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 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 the broad and exceedingly faint
gossamer ring, which extends out beyond the orbit of the moon Amalthea.
Unlike Saturn's intricate and complex ring patterns, Jupiter has a single ring that is
almost uniform in its structure.
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 kilometers
(80,161 miles) from the center of the planet and inward to about 30,000 kilometers (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 kilometers (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 kilometers (466 million miles).