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Today in History: Hubble Telescope reveals new Plutonian moons Nix, Hydra

10/31/2025

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On October 31, 2005, astronomers announced the discovery of Pluto's moons Nix and Hydra, based on Hubble Space Telescope images taken earlier that year. Nix, named after the Greek goddess of night, measures 49.8 km in diameter, while Hydra, named after the nine-headed serpent, is slightly larger at 51 km.

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Story summary

On October 31, 2005, astronomers announced the discovery of Pluto's moons Nix and Hydra, based on Hubble Space Telescope images taken earlier that year. Nix, named after the Greek goddess of night, measures 49.8 km in diameter, while Hydra, named after the nine-headed serpent, is slightly larger at 51 km.