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
Lerna Lerna In classical Greece, Lerna () was a region of springs and a former lake near the east coast of the Peloponnesus, south of Argos. Even though much of the area is marshy, Lerna is located on a geographically narrow point between mountains and the ocean, along an ancient route from the Argolid to the southern Peloponnese; this location could have potentially resulted in the importance of the settlement. Its site near the village Mili at the Argolic Gulf is most famous as the lair of the Lernaean Hydra, the chthonic many-headed water snake, a creature of great antiquity when