The structure of Jupiter's ring system as revealed by the Galileo imaging experiment

The jovian ring system was observed during four orbits of Galileo's nominal mission, when 25 clear-filter images of the rings were taken at spatial re solutions of 23 to 134 km/pixel; the ring appeared fortuitously in an addit ional II images. The tenuous jovian ring system (normal optical depths <10( -5)) has three components: the halo, main ring, and gossamer ring. The innermost component, a toroidal halo, extends radially from approximate ly 92,000 to about 122,500 km (near the 3:2 Lorentz resonance) and has a fu ll-width, half-maximum thickness of 12,500 km; its brightness decreases wit h height off the equatorial plane and decreases as the planet is approached . The main ring reaches from the hare's outer boundary across 6440 to 128,9 40 km, just interior to Adrastea's orbit (128,980 km); at its outer edge, t he main ring takes nearly 1000 km to develop its full brightness. The ring' s brightness noticeably decreases around 127,850 km in the vicinity of Meti s' semimajor axis (127,980 km). The precise location and nature of the main ring's outer periphery may shift slightly from image to image; the same is true for the "notch" near Metis. The main ring has a faint, vertically ext ended component that thickens as the halo region is approached. Brightness variations of +/-10% are visible in the central main ring and may be due to vertical corrugations, density clumps, or "spokes" in the ring. Unexplaine d differences between the near- and far-arm brightnesses are visible. We ha ve discovered that the gossamer ring, lying exterior to the main ring, has two primary components, each of which is fairly uniform: one originates jus t interior to Amalthea's orbit (181,366 km) while the other is situated rad ially interior to Thebe's orbit (221,888 km). Very faint material continues past Thebe, blending into the background at 250,000 km. The gossamer rings have thicknesses that are comparable to the maximum elevations of these sa tellites off Jupiter's equatorial plane; from Galileo's nearly equatorial v iew, the gossamer rings present rectangular end-profiles with greater inten sities along their top and bottom surfaces. The rings seem to be derived fr om the satellites, (C) 1999 Academic Press.