Neptune's natural satellites - AbsoluteAstronomy.com

Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...

has thirteen known moons

Natural satellite

A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....

, by far the largest of which is Triton

Triton (moon)

Triton is the largest moon of the planet Neptune, discovered on October 10, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, which is an orbit in the opposite direction to its planet's rotation. At 2,700 km in diameter, it is...

, discovered by William Lassell

William Lassell

William Lassell FRS was an English merchant and astronomer.Born in Bolton and educated in Rochdale after the death of his father, he was apprenticed from 1814 to 1821 to a merchant in Liverpool. He then made his fortune as a beer brewer, which enabled him to indulge his interest in astronomy...

on October 10, 1846, just 17 days after the discovery of Neptune itself. Over a century passed before the discovery of the second natural satellite, called Nereid

Nereid (moon)

Nereid , also known as Neptune II, is the third-largest moon of Neptune. It has a highly eccentric orbit. Nereid was discovered by Gerard Kuiper in 1949 and was the second moon of Neptune to be discovered.- Discovery and naming :...

. Neptune's moons are named for minor water deities

Water deity

A water deity is a deity in mythology associated with water or various bodies of water. Water deities are common in mythology and were usually more important among civilizations in which the sea or ocean, or a great river was more important...

in Greek mythology

Greek mythology

Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

.

Unique among all large planetary moons, Triton is an irregular satellite
Irregular satellite
In astronomy, an irregular moon is a natural satellite following a distant, inclined, and often eccentric and retrograde orbit. They are believed to have been captured by their parent planet, unlike regular satellites, which form in situ....

, as its orbit is retrograde

Retrograde motion

Retrograde motion is motion in the direction opposite to the movement of something else, and is the contrary of direct or prograde motion. This motion can be the orbit of one body about another body or about some other point, or the rotation of a single body about its axis, or other phenomena such...

to Neptune's rotation and inclined

Inclination

Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...

relative to the planet's equator. The next-largest irregular satellite in the Solar System

Solar System

The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

, Saturn

Saturn

Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...

's moon Phoebe

Phoebe (moon)

Phoebe is an irregular satellite of Saturn. It was discovered by William Henry Pickering on 17 March 1899 from photographic plates that had been taken starting on 16 August 1898 at the Boyden Observatory near Arequipa, Peru, by DeLisle Stewart...

, is only 0.03% Triton's mass. Triton is massive enough to have achieved hydrostatic equilibrium

Hydrostatic equilibrium

Hydrostatic equilibrium or hydrostatic balance is the condition in fluid mechanics where a volume of a fluid is at rest or at constant velocity. This occurs when compression due to gravity is balanced by a pressure gradient force...

and to retain a thin atmosphere capable of forming clouds and hazes. Both its atmosphere and its surface are composed mainly of nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

with small amounts of methane

Methane

Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

and carbon monoxide

Carbon monoxide

Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

. Triton's surface appears relatively young, and was probably modified by internally driven processes within the last few million years. The temperature at its surface is about 38 kelvin (-235.2 °C).

Inward of Triton are six regular satellites, all of which have prograde orbits in planes that lie close to Neptune's equatorial plane. Some of these orbit among Neptune's rings

Rings of Neptune

The rings of Neptune consist primarily of five principal rings predicted in 1984 by André Brahic and imaged in 1989 by the Voyager 2 spacecraft...

. The largest of them is Proteus

Proteus (moon)

Proteus , also known as Neptune VIII, is the second largest Neptunian moon, and Neptune's largest inner satellite. Discovered by Voyager 2 spacecraft in 1989, it is named after Proteus, the shape-changing sea god of Greek mythology...

.

Neptune also has six outer irregular satellites, including Nereid, whose orbits are much farther from Neptune, have high inclination

Inclination

s, and are mixed between prograde and retrograde. The two outermost ones, Psamathe

Psamathe (moon)

Psamathe , also known as Neptune X, is a retrograde irregular satellite of Neptune. It is named after Psamathe, one of the Nereids. This moon was discovered by Scott S. Sheppard and David C. Jewitt in 2003 using the 8.2 meter Subaru telescope...

and Neso, have the largest orbits of any natural satellites discovered in the Solar System to date.

