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 ironclad Hydra heavy service with the Greek Navy. They participated in the Greco–Turkish War in 1897 until the Great Powers intervened and prevented the Greek Navy from capitalizing on their superiority over the Ottoman Navy. "Hydra" saw action in the First Balkan War at the Naval Battle of Elli and was present at the Naval Battle of Lemnos, but was too slow to actively engage the Ottoman forces. She did not see action during World War I, and was reduced to a gunnery training ship after the end of the war. She was ultimately broken up for scrap in 1929. In 1885,