Pluto  

Map of Pluto based on Charon eclipses, approximately true colour and giving the highest resolution currently possible
Discovery
Discovered by	Clyde W. Tombaugh
Discovery date	February 18, 1930
Designations
MPC designation	134340 Pluto
Minor planet category	dwarf planet
Orbital characteristics
Epoch J2000
Aphelion	7,375,927,931 km 49. Charon (ˈʃærən; also, as in Χάρων) discovered in 1978 is either the largest Moon of Pluto or the smaller member of a double Clyde William Tombaugh ( February 4, 1906 &ndash January 17, 1997) was an American Astronomer. Events 3102 BC - Epoch (origin of the Kali Yuga. 1229 - The Sixth Crusade: Frederick II Holy Year 1930 ( MCMXXX) was a Common year starting on Wednesday (link will display 1930 calendar of the Gregorian calendar. 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 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 30503287 AU
Perihelion	4,436,824,613 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 65834067 AU
Semi-major axis	5,906,376,272 km 39. In Geometry, the semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae 48168677 AU
Eccentricity	0. In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape 24880766
Orbital period	90,613. The orbital period is the time taken for a given object to make one complete Orbit about another object 3055 day 248. 09 yr
Synodic period	366. 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 73 day
Average orbital speed	4. 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 666 km/s
Inclination	17. Inclination in general is the Angle between a Reference plane and another plane or axis of direction 14175° 11. 88° to Sun's equator
Longitude of ascending node	110. The longitude of the ascending node (☊ or Ω is one of the Orbital elements used to specify the Orbit of an object in space 30347°
Argument of perihelion	113. The argument of periapsis (or argument of perifocus) ( ω) is the Orbital element describing the Angle of an Orbiting body's periapsis 76329°
Satellites	3
Physical characteristics
Mean radius	1,195 km[1] 0. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. Pluto has three known moons. The largest Charon, is proportionally larger compared to its primary than any other satellite of a known planet or dwarf planet in 19 Earths
Surface area	1. 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^2 795×107 km² 0. 033 Earths
Volume	7. The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically 15×109 km³ 0. 0066 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 305 ± 0. 007)×1022 kg[2] 0. 0021 Earths
Mean density	2. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 03 ± 0. 06 g/cm³[2]
Equatorial surface gravity	0. The surface gravity, g, of an astronomical or other object is the Gravitational acceleration experienced at its surface 58 m/s² 0. 059 g
Escape velocity	1. 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 2 km/s
Sidereal rotation period	−6.387230 day 6 d 9 h 17 m 36 s
Equatorial rotation velocity	47. 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 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. 18 km/h
Axial tilt	119. In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. 591 ± 0. 014° (to orbit)[2][3]
North pole right ascension	133. Right ascension (abbrev RA; symbol α) is the Astronomical term for one of the two Coordinates of a point on the Celestial sphere 046 ± 0. 014°[2]
North pole declination	-6. In Astronomy, declination (abbrev dec or δ) is one of the two coordinates of the Equatorial coordinate system, the other being either 145 ± 0. 014°[2]
Albedo	0. The albedo of an object is the extent to which it diffusely reflects light from the sun 49–0. 66 (varies by 35%)[4][1]
Surface temp.    Kelvin	min mean max 33 K 44 K 55 K
Apparent magnitude	up to 13. 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 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 65 (mean is 15. 1)[1]
Angular diameter	0. The angular diameter of an object as seen from a given position is the "visual diameter" of the object measured as an angle 065" to 0. 115"[1][5]
Adjectives	Plutonian
Atmosphere
Surface pressure	0. 30 Pa (summer maximum)
Composition	nitrogen, methane

Pluto (pronounced /ˈpluːtoʊ/ (help·info), from Latin: Plūto, Greek: Πλούτων), also designated 134340 Pluto, is the second-largest known dwarf planet in the Solar System (after Eris) and the tenth-largest body observed directly orbiting the Sun. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly 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 Solar System consists of the Sun and those celestial objects bound to it by Gravity. The Sun (Sol is the Star at the center of the Solar System. Originally classified as a planet, Pluto is now considered the largest member^[6] of a distinct region called the Kuiper belt. A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is 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 Like other members of the belt, it is composed primarily of rock and ice and is relatively small: approximately a fifth the mass of the Earth's moon and a third its volume. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 It has a highly eccentric and highly inclined orbit. In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape The eccentricity takes it from 30 to 49 AU (4. 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 4–7. 4 billion km) from the Sun, causing Pluto to occasionally come closer to the Sun than Neptune. Pluto and its largest moon, Charon, are often treated together as a binary system because the barycentre of their orbits does not lie within either body. Charon (ˈʃærən; also, as in Χάρων) discovered in 1978 is either the largest Moon of Pluto or the smaller member of a double A binary system is an astronomical term referring to two objects in space (usually Stars but also Planets galaxies or Asteroids which ^[7] The International Astronomical Union (IAU) has yet to formalise a definition for binary dwarf planets, and until it passes such a ruling, Charon is classified as a moon of Pluto. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. ^[8] Pluto has two known smaller moons, Nix and Hydra, discovered in 2005. Nix (ˈnɪks, or as in Greek Νιξ is a Natural satellite of Pluto. Hydra (ˈhaɪdrə, or as in Greek Ύδρα is the outer-most Natural satellite of Pluto. ^[9]

From its discovery in 1930 until 2006, Pluto was counted as the Solar System's ninth planet. In the late 20th and early 21st centuries, however, many objects similar to Pluto were discovered in the outer solar system, notably the scattered disc object Eris, which is 27% more massive than Pluto. 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 ^[10] On August 24, 2006 the IAU defined the term "planet" for the first time. Events 49 BC - Julius Caesar 's General Gaius Scribonius Curio is defeated in the Second Battle of the Bagradas River Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. This definition excluded Pluto, which the IAU reclassified as a member of the new category of dwarf planets along with Eris and Ceres. Ceres (ˈsɪəriːz ^[11] After the reclassification, Pluto was added to the list of minor planets and given the number 134340. Minor planet is a term used since the 19th century to describe objects such as Asteroids that are in Orbit around the Sun but are not Planets In ancient times only the Sun and Moon, a few hundred Stars and the most easily visible Planets had names ^[12][13]

Discovery

Clyde W. Tombaugh, the discoverer of Pluto. Clyde William Tombaugh ( February 4, 1906 &ndash January 17, 1997) was an American Astronomer.

Main article: Planet X

In the 1840s, using Newtonian mechanics, Urbain Le Verrier predicted the position of the then-undiscovered planet Neptune after analysing perturbations in the orbit of Uranus. Classical mechanics is used for describing the motion of Macroscopic objects from Projectiles to parts of Machinery, as well as Astronomical objects Urbain Jean Joseph Le Verrier ( March 11, 1811 &ndash September 23, 1877) was a French Mathematician who specialized in Celestial Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. Hypothesising that the perturbations were caused by the gravitational pull of another planet, Le Verrier sent his calculations to German astronomer Johann Gottfried Galle. Johann Gottfried Galle ( June 9, 1812 &ndash July 10, 1910) was a German Astronomer at the Berlin Observatory On September 23, 1846, the night following his receipt of the letter, Galle and his student Heinrich d'Arrest found Neptune exactly where Le Verrier had predicted. 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 Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. ^[14]

Observations of Neptune in the late 19th century caused astronomers to speculate that Uranus' orbit was being disturbed by another planet in addition to Neptune. In 1905, Percival Lowell, a wealthy Bostonian who had founded the Lowell Observatory in Flagstaff, Arizona in 1894, started an extensive project in search of a possible ninth planet, which he termed "Planet X". Percival Lawrence Lowell ( March 13, 1855 – November 12, 1916) was a businessman author mathematician and Astronomer who fueled Lowell Observatory is an astronomical Observatory in Flagstaff Arizona. Flagstaff (Kinłání is a city located in northern Arizona, in the southwestern United States ^[15] By 1909, Lowell and William H. Pickering had suggested several possible celestial coordinates for such a planet. William Henry Pickering ( February 15, 1858 &ndash January 17, 1938) was an American Astronomer, brother of Edward ^[16] Lowell and his observatory conducted his search from 1905 until his death in 1916, but to no avail.

