... 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 I n Roman mythology, Pluto (Greek: Hades ) is the god of the underworld. ... P luto is locked in a 3:2 resonance with Neptune; i.e. Pluto's orbital period is exactly 1.5 times longer than Neptune's. Its orbital inclination is also much higher than the other planets'. ... Neptune .. ...