Pluto

This article is about the dwarf planet. For other uses, seePluto (disambiguation).

Pluto (minor-planet designation: 134340 Pluto) is adwarf planet in the Kuiper belt and the rst trans-Neptunian object to be discovered. It is the largest andsecond-most massive known dwarf planet in the SolarSystem and the ninth-largest and tenth-most-massiveknown object directly orbiting the Sun. It is the largestknown trans-Neptunian object by volume but is less mas-sive than Eris, a dwarf planet in the scattered disc. Likeother Kuiper belt objects, Pluto is primarily made of iceand rock*[13] and is relatively smallabout one-sixth themass of theMoon and one-third its volume. It has a mod-erately eccentric and inclined orbit during which it rangesfrom 30 to 49 astronomical units (4.47.3 billion km)from the Sun. This means that Pluto periodically comescloser to the Sun than Neptune, but a stable orbital res-onance with Neptune prevents them from colliding. In2014, Pluto was 32.6 AU from the Sun. Light from theSun takes about 5.5 hours to reach Pluto at its averagedistance (39.4 AU).*[14]Pluto was discovered in 1930 and was originally con-sidered the ninth planet from the Sun. After 1992, itsstatus as a planet fell into question following the dis-covery of the Kuiper belt, a ring of objects beyondNeptune that includes Pluto among other large bodies.In 2005, Eris, which is 27% more massive than Pluto,was discovered, which led the International Astronomi-cal Union (IAU) to dene the term planetformallyfor the rst time the following year.*[15] This deni-tion excluded Pluto and reclassied it as a member ofthe new "dwarf planet" category (and specically as aplutoid).*[16] Some astronomers believe Pluto shouldstill be considered a planet.*[17]*[18]*[19]Pluto has ve known moons: Charon (the largest, witha diameter just over half that of Pluto), Styx, Nix,Kerberos, and Hydra.*[20] Pluto and Charon are some-times considered a binary system because the barycenterof their orbits does not lie within either body.*[21] TheIAU has not formalized a denition for binary dwarfplanets, and Charon is ocially classied as a moon ofPluto.*[22]On 14 July 2015, the New Horizons probe ew byPluto,*[23]*[24] making it the rst spacecraft to doso.*[25]*[26] NASA plans for New Horizons to takedetailed measurements and images of Pluto and itsmoons.*[27]*[28]

1 History

1.1 Discovery

Further information: Planets beyond Neptune

In the 1840s, Urbain Le Verrier used Newtonian me-chanics to predict the position of the then-undiscoveredplanet Neptune after analysing perturbations in the orbitof Uranus.*[29] Subsequent observations of Neptune inthe late 19th century led astronomers to speculate thatUranus's orbit was being disturbed by another planet be-sides Neptune.In 1906, Percival Lowella wealthy Bostonian who hadfounded the Lowell Observatory in Flagsta, Arizona, in1894started an extensive project in search of a possibleninth planet, which he termed "Planet X".*[30] By 1909,Lowell and William H. Pickering had suggested severalpossible celestial coordinates for such a planet.*[31] Low-ell and his observatory conducted his search until hisdeath in 1916, but to no avail. Unknown to Lowell, hissurveys had captured two faint images of Pluto on 19March and 7 April 1915, but they were not recognizedfor what they were.*[31]*[32] There are fourteen otherknown prediscovery observations, with the oldest madeby the Yerkes Observatory on 20 August 1909.*[33]

Discovery photographs of Pluto

Because of a ten-year legal battle with Constance Lowell,Percival's widow, who attempted to wrest the observa-tory's million-dollar portion of his legacy for herself, thesearch for Planet X did not resume until 1929,*[34] whenits director, Vesto Melvin Slipher, summarily handed thejob of locating Planet X to Clyde Tombaugh, a 23-year-old Kansan who had just arrived at the Lowell Observa-tory after Slipher had been impressed by a sample of his

1

2 1 HISTORY

astronomical drawings.*[34]Tombaugh's task was to systematically image the nightsky in pairs of photographs, then examine each pair anddetermine whether any objects had shifted position. Us-ing a blink comparator, he rapidly shifted back and forthbetween views of each of the plates to create the illusionof movement of any objects that had changed position orappearance between photographs. On 18 February 1930,after nearly a year of searching, Tombaugh discovered apossible moving object on photographic plates taken on23 and 29 January of that year. A lesser-quality pho-tograph taken on 21 January helped conrm the move-ment.*[35] After the observatory obtained further con-rmatory photographs, news of the discovery was tele-graphed to the Harvard College Observatory on 13March1930.*[31]

