This is an old revision of this page, as edited by Dawnseeker2000 at 10:06, 16 January 2009 (Reverted to revision 264418585 by 22.214.171.124. using TW). The present address (URL) is a permanent link to this revision, which may differ significantly from the .
Neptune from Voyager 2
|Discovered by||Urbain Le Verrier|
John Couch Adams
|Discovery date||September 23, 1846|
Average orbital speed
6.43° to Sun's equator
|24,764 ± 15 km|
|24,341 ± 30 km|
|Flattening||0.0171 ± 0.0013|
Sidereal rotation period
16 h 6 min 36 s
Equatorial rotation velocity
North pole right ascension
|19h 57m 20s|
North pole declination
|8.0 to 7.78|
|19.7 ± 0.6 km|
|Composition by volume|
Neptune (pronounced /ˈnɛptjuːn/ (deprecated template) [AmE: [ˈnɛptun] (help·info)]) is the eighth and farthest planet from the Sun in the Solar System. 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 Earth masses and less dense. The planet is named after the Roman god of the sea. Its astronomical symbol is , a stylized version of the god Neptune's trident.
Discovered on September 23, 1846, Neptune was the only planet found by mathematical prediction rather than regular observation. Unexpected changes in the orbit of Uranus led astronomers to deduce the gravitational perturbation of an unknown planet. Neptune was found within a degree of the predicted position. The moon Triton was found shortly thereafter, but none of the planet's other 12 moons was discovered before the 20th century. Neptune has been visited by only one spacecraft, Voyager 2, which flew by the planet on August 25, 1989.
Neptune is similar in composition to Uranus, and both have compositions which differ from those of the larger gas giants Jupiter and Saturn. As such, astronomers sometimes place Uranus and Neptune in a separate category, the "ice giants". Neptune's atmosphere, while similar to Jupiter's and Saturn's in being composed primarily of hydrogen and helium, contains a higher proportion of "ices" such as water, ammonia and methane, along with the usual traces of hydrocarbons and possibly nitrogen. In contrast, the interior of Neptune is mainly composed of ices and rocks like that of Uranus. Traces of methane in the outermost regions in part account for the planet's blue appearance.
Neptune has the strongest winds of any planet in the Solar System, measured as high as 2,100 kilometres per hour (1,300 mph). At the time of the 1989 Voyager 2 flyby, its southern hemisphere possessed a Great Dark Spot comparable to the Great Red Spot on Jupiter. Neptune's temperature at its cloud tops is usually close to −218 degrees Celsius (55.1 kelvins), one of the coldest in the Solar System, due to its great distance from the Sun. The temperature at Neptune's centre is about 7,000 K (7,000 °C), which is comparable to that at the Sun's surface and similar to that at the centre of most of the other planets of the Solar System. Neptune has a faint and fragmented ring system, which may have been detected during the 1960s but was only indisputably confirmed by Voyager 2.
- 1 History
- 2 Composition and structure
- 3 Climate
- 4 Orbit and rotation
- 5 Formation and migration
- 6 Moons
- 7 Observation
- 8 Exploration
- 9 See also
- 10 References
- 11 Further reading
- 12 External links
Galileo's drawings show that he first observed Neptune on December 28, 1612, and again on January 27, 1613. On both occasions, Galileo mistook Neptune for a fixed star when it appeared very close—in conjunction—to Jupiter in the night sky, hence, he is not credited with Neptune's discovery. During the period of his first observation in December 1612, it was stationary in the sky because it had just turned retrograde that very day. This apparent backward motion is created when the orbit of the Earth takes it past an outer planet. Since Neptune was only beginning its yearly retrograde cycle, the motion of the planet was far too slight to be detected with Galileo's small telescope.
In 1821, Alexis Bouvard published astronomical tables of the orbit of Neptune's neighbor Uranus. Subsequent observations revealed substantial deviations from the tables, leading Bouvard to hypothesize that an unknown body was perturbing the orbit through gravitational interaction. In 1843, John Couch Adams calculated the orbit of a hypothesized eighth planet that would account for Uranus's motion. He sent his calculations to Sir George Airy, the Astronomer Royal, who asked Adams for a clarification. Adams began to draft a reply but never sent it and did not aggressively pursue work on the Uranus problem.
In 1845–46, Urbain Le Verrier, independently of Adams, rapidly developed his own calculations but also experienced difficulties in stimulating any enthusiasm in his compatriots. In June, however, upon seeing Le Verrier's first published estimate of the planet's longitude and its similarity to Adams's estimate, Airy persuaded Cambridge Observatory director James Challis to search for the planet. Challis vainly scoured the sky throughout August and September.
Meantime, Le Verrier by letter urged Berlin Observatory astronomer Johann Gottfried Galle to search with the observatory's refractor. Heinrich d'Arrest, a student at the observatory, suggested to Galle that they could compare a recently drawn chart of the sky in the region of Le Verrier's predicted location with the current sky to seek the displacement characteristic of a planet, as opposed to a fixed star. The very evening of the day of receipt of Le Verrier's letter, Neptune was discovered, September 23, 1846, within 1° of where Le Verrier had predicted it to be, and about 12° from Adams' prediction. Challis later realized that he had observed the planet twice in August, failing to identify it owing to his casual approach to the work.
In the wake of the discovery, there was much nationalistic rivalry between the French and the British over who had priority and deserved credit for the discovery. Eventually an international consensus emerged that both Le Verrier and Adams jointly deserved credit. However, the issue is now being re-evaluated by historians with the rediscovery in 1998 of the "Neptune papers" (historical documents from the Royal Observatory, Greenwich), which had apparently been stolen by astronomer Olin J. Eggen and hoarded for nearly three decades, not to be rediscovered (in his possession) until immediately after his death. After reviewing the documents, some historians now suggest that Adams does not deserve equal credit with Le Verrier. Since 1966 Dennis Rawlins has questioned the credibility of Adams's claim to co-discovery. In a 1992 article in his journal Dio he deemed the British claim "theft". "Adams had done some calculations but he was rather unsure about quite where he was saying Neptune was", said Nicholas Kollerstrom of University College London in 2003.
Shortly after its discovery, Neptune was referred to simply as "the planet exterior to Uranus" or as "Le Verrier's planet". The first suggestion for a name came from Galle, who proposed the name Janus. In England, Challis put forward the name Oceanus.