The observatory's search for Planet X did not resume until 1929,^[17] when its director, Vesto Melvin Slipher, summarily handed the job of locating Planet X to Clyde Tombaugh, a 23-year-old Kansas man who had just arrived at the Lowell Observatory after Slipher had been impressed by a sample of his astronomical drawings. Vesto Melvin Slipher ( November 11, 1875 &ndash November 8, 1969) was an American Astronomer. Clyde William Tombaugh ( February 4, 1906 &ndash January 17, 1997) was an American Astronomer. ^[17]

Discovery photographs of Pluto

Tombaugh's task was systematically to image the night sky in pairs of photographs taken two weeks apart, then examine each pair and determine whether any objects had shifted position. Using a machine called a blink comparator, he rapidly shifted back and forth between views of each of the plates, to create the illusion of movement of any objects that had changed position or appearance between photographs. A blink comparator was a viewing apparatus used by Astronomers to find differences between two photographs of the night sky shot using Optical telescopes On February 18, 1930, after nearly a year of searching, Tombaugh discovered a possible moving object on photographic plates taken on January 23 and January 29 of that year. Events 3102 BC - Epoch (origin of the Kali Yuga. 1229 - The Sixth Crusade: Frederick II Holy Year 1930 ( MCMXXX) was a Common year starting on Wednesday (link will display 1930 calendar of the Gregorian calendar. Events 393 - Roman Emperor Theodosius I proclaims his nine year old son Honorius co-emperor Events 904 - Sergius III comes out of retirement to take over the papacy from the deposed Antipope Christopher. A lesser-quality photograph taken on January 20 helped confirm the movement. Events 250 - Emperor Decius begins a widespread persecution of Christians in Rome. After the observatory obtained further confirmatory photographs, news of the discovery was telegraphed to the Harvard College Observatory on March 13, 1930. The Harvard College Observatory (or HCO is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Department of Astronomy Events 1138 - Cardinal Gregorio Conti is elected Antipope as Victor IV, succeeding Anacletus II. Year 1930 ( MCMXXX) was a Common year starting on Wednesday (link will display 1930 calendar of the Gregorian calendar. The new object would later be found on photographs dating back to March 19, 1915. Events 1279 - A Mongolian victory in the Battle of Yamen ends the Song Dynasty in China. Year 1915 ( MCMXV) was a Common year starting on Friday (link will display the full calendar of the Gregorian calendar (or a Common year ^[16]

Naming

Venetia Burney, the girl who named Pluto

See also: Pluto (mythology)

The right to name the new object belonged to the Lowell Observatory. Venetia Katherine Douglas Phair (née Burney) (born 1919 was the first person to suggest the name Pluto for the object discovered by Clyde W Pluto was the Roman god of the underworld known in Latin as Tertius the counterpart of the Greek Hades. Tombaugh urged Slipher to suggest a name for the new object quickly before someone else did. ^[15] Name suggestions poured in from all over the world. Constance Lowell proposed Zeus, then Lowell, and finally her own first name. Zeus (zjuːs in Greek: nominative: Zeús /zdeús/ genitive: Diós; Modern Greek /'zefs/ in Greek mythology These suggestions were disregarded. ^[18]

The name Pluto was first suggested by Venetia Burney (later Venetia Phair), an eleven-year-old schoolgirl in Oxford, England. Venetia Katherine Douglas Phair (née Burney) (born 1919 was the first person to suggest the name Pluto for the object discovered by Clyde W Oxford is currently bidding for the 2010 Wikimania Conference Oxford () is a city, and the County town of Oxfordshire, England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland ^[19] Venetia was interested in classical mythology as well as astronomy, and considered the name, one of the alternate names of Hades, the Greek god of the Underworld, appropriate for such a presumably dark and cold world. Hades (from Greek, Hadēs, originally, Haidēs or, Aidēs, probably from Indo-European *n̥-wid- 'unseen' refers both to the ancient She suggested it in a conversation with her grandfather Falconer Madan, a former librarian of Oxford University's Bodleian Library. Falconer Madan ( 15 April 1851 - 22 May 1935) was Librarian of the Bodleian Library of Oxford University. The University of Oxford (informally "Oxford University" or simply "Oxford" located in the city of Oxford, Oxfordshire, England is the The Bodleian Library ( the main Research library of the University of Oxford, is one of the oldest libraries in Europe, and in England Madan passed the name to Professor Herbert Hall Turner, who then cabled it to colleagues in America. Herbert Hall Turner ( August 13 1861 &ndash August 20 1930) was a British Astronomer and Seismologist. ^[20]

The object was officially named on March 24, 1930. Events 1401 - Mongol emperor Timur sacks Damascus. 1603 - James VI of Scotland Year 1930 ( MCMXXX) was a Common year starting on Wednesday (link will display 1930 calendar of the Gregorian calendar. ^[21] Each member of the Lowell Observatory was allowed to vote on a short-list of three: "Minerva" (which was already the name for an asteroid), "Cronus" (which had garnered a bad reputation after being suggested by an unpopular astronomer named Thomas Jefferson Jackson See), and Pluto. The MInisterial NEtwoRk for Valorising Activities in digitisation, or MINERVA, is a European Union organization concerned with the digitisation of cultural and Cronus or Kronos, ( Ancient Greek Κρόνος Krónos) was the leader and the youngest of the first generation of Titans, divine descendants Thomas Jefferson Jackson (T J J See, (1866 to July 4 1962 was an American Astronomer (born near Montgomery City, Missouri) who received Pluto received every vote. ^[22] The name was announced on May 1, 1930. Events 305 - Diocletian and Maximian retire from the office of Roman Emperor. Year 1930 ( MCMXXX) was a Common year starting on Wednesday (link will display 1930 calendar of the Gregorian calendar. ^[19] Upon the announcement, Madan gave Venetia five pounds as a reward. The Pound Sterling ( symbol £; ISO code: GBP) subdivided into 100 pence (singular penny) is the Currency ^[19]

The name Pluto was intended to evoke the initials of the astronomer Percival Lowell, a desire echoed in the P-L monogram that is Pluto's astronomical symbol (). Percival Lawrence Lowell ( March 13, 1855 – November 12, 1916) was a businessman author mathematician and Astronomer who fueled A monogram is a motif made by overlapping or combining two or more letters or other Graphemes to form one Symbol. Astronomical symbols are symbols used to represent various Celestial objects theoretical constructs and observational events in Astronomy. ^[23] Pluto's astrological symbol resembles that of Neptune (), but has a circle in place of the middle prong of the trident (). Astrological symbols are images used in various astrological systems to denote relevant objects Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System.

