Pluto has long been known to have its own satellite, named Charon. Recently, two additional moons of Pluto have been discovered.

The fact that Pluto should have any moons at all is puzzling to scientists, since Pluto is only 70% the size of Earth's own moon. The newly discovered moons are less than 180 kilometers in diameter - about one-seventh the size of Charon - and orbit about 44,000 kilometers from their parent planet.

Because of the nature of Pluto - small and rocky like Mars and Mercury - its location, and its eccentric orbit (which passes inside that of Neptune), some scientists are beginning to question whether it is a true planet at all. It may instead be part of the Kuiper Belt, located outside the Solar System proper. At least one object has been discovered in the Kuiper Belt that is larger than Pluto.

One common theory is that Pluto may actually be a former moon of Neptune, which escaped when Neptune or one of its other moons - probably Miranda - collided with another body.