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 the mass of Earth but not as dense.HP 586006-321 Battery
On average, Neptune orbits the Sun at a distance of 30.1 AU, approximately 30 times the Earth–Sun distance. Its astronomical symbol is ?, a stylized version of the god Neptune's trident.
Discovered on September 23, 1846,Neptune was the first planet found by mathematical prediction rather than by empirical observation. HP 586006-361 Battery
Unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce that its orbit was subject to gravitational perturbation by an unknown planet. Neptune was subsequently observed by Johann Galle within a degree of the position predicted by Urbain Le Verrier,HP 586028-341 Battery
and its largest moon,Triton, was discovered shortly thereafter, though none of the planet's remaining 12 moons were located telescopically until the 20th century. Neptune has been visited by only one spacecraft, Voyager 2, which flew by the planet on August 25, 1989.HP h588178-141 Battery
Neptune is similar in composition to Uranus, and both have compositions which differ from those of the larger gas giants Jupiter and Saturn. Neptune's atmosphere, while similar to Jupiter's and Saturn's in that it is composed primarily of hydrogen and helium, along with traces ofhydrocarbons and possibly nitrogen,HP 593553-001 Battery
contains a higher proportion of "ices" such as water, ammonia and methane. Astronomers sometimes categorize Uranus and Neptune as "ice giants" in order to emphasize these distinctions. The interior of Neptune, like that of Uranus, is primarily composed of ices and rock.HP 593554-001 Battery
Traces of methane in the outermost regions in part account for the planet's blue appearance.
In contrast to the relatively featureless atmosphere of Uranus, Neptune's atmosphere is notable for its active and visible weather patterns. HP HSTNN-CB0W Battery
For example, at the time of the 1989 Voyager 2 flyby, the planet's southern hemisphere possessed a Great Dark Spot comparable to the Great Red Spot on Jupiter. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as 2,100 km/h.HP HSTNN-CB0X Battery
Because of its great distance from the Sun, Neptune's outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching ?218 °C (55 K). Temperatures at the planet's centre are approximately 5,400 K(5,000 °C).HP HSTNN-I79C Battery
Neptune has a faint and fragmented ring system, which may have been detected during the 1960s but was only indisputably confirmed in 1989 by Voyager 2.
Discovery
Galileo's drawings show that he first observed Neptune on December 28, 1612, and again on January 27, 1613.HP HSTNN-I81C Battery
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, Neptune was stationary in the sky because it had just turned retrograde that very day.HP HSTNN-IB0N Battery
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. HP HSTNN-IB0X Battery
In July 2009 University of Melbourne physicist David Jamieson announced new evidence suggesting that Galileo was at least aware that the star he had observed had moved relative to the fixed stars.
In 1821, Alexis Bouvard published astronomical tables of the orbit of Neptune's neighbor Uranus.HP HSTNN-LB0W Battery
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 began work on the orbit of Uranus using the data he had. HP HSTNN-OB0X Battery
Via James Challis, he requested from Sir George Airy, theAstronomer Royal, who sent the data in February 1844. Adams continued to work on this in 1845–46 and produced several different estimates of a new planet, but did not respond to a request from Airy about the orbit of Uranus.HP HSTNN-OB0Y Battery
In 1845–46, Urbain Le Verrier, independently of Adams, developed his own calculations but also experienced difficulties in stimulating any enthusiasm in his compatriots. In June 1846, upon seeing Le Verrier's first published estimate of the planet's longitude and its similarity to Adams's estimate, HP HSTNN-Q61C Battery
Airy persuaded Cambridge Observatorydirector 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. HP HSTNN-Q62C Battery
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. HP HSTNN-YB0X Battery
The very evening of the day of receipt of Le Verrier's letter on September 23, 1846, Neptune was discovered 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.HP NBP6A174B1 Battery
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. HP HSTNN-YB0X Battery
Since 1966 Dennis Rawlins has questioned the credibility of Adams's claim to co-discovery and the issue was re-evaluated by historians with the return in 1998 of the "Neptune papers" (historical documents) to the Royal Observatory, Greenwich.HP NBP6A174 Battery
After reviewing the documents, they suggest that "Adams does not deserve equal credit with Le Verrier for the discovery of Neptune. That credit belongs only to the person who succeeded both in predicting the planet's place and in convincing astronomers to search for it."HP NBP6A174B1 Battery
Naming
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.HP NBP6A175 Battery
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 had loyal support in this from the observatory director, François Arago.HP NBP6A175B1 Battery
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.HP WD548AA Battery
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 Earth, were named for Greek and Roman mythology.HP WD549AA Battery
Most languages today, even in countries that have no direct link to Graeco-Roman culture, use some variant of the name "Neptune" for the planet; in Chinese, Japanese and Korean, the planet's name was literally translated as "sea king star" (???), since Neptune was the god of the sea.HP Envy 17 Notebook PC Battery
Status
From its discovery in 1846 until the subsequent discovery of Pluto in 1930, Neptune was the farthest known planet. Upon Pluto's discovery Neptune became the penultimate planet, save for a 20-year period between 1979 and 1999 when Pluto's elliptical orbit brought it closer to the sun than Neptune.HP Envy 17T Battery
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.HP HSTNN-Q61C Battery
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. The planet's surface gravity is only surpassed by Jupiter, making the two gas giants the only planets in the solar system with a surface gravity higher than the Earth.HP GSTNN-Q62C Battery
Neptune's equatorial radius of 24764 km[9] 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.HP HSTNN-IB1E Battery
In the search for extrasolar planetsNeptune 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 bodies as "Jupiters".
Internal structure
Neptune's internal structure resembles that of Uranus. HP HSTNN-IB0X Battery
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.HP HSTNN-OB0X Battery
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.HP HSTNN-YB0X Battery
This fluid, which has a high electrical conductivity, is sometimes called a water-ammonia ocean. At a depth of 7000 km, the conditions may be such that methane decomposes into diamond crystals that then precipitate toward the core. The mantle may consist of a layer of ionic water where the water molecules break down into a soup of hydrogen and oxygen ions,HP 586006-361 Battery
and deeper down superionic water in which the oxygen crystallises but the hydrogen ions float around freely within the oxygen lattice.
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.HP NBP6A174 Battery
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.
