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Voyager Photometry of Saturn's A RingSaturn's A Ring samples a wide range of dynamical environments, from the relatively unperturbed, optically thick inner region to the outer part of the ring, which contains numerous density waves. We analyze Voyager images of the A Ring to determine how the reflectivity of different radial regions varies with lighting and viewing geometry. We model our data with a classical radiative transfer code that includes the illumination of the rings by the Sun and Saturn. The particles in the inner and mid-A Ring have Bond albedos near 0.5 and are more backscattering than satellites of comparable albedo. The region outside the Encke Gap becomes progressively less backscattering with increasing radius. Particle properties change abruptly outside the Keeler Gap; particles here have an albedo near 0.6 and a Lambert-like phase function. In contrast with previous suggestions, the abundance of free, submicrometer "dust" is small throughout the entire A Ring; this conclusion holds even in the outermost A Ring, which is strongly perturbed by density waves. Models derived from low-phase data, assuming only macroscopic particles, correctly predict the highphase reflectivity of the outer A Ring and individual strong density waves in the mid-A Ring. However, the inner and mid-A Ring are typically darker at high phase by a factor of two than our models predict. This discrepancy may be due to the reduced multiple scattering from a layer in which the particles are more closely packed. We have also studied the quadrupole azimuthal brightness asymmetry of the A Ring. The asymmetry has a full amplitude of 35% in the mid-A Ring in low-phase Voyager 2 images. We present results on its behavior and possible implications for the structure of the rings. Finally, we compare our results with studies using other data sets to synthesize our current understanding of the nature of the A Ring.
Document ID
19970007166
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Dones, Luke
(NASA Ames Research Center Moffett Field, CA United States)
Cuzzi, Jeffrey N.
(NASA Ames Research Center Moffett Field, CA United States)
Showalter, Mark R.
(NASA Ames Research Center Moffett Field, CA United States)
Date Acquired
August 17, 2013
Publication Date
January 1, 1993
Publication Information
Publication: ICARUS
Publisher: Academic Press, Inc.
Volume: 105
ISSN: 0019-1035
Subject Category
Lunar And Planetary Exploration
Report/Patent Number
NASA-TM:112107
NAS 1.15:112107
Accession Number
97N70520
Distribution Limits
Public
Copyright
Public Use Permitted.
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