Hydra imaged by LORRI from 231 000 kilometres
Adjective(s) Hydrian
Orbital properties
Aphelion/apoapsis Unknown
Perihelion/periapsis Unknown
Semi-major axis 64749 km
Orbital eccentricity 0.0051
Orbital period 38.206±0.001 d
Average orbital speed Unknown
Physical properties
Radius 30–84 km
Mass 4.2×1017 kg
Mean density Unknown
Escape velocity Unknown
Rotation period Unknown
Average surface temperature 33–55 K
Apparent magnitude Unknown
Moons 22.9–23.3 (measured)

Hydra is the third moon of the planet Pluto.


  • It is the farthest moon from Pluto.
  • It is most likely slightly larger than Nix, because it appears brighter.
  • It was named after a monster in Greek and Roman mythology.
  • It was discovered in 2005 by the Hubble Space Telescope, along with Nix.

Moons of Pluto