We thank Science for their permission to use an
Smith, B. A., et al. 1979.
The Jupiter system through the eyes of Voyager 1
Science 204 (4396), 951-972.
(Excerpt from p. 955.)
Copyright AAAS, June 1, 1979.
The Jupiter System Through the Eyes of Voyager 1
Jupiter's ring was discovered in a narrow-angle frame
targeted halfway between Amalthea and the limb of Jupiter at 16 hours, 52
minutes before closest approach as Voyager 1 crossed the equatorial plane of
the Jovian system
( Fig. 11).
This very long exposure (11 minutes, 12
seconds) shows a composition of multiple images of the ring caused by
the combined motions of the scan platform relative to the spacecraft,
the spacecraft along its trajectory, and a slight rocking of the
spacecraft about its center of gravity. Star trails, which look like
broken hairpins on this image, establish the directions and durations of
these motions when interpreted with the help of engineering data from
the spacecraft. Each kink in the star trails corresponds to one image of
the ring. (Voyager engineers who contributed significantly to the
analysis were C. Hansen, G. Carlisle, T. Duxbury, L. Morabito, and S.
Synnott.) This background of stars from the Praesepe cluster was also
used to verify that the ring was in the planet's equatorial plane. The
ring edge is estimated to be at 1.8 Jupiter radii (RJ) from
the center of the planet and thus is well within the Roche limit
The camera had been oriented to record the central region of a
possible ring system with the same scale as Saturn's; it was thus
entirely fortuitous that it imaged the outer edge of the Jovian rings.
However, Acuna and Ness (16) had predicted a ring or an undiscovered
satellite at 1.83 RJ from an analysis of charged particle data from
Pioneer 11, a prediction in remarkably close agreement with this
At our range of 1.2 e6 km from the ring, the scale of this
picture is ~11 km per picture element, giving an upper limit of ~30 km
for the width of the ring. No gradient from the edge toward Jupiter has
been detected in the ring brightness. Although accurate radiometric
estimates are not available for the ring brightness, the current
estimate is 13th magnitude per linear arc-second. The ring was barely
visible in two wide-angle frames taken 42 minutes later from a position
0.16 degrees below the Jovian equatorial plane.
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