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
Hydra (constellation) to legend, if one of the hydra's heads was cut off, two more would grow in its place. However, Hercules burned out the roots of the heads he severed to prevent them from growing again, and thus overcame the hydra. In Hindu Mythology the star that equivalents Hydra is Ashlesha. In Chinese astronomy, the stars that correspond to Hydra are located within the Vermilion Bird and the Azure Dragon. In Japanese culture, the stars are known as Nuriko. Despite its size, Hydra contains only one reasonably bright star, Alphard, designated Alpha Hydrae. It is an orange giant of magnitude 2.0,