Acknowledgement. We thank Science for their permission to use an excerpt from:

Smith, B. A., et al. 1979. The Galilean satellites and Jupiter: Voyager 2 Imaging Science results. Science 206 (4421), 927-950. (Excerpt from pp. 932-933.)

Copyright AAAS, November 23, 1979.

The Galilean Satellites and Jupiter:
Voyager 2 Imaging Science Results

Jupiter's ring system.

After the discovery of the Jovian ring system by Voyager 1 (1), additional images were planned for Voyager 2 at various illumination and viewing angles. In particular, an effort was made to obtain pictures slightly out of the equatorial plane in order to determine the width and inner structure of the ring system. A more complete account of these results and their interpretation may be found elsewhere (11).

Two Voyager 2 pictures, taken prior to ring plane crossing when the spacecraft was 2.5 degrees above the plane, show distinct inner and outer boundaries of the brightest part of the ring system. In them the rings were viewed in backscattered sunlight, at a time when the center of the 0.1 degree diameter solar disk was 0.03 degrees below the ring plane. Although the signal was weak, no obvious gaps were visible. A second set of images was acquired during the ring plane crossing. They confirmed Voyager 1 observations that the ring system is optically very thin with a well-defined outer edge. Smearing caused by spacecraft motion prevented any improved definition of ring thickness; the 30-km upper limit set by Voyager 1 is still the best estimate.

The most spectacular ring pictures were obtained by Voyager 2 on 11 July at a phase angle of nearly 180 degrees while the spacecraft was 2 degrees below the ring plane and in the shadow of Jupiter. Strong forward scattering by ring particles gave well-exposed images that provided substantially better definition of the ring structure than had been possible earlier. Figures 9 and 10, acquired during this sequence, were taken with both the narrow and the wide-angle cameras through the clear, violet, and orange filters.

The outer part of the ring system is made up of a relatively bright segment about 800 km wide surrounded by a somewhat dimmer and broader segment about 5200 km across. Other, less distinct divisions are barely visible in Fig. 10. The interior of the ring is filled with much fainter material, probably extending downward into the top of the atmosphere of Jupiter itself. This material may contribute to the ultraviolet absorbing haze in Jupiter's upper atmosphere if stratospheric winds could give it planetwide distribution. It is even possible that the ring material is a source of oxygen to the upper atmosphere that could be related to the abundance of carbon monoxide (12). The discovery of this inner material reinforces an earlier suggestion (11) that much of the ring system represents a steady state between loss and supply, being neither a leftover from the original accretion and condensation events that formed the planet (as Saturn's rings may be) nor fragments of a disrupted satellite. Candidates for sources to supply this material include cometary and meteoritic debris, impact ejecta from the inner satellites, and volcanic ejecta removed from Io, possibly by magnetospheric forces. The small newly discovered satellite (13) with an orbital radius of 1.81 Jupiter radii (RJ) may provide an explanation for the location of the outer boundary of the ring system.

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Last updated Feb-27-1997