Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p12b..04h&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P12B-04
Other
[5759] Planetary Sciences: Fluid Planets / Rings And Dust, [6265] Planetary Sciences: Solar System Objects / Planetary Rings
Scientific paper
Infrared spectral data clearly demonstrate that Saturn's main rings are all composed primarily of water ice. However, details of the rings' spectral properties vary on a broad range of spatial scales. Some of these variations reflect differences in the mean free path of photons through the ring-particles' regolith, while others can be ascribed to different concentrations of impurities within the water ice. We will explore the physical processes responsible for the variations in the ring-particles' texture and composition using data obtained by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini Spacecraft. VIMS has performed a number of moderately high-resolution (better than 200 km/pixel) spectral observations of Saturn's main rings between 0.35 and 5 microns, and has also obtained high-resolution profiles of the rings' opacity by observing stellar occultations by the rings. Comparing these two data sets reveals a number of interesting correlations between the rings' spectral and structural properties on spatial scales between 100 and 1000 km. Such correlations provide new insights into how the surface properties of individual ring particles can be influenced by (and thus probe) the local dynamical environment. For example, distinctive spectral features can be found in both the A and B rings near strong mean-motion resonances with Saturn's various moons. These spectral signatures are probably the result of changes in the frequency and speed of inter-particle collisions within the density waves generated by these resonances. In the A ring, we observe a sharp peak in the water-ice band depths at the locations of the appropriate density waves indicating that the enhanced collisional regime in these regions leads to larger grain sizes (i.e. mean free paths for infrared photons) in the particles' regoliths. Outside of this core, a more diffuse ``halo'' of reduced band depths can be observed, indicating that regions adjacent to these waves have smaller typical regolith grain sizes. Similar spectral signatures are also found near certain strong resonances in the denser parts of the B ring. These spectral features may indicate the presence of previously unseen density waves that could provide new probes of the structure and dynamics of the densest parts of Saturn's rings.
Capaccioni Fabrizio
Cassini Vims Team
Ciarniello Mauro
Clark Roger Nelson
Cuzzi Jeff N.
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