Claiming the right to name his discovery, Le Verrier quickly proposed the name Neptune for this new planet, while falsely stating that this had been officially approved by the French Bureau des Longitudes. In October, he sought to name the planet Le Verrier, after himself, and he was patriotically supported in this by the observatory director, François Arago. However, this suggestion met with stiff resistance outside France. French almanacs quickly reintroduced the name Herschel for Uranus, after that planet's discoverer Sir William Herschel, and Leverrier for the new planet.
Struve came out in favour of the name Neptune on December 29, 1846, to the Saint Petersburg Academy of Sciences. Soon Neptune became the internationally accepted name. In Roman mythology, Neptune was the god of the sea, identified with the Greek Poseidon. The demand for a mythological name seemed to be in keeping with the nomenclature of the other planets, all of which, except for Uranus and Earth, were named for Roman gods.
From its discovery until 1930, Neptune was the farthest known planet. Upon the discovery of Pluto in 1930, Neptune became the penultimate planet, save for a 20-year period between 1979 and 1999 when Pluto fell within its orbit. However, the discovery of the Kuiper belt in 1992 led many astronomers to debate whether Pluto should be considered a planet in its own right or part of the belt's larger structure. In 2006, the International Astronomical Union defined the word "planet" for the first time, reclassifying Pluto as a "dwarf planet" and making Neptune once again the last planet in the Solar System.
Composition and structure
With a mass of 1.0243×1026 kg, Neptune is an intermediate body between Earth and the larger gas giants: its mass is seventeen times that of the Earth but just 1/19th that of Jupiter. Neptune's equatorial radius of 24,764 kilometres (15,388 mi) is nearly four times that of the Earth. Neptune and Uranus are often considered a sub-class of gas giant termed "ice giants", due to their smaller size and higher concentrations of volatiles relative to Jupiter and Saturn. In the search for extrasolar planets Neptune has been used as a metonym: discovered bodies of similar mass are often referred to as "Neptunes", just as astronomers refer to various extra-solar "Jupiters".
Neptune's internal structure resembles that of Uranus. Its atmosphere forms about 5 to 10 percent of its mass and extends perhaps 10 to 20 percent of the way towards the core, where it reaches pressures of about 10 GPa. Increasing concentrations of methane, ammonia, and water are found in the lower regions of the atmosphere.
Gradually this darker and hotter region condenses into a superheated liquid mantle, where temperatures reach 2,000 K to 5,000 K. The mantle is equivalent to 10 to 15 Earth masses and is rich in water, ammonia, and methane. As is customary in planetary science, this mixture is referred to as icy even though it is a hot, highly dense fluid. This fluid, which has a high electrical conductivity, is sometimes called a water-ammonia ocean. At a depth of 7,000 kilometres (4,300 mi), the conditions may be such that methane decomposes into diamond crystals that then precipitate toward the core.
The core of Neptune is composed of iron, nickel, and silicates, with an interior model giving a mass about 1.2 times that of the Earth. The pressure at the centre is 7 Mbar (700 GPa), millions of times more than that on the surface of the Earth, and the temperature may be 5,400 K.
At high altitudes, Neptune's atmosphere is 80% hydrogen and 19% helium. A trace amount of methane is also present. Prominent absorption bands of methane occur at wavelengths above 600 nm, in the red and infrared portion of the spectrum. As with Uranus, this absorption of red light by the atmospheric methane is part of what gives Neptune its blue hue, although Neptune's vivid azure differs from Uranus's milder aquamarine. Since Neptune's atmospheric methane content is similar to that of Uranus, some unknown atmospheric constituent is thought to contribute to Neptune's colour.
Neptune's atmosphere is sub-divided into two main regions; the lower troposphere, where temperature decreases with altitude, and the stratosphere, where temperature increases with altitude. The boundary between the two, the tropopause, occurs at a pressure of 0.1 bars (10 kPa). The stratosphere then gives way to the thermosphere at a pressure lower than 10−5 to 10−4 microbars (1 to 10 Pa). The thermosphere gradually transitions to the exosphere.
Models suggest that Neptune's troposphere is banded by clouds of varying compositions depending on altitude. The upper-level clouds occur at pressures below one bar, where the temperature is suitable for methane to condense. For pressures between one and five bars (100 and 500 kPa), clouds of ammonia and hydrogen sulfide are believed to form. Above a pressure of five bars, the clouds may consist of ammonia, ammonium sulfide, hydrogen sulfide, and water. Deeper clouds of water ice should be found at pressures of about 50 bars (5.0 MPa), where the temperature reaches 0 °C. Underneath, clouds of ammonia and hydrogen sulfide may be found.
High-altitude clouds on Neptune have been observed casting shadows on the opaque cloud deck below. There are also high-altitude cloud bands that wrap around the planet at constant latitude. These circumferential bands have widths of 50–150 km (30–90 mi) and lie about 50–110 kilometres (30–70 mi) above the cloud deck.
Neptune's spectra suggest that its lower stratosphere is hazy due to condensation of products of ultraviolet photolysis of methane, such as ethane and acetylene. The stratosphere is also home to trace amounts of carbon monoxide and hydrogen cyanide. The stratosphere of Neptune is warmer than that of Uranus due to elevated concentration of hydrocarbons.
For reasons that remain obscure, the planet's thermosphere is at an anomalously high temperature of about 750 K. The planet is too far from the Sun for this heat to be generated by ultraviolet radiation. One candidate for a heating mechanism is atmospheric interaction with ions in the planet's magnetic field. Other candidates are gravity waves from the interior that dissipate in the atmosphere. The thermosphere contains traces of carbon dioxide and water, which may have been deposited from external sources such as meteorites and dust.
Neptune also resembles Uranus in its magnetosphere, with a magnetic field strongly tilted relative to its rotational axis at 47° and offset at least 0.55 radii, or about 13,500 km (8,400 mi) from the planet's physical centre. Before Voyager 2's arrival at Neptune, it was hypothesised that Uranus's tilted magnetosphere was the result of its sideways rotation. However, in comparing the magnetic fields of the two planets, scientists now think the extreme orientation may be characteristic of flows in the planets' interiors. This field may be generated by convective fluid motions in a thin spherical shell of electrically conducting liquids (probably a combination of ammonia, methane and water) resulting in a dynamo action.
The dipole component of the magnetic field at the magnetic equator of Neptune is about 14 μT (0.14 Gauss). The dipole magnetic moment of Neptune is about 2.2 T·m3 (14 μT·RN3, where RN is the radius of Neptune). Neptune's magnetic field has a complex geometry that includes relatively large contributions from non-dipolar components, including a strong quadrupole moment that may exceed the dipole moment in strength. By contrast, Earth, Jupiter, and Saturn have only relatively small quadrupole moments, and their fields are less tilted from the polar axis. The large quadrupole moment of Neptune may be the result of offset from the planet's center and geometrical constraints of the field's dynamo generator.