Discovery and naming

Discovery

Triton

Triton (moon)

was discovered by William Lassell

William Lassell

in 1846, just seventeen days after the discovery of Neptune

Discovery of Neptune

Neptune was mathematically predicted before it was directly observed. With a prediction by Urbain Le Verrier, telescopic observations confirming the existence of a major planet were made on the night of September 23, 1846, and into the early morning of the 24th, at the Berlin Observatory, by...

. Nereid

Nereid (moon)

was discovered by Gerard P. Kuiper in 1949. The third moon, later named Larissa

Larissa (moon)

Larissa , also known as Neptune VII, is the fifth-closest inner satellite of Neptune. It is named after Larissa, a lover of Poseidon in Greek mythology and eponymous nymph of the city in Thessaly.- Discovery :...

, was first observed by Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky and David J. Tholen

David J. Tholen

David James Tholen is an American astronomer at the Institute for Astronomy of the University of Hawaii, who specializes in planetary and solar system astronomy.-Professional life:...

on May 24, 1981. The astronomers were observing a star's close approach to Neptune, looking for rings similar to those discovered around Uranus

Rings of Uranus

The planet Uranus has a system of rings intermediate in complexity between the more extensive set around Saturn and the simpler systems around Jupiter and Neptune. The rings of Uranus were discovered on March 10, 1977, by James L. Elliot, Edward W. Dunham, and Douglas J. Mink...

four years earlier. If rings were present, the star's luminosity would decrease slightly just before the planet's closest approach. The star's luminosity dipped only for several seconds, which meant that it was due to a moon rather than a ring.

No further moons were found until Voyager 2
Voyager 2
The Voyager 2 spacecraft is a 722-kilogram space probe launched by NASA on August 20, 1977 to study the outer Solar System and eventually interstellar space...

flew by Neptune in 1989. Voyager 2 recovered Larissa and discovered five inner moons: Naiad

Naiad (moon)

Naiad , also known as Neptune III, is the innermost satellite of Neptune, named after the Naiads of Greek legend.Naiad was discovered sometime before mid-September 1989 from the images taken by the Voyager 2 probe. The last moon to be discovered during the flyby, it was designated...

, Thalassa

Thalassa (moon)

Thalassa , also known as Neptune IV, is the second innermost satellite of Neptune. Thalassa was named after sea goddesss Thalassa, a daughter of Aether and Hemera from Greek mythology. "Thalassa" is also the Greek word for "sea"....

, Despina

Despina (moon)

Despina , also known as Neptune V, is the third closest inner satellite of Neptune. It is named after Despoina, a nymph who was a daughter of Poseidon and Demeter....

, Galatea

Galatea (moon)

Galatea , also known as Neptune VI, is the fourth closest inner satellite of Neptune. It is named after Galatea, one of the Nereids of Greek legend.Galatea was discovered in late July 1989 from the images taken by the Voyager 2 probe...

and Proteus

Proteus (moon)

. In 2002 and 2003 two surveys using large ground-based telescopes found five additional outer moons, bringing the total to thirteen. These were Halimede, Sao, Psamathe

Psamathe (moon)

, Laomedeia, and Neso.

Names

Triton did not have an official name until the twentieth century. The name "Triton" was suggested by Camille Flammarion

Camille Flammarion

Nicolas Camille Flammarion was a French astronomer and author. He was a prolific author of more than fifty titles, including popular science works about astronomy, several notable early science fiction novels, and several works about Spiritism and related topics. He also published the magazine...

in his 1880 book Astronomie Populaire, but it did not come into common use until at least the 1930s. Until this time it was usually simply known as "the satellite of Neptune". Other moons of Neptune are also named for Greek and Roman water gods, in keeping with Neptune

Neptune (mythology)

Neptune was the god of water and the sea in Roman mythology and religion. He is analogous with, but not identical to, the Greek god Poseidon. In the Greek-influenced tradition, Neptune was the brother of Jupiter and Pluto, each of them presiding over one of the three realms of the universe,...

