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 destroyer Hydra 1940). During the German invasion of Greece, she was attacked by German bomber aircraft on April 22, 1941 and sunk near the island of Lagousa in the Saronic Gulf, together with her commander, Cmdr. Th. Pezopoulos and 41 members of her crew. Greek destroyer Hydra Hydra () was a Greek destroyer of the "Dardo" class, which served with the Hellenic Navy during the early stages of the Second World War. It was named after the Saronic Gulf island of Hydra, which played an important role in the Greek War of Independence, and was the fourth ship to bear this name.