Arcs and clumps in the Encke division of Saturn's rings

Voyager images of the two narrow ringlets located in the Encke division of Saturn's A ring have been systematically analyzed. Arcs with sharp edges are spread over 70 degrees +/- 30 degrees in azimuth in the central ringlet and over 150 degrees +/- 40 degrees in the inner ringlet. At high resolution, the arcs are made of clumps which may be associated with unresolved kilometer-sized objects. The photometric data from the arcs yield an average optical depth of 0.2 +/- 0.1 and a large dust 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 around Neptune. The origin of these arcs may be explained by a population of moonlets large enough to persist over the age of the solar system in spite of erosion and to replenish the ringlets with material. (C) 1997 Published by Elsevier Science Ltd.