SATURN D-RING IN THE VOYAGER IMAGES

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 onl y marginally resolved, with widths of less than or equal to 40 km, and show no evidence for eccentricities or longitudinal variations. The r egion between D68 and D72 is characterized by fainter material and a d ominant wavelength of 300 km; the region outside D72 shows a 130 km wa velength. 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 gener ally larger than 10 mu m in radius; the remaining 11% is in much large r bodies. D72's radially integrated opacity is similar to 10 m. Little photometric data is available for the other regions of the D Ring, bu t what there is indicates that the dust size distribution is very vari able throughout the system, possibly on spatial scales as small as sim ilar to 300 km. D68 has an integrated opacity of similar to 1 m, where as the remainder of the system has normal opacities of similar to 10(- 5). The dynamical implications of these results are discussed. It is p roposed that D68 and D72 are likely to be results of the fragmentation of small moonlets; the viscous spreading rates in these faint rings a re sufficiently low that no confinement mechanism is required. Additio nal source bodies for the observed dust are probably scattered through out the system. (C) 1996 Academic Press, Inc.