The most famous of Neptune's rings is the thin outer Adams ring, although by comparison with the rings of the planets Saturn or Uranus, it is very hard to see. It was originally named as "1989 N1R". The reason that the Adams ring is famous is that it has a feature that has not been seen on any other planetary rings. These are three long narrow ""arcs"" which are much brighter and look more solid than the rest of the ring system. Each one spans from 4-10° of the whole ring. All the arcs are close to each other, spanning under 40° of longitude, only about 1/8th of the edge of the ring. It has been a puzzle to understand why the stuff in these arcs does not spread out evenly through the whole ring.