Atmosphere
At high altitudes, Neptune's atmosphere is 80% hydrogen and 19% helium.HP NBP6A174B1 Battery
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 cyan. HP 588178-141 Battery
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).HP Pavilion dv5 Adapter
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.Sony NP-F330 Battery
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. Asus Eee PC 904HA Adapter
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.Nikon D80 Battery
There are also high-altitude cloud bands that wrap around the planet at constant latitude. These circumferential bands have widths of 50–150 km and lie about 50–110 km 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.Sony PCGA-AC19V9 Adapter
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 the elevated concentration of hydrocarbons.
For reasons that remain obscure, the planet's thermosphere is at an anomalously high temperature of about 750 K.Dell T555C Battery
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. HP Pavilion DV6-3013SL Battery
The thermosphere contains traces of carbon dioxide and water, which may have been deposited from external sources such as meteorites and dust.
Magnetosphere
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 13500 km from the planet's physical centre.HP Pavilion DV7-2085EL Battery
Before Voyager 2's arrival at Neptune, it was hypothesised that Uranus's tilted magnetosphere was the result of its sideways rotation. In comparing the magnetic fields of the two planets, scientists now think the extreme orientation may be characteristic of flows in the planets' interiors.HP Pavilion DV9700 Battery
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 microteslas (0.14 G).HP Mini 702EA Battery
The dipole magnetic moment of Neptune is about 2.2 × 1017 T·m3 (14 ?T·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.HP Pavilion DV7-1120EO Battery
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.HP Compaq 491278-001 Battery
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.HP Pavilion DV6-1030US Battery
The tail of the magnetosphere extends out to at least 72 times the radius of Neptune, and very likely much farther.
Planetary rings
Neptune has a planetary ring system, though one much less substantial than that of Saturn. HP Compaq 490306-001 Battery
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, 63000 km from the centre of Neptune, the Le Verrier Ring, at 53000 km, and the broader, fainter Galle Ring, at 42000 km.HP Pavilion DV5-1211EM Battery
A faint outward extension to the Le Verrier Ring has been named Lassell; it is bounded at its outer edge by the Arago Ring at 57000 km.
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.HP EliteBook 2530P Battery
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. HP Pavilion DV4385EA Battery
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).Compaq PP2100 Battery
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.HP Compaq KU532AA Battery
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.HP Pavilion DV6-1270EQ Battery
Climate
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.HP Pavilion DV4385EA Battery
Neptune's weather is characterized by extremely dynamic storm systems, with winds reaching speeds of almost 600 m/s—nearly attaining supersonic flow. More typically, by tracking the motion of persistent clouds, wind speeds have been shown to vary from 20 m/s in the easterly direction to 325 m/s westward.HP Compaq Business NC4400 Battery
At the cloud tops, the prevailing winds range in speed from 400 m/s along the equator to 250 m/s 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. HP Pavilion ZD8227 Battery
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.
The abundance of methane, ethane and ethyne at Neptune's equator is 10–100 times greater than at the poles. Nikon D200 Battery
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 warmer than the rest of Neptune, which averages approximately ?200 °C(70 K).Acer PA-1650-02 Adapter
The warmth differential is enough to let methane, which elsewhere lies frozen in Neptune's upper atmosphere, leak out as gas 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. Sony CYBER-SHOT DSC-T10 Battery
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.HP Compaq Business 6715b Battery
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.Kodak KLIC-7004 Battery
Storms
In 1989, the Great Dark Spot, an anti-cyclonic storm system spanning 13000×6600 km, was discovered by NASA's Voyager 2spacecraft. The storm resembled the Great Red Spot of Jupiter. Some five years later, on November 2, 1994, the Hubble Space Telescope did not see the Great Dark Spot on the planet.Acer Aspire 5920G Adapter
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.Canon Digital IXUS 90 IS Battery
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 2approached the planet, a bright core developed and can be seen in most of the highest-resolution images.HP 2133 Mini-Note PC Adapter
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.Toshiba PA3536U-1BRS Battery
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. HP Compaq Business NX6110 Battery
Dark spots may dissipate when they migrate too close to the equator or possibly through some other unknown mechanism.
Internal heat
Neptune's more varied weather when compared to Uranus is believed to be due in part to its higher internal heat.HP Pavilion DV9000 Adapter
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).Dell Studio 1537 Battery
Deeper inside the layers of gas, 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; while Neptune radiates about 2.61 times as much energy as it receives from the Sun.HP PPP009H Adapter
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, conversion of methane under high pressure into hydrogen, Sony VGP-BPS8 Battery
diamond and longer hydrocarbons (the hydrogen and diamond would then rise and sink, respectively, releasing gravitational potential energy), and convection in the lower atmosphere that causes gravity waves to break above the tropopause. Dell PA-12 Adapter
Orbit and rotation
The average distance between Neptune and the Sun is 4.50 billion km (about 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.Sony Cyber-shot DSC-T7/B Battery
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 between perihelion andaphelion, the nearest and most distant points of the planet from the Sun along the orbital path, respectively.Dell LATITUDE M65 Battery
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. The long orbital period of Neptune means that the seasons last for forty Earth years.[76] Its sidereal rotation period (day) is roughly 16.11 hours. HP Compaq 6720s Adapter
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. Acer AS07B41 Battery
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,[92]and it results in strong latitudinal wind shear.Dell Vostro 1310 Battery
Orbital resonances
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.Sony VGP-BPL13 Battery
Much in the same way that Jupiter's gravity dominates the asteroid belt, shaping its structure, so Neptune's gravity 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.Sony VGP-BPS13 Battery
There do exist orbits within these empty regions where objects can survive for the age of the Solar System. These resonances occur when Neptune's orbital period is a precise fraction of that of the object, 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 by the time Neptune returns to its original position. Sony VGP-BPS13/B Battery
The most heavily populated resonance in the Kuiper belt, with over 200 known objects,[95] is the 2:3 resonance. Objects in this resonance complete 2 orbits for every 3 of Neptune, and are known as plutinos because the largest of the known Kuiper belt objects, Pluto, is among them.Sony VGP-BPS13/S Battery
Although Pluto crosses Neptune's orbit regularly, the 2:3 resonance ensures they can never collide.[97] The 3:4, 3:5, 4:7 and 2:5 resonances are less populated.
