Pluto and Charon. Artwork of the cratered surfaces of Pluto (pink) and its moon Charon (grey). Pluto is the most distant planet of the solar system, circling the Sun at a distance of around 6 billion kilometres every 248 years. Charon is only half its size, making this a double planet system. Little is known about these worlds, which are yet to be visited by spacecraft from Earth. Pluto is twenty-five times smaller than the next smallest planet Mercury, and has an extremely eccentric orbit that is highly inclined to the ecliptic plane of the other planetary orbits. Pluto is not therefore seen as a true planet. Some astronomers consider it a large asteroid or minor planet.