Pluto and its three moons were likely formed together when two large objects collided millions of years ago. Charon has been observed for decades, but the two new smaller moons, discovered last year, also orbit in the same plane as Charon and have a similar orbital resonance. It's even possible that Pluto has a ring system. Astronomers now believe that many Kuiper Belt Objects have multiple moons, and even higher order systems will probably be discovered in the years to come.