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Physical Properties
210 km
4.4e19 kg
1.3 g/cm³
0.096
Orbit
Neptune
117,647 km
0.00053
0.524°
1.1223 d
Sources & Further Reading
- NASA — official mission / factsheet page
- Wikipedia — extensive cross-referenced article
- NASA u2014 Proteus
Numerical values (radius, mass, orbital elements, temperatures) are drawn from NASA NSSDC Planetary Fact Sheets, JPL Horizons, and the JPL Small-Body Database. Last refreshed: 2026-04-18 18:19:25.
Proteus is Neptune’s second-most-massive moon — too dark to have been seen from Earth, it was discovered only when Voyager 2 flew past Neptune in 1989. Its irregular, heavily cratered shape and very low albedo (~10%) suggest a primitive, carbon-rich body that survived the disruption caused by Triton’s capture.