's position as god of the sea: either from Greek mythology

Greek mythology

, usually children of Poseidon

Poseidon

Poseidon was the god of the sea, and, as "Earth-Shaker," of the earthquakes in Greek mythology. The name of the sea-god Nethuns in Etruscan was adopted in Latin for Neptune in Roman mythology: both were sea gods analogous to Poseidon...

, the Greek Neptune (Triton, Proteus, Despina, Thalassa); classes of minor Greek water deity (Naiad

Naiad

In Greek mythology, the Naiads or Naiades were a type of nymph who presided over fountains, wells, springs, streams, and brooks....

, Nereid); or specific Nereids (Halimede, Galatea, Neso, Sao, Laomedeia, Psamathe).

Two asteroid

Asteroid

Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...

s share the same names as moons of Neptune: 74 Galatea

74 Galatea

74 Galatea is a large main-belt asteroid. Its surface is very dark in color. Galatea was found by the prolific comet discoverer Ernst Tempel on August 29, 1862, in Marseilles, France. It was his third asteroid discovery. It is named after one of the two Galateas in Greek mythology. A stellar...

and 1162 Larissa

1162 Larissa

1162 Larissa is an outer main belt asteroid orbiting the Sun. Approximately 45 kilometers in diameter, it makes a revolution around the Sun once every 8 years. It was discovered by Karl Wilhelm Reinmuth at Heidelberg, Germany on January 5, 1930. Its provisional designation was 1930 AC.-References:...

Characteristics

The moons of Neptune can be divided into two groups: regular and irregular. The first group includes the six inner moons, which follow circular prograde orbits lying in the equatorial plane of Neptune. The second group consists of all other moons including Triton. They generally follow inclined eccentric and often retrograde orbits far from Neptune; the only exception is Triton, which orbits close to the planet following a circular orbit, though retrograde.

Regular moons

In order of distance from Neptune, the regular moons are Naiad (moon)

Naiad (moon)

, Thalassa (moon)

Thalassa (moon)

, Despina

Despina (moon)

Despina , also known as Neptune V, is the third closest inner satellite of Neptune. It is named after Despoina, a nymph who was a daughter of Poseidon and Demeter....

, Galatea

Galatea (moon)

, Larissa

Larissa (moon)

and Proteus

Proteus (moon)

. Naiad, the closest regular moon, is also the smallest among the inner moons, while Proteus is the largest regular moon. The inner moons are closely associated with Neptune's rings

Rings of Neptune

The rings of Neptune consist primarily of five principal rings predicted in 1984 by André Brahic and imaged in 1989 by the Voyager 2 spacecraft...

. The two innermost satellites, Naiad and Thalassa, orbit between the Galle and LeVerrier rings. Despina may be a shepherd moon of the LeVerrier ring, as its orbit lies just inside this ring.

The next moon, Galatea

Galatea (moon)

, 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 resonance

Orbital resonance

In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...

s between the ring particles and Galatea may also have a role in maintaining the arcs.

Only the two outer 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

Polyhedron

In elementary geometry a polyhedron is a geometric solid in three dimensions with flat faces and straight edges...

, with several flat or slightly concave facets 150 to 250 km in diameter. At about 400 km, it is larger than the Saturnian moon Mimas

Mimas (moon)

Mimas is a moon of Saturn which was discovered in 1789 by William Herschel. It is named after Mimas, a son of Gaia in Greek mythology, and is also designated Saturn I....

, which is fully spherical. 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 geometrical albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

ranges from 7 to 10%. Their spectra

Spectrum

A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...

indicate that they are made from water ice contaminated by some very dark material, probably complex organic compound

Organic compound

An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

s. In this respect, the inner Neptunian moons are similar to the inner moons of Uranus.

Irregular moons

In order of their distance from the planet, the irregular moons are Triton

Triton (moon)

, Nereid

Nereid (moon)

, Halimede, Sao, Laomedeia, Neso and Psamathe

Psamathe (moon)

, a group that includes both prograde and retrograde objects. The five outer moons are similar to the irregular moons of other giant planets.

