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Previous investigations of Saturn's outer D ring (73,200-74,000 km fromSaturn's center) identified periodic brightness variations whose radialwavenumber increased linearly over time. This pattern was attributed to avertical corrugation, and its temporal variability implied that some event--possibly an impact with interplanetary debris-- caused the ring to becometilted out the planet's equatorial plane in 1983. This work examines thesepatterns in greater detail using a more extensive set of Cassini images inorder to obtain additional insights into the 1983 event. These additional datareveal that the D ring is not only corrugated, but also contains atime-variable periodic modulation in its optical depth that probably representsorganized eccentric motions of the D-ring's particles. This second patternsuggests that whatever event tilted the rings also disturbed the radial orazimuthal velocities of the ring particles. Furthermore, the relativeamplitudes of the two patterns indicate that the vertical motions induced bythe 1983 event were 2.3+/-0.5 times larger than the corresponding in-planemotions. If these structures were indeed produced by an impact, material wouldneed to strike the ring at a steep angle (more than 60 degrees from the ringplane) to produce such motions. Meanwhile, the corrugation wavelengths in the Dring are about 0.7% shorter than one would predict based on extrapolations fromsimilar structures in the nearby C ring. This could indicate that the D-ringwas tilted/disturbed about 60 days before the C ring. Such a timing differencecould be explained if the material that struck the ring was derived from debrisreleased when some object broke up near Saturn some months earlier. This debriswould need to have a substantial initial velocity dispersion and have itsorbital properties perturbed by solar tides prior to its collision with therings.

Corrugations and eccentric spirals in Saturn's D ring: New insights into what happened at Saturn in 1983