Neptune's bow shock, where the magnetosphere begins to slow the solar wind, occurs at a distance of 34.9 times the radius of the planet. The magnetopause, where the pressure of the magnetosphere counterbalances the solar wind, lies at a distance of 23–26.5 times the radius of Neptune. The tail of the magnetosphere extends out to at least 72 times the radius of Neptune, and very likely much farther.
Neptune has a planetary ring system, though one much less substantial than that of Saturn. The rings may consist of ice particles coated with silicates or carbon-based material, which most likely gives them a reddish hue. The three main rings are the narrow Adams Ring, 63,000 km (39,000 mi) from the centre of Neptune, the Leverrier Ring, at 53,000 km (33,000 mi), and the broader, fainter Galle Ring, at 42,000 km (26,000 mi). A faint outward extension to the Leverrier Ring has been named Lassell; it is bounded at its outer edge by the Arago Ring at 57,000 km (35,000 mi).
The first of these planetary rings was discovered in 1968 by a team led by Edward Guinan, but it was later thought that this ring might be incomplete. Evidence that the rings might have gaps first arose during a stellar occultation in 1984 when the rings obscured a star on immersion but not on emersion. Images by Voyager 2 in 1989 settled the issue by showing several faint rings. These rings have a clumpy structure, the cause of which is not currently understood but which may be due to the gravitational interaction with small moons in orbit near them.
The outermost ring, Adams, contains five prominent arcs now named Courage, Liberté, Egalité 1, Egalité 2, and Fraternité (Courage, Liberty, Equality, and Fraternity). The existence of arcs was difficult to explain because the laws of motion would predict that arcs would spread out into a uniform ring over very short timescales. Astronomers now believe that the arcs are corralled into their current form by the gravitational effects of Galatea, a moon just inward from the ring.
Earth-based observations announced in 2005 appeared to show that Neptune's rings are much more unstable than previously thought. Images taken from the W. M. Keck Observatory in 2002 and 2003 show considerable decay in the rings when compared to images by Voyager 2. In particular, it seems that the Liberté arc might disappear in as little as one century.
One difference between Neptune and Uranus is the typical level of meteorological activity. When the Voyager 2 spacecraft flew by Uranus in 1986, that planet was visually quite bland. In contrast Neptune exhibited notable weather phenomena during the 1989 Voyager 2 fly-by.
Neptune's weather is characterized by extremely dynamic storm systems, with winds reaching speeds of almost 600 metres per second (1,300 mph)—nearly attaining supersonic flow. More typically, by tracking the motion of persistent clouds, wind speeds have been shown to vary from 20 m/s (45 mph) in the easterly direction to 325 m/s (730 mph) westward. At the cloud tops, the prevailing winds range in speed from 400 m/s (890 mph) along the equator to 250 m/s (560 mph) at the poles. Most of the winds on Neptune move in a direction opposite the planet's rotation. The general pattern of winds showed prograde rotation at high latitudes vs. retrograde rotation at lower latitudes. The difference in flow direction is believed to be a "skin effect" and not due to any deeper atmospheric processes. At 70° S latitude, a high-speed jet travels at a speed of 300 m/s (670 mph).
The abundance of methane, ethane, and acetylene at Neptune's equator is 10–100 times greater than at the poles. This is interpreted as evidence for upwelling at the equator and subsidence near the poles.
In 2007 it was discovered that the upper troposphere of Neptune's south pole was about 10 °C (10 K) warmer than the rest of Neptune, which averages approximately −200 °C (70 K). The warmth differential is enough to let methane gas, which elsewhere lies frozen in Neptune's upper atmosphere, leak out through the south pole and into space. The relative "hot spot" is due to Neptune's axial tilt, which has exposed the south pole to the Sun for the last quarter of Neptune's year, or roughly 40 Earth years. As Neptune slowly moves towards the opposite side of the Sun, the south pole will be darkened and the north pole illuminated, causing the methane release to shift to the north pole.
Because of seasonal changes, the cloud bands in the southern hemisphere of Neptune have been observed to increase in size and albedo. This trend was first seen in 1980 and is expected to last until about 2020. The long orbital period of Neptune results in seasons lasting forty years.
In 1989, the Great Dark Spot, an anti-cyclonic storm system spanning 13,000 km × 6,600 km (8,100 mi × 4,100 mi), was discovered by NASA's Voyager 2 spacecraft. The storm resembled the Great Red Spot of Jupiter. Some five years later, however, on November 2, 1994, the Hubble Space Telescope did not see the Great Dark Spot on the planet. Instead, a new storm similar to the Great Dark Spot was found in the planet's northern hemisphere.
The Scooter is another storm, a white cloud group farther south than the Great Dark Spot. Its nickname is due to the fact that when first detected in the months before the 1989 Voyager 2 encounter it moved faster than the Great Dark Spot. Subsequent images revealed even faster clouds. The Small Dark Spot is a southern cyclonic storm, the second-most-intense storm observed during the 1989 encounter. It initially was completely dark, but as Voyager 2 approached the planet, a bright core developed and can be seen in most of the highest-resolution images.
Neptune's dark spots are thought to occur in the troposphere at lower altitudes than the brighter cloud features, so they appear as holes in the upper cloud decks. As they are stable features that can persist for several months, they are thought to be vortex structures. Often associated with dark spots are brighter, persistent methane clouds that form around the tropopause layer. The persistence of companion clouds shows that some former dark spots may continue to exist as cyclones even though they are no longer visible as a dark feature. Dark spots may also dissipate either when they migrate too close to the equator or possibly through some other unknown mechanism.
Neptune's more varied weather when compared to Uranus is believed to be due in part to its higher internal heat. Although Neptune lies half again as far from the Sun as Uranus, and receives only 40% its amount of sunlight, the two planets' surface temperatures are roughly equal. The upper regions of Neptune's troposphere reach a low temperature of −221.4 °C (51.7 K). At a depth where the atmospheric pressure equals 1 bar (100 kPa), the temperature is −201.15 °C (72.00 K). Deeper inside the layers of gas, however, the temperature rises steadily. As with Uranus, the source of this heating is unknown, but the discrepancy is larger: Uranus only radiates 1.1 times as much energy as it receives from the Sun; Neptune radiates about 2.61 times as much, which means the internal heat source generates 161% of the solar input. Neptune is the farthest planet from the Sun, yet its internal energy is sufficient to drive the fastest planetary winds seen in the Solar System. Several possible explanations have been suggested, including radiogenic heating from the planet's core, dissociation of methane into hydrocarbon chains under atmospheric pressure, and convection in the lower atmosphere that causes gravity waves to break above the tropopause.