Neptune possesses a number of trojan objects occupying the Sun-Neptune L4 Lagrangian point— a gravitationally stable region leading it in its orbit.Sony VGP-BPS13A/B Battery
Neptune trojans can be viewed as being in a 1:1 resonance with Neptune. Neptune trojans are remarkably stable in their orbits, and are likely to have formed alongside Neptune rather than being captured. The first and so far only object identified as associated with Neptune's trailing L5 Lagrangian pointis 2008 LC18.Sony VGP-BPS13A/S Battery
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,Sony VGP-BPS13AS Battery
and various hypotheses have been advanced to explain their creation. 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.Sony VGP-BPS13B/B Battery
An alternative concept is that they formed closer to the Sun, where the matter density was higher, and then subsequentlymigrated to their current orbits after the removal of the gaseous protoplanetary disc. This hypothesis of migration after formation is currently favoured,Sony VGP-BPS13B/Q Battery
due to its ability to better explain the occupancy of the populations of small objects observed in the trans-Neptunian region. The current most widely accepted explanation of the details of this hypothesis is known as the Nice model, which explores the effect of a migrating Neptune and the other giant planets on the structure of the Kuiper belt.Sony VGP-BPS13B/S Battery
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.Sony VGP-BPS13Q Battery
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, Sony VGP-BPS13S Battery
and it is slowly spiraling inward because of tidal acceleration and eventually will be torn apart, in about 3.6 billion years, when it reaches the Roche limit. In 1989, Triton was the coldest object that had yet been measured in the solar system,[110] with estimated temperatures of ?235 °C (38 K). Sony VGP-BPL21 Battery
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.Sony VGP-BPS21 Battery
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. Sony VGP-BPS21/S Battery
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.Sony VGP-BPS21A Battery
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.
Observation
Neptune is never visible to the naked eye, having a brightness between magnitudes +7.7 and +8.0,Sony VGP-BPS21A/B Battery
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.[116] A telescope or strong binoculars will resolve Neptune as a small blue disk, similar in appearance to Uranus.Sony VGP-BPS21B Battery
Because of the distance of Neptune from the Earth, the angular diameter of the planet only ranges from 2.2 to 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.Sony VGP-BPL8 Battery
From the Earth, Neptune goes through apparent retrograde motion every 367 days, resulting in a looping motion against the background stars during eachopposition. These loops carried it close to the 1846 discovery coordinates in April and July 2010 and will again in October and November 2011.Sony VGP-BPL8A Battery
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. Sony VGP-BPL8B Battery
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.
Exploration
Voyager 2's closest approach to Neptune occurred on August 25, 1989. Sony VGP-BPS8 Battery
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, Neptune All Night.Sony VGP-BPS8A Battery
During the encounter, signals from the spacecraft required 246 minutes to reach the Earth. Hence, for the most part, the Voyager 2mission relied on pre-loaded commands for the Neptune encounter. The spacecraft performed a near-encounter with the moon Nereid before it came within 4400 km of Neptune's atmosphere on August 25, Sony VGP-BPS8B Battery
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. HP Compaq Business 6910p Battery
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.Panasonic LUMIX DMC-TZ4S Battery
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.Sony NP-FH100 Battery
Neptune has thirteen known moons, by far the largest of which is Triton, discovered by William Lassell 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. Neptune's moons are named for minor water deities in Greek mythology.Toshiba Equium M50-192 Battery
Unique among all large planetary moons, Triton is an irregular satellite, as its orbit is retrograde to Neptune's rotation and inclined relative to the planet's equator. The next-largest irregular satellite in the Solar System, Saturn's moon Phoebe, is only 0.03% Triton's mass. Apple MacBook Pro Battery
Triton is massive enough to have achieved hydrostatic equilibrium and to retain a thin atmosphere capable of forming clouds and hazes. Both its atmosphere and its surface are composed mainly of nitrogen with small amounts of methane and carbon monoxide.Apple PowerBook G4 Battery
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 K(?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.Acer BATBL50L6 Battery
Some of these orbit among Neptune's rings. The largest of them is Proteus.
Neptune also has six outer irregular satellites, including Nereid, whose orbits are much farther from Neptune, have high inclinations, and are mixed between prograde and retrograde. The two outermost ones, Psamathe and Neso, have the largest orbits of any natural satellites discovered in the Solar System to date.Canon EOS 450D Battery
Discovery
Triton was discovered by William Lassell in 1846, just seventeen days after the discovery of Neptune.[1] Nereid was discovered by Gerard P. Kuiper in 1949. The third moon, later named Larissa, was first observed by Harold J. Reitsema, William B. Hubbard, Larry A. Lebofsky and David J. Dell 451-10617 battery
Tholen on May 24, 1981. The astronomers were observing a star's close approach to Neptune, looking for rings similar to those discovered around Uranus four years earlier.[3] If rings were present, the star's luminosity would decrease slightly just before the planet's closest approach.Acer Travelmate 2400 Battery
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 flew by Neptune in 1989. Voyager 2 recovered Larissa and discovered five inner moons: Naiad, Thalassa,Despina, Galatea and Proteus.Dell Inspiron 1525 Adapter
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, Laomedeia, and Neso.
Names
Triton did not have an official name until the twentieth century.Compaq Presario 2100 Adapter
The name "Triton" was suggested by Camille Flammarion 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's position as god of the sea:Acer Aspire 1362 Battery
either from Greek mythology, usually children of Poseidon, the Greek Neptune (Triton, Proteus, Despina, Thalassa); classes of minor Greek water deity (Naiad, Nereid); or specific Nereids (Halimede, Galatea, Neso, Sao, Laomedeia, Psamathe).[9]
Two asteroids share the same names as moons of Neptune: 74 Galatea and 1162 Larissa.Toshiba Equium M50-192 Battery
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.Dell XPS M1330 Battery
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), Thalassa (moon), Despina, Galatea, Larissa and Proteus.Acer Travelmate 2200 Adapter
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. The two innermost satellites, Naiad and Thalassa, orbit between the Galle and LeVerrier rings.HP Compaq 6735b Adapter
Despina may be a shepherd moon of the LeVerrier ring, as 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.Dell Vostro 1000 Battery
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.HP Compaq nx7300 Adapter
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, with several flat or slightly concave facets 150 to 250 km in diameter.Asus f82 Battery
At about 400 km, it is larger than the Saturnian moon Mimas, 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.Dell XPS M1330 Battery
All of Neptune's inner moons are dark objects: their geometrical albedo ranges from 7 to 10%.[15] 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 moons of Uranus.HP Compaq Business 6910p Battery
Irregular moons
In order of their distance from the planet, the irregular moons are Triton, Nereid, Halimede, Sao, Laomedeia, Neso and Psamathe, a group that includes both prograde and retrograde objects.[10] The five outer moons are similar to the irregular moons of other giant planets.Compaq PRESARIO R3000 Battery
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, which is primarily nitrogen with small amounts of methane and carbon monoxide.[16] The pressure on Triton's surface is about 14 ?bar.HP Compaq Business NX6110 Battery
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 K (?235.2 °C). Its surface is covered by nitrogen, methane, carbon dioxide and water ices and has a high geometrical albedo of more than 70%.Dell Latitude D610 Adapter
The Bond albedo is even higher, reaching up to 90%.Surface features include the large southern polar cap, older cratered planes cross-cut by graben and scarps, as well as youthful features probably formed by endogenic processes like cryovolcanism.Asus Eee PC 701 Adapter
Voyager 2 observations revealed a number of activegeysers within the polar cap heated by the Sun, which eject plumes to the height of up to 8 km.[4] Triton has a relatively high density of about 2 g/cm3 indicating that rocks constitute about two thirds of its mass, and ices (mainly water ice) the remaining one third. HP Compaq Business NX6325 Battery
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.Dell Studio XPS 16 Battery
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 or chaotic rotation combined with an elongated shape and bright or dark spots on the surface.Acer Aspire 5520 Battery
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.Acer TravelMate 5720 Adapter
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 in the solar system, owing primarily to its large distance from the Sun; this allows it to retain control of such distant moons.HP Compaq 6735s Adapter
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. Dell XPS M1330 Battery
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.HP Compaq nc6230 Adapter
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, Dell T117C Battery
the satellite system of Neptune does not follow the 1/10,000 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.Asus x5dij-sx039c Battery
One of them postulates that Triton was captured in a three-bodyencounter. In this scenario, Triton is the surviving member of a binary[note 1] 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.Dell Inspiron 1464 Battery
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.
