Neptune  

Neptune from Voyager 2
Discovery
Discovered by	Urbain Le Verrier John Couch Adams Johann Galle
Discovery date	September 23, 1846[1]
Orbital characteristics[2][3]
Epoch J2000
Aphelion	4,553,946,490 km 30. Urbain Jean Joseph Le Verrier ( March 11, 1811 &ndash September 23, 1877) was a French Mathematician who specialized in Celestial John Couch Adams ( June 5 1819 &ndash January 21, 1892) was a British Mathematician and Astronomer Johann Gottfried Galle ( June 9, 1812 &ndash July 10, 1910) was a German Astronomer at the Berlin Observatory Events 1122 - Concordat of Worms. 1459 - Battle of Blore Heath, the first major battle of the English For the game see 1846 (board game. Year 1846 ( MDCCCXLVI) was a Common year starting on Thursday (link will display In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand 44125206 AU
Perihelion	4,452,940,833 km 29. The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from 76607095 AU
Semi-major axis	4,503,443,661 km 30. In Geometry, the semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae 10366151 AU
Eccentricity	0. In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape 011214269
Orbital period	60,190[4] days 164. The orbital period is the time taken for a given object to make one complete Orbit about another object A day (symbol d is a unit of Time equivalent to 24 Hours and the duration of a single Rotation of planet Earth with respect to the 79 years
Synodic period	367. In Astronomy, a Julian year (symbol a) is a unit of measurement of Time defined The orbital period is the time taken for a given object to make one complete Orbit about another object 49 day[5]
Average orbital speed	5. The orbital speed of a body generally a Planet, a Natural satellite, an artificial satellite, or a Multiple star, is the speed at which it 43 km/s[5]
Mean anomaly	267. In the study of orbital dynamics the mean anomaly of an orbiting body is the Angle the body would have traveled about the center of the orbit's Auxiliary circle 767281°
Inclination	1. Inclination in general is the Angle between a Reference plane and another plane or axis of direction 767975° 6. 43° to Sun's equator
Longitude of ascending node	131. The longitude of the ascending node (☊ or Ω is one of the Orbital elements used to specify the Orbit of an object in space 794310°
Argument of perihelion	265. The argument of periapsis (or argument of perifocus) ( ω) is the Orbital element describing the Angle of an Orbiting body's periapsis 646853°
Satellites	13
Physical characteristics
Equatorial radius	24,764 ± 15 km[6][7] 3. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. Neptune has thirteen known moons. The largest by far is Triton, discovered by William Lassell just seventeen days after the discovery of Neptune itself The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the 883 Earths
Polar radius	24,341 ± 30 km[6][7] 3. A geographical pole, or geographic pole, is either of two fixed points on the surface of a spinning body or Planet, at 90 degrees from the Equator, based 829 Earths
Flattening	0. Ellipticity redirects here For the mathematical topic of ellipticity see Elliptic operator. 0171 ± 0. 0013
Surface area	7. Equation A spheroid centered at the origin and rotated about the z axis is defined by the implicit equation \left(\frac{x}{a}\right^2+\left(\frac{y}{a}\right^2+\left(\frac{z}{b}\right^2 6408×109 km²[4][7] 14. 98 Earths
Volume	6. The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically 254×1013 km³[5][7] 57. 74 Earths
Mass	1. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object 0243×1026 kg[5] 17. 147 Earths
Mean density	1. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 638 g/cm³[5][7]
Equatorial surface gravity	11. The surface gravity, g, of an astronomical or other object is the Gravitational acceleration experienced at its surface 15 m/s²[5][7] 1. 14 g
Escape velocity	23. g-force (also G-force, g-load) is a measurement of an object's Acceleration expressed in g s In Physics, escape velocity is the speed where the Kinetic energy of an object is equal to the magnitude of its Gravitational potential energy 5 km/s[5][7]
Sidereal rotation period	0. The rotation period of an astronomical object is the time it takes to complete one revolution around its Axis of rotation relative to the background stars 6713 day[5] 16 h 6 min 36 s
Equatorial rotation velocity	2. 68 km/s 9,660 km/h
Axial tilt	28. In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. 32°[5]
North pole right ascension	19h 57m 20s[6]
North pole declination	42. Right ascension (abbrev RA; symbol α) is the Astronomical term for one of the two Coordinates of a point on the Celestial sphere In Astronomy, declination (abbrev dec or δ) is one of the two coordinates of the Equatorial coordinate system, the other being either 950°[6]
Albedo	0. The albedo of an object is the extent to which it diffusely reflects light from the sun 290 (bond) 0. The Bond albedo is the fraction of power in the total electromagnetic radiation incident on an astronomical body that is scattered back out into space 41 (geom.)[5]
Surface temp.    1 bar level    0. The geometric albedo of an astronomical body is the ratio of its actual brightness at zero phase angle (i Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature 1 bar	min mean max 72 K[5] 55 K[5]
Apparent magnitude	8. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 0 to 7. 78[5][8]
Angular diameter	2. The angular diameter of an object as seen from a given position is the "visual diameter" of the object measured as an angle 2″—2. A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60 of one degree. 4″[5][8]
Adjectives	Neptunian
Atmosphere[5]
Scale height	19. A scale height is a term often used in scientific contexts for a distance over which a quantity decreases by a factor of e. 7 ± 0. 6 km
Composition	80±3. 2% Hydrogen (H2) 19±3. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 2% Helium 1. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical 5±0. 5% Methane ~0. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. 019% Hydrogen deuteride (HD) ~0. Hydrogen deuteride is a bi-atomic substance of the two isotopes of Hydrogen: the majority isotope 1H protium and 2H Deuterium 00015% Ethane Ices: Ammonia Water Ammonium hydrosulfide(NH4SH) Methane (?)

