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Galileo Saw Jupiter's Rings, Too
I. J. Daubar, M. E. Ockert-Bell, J. A. Burns, J. F. Veverka, and P. Thomas (Cornell Univ.), M. Belton (NOAO), K. Klaasen (JPL), Galileo Imaging Team
Because of better spatial resolution, different phase coverage, and
superior signal-to-noise, Galileo's thirteen clear images of Jupiter's ring
system taken during a single pass through the planet's shadow improve
substantially upon Voyager data. In addition two Adrastea images fortuitously
included the rings at phase angles around .
By assuming a circular and equatorial main ring, and using
the position of a star found in one ansa image, we fix the main ring's outer
radius at 
km, slightly less than Voyager's value of
km, and very close to Adrastea's orbit (128980 km). The ring's
halo rises gradually starting near the 3:2 vertical Lorentz resonance at
122733 km. The gossamer ring, discovered in a single Voyager image, is clearly
visible out to the frame's edge at 2.3 
.
The main ring exhibits a marked drop in brightness at 
km,
lying almost atop Metis's orbit at 127978 km. The ansa images also show
apparent azimuthal structure: longitudinally alternating bright and dim patches.
As previously noted in Voyager images, the brightnesses of the near
and far arms differ by 10% or more. In contrast to Voyager, Galileo
images show the near arm to be brighter. Galileo's shallow viewing angle
( 
above the ring plane) through the diaphanous ring may play a
role in brightness variations.
Results will also be presented describing the morphologies of the halo and gossamer ring, as well as phase functions for the ring's components.