... Pluto and Charon . ... Pluto is the farthest planet from the Sun (usually) and by far the smallest. Pluto is smaller than seven of the solar system's moons (the Moon , Io , Europa , Ganymede , Callisto , Titan and Triton ). orbit : 5,913,520,000 km (39.5 AU ) from the Sun (average) diameter : 2274 km mass : 1.27e22 kg . ... Pluto's radius is not well known. ... Charon ( "KAIR en" ) is Pluto's only known satellite: orbit : 19,640 km from Pluto diameter : 1172 km mass : 1.90e21 kg . ... Sun .. ...