Moon of Neptune
Triton
A captured world orbiting Neptune backward.
Triton is the only large moon in the solar system that orbits backward, opposite to its planet's rotation. That retrograde path suggests Neptune captured it from the Kuiper Belt long ago. It is tidally locked, but its tilted orbit lets both poles take turns facing the Sun.
How it moves
- Triton orbits Neptune every 5.877 days at about 354,760 km.
- Its orbit is retrograde, inclined 157.3 degrees to Neptune's equator.
- The orbit is almost perfectly circular (eccentricity 0.000016).
- It is tidally locked to Neptune, yet both polar regions take turns facing the Sun.
Facts
- Mean radius
- 1,352.6 km
- Mass
- 2.140e+22 kg
- Surface gravity
- 0.781 m/s²
- Rotation period
- 141.044 hours
- Orbital period
- 5.877 days
- Average orbital distance
- 354,760 km
- Eccentricity
- 0.000016
- Discovered
- October 10, 1846, by William Lassell, 17 days after Neptune was found
Triton has geysers that shoot icy material more than 8 km high, even at about -235 C.
Sources: nssdc.gsfc.nasa.gov, ssd.jpl.nasa.gov, ssd.jpl.nasa.gov