Azimuthal distribution of arcs and clumps in the F ring of Saturn during August 1995 ring plane crossing.
C. Ferrari, A. Brahic, S. Charnoz, P. Thebault (Europa, University Paris 7), F. Roddier (IFA, University of Hawaii)
Ground-based observations of the August 1995 Saturn's ring plane
crossing with the University of Hawaii Adaptive Optics System have
led to the discovery of several new objects orbiting around the
planet. Their orbits are known with variable accuracy but most of them
are compatible with the F ring. Some of these objects are clearly
azimuthally elongated structures, possibly arcs, the others are not
resolved. Planetary arcs are swarms of clumps, which largest particles
are most probably unresolved kilometer-sized objects (Ferrari and
Brahic, 1992, 1994, 1997). Are these objects evolving with time ? On
which timescale ? The F ring arcs have been first observed during
the Voyager encounters. New constraints on the evolution of the
brightests of them, on a two-weeks timescale, at the epoch of the
Voyager 2 flyby, are presented. A revised orbit of the F ring is used to
derive an azimuthal distribution of the newly discovered objects at
August 1995 epoch. This is compared with the azimuthal profile of the
F ring observed three months later, during the Sun ring plane crossing
(Nicholson et al., 1996). The possible nature and lifetime of these new
objects is discussed.