Charon is the largest moon of Pluto and orbits the dwarf planet Pluto.
Discovered in 1978 by astronomer James Christy, Charon is unusually large compared with its primary body. Its diameter is about half Pluto’s, and the two objects orbit a shared center of mass located outside Pluto’s surface. For that reason, Pluto and Charon are often described as a binary or double dwarf-planet system, although Charon is officially classified as Pluto’s largest moon.
Charon is tidally locked to Pluto, meaning the same hemisphere of Charon always faces Pluto, while the same side of Pluto always faces Charon. Their mutual orbit takes about 6.4 Earth days. NASA’s New Horizons spacecraft made the first close-up observations of the pair during its Pluto flyby in July 2015.
Charon is not the only moon orbiting Pluto: Styx, Nix, Kerberos, and Hydra are smaller satellites. A common mix-up is saying Charon orbits the Sun directly; the Pluto–Charon system does travel around the Sun, but Charon’s immediate orbital partner is Pluto.