Mapping spiral waves and other radial features in Saturn's rings

Abstract:

We have carried out a comprehensive survey of the best Cassini ISS data of Saturn's main rings for the purpose of cataloguing all observed spiral density waves, spiral bending waves, and other radial and quasi-radial ring structure. Our survey has revealed a number of new features, including the first known resonant waves raised by Enceladus and Hyperion, thus increasing the number of points at which the local surface density and viscosity of the rings can be measured (cf. Tiscareno et al. 2007, Icarus).

We convert each 2-D image taken by the Imaging Science Subsystem (ISS) into a 1-D "radial scan" by combining as many as a thousand pixels at each radial location. This process suppresses local structure, azimuthal structure, and random noise, causing ISS to be the optimal Cassini instrument for detecting a certain class of low-amplitude features. Finally, we employ wavelet techniques (cf. Tiscareno et al. 2007, Icarus) to elucidate subtle periodic and quasi-periodic features in the radial scan data.

Resonant perturbations in the rings can be ranked according to their relative strengths (Lissauer and Cuzzi 1982, AJ). We will present an update of that work along with a comprehensive map of the resonances that produce observed features in the rings. We will identify the strongest expected perturbations that do not have observed manifestations, and will discuss whether the absence is likely to reflect a real limit of ring responsiveness, or (as with previous observations) to reflect sensitivity limits. We will also present a catalogue of wave-like features whose cause is unknown, posing new puzzles.