Boundary Layers of Circumplanetary Disks around Spinning Planets I. Effects of Rossby Waves

TL;DR

This paper explores how planetary spin influences wave behaviors in circumplanetary disk boundary layers, revealing new Rossby modes that regulate planetary spin and mass through angular momentum exchange.

Contribution

It introduces the Rossby mode in boundary layers of spinning planets, showing its role in angular momentum outflow and planetary regulation, extending prior non-spinning planet studies.

Findings

Rossby mode causes angular momentum outflow and gas decretion.

Global inertia-acoustic mode promotes gas inflow and accretion.

Results elucidate mechanisms behind planetary spin regulation and mass limits.

Abstract

Gas giant planets are believed to accrete from their circumplanetary disks (CPDs). The CPDs usually involve accretion through the boundary layer (BL) in the vicinity of planets. Prior studies have concentrated on the BL of non-spinning planets. We investigate the influence of planetary spin on the wave behaviors within the BL. The rotation profile in such BLs would show sharp transition from the rigid rotation to the Keplerian rotation. We examine the angular momentum transport in these BL in terms of linear perturbation analysis. We find that the global inertia-acoustic mode associated with spinning planets would give rise to the inflow of angular momentum and the accretion of gas. In this work, we identify a new kind of global mode, namely the Rossby mode. The Rossby mode can lead to the outflow of angular momentum and the decretion of gas from a spinning planet. The Rossby mode provide a negative feedback that regulates the planetary spin and mass. We compare the growth rate of the two modes as a function of the width of BL, the Mach number and the spin rate of planet. Our results reveal the underlying hydrodynamic mechanism of terminal spins and asymptotic mass of the giant planets.