The Kuiper Belt Buckle
Pluto was demoted from its status as "planet" because we now know it is only the closest (and therefore, the brightest) of thousands of tiny, bodies that orbit the sun past the orbit of Neptune. Quite a few of these icy little worlds have been discovered, and even though they are often quite small, many of them have orbiting comapanions.
Why this should be so is not clear, and no doubt is some kind of clue as to how the solar sytem formed from the primordial nebula five billion years ago. We live in exciting times.