Observations

The Io plasma torus is confined by Jupiter's magnetic field to the centrifugal symmetry surface (CSS): the locus of points each of which, among all points on its magnetic field line, is farthest from the planet's spin axis. The torus therefore revolves around Jupiter with its magnetic field (T = 9.925 hours), and, because the CSS is tilted ~ 7° with respect to the spin equator, the torus "wobbles" as well. To prevent these motions from smearing our images, we restricted integration times to ten minutes (sometimes twelve). This time constraint, combined with the modest (0.81 m) primary aperture, yields barely enough photons to produce a useful image; nonetheless, in the first year of this program, we obtained 260 useful images of the plasma torus. One night's worth of data are shown in mosaic form in fig. 2 and in animated form in video 1. Although these data are only partially reduced, the torus and its changing position and intensity are clearly visible. The data are well-distributed in System III (fig. 3), the jovian magnetic longitude system in which many features of the torus are organized (or believed to be).

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Figure 1    Figure 2    Figure 3    Video 1

Copyright © 1999 R. Carey Woodward, Jr. and/or the Board of Regents of the University of Wisconsin, as their interests may lie. All rights reserved. When citing this paper, please use this information.