Neptune (pronounced /ˈnɛptjuːn/^[9], AmE: [ˈnɛp·tuːn] (help·info)) is the eighth and farthest planet from the Sun in the Solar System. ETHANE is a mnemonic indicating a protocol used by Emergency services to report situations which they may be faced with especially as it relates to major incidents where Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Water is a common Chemical substance that is essential for the survival of all known forms of Life. Ammonium hydrosulfide is the Chemical compound with the formula (NH4SH Phonology North American English regional phonology In many ways compared to English English, North American English is conservative in its Phonology. A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is The Sun (Sol is the Star at the center of the Solar System. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. 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. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 ^[10] The planet is named after the Roman god of the sea. Neptune (Neptūnus is the god of water and the sea in Roman mythology, a brother of Jupiter and Pluto. Its astronomical symbol is , a stylized version of the god Neptune's trident. Astronomical symbols are symbols used to represent various Celestial objects theoretical constructs and observational events in Astronomy. A trident (ˈtrаɪdənt also called a leister or gig, is a three- pronged Spear.

Discovered on September 23, 1846,^[1] Neptune was the first planet found by mathematical prediction rather than regular observation. Events 1122 - Concordat of Worms. 1459 - Battle of Blore Heath, the first major battle of the English For the game see 1846 (board game. Year 1846 ( MDCCCXLVI) was a Common year starting on Thursday (link will display Unexpected changes in the orbit of Uranus led astronomers to deduce the gravitational perturbation of an unknown planet. Gravitation is a natural Phenomenon by which objects with Mass attract one another 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 were discovered before the 20th century. TemplateInfobox Planet.--> Triton (ˈtraɪtən, or as in Greek Neptune has thirteen known moons. The largest by far is Triton, discovered by William Lassell just seventeen days after the discovery of Neptune itself Neptune has been visited by only one spacecraft, Voyager 2, which flew by the planet on August 25, 1989. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. Events 1248 - The Dutch city of Ommen receives city rights and fortification rights from Otto III the Year 1989 ( MCMLXXXIX) was a Common year starting on Sunday (link displays 1989 Gregorian calendar)

Neptune's atmosphere is primarily composed of hydrogen and helium along with traces of methane. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. The methane in the atmosphere, in part, accounts for the planet's blue appearance. Azure is a Blue Color on the HSV color wheel at 210 degrees Azure is the Hue that is halfway between Blue and Cyan ^[11] Neptune also has the strongest winds of any planet in the solar system, measured as high as 2,100 kilometres per hour (1,300 mph). (For the South African airport with IATA code "KMH" see Johan Pienaar Airport. ^[12] 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. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. A space probe is a scientific Space exploration mission in which a Robotic spacecraft leaves the Gravity well of Earth and approaches the Neptune's temperature at its cloud tops is usually close to −218 °C (55. The Celsius Temperature scale was previously known as the centigrade scale. 1 K), one of the coldest in the solar system, due to its great distance from the Sun. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The temperature in Neptune's centre is about 7,000 °C (7,270 K), which is comparable to the Sun's surface and similar to most other known planets. Neptune has a faint and fragmented ring system, which may have been detected during the 1960s but was only indisputably confirmed by Voyager 2. A planetary ring is a ring of Cosmic dust and other small particles Orbiting around a Planet in a flat disc-shaped region ^[13]

History

Discovery

Main article: Discovery of Neptune

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. The discovery of the planet Neptune remains notable because it resulted from theoretical prediction of the existence of a major solar-system body without having previously seen Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher Events 1065 - Westminster Abbey is Consecrated. 1308 - The reign of Emperor Hanazono, Emperor of Events 98 - Trajan becomes Roman Emperor after the death of Nerva. The fixed stars (from the Latin stellae fixae) are celestial objects that do not seem to move in relation to the other stars of the night sky Conjunction is a term used in Positional astronomy and Astrology. ^[14] 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. Direct motion is the motion of a Planetary body in a direction similar to that of other bodies within its system and is sometimes called prograde motion. 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. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. ^[15]

