Charon (moon) Charon (moon) Charon, also 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. 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). With half the diameter and one eighth the mass of Pluto, Charon is a very large moon in comparison to its parent body. Its gravitational influence is such that the barycenter of the Plutonian system lies outside Pluto. The reddish-brown cap of
Eris (dwarf planet) decide the issue. This was announced as the IAU's "Definition of a Planet in the Solar System," adopted on 24 August 2006. At this time, both Eris and Pluto were classified as "dwarf planets," a category distinct from the new definition of "planet." Brown has since stated his approval of this classification. The IAU subsequently added Eris to its Minor Planet Catalogue, designating it "(136199) Eris." Eris has an orbital period of 558 years. Its maximum possible distance from the Sun (aphelion) is 97.65 AU, and its closest (perihelion) is 37.91 AU. It came to perihelion between 1698 and 1699,