Hydra
Pluto's outermost known moon, its surface almost pure water ice.
Where it is right now
Hydra is in Capricornus, 34.6 AU away.
Computed for 2 August 2026, 20:00 UTC, and recomputed at least hourly. This page is cached, so treat the line above as accurate to the hour rather than to the second. The map shows the live position.
Position from a Kepler propagation of the published elements below, accurate to about an arcminute.
Facts
Every line carries the source it came from.
- Mean radius
- 18.5 kmSource: NASA/JPL Planetary Satellite Physical Parameters
- Orbits
- Pluto, 65,200 km out on averageSource: NASA/JPL Planetary Satellite Mean Elements
- Orbital period
- 38.2 daysSource: NASA/JPL Planetary Satellite Mean Elements
- Orbit shape
- eccentricity 0.0090, inclined 0.30 degrees to Pluto's equatorSource: NASA/JPL Planetary Satellite Mean Elements
- Discovered
- 2005 by 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. YoungSource: NASA/JPL Planetary Satellite Discovery Circumstances
Physical size
- Mean radius
- 18.5 km
- Diameter
- 37 km across
Orbit
Elements are relative to 134340 Pluto.
- Average distance from 134340 Pluto
- 65,200 km
- Eccentricity
- 0.0090, almost perfectly circular
- Inclination to 134340 Pluto's reference plane
- 112.62 degrees
- Orbital period
- 38.2 days
- Longitude of ascending node
- 227.59 degrees
- Argument of periapsis
- 270.81 degrees
- Mean anomaly at J2000.0
- 335.00 degrees
Family
Orbits 134340 Pluto.
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Catalog id hydra. 3,172 objects on the map, of which 171 are hand-authored with sourced facts.