In 1821, Alexis Bouvard published astronomical tables of the orbit of Uranus. Alexis Bouvard ( June 27, 1767 &ndash June 7, 1843) was a French Astronomer. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star ^[16] Subsequent observations revealed substantial deviations from the tables, leading Bouvard to hypothesize that an unknown body was perturbing the orbit through gravitational interaction. Gravitation is a natural Phenomenon by which objects with Mass attract one another In 1843, John Couch Adams calculated the orbit of a hypothesized eighth planet that would account for Uranus' motion. John Couch Adams ( June 5 1819 &ndash January 21, 1892) was a British Mathematician and Astronomer He sent his calculations to Sir George Airy, the Astronomer Royal, who asked Adams for a clarification. Sir George Biddell Airy FRS (27 July 1801&ndash2 January 1892 was an English Mathematician and Astronomer, Astronomer Royal Astronomer Royal is a senior post in the Royal Household of the Sovereign of the United Kingdom. Adams began to draft a reply but never sent it and did not aggressively pursue work on the Uranus problem. ^[17][18]

Urbain Le Verrier, the mathematician who codiscovered Neptune. Urbain Jean Joseph Le Verrier ( March 11, 1811 &ndash September 23, 1877) was a French Mathematician who specialized in Celestial

In 1845–46, Urbain Le Verrier, independently of Adams, rapidly developed his own calculations but also experienced difficulties in encouraging any enthusiasm in his compatriots. Urbain Jean Joseph Le Verrier ( March 11, 1811 &ndash September 23, 1877) was a French Mathematician who specialized in Celestial 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. James Challis FRS ( 12 December 1803 &ndash 3 December 1882) was an English Clergyman Physicist and Challis vainly scoured the sky throughout August and September. ^[19][20]

Meantime, Le Verrier by letter urged Berlin Observatory astronomer Johann Gottfried Galle to search with the observatory's refractor. The Berlin Observatory ( Berliner Sternwarte in German has its origins in 1700 when Gottfried Leibniz initiated the Societät der Wissenschaften (Brandenburgische Johann Gottfried Galle ( June 9, 1812 &ndash July 10, 1910) was a German Astronomer at the Berlin Observatory A refracting or refractor telescope is a dioptric Telescope that uses a lens as its objective to form an image Heinrich d'Arrest, a student at the observatory, suggested to Galle that they could compare 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. A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is 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. Events 1122 - Concordat of Worms. 1459 - Battle of Blore Heath, the first major battle of the English For the game see 1846 (board game. Year 1846 ( MDCCCXLVI) was a Common year starting on Thursday (link will display Challis later realized that he had observed the planet twice in August, failing to identify it owing to his casual approach to the work. ^[19][21]

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 misappropriated by astronomer Olin J. Eggen for nearly three decades and were only rediscovered (in his possession) immediately after his death. The Royal Observatory Greenwich (formerly the Royal Greenwich Observatory or RGO) was commissioned in 1675 by King Charles II, with the Olin Jeuck Eggen ( July 9 1919 &ndash October 2 1998) was an American Astronomer. ^[22] 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. Dennis Rawlins ( 1937 Baltimore Maryland, US &ndash is an American astronomer historian and publisher In a 1992 article in the journal Dio he deemed the British claim "theft". ^[23] "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. University College London ( UCL) is a multi-faculty university institution based in the United Kingdom and a constituent college of the University of London ^[24][25]

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 Roman mythology, Janus (or Ianus was the god of Gates Doors doorways beginnings and endings In England, Challis put forward the name Oceanus. Ocean (Ὠκεανός was believed to be the world-ocean in Classical antiquity, which the ancient Romans and Greeks considered to be ^[26]

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. The Bureau des Longitudes is a French scientific institution founded by decree of June 25 1795 and charged with the improvement of nautical Navigation ^[27] 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. François Jean Dominique Arago ( Francesc Joan Dominic Aragó; 26 February 1786 2 October 1853 was a French Catalan Mathematician, However, this suggestion met with stiff resistance outside France. This article is about the country For a topic outline on this subject see List of basic France topics. ^[28] French almanacs quickly reintroduced the name Herschel for Uranus, after that planet's discoverer Sir William Herschel, and Leverrier for the new planet. Sir Frederick William Herschel FRS KH ( 15 November 1738 – 25 August 1822) was a German -born British ^[29]

Struve came out in favor of the name Neptune on December 29, 1846, to the Saint Petersburg Academy of Sciences. Friedrich Georg Wilhelm von Struve (Vasily Yakovlevich Struve ( April 15, 1793 &ndash November 23, 1864 ( Julian calendar Events 1170 - Thomas Becket: Thomas Becket Archbishop of Canterbury is assassinated inside Canterbury Cathedral by followers of King Henry II For the game see 1846 (board game. Year 1846 ( MDCCCXLVI) was a Common year starting on Thursday (link will display Saint Petersburg ( tr: Sankt-Peterburg,) is a city and a federal subject of Russia located on the Neva River ^[30] Soon Neptune became the internationally accepted name. In Roman mythology, Neptune was the god of the sea, identified with the Greek Poseidon. Roman mythology, or more appropriately Latin mythology, refers to the mythological beliefs of the Italic people inhabiting the region of Latium and its Neptune (Neptūnus is the god of water and the sea in Roman mythology, a brother of Jupiter and Pluto. In Greek mythology, Poseidon ( Greek:; Latin: Neptūnus) was the god of the Sea and as "Earth-Shaker" 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. ^[31]

Status

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. ^[32] However, the discovery of the Kuiper belt in 1992 led many astronomers to debate whether or not Pluto should be considered a planet in its own right or as part of the belt's larger structure. The Kuiper belt (ˈkaɪpɚ to rhyme with "viper" sometimes called the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending ^[33][34] 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. A dwarf planet, as defined by the International Astronomical Union (IAU is a Celestial body Orbiting the Sun that is massive enough to be rounded ^[35]

Composition and structure

A size comparison of Neptune and Earth.

