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