charon

Charon is the largest moon of the dwarf planet Pluto. It was discovered in 1978 by James W. Christy, who identified a secondary body orbiting Pluto in photographic plates from the U.S. Naval Observatory. Charon's diameter is about 1,212 kilometers. It orbits Pluto with a period of roughly 6.4 days, and the Pluto–Charon system has a barycenter located outside Pluto, effectively forming a binary world.

Charon is named after the mythological ferryman of the dead in Greek mythology. The name was adopted by the International Astronomical Union in 1985.

Geologically, Charon's surface is dominated by water ice, with darker regions of likely non-ice material. The terrain includes heavily cratered plains and areas showing evidence of tectonic activity, including an extensive canyon system. A notable dark region called Mordor Macula has been identified on its surface from New Horizons imagery.

No substantial atmosphere surrounds Charon. The body is thought to be internally differentiated, with a rocky core overlain by an icy mantle, and surface temperatures are extremely cold.

Charon was studied in detail during NASA's New Horizons flyby of the Pluto–Charon system in 2015, which produced high-resolution images and data that clarified its geology, composition, and relationship to Pluto.