Other
Scientific paper
Jun 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006dda....37.0801f&link_type=abstract
American Astronomical Society, DDA meeting #37, #8.01; Bulletin of the American Astronomical Society, Vol. 38, p.670
Other
Scientific paper
The well-known quadrupole brightness asymmetry of Saturn's rings is a natural consequence of the competition between the tendency of particles to clump gravitationally and the frustration of this process by tidal shearing interior to the Roche limit. The resulting Julian-Toomre wake structures are tilted by about 23 degrees relative to circular ring features, and when viewed along their length, the rings appear dimmer because ring particles hide each other and more of the dark sky is visible between particle streams. We present an overview of the brightness asymmetries detected in the A and B rings from a decade of Hubble Space Telescope UBVRI images obtained with WFPC2 over a full Saturn season, spanning the full range of solar phase angles accessible from the Earth images. We have developed dynamical models for gravity wakes and photometric procedures to calculate the resultant wake-driven brightness asymmetry for any given illumination and viewing geometry. We examine the detailed dependence of the asymmetry amplitude and longitude of minimum brightness on elevation angle, solar phase angle, and wavelength.
For example, the phase angle and wavelength dependence helps to distinguish between the single and multiple scattering contributions to the observed brightness, as stronger asymmetry is expected in multiply-scattered light. Similarly, the variation of asymmetry amplitude with ring opening angle is highly sensitive to the vertical structure of rings. Finally, we examine the radial variations of the strength of the asymmetry, and explore the dependence on ring optical depth, density wave activity, and the strength of keplerian shear. This work was supported in part by the NSF and by the NASA PG&G program.
Dones Luke
French Richard G.
McGhee Colleen
Salo Heikki
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