Meridional Circulation of Dust and Gas in the Circumstellar Disk: Delivery of Solids onto the Circumplanetary Region

TL;DR

This study uses 3D hydrodynamic simulations to show how meridional circulation transports dust and gas vertically in circumstellar disks, influencing solid delivery to circumplanetary regions and disk composition.

Contribution

It demonstrates the role of meridional circulation in delivering dust and gas onto circumplanetary regions across different planet masses, highlighting the impact on disk enrichment.

Findings

Meridional circulation drives strong vertical dust flows.

Dust delivery rates increase with planetary mass.

Larger planets lift more dust and enrich circumplanetary disks.

Abstract

We carried out 3D dust+gas radiative hydrodynamic simulations of forming planets. We investigated a parameter grid of Neptune-, Saturn-, Jupiter-, and 5 Jupiter-mass planets at 5.2, 30, 50 AU distance from their star. We found that the meridional circulation \citep{Szulagyi14,FC16} drives a strong vertical flow for the dust as well, hence the dust is not settled in the midplane, even for mm-sized grains. The meridional circulation will deliver dust and gas vertically onto the circumplanetary region, efficiently bridging over the gap. The Hill-sphere accretion rates for the dust are $\sim10^{-8}$ to $10^{-10}$ $\rm{M_{Jup}/yr}$, increasing with planet-mass. For the gas component, the gain is $10^{-6}$ to $10^{-8}$ $\rm{M_{Jup}/yr}$. The difference between the dust and gas accretion rates is smaller with decreasing planetary mass. In the vicinity of the planet, the mm-grains can get trapped easier than the gas, which means the circumplanetary disk might be enriched with solids in comparison to the circumstellar disk. We calculated the local dust-to-gas ratio (DTG) everywhere in the circumstellar disk and identified the altitude above the midplane where the DTG is 1, 0.1, 0.01, 0.001. The larger the planetary mass, the higher the mm-sized dust is delivered and a larger fraction of the dust disk is lifted by the planet. The stirring of mm-dust is negligible for Neptune-mass planets or below, but significant above Saturn-mass.