1.2 Name

See also: Venetia Burney

The discovery made headlines across the globe. TheLowell Observatory, which had the right to name thenew object, received over 1,000 suggestions from all overthe world, ranging from Atlas to Zymal.*[36] Tombaughurged Slipher to suggest a name for the new object quicklybefore someone else did.*[36] Constance Lowell pro-posed Zeus, then Percival and nally Constance. Thesesuggestions were disregarded.*[37]The name Pluto, after the god of the underworld, wasproposed by Venetia Burney (19182009), a then eleven-year-old schoolgirl in Oxford, England, who was inter-ested in classical mythology.*[38] She suggested it ina conversation with her grandfather Falconer Madan, aformer librarian at the University of Oxford's BodleianLibrary, who passed the name to astronomy professorHerbert Hall Turner, who cabled it to colleagues in theUnited States.*[38]The object was ocially named on 24 March1930.*[39]*[40] Each member of the Lowell Ob-servatory was allowed to vote on a short-list of three:Minerva (which was already the name for an asteroid),Cronus (which had lost reputation through being pro-posed by the unpopular astronomer Thomas JeersonJackson See), and Pluto. Pluto received every vote.*[41]The name was announced on 1 May 1930.*[38] Uponthe announcement, Madan gave Venetia 5 (equivalentto 282, or $430 USD in 2015),*[42] as a reward.*[38]The choice of name was partly inspired by the fact thatthe rst two letters of Pluto are the initials of PercivalLowell, and Pluto's astronomical symbol ( , unicodeU+2647, ) is a monogram constructed from the letters'PL'.*[43] Pluto's astrological symbol resembles that ofNeptune ( ), but has a circle in place of the middle

prong of the trident ( ).The name was soon embraced by wider culture. In 1930,Walt Disney was apparently inspired by it when he in-troduced for Mickey Mouse a canine companion namedPluto, although Disney animator Ben Sharpsteen couldnot conrmwhy the namewas given.*[44] In 1941, GlennT. Seaborg named the newly created element plutoniumafter Pluto, in keeping with the tradition of naming ele-ments after newly discovered planets, following uranium,which was named after Uranus, and neptunium, whichwas named after Neptune.*[45]Most languages use the namePlutoin various translit-erations.*[lower-alpha 8] In Japanese, Houei Nojiri sug-gested the translation Meisei (*?, Star of theKing (God) of the Underworld) , and this was borrowedinto Chinese, Korean, and Vietnamese.*[46]*[47]*[48]Some Indian languages use the name Pluto, but others,such as Hindi, use the name of Yama, the Guardianof Hell in Hindu and Buddhist mythology, as doesVietnamese.*[47] Polynesian languages also tend to usethe indigenous god of the underworld, as in MaoriWhiro.*[47]

1.3 Planet X disproved

Once found, Pluto's faintness and lack of a resolvabledisc cast doubt on the idea that it was Lowell's PlanetX.*[30] Estimates of Pluto's mass were revised down-ward throughout the 20th century.*[49]Astronomers initially calculated its mass based on its pre-sumed eect on Neptune and Uranus. In 1931 Pluto wascalculated to be roughly the mass of Earth, with furthercalculations in 1948 bringing the mass down to roughlythat of Mars.*[51]*[53] In 1976, Dale Cruikshank, CarlPilcher and David Morrison of the University of Hawaiicalculated Pluto's albedo for the rst time, nding that itmatched that for methane ice; this meant Pluto had to beexceptionally luminous for its size and therefore could notbe more than 1 percent the mass of Earth.*[54] (Pluto'salbedo is 1.32.0 times greater than that of Earth.*[3])In 1978, the discovery of Pluto's moon Charon al-lowed the measurement of Pluto's mass for the rst time:roughly 0.2% that of Earth, and far too small to accountfor the discrepancies in the orbit of Uranus. Subsequentsearches for an alternative Planet X, notably by RobertSutton Harrington,*[56] failed. In 1992, Myles Standishused data from Voyager 2's yby of Neptune in 1989,which had revised the estimates of Neptune's mass down-ward by 0.5%an amount comparable to the mass ofMarsto recalculate its gravitational eect on Uranus.With the new gures added in, the discrepancies, andwith them the need for a Planet X, vanished.*[57] Today,the majority of scientists agree that Planet X, as Lowelldened it, does not exist.*[58] Lowell had made a pre-diction of Planet X's orbit and position in 1915 that was

