Dust evolution and satellitesimal formation in circumplanetary disks

TL;DR

This study demonstrates that dust traps within circumplanetary disks enable efficient satellitesimal formation through streaming instability, driven by dust growth and inward drift, acting as a continuous factory for satellite seeds.

Contribution

It combines hydrodynamical simulations with dust evolution models to identify natural dust traps that facilitate satellitesimal formation in circumplanetary disks.

Findings

Dust traps form at ~85 R_J due to outward gas flow.

Streaming instability triggers satellitesimal formation in the dust trap.

Circumplanetary disks act as ongoing satellitesimal factories.

Abstract

It is believed that satellites of giant planets form in circumplanetary disks. Many of the previous contributions assumed that their formation process proceeds similarly to rocky planet formation, via accretion of the satellite seeds, called satellitesimals. However, the satellitesimal formation itself poses a nontrivial problem as the dust evolution in the circumplanetary disk is heavily impacted by fast radial drift and thus dust growth to satellitesimals is hindered. To address this problem, we connected state-of-the-art hydrodynamical simulations of a circumplanetary disk around a Jupiter-mass planet with dust growth and drift model in a post-processing step. We found that there is an efficient pathway to satellitesimal formation if there is a dust trap forming within the disk. Thanks to the natural existence of an outward gas flow region in the hydrodynamical simulation, a significant dust trap arises at the radial distance of 85~R$_{\rm J}$ from the planet, where the dust-to-gas ratio becomes high enough to trigger streaming instability. The streaming instability leads to the efficient formation of the satellite seeds. Because of the constant infall of material from the circumstellar disk and the very short timescale of dust evolution, the circumplanetary disk acts as a satellitesimal factory, constantly processing the infalling dust to pebbles that gather in the dust trap and undergo the streaming instability.