Formation of a Propeller Structure by a Moonlet in a Dense Planetary Ring

TL;DR

This paper investigates how embedded moonlets create propeller-shaped structures in dense planetary rings, considering the influence of gravitational wakes, and establishes a formation condition confirmed by simulations and observations.

Contribution

It derives a new formation condition for propeller structures in dense rings accounting for gravitational wakes, supported by numerical simulations and observational consistency.

Findings

Propeller structures form when wake wavelength is smaller than moonlet Hill radius.

The derived condition matches observed propeller features in Saturn's A ring.

Numerical simulations confirm the theoretical formation criterion.

Abstract

The Cassini spacecraft discovered a propeller-shaped structure in Saturn's A ring. This propeller structure is thought to be formed by gravitational scattering of ring particles by an unseen embedded moonlet. Self-gravity wakes are prevalent in dense rings due to gravitational instability. Strong gravitational wakes affect the propeller structure. Here, we derive the condition for formation of a propeller structure by a moonlet embedded in a dense ring with gravitational wakes. We find that a propeller structure is formed when the wavelength of the gravitational wakes is smaller than the Hill radius of the moonlet. We confirm this formation condition by performing numerical simulations. This condition is consistent with observations of propeller structures in Saturn's A ring.