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Photometry of Saturn’s F Ring During the Cassini Mission: An Update

Presentation #317.01 in the session Ring Systems: Planetary Rosetta Stones (iPosters).

Published onOct 20, 2022
Photometry of Saturn’s F Ring During the Cassini Mission: An Update

Saturn’s F ring is highly variable due to its position near the planet’s Roche Limit and gravitational effects from the moon Prometheus, exhibiting dynamic behavior on a timescale of hours to weeks. The ring consists of a denser core surrounded by a more-tenuous skirt composed of dust-sized particles. Previous work by French et al. (2012, Icarus, 219, 181-193) examined five years (2004-2009) of F ring image data from Cassini’s ISS instrument, concluding that the ring was noticeably brighter than in images from the two Voyager flybys, but found no noticeable trend in brightness over time within the Cassini data. Here we expand upon this research by analyzing observations of the F ring from Cassini’s ISS, UVIS, and VIMS instruments over the full range of Cassini’s tenure at Saturn (2004-2017). Notably, this longer baseline of observations covers both before and after Prometheus’s pericenter anti-alignment in 2009. We continue to find that the extended F ring core has sufficient optical depth to require modeling of shadowing and obscuration. We employ a new “3 zone” model of the F ring, applying an optical depth correction solely to the 100 km-wide central core region and not to the outer skirt due to the latter’s low density. We find the F ring phase curve is well-modeled by a linear combination of two Henyey-Greenstein functions with parameters similar to those of Saturn’s other dusty rings. We identify a number of long-lasting, bright clumps in the Cassini ISS images, and find a suggestion of a change in mean brightness that is out of phase with the closest approach of Prometheus. Finally, we analyze stellar occultations from Cassini’s UVIS (~0.1-0.2 μm) and VIMS (~1-5 μm) instruments. We find that the median equivalent depths are similar between the two, placing new constraints on the particle size distribution. We will present our most recent findings.

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