The rings of Neptune consist primarily of five principal rings predicted in 1984 by André Brahic and imaged in 1989 by the Voyager 2spacecraft.HP Compaq 6720s Adapter
At their densest, they are comparable to the less-dense portions of Saturn's main rings such as the C ring and the Cassini Division, and much of Neptune's ring system is quite tenuous, faint and dusty, more closely resembling the rings of Jupiter. Neptune's rings are named after astronomers who contributed important work on the planet:Dell Latitude D630 Adapter
Galle, Le Verrier, Lassell, Arago, and Adams. Neptune also has a faint unnamed ring coincident with the orbit of Neptunian moon Galatea. Three other moons orbit between the rings: Naiad, Thalassa andDespina.
The rings of Neptune are made of extremely dark material, likely organic compounds processed by radiation, similar to that found in the rings of Uranus.HP Pavilion dm4 Battery
The proportion of dust in the rings (between 20% and 70%) is high,[4] while their optical depth is low to moderate, at less than 0.1.Uniquely, the Adams ring includes five distinct arcs, named Fraternité, Égalité 1 and 2, Liberté, and Courage. Sony NP-FS11 Battery
The arcs occupy a narrow range of orbital longitudes and are remarkably stable, having changed only slightly since their initial detection in 1980. How the arcs are stabilized is still under debate. However, their stability is probably related to the resonant interaction between the Adams ring and its inner shepherd moon, Galatea.Dell Inspiron 1520 Adapter
Discovery and observations
The first mention of rings around Neptune dates back to 1846 when William Lassell, the discoverer of Neptune's largest moon Triton, thought he had seen a ring around the planet. However, his claim was never confirmed and it is likely that it was an observational artifact. Toshiba PA3399U-1BRS Battery
The first reliable detection of a ring was made in 1968 by stellar occultation, although that result would go unnoticed until 1977 when the rings of Uranus were discovered. Soon after the Uranus discovery, a team from Villanova University led by Harold J. Reitsema began searching for rings around Neptune. Acer Aspire 5920G Adapter
On 24 May 1981, they detected a dip in a star's brightness during one occultation; however, the manner in which the star dimmed did not suggest a ring. Later, after the Voyager fly-by, it was found that the occultation was due to the small Neptunian moonLarissa, a highly unusual event.Acer Aspire 5920 Battery
In the 1980s, significant occultations were much rarer for Neptune than for Uranus, which lay near the Milky Way at the time and was thus moving against a denser field of stars. Neptune's next occultation, on 12 September 1983, resulted in a possible detection of a ring.IBM Thinkpad T40 Adapter
However, ground-based results were inconclusive. Over the next six years, approximately 50 other occultations were observed with only about one-third of them yielding positive results.Something (probably incomplete arcs) definitely existed around Neptune, but the features of the ring system remained a mystery.Nikon COOLPIX 4300 Battery
The Voyager 2 spacecraft made the definitive discovery of the Neptunian rings during its fly-by of Neptune in 1989. It confirmed that occasional occultation events observed before were indeed caused by the arcs within the Adams ring (see below).Apple MB771 Battery
After the Voyager fly-by the previous terrestrial occultation observations were reanalyzed yielding features of the ring's arcs as they were in 1980s, which matched those found by Voyager almost perfectly.
Since Voyager's fly-by, the brightest rings (Adams and Le Verrier) have been imaged with the Hubble Space Telescope and Earth-based telescopes, owing to advances in resolution and light-gathering power.Sony DSC-P5 Battery
They are visible, slightly above background noise levels, at methane-absorbing wavelengths in which the glare from Neptune is significantly reduced. The fainter rings are still far below the visibility threshold.Dell Inspiron 6400 Adapter
General properties
Neptune possesses five distinct rings named, in order of increasing distance from the planet, Galle, Le Verrier, Lassell, Arago and Adams. In addition to these well-defined rings, Neptune may also possess an extremely faint sheet of material stretching inward from the Le Verrier to the Galle ring, and possibly farther in toward the planet.Toshiba PA3534U-1BRS Battery
Three of the Neptunian rings are narrow, with widths of about 100 km or less; in contrast, the Galle and Lassell rings are broad—their widths are between 2,000 and 5,000 km.[4] The Adams ring consists of five bright arcs embedded in a fainter continuous ring.Sony NP-FP50 Battery
Proceeding counterclockwise, the arcs are: Fraternité, Égalité 1 and 2, Liberté, and Courage. The first three names mean liberty, equality, and fraternity, after the famous motto of the French Revolution. The terminology was suggested by their original discoverers, who had found them during stellar occultations in 1984 and 1985.HP Compaq nx7300 Adapter
Four small Neptunian moons have orbits inside the ring system: Naiad and Thalassa orbit in the gap between the Galle and Le Verrier rings; Despina is just inward of the Le Verrier ring; and Galatea lies slightly inward of the Adams ring,[3] embedded in an unnamed faint, narrow ringlet.Dell Latitude D820 Adapter
The Neptunian rings contain a large quantity of micrometer-sized dust: the dust fraction by cross-section area is between 20% and 70%.[6] In this respect they are similar to the rings of Jupiter, in which the dust fraction is 50%–100%, and are very different from the rings of Saturn and Uranus, which contain little dust (less than 0.1%).Toshiba PA3399U-1BRS Battery
The particles in Neptune's rings are made from a dark material; probably a mixture of ice with radiation-processed organics. The rings are reddish in color, and their geometrical (0.05) and Bond (0.01–0.02) albedos are similar to those of the Uranian rings' particles and the inner Neptunian moons.Dell Studio XPS 1640 Battery
The rings are generally optically thin (transparent); their normal optical depths do not exceed 0.1.[4] As a whole, the Neptunian rings resemble those of Jupiter; both systems consist of faint, narrow, dusty ringlets and even fainter broad dusty rings.[Dell Latitude D830 Battery
The rings of Neptune, like those of Uranus, are thought to be relatively young; their age is probably significantly less than that of the Solar System.[4] Also, like those of Uranus, Neptune's rings likely resulted from the collisional fragmentation of onetime inner moons.Dell Inspiron E1505 Adapter
Such events create moonlet belts, which act as the sources of dust for the rings. In this respect the rings of Neptune are similar to faint dusty bands observed by Voyager 2 between the main rings of Uranus.