In Chinese, Japanese, Korean and Vietnamese, the name was translated as underworld king star (冥王星),^[24][25] as suggested by Houei Nojiri in 1930. is a language spoken by over 130 million people in Japan and in Japanese emigrant communities This article is mainly about the spoken Korean language See Hangul for details on the native Korean writing system Vietnamese ( tiếng Việt, or less commonly Việt ngữ) formerly known under French colonization as Annamese ( see Annam) was a Japanese essayist and astronomer In 1930 he coined the Japanese word for the newly-discovered planet Pluto. ^[26] Many other non-European languages use a transliteration of "Pluto" as their name for the object; however, some Indian languages may use a form of Yama, the Guardian of Hell in Hindu mythology, such as the Gujarati Yamdev. Yama is the name of the Buddhist Dharmapala and judge of the dead who presides over the Buddhist Narakas ( Pāli: Nirayas "Hells" A Hindu ( Devanagari: हिन्दू is an adherent of the philosophies and scriptures of Hinduism, a set of religious, Philosophical Gujarati (ગુજરાતી Gujǎrātī ? ^[24]

Demise of Planet X

Once found, Pluto's faintness and lack of a resolvable disc cast doubt on the idea that it could be Lowell's Planet X. Throughout the mid-20th century, estimates of Pluto's mass were often revised downward. In 1978, the discovery of Pluto's moon Charon allowed the measurement of Pluto's mass for the first time. Charon (ˈʃærən; also, as in Χάρων) discovered in 1978 is either the largest Moon of Pluto or the smaller member of a double Its mass, roughly 0. 2 percent that of the Earth, was far too small to account for the discrepancies in Uranus. Subsequent searches for an alternate Planet X, notably by Robert Harrington,^[27] failed. Robert Harrington may refer to Robert G Harrington, astronomer worked at Palomar Observatory Robert Sutton Harrington (1942&ndash1993 In 1993, Myles Standish used data from Voyager 2's 1989 flyby of Neptune, which had revised the planet's total mass downward by 0. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. 5 percent, to recalculate its gravitational effect on Uranus. With the new figures added in, the discrepancies, and with them the need for a Planet X, vanished. ^[28] Today the overwhelming consensus among astronomers is that Planet X, as Lowell defined it, does not exist. Lowell had made a prediction of Planet X's position in 1915 that was fairly close to Pluto's actual position at that time; however, Ernest W. Brown concluded almost immediately that this was a coincidence, a view still held today. Ernest William Brown ( November 29 1866 &ndash July 22 1938) was an English Mathematician and Astronomer, who ^[29]

Physical characteristics

The largest plutinos compared in size, albedo and color. In Astronomy, a plutino is a Trans-Neptunian object in 23 mean motion resonance with Neptune. The albedo of an object is the extent to which it diffusely reflects light from the sun In Astronomy, the color index is a simple numerical expression that determines the color of an object which in the case of a Star gives its Temperature (Pluto is shown with its large satellite Charon, and its two tiny satellites Nix and Hydra. )

Possible structure of Pluto.
1. Frozen nitrogen
2. Water ice
3. Silicate and water ice

Pluto's distance from Earth makes in-depth investigation difficult. Many details about Pluto will remain unknown until 2015, when the New Horizons spacecraft is expected to arrive there. New Horizons is a Robotic spacecraft mission by NASA currently underway ^[30]

Appearance and composition

Pluto's apparent magnitude averages 15. 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 1, brightening to 13. 65 at perihelion. ^[1] To see it, a telescope is required; around 30 cm (12 in) aperture being desirable. ^[31] It looks indistinct and star-like even in very large telescopes because its angular diameter is only 0. The angular diameter of an object as seen from a given position is the "visual diameter" of the object measured as an angle 11". It is light brown with a very slight tint of yellow. ^[32]

Spectroscopic analysis of Pluto's surface reveals it to be composed of more than 98 percent nitrogen ice, with traces of methane and carbon monoxide. Spectroscopy was originally the study of the interaction between Radiation and Matter as a function of Wavelength (λ Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 ^[33][34] Distance and current limits on telescope technology make it impossible directly to photograph surface details on Pluto. Images from the Hubble Space Telescope barely show any distinguishable surface definitions or markings. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into ^[35]

The best images of Pluto derive from brightness maps created from close observations of eclipses by its largest moon, Charon. Using computer processing, observations are made in brightness factors as Pluto is eclipsed by Charon. For example, eclipsing a bright spot on Pluto makes a bigger total brightness change than eclipsing a dark spot. Using this technique, one can measure the total average brightness of the Pluto-Charon system and track changes in brightness over time. ^[36] Maps composed by the Hubble Space Telescope reveal that Pluto's surface is remarkably heterogeneous, a fact also evidenced by its lightcurve and by periodic variations in its infrared spectra. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into Heterogeneous is an adjective used to describe an object or system consisting of multiple items having a large number of structural variations The face of Pluto oriented toward Charon contains more methane ice, while the opposite face contains more nitrogen and carbon monoxide ice. Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. This makes Pluto the second most contrasted body in the Solar System after Iapetus. TemplateInfobox Planet.--> Iapetus (aɪˈæpɨtəs, or as in Greek ^[37]

The Hubble Space Telescope places Pluto's density at between 1. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into 8 and 2. 1 g/cm³, suggesting its internal composition consists of roughly 50–70 percent rock and 30–50 percent ice. ^[34] Because decay of radioactive minerals would eventually heat the ices enough for them to separate from rock, scientists expect that Pluto's internal structure is differentiated, with the rocky material having settled into a dense core surrounded by a mantle of ice. The interior of Earth, similar to the other Terrestrial planets, is Chemically divided into layers The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided It is also possible that such heating may continue today, creating a subsurface ocean of liquid water. ^[38]

Mass and size

Pluto's volume is about 0. 66% that of Earth

Astronomers, assuming Pluto to be Lowell's Planet X, initially calculated its mass on the basis of its presumed effect on Neptune and Uranus. In 1955 Pluto was calculated to be roughly the mass of the Earth, with further calculations in 1971 bringing the mass down to roughly that of Mars. ^[39] However, in 1976, Dale Cruikshank, Carl Pilcher and David Morrison of the University of Hawaii calculated Pluto's albedo for the first time, finding that it matched that for methane ice; this meant Pluto had to be exceptionally luminous for its size and therefore could not be more than 1 percent the mass of the Earth. The University of Hawaii, formally the University of Hawaii System and popularly known as UH, is a public co-educational college and university system that confers The albedo of an object is the extent to which it diffusely reflects light from the sun Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. ^[39][40]

The discovery of Pluto's satellite Charon in 1978 enabled a determination of the mass of the Pluto–Charon system by application of Newton's formulation of Kepler's third law. Charon (ˈʃærən; also, as in Χάρων) discovered in 1978 is either the largest Moon of Pluto or the smaller member of a double In Astronomy, Kepler's Laws of Planetary Motion are three mathematical laws that describe the motion of Planets in the Solar System. Once Charon's gravitational effect on Pluto was measured, estimates of Pluto's mass fell to 1. 31×10²² kg—less than 0. 24 percent that of the Earth. ^[41] Observations of Pluto in occultation with Charon were able to fix Pluto's diameter at roughly 2,390 km. ^[42] With the invention of adaptive optics astronomers were able to determine its shape accurately. Adaptive optics (AO is a Technology used to improve the performance of optical systems by reducing the effects of rapidly changing optical distortion ^[43]

Pluto (bottom right) compared in size to the largest satellites in the solar system (from left to right and top to bottom): Ganymede, Titan, Callisto, Io, the Moon, Europa, and Triton

Among the objects of the Solar System, Pluto is not only smaller and much less massive than any planet, but at less than 0. 2 lunar masses it is also smaller than seven of the moons: Ganymede, Titan, Callisto, Io, Earth's Moon, Europa and Triton. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. TemplateInfobox Planet.--> Ganymede (ˈgænɨmiːd, or as Greek TemplateInfobox Planet.--> Titan (ˈtaɪtən, or as TemplateInfobox Planet.--> Callisto (kəˈlɪstoʊ, or as Greek TemplateInfobox Planet.--> Io (ˈaɪoʊ, or as Greek TemplateInfobox Planet.--> Europa (jʊˈroʊpə; or as TemplateInfobox Planet.--> Triton (ˈtraɪtən, or as in Greek Pluto is more than twice the diameter and a dozen times the mass of the dwarf planet Ceres, the largest object in the asteroid belt. 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 The asteroid belt is the region of the Solar System located roughly between the orbits of the Planets Mars and Jupiter. However, it is smaller than the dwarf planet Eris, a trans-Neptunian object discovered in 2005. A trans-Neptunian object (TNO is any object in the Solar system that Orbits the sun at a greater distance on average than Neptune.

