Hedman, M.M., Burns, J.A., Tiscareno, M.S. (2011). "Of Horseshoes and Heliotropes: The Dynamics of Dust in the Encke Gap" American Astronomical Society, DDA meeting #42 #8.02.

The 320-km-wide Encke Gap in Saturn's outer A ring is held open by the small moon Pan. This gap contains three narrow ringlets: one near Pan's orbit at 133,585 km from Saturn's center, a central one at 133,485 km near the gap's inner edge and one at 133,720 km near the gap's outer edge. All three ringlets contain localized clumps of material that can be tracked over several years. These structures exhibit several unexpected dynamical properties. For example, the clumps in the central ringlet are always asymmetrically distributed with respect to Pan, and their motion is inconsistent with that expected for particles on simple horseshoe or tadpole orbits. Such anomalies probably occur because the Encke Gap ringlets are composed primarily of small grains 1-100 microns across, so the particles' orbital properties are perturbed not only by close encounters with Pan, but also by various non-gravitational forces. Indeed, the ringlets exhibit significant forced eccentricities induced by solar radiation pressure. We will explore how the interplay between gravitational and non-gravitational processes shape the structure and dynamics of these dusty ringlets.