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[61.11] Where are the spokes in Saturn's B ring?

C.J. Mitchell, M. Mihaly Horanyi (University of Colorado)

The spokes in Saturn's B ring are radial features which appear dark in backscattered light but bright in forward scattered light, indicating that they are composed of small dust particles. First observed by the Voyager imaging experiment, they were also observed during the last ring plane crossing by McGhee et al. (2005) using the Hubble Space Telescope, but they have yet to be observed by Cassini.

In order to explain the lack of spokes, we expand on the work of Nitter et al. (1998) where the plasma environment and electric field immediately above the ring affects the motion of the spoke particles due to their charge. As the charging conditions change due to variations in the ambient plasma environment and the solar elevation angle, spoke particles which would survive above the ring for several hours during the Voyager flybys are very rapidly pulled back down onto the ring under the current conditions, preventing spoke formation.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.