# DDA 2015 – Saturn’s F ring – A decade of perturbations and collisions

This is one of a series of notes taken during the 2015 meeting of the AAS Division on Dynamical Astronomy, 3-7 May, at CalTech. An index to this series (all the papers presented at the meeting) is here.

Carl D Murray (Queen Mary University of London)

#### Abstract

We present an overview of the gravitational and collisional processes at work in Saturn’s F ring deduced from images obtained by the Imaging Science Subsystem (ISS) on the Cassini spacecraft since 2004. The moon Prometheus exerts the dominant gravitational perturbation on the ring. As well as creating the observed periodic tistreamer-channelti structures in the ring, there is evidence that Prometheus also causes the formation and orbital evolution of clumps that can, in turn, perturb local ring particles. We show how Prometheus’ effect can be understood in terms of a simple epicyclic model. Jets of material seen emanating from the F ring are produced when objects orbiting nearby collide with material in the core. We show that there are fundamental differences between the larger and smaller jets even though both are caused by collisions. A comparison between the morphology seen in ISS observations and the results of simulations suggests that both the impactors and the core material are in the form of aggregates of material. We present the results of a study of one particular sheared jet and its associated clumps over a two-month interval in early 2008, deriving orbits for the clumps and showing how they change as they encounter Prometheus.

#### Notes

• F ring:
• 16,150 images
• FWHM is $16 \pm 9$km
• eccentric
• Clear evidence of grav. effect of Prometheus, collisions with smaller bodies
• Jets & strands are the result of collisions
• “streamer channels” from both Prometheus and Pandora
• Evidence for embedded eccentric objects
• “Fan” structures (Beurle et al. 2010)
• Evidence for collisions in F ring core
• “mini-jets”
• $\Delta a = a \Delta e$
• ~1 m/s impacts
• Appearsto be clusters of objects colliding with clusters of objects
• from collisional simulations
• best agreement with observations
• Clumps in strands
• $\Delta a > a \Delta e$
• $\rightarrow$ suppression of $\Delta e$ by apse alignment?