With a mass of 1. 0243×10²⁶ kg,^[5] 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. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 A gas giant (sometimes also known as a Jovian planet after the planet Jupiter, or giant planet) is a large Planet that is not primarily ^[10] Neptune's equatorial radius of 24,764 km^[6] is nearly four times that of the Earth. The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the 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. A gas giant (sometimes also known as a Jovian planet after the planet Jupiter, or giant planet) is a large Planet that is not primarily In Planetary science, volatiles, are that group of elements and compounds with low boiling points (see volatile) that are associated with a planet's or moon's ^[36] In the search for extrasolar planets Neptune has been used as a metonym: discovered bodies of similar mass are often referred to as "Neptunes",^[37] just as astronomers refer to various extra-solar "Jupiters. An extrasolar planet, or exoplanet, is a Planet beyond the Solar System, orbiting around other Stars As of September 2008 312 In Rhetoric, metonymy (mɨˈtɒnɨmi is the use of a word for a concept or object associated with the concept/object originally denoted by the word "

Internal structure

Neptune's internal structure resembles that of Uranus. Its atmosphere forms about 5–10% of its mass and extends perhaps 10–20% 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. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Water is a common Chemical substance that is essential for the survival of all known forms of Life. ^[38]

The internal structure of Neptune.

Gradually this darker and hotter region condenses into a superheated liquid mantle, where temperatures reach 2–5,000 K. The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided The mantle is equivalent to 10–15 Earth masses, and is rich in water, ammonia, methane, and other compounds. ^[1] As is customary in planetary science, this mixture is referred to as icy even though it is a hot, highly dense fluid. In Planetary science, volatiles, are that group of elements and compounds with low boiling points (see volatile) that are associated with a planet's or moon's This fluid, which has a high electrical conductivity, is sometimes called a water–ammonia ocean. ^[39] At a depth of 7,000 km, the conditions may be such that methane decomposes into diamond crystals that then precipitate toward the core. ^[40]

The core of Neptune is composed of iron, nickel and silicates, with an interior model giving a mass about 1. The planetary core consists of the innermost layer(s of a Planet. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Nickel (ˈnɪkəl is a metallic Chemical element with the symbol Ni and Atomic number 28 For the Artificial intelligence Androids of the 1990s Science fiction series Space Above and Beyond, see Silicate (AI 2 times that of the Earth. ^[41] The pressure at the centre is 7 Mbar—millions of times more than that on the surface of the Earth, and the temperature may be 5,400 K. The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 ^[38][42]

Atmosphere

At high altitudes, Neptune's atmosphere is 80% hydrogen and 19% helium. ^[38] 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,^[43] although Neptune's vivid azure differs from Uranus's milder aquamarine. Azure is a Blue Color on the HSV color wheel at 210 degrees Azure is the Hue that is halfway between Blue and Cyan Aquamarine is Color that is a Tint of Cyan.It is named after the mineral 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. ^[11]

Neptune's atmosphere is divided into two main regions; the lower troposphere, where temperature decreases with altitude, and the stratosphere, where temperature increases with altitude. The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its Water vapor and The stratosphere is the second major layer of Earth's atmosphere, just above the Troposphere, and below the Mesosphere. The boundary between the two, the tropopause, occurs at a pressure of 0. The tropopause is in the atmosphere between the Troposphere and the Stratosphere. 1 bars. ^[44] The stratosphere then gives way to the thermosphere at a pressure lower than 10⁻⁴–10⁻⁵ microbars. The thermosphere is the layer of the Earth's atmosphere directly above the Mesosphere and directly below the Exosphere. ^[44] The thermosphere gradually transitions to the exosphere. The exosphere is the uppermost layer of the atmosphere. On Earth, its lower boundary at the edge of the Thermosphere is estimated to be 500 km to

A band of high altitude clouds is shown casting shadows on Neptune's lower cloud deck.

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, 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. Ammonium sulfide, also known as diammonium sulfide, is a hypothetical salt with the formula 2S Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. Deeper clouds of water ice should be found at pressures of about 50 bars, where the temperature reaches 0 C. Underneath, clouds of ammonia and hydrogen sulfide may be found. ^[45]

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, and lie about 50–110 km above the cloud deck. ^[46]

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. Photodissociation, photolysis, or photodecomposition is a Chemical reaction in which a Chemical compound is broken down by Photons ^[38][44] The stratosphere is also home to trace amounts of carbon monoxide and hydrogen cyanide. Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. Hydrogen cyanide is a Chemical compound with Chemical formula HCN ^[44][47] The stratosphere of Neptune is warmer than that of Uranus due to elevated concentration of hydrocarbons. ^[44]

