Jupiter's Rings
Jupiter has rings like Saturn's, but much fainter and smaller. They were totally unexpected and were only discovered when two of the Voyager 1 scientists insisted that after traveling 1 billion km it was at least worth a quick look to see if any rings might be present.
Everyone else thought that the chance of finding anything was nil, but there they were. It was a major coup. They have since been imaged in the infra-red from ground-based telescopes and by Galileo.
Unlike Saturn's, Jupiter's rings are dark and have an albedo about .05. They're probably composed of very small grains of rocky material. Unlike Saturn's rings, they seem to contain no ice.
The ring is now known to be composed of three major components. The main ring is about 7000 km wide and has an abrupt outer boundary 129,130 km from the center of the planet. The main ring encompasses the orbits of two small moons, Adrastea and Metis, which may act as the source for the dust that makes up most of the ring.
At its inner edge the main ring merges gradually into the halo. The halo is a broad, faint torus of material about 20,000 km thick and extending halfway from the main ring down to the planet's cloudtops. Just outside the main ring is a pair of broad and exceedingly faint gossamer rings, one bounded by the moon Amalthea and the other bounded by the moon Thebe.
Particles in Jupiter's rings probably don't stay there for long due to atmospheric and magnetic drag. The Galileo spacecraft found clear evidence that the rings are continuously resupplied by dust formed by micrometeor impacts on the four inner moons, which are very energetic because of Jupiter's large gravitational field. The inner halo ring is broadened by interactions with Jupiter's magnetic field.
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