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

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.

12 pages, 4 figures. Accepted for publication in ApJ Letters

References in corpus (5)

• Cassini Imaging of Saturn's Rings II: A Wavelet Technique for Analysis of Density Waves and Other Radial Structure in the Rings
• Spatial Structure and Coherent Motion in Dense Planetary Rings Induced by Self-Gravitational Instability
• The population of propellers in Saturn's A Ring
• Physical characteristics and non-keplerian orbital motion of "propeller" moons embedded in Saturn's rings
• Free Unstable Modes and Massive Bodies in Saturn's Outer B Ring

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• Mean Motion Resonances With Nearby Moons: An Unlikely Origin For The Gaps Observed In The Ring Around The Exoplanet J1407b