Evidence for a new type of moonlet wake near Enceladus

Enceladus' cryovolcanic activity causes water ice particles to be ejected from the moon's surface and populate a broad and diffuse ring known as the E ring. We examine a localized enhancement in the E-ring's particle density that lies about 20,000 km ahead of Enceladus. The location of this features matches a location where the trajectories of particles following horseshoe orbits begin to approach and cross each other due to the finite eccentricities induced during their closest approach to the moon. This feature could therefore represent a new type of structure generated in a disk by gravitational perturbations from a massive embedded object. It would also imply that some E-ring particles follow horseshoe orbits relative to Enceladus, which has implications for the orbital evolution of small particles within the E ring.