For reasons that remain obscure, the planet's thermosphere is at an anomalously high temperature of about 750 K. ^[48][49] The planet is too far from the Sun for this heat to be generated by ultraviolet radiation. Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays 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. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single A meteorite is a natural object originating in Outer space that survives an impact with the Earth 's surface ^[45][47]

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. A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation 55 radii (about 13,500 kilometres) 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)^[45] resulting in a dynamo action. Convection in the most general terms refers to the movement of molecules within Fluids (i In Science and engineering, a conductor is a material which contains movable Electric charges. A dynamo, originally another name for an Electrical generator, now means a generator that produces Direct current with the use of a commutator. ^[50]

The magnetic field at the equatorial surface of Neptune is estimated at 1. 42 μT, for a magnetic moment of 2. The tesla (symbol T) is the SI derived unit of Magnetic field B (which is also known as "magnetic flux density" and "magnetic In Physics, Astronomy, Chemistry, and Electrical engineering, the term magnetic moment of a system (such as a loop of Electric current 16×10¹⁷ Tm³. 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. A quadrupole or quadrapole is one of a sequence of configurations of — for example — electric charge or current or gravitational mass that can exist in ideal form but it In Physics, Astronomy, Chemistry, and Electrical engineering, the term magnetic moment of a system (such as a loop of Electric current By contrast, Earth, Jupiter and Saturn only have 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. ^[51][52]

Neptune's bow shock, where the magnetosphere begins to slow the solar wind, occurs at a distance of 34. A bow shock is a boundary between a Magnetosphere and an ambient medium The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. 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. A magnetopause flows along the boundary between a Magnetic field, (see Magnetosphere) and surrounding plasma. 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 further. ^[51]

Planetary rings

Main article: Rings of Neptune

Neptune's rings, taken by Voyager 2. Neptune has a faint dusty Planetary ring system, which was discovered in 1989 by Voyager 2 spacecraft

Neptune has a planetary ring system, though one much less substantial than that of Saturn. A planetary ring is a ring of Cosmic dust and other small particles Orbiting around a Planet in a flat disc-shaped region Saturn has the most extensive Planetary ring system of any planet in the Solar System. The rings may consist of ice particles coated with silicates or carbon-based material, which most likely gives them a reddish hue. ^[53] In addition to the narrow Adams Ring, 63,000 km from the centre of Neptune, the Leverrier Ring is at 53,000 km and the broader, fainter Galle Ring is at 42,000 km. 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. ^[54]

The first of these planetary rings was discovered in 1968 by a team led by Edward Guinan,^[13][55] but it was later thought that this ring might be incomplete. A planetary ring is a ring of Cosmic dust and other small particles Orbiting around a Planet in a flat disc-shaped region Edward Guinan is currently a professor in Villanova University 's Department of Astronomy and Astrophysics. ^[56] 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. In Shia Islam The Occultation is a term used to designate the hidden state of the Imam of the Time. ^[57] Images by Voyager 2 in 1989 settled the issue by showing several faint rings. These rings have a clumpy structure,^[58] the cause of which is not currently understood but which may be due to the gravitational interaction with small moons in orbit near them. ^[59]

The outermost ring, Adams, contains five prominent arcs now named Courage, Liberté, Egalité 1, Egalité 2, and Fraternité (Liberty, Equality, and Fraternity). ^[60] 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. See also ^[61][62]

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. The W M Keck Observatory is a two-telescope Astronomical observatory at the 4145 meter (13600 ft summit of Mauna Kea in Hawai'i. In particular, it seems that the Liberté arc might disappear in as little as one century. ^[63]

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. ^[64]

The Great Dark Spot (top), Scooter (middle white cloud),^[65] and the Small Dark Spot (bottom). The Small Dark Spot, sometimes also called Dark Spot 2 or The Wizard's Eye, was a southern Cyclonic storm on the Planet Neptune.

Neptune's weather is characterized by extremely dynamic storm systems, with winds reaching near-supersonic speeds of nearly 600 m/s. For other uses see Supersonic. The term supersonic is used to define a speed that is over the Speed of sound ( Mach 1 ^[66] 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. ^[67] At the cloud tops, the prevailing winds range in speed from 400 m/s along the equator to 250 m/s at the poles. ^[45] Most of the winds on Neptune move in a direction opposite the planet's rotation. ^[68] 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. ^[44] At 70° S latitude, a high speed jet travels at a speed of 300 m s⁻¹. ^[44]

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. ^[44]

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 (73. 1 K). ^[69] 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. In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. The Sun (Sol is the Star at the center of the Solar System. 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. ^[70]

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. ^[71]

Storms

The Great Dark Spot, as seen from Voyager 2.