Atmosphere

Artist's conception of the New Horizons spacecraft passing over Pluto, showing its tenuous atmosphere

Pluto's atmosphere consists of a thin envelope of nitrogen, methane, and carbon monoxide, derived from the ices on its surface. New Horizons is a Robotic spacecraft mission by NASA currently underway Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Methane is a Chemical compound with the molecular formula. It is the simplest Alkane, and the principal component of Natural gas. Carbon monoxide, with the chemical formula CO is a colorless odorless tasteless yet highly toxic Gas. ^[44] As Pluto moves away from the Sun, its atmosphere gradually freezes and falls to the ground. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " As it edges closer to the Sun, the temperature of Pluto's solid surface increases, causing the ices to sublimate into gas. Sublimation of an element or compound is a transition from the Solid to Gas phase with no intermediate liquid stage This creates an anti-greenhouse effect; much like sweat cools the body as it evaporates from the surface of the skin, this sublimation has a cooling effect on the surface of Pluto. The anti-greenhouse effect is a Neologism used to describe two different effects coming under the header of "the cooling effect an atmosphere has on the ambient temperature Scientists have recently discovered,^[45] by use of the Submillimeter Array, that Pluto's temperature is 43 kelvins, 10 K colder than expected. The Submillimeter Array (SMA consists of eight 6 m diameter Radio telescopes arranged as an Interferometer for submillimeter wavelength observations 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

Pluto was found to have an atmosphere from an occultation observation in 1985; the finding was confirmed and significantly strengthened by extensive observations of another occultation in 1988. In Shia Islam The Occultation is a term used to designate the hidden state of the Imam of the Time. When an object with no atmosphere occults a star, the star abruptly disappears; in the case of Pluto, the star dimmed out gradually. ^[46] From the rate of dimming, the atmospheric pressure was determined to be 0. 15 pascal, roughly 1/700,000 that of Earth. ^[47]

In 2002, another occultation of a star by Pluto was observed and analysed by teams led by Bruno Sicardy of the Paris Observatory,^[48] James L. Elliot of MIT,^[49] and Jay Pasachoff of Williams College. The Paris Observatory (in French Observatoire de Paris or Observatoire de Paris-Meudon) is the foremost astronomical observatory of France, James L Elliot is a Professor of Physics Professor of Earth Atmospheric and Planetary Sciences and the Director George R Jay Myron Pasachoff (born 1943) is an American Astronomer. Pasachoff is Field Memorial Professor of Astronomy at Williams College and the Williams College is a highly selective private liberal arts college located in Williamstown, Massachusetts. ^[50] The atmospheric pressure was estimated to be 0. 3 pascal, even though Pluto was farther from the Sun than in 1988 and thus should have been colder and had a more rarefied atmosphere. One explanation for the discrepancy is that in 1987 the south pole of Pluto came out of shadow for the first time in 120 years, causing extra nitrogen to sublimate from the polar cap. It will take decades for the excess nitrogen to condense out of the atmosphere. ^[51] Another stellar occultation was observed by the MIT-Williams College team of James Elliot, Jay Pasachoff, and a Southwest Research Institute team led by Leslie Young on 12 June 2006 from sites in Australia. Jay Myron Pasachoff (born 1943) is an American Astronomer. Pasachoff is Field Memorial Professor of Astronomy at Williams College and the Southwest Research Institute ( SwRI) headquartered in San Antonio Texas, is one of the oldest and largest independent Nonprofit, applied Research Events 1381 - Peasants' Revolt: in England, rebels arrive at Blackheath. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. ^[52]

In October 2006, Dale Cruikshank of NASA/Ames Research Center (a New Horizons co-investigator) and his colleagues announced the spectroscopic discovery of ethane on Pluto's surface. 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 This ethane is produced from the photolysis or radiolysis (i. e. , the chemical conversion driven by sunlight and charged particles) of frozen methane on Pluto's surface and suspended in its atmosphere. ^[53]

Orbit

Orbit of Pluto – ecliptic view. This 'side view' of Pluto's orbit (in red) shows its large inclination to Neptune's orbit (in blue). Inclination in general is the Angle between a Reference plane and another plane or axis of direction The ecliptic is horizontal

Pluto's orbit is markedly different from those of the planets. The ecliptic is the apparent path that the Sun traces out in the sky during the year The planets all orbit the Sun close to a flat reference plane called the ecliptic and have nearly circular orbits. The ecliptic is the apparent path that the Sun traces out in the sky during the year In contrast, Pluto's orbit is highly inclined relative to the ecliptic (over 17°) and highly eccentric (elliptical). Inclination in general is the Angle between a Reference plane and another plane or axis of direction In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape In Mathematics, an ellipse (from the Greek ἔλλειψις literally absence) is a Conic section, the locus of points in a This high eccentricity leads to a small region of Pluto's orbit lying closer to the Sun than Neptune's. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. Pluto was last interior to Neptune's orbit between February 7, 1979 and February 11, 1999. Events 457 - Leo I becomes emperor of the Byzantine Empire. 1074 - Battle of Montesarchio in which the Prince Year 1979 ( MCMLXXIX) was a Common year starting on Monday (link displays the 1979 Gregorian calendar) Events 660 BC - Traditional founding date of Japan by Emperor Jimmu. Year 1999 ( MCMXCIX) was a Common year starting on Friday (link will display full 1999 Gregorian calendar) Detailed calculations indicate that the previous such occurrence lasted only fourteen years, from July 11, 1735 to September 15, 1749, whereas between April 30, 1483 and July 23, 1503, it had also lasted 20 years. Events 911 - Signing of the Treaty of Saint-Clair-sur-Epte between Charles the Simple and Rollo of Normandy. Year 1735 ( MDCCXXXV) was a Common year starting on Saturday (link will display the full calendar of the Gregorian calendar (or a Events 668 - Eastern Roman Emperor Constans II is assassinated in his bath at Syracuse Italy. Year 1749 ( MDCCXLIX) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or a Events 313 - Roman emperor Licinius unifies the entire Eastern Roman Empire under his rule Events 1632 - Three hundred colonists bound for New France depart from Dieppe France.

Although this repeating pattern may suggest a regular structure, in the long term Pluto's orbit is in fact chaotic. In Mathematics, chaos theory describes the behavior of certain dynamical systems – that is systems whose state evolves with time – that may exhibit dynamics that While computer simulations can be used to predict its position for several million years (both forward and backward in time), after intervals longer than the Lyapunov time of 10–20 million years, it is impossible to determine exactly where Pluto will be because its position becomes too sensitive to unmeasurably small details of the present state of the solar system. Time reversibility is an attribute of some stochastic processes and some Deterministic processes In Mathematics, the Lyapunov time is the length of time for a Dynamical system to become chaotic. ^[54][55] For example, at any specific time many millions of years from now, Pluto may be at aphelion or perihelion (or anywhere in between), with no way for us to predict which. 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 This does not mean that the orbit of Pluto itself is unstable, however, only that its position along that orbit is impossible to determine far into the future. In fact, several resonances and other dynamical effects conspire to keep Pluto's orbit stable, safe from planetary collision or scattering.

