Exploring overstabilities in Saturn's A ring using two stellar occultations

TL;DR

This study analyzes Cassini VIMS data of Saturn's A ring to characterize periodic opacity variations, revealing their systematic wavelength and intensity changes, as well as their azimuthal coherence scale, linked to viscous overstabilities.

Contribution

First observational evidence of systematic variation in wavelength and intensity of overstability patterns in Saturn's A ring from stellar occultations.

Findings

Opacity variations have azimuthal coherence scale of ~3000 km.

Wavelengths and intensities vary systematically but are not solely determined by optical depth.

Patterns are consistent with viscous overstability phenomena.

Abstract

Certain regions of Saturn's rings exhibit periodic opacity variations with characteristic radial wavelengths of up to a few hundred meters that have been attributed to viscous overstabilities. The Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft observed two stellar occultations of the star gamma Crucis that had sufficient resolution to discern a sub-set of these periodic patterns in a portion of the A ring between 124,000 and 125,000 km from Saturn center. These data reveal that the wavelengths and intensities of the patterns vary systematically across this region, but that these parameters are not strictly determined by the ring's average optical depth. Furthermore, our observations indicate that these opacity variations have an azimuthal coherence scale of around 3000 km.