In 1989, the Great Dark Spot, an anti-cyclonic storm system spanning 13,000 × 6,600 km,^[64] was discovered by NASA's Voyager 2 spacecraft. In Meteorology, an anticyclone (that is opposite to a Cyclone) is a Weather phenomenon in which there is a descending movement of the air and The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. The storm resembled the Great Red Spot of Jupiter. However, on November 2, 1994, the Hubble Space Telescope did not see the Great Dark Spot on the planet. Events 1570 - A Tidal wave in the North Sea devastates the coast from Holland to Jutland, killing more than 1000 Year 1994 ( MCMXCIV) was a Common year starting on Saturday (link will display full 1994 Gregorian calendar) The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into Instead, a new storm similar to the Great Dark Spot was found in the planet's northern hemisphere. ^[72]

The Scooter is another storm, a white cloud group further 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. ^[68] Subsequent images revealed even faster clouds. The Small Dark Spot is a southern cyclonic storm, the second most intensive storm observed during the 1989 encounter. The Small Dark Spot, sometimes also called Dark Spot 2 or The Wizard's Eye, was a southern Cyclonic storm on the Planet Neptune. 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. ^[73]

Neptune's dark spots are thought to occur in the troposphere at lower altitudes than the brighter cloud features,^[74] so they appear as holes in the upper cloud decks. The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its Water vapor and As they are stable features that can persist for several months, they are thought to be vortex structures. ^[46] Often associated with dark spots are brighter, persistent methane clouds that form around the tropopause layer. The tropopause is in the atmosphere between the Troposphere and the Stratosphere. ^[75] The persistence of companion clouds shows that some former dark spots may continue to exist as a cyclone 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. ^[76]

Internal heat

Neptune's more varied weather when compared to Uranus is believed to be due in part to its higher internal heat. ^[77] Although Neptune lies half again as far from the Sun as Uranus, and receives only 40% its amount of sunlight,^[44] the two planets' surface temperatures are roughly equal. ^[77] The upper regions of Neptune's troposphere reach a low temperature of −221. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature 4 °C (51. 7 K). At a depth where the atmospheric pressure equals 1 bar, the temperature is −201. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. 15 °C (72. 0 K). ^[78] 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;^[79] Neptune radiates about 2. 61 times as much, which means the internal heat source generates 161% of the solar input. ^[80] 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,^[81] dissociation of methane into hydrocarbon chains under atmospheric pressure,^[82][81] and convection in the lower atmosphere that causes gravity waves to break above the tropopause. A radiogenic Nuclide is one that is produced by a process of Radioactive decay. In Organic chemistry, a hydrocarbon is an Organic compound consisting entirely of Hydrogen and Carbon. Convection in the most general terms refers to the movement of molecules within Fluids (i In Fluid dynamics, gravity waves are waves generated in a Fluid medium or at the interface between two media (e The tropopause is in the atmosphere between the Troposphere and the Stratosphere. ^[83][84]

Orbit and rotation

The average distance between Neptune and the Sun is 4. 55 billion km (about 30. 1 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,^[85][4] although it will not appear at its exact discovery position in our sky due to the Earth being in a different location in its 365. Events 1191 - Saladin 's garrison surrenders ending the two-year Siege of Acre. 2011 ( MMXI) will be a Common year starting on Saturday of the Gregorian calendar. 25 day orbit.

The elliptical orbit of Neptune is inclined 1. 77° compared to the Earth. Because of an eccentricity of 0. In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape 011, the distance from Neptune and the Sun varies by 101 million km between perihelion and aphelion, or the nearest and most distant points of the planet along the orbital path respectively. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from ^[2]

The axial tilt of Neptune is 28. 32°,^[86] which is similar to the tilt of Earth and Mars. 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. ^[71] Its sidereal rotation period (day) is roughly 16. 11 hours long. ^[4] Since its axial tilt is comparable to the Earth's (23°), the variation in the length of its days over the course of its long year is not any more extreme.

Because Neptune is not a solid body, its atmosphere undergoes differential rotation. Differential rotation is seen when different parts of a rotating object move with different angular velocities (rates of 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,^[87] and it results in strong latitudinal wind shear. ^[46]

Orbital resonances

Main article: Kuiper belt

A diagram showing the orbital resonances in the Kuiper belt caused by Neptune: the highlighted regions are the 2/3 resonance (Plutinos), the "classical belt", with orbits unaffected by Neptune, and the 1/2 resonance (twotinos). The Kuiper belt (ˈkaɪpɚ to rhyme with "viper" sometimes called the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending In astronomy a classical Kuiper Belt object, also called a cubewano (ˌkjuːbiːˈwɑːnoʊ is a Kuiper belt object that Orbits beyond Neptune In Astronomy, a resonant trans-Neptunian object is a Trans-Neptunian object (TNO in mean motion Orbital resonance with Neptune

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. The asteroid belt is the region of the Solar System located roughly between the orbits of the Planets Mars and Jupiter. ^[88] 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. The asteroid belt is the region of the Solar System located roughly between the orbits of the Planets Mars and Jupiter. The Kuiper belt (ˈkaɪpɚ to rhyme with "viper" sometimes called the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending 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. ^[89]

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. In Celestial mechanics, an orbital resonance occurs when two Orbiting bodies exert a regular periodic gravitational influence on each other usually due to their 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,^[90] 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. In Astronomy, a plutino is a Trans-Neptunian object in 23 mean motion resonance with Neptune. ^[91] Although Pluto crosses Neptune's orbit regularly, the 2/3 resonance means they can never collide. ^[92] Other, less populated resonances exist at 3/4, 3/5, 4/7 and 2/5. ^[93]

