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

Abstract

We carried out 3D dust + gas radiative hydrodynamic simulations of forming planets. We investigated a parameter grid of a Neptune-mass, a Saturn-mass, a Jupiter-mass, and a five-Jupiter-mass planet at 5.2, 30, and 50 au distance from their star. We found that the meridional circulation (Szulágyi et al. 2014; Fung & Chiang 2016) drives a strong vertical flow for the dust as well, hence the dust is not settled in the midplane, even for millimeter-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 ∼10−8–10−10 MJup yr−1, increasing with planet mass. For the gas component, the gain is 10−6–10−8 MJup yr−1. The difference between the dust and gas-accretion rates is smaller with decreasing planetary mass. In the vicinity of the planet, the millimeter-sized 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, and 0.001. The larger the planetary mass, the more the millimeter-sized dust is delivered and a larger fraction of the dust disk is lifted by the planet. The stirring of millimeter-sized dust is negligible for Neptune-mass planets or below, but significant above Saturn-mass planets.