Unusual one-armed density waves in the Cassini Division of Saturn's rings

Abstract

We identify several unusual one-armed density waves in Saturn's Cassini Division, using occultation observations from the Cassini RSS and VIMS instruments. In the inner Cassini Division, we identify outward-propagating density waves with wavenumber m = 1 located near 118,050 km (W118.05), 118,400 km (W118.40), and 118,530 km (W118.53). From Cassini ISS images taken at very low incidence angles we find evidence for vertical structure in these waves, which may be evidence for splashing of ring material in the crests of the waves. We propose that these waves are driven by nearby eccentric ringlets, probably the Strange (or R6) and Herschel ringlets. In the outer Cassini Division, we identify a wave structure near 120,200 km (W120.20), between the Laplace and Bessel gaps, as a conspicuous example of a standing wave in a planetary ring system. It appears to be the superposition of an outward-propagating m = 1 density wave, probably driven by the nearby Laplace ringlet, and its reflection at the inner edge of the Bessel gap.