Effective dust growth in laminar circumplanetary discs with magnetic wind-driven accretion

TL;DR

This paper demonstrates that in laminar circumplanetary discs driven by magnetic wind accretion, dust can grow efficiently and form satellitesimals at lower dust-to-gas ratios than previously thought, facilitating satellite formation.

Contribution

It combines 3D MHD simulations with 1D disc modeling to show that magnetic wind-driven laminar CPDs enable satellitesimal formation at significantly lower dust-to-gas ratios.

Findings

Satellitesimals can form if dust-to-gas ratio exceeds 0.02.

Magnetic wind-driven accretion results in more efficient dust growth.

Formation conditions are favorable at gas pressure bumps near planets.

Abstract

It has been considered that large satellites around gas planets form in-situ circumplanetary discs (CPDs). However, dust particles supplied into CPDs drift toward the central planets before they grow into satellitesimals, building blocks of the satellites. We investigate the dust growth in laminar CPDs with magnetic wind-driven accretion. In such laminar discs, dust particles can settle onto the mid-plane and grow large by mutual collision more efficient than in classical turbulent CPDs. First, we carry out 3D local MHD simulations of a CPD including all the nonideal MHD effects (Ohmic resistivity, Hall effect and ambipolar diffusion). We investigate if the disc accretion can be governed by magnetic wind-driven accretion and how laminar the disc can be, in a situation where the magnetic disc wind can be launched from the disc. Second, we model 1D steady CPDs consistent with the results of the MHD simulations and calculate the steady radial distributions of the dust profiles in the modeled discs, taking account of the collisional growth, radial drift, fragmentation, and vertical stirring by the Kelvin-Helmholtz instability. We show that satellitesimals can form in such CPDs if the dust-to-gas mass ratio of the inflow to the discs is larger than 0.02, which is 50 times smaller than the critical value in turbulent CPDs. This condition can be satisfied when enough amount of dust piles up at the gas pressure bump created by the planets. This result shows that satellitesimals would form in laminar CPDs with magnetic wind-driven accretion.