Figure 8-5 Pluto and Its Five Known Moons Observations by the Hubble Space Telescope in 2005 revealed two intermediate-sized moons, each about 5000 times dimmer than Pluto. Named Nix and Hydra, they are each about 75 km (50 mi) across and between 2 and 3 times farther from Pluto than its moon Charon. Kerberos and Styx are each about 25 km (15 mi) in diameter.