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 the existence of this corpus of data is a strong indication that many elements of Greek mythology have strong factual and historical roots. Mythical narration plays an important role in nearly every genre of Greek literature. Nevertheless, the only general mythographical handbook to survive from Greek antiquity was the "Library" of Pseudo-Apollodorus. This work attempts to reconcile the contradictory tales of the poets and provides a grand summary of traditional Greek mythology and heroic legends. Apollodorus of Athens lived from to and wrote on many of these topics. His writings may have formed the basis for the collection; however the