Orbit and rotation
The average distance between Neptune and the Sun is 4.55 billion km (2.83 billion miles, about 30 times the average distance from the Earth to the Sun, or 30.1 AU), and it completes an orbit every 164.79 years. On July 12, 2011, Neptune will have completed the first full orbit since its discovery in 1846, although it will not appear at its exact discovery position in our sky because the Earth will be in a different location in its 365.25-day orbit.
The elliptical orbit of Neptune is inclined 1.77° compared to the Earth. Because of an eccentricity of 0.011, the distance between Neptune and the Sun varies by 101 million km (63 million mi) between perihelion and aphelion, the nearest and most distant points of the planet from the Sun along the orbital path, respectively.
The axial tilt of Neptune is 28.32°, which is similar to the tilts of Earth (23°) and Mars (25°). As a result, this planet experiences similar seasonal changes. However, the long orbital period of Neptune means that the seasons last for forty Earth years. Its sidereal rotation period (day) is roughly 16.11 hours. Since its axial tilt is comparable to the Earth's, the variation in the length of its day over the course of its long year is not any more extreme.
Because Neptune is not a solid body, its atmosphere undergoes differential rotation. The wide equatorial zone rotates with a period of about 18 hours, which is slower than the 16.1-hour rotation of the planet's magnetic field. By contrast, the reverse is true for the polar regions where the rotation period is 12 hours. This differential rotation is the most pronounced of any planet in the Solar System, and it results in strong latitudinal wind shear.
Neptune's orbit has a profound impact on the region directly beyond it, known as the Kuiper belt. The Kuiper belt is a ring of small icy worlds, similar to the asteroid belt but far larger, extending from Neptune's orbit at 30 AU out to about 55 AU from the Sun. Much in the same way that Jupiter's gravity dominates the asteroid belt, shaping its structure, so Neptune's gravity completely dominates the Kuiper belt. Over the age of the Solar System, certain regions of the Kuiper belt become destabilized by Neptune's gravity, creating gaps in the Kuiper belt's structure. The region between 40 and 42 AU is an example.
There do, however, exist orbits within these empty regions where objects can survive for the age of the Solar System. These resonances occur when an object's orbit around the Sun is a precise fraction of Neptune's, such as 1:2, or 3:4. If, say, an object orbits the Sun once for every two Neptune orbits, it will only complete half an orbit every time Neptune returns to its original position, and so will always be on the other side of the Sun. The most heavily populated resonant orbit in the Kuiper belt, with over 200 known objects, is the 2:3 resonance. Objects in this orbit complete 1 orbit for every 1½ of Neptune's, and are known as Plutinos because the largest of the Kuiper belt objects, Pluto, lies among them. Although Pluto crosses Neptune's orbit regularly, the 2:3 resonance means they can never collide. Other, less populated resonances exist at 3:4, 3:5, 4:7, and 2:5.
Neptune possesses a number of trojan objects, which occupy its L4 and L5 points—gravitationally stable regions leading and trailing it in its orbit. Neptune trojans are often described as being in a 1:1 resonance with Neptune. Neptune trojans are remarkably stable in their orbits and are unlikely to have been captured by Neptune, but rather to have formed alongside it.
Formation and migration
The formation of the ice giants, Neptune and Uranus, has proven difficult to model precisely. Current models suggest that the matter density in the outer regions of the Solar System was too low to account for the formation of such large bodies from the traditionally accepted method of core accretion, and various hypotheses have been advanced to explain their evolution. One is that the ice giants were not created by core accretion but from instabilities within the original protoplanetary disc, and later had their atmospheres blasted away by radiation from a nearby massive OB star. An alternative concept is that they formed closer to the Sun, where the matter density was higher, and then subsequently migrated to their current orbits.
The migration hypothesis is favoured for its ability to explain current orbital resonances in the Kuiper belt, particularly the 2:5 resonance. As Neptune migrated outward, it collided with the objects in the proto-Kuiper belt, creating new resonances and sending other orbits into chaos. The objects in the scattered disc are believed to have been placed in their current positions by interactions with the resonances created by Neptune's migration. A 2004 computer model by Alessandro Morbidelli of the Observatoire de la Côte d'Azur in Nice suggested that the migration of Neptune into the Kuiper belt may have been triggered by the formation of a 1:2 resonance in the orbits of Jupiter and Saturn, which created a gravitational push that propelled both Uranus and Neptune into higher orbits and caused them to switch places. The resultant expulsion of objects from the proto-Kuiper belt could also explain the Late Heavy Bombardment 600 million years after the Solar System's formation and the appearance of Jupiter's Trojan asteroids.
- For a timeline of discovery dates, see Timeline of discovery of Solar System planets and their moons
Neptune has 13 known moons. The largest by far, comprising more than 99.5 percent of the mass in orbit around Neptune and the only one massive enough to be spheroidal, is Triton, discovered by William Lassell just 17 days after the discovery of Neptune itself. Unlike all other large planetary moons in the Solar System, Triton has a retrograde orbit, indicating that it was captured rather than forming in place; it probably was once a dwarf planet in the Kuiper belt. It is close enough to Neptune to be locked into a synchronous rotation, and it is slowly spiraling inward because of tidal acceleration and eventually will be torn apart when it reaches the Roche limit. In 1989, Triton was the coldest object that had yet been measured in the solar system, with estimated temperatures of −235 °C (38 K).
Neptune's second known satellite (by order of discovery), the irregular moon Nereid, has one of the most eccentric orbits of any satellite in the solar system. The eccentricity of 0.7512 gives it an apoapsis that is seven times its periapsis distance from Neptune.
From July to September 1989, Voyager 2 discovered six new Neptunian moons. Of these, the irregularly shaped Proteus is notable for being as large as a body of its density can be without being pulled into a spherical shape by its own gravity. Although the second-most-massive Neptunian moon, it is only one-quarter of one percent the mass of Triton. Neptune's innermost four moons—Naiad, Thalassa, Despina, and Galatea—orbit close enough to be within Neptune's rings. The next-farthest out, Larissa was originally discovered in 1981 when it had occulted a star. This occultation had been attributed to ring arcs, but when Voyager 2 observed Neptune in 1989, it was found to have been caused by the moon. Five new irregular moons discovered between 2002 and 2003 were announced in 2004. As Neptune was the Roman god of the sea, the planet's moons have been named after lesser sea gods.
