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Investigating Irregular Vertical Structures at the Edges of Saturn’s A and B Rings

Presentation #112.08 in the session Many Planets, More Rings (Oral Presentation)

Published onOct 23, 2023
Investigating Irregular Vertical Structures at the Edges of Saturn’s A and B Rings

In July 2009, near the 11 Aug 2009 Saturn equinox, the Cassini spacecraft imaged an astonishing irregular-looking structure near the outer edge of the B ring. Because of the low sun angle (0.24 deg), features protruding out of the ring plane were easily identifiable by the shadows that they cast on the rings. The structure in question occupied a radial region of about 150 km in width and cast shadows indicating that it reached heights up to about 3.5 km out of the ring plane. A preliminary study of this structure[1] linked it kinematically with other disorganized structures seen in non-equinox images of the ring edge, but its dynamics have not yet been analyzed. Subtler irregular vertical structures (IVSs) were also spotted near the outer edge of the A ring during the equinox period, and have yet to be examined. Our hypothesis is that the IVSs represent pile-ups, and possibly plumes of ring particles on ballistic trajectories, generated in regions where the ring is sufficiently compressed by its radial variation (as large as ~140-km peak-to-peak at the B-ring edge[1], and ~50 km[2] at the A-ring edge) to force particles to leave the ring plane. We have recently begun a focused investigation into the IVS phenomena using Cassini observations, kinematic modeling, and N-body simulations. Here, we report on early results of the first phase of the investigation, which is to survey the Cassini images for other candidate IVS sightings. In this phase, we performed a blind search (i.e., not biased by our hypothesis as to where they would be expected to occur). Later, we will test this hypothesis by predicting in which images we would expect to find IVSs (or more importantly, in which ones we would expect to *not* find them). Identification of IVSs in non-equinox images is difficult because the vertical component is not obvious due to the absence of unambiguous shadows. We will present a number of examples of structures at both the A- and B-ring edges that exhibit various properties that we expect to be present in IVSs. [1] Spitale and Porco 2010; AJ 140 [2] Spitale and Porco 2009; AJ 138

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