Inner rings
The innermost ring of Neptune is called the Galle ring after Johann Gottfried Galle, the first person to see Neptune through a telescope (1846).Asus Eee PC 1201PN Battery
It is about 2,000 km wide and orbits 41,000–43,000 km from the planet. It is a faint ring with an average normal optical depth of around 10?4, and with an equivalent depth of 0.15 km. The fraction of dust in this ring is estimated from 40% to 70%.
The next ring is named the Le Verrier ring after Urbain Le Verrier, who predicted Neptune's position in 1846.Asus Eee PC 701 Adapter
With an orbital radius of about 53,200 km, it is narrow, with a width of about 113 km.[5]Its normal optical depth is 0.0062 ± 0.0015, which corresponds to an equivalent depth of 0.7 ± 0.2 km.[5] The dust fraction in the Le Verrier ring ranges from 40% to 70%.Dell XPS M1330 Battery
The small Neptunian moon Despina, which orbits just inside of it at 52,526 km, may play a role in the ring's confinement by acting as a shepherd.
The Lassell ring, also known as the plateau, is the broadest ring in the Neptunian system.fujifilm np95 Battery
It is the namesake of William Lassell, the English astronomer who discovered Neptune's largest moon,Triton. This ring is a faint sheet of material occupying the space between the Le Verrier ring at about 53,200 km and the Arago ring at 57,200 km.[3] Its average normal optical depth is around 10?4, which corresponds to an equivalent depth of 0.4 km.Asus Eee PC 900 Adapter
The ring's dust fraction is in the range from 20% to 40%.
There is a small peak of brightness near the outer edge of the Lassell ring, located at 57,200 km from Neptune and less than 100 km wide,[3] which some planetary scientists call the Arago ring afterFrançois Arago, a French mathematician, physicist, astronomer and politician.[16] However, many publications do not mention the Arago ring at all.Sony VAIO PCG-713 Battery
Adams ring
The outer Adams ring, with an orbital radius of about 63,930 km,[3] is the best studied of Neptune's rings.[3] It is named after John Couch Adams, who predicted the position of Neptune independently of Le Verrier.Dell Latitude D830 Adapter
This ring is narrow, slightly eccentric and inclined, with total width of about 35 km (15–50 km), and its normal optical depth is around 0.011 ± 0.003 outside the arcs, which corresponds to the equivalent depth of about 0.4 km.[5] The fraction of dust in this ring is from 20% to 40%—lower than in other narrow rings.Dell Studio XPS 1640 Battery
Neptune's small moon Galatea, which orbits just inside of the Adams ring at 61,953 km, acts like a shepherd, keeping ring particles inside a narrow range of orbital radii through a 42:43 outerLindblad resonance.[11] Galatea's gravitational influence creates 42 radial wiggles in the Adams ring with an amplitude of about 30 km, which have been used to infer Galatea's mass.Panasonic LUMIX DMC-TZ4S Battery
Arcs
The brightest parts of the Adams ring, the ring arcs, were the first elements of Neptune's ring system to be discovered.The arcs are discrete regions within the ring in which the particles that comprise it are mysteriously clustered together. The Adams ring is known to comprise five short arcs, which occupy a relatively narrow range of longitudes from 247° to 294°.HP Compaq Business NX6320 Battery
In 1986 they were located between longitudes of:
- 247–257° (Fraternité),
- 261–264° (Égalité 1),
- 265–266° (Égalité 2), Canon POWERSHOT G2 Battery
- 276–280° (Liberté),
- 284.5–285.5° (Courage).
The brightest and longest arc was Fraternité; the faintest was Courage. The normal optical depths of the arcs are estimated to lie in the range 0.03–0.09 (0.034 ± 0.005 for the leading edge of Liberté arc as measured by stellar occultation);[5] the radial widths are approximately the same as those of the continuous ring—about 30 km.Dell Latitude E6500 Battery
The equivalent depths of arcs vary in the range 1.25–2.15 km (0.77 ± 0.13 km for the leading edge of Liberté arc).[5] The fraction of dust in the arcs is from 40% to 70%.[13] The arcs in the Adams ring are somewhat similar to the arc in Saturn's G ring.Dell LATITUDE D630 Battery
The highest resolution Voyager 2 images revealed a pronounced clumpiness in the arcs, with a typical separation between visible clumps of 0.1° to 0.2°, which corresponds to 100–200 km along the ring. Because the clumps were not resolved, they may or may not include larger bodies,Asus R33030 Adapter
but are certainly associated with concentrations of microscopic dust as evidenced by their enhanced brightness when backlit by the Sun.
The arcs are quite stable structures. They were detected by ground based stellar occultations in the 1980s, Dell Mini 1011 Battery
by Voyager 2 in 1989 and by Hubble Space Telescope and ground based telescopes in 1997–2005 and remained at approximately the same orbital longitudes.However some changes have been noticed. The overall brightness of arcs decreased since 1986.Acer Aspire 5052ANWXMi Battery
The Courage arc jumped forward by 8° to 294° (it probably jumped over to the next stable co-rotation resonance position) while the Liberté arc had almost disappeared by 2003.[19] The Fraternité and Égalité (1 and 2) arcs have demonstrated irregular variations in their relative brightness. Dell Mini 1011v Battery
Their observed dynamics is probably related to the exchange of dust between them. Courage, a very faint arc found during the Voyager flyby, was seen to flare in brightness in 1998, while more recently it was back to its usual dimness. HP Compaq nx7300 Adapter
Visible light observations show that the total amount of material in the arcs has remained approximately constant, but they are dimmer in the infrared light wavelengths where previous observations were taken.
