Tiscareno, M.S., Nicholson, P., Burns, J., Hedman, M., Porco, C. (2006). "Disk Response to Variable Forcing: The Rings and Co-orbital Satellites of Saturn." American Astronomical Society, DDA meeting #37, #8.04.


Abstract
Density waves raised in Saturn's rings at inner Lindblad resonances (ILRs) with the co-orbital satellites Janus and Epimetheus have an unusual and complex structure, making their interpretation difficult. High-resolution Cassini images have revealed much new detail not only of the waves raised at first-order ILRs, but also at second-order and even third-order ILRs. Because the latter resonances are weaker, the induced density perturbations are much smaller than the background density, allowing linear superposition of overlapping waves.Janus and Epimetheus are in a mutual horseshoe configuration, as they orbit Saturn, one satellite is slightly inward of the other, but they effectively switch places every 4 years. In some regions of the rings, the low group velocity yields a density wave propagation time that is comparable to the period of the satellites' libration.
We propose that the complex co-orbital density wave morphology can be explained by the superposition of multiple wave segments, starting and stopping at different locations as the satellite forcing changes, and propagating outwards with group velocities as low as 6 km/yr. We will present preliminary results from a linear model, along with supporting evidence from wavelet analysis of Cassini images that substantiates our claim.