Pluto and Charon. Artwork of the surface of Pluto with its moon Charon in the sky at upper left. Pluto is the furthest planet out from the Sun for most of its orbit, although its orbit is so eccentric that it sometimes comes slightly closer than Neptune. Pluto and Charon are gravitationally locked together, so both appear fixed in their respective skies, and both always see the same face of the other. Pluto is just 2300 kilometres is diameter, far smaller than the Moon. Charon is about 1200 kilometres in diameter and less than 20,000 kilometres from Pluto. Pluto is considered by some to be a Kuiper Belt Object rather than a true planet.