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D.A. Gurnett, W.S. Kurth, G.B. Hospodarsky, A.M. Persoon, L. Xin (Univ. of Iowa), W. Farrell (NASA/Goddard Space Flight Ctr.), A. Lecacheux (Observatoire de Paris/Meudon), J.-E. Wahlund (Swedish Inst. of Space Physics)
During the Cassini passage through the inner region of the Saturnian system, the Radio and Plasma Wave Science (RPWS) instrument observed several effects associated with the rings. First, during both the inbound and outbound ring plane crossings, which were between the F and G rings, numerous impulsive signals with durations of several hundred microseconds were detected by the RPWS electric field antenna. Impulsive signals of this type were first observed at Saturn by the Voyager spacecraft and are attributed to the impact of small micron-sized particles on the spacecraft. Second, during the passage over the B ring a broad-band emission was observed with a v-shaped low-frequency cutoff similar to a terrestrial whistler-mode emission called auroral hiss. Ray tracing studies indicate that this radiation is generated very close to the rings. Since auroral hiss at Earth is known to be generated by electron beams associated with magnetic field-aligned currents, these observations suggest that the comparable emission at Saturn is produced by an electrodynamic interaction between the rings and the co-rotating magnetosphere of Saturn. Third, during the passage over the ring plane many impulsive narrowband emissions, lasting typically about 1 to 3 seconds, were detected in the frequency range from about 1 to 10 kHz at occurrence rates of about 1 sec-1. These signals are directly correlated with the passage over the rings, and a good case can be made that the radiation is propagating along the whistler-mode resonance cone, which means that the source lies along a cone extended downward along the magnetic field, at a half-angles ranging from about 10 to 60 degrees. The impulsive character of the emissions suggests that the radiation is generated by a transient energetic process in the rings. The leading candidate is believed to be meteoroid impacts on the rings.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.