DPS Meeting, Madison, October 1998
Session 15. Rings I
Contributed Oral Parallel Session, Tuesday, October 13, 1998, 9:00-10:10am, Madison Ballroom C

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[15.02] Keck Infrared Observations of Jupiter's Ring System

Imke de Pater, J. R. Graham, M. C. Liu (UC Berkeley), M. R. Showalter (Stanford Univ.), J. A. Burns, P. D. Nicholson (Cornell Univ.), D. P. Hamilton (Univ. of Maryland)

We imaged the Jovian ring system at a wavelength of 2.27 \mum with the 10-m W.M. Keck telescope in August and October 1997, when the ring plane was almost edge-on. We obtained the first images of the Jovian halo and gossamer ring in back-scattered light, and the best ground-based images to date of Jupiter's main ring. The main ring is radially confined between 1.70 -- 1.82 RJ, with a maximum (after inversion) at 1.79 RJ, in agreement with the Voyager findings (1 RJ=71398 km). The halo extends inwards from the main ring (at 1.71 RJ) down to 1.40 RJ, bounded by the locations of Lorentz resonances. Roughly 50% of the halo's intensity originates from a region within ~700 km from the equatorial plane, while the halo is visible up to ~ 10,000 km above and below the plane. Although the vertical extent agrees with Voyager findings, the halo's intensity relative to that of the main ring in the Keck images is much less than in Voyager images, which is attributed to the fact that the halo contains fewer macroscopic particles, which preferentially backscatter visible light.

The gossamer ring is found to have two components, with steep dropoffs in brightness at the orbits of Amalthea and Thebe. The first, Amalthea's gossamer ring, is visible between the main ring's periphery and ~ 2.5 RJ; it is relatively uniform in brightness and has a vertical thickness (FWHM) of 0.06 RJ, clearly broader than the FWHM of the main ring (0.045 RJ) and image resolution of 0.6\prime\prime=0.025\;RJ. The other component, a factor of five fainter than Amalthea's ring and about twice as broad vertically (FWHM \approx 0.12 \; RJ), is seen inwards from 3.11 RJ, i.e., inwards of Thebe's orbit. Additional material still seems present, albeit barely, at larger distances, until ~ 3.6 RJ, near the edge of our images.

Our data are consistent with the Galileo results, and suggest the ring material originates at the bounding satellites Thebe, Amalthea, Adrastea and Metis (see abstracts by Burns et al., and Hamilton et al.)

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