Moons of Neptune

The planet Neptune has 14 known moons, which are named for minor water deities in Greek mythology. By far the largest of them is Triton, discovered by William Lassell on October 10, 1846, 17 days after the discovery of Neptune itself. Over a century passed before the discovery of the second natural satellite, Nereid. Neptune's outermost moon Neso, which has an orbital period of about 27 Julian years, orbits farther from its planet than any other moon in the Solar System.
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Moons of Mars
Moons of Jupiter
Moons of Saturn
Moons of Uranus
Moons of Neptune
Moons of Pluto
Moons of Haumea
==Groups==
===Regular Moons===
In order of distance from Neptune, the regular moons are Naiad, Thalassa, Despina, Galatea, Larissa, Hippocamp, and Proteus. All but the outer two are within Neptune-synchronous orbit (Neptune's rotational period is 0.6713 day or 16 hours) and thus are being tidally decelerated. Naiad, the closest regular moon, is also the second smallest among the inner moons (following the discovery of Hippocamp), whereas Proteus is the largest regular moon and the second largest moon of Neptune. The first five moons orbit much faster than Neptune's rotation itself ranging from 7 hours for Naiad and Thalassa, to 13 hours for Larissa.
The inner moons are closely associated with Neptune's rings. The two innermost satellites, Naiad and Thalassa, orbit between the Galle and LeVerrier rings. Despina may be a shepherd moon of the LeVerrier ring, because its orbit lies just inside this ring. The next moon, Galatea, orbits just inside the most prominent of Neptune's rings, the Adams ring. This ring is very narrow, with a width not exceeding 50 km, and has five embedded bright arcs. The gravity of Galatea helps confine the ring particles within a limited region in the radial direction, maintaining the narrow ring. Various resonances between the ring particles and Galatea may also have a role in maintaining the arcs.
Only the two largest regular moons have been imaged with a resolution sufficient to discern their shapes and surface features. Larissa, about 200 km in diameter, is elongated. Proteus is not significantly elongated, but not fully spherical either: it resembles an irregular polyhedron, with several flat or slightly concave facets 150 to 250 km in diameter. At about 400 km in diameter, it is larger than the Saturnian moon Mimas, which is fully ellipsoidal. This difference may be due to a past collisional disruption of Proteus. The surface of Proteus is heavily cratered and shows a number of linear features. Its largest crater, Pharos, is more than 150 km in diameter.
All of Neptune's inner moons are dark objects: their geometric albedo ranges from 7 to 10%. Their spectra indicate that they are made from water ice contaminated by some very dark material, probably complex organic compounds. In this respect, the inner Neptunian moons are similar to the inner Uranian moons.
===Irregular Moons===
In order of their distance from the planet, the irregular moons are Triton, Nereid, Halimede, Sao, Laomedeia, Psamathe, and Neso, a group that includes both prograde and retrograde objects. The five outermost moons are similar to the irregular moons of other giant planets, and are thought to have been gravitationally captured by Neptune, unlike the regular satellites, which probably formed in situ.
Triton and Nereid are unusual irregular satellites and are thus treated separately from the other five irregular Neptunian moons, which are more like the outer irregular satellites of the other outer planets. Firstly, they are the largest two known irregular moons in the Solar System, with Triton being almost an order of magnitude larger than all other known irregular moons. Secondly, they both have atypically small semi-major axes, with Triton's being over an order of magnitude smaller than those of all other known irregular moons. Thirdly, they both have unusual orbital eccentricities: Nereid has one of the most eccentric orbits of any known irregular satellite, and Triton's orbit is a nearly perfect circle. Finally, Nereid also has the lowest inclination of any known irregular satellite.
===Normal Irregular Moons===
Among the remaining irregular moons, Sao and Laomedeia follow prograde orbits, whereas Halimede, Psamathe and Neso follow retrograde orbits. Given the similarity of their orbits, it was suggested that Neso and Psamathe could have a common origin in the break-up of a larger moon. Psamathe and Neso have the largest orbits of any natural satellites discovered in the Solar system to date. They take over 25 years to orbit Neptune at an average of 125 times the distance between Earth and the Moon. Neptune has the largest Hill sphere in the Solar System, owing primarily to its large distance from the Sun; this allows it to retain control of such distant moons. Nevertheless, the Jovian moons in the Carme and Pasiphae groups orbit at a greater percentage of their primary's Hill radius than Psamathe and Neso.
Key
Inner Regular	Prograde Irregular	Retrograde Irregular
  	‡ 	♠
==List==
Roman Numeral	Name 	Diameter 	Gravity 	Escape Velocity	Orbital Period 	Group Label	Date of Discovery
- 	Neptune 	~49,244 km 	11.15 m/s2 	23.5 km/s 	165 earth years 	- 	September 23, 1846
I 	Triton 	2705.2±4.8 	0.779 m/s2 	1.455 km/s 	5.8769 days 	♠ 	October 10, 1846
II 	Nereid 	357 ± 13 km	? 	? 	360.14 days 	‡ 	May 1, 1949
III 	Naiad 	60.4 km 	? 	? 	0.29544 days 	  	September 1989
IV 	Thalassa 	81.4 km 	? 	? 	0.135 days 	  	September 1989
V 	Despina 	156 km 	~0.026 m/s2	~0.063 km/s 	0.3346 days 	  	September 1989
VI 	Galatea 	174.8 km 	~0.018 m/s2	~0.056 km/s 	0.2487 days 	  	September 1989
VII 	Larissa 	194 km 	~0.03 m/s2 	~0.076 km/s 	0.556 days 	  	May 24, 1981
VIII 	Proteus 	420 km 	0.07 m/s2 	0.17 km/s 	1.1223 days 	  	September 1989
IX 	Halimede 	62 km 	? 	? 	5.14 earth years 	♠ 	August 14, 2002
X 	Psamathe 	40 km 	? 	? 	25.06 earth years	♠ 	August 19, 2003
XI 	Sao 	44 km 	? 	? 	7.9 earth years 	‡ 	August 14, 2002
XII 	Laomedeia	42 km 	? 	? 	8.7 earth years 	‡ 	February 3, 2002
XIII 	Neso 	60 km 	? 	? 	26.8 earth years 	♠ 	August 14, 2002
XIV 	Hippocamp	34.8±4.0 	? 	? 	0.95 days 	  	July 1, 2013
=== Unconfirmed Satellites ===
Unconfirmed Satellites
Name 	Apparent Magnitude	Diameter	Discovery Year	Remarks
c02N4	25.3 	≈ 33 	2002 	Possibly a centaur or irregular satellite candidate; was detected in August and September 2002 before being subsequently lost after failed attempts to recover the object
== Gallery ==
File:Proteus.jpg|Proteus
File:TRITON.jpg|Triton
File:Psamathe.png|Psamathe
File:Neso.gif|Neso
File:Sao.gif|Sao
File:Neptune Trio.jpg|Three Moons in One Frame
File:Galatea.jpg|Galatea
File:Larissa.jpg|Larissa
File:Naiad.png|Naiad
File:Hippocamp.jpg|Hippocamp
File:Nereid.jpg|Nereid
File:Halimede.jpg|Halimede
File:Laomedeia.gif|Laomedeia
File:Despina.jpg|Despina
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