Neptune-avoiding orbit

Orbit of Pluto — polar view. This 'view from above' shows how Pluto's orbit (in red) is less circular than Neptune's (in blue), and how Pluto is sometimes closer to the Sun than Neptune. The darker halves of both orbits show where they pass below the plane of the ecliptic. The ecliptic is the apparent path that the Sun traces out in the sky during the year The positions of both bodies are as of April 16, 2006; by April 2007 they had changed by about three pixels (~1 AU). Events 1178 BC - A Solar eclipse may have marked the return of Odysseus, legendary King of Ithaca, to his kingdom Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar.

Despite Pluto's orbit apparently crossing that of Neptune when viewed from directly above the ecliptic, the two objects cannot collide. The ecliptic is the apparent path that the Sun traces out in the sky during the year This is because their orbits are aligned so that Pluto and Neptune can never approach closely. Several factors contribute to this.

At the simplest level, one can examine the two orbits and see that they do not intersect. When Pluto is closest to the Sun, and hence closest to Neptune's orbit as viewed in a top-down projection, it is also the farthest above the ecliptic. This means Pluto's orbit actually passes above that of Neptune, preventing a collision. ^[56] Indeed, the part of Pluto's orbit that lies as close or closer to the Sun than that of Neptune lies about 8 AU above the ecliptic,^[57] and so a similar distance above Neptune's orbit. 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 ^[58] Pluto's ascending node, the point at which the orbit crosses the ecliptic, is currently separated from Neptune's by over 21°;^[59] their descending nodes are separated by a similar angular distance (see diagram). An orbital node is one of the two points where an Orbit crosses a Plane of reference which it is inclined to Since Neptune's orbit is almost flat with respect to the ecliptic, Pluto is far above it by the time the two orbits cross.

This alone is not enough to protect Pluto; perturbations (e. g. , orbital precession) from the planets, particularly Neptune, would adjust Pluto's orbit, so that over millions of years a collision could be possible. Precession refers to a change in the direction of the axis of a rotating object Some other mechanism or mechanisms must therefore be at work. The most significant of these is a mean motion resonance with Neptune. In Celestial mechanics, an orbital resonance occurs when two Orbiting bodies exert a regular periodic gravitational influence on each other usually due to their

This diagram shows the relative positions of Pluto (red) and Neptune (blue) on selected dates. The size of Neptune and Pluto is depicted as inversely proportional to the distance between them to emphasise the closest approach in 1896.

Pluto lies in the 3:2 mean motion resonance of Neptune: for every three orbits of Neptune around the Sun, Pluto makes two. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. The two objects then return to their initial positions and the cycle repeats, each cycle lasting about 500 years. This pattern is configured so that, in each 500-year cycle, the first time Pluto is near perihelion Neptune is over 50° behind Pluto. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from By Pluto's second perihelion, Neptune will have completed a further one and a half of its own orbits, and so will be a similar distance ahead of Pluto. In fact, the minimum separation of Pluto and Neptune is over 17 AU; Pluto actually comes closer (11 AU) to Uranus than it does to Neptune. ^[58]

The 3:2 resonance between the two bodies is highly stable, and is preserved over millions of years. ^[60] This prevents their orbits from changing relative to one another — the cycle always repeats in the same way — and so the two bodies can never pass near to each other. Thus, even if Pluto's orbit were not highly inclined the two bodies could never collide. ^[58]

Other factors governing Pluto's orbit

Diagram of the argument of perihelion

Numerical studies have shown that over periods of millions of years, the general nature of the alignment between Pluto's and Neptune's orbits does not change. ^[56][61] However, there are several other resonances and interactions that govern the details of their relative motion, and enhance Pluto's stability. These arise principally from two additional mechanisms (in addition to the 3:2 mean motion resonance).

First, Pluto's argument of perihelion, the angle between the point where it crosses the ecliptic and the point where it is closest to the Sun, librates around 90°. The argument of periapsis (or argument of perifocus) ( ω) is the Orbital element describing the Angle of an Orbiting body's periapsis In Astronomy libration (from the Latin verb librare "to balance to sway" cf ^[61] This means that when Pluto is nearest the Sun, it is at its farthest above the plane of the solar system, preventing encounters with Neptune. This is a direct consequence of the Kozai mechanism,^[56] which relates the eccentricity of an orbit to its inclination, relative to a larger perturbing body — in this case Neptune. In Celestial mechanics, the Kozai mechanism is a secular perturbative effect on certain orbits Relative to Neptune, the amplitude of libration is 38°, and so the angular separation of Pluto's perihelion to the orbit of Neptune is always greater than 52° (= 90°–38°). The closest such angular separation occurs every 10,000 years. ^[60]

Second, the longitudes of ascending node of the two bodies — the points where they cross the ecliptic - are in near-resonance with the above libration. When the two longitudes are the same — that is, when one could draw a straight line through both nodes and the Sun — Pluto's perihelion lies exactly at 90°, and it comes closest to the Sun at its peak above Neptune's orbit. In other words, when Pluto most closely intersects the plane of Neptune's orbit, it must be at its farthest beyond it. This is known as the 1:1 superresonance. ^[56]

To understand the nature of the libration, imagine a polar point of view, looking down on the ecliptic from a distant vantage point where the planets orbit counter-clockwise. A clockwise motion is one that proceeds 'like the Clock 's hands' from the top to the right then down and then to the left and back to the top After passing the ascending node, Pluto is interior to Neptune's orbit and moving faster, approaching Neptune from behind. The strong gravitational pull between the two causes angular momentum to be transferred to Pluto, at Neptune's expense. In Physics, the angular momentum of a particle about an origin is a vector quantity equal to the mass of the particle multiplied by the Cross product of the position This moves Pluto into a slightly larger orbit, where it travels slightly slower, in accordance with Kepler's third law. In Astronomy, Kepler's Laws of Planetary Motion are three mathematical laws that describe the motion of Planets in the Solar System. As its orbit changes, this has the gradual effect of changing the pericentre and longitudes of Pluto (and, to a lesser degree, of Neptune). After many such repetitions, Pluto is sufficiently slowed, and Neptune sufficiently speeded up, that Neptune begins to catch Pluto at the opposite side of its orbit (near the opposing node to where we began). The process is then reversed, and Pluto loses angular momentum to Neptune, until Pluto is sufficiently speeded up that it begins to catch Neptune once again at the original node. The whole process takes about 20,000 years to complete. ^[58][60]

Moons

Main article: Moons of Pluto

Pluto and its three known moons. Pluto has three known moons. The largest Charon, is proportionally larger compared to its primary than any other satellite of a known planet or dwarf planet in Pluto and Charon are the bright objects in the center, the two smaller moons are at the right and bottom, farther out.

The Pluto system. The region around Pluto and Charon was reduced in brightness so that all four objects could be shown individually in a single image. Photo by David Tholen.

