Just a few decades ago, astronomers thought Pluto was a solitary object, just another ball of ice and rock in the Kuiper Belt. But then in 1978, astronomers discovered that it has a moon half its size, later named Charon.
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But that was just the beginning. Observations in 2005 captured by NASA’s Hubble Space Telescope turned up two additional moons orbiting the dwarf planet. They were provisionally designated X/2005 P1 and S/2005 P2, but later named Hydra and Nix.
Hydra is the outer-most natural satellite of Pluto, orbiting the dwarf planet at a distance of 65,000 km. Unlike the other moons of Pluto, Hydra’s orbit is almost perfectly circular. It takes almost 38 days to orbit Pluto.
The tiny moon measures 61 km across, estimated based on its brightness.
Its final name was announced by the International Astronomical Union on June 21, 2006. In ancient Greek mythology, the hydra was a multi-headed beast who guarded the waters of Pluto/Hades’ underworld.
As with the rest of the Pluto system, Hydra will be imaged by NASA’s New Horizons spacecraft in 2015.
Here’s a link to the constellation Hydra.