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 a "salpinx," while a lamb was cast into the waters as an offering for the "Keeper of the Gate." The keeper of the gate to the Underworld that lay in the waters of Lerna was the Hydra. Excavations at the site were initiated under John L. Caskey in 1952, whose efforts initiated the series of publications of Bronze Age Lerna, "Lerna" I-V, inspiring many other publications. Lerna was occupied in Neolithic times, as early as the fifth millennium BCE, then was abandoned for a time before the sequence of occupation from the Early Bronze Age (Helladic period through the Mycenaean).