ARCS AND CLUMPS IN THE ENCKE DIVISION OF SATURNS RINGS

Voyager images of the two narrow ringlets located in the Encke divisio n of Saturn's A ring have been systematically analyzed. Arcs with shar p edges are spread over 70 degrees +/- 30 degrees in azimuth in the ce ntral ringlet and over 150 degrees +/- 40 degrees in the inner ringlet . At high resolution, the arcs are made of clumps which may be associa ted with unresolved kilometer-sized objects. The photometric data from the arcs yield an average optical depth of 0.2 +/- 0.1 and a large du st fraction (80% +/- 20%). The dust particles are probably quite small (<0.1 mu m). The Encke arcs are very clumpy and dusty like the arcs a round Neptune. The origin of these arcs may be explained by a populati on of moonlets large enough to persist over the age of the solar syste m in spite of erosion and to replenish the ringlets with material. (C) 1997 Published by Elsevier Science Ltd.