Physics
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusm.p31a..03c&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #P31A-03
Physics
5749 Origin And Evolution, 5759 Rings And Dust, 6265 Planetary Rings, 6275 Saturn
Scientific paper
The fundamental questions of the age and origin of Saturn's rings remain open. A fundamental property of the rings that bears on this question is the mass of the rings. Youthful features of the rings (high albedo in the face of dark interplanetary micrometeroid bombardment, transfer of angular momentum to nearby small moons through gravitational resonances) may not imply a recent origin for the rings if the mass of the rings is higher than previous estimates. Conversely, low mass regions such as the Cassini Division between the A and B rings are quickly darkened and eroded by micrometeroid impacts, suggesting a recent origin or rapid evolution for at least some aspects of the rings. Mass estimates of the rings have been based on analysis of the dispersion of spiral density waves launched at orbital resonances with satellites in and near the rings. Observations from Cassini reveal nonlinear behavior in the waves. Variations in the background ring surface mass density as well as changes in the orbits of the moons that excite the waves also complicate the dispersion from the linear model. Here we present analysis of density waves in the Cassini Division. These waves are weaker than their more numerous counterparts in the A ring. We combine multiple stellar occultations observed by the Cassini Ultraviolet Imaging Spectrograph (UVIS) to determine local surface mass densities in the Cassini Division. Self-gravity wakes, which are elongated ephemeral agglomerations of ring particles, complicate the measurement of optical depth in the A and B rings, but are virtually absent from the Cassini Division. By comparison of the surface mass densities in regions of the Cassini Division with different optical depths we can estimate a total mass of the Cassini Division. The damping of these waves depends on the ring viscosity and provides an estimate of ring thickness under the assumption that the particles' velocities in the frame moving at their orbital speed is isotropic. This assumption is best met in the Cassini Division (and the C ring) where self-gravity wakes do not play a role in particle motions. An independent measure of ring thickness can be obtained by analyzing the profile of the UVIS occultation lightcurves at sharp ring edges. We present our analysis of waves and edges in the Cassini Division and discuss implications for the age of this feature of Saturn's rings.
Colwell Joshua E.
Cooney J. H.
Esposito W. L. W. L.
Jerousek Richard G.
Lissauer Jack . J.
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