Charon
Charon is Pluto’s largest moon. Pluto and Charon are tidally locked to each other, so each always presents the same hemisphere to the other.
Tidal locking: A state in which an orbiting body rotates once per orbit, keeping the same hemisphere facing its partner. Tidal forces synchronized Charon’s rotation with its orbit around Pluto.
Mordor Macula: A reddish region near Charon’s north pole, likely colored by processed gases escaping from Pluto. Its distinctive dark-red cap is among Charon’s most recognizable surface features.
James Christy: An American astronomer who discovered Charon in 1978 while examining images of Pluto. Christy recognized Charon as the source of an apparent elongation in Pluto’s images.
Earth's Moon: Earth’s only natural satellite and the fifth-largest moon in the Solar System. Unlike Earth and its Moon, Pluto and Charon orbit a barycenter outside the larger body.
Pluto–Charon barycenter: The shared center of mass around which Pluto and Charon orbit. Their comparable masses place this center outside Pluto, making their motion a binary-like orbit.
Serenity Chasma: A vast canyon system on Charon extending across part of its equatorial region. The canyon’s scale records major deformation in Charon’s icy crust.
United States Naval Observatory: A United States institution that conducts astronomical research and maintains precision timekeeping services. Charon was discovered in images taken at this observatory.
Pluto's moons: The five known natural satellites orbiting Pluto: Charon, Styx, Nix, Kerberos, and Hydra. Charon dominates this system in size and mass; the other four moons are much smaller.
Orbital resonance: A gravitational relationship in which orbiting bodies’ orbital periods form a ratio of small integers. Pluto’s small moons are kept in resonances associated with the Pluto–Charon system.
Oz Terra: A rugged northern region of Charon marked by craters, canyons, and varied terrain. New Horizons images revealed this region’s sharply contrasting landscapes.