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C. A. McGhee, R. G. French (Wellesley Coll.), E. A. Marouf (San Jose State Univ.), N. J. Rappaport (Jet Propulsion Laboratory), P.J. Schinder (Cornell Univ. & NASA GSFC), A. Anabtawi, S. Asmar, E. Barbinis, D. Fleischman, G. Goltz, D. Johnston, D. Rochblatt (Jet Propulsion Laboratory)
On May 3, 2005, the first of a series of eight nearly diametric occultations by Saturn's rings and atmosphere took place, observed by the Cassini Radio Science (RSS) team. Simultaneous high SNR measurements at the Deep Space Network (DSN) at S, X, and Ka bands (\lambda= 13, 3.6, and 0.9 cm) have provided a remarkably detailed look at the radial structure and particle scattering behavior of the rings. By virtue of the relatively large ring opening angle (B=-23.6\circ), the slant path optical depth of the rings was much lower than during the Voyager epoch (B=5.9\circ), making it possible to detect many density waves and other ring features in the Cassini RSS data that were lost in the noise in the Voyager RSS experiment. Ultimately, diffraction correction of the ring optical depth profiles will yield radial resolution as small as tens of meters for the highest SNR data. At Ka band, the Fresnel scale is only 1--1.5 km, and thus even without diffraction correction, the ring profiles show a stunning array of density waves. The A ring is replete with dozens of Pandora and Prometheus inner Lindblad resonance features, and the Janus 2:1 density wave in the B ring is revealed with exceptional clarity for the first time at radio wavelengths. Weaker waves are abundant as well, and multiple occultation chords sample a variety of wave phases. We estimate the surface mass density of the rings from linear density wave models of the weaker waves. For stronger waves, non-linear models are required, providing more accurate estimates of the wave dispersion relation, the ring surface mass density, and the angular momentum exchange between the rings and satellite. We thank the DSN staff for their superb support of these complex observations.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.