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

J Szulágyi,F Binkert,C Surville

doi:10.3847/1538-4357/ac32d1

J Szulágyi, F Binkert + Show 1 more

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https://doi.org/10.3847/1538-4357/ac32d1

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Abstract

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 M Jup yr−1, increasing with planet mass. For the gas component, the gain is 10−6–10−8 M Jup 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.

Highlights

Dust processes in circumstellar disks are extremely crucial to understanding disk evolution, the formation of planetary building blocks, chemical processes in the disks and the observability of these disks.Observations of circumstellar disks provide an insight into the dust settling and dust-to-gas ratios of these disks
The dust-to-gas ratio of the circumstellar disk is crucial for multiple processes, for example the formation of planetesimals via streaming instability (e.g. Goodman & Pindor 2000; Youdin & Goodman 2005), that requires a local dust-to-gas ratio of one
We show a representative streamline plot which shows a vertical slice of the dust velocities (Fig. 3), that visualizes how the planet generated spiral arms vertically mix the dust, and that the spiral wakes of planets are responsible for the meridional circulation, as it was found in Szulagyi et al (2014) and Fung & Chiang (2016)

Summary

Introduction

Dust processes in circumstellar disks are extremely crucial to understanding disk evolution, the formation of planetary building blocks, chemical processes in the disks and the observability of these disks. Observations of circumstellar disks provide an insight into the dust settling and dust-to-gas ratios of these disks. The dust-to-gas ratio of the circumstellar disk is crucial for multiple processes, for example the formation of planetesimals via streaming instability Observations nowadays can estimate the (global) dust-to-gas ratio in disks and compare them to theoretical model predictions (Turrini et al 2019; Horne et al 2012). To understand which part of the disk can have a high enough dust-togas ratio for streaming instability to operate, we have to rely on dust+gas hydrodynamic simulations

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