1.4 Classication 3

fairly close to Pluto's actual orbit and its position at thattime; Ernest W. Brown concluded soon after Pluto's dis-covery that this was a coincidence,*[59] a view still heldtoday.*[57]

1.4 ClassicationFurther information: Denition of planet

Artistic comparison of Eris, Pluto, Makemake, Haumea,Sedna, 2007 OR10, Quaoar, Orcus, and Earth.(This box:

view talk edit

)

From 1992 onward, many bodies were discovered or-biting in the same area as Pluto, showing that Pluto ispart of a population of objects called the Kuiper belt.This made its ocial status as a planet controversial, withmany questioning whether Pluto should be considered to-gether with or separately from its surrounding population.Museum and planetarium directors occasionally createdcontroversy by omitting Pluto from planetary models ofthe Solar System. The Hayden Planetarium reopenedin February 2000, after renovationwith a model ofonly eight planets, which made headlines almost a yearlater.*[60]As objects increasingly closer in size to Pluto were dis-covered in the region, it was argued that Pluto shouldbe reclassied as one of the Kuiper belt objects, just asCeres, Pallas, Juno and Vesta eventually lost their planetstatus after the discovery of many other asteroids. On 29July 2005, the discovery of a new trans-Neptunian object,Eris, was announced, which was thought to be substan-tially larger than Pluto. This was the largest object dis-covered in the Solar System since Triton in 1846. Its dis-coverers and the press initially called it the tenth planet,although there was no ocial consensus at the time onwhether to call it a planet.*[61] Others in the astronomi-cal community considered the discovery the strongest ar-gument for reclassifying Pluto as a minor planet.*[62]

1.4.1 IAU classication

Main article: IAU denition of planet

The debate came to a head on 24 August 2006 with anIAU resolution that created an ocial denition for thetermplanet. 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.2. The object must be massive enough to be rounded

by its own gravity. More specically, its own gravityshould pull it into a shape of hydrostatic equilibrium.

3. It must have cleared the neighborhood around its or-bit.*[63]*[64]

Pluto fails to meet the third condition, because its massis only 0.07 times that of the mass of the other objectsin its orbit (Earth's mass, by contrast, is 1.7 million timesthe remaining mass in its own orbit).*[62]*[64] The IAUfurther decided that bodies that, like Pluto, do not meetcriterion 3 would be called dwarf planets. On 13 Septem-ber 2006, the IAU included Pluto and Eris and its moonDysnomia in their Minor Planet Catalogue, giving themthe ocial minor planet designations "(134340) Pluto,"(136199) Eris, and "(136199) Eris I Dysnomia.*[65]If Pluto had been given one upon its discovery, the num-ber would have been about 1,164 instead of 134,340.There has been some resistance within the astronomicalcommunity toward the reclassication.*[66]*[67]*[68]Alan Stern, principal investigator with NASA's NewHorizons mission to Pluto, publicly derided the IAU res-olution, stating that the denition stinks, for techni-cal reasons.*[69] Stern's contention was that by theterms of the new denition Earth, Mars, Jupiter, andNeptune, all of which share their orbits with asteroids,would be excluded.*[70] He argued that all big spheri-cal moons, including the Moon, should likewise be con-sidered planets.*[19] His other claim was that becauseless than ve percent of astronomers voted for it, thedecision was not representative of the entire astronom-ical community.*[70] Marc W. Buie, then at Lowell Ob-servatory, voiced his opinion on the new denition onhis website and petitioned against the denition.*[71]Others have supported the IAU. Mike Brown, the as-tronomer who discovered Eris, saidthrough this wholecrazy circus-like procedure, somehow the right answerwas stumbled on. It's been a long time coming. Scienceis self-correcting eventually, even when strong emotionsare involved.*[72]Public reception to the IAU decision was mixed. Al-though many accepted the reclassication, some soughtto overturn the decision with online petitions urging theIAU to consider reinstatement. A resolution introducedby some members of the California State Assembly face-tiously called the IAU decision ascientic heresy.*[73]The New Mexico House of Representatives passed a res-olution in honor of Tombaugh, a longtime resident of thatstate, that declared that Pluto will always be considereda planet while in New Mexican skies and that 13 March2007, was Pluto Planet Day.*[74]*[75] The Illinois Sen-ate passed a similar resolution in 2009, on the basis that

