The Secular Evolution of a Close Ring-Satellite System: The Excitation of Spiral Bending Waves at a Nearby Gap Edge

TL;DR

This paper investigates how inclined satellites in planetary rings excite spiral bending waves and damp their inclinations, explaining the orbital confinement of moons like Pan and Daphnis through secular perturbation analysis.

Contribution

It introduces a model for the excitation and propagation of spiral bending waves caused by satellites in planetary rings, and compares secular inclination damping with resonance effects.

Findings

Spiral bending waves' amplitude and wavelength are derived.

Inclination damping can confine moons to the ring plane.

Secular perturbations significantly influence satellite and ring dynamics.

Abstract

The secular perturbations exerted by an inclined satellite orbiting in a gap in a broad planetary ring tends to excite the inclinations of the nearby ring particles, and the ring's self-gravity can allow that disturbance to propagate away in the form of a spiral bending wave. The amplitude of this spiral bending wave is determined, as well as the wavelength, which shrinks as the waves propagate outwards due to the effects of the central planet's oblateness. The excitation of these bending waves also damps the satellite's inclination I. This secular I damping is also compared to the inclination excitation that is due to the satellite's many other vertical resonances in the ring, and the condition for inclination damping is determined. The secular I damping is likely responsible for confining the orbits of Saturn's two known gap-embedded moons, Pan and Daphnis, to the ring plane.