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The motion of satellite self-gravity wakes under the effects of tidal forces and shear: a case study of the Rings of Saturn

Presentation #402.03 in the session Planetary Rings.

Published onApr 25, 2022
The motion of satellite self-gravity wakes under the effects of tidal forces and shear: a case study of the Rings of Saturn

Elongated aggregates of the order of a Toomre wavelength have been known to exist in the denser rings of Saturn. They occur in the A and B ring at distances from Saturn where the average particles are not big enough to fill their Hill sphere, and they are usually understood in the framework of non-asymmetric disk responses to density irregularities in a Keplerean disk that have a pitch angle of about 20°, and which has been confirmed by Cassini data for the case of the rings (Jeousek et al., Icarus 279:16–50, 2016). Unlike the stellar disk case however, the self-gravity wakes in the rings are satellite aggregates orbiting at the rate of their common center of mass. To study their motion we first model them as rigid bodies subject to different gravitational and concessional torques. With this simplistic model we manage to reproduce the observed pitch angle, and we can derive a relationship between the pitch angle and the shear rate of the disk which is consistent with numerical simulation of rings (Salo et al. Icarus 170:36-50, 2004) and of galactic spiral arms (Mishikoshi & Kokubo, ApJ 787:174, 2014). Finally, we introduce these wakes within a vertically perturbed disk with a propagating Bending Wave and find that their motion in this environment can lead to high velocity impacts that generate ejecta and an optical depth signal that depends on the slope of the wave. This ejecta can help to explain some surprising features seen in Bending Waves by the Cassini spacecraft.


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