4 2 ORBIT AND ROTATION

A promotional event with a staged Plutoprotest. Membersplaying protesters of the reclassication of Pluto on the left, withthose playing counter-protesters on the right

Clyde Tombaugh, the discoverer of Pluto, was born inIllinois. The resolution asserted that Pluto wasunfairlydowngraded to a 'dwarf' planetby the IAU.*[76] Somemembers of the public have also rejected the change,citing the disagreement within the scientic communityon the issue, or for sentimental reasons, maintaining thatthey have always known Pluto as a planet and will con-tinue to do so regardless of the IAU decision.*[77]In 2006, in its 17th annual words of the year vote, theAmerican Dialect Society voted plutoed as the word ofthe year. Toplutois todemote or devalue someoneor something.*[78]Researchers on both sides of the debate gathered on1416 August 2008, at the Johns Hopkins UniversityApplied Physics Laboratory for a conference that in-cluded back-to-back talks on the current IAU deni-tion of a planet.*[79] Entitled The Great Planet De-bate,*[80] the conference published a post-conferencepress release indicating that scientists could not cometo a consensus about the denition of planet.*[81] Justbefore the conference, on 11 June 2008, the IAU an-nounced in a press release that the term "plutoid" wouldhenceforth be used to refer to Pluto and other objectsthat have an orbital semi-major axis greater than thatof Neptune and enough mass to be of near-sphericalshape.*[82]*[83]*[84]

2 Orbit and rotationPluto's orbital period is 248 Earth years. Its orbital char-acteristics are substantially dierent from those of theplanets, which follow nearly circular orbits around theSun close to a at reference plane called the ecliptic.In contrast, Pluto's orbit is highly inclined relative tothe ecliptic (over 17) and highly eccentric (elliptical).This high eccentricity means a small region of Pluto'sorbit lies nearer the Sun than Neptune's. The PlutoCharon barycenter came to perihelion on 5 September1989,*[2]*[lower-alpha 9] and was last closer to the Sunthan Neptune between 7 February 1979, and 11 February1999.*[85]

In the long term, Pluto's orbit is chaotic. Althoughcomputer simulations can be used to predict its posi-tion for several million years (both forward and backwardin time), after intervals longer than the Lyapunov timeof 1020 million years, calculations become speculative:Pluto is sensitive to unmeasurably small details of the So-lar System, hard-to-predict factors that will gradually dis-rupt its orbit.*[86]*[87]

Orbit of Plutoecliptic view. This side viewofPluto's orbit (in red) shows its large inclination to theecliptic.

Pluto

Q

q

Neptune

Q

q

0010 1020 2030 30 [AU]

Orbit of Plutopolar view. This view from aboveshows how Pluto's orbit (in red) is less circular thanNeptune's (in blue), and how Pluto is sometimes closer tothe Sun than Neptune. The darker halves of both orbitsshow where they pass below the plane of the ecliptic.

2.2 Other factors 5

Images of one orbit of Charon around Pluto, acquired byNew Horizons along the ecliptic MayJune 2015