Pluto has three known natural satellites: Charon, first identified in 1978 by astronomer James Christy; and two smaller moons, Nix and Hydra, both discovered in 2005. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. Charon (ˈʃærən; also, as in Χάρων) discovered in 1978 is either the largest Moon of Pluto or the smaller member of a double James Walter Christy (born 1938 is an American Astronomer. Working at the United States Naval Observatory, on June 22 1978 he discovered that Pluto Nix (ˈnɪks, or as in Greek Νιξ is a Natural satellite of Pluto. Hydra (ˈhaɪdrə, or as in Greek Ύδρα is the outer-most Natural satellite of Pluto. ^[62]

The Plutonian moons are unusually close to Pluto, compared to other observed systems. Moons could potentially orbit Pluto up to 53% (or 69%, if retrograde) of the Hill sphere radius, the stable gravitational zone of Pluto's influence. A Hill sphere is roughly the volume around an Astronomical body (such as a Planet) where it dominates in attraction of Satellites to that body rather For example, Psamathe orbits Neptune at 40% of the Hill radius. Psamathe (, or as in Latin Psamathē Greek Ψαμάθη In the case of Pluto, only the inner 3% of the zone is known to be occupied by satellites. In the discoverers’ terms, the Plutonian system appears to be "highly compact and largely empty. "^[63]

Charon

The Pluto-Charon system is noteworthy for being the largest of the solar system's few binary systems, defined as those whose barycentre lies above the primary's surface (617 Patroclus is a smaller example). 617 Patroclus (pə-troe'-kləs pəˈtroʊkləs is a binary Minor planet made up of two similarly-sized objects orbiting their common Centre ^[64] This and the large size of Charon relative to Pluto has led some astronomers to call it a dwarf double planet. " Double planet " is an informal term used to describe a Planet with a moon that may be large enough to be considered a planet in its own right a common definition ^[65] The system is also unusual among planetary systems in that each is tidally locked to the other: Charon always presents the same face to Pluto, and Pluto always presents the same face to Charon. A separate article treats the phenomenon of Tidal resonance in Oceanography. If one were standing on Pluto's near side, Charon would hover in the sky without moving; if one were to travel to the far side, one would never see Charon at all. ^[66] In 2007, observations by the Gemini Observatory of patches of ammonia hydrates and water crystals on the surface of Charon suggested the presence of active cryo-geysers. The Gemini Observatory is an astronomical observatory consisting of two 8-metre Telescopes at different sites ^[67]

Nix and Hydra

Artist's concept of the surface of Hydra. Hydra (ˈhaɪdrə, or as in Greek Ύδρα is the outer-most Natural satellite of Pluto. Pluto with Charon (right) and Nix (bright dot on left). Charon (ˈʃærən; also, as in Χάρων) discovered in 1978 is either the largest Moon of Pluto or the smaller member of a double Nix (ˈnɪks, or as in Greek Νιξ is a Natural satellite of Pluto.

Diagram of the Plutonian system. P 1 is Hydra, and P 2 is Nix.

Two additional moons of Pluto were imaged by astronomers working with the Hubble Space Telescope on May 15, 2005, and received provisional designations of S/2005 P 1 and S/2005 P 2. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into Events 1252 - Pope Innocent IV issues the Papal bull Ad exstirpanda, which authorizes but also limits the Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. A provisional designation in astronomy is the naming convention applied to Astronomical objects immediately following their discovery The International Astronomical Union officially named Pluto's newest moons Nix (or Pluto II, the inner of the two moons, formerly P 2) and Hydra (Pluto III, the outer moon, formerly P 1), on June 21, 2006. Nix (ˈnɪks, or as in Greek Νιξ is a Natural satellite of Pluto. Hydra (ˈhaɪdrə, or as in Greek Ύδρα is the outer-most Natural satellite of Pluto. Events 524 - Godomar, King of the Burgundians defeats the Franks at the Battle of Vézeronce. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. ^[68]

These small moons orbit Pluto at approximately two and three times the distance of Charon: Nix at 48,700 kilometres and Hydra at 64,800 kilometres from the barycenter of the system. They have nearly circular prograde orbits in the same orbital plane as Charon, and are very close to (but not in) 4:1 and 6:1 mean motion orbital resonances with Charon. 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. In Celestial mechanics, an orbital resonance occurs when two Orbiting bodies exert a regular periodic gravitational influence on each other usually due to their ^[69]

Observations of Nix and Hydra to determine individual characteristics are ongoing. Hydra is sometimes brighter than Nix, suggesting either that it is larger or that different parts of its surface may vary in brightness. Sizes are estimated from albedos. The moons' spectral similarity to Charon suggests a 35% albedo similar to Charon's; this value results in diameter estimates of 46 kilometres for Nix and 61 kilometres for the brighter Hydra. Upper limits on their diameters can be estimated by assuming the 4% albedo of the darkest Kuiper Belt objects; these bounds are 137 ± 11 km and 167 ± 10 km, respectively. At the larger end of this range, the inferred masses are less than 0. 3% that of Charon, or 0. 03% of Pluto's. ^[70]

The discovery of the two small moons suggests that Pluto may possess a variable ring system. A planetary ring is a ring of Cosmic dust and other small particles Orbiting around a Planet in a flat disc-shaped region Small body impacts can create debris that can form into planetary rings. Data from a deep optical survey by the Advanced Camera for Surveys on the Hubble Space Telescope suggest that no ring system is present. The Advanced Camera for Surveys (ACS is a third generation axial instrument aboard the Hubble Space Telescope (HST The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into If such a system exists, it is either tenuous like the rings of Jupiter or is tightly confined to less than 1,000 km in width. The planet Jupiter has a system of rings known as the rings of Jupiter or the Jovian ring system. ^[71]

In imaging the Plutonian system, observations from Hubble placed limits on any additional moons. With 90% confidence, no additional moons larger than 12 km (or a maximum of 37 km with an albedo of 0. 041) exist beyond the glare of Pluto 5 arcseconds from the dwarf planet. This assumes a Charon-like albedo of 0. 38; at a 50% confidence level the limit is 8 kilometres. ^[72]

Kuiper belt

Main article: Kuiper belt

Plot of all known Kuiper belt objects, set against the four outer planets

Pluto's origin and identity have long puzzled astronomers. 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 the 1950s it was suggested that Pluto was an escaped moon of Neptune, knocked out of orbit by its largest current moon, Triton. TemplateInfobox Planet.--> Triton (ˈtraɪtən, or as in Greek This notion has been heavily criticised because, as explained above, Pluto never actually comes near the planet. ^[73]

Beginning in 1992, astronomers began to discover a large population of small icy objects beyond Neptune that were similar to Pluto not only in orbit but also in size and composition. This belt, known as the Kuiper belt after one of the astronomers who first speculated on the nature of a trans-Neptunian population, is believed to be the source of many short-period comets. 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 Gerard Peter Kuiper ( born Gerrit Pieter Kuiper ( ( December 7 1905, Harenkarspel ( Tuitjenhorn) Netherlands &ndash Periodic comets are defined for these purposes as those Comets having orbital periods of less than 200 years (also known as "short-period comets" or which Astronomers now believe Pluto to be the largest^[6] of the known Kuiper belt objects (KBOs). 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 Like other KBOs, Pluto shares features with comets; for example, the solar wind is gradually blowing Pluto's surface into space, in the manner of a comet. A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. ^[74] If Pluto were placed as near to the Sun as Earth, it would develop a tail, as comets do. ^[75]

Though Pluto is the largest of the Kuiper belt objects discovered so far, Triton, which is slightly larger than Pluto, shares many atmospherical and geological composition similarities with Pluto and is believed to be a captured Kuiper belt object. TemplateInfobox Planet.--> Triton (ˈtraɪtən, or as in Greek ^[76] Eris (see below) is also larger than Pluto but is not strictly considered a member of the Kuiper belt population. Rather, it is considered a member of a linked population called the scattered disc. 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

A large number of Kuiper belt objects, like Pluto, possess a 3:2 orbital resonance with Neptune. KBOs with this orbital resonance are called "plutinos", after Pluto. In Astronomy, a plutino is a Trans-Neptunian object in 23 mean motion resonance with Neptune. ^[77]

