Space · Moons
Nereid
A moon of Neptune — An unusual orbit — the most eccentric of any major moon, ranging from 1.4 to 9.6 million km from Neptune.
Quick facts
Parent planet
Diameter (mean)
340 km
Mass
3.1 × 10¹⁹ kg
0.000421 Moon masses
Mean orbital radius
5,513,400 km
Orbital period
360.13 Earth days
Discovery year
1949
Discoverer
Gerard P. Kuiper
Naming origin
Sea nymphs of Greek mythology
Surface conditions
Nereid has the most eccentric orbit of any major moon in the solar system (eccentricity 0.75), ranging from 1.4 million km to 9.6 million km from Neptune over its 360-day orbital period. This extreme orbit, together with Triton's retrograde orbit, suggests that Triton's capture disrupted Neptune's primordial satellite system; Nereid may be either a captured asteroid or a survivor of that disruption.
Missions and observations
Every Neptune-system mission has had an opportunity to image or characterize Nereid. The list below is the Neptune-system mission catalog; specific Nereid encounters are documented in mission archives.
| Mission | Year at Neptune | Status |
|---|---|---|
|
Voyager 2 NASA |
1989 | Completed |
Naming etymology
The Nereids were the fifty sea nymphs of Greek mythology, daughters of the sea god Nereus. The name 'Nereid' is the singular form. Gerard Kuiper discovered the moon in 1949 and proposed the name himself.
Methodology & sources
Diameter, mass, and orbital parameters from JPL Solar System Dynamics — Physical Parameters. Discovery year and discoverer from the JPL Satellite Discovery Circumstances. Naming etymology from the IAU Working Group for Planetary System Nomenclature. Stylized SVG hero composed from NASA / JPL imagery as visual reference; no photographs are reproduced.