Pluto is the second-largest object in the outer reaches of our solar system, barely smaller than another dwarf planet, Eris.
Charon, Pluto’s most massive moon, was discovered in 1978. Charon has a diameter of 648 miles (1,043 kilometers) and orbits Pluto at a distance of 12,200 miles (19,640 kilometers).
Charon completes one orbit in 6.4 Earth days, which is the same time it takes Pluto to rotate once on its axis. As a result, the two bodies are tidally locked, eternally facing one another, just as our moon always presents the same face to Earth. [Photos: Pluto and its Moons]
In recent years, other small moons of Pluto have been discovered orbiting the distant dwarf planet. Nix and Hydra, both discovered in 2005, each have a diameter of about 31 to 62 miles (50 to 100 kilometers).
Kerberos, found in 2011, is smaller at 8 to 21 miles in diameter (13 to 34 kilometers). The latest discovery, Styx, was found in 2012 and is the smallest moon so far, only 6 to 15 miles across (10 to 25 kilometers).