2.1 Relationship with Neptune

Despite Pluto's orbit appearing to cross that of Neptunewhen viewed from directly above, the two objects' orbitsare aligned so that they can never collide or even approachclosely. There are several reasons why.At the simplest level, one can examine the two orbits andsee that they do not intersect. When Pluto is closest tothe Sun, and hence closest to Neptune's orbit as viewedfrom above, it is also the farthest above Neptune's path.Pluto's orbit passes about 8 AU above that of Neptune,preventing a collision.*[88]*[89]*[90] Pluto's ascendingand descending nodes, the points at which its orbit crossesthe ecliptic, are currently separated from Neptune's byover 21.*[91]This alone is not enough to protect Pluto; perturbationsfrom the planets (especially Neptune) could alter aspectsof Pluto's orbit (such as its orbital precession) over mil-lions of years so that a collision could be possible. Someother mechanism or mechanisms must therefore be atwork. Themost signicant of these is that Pluto lies in the2:3 mean-motion resonance with Neptune: for every twoorbits that Pluto makes around the Sun, Neptune makesthree. The two objects then return to their initial posi-tions and the cycle repeats, each cycle lasting about 500years. This pattern is such that, in each 500-year cycle,the rst time Pluto is near perihelion, Neptune is over50 behind Pluto. By Pluto's second perihelion, Neptunewill have completed a further one and a half of its ownorbits, and so will be a similar distance ahead of Pluto.Pluto and Neptune's minimum separation is over 17 AU,which is greater than Pluto's minimum separation fromUranus (11 AU).*[90]The 2:3 resonance between the two bodies is highly sta-ble, and is preserved over millions of years.*[92] Thisprevents their orbits from changing relative to one an-other; the cycle always repeats in the same way, and sothe two bodies can never pass near each other. Thus, even

if Pluto's orbit were not highly inclined, the two bodiescould never collide.*[90]

2.2 Other factors

Numerical studies have shown that over periods of mil-lions of years, the general nature of the alignmentbetween the orbits of Pluto and Neptune does notchange.*[88]*[93] There are several other resonances andinteractions that govern the details of their relative mo-tion, and enhance Pluto's stability. These arise principallyfrom two additional mechanisms (besides the 2:3 mean-motion resonance).First, Pluto's argument of perihelion, the angle betweenthe point where it crosses the ecliptic and the point whereit is closest to the Sun, librates around 90.*[93] Thismeans that when Pluto is closest to the Sun, it is at itsfarthest above the plane of the Solar System, preventingencounters with Neptune. This is a direct consequence ofthe Kozai mechanism,*[88] which relates the eccentricityof an orbit to its inclination to a larger perturbing bodyin this case Neptune. Relative to Neptune, the amplitudeof libration is 38, and so the angular separation of Pluto'sperihelion to the orbit of Neptune is always greater than52 (9038). The closest such angular separation oc-curs every 10,000 years.*[92]Second, the longitudes of ascending nodes of the twobodiesthe points where they cross the eclipticare innear-resonance with the above libration. When the twolongitudes are the samethat is, when one could drawa straight line through both nodes and the SunPluto'sperihelion lies exactly at 90, and hence it comes closestto the Sun when it is highest above Neptune's orbit. Thisis known as the 1:1 superresonance. All the Jovian plan-ets, particularly Jupiter, play a role in the creation of thesuperresonance.*[88]To understand the nature of the libration, imagine a polarpoint of view, looking down on the ecliptic from a distantvantage point where the planets orbit counterclockwise.After passing the ascending node, Pluto is interior toNeptune's orbit and moving faster, approaching Neptunefrom behind. The strong gravitational pull between thetwo causes angular momentum to be transferred to Pluto,at Neptune's expense. This moves Pluto into a slightlylarger orbit, where it travels slightly more slowly, accord-ing to Kepler's third law. As its orbit changes, this hasthe gradual eect of changing the perihelion and lon-gitude of Pluto's orbit (and, to a lesser degree, of Nep-tune). After many such repetitions, Pluto is sucientlyslowed, and Neptune suciently speeded up, that Nep-tune begins to catch up with Pluto at the opposite sideof its orbit (near the opposing node to where we began).The process is then reversed, and Pluto loses angular mo-mentum to Neptune, until Pluto is suciently speededup that it begins to catch Neptune again at the originalnode. The whole process takes about 20,000 years to

6 3 GEOLOGY

complete.*[90]*[92]

2.3 Rotation

Pluto's rotation period, its day, is equal to 6.39 Earthdays.*[94] Like Uranus, Pluto rotates on itssideon itsorbital plane, with an axial tilt of 120, and so its seasonalvariation is extreme; at its solstices, one-fourth of its sur-face is in continuous daylight, whereas another fourth isin continuous darkness.*[95] Daylight on Pluto is weak,analogous to twilight on Earth; NASAhas posted aPlutoTimecalculator that determines when the light on Earthis equivalent to that on Pluto on a clear day. For exam-ple, on 13 July 2015, at the coordinates of the AppliedPhysics Laboratory where the probe was constructed, thePluto Time was 8:38 p.m.,*[96]*[97] four minutes laterthan the apparent sunset of 8:34 p.m. reported for thatlocation by NOAA.*[98]

2.4 Quasi-satellite

At least one minor body, (15810) 1994 JR1, is a quasi-satellite of Pluto, a specic type of co-orbital congura-tion.*[99] It has been a quasi-satellite of Pluto for about100,000 years and it will remain so for perhaps another250,000 years. Its quasi-satellite behavior is recurrentwith a periodicity of 2 million years.*[99]*[100] Theremay be additional Pluto co-orbitals.

