Charon, known as (134340) Pluto I, is the largest of the five known natural satellites of the dwarf planet Pluto. It has a mean radius of 606 km (377 mi). Charon is the sixth-largest known trans-Neptunian object after Pluto, Eris, Haumea, Makemake, and Gonggong. It was discovered in 1978 at the United States Naval Observatory in Washington, D.C., using photographic plates taken at the United States Naval Observatory Flagstaff Station (NOFS).
Charon as imaged by the New Horizons spacecraft, July 2015. A massive fault system involving Serenity Chasma and Mandjet Chasma crosses Charon's equator, while Charon's north pole is covered by the dark Mordor Macula
Charon's discovery at the Naval Observatory Flagstaff Station as a time-varying bulge on the image of Pluto (seen near the top at left, but absent on the right). Negative image.
Size comparisons: Earth, the Moon, and Charon
Comparison between Pluto's Sputnik Planitia and Charon's informally named Vulcan Planitia
The dwarf planet Pluto has five natural satellites. In order of distance from Pluto, they are Charon, Styx, Nix, Kerberos, and Hydra. Charon, the largest, is mutually tidally locked with Pluto, and is massive enough that Pluto and Charon are sometimes considered a binary dwarf planet.
Charon and Pluto, to scale. Photo taken by New Horizons on approach.
The Hubble discovery image of Nix and Hydra
Discovery image of Styx, overlaid with orbits of the satellite system
Formation of Pluto's moons. 1: a Kuiper belt object approaches Pluto; 2: it collides with Pluto; 3: a dust ring forms around Pluto; 4: the debris aggregates to form Charon; 5: Pluto and Charon relax into spherical bodies.