Exploration of Pluto

Main article: New Horizons

New Horizons, launched on January 19, 2006

Pluto presents significant challenges for spacecraft because of its small mass and great distance from Earth. New Horizons is a Robotic spacecraft mission by NASA currently underway New Horizons is a Robotic spacecraft mission by NASA currently underway Events 1419 - Hundred Years' War: Rouen surrenders to Henry V of England completing his reconquest of Normandy. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Voyager 1 could have visited Pluto, but controllers opted instead for a close flyby of Saturn's moon Titan, resulting in a trajectory incompatible with a Pluto flyby. The Voyager 1 spacecraft is a 722-kilogram robotic Space probe of the outer Solar system and beyond launched September 5, Voyager 2 never had a plausible trajectory for reaching Pluto. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. ^[78] No serious attempt to explore Pluto via spacecraft occurred until the last decade of the 20th century. In August 1992, JPL scientist Robert Staehle telephoned Pluto's discoverer, Clyde Tombaugh, requesting permission to visit his planet. "I told him he was welcome to it," Tombaugh later remembered, "though he's got to go one long, cold trip. "^[79] Despite this early momentum, in 2000, NASA cancelled the Pluto Kuiper Express mission, citing increasing costs and launch vehicle delays. The Pluto Kuiper Express mission was a space mission designed to fly by the Pluto - Charon system and at least one large object in the Kuiper belt beyond ^[80]

After an intense political battle, a revised mission to Pluto, dubbed New Horizons, was granted funding from the US government in 2003. New Horizons is a Robotic spacecraft mission by NASA currently underway ^[81] New Horizons was launched successfully on January 19, 2006. Events 1419 - Hundred Years' War: Rouen surrenders to Henry V of England completing his reconquest of Normandy. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. The mission leader, S. Alan Stern, confirmed that some of the ashes of Clyde Tombaugh, who died in 1997, had been placed aboard the spacecraft. S Alan Stern is an American planetary scientist, born 22 November 1957 New Orleans Louisiana married (three children ^[82]

In early 2007 the craft made use of a gravity assist from Jupiter. In Orbital mechanics and Aerospace engineering, a gravitational slingshot, gravity assist or swing-by is the use of the relative movement and Its closest approach to Pluto will be on July 14, 2015; scientific observations of Pluto will begin 5 months prior to closest approach and will continue for at least a month after the encounter. Events 1223 - Louis VIII becomes King of France upon the death of his father Philip II of France. 2015 ( MMXV) will be a Common year starting on Thursday of the Gregorian calendar. New Horizons captured its first (distant) images of Pluto in late September 2006, during a test of the Long Range Reconnaissance Imager (LORRI). ^[83] The images, taken from a distance of approximately 4. 2 billion kilometres, confirm the spacecraft's ability to track distant targets, critical for maneuvering toward Pluto and other Kuiper Belt objects.

First Pluto sighting from New Horizons

New Horizons will use a remote sensing package that includes imaging instruments and a radio science investigation tool, as well as spectroscopic and other experiments, to characterise the global geology and morphology of Pluto and its moon Charon, map their surface composition and analyse Pluto's neutral atmosphere and its escape rate. New Horizons will also photograph the surfaces of Pluto and Charon.

Discovery of moons Nix and Hydra may present unforeseen challenges for the probe. Debris from collisions between Kuiper belt objects and the smaller moons, with their relatively low escape velocities, may produce a tenuous dusty ring. Were New Horizons to fly through such a ring system, there would be an increased potential for micrometeorite damage that could disable the probe. ^[71]

Planetary status controversy

See also: Definition of planet

Pluto's official status as a planet has been a subject of controversy since at least 1992, when the first Kuiper Belt Object, (15760) 1992 QB₁, was discovered. From its beginnings denoting the "wandering stars" of the classical world the definition of " Planet " has been fraught with ambiguity 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 Since then, further discoveries have intensified the debate.

Commemoration as a planet

Pluto is shown as a planet on the Pioneer plaque, an inscription on the space probes Pioneer 10 and Pioneer 11, launched in the early 1970s. The Pioneer plaques are a pair of Gold anodized Aluminum plaques which were placed on board the 1972 Pioneer 10 and 1973 Pioneer 10 ( Pioneer-F) was the first Spacecraft to travel through the Asteroid belt, which it entered on July 15, 1972 Pioneer 11 was the second mission (after its sister probe Pioneer 10) to investigate Jupiter and the Outer solar system and the first to explore the planet The plaque, intended to give information about the origin of the probes to any alien civilization that might in the future encounter the vehicles, includes a diagram of our solar system, showing nine planets. ^[84] Similarly, an analog image contained within the Voyager Golden Record included on the probes Voyager 1 and Voyager 2 (also launched in the 1970s) includes data regarding Pluto and again shows it as the ninth planet. The Voyager Golden Record is a Phonograph record included in the two Voyager Spacecraft launched in 1977 The Voyager 1 spacecraft is a 722-kilogram robotic Space probe of the outer Solar system and beyond launched September 5, Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. ^[85] The Disney character Pluto, introduced in 1930, was also named in honour of the planet. Pluto (formerly known as Pluto the Pup) is an Animated cartoon character made famous in a series of Disney short cartoons. ^[86] In 1941, Glenn T. Seaborg named the newly created element plutonium in Pluto's honour, in keeping with the tradition of naming elements after newly discovered planets (uranium after Uranus and neptunium after Neptune, although this tradition is also used for some non-planets: cerium is named after Ceres and palladium after Pallas). Glenn Theodore Seaborg ( Glenn Teodor Sjöberg) ( April 19, 1912 &ndash February 25, 1999) won the 1951 Nobel Prize in Chemistry Uranium (jʊˈreɪniəm is a silvery-gray Metallic Chemical element in the Neptunium (nɛpˈtjuːniəm is a Chemical element with the symbol Np and Atomic number 93 Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. Cerium (ˈsɪəriəm is a Chemical element with the symbol Ce and Atomic number 58 Ceres (ˈsɪəriːz Palladium (pronounced \pəˈleɪdiəm\ is a rare and lustrous silvery-white metal that was discovered in 1803 by William Hyde Wollaston, who named it palladium after the TemplateInfobox Planet. --> 2 Pallas (ˈpæləs, or as Παλλάς) is one of the largest ^[87]

New discoveries ignite debate

Pluto compared to Eris, (136472) 2005 FY₉, (136108) 2003 EL₆₁, Sedna, Orcus, Quaoar, and Varuna compared to Earth (artist's impressions; no detailed photographs exist).

The discovery of the Kuiper belt and Pluto's relation to it led many to question whether Pluto could be considered separately from others in its population. 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 2002, the KBO 50000 Quaoar was discovered, with a diameter of roughly 1,280 kilometres, about half that of Pluto. ^[88] In 2004, the discoverers of 90377 Sedna placed an upper limit of 1,800 kilometres on its diameter, near Pluto's diameter of 2,320 kilometres. TemplateInfobox Planet.--> 90377 Sedna (ˈsɛdnə) is a Trans-Neptunian ^[89] Just as Ceres eventually lost its planet status after the discovery of the other asteroids, so, it was argued, Pluto should be reclassified as one of the Kuiper belt objects. Ceres (ˈsɪəriːz Asteroids, sometimes called Minor planets or planetoids', are bodies—primarily of the inner Solar System —that are smaller than planets but

On July 29, 2005, the discovery of a new Trans-Neptunian object was announced. Events 1014 - Byzantine-Bulgarian Wars: Battle of Kleidion: Byzantine emperor Basil II inflicts a decisive defeat Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. A trans-Neptunian object (TNO is any object in the Solar system that Orbits the sun at a greater distance on average than Neptune. Named Eris, it is now known to be slightly larger than Pluto. ^[90] This was the largest object discovered in the solar system since Triton in 1846. TemplateInfobox Planet.--> Triton (ˈtraɪtən, or as in Greek Its discoverers and the press initially called it the "tenth planet", although there was no official consensus at the time on whether to call it a planet. ^[91] Others in the astronomical community considered the discovery the strongest argument for reclassifying Pluto as a minor planet. ^[92]

