomy, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
⁵ Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-8902, Japan
⁶ National Institute of Technology, Ichinoseki College, Takanashi, Hagisho, Ichinoseki-shi, Iwate 021-8511, Japan

^★ Corresponding author; ayumu.kuwahara@sund.ku.dk

Received: 18 June 2024
Accepted: 22 October 2024

Abstract

The observed dust rings and gaps in protoplanetary disks could be imprints of forming planets. Even low-mass planets in the 1-10 Earth-mass regime, which have not yet carved deep gas gaps, can generate such dust rings and gaps by driving a radially-outward 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 (St ≲ 10⁻²) and that the disk midplane is weakly turbulent (α_diff ≲10⁻⁴). 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 of a few to several orders of magnitude, depending on planet mass and the level of midplane particle diffusion. We constructed a semi-analytic model describing the width of the dust ring and gap, and then compared 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 α_diff = 10⁻⁵ and 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 (St = 10⁻⁴). Further work is needed to explore the role of pebble fragmentation, planet migration, and the effect of multiple planets.