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HYDRA

A small, elongated moon of Pluto discovered with the Hubble Space Telescope and observed by New Horizons in 2015.
THE OUTER MOON
Hydra is one of Pluto's five known moons. It was discovered in 2005 using the Hubble Space Telescope. The moon is named after the Hydra, a many-headed serpent from Greek mythology. Hydra has an elongated, irregular shape and is located farther from Pluto than Charon, Styx and Nix. The New Horizons spacecraft photographed Hydra during its historic flyby of the Pluto system in July 2015.
~65 × 45 km
APPROXIMATE DIMENSIONS
38.2 DAYS
ORBITAL PERIOD
~64,700 km
AVERAGE DISTANCE FROM PLUTO
2005
DISCOVERED
IRREGULAR
SHAPE
2015
NEW HORIZONS OBSERVATION
AN ICY AND ELONGATED WORLD
Hydra is a small icy moon orbiting the Pluto-Charon system. Its elongated shape shows that Hydra is not massive enough for its own gravity to make it spherical. New Horizons revealed that Hydra has a highly reflective surface, suggesting that it is covered with relatively clean water ice. Hydra also rotates in a chaotic way. Unlike Earth's Moon, it does not keep the same side facing Pluto. Its rotation is affected by the complex gravitational field created by Pluto and Charon. Hydra is the outermost of Pluto's five known moons.
HYDRA FEATURES
WATER ICE
Hydra has a highly reflective surface that is consistent with abundant water ice.
CHAOTIC ROTATION
Hydra can change its orientation unpredictably because of the gravitational influence of Pluto and Charon.
NEW HORIZONS
New Horizons photographed Hydra during its 2015 flyby, providing the first close-up observations of the moon.
DID YOU KNOW?
Hydra is the outermost known moon of Pluto and has a surface that reflects a large amount of sunlight.
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