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 Greece ordered three new ironclads of the . "Hydra" was ordered from the "Ateliers et Chantiers de la Loire" shipyard in St. Nazaire, France during the premiership of Charilaos Trikoupis. The ship, named for the island of Hydra, was launched in 1889, and by 1892, she and her sister-ships "Spetsai" and "Psara" were delivered to the Greek fleet. The ship was long between perpendiculars and had a beam of and a mean draft of . She displaced as built. She was powered by a pair of steam engines of unknown type; they were rated at and provided a top speed