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Saturn's D Ring in the Voyager Images

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DOI: 10.1006/icar.1996.0241


Abstract Voyager observations of Saturn's innermost D Ring reveal a variety of structures from narrow rings to broad, wave-like patterns. Two narrow ringlets fall at radii of 67,580 ± 10 km and 71,710 ± 10 km, while a broader, somewhat fainter feature falls at 73,145 ± 10 km; these are identified as D68, D72, and D73, respectively. D68 and D72 are only marginally resolved, with widths of ≤40 km, and show no evidence for eccentricities or longitudinal variations. The region between D68 and D72 is characterized by fainter material and a dominant wavelength of 300 km; the region outside D72 shows a 130 km wavelength. The ring's inner boundary is 66,000 km. Photometric modeling reveals that 89% ± 4% of D72's opacity is composed of dust obeying a relatively flat power-law size distribution, or else particles generally larger than 10 μm in radius; the remaining 11% is in much larger bodies. D72's radially integrated opacity is ∼10 m. Little photometric data is available for the other regions of the D Ring, but what there is indicates that the dust size distribution is very variable throughout the system, possibly on spatial scales as small as ∼300 km. D68 has an integrated opacity of ∼1 m, whereas the remainder of the system has normal opacities of ∼10 −5. The dynamical implications of these results are discussed. It is proposed that D68 and D72 are likely to be results of the fragmentation of small moonlets; the viscous spreading rates in these faint rings are sufficiently low that no confinement mechanism is required. Additional source bodies for the observed dust are probably scattered throughout the system.

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