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
15810 Arawn resonance with Neptune, similarly to dwarf planet Pluto, the largest known plutino. It measures approximately in diameter, based on an absolute magnitude of 7.6, and estimated albedo of 0.1. In April 2016, a rotation period of 5.47 hours was determined for this minor planet. In 2012, Arawn was hypothesized to be in a quasi-satellite loop around Pluto, as part of a recurring pattern, becoming a Plutonian quasi-satellite every 2 Myr and remaining in that phase for nearly 350,000 years. Measurements made by the "New Horizons" probe in 2015 made it possible to calculate the motion of Arawn much more accurately.