Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p23b1627m&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P23B-1627
Mathematics
Logic
[5759] Planetary Sciences: Fluid Planets / Rings And Dust, [6265] Planetary Sciences: Solar System Objects / Planetary Rings
Scientific paper
The Cassini Ultraviolet Imaging Spectrograph (UVIS) has observed 25 statistically significant F ring features in 91 occultations since July 2004. This work nearly doubles the number of features reported by Esposito et al. (2008). As the number of statistically significant features has grown, it has become useful to classify them for the purposes of cataloging. We define three categories: Moonlet, Core, and Icicle, which classify the shapes of features seen to date in the occultation profiles of the F ring. Two features fall into the Moonlet class. Each is opaque in its occultation, which makes them candidates for solid objects. We classify 15 of the significant observed features 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. Finally, the variety of core region shapes displays that even the general shape of the F ring is ever-changing. The core region of the F ring usually has a smooth U-shape to it, but the core region takes the shape of Ws and Vs in some occultation profiles. We seek to understand the types of objects embedded in the F ring that give rise to the 17 Moonlet and Icicle features. Because a UVIS occultation probes only one dimension of ring structure, we compare occultations with images of F ring features to explore the shapes of objects embedded in the ring. The resolution of the UVIS occultations pushes the observed size range to smaller sizes, some just tens of meters in radial width. Meanwhile, images from Cassini ISS show larger-scale (few-tens of km) features such as gores and fans that are extended in azimuth. Although on different size scales, the UVIS features are morphologically similar to those from images, specifically with regard to the elongation of clumps of material in the F ring. Moonlet and Icicle occultation features are probably due to elongated aggregates of ring material that are better represented as tri-axial ellipsoids than spherical bodies, and we discuss the constraints on the dimensions of these bodies. We present the size distribution of observed F ring features and compare it to that modeled in Barbara and Esposito (2002). The Barbara and Esposito (2002) model of the size distribution of bodies in the F ring is overly-simplified, as they assume the aggregates are spheres, and vastly outnumbered by the transient aggregates included in the observed distribution. This research was supported by the Cassini Project.
Albers Nicole
Esposito W. L. W. L.
Meinke Bonnie K.
Miodrag Sremčević
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