inner moon · moon of Neptune
Larissa
A small, irregular inner moon of Neptune, confirmed by Voyager 2 and slowly spiralling inward toward the planet.
- Distance from Earth today
- 4.35 billion km29.08 AU · light: 4 h 2 min
- Distance from the Sun today
- 4.47 billion km29.88 AU
- As of
- 2 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
- 192 km
- Mass
- 3.82 × 10¹⁸ kg
- Density
- 1,030 kg/m³
- Mean distance from the planet
- 73,600 km
- Orbital period
- 13.3 h
- Orbital eccentricity
- 0.0010
- Orbital inclination
- 0.2°
Source of the figures: JPL SSD – Planetary Satellites (public domain).
Discovery: 1989 – Voyager science team
Description
Larissa is one of Neptune's small inner moons, orbiting just inside the path of Proteus. It may have been glimpsed in 1981 when it briefly blocked the light of a star, but it was confirmed and catalogued only after Voyager 2 imaged it in 1989. Voyager's pictures show an elongated, cratered body with no sign of geological activity. Its orbit lies inside the distance at which a moon circles as fast as Neptune spins, so tidal forces are gradually drawing it closer to the planet.