Moon of Neptune · Updated May 2026
Nereid.
Nereid is one of Neptune's outer moons, just 340 km across. It has one of the most eccentric orbits of any moon (e = 0.75), swinging between 1.4 and 9.7 million km from Neptune across its 360-day year — strong evidence it was captured rather than forming in place.
View Neptune system in 3D →Key facts
Nereid's orbital eccentricity is so extreme that the moon's distance from Neptune varies by a factor of seven across a single orbit.
About Nereid
Nereid was discovered by Gerard Kuiper in 1949 and was, until Voyager 2's 1989 flyby revealed Triton's smaller siblings, the only known moon of Neptune besides Triton itself.
How to view Nereid in 3D
Nereid orbits Neptune in real time inside the interactive viewer. Open the parent body to see the orbital geometry, or use the object browser to fly directly to the moon and observe its rotation, surface, and orbit.
Open the Neptune system →Sources & methodology
Numbers cross-referenced with the sources below; updated May 2026.