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 On-site techniques of flint-knapping with imported obsidian and chert attest to cultural continuity over this long stretch of time, with reduction in the supply of obsidian from Melos testifying to reduced long-distance trade at the end of Early Helladic III, corresponding to Lerna IV. Lerna has one of the largest prehistoric tumuli of Greece, accumulated during a long Neolithic occupation; then its crest was levelled and extended — as at Early Helladic Eutresis and Orchomenus— in a new settlement: this stratum, called Lerna III in the site's stratigraphy, corresponds with Early Helladic II at other sites. Lerna III lacks signs