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Greek ironclad Hydra fleet, which included "Turgut Reis", "Barbaros Hayreddin", two outdated ironclad battleships, nine destroyers and six torpedo boats, sortied from the Dardanelles at 9:30. The smaller ships remained at the mouth of the straits while the battleships sailed north, remaining near to the coast. The Greek flotilla, which included the armored cruiser "Georgios Averof" and "Hydra" and her sisters, had been sailing from the island of Imbros to the patrol line outside the straits. When the Ottomans were sighted, the Greeks altered course to the northeast, in order to block the advance of their opponents. In the ensuing Naval Battle of