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Neptune's natural satellites

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).

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