Neptune possesses a number of trojan objects, which occupy its L₄ and L₅ points; gravitationally stable regions leading and trailing it in its orbit. As of May 2008, there are six known Neptune trojans (named by analogy to the Trojan asteroids which have the same orbital period as Neptune. 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. ^[94]

Formation and migration

Main article: Formation and evolution of the Solar System

A simulation showing Outer Planets and Kuiper Belt: a)Before Jupiter/Saturn 2:1 resonance b)Scattering of Kuiper Belt objects into the solar system after the orbital shift of Neptune c)After ejection of Kuiper Belt bodies by Jupiter

The formation of the ice giants, Neptune and Uranus, has proven difficult to model precisely. The formation and evolution of the Solar System is estimated to have begun 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. In Astrophysics, the term accretion is used for at least two distinct processes 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. A protoplanetary disk (or proplyd) is a rotating Circumstellar disk of dense gas surrounding a young newly formed star a T Tauri star or Herbig star OB stars are hot massive Stars of spectral types O or B which form in loosely organized groups called OB associations They are short lived and ^[95] 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. ^[96]

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. The scattered disc (or scattered disk) is a distant region of the Solar System that is sparsely populated by icy Minor planets known as scattered ^[97] 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 Observatoire de la Côte d'Azur (OCA Côte d'Azur Observatory) originated in 1988 with the merger of two observatories: Observatoire Nice (nis Niçard Occitan: Niça norm or Nissa, Italian: Nizza or Nizza Marittima, Greek 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. The Late Heavy Bombardment (commonly referred to as the lunar cataclysm, or LHB) is a period of time approximately 3800 to 4100 million years ago ( mya ^[98]

Moons

Neptune (top) and Triton (bottom). TemplateInfobox Planet.--> Triton (ˈtraɪtən, or as in Greek

Main article: Moons of Neptune

For a timeline of discovery dates, see Timeline of discovery of Solar System planets and their moons

Neptune has 13 known moons. Neptune has thirteen known moons. The largest by far is Triton, discovered by William Lassell just seventeen days after the discovery of Neptune itself Wikipedia talkFeatured lists for an explanation of this and other inclusion tags below-->This timeline of discovery of Solar System planets and their natural A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. ^[5] The largest by far, comprising more than 99. 5 percent of the mass in orbit around Neptune^[99] and the only one massive enough to be spheroidal, is Triton, discovered by William Lassell just 17 days after the discovery of Neptune itself. Equation A spheroid centered at the origin and rotated about the z axis is defined by the implicit equation \left(\frac{x}{a}\right^2+\left(\frac{y}{a}\right^2+\left(\frac{z}{b}\right^2 TemplateInfobox Planet.--> Triton (ˈtraɪtən, or as in Greek William Lassell ( June 18 1799 &ndash October 5 1880) was an English Astronomer. 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, and probably was once a dwarf planet in the Kuiper belt. Direct motion is the motion of a Planetary body in a direction similar to that of other bodies within its system and is sometimes called prograde motion. A dwarf planet, as defined by the International Astronomical Union (IAU is a Celestial body Orbiting the Sun that is massive enough to be rounded The Kuiper belt (ˈkaɪpɚ to rhyme with "viper" sometimes called the Edgeworth-Kuiper belt, is a region of the Solar System beyond the planets extending ^[100] It is close enough to Neptune to be locked into a synchronous rotation, and is slowly spiraling inward and eventually will be torn apart when it reaches the Roche limit. In Astronomy, synchronous rotation is a planetological term describing a body orbiting another where the orbiting body takes as long to rotate Tidal acceleration is an effect of the Tidal forces between an orbiting Natural satellite ( i Determining the Roche limit The Roche limit depends on the rigidity of the satellite ^[101] In 1989, Triton was the coldest object that had yet been measured in the solar system,^[102] with estimated temperatures of −235 °C (38 K). ^[103]

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. Nereid (; also as in Greek Νηρηΐδα also known as Neptune II, is a moon of Neptune. The eccentricity of 0. 7512 gives it an apoapsis that is seven times its periapsis distance from Neptune. ^[104]

Neptune's moon Proteus. There is also an Asteroid called 9313 Protea.

From July to September 1989, Voyager 2 discovered six new Neptunian moons. ^[51] 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. There is also an Asteroid called 9313 Protea. ^[105] Although the second most massive Neptunian moon, it is only one quarter of one percent of the mass of Triton. Neptune's innermost four moons, Naiad, Thalassa, Despina, and Galatea, orbit close enough to be within Neptune's rings. See also The next farthest out, Larissa was originally discovered in 1981 when it had occulted a star. Discovery It was first discovered by Harold J Reitsema, William B This 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. ^[106][107] As Neptune was the Roman god of the sea, the planet's moons have been named after lesser sea gods. ^[31]

