Pluto and its large moon Charon have some company in the underworld. Two recently discovered small moons orbiting Pluto have now been officially dubbed Nix and Hydra. Nix is the mythological goddess of the night. One of Nix's offspring was Charon, who ferried the dead across the river Styx to hell. Hydra was a nine-headed, poisonous serpent that resided at the gate.