Classification of F ring features observed in Cassini UVIS occultations
- 作者：Bonnie K. Meinke
- 关键词：Occultations ; Planetary rings ; Saturn ; Rings ; Ultraviolet observations
- 刊名：Icarus
- 出版年：2012
- 期刊代码：90_00191035
- 类别：ph
- 出版时间：March, 2012
- 卷：218
- 期：1
- 页码：545-554
- 文件大小：740 K
摘要
The Cassini Ultraviolet Imaging Spectrograph (UVIS) has detected 27 statistically significant features in 101 occultations by Saturn鈥檚 F ring since July 2004. This work nearly doubles the number of features reported by Esposito et al. (Esposito, L.W. et al. [2008]. Icarus 194, 278-289). As the number of statistically significant features has grown, it has become useful to classify them for the purposes of cataloging. We define three classes: Moonlet, Icicle, and Core, which visually classify the shapes of features seen to date in the occultation profiles of Saturn鈥檚 F ring. Two features fall into the Moonlet class. 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. Finally, the variety of core region shapes displays how even the general shape of the F ring is ever-changing. The core region of the F ring (typically 鈭?0 km wide) usually has a smooth U-shape to it, but the core region takes the shape of Ws and Vs in some occultation profiles. 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.