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
Drakaina (mythology) generally slain only by gods or demigods. Zeus slew Delphyne and Campe, Apollo slew Python, and Argus Panoptes slew Echidna. Echidna was the mother of a huge brood of monsters, including other dragon-like creatures. According to Hesiod, Echidna gave birth to Cerberus, Orthrus, the Chimera, the Nemean lion, the Sphinx and the Hydra. (Other ancient authors, such as Hyginus, attribute even more monsters as children of Echidna such as the Caucasian eagle, the Crommyonian Sow, the Colchian dragon, the Harpies and Scylla.) Drakaina (mythology) In Greek mythology, a drakaina () is a female serpent or dragon, sometimes with humanlike features.