3 Geology

Main article: Geology of Pluto

New Horizons map of Pluto's surface

Hubble map of Pluto's surface

Theoretical structure of Pluto*[101]

1. Frozen nitrogen*[102]

2. Water ice

3. Rock

Due to Pluto's distance from Earth, in-depth study fromEarth is dicult. On 14 July 2015, NASA's New Hori-zons space probe ew through the Pluto system, whichwill provide much information about it.*[25]

3.1 Surface

Pluto's surface is composed of more than 98 percentnitrogen ice, with traces of methane and carbon monox-ide.*[102] The face of Pluto oriented toward Charoncontains more methane ice, whereas the opposite facecontains more nitrogen and carbon monoxide ice.*[103]Pluto's surface is very varied, with large dierences inboth brightness and color.*[104] Pluto is one of the mostcontrastive bodies in the Solar System, with as much con-trast as Saturn's moon Iapetus.*[105] The color variesbetween charcoal black, dark orange and white.*[106]Pluto's color is more similar to that of Io with slightlymore orange, signicantly less red than Mars.*[107]

3.2 Internal structure

Pluto's density is 2.030.06 g/cm3.*[7] Because the de-cay of radioactive elements would eventually heat the icesenough for the rock to separate from them, scientists ex-pect that Pluto's internal structure is dierentiated, withthe rocky material having settled into a dense core sur-rounded by a mantle of water ice. The diameter of thecore is hypothesized to be approximately 1700 km, 70%of Pluto's diameter.*[101] It is possible that such heatingcontinues today, creating a subsurface ocean layer of liq-uid water some 100 to 180 km thick at the coremantleboundary.*[101]*[108]

7First signs of geological features on Pluto (9 July 2015)

4 Mass and size

Pluto's mass is 1.311022 kg, less than 0.24 percentthat of Earth,*[115] and its diameter is 2370 km.*[5] Itssurface area is 1.66510*7 km2, or roughly the same sur-face area as Russia. Its surface gravity is 0.067g (com-pared to 1g for Earth).The discovery of Pluto's satellite Charon in 1978 enableda determination of the mass of the PlutoCharon systemby application of Newton's formulation of Kepler's thirdlaw. Observations of Pluto in occultation with Charonallowed scientists to establish Pluto's diameter more ac-curately, whereas the invention of adaptive optics allowedthem to determine its shape more accurately.*[116]With less than 0.2 lunar masses, Pluto is much less mas-sive than the terrestrial planets, and also less massive thanseven moons, Ganymede, Titan, Callisto, Io, the Moon,Europa, and Triton. The mass is much less than thoughtbefore Charon was discovered.Pluto is more than twice the diameter and a dozen timesthe mass of the dwarf planet Ceres, the largest objectin the asteroid belt. It is less massive than the dwarfplanet Eris, a trans-Neptunian object discovered in 2005,though Pluto has a larger diameter of 2370 km comparedto Eris's approximate diameter of 2326 km.*[5]Determinations of Pluto's size had been complicatedby its atmosphere,*[112] and possible hydrocarbonhaze.*[110] In March 2014, Lellouch, de Bergh et al.published ndings regarding methane mixing ratios inPluto's atmosphere consistent with a Plutonian diam-eter greater than 2360 km, with a best guessof2368 km.*[114] On 13 July 2015 NASA's New Horizonsmission Long Range Reconnaissance Imager determinedPluto's diameter to be 2,370 km (1,470 mi).*[5]*[6]

Size comparisons: Left: Earth, Moon and Pluto.Center: Pluto and Charon compared to Earth. Right:Pluto and Charon compared to the United States.

