Charon (moon of Pluto)

Charon is the largest moon orbiting Pluto, a dwarf planet in the Kuiper Belt, the distant icy region beyond Neptune's orbit. Charon has a diameter of approximately 1,200 kilometers, roughly half that of Pluto. Because of this size similarity, some scientists classify the system as a 'binary' or double-object system, rather than as a conventional planet and moon.

Charon was discovered in 1978, when American astronomer James Christy noticed distortions in telescope images of Pluto that changed systematically and persistently. The name comes from Charon, the figure in Greek mythology who ferries souls across the river Styx. The names of Pluto's other moons—Nix, Hydra, Kerberos, and Styx—likewise derive from the same mythological tradition.

Orbit and relationship to Pluto

Charon orbits Pluto at a distance of approximately 19,600 kilometers, completing one orbit in about 6.4 days. The two bodies are locked in what is called 'tidal locking': each always presents the same face to the other. Because of this, an observer on Pluto's surface would always see Charon in the same place in the sky. The center of mass (barycenter) of the two bodies lies outside Pluto's surface, distinguishing this system from most planet-moon systems in the solar system.

Composition and surface

Charon consists of a mixture of water ice and rock. Its surface is dominated by water ice, unlike Pluto, whose surface shows lighter ices such as nitrogen and methane. Its surface features and appearance suggest it has a rocky core beneath an icy layer.

New Horizons flyby

In July 2015, NASA's spacecraft New Horizons passed close to the Pluto system and returned detailed images of Charon. These images revealed deep canyons with lengths reaching tens of kilometers, and relatively smooth terrain that appears younger than other regions, suggesting past geological activity. A dark region on the northern rim was informally named Mordor Macula.