Charonball is the
frozen mass relay of Sunball Plutoball's binary companion.
Charonball was once thought to be Plutoball's largest moon. However, he is massive enough that both he and Plutoball instead orbit a barycenter outside of Plutoball, thus making them the Solar System's one of three binary (dwarf) planets.
He is rather large, at 1212 km in diameter, which is about half of Plutoball's.
His composition is somewhat similar to Plutoball. However, there are very significant differences. Charonball is composed of ~55% silicates to ~45% ice, while Plutoball is composed of ~70% silicates. Prior to New Horizons' flyby of the Plutonian system, there were two conflicting theories about Charon's internal structure. Data from the flyby later revealed that most likely, he has a diffrientiated interior. His surface also seems to lack the nitrogen and methane ices Plutoball has, and patches of ammonia hydrates suggest active cyrogeysers or cyrovolcanoes. To further support this, his surface is coated with crystalline ice, which was recently deposited on his surface.
Orbit - Rotation
A real life photo of Charon for reference