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Ann. Geophys., 21, 661-669, 2003
www.ann-geophys.net/21/661/2003/
© European Geosciences Union 2003
A note on the ring current in Saturn’s magnetosphere: Comparison of magnetic data obtained during the Pioneer-11 and Voyager-1 and -2 fly-bys
E. J. Bunce and S. W. H. Cowley
Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
Abstract. We examine the residual
(measured minus internal) magnetic field vectors observed in Saturn’s
magnetosphere during the Pioneer-11 fly-by in 1979, and compare them with those
observed during the Voyager-1 and -2 fly-bys in 1980 and 1981. We show for the
first time that a ring current system was present within the magnetosphere
during the Pioneer-11 encounter, which was qualitatively similar to those
present during the Voyager fly-bys. The analysis also shows, however, that the
ring current was located closer to the planet during the Pioneer-11 encounter
than during the comparable Voyager-1 fly-by, reflecting the more com-pressed
nature of the magnetosphere at the time. The residual field vectors have been
fit using an adaptation of the current system proposed for Jupiter by Connerney
et al. (1981a). A model that provides a reasonably good fit to the Pioneer-11
Saturn data extends radially between 6.5 and 12.5 RS (compared with a
noon-sector magnetopause distance of 17 RS), has a north-south extent of
4 RS, and carries a total current of 9.6 MA. A corresponding model that
provides a qualitatively similar fit to the Voyager data, determined previously
by Connerney et al. (1983), extends radially between 8 and 15.5 RS
(compared with a noon-sector magnetopause distance for Voyager-1 of 23–24 RS),
has a north-south extent of 6 RS, and carries a total current of 11.5
MA.
Key words. Magnetospheric physics
(current systems, magnetospheric configuration and dynamics, planetary
magnetospheres)
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