Density Waves in Saturn's Rings: Non-linear Dispersion and Moon Libration Effects

Details Density Waves in Saturn's Rings: Non-linear Dispersion and Moon Libration Effects Density Waves in Saturn's Rings: Non-linear Dispersion and Moon Libration Effects

May 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dda....39.1805s&link_type=abstract

American Astronomical Society, DDA meeting #39, #18.05

Astronomy and Astrophysics

Astronomy

Scientific paper

We analyze strong spiral density waves in stellar occultations by Saturn's A ring observed with the Cassini Ultraviolet Imaging Spectrograph (UVIS) and find that waves dispersion relation exhibits a clear deviation from the linear trend. All waves examined here reveal an intrinsic quadratic radial dependence on the wavenumber. We provide evidence that the deviation from the linear trend is caused by the ring's pressure term acting against the self-gravity of the ring particles. From the observed dispersion relation and using the theory of Goldreich and Tremaine (1978, 1979, ApJ) where the pressure is parameterized as p=σ c2, we measure the velocity dispersion c=2-5 mm/s in the A ring.
Additionally, in all first order Pandora waves the dispersion relation exhibits a wiggly structure. Comparing 60 stellar UVIS occultations between 2004 and 2008 we infer that this wavenumber oscillation propagates away from the resonance location with a period of about 600 days. This inferred period is consistent with the 3:2 near corotation resonance between Pandora and Mimas (French et al., 2003, Icarus). The observed libration in wavenumber allows us to accurately measure the group velocity in the rings and obtain independent estimates of both surface density and velocity dispersion of the rings.

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