Confinement
The arcs in the Adams ring remain unexplained.Dell Vostro 1510 Battery
Their existence is a puzzle because basic orbital dynamics imply that they should spread out into a uniform ring over a matter of years. Several theories about the arcs' confinement have been suggested, the most widely publicized of which holds that Galatea confines the arcs via its 42:43 co-rotational inclination resonance (CIR).Toshiba PA3534U-1BRS Battery
The resonance creates 84 stable sites along the ring's orbit, each 4° long, with arcs residing in the adjacent sites. However measurements of the rings' mean motion with Hubble and Keck telescopes in 1998 led to the conclusion that the rings are not in CIR with Galatea.Asus M50 Battery
A later model suggested that confinement resulted from a co-rotational eccentricity resonance (CER).The model takes into account the finite mass of the Adams ring, which is necessary to move the resonance closer to the ring. A byproduct of this theory is a mass estimate for the Adams ring—about 0.002 of the mass of Galatea.Asus Eee PC 901 Battery
A third theory proposed in 1986 requires an additional moon orbiting inside the ring; the arcs in this case are trapped in its stable Lagrangian points. However Voyager 2's observations placed strict constraints on the size and mass of any undiscovered moons, making such a theory unlikely.Dell Inspiron 6400 Battery
Some other more complicated theories hold that a number of moonlets are trapped in co-rotational resonances with Galatea, providing confinement of the arcs and simultaneously serving as sources of the dust.HP Compaq Business NC6220 Battery
Exploration
The rings were investigated in detail during the Voyager 2 spacecraft's flyby of Neptune in August 1989.[4] They were studied with optical imaging, and through observations of occultations in ultraviolet and visible light.Sony VGP-BPS9 Battery
Voyager 2 observed the rings in different geometries relative to the Sun, producing images of back-scattered, forward-scattered and side-scattered light.[g][4] Analysis of these images allowed derivation of the phase function (dependence of the ring's reflectivity on the angle between the observer and Sun), and geometrical and Bond albedo of ring particles.Sony VGP-BPS13 Battery
Analysis of Voyager's images also led to discovery of six inner moons of Neptune, including the Adams ring shepherd Galatea.
Neptune was mathematically predicted before it was directly observed.HP Compaq nx7300 Adapter
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 astronomer Johann Gottfried Galle (assisted by Heinrich Louis d'Arrest), working from Le Verrier's calculations. HP Compaq 2510p Adapter
It was a sensational moment of 19th century science and dramatic confirmation of Newtonian gravitational theory. In François Arago's apt phrase, Le Verrier had discovered a planet "with the point of his pen."
In retrospect, after it was discovered it turned out it had been observed many times before, Dell Studio PP39L Battery
but not recognized, and there were others who made various calculations about its location, but did not lead to its observation. By 1846, the planet Uranus had completed nearly one full orbit since its discovery byWilliam Herschel in 1781, and astronomers had detected a series of irregularities in its path which could not be entirely explained by Newton's law of gravitation.Nikon COOLPIX 5700 Battery
These irregularities could, however, be resolved if the gravity of a farther, unknown planet were disturbing its path around the Sun. In 1845, astronomers Urbain Le Verrier in Paris and John Couch Adams in Cambridge separately began calculations to determine the nature and position of such a planet. Dell Studio XPS 16 Battery
Unfortunately, Le Verrier's triumph also led to a tense international dispute over priority, as, shortly after the discovery, George Airy, at the time British Astronomer Royal, announced that Adams had also predicted the discovery of the planet. Nevertheless, the Royal Society awarded Le Verrierthe Copley medal in 1846 for his achievement, without mention of Adams.HP Compaq nx7400 Adapter
The discovery of Neptune led to the discovery of its moon Triton by William Lassell just seventeen days later.
Earlier observations
Neptune is invisible to the naked eye as it is too dim (apparent magnitude is never less than 7.7 ) and too small (peak angular size is 2.4 arcseconds ). HP Pavilion DV6500 Adapter
Therefore, the first observations of Neptune were only possible after the invention of the telescope. There is evidence that Neptune was seen and recorded by Galileo Galilei in 1613, Jérôme Lalande in 1795 and John Herschel in 1830, but none is known to have recognized it as a planet at the time.Dell T117C Battery
These pre-discovery observations were important in accurately determining the orbit of Neptune. Neptune would appear prominently even in early telescopes so other pre-discovery observation records are likely.
Galileo's drawings show that he observed Neptune on December 28, 1612, and again on January 27, 1613;Acer PA-1650-02 Adapter
on both occasions, Galileo mistook Neptune for a fixed star when it appeared very close (inconjunction) to Jupiter in the night sky.[9] Historically it was thought that he believed it to be a fixed blue star, and so he is not credited with its discovery. Acer Aspire 5920G Adapter
At the time of his first observation in December 1612, it was stationary in the sky because it had just turned retrograde that very day; because it was only beginning its yearly retrograde cycle, Neptune's motion was thought to be too slight, and its apparent size too small, to clearly appear to be a planet in Galileo's small telescope.Asus S1 Adapter
However, in July 2009 University of Melbourne physicist David Jamieson announced new evidence suggesting that Galileo was indeed aware that he had discovered something unusual about this star. Galileo, in one of his notebooks, noted the movement of a background star (Neptune) on January 28 and a dot (in Neptune's position)HP Pavilion dv6000 Battery
drawn in a different ink suggests that he found it on an earlier sketch, drawn on the night of January 6, suggesting a systematic search among his earlier observations. However, so far there is neither clear evidence that he identified this moving object as a planet, nor that he published these observations of it. There is no evidence that he ever attempted to observe it again.Ibm Thinkpad T30 Battery
In 1847, Sears C. Walker of the U.S. Naval Observatory searched historical records and surveys for possible prediscovery sightings of the planet Neptune. He found that observations made by Lalande'sstaff at the Paris Observatory in 1795 were in the direction of Neptune's position in the sky. Dell Studio PP39L Battery
In the catalog observations for May 8 and again on May 10 of 1795 a star was observed in the approximate position expected for Neptune. The uncertainty of the position was noted with a colon. HP Pavilion dv5 Adapter
This notation was also used to indicate an observation error so it was not until the original records of the observatory were reviewed that it was established with certainty that the object was Neptune and the position error in the observations made two nights apart was due to the planet's motion across the sky.HP Compaq Business NC6400 Battery
The discovery of these records of Neptune's position in 1795 led to a better calculation of the planet's orbit.
