Observations and Models of Accretion in Saturn’s F Ring

Meinke, Bonnie Kathleen

Graduate Thesis Or Dissertation

Observations and Models of Accretion in Saturn’s F Ring Público Deposited

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Citations

Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/5425k970t

Abstract

Saturn's F ring is the solar system's principal natural laboratory for direct observation of accretion and disruption processes. Among the structures contained in its meager ~10 km radial width are jets, strands, and moonlets over an azimuthally asymmetric span. The nearby moons Prometheus and Pandora stir up ring material and create observably changing structures on timescales of days to decades. In addition to the observations over the last three decades, the Cassini Ultraviolet Imaging Spectrograph (UVIS) has detected 27 statistically significant features in 101 occultations by Saturn's F ring since July 2004. Visual classification of the shapes of these 27 features divides the data set into three classes: Moonlet, Icicle, and Core. Two features are classified as Moonlets because each is opaque in its occultation, which makes them candidates for solid objects. A majority of features are classified as Icicles, which partially block stellar signal for 22 m to just over 3.7 km along the radial expanse of the occultation. The density enhancements responsible for such signal attenuations are likely due to transient clumping of material, evidence that aggregations of material are ubiquitous in the F ring. Our lengthy observing campaign reveals that Icicles are likely transient clumps, moonlets are possible solid objects, and cores show the variety of F ring morphology. We suggest that Icicles may evolve into Moonlets, which are an order of magnitude less abundant. The locations of the Icicles and Moonlets are weakly correlated to the location of Prometheus. Motivated by the observations and previous models, I develop a more rigorous model of the evolution of aggregates in Saturn's F ring via tidally-modified accretion. For the first time, I assess the multimodal distribution resultant of collisional models and diagnose the cause. I apply the model to the F ring for constant body densities; then I assess how the system evolves when compaction is allowed. I develop an additional production term describing enhanced accretion of larger bodies in high-density regions produced by Prometheus, which results in the modeled distribution evolving to a state consistent with observations. Finally, I discuss the model's applicability to other astrophysical collisional systems.

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