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
Battle of the Lerna Mills Phillips places the number at 250). Prince Demetrios Ypsilantis and several philhellenes volunteered in the defense of the garrison. Protecting Lerna was vital since the mills contained large quantities of grain that supplied food to Nafplion. The mills of Lerna were surrounded by a stone wall that was flanked by a deep pond and a marsh. Moreover, the garrison was supported by two gunboats that were anchored a short distance (or "musket-shot distance") from the shore. Unfortunately, the Greeks did not repair a small break in the stone wall. As a result, a small contingent of Arabs exploited this weakness