Jupiter also has a thin planetary ring system. These rings are difficult to see and were not discovered until 1979 by NASA's Voyager 1 probe. There are four parts to Jupiter's rings. The closest ring to Jupiter is called the Halo Ring. The next ring is called the Main Ring. It is about 6,440 km wide and only 30 km thick. The third and fourth rings, called the Gossamer Rings, are transparent (see-through) and are made from microscopic debris and dust. The third ring is called the Amalthea Gossamer Ring, named after the moon Amalthea. The outer ring, the Thebe Gossamer Ring, is named after the moon Thebe. The outer edge of this ring is about 220,000 km from Jupiter.