Yet another remarkable finding of the 1979 Voyager missions was the discovery of a faint ring of matter encircling Jupiter in the plane of the planet's equator (see Figure 11.23). This ring lies roughly 50,000 km above the top cloud layer of the planet, inside the orbit of the innermost moon. A thin sheet of material may extend all the way down to Jupiter's cloud tops, but most of the ring is confined within a region only a few thousand kilometers across. The outer edge of the ring is quite sharply defined. In the direction perpendicular to the equatorial plane, the ring is only a few tens of kilometers thick. The small, dark particles that make up the ring may be fragments chipped off by meteorite impacts from two small moons—Metis and Adastrea, discovered by Voyager—that lie very close to the ring itself.

Despite differences in appearance and structure, Jupiter's ring can perhaps be best understood by studying the most famous planetary ring system—that of Saturn—so we will postpone further discussion of ring properties until the next chapter.

Figure 11.23 Jupiter's faint ring, as photographed (nearly edge-on) by Voyager 2. The ring, made up of dark fragments of rock and dust, possibly chipped off the innermost moons by meteorites, was unknown before the two Voyager spacecraft arrived at the planet. It lies in Jupiter's equatorial plane, only 50,000 km above the cloud tops.