Observation

Neptune is never visible to the naked eye, having a brightness between magnitudes +7. The naked eye is a Figure of speech referring to human Visual perception that is unaided by enhancing equipment such as a Telescope or The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 7 and +8. 0,^[8][5] 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. The Galilean moons are the four moons of Jupiter discovered by Galileo Galilei. A dwarf planet, as defined by the International Astronomical Union (IAU is a Celestial body Orbiting the Sun that is massive enough to be rounded Ceres (ˈsɪəriːz Asteroids, sometimes called Minor planets or planetoids', are bodies—primarily of the inner Solar System —that are smaller than planets but TemplateInfobox Planet. --> 4 Vesta (ˈvɛstə Vesta is the second most massive object in the Asteroid belt TemplateInfobox Planet. --> 2 Pallas (ˈpæləs, or as Παλλάς) is one of the largest TemplateInfobox Planet. --> 7 Iris (ˈaɪrɪs Ίρις) is a large Main belt TemplateInfobox Planet. --> Juno (ˈdʒuːnoʊ or as Iūno designated 3 Juno in the Minor Planet TemplateInfobox Planet. --> 6 Hebe (ˈhiːbi, ‘Ήβη) is a large Main belt ^[108] A telescope or strong binoculars will resolve Neptune as a small blue disk, similar in appearance to Uranus. ^[109]

Because of the distance of Neptune from the Earth, the angular diameter of the planet only ranges from 2. The angular diameter of an object as seen from a given position is the "visual diameter" of the object measured as an angle 2–2. 4 arcseconds;^[5][8] the smallest of the Solar System planets. A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60 of one degree. 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. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into Adaptive optics (AO is a Technology used to improve the performance of optical systems by reducing the effects of rapidly changing optical distortion ^[110][111]

From the Earth, Neptune goes through apparent retrograde motion every 367 days, resulting in a looping motion against the background stars during each opposition. Direct motion is the motion of a Planetary body in a direction similar to that of other bodies within its system and is sometimes called prograde motion. Opposition is a term used in Positional astronomy and Astrology to indicate when one celestial body is on the opposite side of the sky when viewed from These loops will carry it close to the 1846 discovery coordinates in April and July 2010 and in October and November 2011. ^[85]

Observation of Neptune in the radio frequency band shows that the planet is a source of both continuous emission and irregular bursts. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. Both sources are believed to originate from the planet's rotating magnetic field. ^[45] 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. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of ^[112]

Exploration

Main article: Exploration of Neptune

Voyager 2's closest approach to Neptune occurred on August 25, 1989. The exploration of Neptune has only begun with one explorer Voyager 2, which visited on August 25, 1989. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. Events 1248 - The Dutch city of Ommen receives city rights and fortification rights from Otto III the Year 1989 ( MCMLXXXIX) was a Common year starting on Sunday (link displays 1989 Gregorian calendar) 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. TemplateInfobox Planet.--> Triton (ˈtraɪtən, or as in Greek The Voyager 1 spacecraft is a 722-kilogram robotic Space probe of the outer Solar system and beyond launched September 5, TemplateInfobox Planet.--> Titan (ˈtaɪtən, or as The images relayed back to Earth from Voyager 2 became the basis of a 1989 PBS all-night program called Neptune All Night. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The Public Broadcasting Service ( PBS) is a Non-profit Public broadcasting Television service with 354 member TV stations in the ^[113]

A Voyager 2 image of Triton

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 of Neptune's atmosphere on August 25, then passed close to the planet's largest moon Triton later the same day. Nereid (; also as in Greek Νηρηΐδα also known as Neptune II, is a moon of Neptune. Events 1248 - The Dutch city of Ommen receives city rights and fortification rights from Otto III the TemplateInfobox Planet.--> Triton (ˈtraɪtən, or as in Greek ^[114]

The spacecraft verified the existence of a magnetic field about the planet, and discovered that the field was offset from the center 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 the Neptune had a surprisingly active weather system. Six new moons were discovered, and the planet was shown to have more than one ring. ^[114][51]

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 National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program Neptune Orbiter is a proposed NASA unmanned planetary spacecraft to explore the planet Neptune. Cassini–Huygens is a joint NASA / ESA / ASI Robotic spacecraft mission currently studying the planet Saturn and its The work is being done in conjunction with JPL and the California Institute of Technology. The California Institute of Technology (commonly referred to as Caltech) is a private, Coeducational research university located in Pasadena ^[115]

See also

• Neptune in astrology
• Neptune in fiction
• Neptune Orbiter – proposed space probe to Neptune to be launched after 2030
• 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

References

Further reading

• Baum, Richard; Sheehan, William (2003). In Search of Planet Vulcan: The Ghost in Newton's Clockwork Universe. Oxford University Press. ISBN 0738208892.  
• 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. ; Wessen, Randii R. (2002). Neptune: The Planet, Rings, and Satellites. Springer-Verlag. ISBN 1-85233-216-6.  
• Moore, Patrick (2000). Sir Alfred Patrick Caldwell-Moore, CBE, HonFRS, FRAS (born 4 March 1923 in Pinner) known as Patrick Moore, is The Data Book of Astronomy. CRC Press. ISBN 0-7503-0620-3.  

External links

• 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. Astronomy Cast is an educational Nonprofit Podcast discussing various topics in the field of Astronomy.