The Structure and Stability of Extended, Inclined Circumplanetary Disk or Ring Systems

TL;DR

This study uses N-body simulations to analyze the structure and stability of inclined circumplanetary disks or rings, demonstrating their potential stability over millions of years despite dynamical resonances, and constraining their maximum size.

Contribution

It provides the first detailed dynamical analysis of inclined, extended circumplanetary disks considering planetary quadrupole effects and identifies key resonances affecting their stability.

Findings

Many inclined disks remain stable over 3-16 million years.

Lidov-Kozai and ivection resonances influence disk dynamics.

Gaps in disks do not necessarily indicate exomoons.

Abstract

Large dips in the brightness for a number of stars have been observed, for which the tentative explanation is occultation of the star by a transiting circumplanetary disk or ring system. In order for the circumplanetary disk/rings to block the host star's light, the disk must be tilted out of the planet's orbital plane, which poses stability problems due to the radial extent of the disk required to explain the brightness dip durations. This work uses N-body integrations to study the structure and stability of circumplanetary disk/ring systems tilted out of the planet's orbital plane by the spinning planet's mass quadrupole. Simulating the disk as a collection of test particles with orbits initialized near the Laplace surface (equilibrium between tidal force from host star and force from planet's mass quadrupole), we find that many extended, inclined circumplanetary disks remain stable over the duration of the integrations (~3-16 Myr). Two dynamical resonances/instabilities excite the particle eccentricities and inclinations: the Lidov-Kozai effect which occurs in the disk's outer regions, and ivection resonance which occurs in the disk's inner regions. Our work places constraints on the maximum radial extent of inclined circumplanetary disk/ring systems, and shows that gaps present in circumplanetary disks do not necessarily imply the presence of exomoons.