How did Pluto and its moons get their names?
The Romans named the five planets closest to the Sun after their most important gods. These were the only planets that were bright enough for them to see. Later, when telescopes were used, other planets were discovered. Astronomers decided to continue naming the planets after Roman gods. At the time of Pluto's discovery, it was considered to be a planet (it is now classified as a dwarf planet). Being very cold and the farthest from the Sun, Pluto was named after the Roman god of death. According to Roman myth, when someone died, they traveled down to the Underworld. First, they had to cross the River of the Dead, called the river Styx. Everyone was buried with a coin, to pay the ferryman, Charon, who would carry the dead across the river Styx in his boat. Pluto's moon is named Charon after this ferryman of the Underworld. The naming of Pluto's other moons follows this same basic scheme -- Nix is the Greek goddess of darkness and night and mother of Charon, Hydra is the nine-headed serpent which battled Hercules, Kerberos is many-headed dog that guarded the entrance to the underworld in Greek mythology, and Styx is the river that souls had to cross over to get to Hades, or the underworld, and the goddess who ruled over it. The International Astronomical Union (IAU) is the final arbiter in naming celestial objects.