Pluto from Charon. Computer artwork of Pluto from the cratered rock and ice surface of its moon Charon. Charon is casting a sharp shadow on the surface of Pluto. Pluto is the most distant planet of the solar system, circling the Sun every 248 years at a distance of around 6 billion kilometres. Charon is half Pluto's size, so this is sometimes called a double planet system. Little is known about these worlds, which are yet to be visited by spacecraft from Earth. At less than 2300 kilometres across, Pluto is by far the smallest planet. Some astronomers do not consider Pluto to be a true planet, instead classifying it as an object in the Kuiper Belt.