The structure of Saturn's rings: Implications from the Voyager stellar occultation

Abstract

The Voyager 2 photopolarimeter observed the star δ Scorpii as it was occulted by Saturn's rings, giving ∼ 100 m resolution in the radial direction across the entire ring system. Radial structure can be seen down to the resolution limit and considerable new structure is seen. In the outer B ring none of this structure is due to imbedded large particles (moonlets) in the ring system. An automatic search with finite Fourier transforms located 13 density waves exicted by resonances with Saturn's satellites. More waves were found in searches by eye of predicted resonance locations. Although strong density waves can be located quite easily, no waves have been identified having predicted torques per surface mass density less than 4 × 10 16 cm 4/sec 2. This puts a limit of less than 100 waves likely to be found in Saturn's rings, mostly in the A ring. Unresolved or overlapping waves do not play a major role in creating the most obvious radial structure. The total mass of Saturn's rings is estimated as 5 × 10 −8 of the mass of Saturn. Measurements of wave damping imply a ring thickness of ∼ 30 m in the outer A ring. The power spectrum for the rings shows no dominant individual wavelengths: A preferred size for radial structure in the rings is not seen. At wavelengths less than ∼ 15 km the ring power spectrum drops below the power of noise in the data. The majority of the variance in the ring system is characterized by distance scales greater than 20 km. It is concluded that the majority of ring structures and the majority of variance in ring optical depth are not explained by currently proposed physical mechanisms.