Jupiter's ring was discovered by Voyager 1 in a single image that was targeted specifically to search for a faint ring system. Subsequently, Voyager 2 was reprogrammed to take a more complete set of images. The ring is now known to be composed of three major components. The "Main" ring is about 7,000 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 the broad and exceedingly faint "Gossamer" ring, which extends out beyond the orbit of the moon Amalthea. It is probably composed of dust particles less than 10 microns in diameter -- about the size of cigarette smoke particles. It extends to an outer edge of about 129,000 km (80,161 miles) from the center of the planet and inward to about 30,000 km (18,642 miles). The origin of the ring is probably from micrometeorite bombardment of the tiny moons orbiting within the ring.
Jupiter's rings and moons exist within an intense radiation belt of electrons and ions trapped in the planet's magnetic field. These particles and fields comprise the Jovian magnetosphere or magnetic environment, which extends 3 to 7 million km (1.9 to 4.3 million miles) toward the sun, and stretches in a windsock shape at least as far as Saturn's orbit -- a distance of 750 million km (466 million miles).
Reference: USGS Astrogeology: Gazetteer of Planetary Nomenclature -- Ring Nomenclature