Triton follows a retrograde and quasi-circular orbit, and is thought to be a gravitationally captured satellite. It is the second known moon in the Solar System to have a substantial atmosphere

Atmosphere

An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

, which is primarily nitrogen

Nitrogen

with small amounts of methane

Methane

and carbon monoxide

Carbon monoxide

. The pressure on Triton's surface is about 14 μbar

Bar (unit)

The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...

. In 1986 the Voyager 2 spacecraft observed what appeared to be clouds and hazes in this thin atmosphere. Triton is one of the coldest bodies in the Solar System, with a surface temperature of about 38 kelvin (-235.2 °C). Its surface is covered by nitrogen, methane, carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

and water ices

Volatiles

In planetary science, volatiles are that group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, and methane, all compounds of C, H, O...

and has a high geometrical albedo of more than 70%. The Bond albedo

Bond albedo

The Bond albedo, named after the American astronomer George Phillips Bond , who originally proposed it, is the fraction of power in the total electromagnetic radiation incident on an astronomical body that is scattered back out into space...

is even higher, reaching up to 90%. Surface features include the large southern polar cap, older cratered planes cross-cut by graben

Graben

In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....

and scarp

Escarpment

An escarpment is a steep slope or long cliff that occurs from erosion or faulting and separates two relatively level areas of differing elevations.-Description and variants:...

s, as well as youthful features probably formed by endogenic processes like cryovolcanism. Voyager 2 observations revealed a number of active geyser

Geyser

A geyser is a spring characterized by intermittent discharge of water ejected turbulently and accompanied by a vapour phase . The word geyser comes from Geysir, the name of an erupting spring at Haukadalur, Iceland; that name, in turn, comes from the Icelandic verb geysa, "to gush", the verb...

s within the polar cap heated by the Sun, which eject plumes to the height of up to 8 km. Triton has a relatively high density of about 2 g/cm³ indicating that rock

Rock (geology)

In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

s constitute about two thirds of its mass, and ices (mainly water ice) the remaining one third. There may be a layer of liquid water deep inside Triton, forming a subterranean ocean.

Nereid is the third largest moon of Neptune. It has a prograde but very eccentric orbit and is believed to be a former regular satellite that was shifted to its current orbit through gravitational interactions during Triton's capture. Water ice has been spectroscopically detected on its surface. Nereid shows irregular large variations of its visible magnitude, which are probably caused by forced precession

Precession

Precession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...

or chaotic rotation combined with an elongated shape and bright or dark spots on the surface.

Among the remaining irregular moons, Sao and Laomedeia follow prograde orbits, while 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 25 years to orbit Neptune at an average of 125 times the distance between Earth and the Moon. Neptune has the largest Hill sphere

Hill sphere

An astronomical body's Hill sphere is the region in which it dominates the attraction of satellites. To be retained by a planet, a moon must have an orbit that lies within the planet's Hill sphere. That moon would, in turn, have a Hill sphere of its own...

in the solar system, owing primarily to its large distance from the Sun; this allows it to retain control of such distant moons.

Formation

The mass distribution of the Neptunian moons is the most lopsided of any group of satellites in the Solar System. One moon, Triton, makes up nearly all of the mass of the system, with all other moons together comprising only one third of one percent. This may be because Triton was captured well after the formation of Neptune's original satellite system, much of which would have been destroyed in the process of capture.

Triton's orbit upon capture would have been highly eccentric, and would have caused chaotic perturbations in the orbits of the original inner Neptunian satellites, causing them to collide and reduce to a disc of rubble. This means it is likely that Neptune's present inner satellites are not the original bodies that formed with Neptune. Only after Triton's orbit became circularised could some of the rubble re-accrete into the present-day regular moons. It is possible that because of this great perturbation, the satellite system of Neptune does not follow the 10,000:1 ratio of mass between the parent planet versus all its moons seen in all other gas giants.

