outer "gossamer rings", named after the moons of whose material they are composed: Amalthea and Thebe. The principal attributes of the known Jovian Rings are listed in the table. Main ring Appearance and structure The narrow and relatively thin main ring is the brightest part of Jupiter's ring system. Its outer edge is located at a radius of about (; = equatorial radius of Jupiter or ) and coincides with the orbit of Jupiter's smallest inner satellite, Adrastea. Its inner edge is not marked by any satellite and is located at about (). Thus the width of the main ring is around . The appearance of the main ring depends on the viewing geometry. In forward-scattered light the brightness of the main ring begins to decrease steeply at (just inward of the Adrastean orbit) and reaches the background level at —just outward of the Adrastean orbit. Therefore, Adrastea at clearly shepherds the ring. The brightness continues to increase in the direction of Jupiter and has a maximum near the ring's center at , although there is a pronounced gap (notch) near the Metidian orbit at . The inner boundary of the main ring, in contrast, appears to fade off slowly from to , merging into the halo ring. In forward-scattered light all Jovian rings are especially bright. In back-scattered light the situation is different. The outer boundary of the main ring, located at , or slightly beyond the orbit of Adrastea, is very steep. The orbit of the moon is marked by a gap in the ring so there is a thin ringlet just outside its orbit. There is another ringlet just inside Adrastean orbit followed by a gap of unknown origin located at about . The third ringlet is found inward of the central gap, outside the orbit of Metis. The ring's brightness drops sharply just outward of the Metidian orbit, forming the Metis notch. Inward of the orbit of Metis, the brightness of the ring rises much less than in forward-scattered light. So in the back-scattered geometry the main ring appears to consist of two different parts: a narrow outer part extending from to , which itself includes three narrow ringlets separated by notches, and a fainter inner part from to , which lacks any visible structure like in the forward-scattering geometry. The Metis notch serves as their boundary. The fine structure of the main ring was discovered