John Herschel almost discovered Neptune the same way his father, William Herschel, had discovered Uranus in 1781, by chance observation. HP Compaq 490306-001 Battery
In an 1846 letter to Wilhelm Struve, John Herschel states that he observed Neptune during a sweep of the sky on July 14, 1830. Although his telescope was powerful enough to resolve Neptune into a small blue disk and show it to be a planet, he did not recognize it at the time and mistook it for a star. Compaq Presario CQ35-100 Battery
Irregularities in Uranus's orbit
In 1781, Anders Johan Lexell was the first to compute the orbit of Uranus and notice that it had irregularities. He suggested that there might be other planets in Solar system that perturb the orbit ofUranus, with the Solar system ranging as far as 100 A. U.HP Compaq HSTNN-LB51 Battery
In 1821, Alexis Bouvard had published astronomical tables of the orbit of Uranus, making predictions of future positions based on Newton's laws of motion and gravitation. Subsequent observations revealed substantial deviations from the tables, leading Bouvard to hypothesize some perturbing body.HP Pavilion ZE4500 Battery
These irregularities or "residuals", both in the planet's ecliptic longitude and in its distance from the Sun, or radius vector, might be explained by a number of hypotheses: the effect of the Sun's gravity, at such a great distance, might differ from Newton's description;HP G62-100EB Battery
or the discrepancies might simply be observational error; or perhaps Uranus was being pulled, or perturbed, by an as-yet undiscovered eighth planet.
Adams learned of the irregularities while still an undergraduate and became convinced of the "perturbation" hypothesis. HP Pavilion DV6-1211AX Battery
Adams believed, in the face of anything that had been attempted before, that he could use the observed data on Uranus, and utilising nothing more than Newton's law of gravitation, deduce the mass, position and orbit of the perturbing body.
After his final examinations in 1843, Adams was elected fellow of his college and spent the summer vacation in Cornwall calculating the first of six iterations.HP Pavilion DV6-1220SO Battery
In modern terms, the problem is an inverse problem, an attempt to deduce the parameters of a mathematical model from observed data. Though the problem is a simple one for modern mathematics after the advent ofelectronic computers, at the time it involved much laborious hand calculation. HP EliteBook 6930P Battery
Adams began by assuming a nominal position for the hypothesised body, using the empirical Bode's law. He then calculated the path of Uranus using the assumed position of the perturbing body and calculated the difference between his calculated path and the observations, in modern terms the residuals.HP Pavilion DV6-1210SA Battery
He then adjusted the characteristics of the perturbing body in a way suggested by the residuals and repeated the process, a process similar to regression analysis.
On 13 February 1844, James Challis, director of the Cambridge Observatory, requested data on the position of Uranus, Compaq Presario CQ71 Battery
for Adams, from Astronomer Royal George Biddell Airy at the Royal Observatory, Greenwich.[1] Adams certainly completed some calculations on 18 September 1845.
Supposedly, Adams communicated his work to Challis in mid-September 1845 but there is some controversy as to how. HP Pavilion DV7-1290EO Battery
The story and date of this communication only seem to have come to light in a letter from Challis to the Athenaeum dated 17 October 1846. However, no document was identified until 1904 when Sampson suggested a note in Adams's papers that describes "the New Planet" and is endorsed, in handwriting not Adams's, with the note "Received in September 1845".HP G6000 Battery
Though this has often been taken to establish Adams's priority, some historians have disputed its authenticity, on the basis that "the New Planet" was not a term current in 1845, and on the basis that the note is dated only after the fact by someone other than Adams.HP HDX X18-1005EA Battery
Further, the results of the calculations are different from those communicated to Airy a few weeks later. Adams certainly gave Challis no detailed calculations and Challis was unimpressed by the description of his method of successively approximating the position of the body,HP Pavilion DV6-3013SL Battery
being disinclined to start a laborious observational programme at the observatory, remarking "while the labour was certain, success appeared to be so uncertain."
Meanwhile, Urbain Le Verrier, on November 10, 1845, presented to the Académie des sciences in Paris a memoir on Uranus, showing that the pre-existing theory failed to account for its motion.HP Compaq HSTNN-IB62 Battery
Unaware of Adams's work, he attempted a similar investigation, and on June 1, 1846, in a second memoir presented to a public meeting of the Académie, gave the position, but not the mass or orbit, of the proposed perturbing body. Le Verrier located Neptune within one degree of its predicted position.HP Pavilion DV6100 Battery
The search
Upon receiving in England the news of Le Verrier's June prediction, George Airy immediately recognized the similarity of Le Verrier's and Adams' solutions. Up until that moment, Adams' work had been little more than a curiosity, but independent confirmation from Le Verrier spurred Airy to organize a secret attempt to find the planet.HP EliteBook 2730P Battery
At a July 1846 meeting of the Board of Visitors of the Greenwich Observatory, with Challis and Sir John Herschel present, Airy suggested that Challis urgently look for the planet with the Cambridge 11.25 inch equatorial telescope, "in the hope of rescuing the matter from a state which is ... almost desperate".HP Pavilion DV9000 Battery
The search was begun by a laborious method on 29 July. Adams continued to work on the problem, providing the British team with six solutions in 1845 and 1846 which sent Challis searching the wrong part of the sky. HP Pavilion DV7 Battery
Only after the discovery of Neptune had been announced in Paris and Berlin did it become apparent that Neptune had been observed on August the 8th and August the 12th but because Challis lacked an up-to-date star-map, it was not recognized as a planet. HP Pavilion DV7-1290EO Battery
Discovery Observation: September 24th 1846
Le Verrier was unaware that his public confirmation of Adams' private computations had set in motion a British search for the purported planet. On 31 August, Le Verrier presented a third memoir, now giving the mass and orbit of the new body.HP Compaq Business 6735S Battery
Having been unsuccessful in his efforts to interest any French astronomer in the problem, Le Verrier finally sent his results by post to Johann Gottfried Galleat the Berlin Observatory. Galle received Le Verrier's letter on 23 September and immediately set to work observing in the region suggested by Le Verrier.HP 540 Battery
Galle's student, Heinrich Louis d'Arrest, suggested that a recently drawn chart of the sky, in the region of Le Verrier's predicted location, could be compared with the current sky to seek the displacement characteristic of a planet, as opposed to a stationary star.HP Compaq Business NW9440 Battery
Neptune was discovered just after midnight, after less than an hour of searching and less than 1 degree from the position Le Verrier had predicted, a remarkable match. After two further nights of observations in which its position and movement were verified, Galle replied to Le Verrier with astonishment: HP Compaq Business TC4400 Battery
"the planet whose place you have [computed] really exists" (emphasis in original). The discovery telescope was an equatorial mounted achromatic refractor by Joseph Fraunhofer's firm Merz und Mahler.
