Detection of Low-velocity Collisions in Saturn's F Ring

Abstract

Jets of material extending several hundred kilometers from Saturn's F ring are thought to be caused by collisions at speeds of several tens of ms^-1 between ~10 km diameter objects such as S/2004 S 6 and the core of the ring. The subsequent effects of Keplerian shear give rise to the multi-stranded nature of the F ring. Observations of the ring by the Imaging Science Subsystem experiment on the Cassini spacecraft have provided evidence that some smaller protrusions from the ring's core are the result of low-velocity collisions with nearby objects. We refer to these protrusions as "mini-jets" and one such feature has been observed for ~7.5 hr as its length changed from ~75 km to ~250 km while it simultaneously appeared to collapse into the core. Orbit determinations suggest that such mini-jets consist of ring material displaced by a ~1 ms^-1 collision with a nearby moonlet, resulting in paths relative to the core that are due to a combination of Keplerian shear and epicyclic motion. Detections of mini-jets in the Cassini images suggest that it may now be possible to understand most small-scale F ring structure as the result of such collisions. A study of these mini-jets will therefore put constraints on the properties of the colliding population as well as improve our understanding of low-velocity collisions between icy objects.