Abstract/Details

SPOKES IN SATURN'S B RING: DYNAMICAL AND PHYSICAL PROPERTIES DEDUCED FROM VOYAGER SATURN RING IMAGES


1987 1987

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Abstract (summary)

The two Voyager spacecraft discovered small-scale, radially-extended features in the central region of Saturn's B Ring. These "spokes" are "clouds" of submicron-size ice grains which are electrostatically levitated above the ring plane and which appear to travel about Saturn in Keplerian orbits (Smith et al., 1981, Science 212, 163-191).

This research project is a study of the dynamical and physical properties of spokes as deduced from Voyager Saturn ring images. An analysis of the orbital motion of two dynamically-anomalous spokes, in particular, has set limits on the charge-to-mass ratios of spoke particles at various times during their dynamical evolution. These two spokes have charge-to-mass ratios of at least -60 (+OR-) 3 C kg('-1) while corotating with Saturn, and charge-to-mass ratios of no more than -22 (+OR-) 2 C kg('-1) while orbiting Saturn at Keplerian velocities. Additionally, charge decay on the grains of these spokes, caused by solar UV photoemission, has allowed a lower limit of 0.10 (+OR-) 0.03 (mu)m to be placed on the range of radii for spoke particles. In a study of spoke photometry, a single-scattering analysis of the 0.470-(mu)m phase function for spokes has set a mean radius for the dominant scatterers (at this wavelength) of 0.22 (+OR-) 0.02 (mu)m. Also, a multispectral analysis of spokes has determined the spectral index of the size distribution for spoke particles to be 2.1 (+OR-) 0.2. These dynamical and physical properties of spokes have been combined with theoretical explanations of spoke activity to develop a phenomenological model of spoke formation and evolution.

The transport of angular momentum within the rings due to the radial motion of spoke grains is shown to be the most significant effect of spoke activity on the dynamical evolution of the B Ring, as was predicted by Goertz et al. (1986, Nature 320, 141-143). The radial mass transport velocity due to highly-charged spokes is -1 x 10('-9)m s('-1). The subsequent spreading time for the B Ring is 600 million years, which is significantly less than the 4.6 billion-year age of the solar system.

Indexing (details)


Subject
Astronomy;
Astrophysics
Classification
0606: Astronomy
0606: Astrophysics
Identifier / keyword
Pure sciences
Title
SPOKES IN SATURN'S B RING: DYNAMICAL AND PHYSICAL PROPERTIES DEDUCED FROM VOYAGER SATURN RING IMAGES
Author
EPLEE, ROBERT EUGENE, JR.
Number of pages
160
Publication year
1987
Degree date
1987
School code
0009
Source
DAI-B 48/03, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
University/institution
The University of Arizona
University location
United States -- Arizona
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
8712872
ProQuest document ID
303563064
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/303563064
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