Neptune is never visible to the naked eye, having a brightness between magnitudes +7.7 and +8.0, which can be outshone by Jupiter's Galilean moons, the dwarf planet Ceres and the asteroids 4 Vesta, 2 Pallas, 7 Iris, 3 Juno and 6 Hebe. A telescope or strong binoculars will resolve Neptune as a small blue disk, similar in appearance to Uranus.
Because of the distance of Neptune from the Earth, the angular diameter of the planet only ranges from 2.2–2.4 arcseconds; the smallest of the Solar System planets. Its small apparent size has made it challenging to study visually; most telescopic data was fairly limited until the advent of Hubble Space Telescope and large ground-based telescopes with adaptive optics.
From the Earth, Neptune goes through apparent retrograde motion every 367 days, resulting in a looping motion against the background stars during each opposition. These loops will carry it close to the 1846 discovery coordinates in April and July 2010 and in October and November 2011.
Observation of Neptune in the radio frequency band shows that the planet is a source of both continuous emission and irregular bursts. Both sources are believed to originate from the planet's rotating magnetic field. In the infrared part of the spectrum, Neptune's storms appear bright against the cooler background, allowing the size and shape of these features to be readily tracked.
Voyager 2's closest approach to Neptune occurred on August 25, 1989. Since this was the last major planet the spacecraft could visit, it was decided to make a close flyby of the moon Triton, regardless of the consequences to the trajectory, similarly to what was done for Voyager 1's encounter with Saturn and its moon Titan. The images relayed back to Earth from Voyager 2 became the basis of a 1989 PBS all-night program called "Neptune All Night".
During the encounter, signals from the spacecraft required 246 minutes to reach the Earth. Hence, for the most part, the Voyager 2 mission relied on pre-loaded commands for the Neptune encounter. The spacecraft performed a near-encounter with the moon Nereid before it came within 4,400 km (2,700 mi) of Neptune's atmosphere on August 25, then passed close to the planet's largest moon Triton later the same day.
The spacecraft verified the existence of a magnetic field surrounding the planet and discovered that the field was offset from the centre and tilted in a manner similar to the field around Uranus. The question of the planet's rotation period was settled using measurements of radio emissions. Voyager 2 also showed that Neptune had a surprisingly active weather system. Six new moons were discovered, and the planet was shown to have more than one ring.
In 2003, there was a proposal to NASA's "Vision Missions Studies" to implement a "Neptune Orbiter with Probes" mission that does Cassini-level science without fission-based electric power or propulsion. The work is being done in conjunction with JPL and the California Institute of Technology.
- Neptune in astrology
- Neptune in fiction
- Colonization of Neptune
- Neptune Orbiter – proposed space probe to Neptune (not before 2035- may have been indefinitely postponed, as NASA's Strategic Exploration Plan no longer includes it)
- Neptune Trojan – asteroids orbiting in Neptune's Lagrangian points
- The Planets – Neptune is one of the seven movements in Gustav Holst's orchestral suite, The Planets
- Hamilton, Calvin J. (August 4, 2001). "Neptune". Views of the Solar System. Retrieved 2007-08-13.
- Munsell, K. (November 13, 2007). "Neptune: Facts & Figures". NASA. Retrieved 2007-08-14. Unknown parameter
- Williams, David R. (September 1, 2004). "Neptune Fact Sheet". NASA. Retrieved 2007-08-14.
- Yeomans, Donald K. (July 13, 2006). "HORIZONS System". NASA JPL. Retrieved 2007-08-08.—At the site, go to the "web interface" then select "Ephemeris Type: ELEMENTS", "Target Body: Neptune Barycenter" and "Center: Sun".
- Orbital elements refer to the barycentre of the Neptune system, and are the instantaneous osculating values at the precise J2000 epoch. Barycentre quantities are given because, in contrast to the planetary centre, they do not experience appreciable changes on a day-to-day basis from to the motion of the moons.
- P. Kenneth, Seidelmann (2007). "Report of the IAU/IAGWorking Group on cartographic coordinates and rotational elements". Celestial Mechanics and Dynamical Astronomy. Springer Netherlands. 90: 155–180. doi:10.1007/s10569-007-9072-y. ISSN (Print) 0923-2958 (Print) Check
|issn=value (help). Retrieved 2008-03-07. Unknown parameter
- Refers to the level of 1 bar (100 kPa) atmospheric pressure
- Espenak, Fred (July 20, 2005). "Twelve Year Planetary Ephemeris: 1995–2006". NASA. Retrieved 2008-03-01.
- Walter, Elizabeth (April 21, 2003). Cambridge Advanced Learner's Dictionary (Second Edition ed.). Cambridge University Press. ISBN 0521531063.CS1 maint: extra text (link)
- The mass of the Earth is
5.9736×1024 kg, giving a mass ratio of:
- Lunine, Jonathan I. (1993). "The Atmospheres of Uranus and Neptune" (PDF). Lunar and Planetary Observatory, University of Arizona. Retrieved 2008-03-10.
- Podolak, M. (1995). "Comparative models of Uranus and Neptune". Planetary and Space Science. 43 (12): 1517–1522. doi:10.1016/0032-0633(95)00061-5. Unknown parameter
- Munsell, Kirk (November 13, 2007). "Neptune overview". Solar System Exploration. NASA. Retrieved 2008-02-20. Unknown parameter
- Suomi, V. E. (1991). "High Winds of Neptune: A possible mechanism". Science. AAAS (USA). 251 (4996): 929–932. doi:10.1126/science.251.4996.929. PMID 17847386. Unknown parameter
- Wilford, John N. (June 10, 1982). "Data Shows 2 Rings Circling Neptune". The New York Times. Retrieved 2008-02-29.
- Hirschfeld, Alan (2001). Parallax: The Race to Measure the Cosmos. New York, New York: Henry Holt. ISBN 0-8050-7133-4.
- Littmann, Mark (2004). Planets Beyond: Discovering the Outer Solar System. Courier Dover Publications. ISBN 0-4864-3602-0. Unknown parameter
- Bouvard, A. (1821). Tables astronomiques publiées par le Bureau des Longitudes de France. Paris: Bachelier.