The mechanism of Triton’s capture has been the subject of several theories over the years. One of them postulates that Triton was captured in a three-body

Three-body problem

Three-body problem has two distinguishable meanings in physics and classical mechanics:# In its traditional sense the three-body problem is the problem of taking an initial set of data that specifies the positions, masses and velocities of three bodies for some particular point in time and then...

encounter. In this scenario, Triton is the surviving member of a binary

Binary asteroid

A binary asteroid is a system of two asteroids orbiting their common center of mass, in analogy with binary stars. 243 Ida was the first binary asteroid to be identified when the Galileo spacecraft did a flyby in 1993...

disrupted by its encounter with Neptune.

Numerical simulations show that there is a 0.41 probability that the moon Halimede collided with Nereid at some time in the past. Although it is not known whether any collision has taken place, both moons appear to have similar ("grey") colors, implying that Halimede could be a fragment of Nereid.

Table

Key
^‡ Prograde irregular moons	^♠ Retrograde irregular moons

The Neptunian moons are listed here by orbital period, from shortest to longest. Irregular (captured) moons are marked by color.

Neptunian moons
Order Order refers to the position among other moons with respect to their average distance from Neptune.	Name	Pronunciation (key)	Semi-major axis Semi-major axis The major axis of an ellipse is its longest diameter, a line that runs through the centre and both foci, its ends being at the widest points of the shape... (km)	Orbital period Orbital period The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of... (d Day A day is a unit of time, commonly defined as an interval equal to 24 hours. It also can mean that portion of the full day during which a location is illuminated by the light of the sun... )	Inclination Inclination Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit... (° Degree (angle) A degree , usually denoted by ° , is a measurement of plane angle, representing 1⁄360 of a full rotation; one degree is equivalent to π/180 radians... )Each moon's inclination is given relative to its local Laplace plane Laplace plane The Laplace plane or Laplacian plane of a planetary satellite, named after its discoverer Pierre-Simon Laplace , is a mean or reference plane about whose axis the instantaneous orbital plane of a satellite precesses.... . Inclinations greater than 90° indicate retrograde orbits (in the direction opposite to the planet's rotation).	Eccentricity Orbital eccentricity The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...	Discovery year	Discoverer
1	Naiad Naiad (moon) Naiad , also known as Neptune III, is the innermost satellite of Neptune, named after the Naiads of Greek legend.Naiad was discovered sometime before mid-September 1989 from the images taken by the Voyager 2 probe. The last moon to be discovered during the flyby, it was designated...	ˈneɪ.əd	48,227	0.294	4.691	0.0003	1989	Voyager Science Team
2	Thalassa Thalassa (moon) Thalassa , also known as Neptune IV, is the second innermost satellite of Neptune. Thalassa was named after sea goddesss Thalassa, a daughter of Aether and Hemera from Greek mythology. "Thalassa" is also the Greek word for "sea"....	θəˈlæsə	50,074	0.311	0.135	0.0002	1989	Voyager Science Team
3	Despina Despina (moon) Despina , also known as Neptune V, is the third closest inner satellite of Neptune. It is named after Despoina, a nymph who was a daughter of Poseidon and Demeter....	dɨsˈpiːnə	52,526	0.335	0.068	0.0002	1989	Voyager Science Team
4	Galatea Galatea (moon) Galatea , also known as Neptune VI, is the fourth closest inner satellite of Neptune. It is named after Galatea, one of the Nereids of Greek legend.Galatea was discovered in late July 1989 from the images taken by the Voyager 2 probe...	ˌɡæləˈtiːə	61,953	0.429	0.034	0.0001	1989	Voyager Science Team
