Way beyond Saturn’s main rings lies the narrow, braided multistrand F ring, discovered by Pioneer 11 about 30 years ago. This unique region changes its appearance on a variety of timescales, presenting an interesting puzzle. Now astronomers from the University of London and from Université Paris have analysed images from the Cassini Imaging Science Subsystem to show that small satellites embedded in the core of the ring are continually interacting and colliding with each other. The subsystem includes narrow- and wide-angle cameras covering the wavelength range from 2000 Å to 1.1 μm.Saturn’s F ring has multiple structures and changes its appearance over hours and years. Courtesy of NASA/JPL/Space Science Institute.The scientists are studying the streamers and fans that appear in the F ring and are using numerical simulation to explore the physical explanations. The moon Prometheus passes a particular point in the F ring every 67.65 days, and its gravitational attraction produces streamers in the ring. But localized disturbances persist long after the moon has passed, and numerical modelling suggests that they could be caused by perturbation of embedded moonlets, which then continue to jostle and to create additional jets of material from colliding objects.(Nature, 5 June 2008, pp. 739-744)