HR: 15:10h
AN: P53E-03 INVITED    [Abstracts]
TI: F Ring Objects and Ring History
AU: * Murray, C D
EM: C.D.Murray@qmul.ac.uk
AF: Astronomy Unit, Queen Mary, University of London, Mile End Road, London, E1 4NS, United Kingdom
AB: The peculiar nature of Saturn's narrow F ring has been a puzzle to dynamicists since the ring was first detected by the Pioneer 11 spacecraft in 1979. Most explanations for its unusual structure have involved the gravitational effects of the shepherding satellites Prometheus and Pandora, or perturbations and even collisions with an unseen population of smaller objects in the vicinity of the ring. Images of the F ring acquired by the Imaging Science Subsystem (ISS) on the Cassini spacecraft have shown a multi-stranded ring with extensive azimuthal structure. The mechanism by which Prometheus creates the observed "streamers" and "channels" in the F ring is understood and similar, regular structures due to Pandora have now been detected. However, these satellites are not sufficient in themselves to explain the observed radial and azimuthal structure in the ring. Occultation data from Cassini's Ultraviolet Imaging Spectrograph have revealed the presence of objects with diameters in the range 30m to 600m in the vicinity of the F ring. Several objects have also been detected in sequences of high resolution ISS images but their nature is uncertain. A series of ISS observations of the F ring obtained between September 2006 and May 2007 has provided dramatic evidence of collisional events taking place in the F ring. An object, believed to be S/2004 S 6, appears to have undergone a series of collisions with the F ring core beginning in late 2006. The ISS images show clear evidence for the formation and subsequent shearing of a succession of ~~1000km long radial "jets". The resulting F ring is remarkably similar to its state in April 2005 suggesting that collisions may occur in cycles. The images suggest that there may be other objects undergoing collisions with the F ring. Furthermore, a detailed examination of the evolving nature of small-scale azimuthal structure and numerical modelling suggest the presence of an additional population of small (diameter <1km) objects interacting with ring material. These observations may help to explain the dynamical evolution of the F ring region on a variety of timescales.
DE: 6265 Planetary rings
DE: 6280 Saturnian satellites
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting