Cassini scientists will provide evidence in this week’s issue of Science that the previously labeled ringlets near Saturn’s F ring are instead a single spiral arm surrounding a core ring. No such object has ever before been observed in our solar system.
The F ring is a thin but complex feature beyond Saturn’s more prominent A ring. The imaging team responsible for the discovery used a 360 degree map created from images of the F ring taken by Cassini. The resulting map clearly revealed a continuous spiral circling Saturn. Because the spiral is wrapped so tightly on itself, it appeared to be several distinct ringlets, until the close proximity of Cassini instruments finally reveal its true structure.
The reporting scientists believe a collision between the core F ring and a small moon or moonlet led to a secondary spiral of particles. These collisions may happen frequently, suggesting that the spiral is a transitory structure. The tiny shepherd moon Pandora is set to collide with the core F ring in 2009, an event that could provide more details about the phenomena.