- O'Connor, John J. (2006). "John Couch Adams' account of the discovery of Neptune". University of St Andrews. Retrieved 2008-02-18. Unknown parameter
|month=ignored (help); Unknown parameter
- Adams, J. C. (November 13, 1846). "Explanation of the observed irregularities in the motion of Uranus, on the hypothesis of disturbance by a more distant planet". Monthly Notices of the Royal Astronomical Society. Blackwell Publishing. 7: 149. Retrieved 2008-02-18.
- Airy, G. B. (November 13, 1846). "Account of some circumstances historically connected with the discovery of the planet exterior to Uranus". Monthly Notices of the Royal Astronomical Society. Blackwell Publishing. 7: 121–144. Retrieved 2008-02-18.
- Challis, Rev. J. (November 13, 1846). "Account of observations at the Cambridge observatory for detecting the planet exterior to Uranus". Monthly Notices of the Royal Astronomical Society. Blackwell Publishing. 7: 145–149. Retrieved 2008-02-18.
- Galle, J. G. (November 13, 1846). "Account of the discovery of the planet of Le Verrier at Berlin". Monthly Notices of the Royal Astronomical Society. Blackwell Publishing. 7: 153. Retrieved 2008-02-18.
- Kollerstrom, Nick (2001). "Neptune's Discovery. The British Case for Co-Prediction". University College London. Archived from the original on 2005-11-11. Retrieved 2007-03-19.
- Rawlins, Dennis (1992). "The Neptune Conspiracy: British Astronomy's PostDiscovery Discovery" (PDF). Dio. Retrieved 2008-03-10. soft hyphen character in
|title=at position 49 (help)
- McGourty, Christine (2003). "Lost letters' Neptune revelations". BBC News. Retrieved 2008-03-10.
- Summations following the Neptune documents' 1998 recovery appeared in DIO 9.1 (1999) and William Sheehan, Nicholas Kollerstrom, Craig B. Waff (December 2004), The Case of the Pilfered Planet - Did the British steal Neptune? Scientific American.
- Moore (2000):206
- Littmann (2004):50
- Baum & Sheehan (2003):109–110
- Gingerich, Owen (1958). "The Naming of Uranus and Neptune". Astronomical Society of the Pacific Leaflets. 8: 9–15. Retrieved 2008-02-19.
- Hind, J. R. (1847). "Second report of proceedings in the Cambridge Observatory relating to the new Planet (Neptune)". Astronomische Nachrichten. 25: 309. doi:10.1002/asna.18470252102. Retrieved 2008-02-18. Smithsonian/NASA Astrophysics Data System (ADS).
- Blue, Jennifer (December 17, 2008). "Planet and Satellite Names and Discoverers". USGS. Retrieved 2008-02-18.
- Tony Long (2008). "Jan. 21, 1979: Neptune Moves Outside Pluto's Wacky Orbit". wired.com. Retrieved 2008-03-13.
- Weissman, Paul R. "The Kuiper Belt". Annual Review of Astronomy and Astrophysics. Retrieved 2006-10-04.
- "The Status of Pluto:A clarification". International Astronomical Union, Press release. 1999. Retrieved 2006-05-25.
- "IAU 2006 General Assembly: Resolutions 5 and 6" (PDF). IAU. August 24, 2006.
- See for example: Boss, Alan P. (2002). "Formation of gas and ice giant planets". Earth and Planetary Science Letters. 202 (3–4): 513–523. doi:10.1016/S0012-821X(02)00808-7.
- Lovis, C. (May 18, 2006). "Trio of Neptunes and their Belt". ESO. Retrieved 2008-02-25. Unknown parameter
- Hubbard, W. B. (1997). "Neptune's Deep Chemistry". Science. 275 (5304): 1279–1280. doi:10.1126/science.275.5304.1279. PMID 9064785. Retrieved 2008-02-19.
- Atreya, S. (2006). "Water-ammonia ionic ocean on Uranus and Neptune?" (pdf). Geophysical Research Abstracts. 8: 05179. Unknown parameter
- Kerr, Richard A. (1999). "Neptune May Crush Methane Into Diamonds". Science. 286 (5437): 25. doi:10.1126/science.286.5437.25a. Retrieved 2007-02-26.
- Podolak, M. (1995). "Comparative models of Uranus and Neptune". Planetary and Space Science. 43 (12): 1517–1522. doi:10.1016/0032-0633(95)00061-5. Unknown parameter
- Nettelmann, N. "Interior Models of Jupiter, Saturn and Neptune" (PDF). University of Rostock. Retrieved 2008-02-25. Unknown parameter
- Crisp, D. (June 14, 1995). "Hubble Space Telescope Observations of Neptune". Hubble News Center. Retrieved 2007-04-22. Unknown parameter
- Elkins-Tanton (2006):79–83.
- Max, C. E. (2003). "Cloud Structures on Neptune Observed with Keck Telescope Adaptive Optics". The Astronomical Journal,. 125 (1): 364–375. doi:10.1086/344943. Retrieved 2008-02-27. Unknown parameter
|author=suggested) (help)CS1 maint: extra punctuation (link)
- Encrenaz, Therese (2003). "ISO observations of the giant planets and Titan: what have we learnt?". Planet. Space Sci. 51: 89–103. doi:10.1016/S0032-0633(02)00145-9.
- Broadfoot, A.L. (1999). "Ultraviolet Spectrometer Observations of Neptune and Triton" (pdf). Science. 246: 1459–1456. doi:10.1126/science.246.4936.1459. PMID 17756000. Unknown parameter
- Herbert, Floyd (1999). "Ultraviolet Observations of Uranus and Neptune". Planet.Space Sci. 47: 1119–1139. doi:10.1016/S0032-0633(98)00142-1. Unknown parameter
- Stanley, Sabine (March 11, 2004). "Convective-region geometry as the cause of Uranus' and Neptune's unusual magnetic fields". Nature. 428: 151–153. doi:10.1038/nature02376. Unknown parameter
- Connerney, J.E.P. (1991). "The magnetic field of Neptune". Journal of Geophysics Research. 96: 19, 023–42. Unknown parameter
- Ness, N. F. (1989). "Magnetic Fields at Neptune". Science. 246 (4936): 1473–1478. doi:10.1126/science.246.4936.1473. PMID 17756002. Retrieved 2008-02-25. Unknown parameter
|author=suggested) (help) Cite error: The named reference "science4936" was defined multiple times with different content (see the help page).
