DETECTION OF LOW-VELOCITY COLLISIONS IN SATURN'S F RING

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 similar to 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 similar to 7.5 hr as its length changed from similar to 75 km to similar 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 similar to 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.