Axisymmetric density waves in Saturn’s rings

Abstract

Density waves in Saturn's rings are usually tightly wrapped spiral patterns generated by resonances with either Saturn's moons or structures inside the planet. However, between the Barnard and Bessel Gaps in the Cassini Division (i.e. between 120,240 and 120,300 km from Saturn's spin axis), there are density variations that appear to form an axisymmetric density wave consisting of concentric zones of varying densities that propagate radially through the rings. Axisymmetric waves cannot be generated directly by a satellite resonance, but instead appear to be excited by interference between a nearby satellite resonance and normal mode oscillations on the inner edge of the Barnard Gap. Similar axisymmetric waves may exist just interior to other resonantly confined edges that exhibit a large number of normal modes, including the Dawes ringlet in the outer C ring and the outermost part of the B ring.

Occultation observations of Saturn's rings with Cassini VIMS

“…Although the radial velocities are all ∼ 6.5 km s −1 , the radial resolution of these data sets is somewhat variable due to variations in the sampling interval, ranging from 150 to 400 m. The unocculted stellar signal levels are 540-720 DN in 40 msec, except for revs 71, 77, 96 and 101, which suffered from poor pointing. The consistent geometry and generally high SNR of these data have made this set of occultations invaluable for studies of weak density waves in Saturn's rings , 2019a, while several of these events also provide our best limits on the maximum optical depth in the central B ring. See Figs.…”