Discovery of an arc of particles near Enceladus’ orbit: a possible key to the origin of the E ring

High angular resolution (adaptive optics) images taken on August 12, 1995 between 11:26 and 12:23 (UT) show a faint elongated structure apparently moving away from Saturn. The structure is consistent with light scattered by an arc of particles on a Keplerian orbit close to that of Enceladus. The orbit is slightly inclined (1.8 ̊), and the arc is 76 ̊ ahead of the satellite. It appears to be a transient phenomenon since the arc brightness decreased by almost a factor two during the observations, and no such structure was observed at the same orbital position two days before. A possible explanation is that a large block of ice previously ejected by Enceladus collided with ice fragments trapped on the satellite orbit near its L 4 Lagrange point. The collision likely occurred about 6 h before observations started and produced a rapidly expanding cloud of small particles. We estimate the total mass of particles to be at least 10 kg.