Presentation #402.01 in the session Planetary Rings.
Dense disks like Saturn’s rings contain spiral structures known as density waves that are generated by mean-motion resonances with external gravitational perturbations from satellites or structures inside the planet. Classic density-wave theory assumes that these gravitational perturbations have a fixed rotation period, but this is not a valid assumption for certain satellites on time-variable orbits and some of the anomalies in Saturn’s gravitational field. We have therefore developed semi-empirical extensions of density wave theory that can account for perturbations with time-variable periods and amplitudes. These new models reveal that the observed properties of these structures encode information about how the rotation rates and amplitudes of the relevant gravitational anomalies have changed over time. Indeed, analyses of selected density waves in Saturn’s rings demonstrate how these features can be used to trace the history of changes in satellite’s orbit periods and the planet’s internal structure over several decades. These insights may be useful for interpreting structures in other disks subject to time-variable perturbations.