irregular moon · moon of Neptune
Nereid
A moon of Neptune on one of the most stretched-out orbits of any known satellite, swinging far from the planet and back.
- 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
- 340 km
- Mean distance from the planet
- 5,513,900 km
- Orbital period
- 360.1 days (0.99 years)
- Orbital eccentricity
- 0.751
- Orbital inclination
- 5.1°
Source of the figures: JPL SSD – Planetary Satellites (public domain).
Discovery: 1949 – Gerard Kuiper
Description
Nereid was discovered by Gerard Kuiper in 1949, the second moon of Neptune to be found, a century after Triton. Its orbit is one of the most eccentric of any moon in the Solar System, carrying it from relatively close to Neptune out to a great distance. Astronomers suspect it was either captured or thrown onto this path when Triton was captured. Voyager 2 saw Nereid only from far away in 1989, so its shape and surface remain poorly known, though telescopes have detected water ice on it.