Moons of Neptune

name mean distance from centre of Neptune (orbital radius; km) orbital period (sidereal period; Earth days)* inclination of orbit to planet's equator (degrees) eccentricity of orbit

Naiad 48,227 0.2944R 4.75 0.0004

Thalassa 50,075 0.3115R 0.21 0.0002

Despina 52,526 0.3347R 0.22 0.0002

Galatea 61,953 0.4287R 0.05 0

Larissa 73,548 0.5548R 0.25 0.0014

Proteus 117,647 1.1223R 0.52 0.0005

Triton 354,800 5.8768R 157.3 0

Nereid 5,513,400 360.1468R 32.6 0.7512

Halimede 15,728,000 1,879.71R 134.1 0.5711

Sao 22,422,000 2,914.07R 48.5 0.2931

Laomedeia 23,571,000 3,167.85R 35 0.4237

Psamathe 46,695,000 9,115.91R 146.6 0.4499

Neso 48,387,000 9,373.99R 132 0.4945

name rotation period (Earth days)** radius or radial dimensions (km) mass (10²⁰ kg)*** mean density (g/cm³)

Naiad likely sync. 48×30×26 (0.002)

Thalassa likely sync. 54×50×26 (0.004)

Despina likely sync. 90×74×64 (0.02)

Galatea likely sync. 102×92×72 (0.04)

Larissa likely sync. 108×102×84 (0.05)

Proteus likely sync. 220×208×202 (0.5)

Triton sync. 1,353.40 214 2.061

Nereid not sync. 170 (0.3)

Halimede 31 (0.001)

Sao 22 (0.001)

Laomedeia 21 (0.001)

Psamathe 20 (0.0002)

Neso 30 (0.001)

*R following the quantity indicates a retrograde orbit.

**Sync. = synchronous rotation; the rotation and orbital periods are the same.

***Mass values in parentheses are poorly known.