Space · Moons
Neso
A moon of Neptune — The farthest-orbiting moon of any planet in the solar system — orbital radius 50 million km.
Quick facts
Parent planet
Diameter (mean)
60 km
Mass
1.5 × 10¹⁷ kg
2e-06 Moon masses
Mean orbital radius
50,258,000 km
Orbital period
9740.7 Earth days
Discovery year
2002
Discoverer
Matthew J. Holman et al.
Naming origin
One of the Nereids
Surface conditions
Neso has the largest orbit of any known moon of any planet — 50 million km from Neptune, a 27-year orbital period. The orbit is so eccentric that at apoapsis Neso is 72 million km from Neptune — farther than Mercury is from the Sun.
Missions and observations
Every Neptune-system mission has had an opportunity to image or characterize Neso. The list below is the Neptune-system mission catalog; specific Neso encounters are documented in mission archives.
| Mission | Year at Neptune | Status |
|---|---|---|
|
Voyager 2 NASA |
1989 | Completed |
Naming etymology
Neso was a Nereid sea nymph. Adopted by the IAU in 2007.
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.