Neptune has 13 known moons. The largest by far is Triton, discovered by William Lassell just 17 days after the discovery of Neptune itself. Two moons discovered in 2002 and 2003, as yet unnamed, have the largest orbital radii and longest orbital periods of any moons discovered to date.
The Natural Satellites
Name
(Pronunciation key)
| Diameter (km)
| Mass
(1016 kg)
| Mean orbital radius (km)
| Orbital period** (d)
|
| Neptune III
| Naiad
| nye'-ad
| 58
| ~19
| 48,227
| 0.294
|
| Neptune IV
| Thalassa
| tha-las'-a
| 80
| ~37
| 50,075
| 0.311
|
| Neptune V
| Despina
| des-pee'-na
| 148
| ~210
| 52,526
| 0.335
|
| Neptune VI
| Galatea
| gal'-a-tee'-a
| 158
| ~370
| 61,593
| 0.429
|
| Neptune VII
| Larissa
| la-ris'-a
| 193 (208 × 178)
| ~490
| 73,548
| 0.555
|
| Neptune VIII
| Proteus
| proh'-tee-us
| 418 (436 × 416 × 402)
| ~5,000
| 117,647
| 1.122
|
| Neptune I
| Triton
| trye'-ton
| 2700
| 2,140,000
| 354,800
| -5.877
|
| Neptune II
| Nereid
| neer'-ee-id
| 340
| ~3,100
| 5,513,400
| 360.14
|
|
| S/2002 N 1*
|
| 60
| ~9
| 15,728,000
| -1879.71
|
|
| S/2002 N 2*
|
| 38
| ~9
| 22,422,000
| 2914.07
|
|
| S/2002 N 3*
|
| 38
| ~9
| 23,571,000
| 3167.85
|
|
| S/2003 N 1*
|
| 28
| ~1.5
| 46,695,000
| -9115.91
|
|
| S/2002 N 4*
|
| 60
| ~9
| 48,387,000
| -9373.99
|
* Awaiting confirmation and naming.
** Negative orbital periods indicate a retrograde orbit around Neptune (opposite to the planet's rotation)
Naming notes
Some asteroids share the same names as moons of Neptune: 74 Galatea, 1162 Larissa . Note that Triton did not have an official name until the 20th century. Although the name was suggested in 1880 by Camille Flammarion, it did not come into common use until at least the 1930s. Usually, it was simply known as "the satellite of Neptune" (the second satellite, Nereid, was not discovered until 1949).
See also