- Russell, C. T. (1997). "Neptune: Magnetic Field and Magnetosphere". University of California, Los Angeles. Retrieved 2006-08-10. Unknown parameter
- Cruikshank (1996):703–804
- Blue, Jennifer (December 8, 2004). "Nomenclature Ring and Ring Gap Nomenclature". Gazetteer of Planetary. USGS. Retrieved 2008-02-28.
- Guinan, E. F. (1982). "Evidence for a Ring System of Neptune". Bulletin of the American Astronomical Society. 14: 658. Retrieved 2008-02-28. Unknown parameter
- Goldreich, P. (1986). "Towards a theory for Neptune's arc rings". Astronomical Journal. 92: 490–494. doi:10.1086/114178. Retrieved 2008-02-28. Unknown parameter
- Nicholson, P. D.; et al. (1990). "Five Stellar Occultations by Neptune: Further Observations of Ring Arcs". Icarus. 87: 1. doi:10.1016/0019-1035(90)90020-A. Retrieved 2007-12-16. Explicit use of et al. in:
- "Missions to Neptune". The Planetary Society. 2007. Retrieved 2007-10-11.
- Wilford, John Noble (December 15, 1989). "Scientists Puzzled by Unusual Neptune Rings". Hubble News Desk. Retrieved 2008-02-29.
- Cox, Arthur N. (2001). Allen's Astrophysical Quantities. Springer. ISBN 0387987460.
- Munsell, Kirk (November 13, 2007). "Planets: Neptune: Rings". Solar System Exploration. NASA. Retrieved 2008-02-29. Unknown parameter
- Salo, Heikki (1998). "Neptune's Partial Rings: Action of Galatea on Self-Gravitating Arc Particles". Science. 282 (5391): 1102–1104. doi:10.1126/science.282.5391.1102. PMID 9804544. Retrieved 2008-02-29. Unknown parameter
- Staff (March 26, 2005). "Neptune's rings are fading away". New Scientist. Retrieved 2007-08-06.
- Lavoie, Sue (February 16, 2000). "PIA02245: Neptune's blue-green atmosphere". NASA JPL. Retrieved 2008-02-28.
- Lavoie, Sue (January 8, 1998). "PIA01142: Neptune Scooter". NASA. Retrieved 2006-03-26.
- Suomi, V. E. (1991). "High Winds of Neptune: A Possible Mechanism". Science. 251 (4996): 929–932. doi:10.1126/science.251.4996.929. PMID 17847386. Retrieved 2008-02-25. Unknown parameter
- Hammel, H. B. (1989). "Neptune's wind speeds obtained by tracking clouds in Voyager 2 images". Science. 245: 1367–1369. doi:10.1126/science.245.4924.1367. PMID 17798743. Retrieved 2008-02-27. Unknown parameter
- Burgess (1991):64–70.
- Orton, G. S., Encrenaz T., Leyrat C., Puetter, R. and Friedson, A. J. (2007). "Evidence for methane escape and strong seasonal and dynamical perturbations of Neptune's atmospheric temperatures". Astronomy and Astrophysics. Retrieved 2008-03-10.CS1 maint: multiple names: authors list (link)
- Orton, Glenn (September 18, 2007). "A Warm South Pole? Yes, On Neptune!". ESO. Retrieved 2007-09-20. Unknown parameter
- Villard, Ray (May 15, 2003). "Brighter Neptune Suggests A Planetary Change Of Seasons". Hubble News Center. Retrieved 2008-02-26. Unknown parameter
- Hammel, H. B. (1995). "Hubble Space Telescope Imaging of Neptune's Cloud Structure in 1994". Science. 268 (5218): 1740–1742. doi:10.1126/science.268.5218.1740. PMID 17834994. Retrieved 2008-02-25. Unknown parameter
- Lavoie, Sue (January 29, 1996). "PIA00064: Neptune's Dark Spot (D2) at High Resolution". NASA JPL. Retrieved 2008-02-28.
- S. G., Gibbard (2003). "The altitude of Neptune cloud features from high-spatial-resolution near-infrared spectra" (PDF). Icarus. 166 (2): 359–374. doi:10.1016/j.icarus.2003.07.006. Retrieved 2008-02-26. Unknown parameter
- Stratman, P. W. (2001). "EPIC Simulations of Bright Companions to Neptune's Great Dark Spots" (PDF). Icarus. 151 (2): 275–285. doi:10.1006/icar.1998.5918. Retrieved 2008-02-26. Unknown parameter
- Sromovsky, L. A. (2000). "The unusual dynamics of new dark spots on Neptune". Bulletin of the American Astronomical Society. 32: 1005. Retrieved 2008-02-29. Unknown parameter
- Williams, Sam (2004). "Heat Sources within the Giant Planets". University of California, Berkeley. Retrieved 2008-03-10.
- Lindal, Gunnar F. (1992). "The atmosphere of Neptune - an analysis of radio occultation data acquired with Voyager 2". Astronomical Journal. 103: 967–982. doi:10.1086/116119. Retrieved 2008-02-25.
- "Class 12 - Giant Planets - Heat and Formation". 3750 - Planets, Moons & Rings. Colorado University, Boulder. 2004. Retrieved 2008-03-13.
- Pearl, J. C. (1991). "The albedo, effective temperature, and energy balance of Neptune, as determined from Voyager data". Journal of Geophysical Research Supplement. 96: 18, 921–18, 930. Retrieved 2008-02-20. Unknown parameter
- Williams, Sam (November 24, 2004). "Heat Sources Within the Giant Planets" (DOC). UC Berkeley. Retrieved 2008-02-20. Cite journal requires
- Scandolo, Sandro (2003). "The Centers of Planets". American Scientist. 91 (6): 516. doi:10.1511/2003.6.516. Unknown parameter
- McHugh, J. P. (1999). "Computation of Gravity Waves near the Tropopause". American Astronomical Society, DPS meeting #31, #53.07. Retrieved 2008-02-19. Unknown parameter
- McHugh, J. P. (1996). "Neptune's Energy Crisis: Gravity Wave Heating of the Stratosphere of Neptune". Bulletin of the American Astronomical Society: 1078. Retrieved 2008-02-19. Unknown parameter
|author=suggested) (help); Unknown parameter
- Anonymous (February 9, 2007). "Horizons Output for Neptune 2010–2011". Retrieved 2008-02-25.—Numbers generated using the Solar System Dynamics Group, Horizons On-Line Ephemeris System.
- Williams, David R. (January 6, 2005). "Planetary Fact Sheets". NASA. Retrieved 2008-02-28.
