Saturn's F ring as seen by Cassini UVIS: Kinematics and statistics

    Authors

    N. Albers; M. Sremcevic; J. E. Colwell;L. W. Esposito

    Comments

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    Abbreviated Journal Title

    Icarus

    Keywords

    Saturn, Rings; Occultations; Orbit determination; SELF-GRAVITY WAKES; STELLAR OCCULTATION; VOYAGER OBSERVATIONS; RADIO; OCCULTATION; PLANE CROSSINGS; IMAGING SCIENCE; NEARBY MOONLETS; NOVEMBER; 1995; PROMETHEUS; PHOTOPOLARIMETER; Astronomy & Astrophysics

    Abstract

    We present a new orbital model of Saturn's F ring core based on 93 occultations by the Cassini Ultraviolet Imaging Spectrograph (UVIS) and the Voyager radio and stellar occultations. We demonstrate that the core, despite its intrinsic variability, is well-described as an inclined, freely precessing ellipse. We find that post-fit residuals with a root-mean-square of 24 km are genuine, representing the well-known non-Keplerian features observed in the ring. Over the nearly 4 years of UVIS observations we find the residual variance to increase, coincident with the apse anti-alignment of Prometheus and F ring core in December 2009. This increase in dynamical F ring core temperature most likely reflects the ever-stronger perturbations by Prometheus. Our results are in good agreement with Earth-based and HST observations as well as Voyager imaging. Cassini UVIS stellar occultations resolve the F ring at unprecedented resolutions of a few meters and we identify the F ring core and inner and outer strands. We infer their normal optical depth and full width at half maximum (FWHM) and show that core and strands form distinct morphological groups. Typically, a strand is about ten times wider than the core (average FVVHM is similar to 10 km) while having a ten times smaller optical depth. Unlike in pre-Cassini occultations the F ring core displays significant optical depth with in some cases > 3. In many cases we find a narrow optically thick component (similar to few km and tau > 0.5) embedded in the F ring core. Entertaining the possibility that this is the actual, "true" F ring core then UVIS results suggest that this "true" core is highly non-continuous. In addition, we report the detection of a previously unknown structure - dubbed the "secondary" as it visually resembles the F ring core. Its morphology is similar to that of the core in optical depth and FWHM and it displays individual opaque features. Despite its core-like appearance, we show that its kinematics is consistent with that of strands. We conclude that it is the most prominent strand seen to date. It represents a striking example of strand creation resulting in what could be called a morphological "small-scale" version of the F ring core. This extraordinary object should be one of the prime targets of future F ring studies. (C) 2011 Elsevier Inc. All rights reserved.

    Journal Title

    Icarus

    Volume

    217

    Issue/Number

    1

    Publication Date

    1-1-2012

    Document Type

    Article

    Language

    English

    First Page

    367

    Last Page

    388

    WOS Identifier

    WOS:000299130900029

    ISSN

    0019-1035

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