Hydra (moon) the Hydra, the nine-headed serpent that battled Heracles in Greek mythology. The nine heads of Hydra are a reference to Pluto's tenure as the ninth planet; its initial, "H", refers to the Hubble Telescope, which discovered Hydra and, together with Nix, to the "New Horizons" mission whose safe passage was the motivation for taking the Hubble images. Hydra orbits the barycenter of the system in the same plane as Charon and Nix, at a distance of about 65,000 km. Its eccentricity of 0.0059 is small, but significantly non-zero, and the largest of those of Pluto's small moons (slightly larger than
Greek mythology subterranean house of Hades and his predecessors, home of the dead. Influences from other cultures always afforded new themes. According to Classical-era mythology, after the overthrow of the Titans, the new pantheon of gods and goddesses was confirmed. Among the principal Greek gods were the Olympians, residing on Mount Olympus under the eye of Zeus. (The limitation of their number to twelve seems to have been a comparatively modern idea.) Besides the Olympians, the Greeks worshipped various gods of the countryside, the satyr-god Pan, Nymphs (spirits of rivers), Naiads (who dwelled in springs), Dryads (who were spirits of the trees),