- Hubbard, W. B. (1991). "Interior Structure of Neptune: Comparison with Uranus". Science. 253 (5020): 648–651. doi:10.1126/science.253.5020.648. PMID 17772369. Retrieved 2008-02-28. Unknown parameter
- Stern, S. Alan (1997). "Collisional Erosion in the Primordial Edgeworth-Kuiper Belt and the Generation of the 30–50 AU Kuiper Gap". Geophysical, Astrophysical, and Planetary Sciences, Space Science Department, Southwest Research Institute. Retrieved 2007-06-01.
- Petit, Jean-Marc (1998). "Large Scattered Planetesimals and the Excitation of the Small Body Belts" (PDF). Retrieved 2007-06-23. Unknown parameter
- "List Of Transneptunian Objects". Minor Planet Center. Retrieved 2007-06-23.
- Jewitt, David (2004). "The Plutinos". University of Hawaii. Retrieved 2008-02-28. Unknown parameter
- Varadi, F. (1999). "Periodic Orbits in the 3:2 Orbital Resonance and Their Stability". The Astronomical Journal. 118: 2526–2531. doi:10.1086/301088. Retrieved 2008-02-28.
- John Davies (2001). Beyond Pluto: Exploring the outer limits of the solar system. Cambridge University Press. p. 104.
- Chiang, E. I. (2003). "Resonance Occupation in the Kuiper Belt: Case Examples of the 5 : 2 and Trojan Resonances". Retrieved 2007-08-17. Unknown parameter
- Boss, Alan P. (2002-09-30). "Formation of gas and ice giant planets". Earth and Planetary Science Letters. ELSEVIER. Retrieved 2008-03-05.
- Thommes, Edward W. (2001). "The formation of Uranus and Neptune among Jupiter and Saturn". Retrieved 2008-03-05. Unknown parameter
- Hahn, Joseph M. (2005). "Neptune's Migration into a Stirred–Up Kuiper Belt: A Detailed Comparison of Simulations to Observations". Saint Mary’s University. Retrieved 2008-03-05.
- Hansen, Kathryn (June 7, 2005). "Orbital shuffle for early solar system". Geotimes. Retrieved 2007-08-26.
- Mass of Triton: 2.14×1022 kg. Combined mass of 12 other known moons of Neptune: 7.53×1019 kg, or 0.35 percent. The mass of the rings is negligible.
- Agnor, Craig B. (2006). "Neptune's capture of its moon Triton in a binary–planet gravitational encounter". Nature. Nature Publishing Group. 441 (7090): 192–194. doi:10.1038/nature04792. Retrieved 2008-02-28. Unknown parameter
|author=suggested) (help); Unknown parameter
- Chyba, Christopher F. (1989). "Tidal evolution in the Neptune-Triton system". Astronomy and Astrophysics. EDP Sciences. 219 (1–2): L23–L26. Retrieved 2006-05-10. Unknown parameter
|author=suggested) (help); Unknown parameter
- Wilford, John N. (August 29, 1989). "Triton May Be Coldest Spot in Solar System". The New York Times. Retrieved 2008-02-29.
- R. M., Nelson (1990). "Temperature and Thermal Emissivity of the Surface of Neptune's Satellite Triton". Science. AAAS (USA). 250 (4979): 429–431. doi:10.1126/science.250.4979.429. PMID 17793020. Retrieved 2008-02-29. Unknown parameter
- Using the values from the Neieid article:
- Brown, Michael E. "The Dwarf Planets". California Institute of Technology, Department of Geological Sciences. Retrieved 2008-02-09.
- Holman, Matthew J.; et al. (August 19, 2004). "Discovery of five irregular moons of Neptune". Nature. Nature Publishing Group. 430: 865–867. doi:10.1038/nature02832. Retrieved 2008-02-09. Explicit use of et al. in:
- Staff (August 18, 2004). "Five new moons for planet Neptune". BBC News. Retrieved 2007-08-06.
- See the respective articles for magnitude data.
- Moore (2000):207.
- In 1977, for example, even the rotation period of Neptune remained uncertain. See: Cruikshank, D. P. (March 1, 1978). "On the rotation period of Neptune". Astrophysical Journal, Part 2 - Letters to the Editor. University of Chicago Press. 220: L57–L59. doi:10.1086/182636. Retrieved 2008-03-01.
- Max, C. (1999). "Adaptive Optics Imaging of Neptune and Titan with the W.M. Keck Telescope". Bulletin of the American Astronomical Society. American Astronomical Society. 31: 1512. Retrieved 2008-03-01. Unknown parameter
- Gibbard, S. G. (1999). "High-Resolution Infrared Imaging of Neptune from the Keck Telescope". Icarus. Elsevier. 156: 1–15. doi:10.1006/icar.2001.6766. Retrieved 2008-03-01. Unknown parameter
- Phillips, Cynthia (August 5, 2003). "Fascination with Distant Worlds". SETI Institute. Retrieved 2007-10-03.
- Burgess (1991):46–55.
- Spilker, T. R. (2004). "Outstanding Science in the Neptune System From an Aerocaptured Vision Mission". Bulletin of the American Astronomical Society. American Astronomical Society. 36: 1094. Retrieved 2008-02-26. Unknown parameter
- Baum, Richard (2003). In Search of Planet Vulcan: The Ghost in Newton's Clockwork Universe. Oxford University Press. ISBN 0738208892. Unknown parameter
- Burgess, Eric (1991). Far Encounter: The Neptune System. Columbia University Press. ISBN 0-231-07412-3.
- Cruikshank, Dale P. (1996). Neptune and Triton. University of Arizona Press. ISBN 0-8165-1525-5.
- Elkins-Tanton, Linda T. (2006). Uranus, Neptune, Pluto, and the Outer Solar System. New York: Chelsea House. ISBN 0-8160-5197-6.
- Littmann, Mark (2004). Planets Beyond, Exploring the Outer Solar System. Courier Dover Publications. ISBN 0486436020.
- Miner, Ellis D. (2002). Neptune: The Planet, Rings, and Satellites. Springer-Verlag. ISBN 1-85233-216-6. Unknown parameter
- Moore, Patrick (2000). The Data Book of Astronomy. CRC Press. ISBN 0-7503-0620-3.
- Smith, Bradford A. "Neptune." World Book Online Reference Center. 2004. World Book, Inc. (NASA.gov)
- NASA's Neptune fact sheet
- Neptune Profile by NASA's Solar System Exploration
- Planets – Neptune A kid's guide to Neptune.
- Neptune from Bill Arnett's nineplanets.org
- Neptune Astronomy Cast episode #63, includes full transcript.