Pluto · natural satellite of a dwarf planet

Hydra

Mean diameter: 37 km
Mean orbital distance: 65,200 km from centre
Orbital period: 38.2 Earth days

Compared with our Moon

Hydra · 37 km

Moon · 3,474.8 km

One diameter scale. Circle shapes compare volume-equivalent diameters; irregular moons are not spheres.

Orbit & discovery

Surface gravity: 0.006 m/s²
Discovery: 2005
Discoverer / team: H.A. Weaver, S.A. Stern, M.J. Mutchler, A.J. Steffl, M.W. Buie, W.J. Merline, J.R. Spencer, E.F. Young, L.A. Young
Provisional designation: S/2005 P1
JPL satellite ID: 903
Orbital eccentricity: 0.009
Inclination: 0.3 degrees

Inclination reference: equatorial. Mean-element epoch: 2000-01-01.5 TDB · PLU060.

Diameters use volume-equivalent mean radii, including for irregular bodies. Mean orbital elements describe an orbit; they are not live positions. Missing physical measurements remain unavailable.

Physical measurements & uncertainties

Mean radius · km: 18.5 ±1.0 [3]
GM · km³/s²: 0.0020 ±0.0003 [PLU060]
Density · g/cm³: 1.21 ±0.19 [*]

Missions in the Pluto system · 1 records

1 launches · 0 linked events

These records cover the planetary system. A system mission did not necessarily visit this moon. Dedicated targets are marked separately; programme events include the journey and briefings. Launch outcomes do not establish arrival, landing success or present spacecraft operation.

Dedicated targets only

PLANETARY SYSTEM

New Horizons

January 19, 2006 · UTC

United Launch Alliance · Atlas V 551

1 records from the complete 9,386‑record production catalogue.

Sources & measurements