Resonance structures in Saturn's rings probed by radio occultation: I. Methods and examples

Abstract

Optical depth profiles of Saturn's rings derived from Voyager 1 radio occultation reveal a remarkable array of wave-like features. Many are the signatures of spiral density waves and bending waves excited by gravitational resonances with Saturn's satellites. Twenty-nine wave features—18 in Ring A, 1 in Ring B, and 10 in Ring C—are analyzed, individually and comparatively. Of the wave features originally seen in the data, only 20 could be identified readily with known resonances; all 8 still unexplained wave features are located in Ring C. A new technique for locating wave-form extrema, which fits a sinusoid to each half cycle of wave data, quantifies the wavelength variation across a feature. Fitting five dispersion models to the derived wavelengths provides new estimates of resonance location and ambient surface mass density in each wave region. Optical depth peaks are unresolved, saturated by noise, or both, leading to modeling biases typically of the order of 10–20% in dispersion fits. For 14 weak density waves in Ring A, modeling of the waveform near resonance with linear density wave theory gives independent estimates of surface mass density, as well as reliable estimates of resonance location. The methods are described, and applied to the Mimas 5:3, Prometheus 12:11, and Mimas 4:1 density waves as illustration. A companion paper (Rosen et al. 1991, Icarus 93, 25–44) summarizes the results of analysis for all wave features, comparing them to other resonantly induced structures in the rings. The limitations of the analysis due to noise argue strongly for an “uplink” radio occultation of the rings.