Aftermath
On the announcement of the discovery, Herschel, Challis and Richard Sheepshanks, foreign secretary of the Royal Astronomical Society, HP Compaq 491278-001 Battery
announced that Adams had already calculated the planet's characteristics and position. Airy, at length, published an account of the circumstances, and Adams's memoir was printed as an appendix to the Nautical Almanac. However, it appears that the version published by HP HSTNN-LB31 Battery
Airy had been edited by the omission of a "crucial phrase" to disguise the fact that Adams had quoted only mean longitude and not the orbital elements.
A keen controversy arose in France and England as to the merits of the two astronomers. HP Pavilion DV3-4000 Battery
There was much criticism of Airy in England. Adams was a diffident young man who was naturally reluctant to publish a result that would establish or ruin his career. Airy and Challis were criticised, particularly by James Glaisher, as failing to exercise their proper role as mentors of a young talent. HP Pavilion TX1000 Battery
Challis was contrite but Airy defended his own behaviour, claiming that the search for a planet was not the role of the Greenwich Observatory. On the whole, Airy has been defended by his biographers. In France the claims made for an unknown Englishman were resented as detracting from the credit due to Le Verrier's achievement.HP Pavilion DV6-1210SA Battery
The Royal Society awarded Le Verrier the Copley medal in 1846 for his achievement, without mention of Adams, but Adams's academic reputation at Cambridge, and in society, was assured. As the facts became known, some British astronomers pushed the view that the two astronomers had independently solved the problem of Uranus, and ascribed equal importance to each.HP 448007-001 Battery
But Adams himself publicly acknowledged Le Verrier's priority and credit (not forgetting to mention the role of Galle) in the paper that he gave to the Royal Astronomical Society in November 1846:HP Compaq Business 6530B Battery
I mention these dates merely to show that my results were arrived at independently, and previously to the publication of those of M. Le Verrier, and not with the intention of interfering with his just claims to the honours of the discovery ;HP Pavilion DV5-1015EA Battery
for there is no doubt that his researches were first published to the world, and led to the actual discovery of the planet by Dr. Galle, so that the facts stated above cannot detract, in the slightest degree, from the credit due to M. Le Verrier.HP Pavilion DV6-1230SB Battery
The criticism was soon afterwards made, that both Adams and Le Verrier had been over-optimistic in the precision they claimed for their calculations, and both had greatly overestimated the planet's distance from the sun. Further, it was suggested that they both succeeded in getting the longitude almost right only because of a "fluke of orbital timing". HP Pavilion ZD8181EA Battery
This criticism was discussed in detail by Danjon (1946) who illustrated with a diagram and discussion that while hypothetical orbits calculated by both LeVerrier and Adams for the new planet were indeed of very different size on the whole from that of the real Neptune (and actually similar to each other),HP Pavilion DV9500 Battery
they were both much closer to the real Neptune over that crucial segment of orbit covering the interval of years for which the observations and calculations were made, than they were for the rest of the calculated orbits. So the fact that both the calculators used a much larger orbital major axis than the reality was shown to be not so important, and not the most relevant parameter.HP Pavilion DV4-1125BR Battery
The new planet, at first called "Le Verrier" by Francois Arago, received by consensus the neutral name of Neptune. Its mathematical prediction was a great intellectual feat, but it showed also that Newton's law of gravitation, which Airy had almost called in question, prevailed even at the limits of the solar system.HP Pavilion DV5-1111EA Battery
Adams held no bitterness towards Challis or Airy and acknowledged his own failure to convince the astronomical world:
I could not expect however that practical astronomers, who were already fully occupied with important labours, would feel as much confidence in the results of my investigations, as I myself did.HP Pavilion DV6-1234TX Battery
By contrast, Le Verrier was arrogant and assertive, enabling the British scientific establishment to close ranks behind Adams while the French, in general, found little sympathy with Le Verrier. In 1874–1876, Adams was president of the Royal Astronomical Society when it fell to him to present the gold medal of the year to Le Verrier.HP Pavilion DV3-2008TX Battery
Later analysis
The conventional wisdom that Neptune's discovery should be "credited to both Adams and Le Verrier" has recently been challenged putting in doubt the accounts of Airy, Challis and Adams in 1846.HP Pavilion DV8 Battery
In 1999, Adams's correspondence with Airy, which had been lost by the Royal Greenwich Observatory, was rediscovered in Chile among the possessions of astronomer Olin J. Eggen after his death. In an interview in 2003, historian Nicholas Kollerstrom concluded that Adams's claim to Neptune was far weaker than had been suggested, HP Pavilion DV6-1215SA Battery
as he had vacillated repeatedly over the planet's exact location, with estimates ranging across 20 degrees of arc. Airy's role as the hidebound superior willfully ignoring the upstart young intellect was, according to Kollerstrom, largely constructed after the planet was found, in order to boost Adams's, and therefore Britain's, credit for the discovery.HP Compaq 490306-001 Battery
A later Scientific American article by Sheehan, Kollerstrom and Waff claimed more boldly "The Brits Stole Neptune" and concluded "The achievement was Le Verrier's alone."
Neptune Discovery Telescope
The telescope at New Berlin Observatory (1835–1913), that discovered Neptune, was an achromatic refractor of 9 Paris inch (9.6 English inches or 24.4 cm)Compaq Presario CQ50 Battery
aperture made by the late Joseph Fraunhofer's firm, Merz und Mahler. It was a high performance telescope of its era, with one of the largest achromatic doublets available and a finely made equatorial mount, with a clockwork drive to move the 4 m (13.4?) main tube in time with Earth's rotation.HP Pavilion DV6-1223EO Battery
Eventually the telescope was moved to Deutsches Museum in München, Germany, where it can still be seen in the 21st century as an exhibit.HP Compaq 490306-001 Battery,HP Pavilion DM4 Battery,Dell Latitude E6400 Battery,HP Pavilion DV6-1020ED Battery,HP Pavilion DV7-1290EO Battery
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