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 Nereids (who inhabited the sea), river gods, Satyrs, and others. In addition, there were the dark powers of the underworld, such as the Erinyes (or Furies), said to pursue those guilty of crimes against blood-relatives. In order to honor the Ancient Greek pantheon, poets composed the Homeric Hymns (a group of thirty-three songs). Gregory Nagy regards "the larger Homeric Hymns as simple preludes (compared with "Theogony"), each of which invokes one god". The gods of Greek mythology are described as having essentially corporeal but ideal bodies. According to Walter Burkert, the defining characteristic of Greek anthropomorphism is that "the Greek