major moon · moon of Neptune
Triton
Neptune's largest moon, orbiting backwards – probably a captured Kuiper belt world with nitrogen geysers and a frozen surface.
- Distance from Earth today
- 4.35 billion km29.11 AU · light: 4 h 2 min
- Distance from the Sun today
- 4.47 billion km29.88 AU
- As of
- 4 November 2026position from NASA/JPL orbital elements
Where it is today
Top view of the plane of Earth’s orbit, compressed distance scale. Open on the big map with the time slider →
Facts
- Diameter
- 2,705 km
- Mass
- 21,403 × 10¹⁸ kg
- Density
- 2,065 kg/m³
- Mean distance from the planet
- 354,800 km
- Orbital period
- 5.88 days
- Orbital eccentricity
- 0.0000
- Orbital inclination
- 157.3°
Source of the figures: JPL SSD – Planetary Satellites (public domain).
Discovery: 1846 – William Lassell
Description
Triton is by far the largest moon of Neptune, discovered by William Lassell in 1846, only weeks after the planet itself was found. It is the only large moon in the Solar System that orbits in the direction opposite to its planet's rotation, which strongly suggests it was captured from the Kuiper belt. Its surface is one of the coldest measured anywhere, covered in frozen nitrogen, and includes a strange wrinkled area nicknamed the "cantaloupe terrain". During its 1989 flyby, Voyager 2 spotted dark plumes rising from geyser-like vents and a thin nitrogen atmosphere. Tidal forces are slowly pulling Triton inward.