Of Horseshoes and Heliotropes: Dynamics of Dust in the Encke Gap

TL;DR

This study uses Cassini images to analyze dust particle dynamics in Saturn's Encke Gap, revealing complex behaviors influenced by solar radiation, gravitational perturbations, and collisions, challenging previous simplified models.

Contribution

It provides new insights into dust particle motions and orbital properties in the Encke Gap, highlighting the roles of radiation pressure and local perturbations.

Findings

Dust particles have forced eccentricities from solar radiation pressure.

Particle orbits vary with co-rotating longitude due to multiple forces.

Dust dynamics are more complex than previously modeled.

Abstract

The Encke Gap is a 320-km-wide opening in Saturn's outer A ring that contains the orbit of the small moon Pan and an array of dusty features composed of particles less than 100 microns across. In particular, there are three narrow ringlets in this region that are not longitudinally homogeneous, but instead contain series of bright clumps. Using images obtained by the Cassini spacecraft, we track the motions of these clumps and demonstrate that they do not follow the predicted trajectories of isolated ring particles moving under the influence of Saturn's and Pan's gravitational fields. We also examine the orbital properties of these ringlets by comparing images taken at different longitudes and times. We find evidence that the orbits of these particles have forced eccentricities induced by solar radiation pressure. In addition, the mean radial positions of the particles in these ringlets appear to vary with local co-rotating longitude, perhaps due to the combined action of drag forces, gravitational perturbations from Pan, and collisions among the ring particles. The dynamics of the dust within this gap therefore appears to be much more complex than previously appreciated.