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 tex2html_wrap_inline14 .

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 tex2html_wrap_inline16 km, slightly less than Voyager's value of tex2html_wrap_inline18 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 tex2html_wrap_inline20 .

The main ring exhibits a marked drop in brightness at tex2html_wrap_inline22 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 ( tex2html_wrap_inline24 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.