The last remaining distinguishing features of Pluto were now its large moon, Charon, and its atmosphere. Charon (ˈʃærən; also, as in Χάρων) discovered in 1978 is either the largest Moon of Pluto or the smaller member of a double These characteristics are probably not unique to Pluto: several other Trans-Neptunian objects have satellites, and Eris's spectrum suggests that its surface has a composition similar to Pluto's. ^[93] It also possesses a moon, Dysnomia, discovered in September 2005. Dysnomia (,, or as in Greek Δυσνομία officially (136199 Eris I Dysnomia, is the only known moon of the Dwarf planet Eris

Museum and planetarium directors occasionally created controversy by omitting Pluto from planetary models of the solar system. Some omissions were intentional; the Hayden Planetarium reopened after renovation in 2000 with a model of only eight planets. |-| |-| |-| |}The Hayden Planetarium is a public Planetarium located on Central Park West, New York City, next to and organizationally part of the The controversy made headlines at the time. ^[94]

IAU decision to reclassify Pluto

Main article: 2006 definition of planet

The debate came to a head in 2006 with an IAU resolution that created an official definition for the term "planet". According to this resolution, there are three main conditions for an object to be considered a 'planet':

1. The object must be in orbit around the Sun. The Sun (Sol is the Star at the center of the Solar System.
2. The object must be massive enough to be a sphere by its own gravitational force. More specifically, its own gravity should pull it into a shape of hydrostatic equilibrium. Hydrostatic equilibrium occurs when compression due to Gravity is balanced by a Pressure gradient which creates a Pressure gradient force in the opposite
3. It must have cleared the neighbourhood around its orbit. ^[95]

Pluto fails to meet the third condition, since its mass was only 0. 07 times that of the mass of the other objects in its orbit (Earth's mass, by contrast, is 1. 7 million times the remaining mass in its own orbit). ^[96][97] The IAU further resolved that Pluto be classified in the simultaneously created dwarf planet category, and that it act as prototype for a yet-to-be-named category of trans-Neptunian objects, in which it would be separately, but concurrently, classified. 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 A trans-Neptunian object (TNO is any object in the Solar system that Orbits the sun at a greater distance on average than Neptune.

On September 13, 2006, the IAU included Pluto, Eris, and the Eridian moon Dysnomia in their Minor Planet Catalogue, giving them the official minor planet designations "(134340) Pluto", "(136199) Eris", and "(136199) Eris I Dysnomia". Events 509 BC - The Temple of Jupiter on Rome 's Capitoline Hill is dedicated on the ides of September Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Dysnomia (,, or as in Greek Δυσνομία officially (136199 Eris I Dysnomia, is the only known moon of the Dwarf planet Eris This is a list of numbered Minor planets in sequential order there are 192280 numbered minor planets and many more not yet numbered ^[98] If Pluto had been given a minor planet name upon its discovery, the number would have been a little over a thousand rather than over 100,000. The first minor planet to be found after Pluto was 1164 Kobolda, a month later.

There has been some resistance within the astronomical community toward the reclassification. ^{[99][100][101]} Alan Stern, principal investigator with NASA's New Horizons mission to Pluto, has publicly derided the IAU resolution, stating that "the definition stinks, for technical reasons. S Alan Stern is an American planetary scientist, born 22 November 1957 New Orleans Louisiana married (three children The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program New Horizons is a Robotic spacecraft mission by NASA currently underway "^[102] Stern's current contention is that by the terms of the new definition Earth, Mars, Jupiter, and Neptune, all of which share their orbits with asteroids, would be excluded. ^[103] His other claim is that because less than five percent of astronomers voted for it, the decision was not representative of the entire astronomical community. ^[103] Marc W. Buie of the Lowell observatory has voiced his opinion on the new definition on his website and is one of the petitioners against the definition. ^[104] Others have supported the IAU. Mike Brown, the astronomer who discovered Eris, said "through this whole crazy circus-like procedure, somehow the right answer was stumbled on. It’s been a long time coming. Science is self-correcting eventually, even when strong emotions are involved. "^[105]

Children protest the reclassification of Pluto, police keep counter-protesters on a different corner.

Among the general public, reception is mixed. Some have accepted the reclassification; others seek to overturn the decision with online petitions urging the IAU to consider reinstatement. A resolution introduced by some members of the California state assembly light-heartedly denounces the IAU for "scientific heresy," among other crimes. ^[106] The U. S. state of New Mexico's House of Representatives passed a resolution declaring that, in honour of Tombaugh, a longtime resident of that state, Pluto will always be considered a planet while in New Mexican skies, with March 13 being known as "Pluto Planet Day". Events 1138 - Cardinal Gregorio Conti is elected Antipope as Victor IV, succeeding Anacletus II. ^[107] Some reject the change for sentimental reasons, citing that they have always known Pluto as a planet and will continue to do so regardless of the IAU decision. ^[108] Others view this rejection as an attempt to bend the rules in order to keep the only planet discovered by an American classified as such. ^[109]

The ongoing debate over the status of Pluto continues to be acknowledged by the Jet Propulsion Laboratory which, as recently as January 2008, continued to reference it on JPL Photojournal webpages dedicated to Pluto. ^[110] Researchers on both sides of the debate will gather in August 2008 at Johns Hopkins University for a conference that includes back-to-back talks on the current IAU definition of a planet. ^[111]

"Plutoed"

The verb "to pluto" (preterite and past participle: "plutoed") is a neologism coined in the aftermath of the decision. This article is about the grammatical term To see the article relating to Eschatology and the Book of Revelation, see Preterism. In Linguistics, a participle (from Latin participium, a Calque of Greek μετοχη "partaking" is a derivative of a non-finite A neologism (from Greek neo = "new" + logos = "word" is a word that although devised relatively recently in a specific time period has been In January 2007, the American Dialect Society chose "plutoed" as its 2006 Word of the Year, defining "to pluto" as "to demote or devalue someone or something", "as happened to the former planet Pluto when the General Assembly of the International Astronomical Union decided Pluto no longer met its definition of a planet. The American Dialect Society, founded in 1889 is a Learned society "dedicated to the study of the English language in North America, and of other "^[112][113]

Society president Cleveland Evans stated the reason for the organization's selection of "plutoed": "Our members believe the great emotional reaction of the public to the demotion of Pluto shows the importance of Pluto as a name. We may no longer believe in the Roman god Pluto, but we still have a sense of connection with the former planet. Pluto was the Roman god of the underworld known in Latin as Tertius the counterpart of the Greek Hades. "^[114]

See also

• Jovian-Plutonian gravitational effect
• Plutino
• Pluto in astrology
• Pluto in fiction
• Pluto prototype
• Solar eclipses on Pluto
• Solar System bodies formerly considered to be planets

References

External links

• Nunberg, G. (August 28, 2006). Dwarfing Pluto. NPR. An examination of the redefinition of Pluto from a linguistic perspective.
• Pluto Profile by NASA's Solar System Exploration
• Lowell Observatory (2007). Website of the observatory that discovered Pluto
• Williams, D. R. (September 7, 2006). Pluto Fact Sheet. NASA.
• Dunn, T. (2006). Pluto's 3:2 Resonance with Neptune. Gravity Simulator.
• Fraknoi, A. (2006). Teaching What a Planet Is: A Roundtable on the Educational Implications of the New Definition of a Planet. Astronomy Education Review. Series of personal articles written by astronomers involved in the debate.
• "plutoed" - entries in the Urban Dictionary