Arcs and clumps in the Encke division of Saturnʹs rings

Voyager images of the two narrow ringlets located in the Encke division of Saturnʹs A ring have been systematically analyzed. Arcs with sharp edges are spread over 70° ± 30° in azimuth in the central ringlet and over 150° ± 40° 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 μm). 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.