Space · Moons
Proteus
A moon of Neptune — Neptune's second-largest moon — heavily cratered, irregularly shaped, and dark.
Quick facts
Parent planet
Diameter (mean)
420 km
Mass
5.04 × 10¹⁹ kg
0.000686 Moon masses
Mean orbital radius
117,647 km
Orbital period
1.122 Earth days
Discovery year
1989
Discoverer
Voyager 2 imaging team
Naming origin
Greek shape-shifting sea god
Surface conditions
Proteus is Neptune's second-largest moon, an irregularly-shaped 420-km body. The surface is dark (albedo 0.10) and heavily cratered. The dominant impact feature is Pharos, a 230-km crater. Proteus is so dark that ground-based telescopes never detected it; Voyager 2 found it during the 1989 flyby.
Missions and observations
Every Neptune-system mission has had an opportunity to image or characterize Proteus. The list below is the Neptune-system mission catalog; specific Proteus encounters are documented in mission archives.
| Mission | Year at Neptune | Status |
|---|---|---|
|
Voyager 2 NASA |
1989 | Completed |
Naming etymology
Proteus was the shape-shifting sea god of Greek mythology, who would change form to escape capture. The IAU adopted the name in 1991.
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.