5	Larissa Larissa (moon) Larissa , also known as Neptune VII, is the fifth-closest inner satellite of Neptune. It is named after Larissa, a lover of Poseidon in Greek mythology and eponymous nymph of the city in Thessaly.- Discovery :...	ləˈrɪsə	73,548	0.555	0.205	0.0014	1981	H. Reitsema, W. Hubbard, L. Lebofsky, and D. J. Tholen
6	Proteus Proteus (moon) Proteus , also known as Neptune VIII, is the second largest Neptunian moon, and Neptune's largest inner satellite. Discovered by Voyager 2 spacecraft in 1989, it is named after Proteus, the shape-changing sea god of Greek mythology...	ˈproʊtiəs	117,646	1.122	0.075	0.0005	1989	Voyager Science Team
7	Triton Triton (moon) Triton is the largest moon of the planet Neptune, discovered on October 10, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, which is an orbit in the opposite direction to its planet's rotation. At 2,700 km in diameter, it is... ^♠	ˈtraɪtən	354,759	5.877	156.865	0.0000	1846	W. Lassell William Lassell William Lassell FRS was an English merchant and astronomer.Born in Bolton and educated in Rochdale after the death of his father, he was apprenticed from 1814 to 1821 to a merchant in Liverpool. He then made his fortune as a beer brewer, which enabled him to indulge his interest in astronomy...
8	Nereid Nereid (moon) Nereid , also known as Neptune II, is the third-largest moon of Neptune. It has a highly eccentric orbit. Nereid was discovered by Gerard Kuiper in 1949 and was the second moon of Neptune to be discovered.- Discovery and naming :... ^‡	ˈnɪəriː.ɪd	5,513,818	360.136	7.090	0.7507	1949	G.P. Kuiper
9	Halimede^♠	ˌhælɨˈmiːdiː	16,611,000	1,879.08	112.712	0.2646	2002	M. Holman Matthew J. Holman Matthew J. Holman is a Smithsonian Astrophysicist and lecturer at Harvard University. Holman studied at MIT, where he received his bachelor's degree in mathematics in 1989 and his PhD in planetary science in 1994.... , J. Kavelaars John J. Kavelaars John J. Kavelaars, better known as JJ Kavelaars, is a Canadian astronomer who was part of a team that discovered several moons of Jupiter, Saturn, Uranus, and Neptune.... , T. Grav, W. Fraser, and D. Milisavljevic Dan Milisavljevic Dan Milisavljevic is a Canadian astronomer known for aiding in the discovery of Uranus's moons Ferdinand, Trinculo, and Francisco; and Neptune's moons Halimede, Sao, Laomedeia and Neso....
10	Sao^‡	ˈseɪ.oʊ	22,228,000	2,912.72	53.483	0.1365	2002	M. Holman, J. Kavelaars, T. Grav, W. Fraser, and D. Milisavljevic
11	Laomedeia^‡	ˌleɪ.ɵmɨˈdiːə	23,567,000	3,171.33	37.874	0.3969	2002	M. Holman, J. Kavelaars, T. Grav, W. Fraser, and D. Milisavljevic
12	Psamathe Psamathe (moon) Psamathe , also known as Neptune X, is a retrograde irregular satellite of Neptune. It is named after Psamathe, one of the Nereids. This moon was discovered by Scott S. Sheppard and David C. Jewitt in 2003 using the 8.2 meter Subaru telescope... ^♠	ˈsæməθiː	48,096,000	9,074.30	126.312	0.3809	2003	S.S. Sheppard Scott S. Sheppard Scott S. Sheppard is an astronomer in the Department of Terrestrial Magnetism at the Carnegie Institution for Science. Starting as a graduate student at the Institute for Astronomy at the University of Hawaii, he was credited with the discovery of many small moons of Jupiter, Saturn, Uranus, and... , D.C. Jewitt David C. Jewitt David C. Jewitt is a professor of astronomy formerly at the University of Hawaii Institute for Astronomy, now at UCLA. He was born in 1958 in England, and is a 1979 graduate of the University of London. Jewitt received an M.Sc. and a Ph.D. in astronomy at the California Institute of Technology in... , and J. Kleyna Jan Kleyna Jan Kleyna is a postdoctoral astronomy researcher at the University of Hawaii Institute for Astronomy. His area of interest is galaxy dynamics, and he has worked to develop codes for the real-time detection of moving objects such as Jovian satellites. He has also co-discovered several of...
13	Neso^♠	ˈniːsoʊ	49,285,000	9,740.73	136.439	0.5714	2002	M. Holman, J. Kavelaars, T. Grav, W. Fraser, and D. Milisavljevic

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