Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p54a..04a&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P54A-04
Physics
[5759] Planetary Sciences: Fluid Planets / Rings And Dust, [6265] Planetary Sciences: Solar System Objects / Planetary Rings
Scientific paper
Cassini observations have revealed unprecedented details of macro- and microstructures in the rings. In between 2004 and 2009 the Cassini Ultraviolet Spectrometer (UVIS) High Speed Photometer (HSP) recorded more than hundred stellar occultations by Saturn's rings. These observations resolve the rings typically to within a few dozen meters enabling high-resolution studies of the entire system. In this paper we show evidence for sub-km structures found at various places in the rings that are closely connected to moon-driven perturbations. We find these structures in the F ring, strong density waves in the A ring and at the B ring edge. In strong density waves in the A ring we find structures on scales between 200m and 2km using spectral analysis methods (wavelets). These structures are not axisymmetric and are most likely identical to the reported straw features seen in images. Interestingly, their relative strength strongly correlates with the predicted resonance torques. Likewise, we find structure on similar scales at the B ring edge (including the region 50 - 150km radially inward) which is driven by Mimas through its 2:1 inner Lindblad resonance. This structure correlates with the location of Mimas, and we find it to be the most abundant at +/-90 degrees from Mimas. Similarly, we observe the optical depth to be consistent with the compression and decompression phase of the edge. Initial kinematic studies of the edge shape show that the expected m=2 pattern is changing in time and that deviations from it are exceptionally strong. Likewise, we find a constant increase in structure strength and optical depth that is, for instance, not found in Mimas' density wave in the A ring. This temporal variability over merely a few years is completely unexpected and remains unexplained. In the case of the F ring, the core is well-described by a precessing ellipse that is inclined towards Saturn's equatorial plane. Radial excursions from this model, however, carry a clear signature of Prometheus and are increasing in time coincident with the upcoming anti-apse alignment of ring and moon. The F ring is known to harbor clumps and moonlets [Esposito et al. (2008, Icarus)] that were identified in UVIS data using statistical tests. The peak optical depth of these clumps correlates with the relative azimuthal distance to Prometheus and is largest on the trailing of the moon.
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