5 AtmosphereMain article: Atmosphere of Pluto

Pluto has a thin atmosphere consisting of nitrogen (N2),methane (CH4), and carbon monoxide (CO), which arein equilibrium with their ices on Pluto's surface.*[117]The surface pressure ranges from 6.5 to 24 bar (0.65 to2.4 Pa),*[118] roughly one million to 100,000 times lessthan Earth's atmospheric pressure. Pluto's elliptical orbitis predicted to have a major eect on its atmosphere: asPluto moves away from the Sun, its atmosphere shouldgradually freeze out. When Pluto is closer to the Sun,the temperature of Pluto's solid surface increases, caus-ing the ices to sublimate. Just like sweat cools the bodyas it evaporates from the skin, this sublimation cools thesurface of Pluto.*[119]The presence of methane, a powerful greenhouse gas, inPluto's atmosphere creates a temperature inversion, withaverage temperatures 36 K warmer 10 km above the sur-face.*[120] The lower atmosphere contains a higher con-

8 7 ORIGINS

centration of methane than its upper atmosphere.*[120]Even though Pluto is receding from the Sun, in 2002 theatmospheric pressure (0.3 Pa) was higher than in 1988,because in 1987 the south pole of Pluto came out of theshadow for the rst time in 120 years, causing extra nitro-gen to start sublimating from the polar cap. It will takedecades for this nitrogen to condense out of the atmo-sphere as it freezes onto Pluto's now continuously darknorth pole's ice cap.*[121]

6 SatellitesMain article: Moons of Pluto

Pluto has ve known natural satellites: Charon, rstidentied in 1978 by astronomer James Christy; Nixand Hydra, both discovered in 2005;*[122] Kerberos,discovered in 2011;*[123] and Styx, discovered in2012.*[124] The satellites' orbits are circular (eccentric-ity < 0.006) and coplanar with Pluto's equator (incli-nation < 1),*[125]*[126] and therefore tilted approxi-mately 120 relative to Pluto's orbit. The Plutonian sys-tem is highly compact: the ve known satellites orbitwithin the inner 3% of the region where prograde orbitswould be stable.*[127] Closest to Pluto orbits Charon,which is large enough to be in hydrostatic equilibrium andfor the system's barycenter to be outside Pluto. BeyondCharon orbit Pluto's smaller circumbinary moons, Styx,Nix, Kerberos, and Hydra, respectively.The orbital periods of all of Pluto's moons are linkedin a system of orbital resonances and near reso-nances.*[128]*[126] When precession is accounted for,the orbital periods of Styx, Nix, and Hydra are in an ex-act 18:22:33 ratio.*[126] There is also a 3:4:5:6 sequenceof approximate ratios between the periods of Styx, Nix,Kerberos and Hydra with that of Charon, which becomescloser to exact going outward.*[126]*[129]The PlutoCharon system is one of the few systems inthe Solar System whose barycenter lies above the pri-mary's surface (617 Patroclus is a smaller example, theSun and Jupiter the only larger one).*[130] This and thelarge size of Charon relative to Pluto have led some as-tronomers to call it a double dwarf planet.*[131] The sys-tem is also unusual among planetary systems in that eachis tidally locked to the other: Charon always presentsthe same face to Pluto, and Pluto always presents thesame face to Charon: from any position on either body,the other is always at the same position in the sky, oralways obscured.*[132] This also means that the rota-tion period of each is equal to the time it takes the en-tire system to rotate around its common center of grav-ity.*[94] In 2007, observations by the Gemini Observa-tory of patches of ammonia hydrates and water crystalson the surface of Charon suggested the presence of activecryo-geysers.*[133]

Pluto's moons are believed to have been formed by a col-lision between Pluto and a similar-sized body early in thehistory of the Solar System. The collision released mate-rial that consolidated into the moons around Pluto.*[134]However, Kerberos has a much lower albedo than theother moons of Pluto,*[135] which is dicult to explainwith a giant collision.*[136]

(Left): The Pluto system: Pluto, Charon, Styx, Nix,Kerberos, and Hydra, imaged by the Hubble SpaceTelescope in July 2012. (Middle): Pluto and Charon, toscale. Image acquired by New Horizons on 8 July 2015.(Right): Comparison of the scale and brightness of themoons of Pluto (artist's concept).*[137]

7 OriginsFurther information: Kuiper belt and Nice modelPluto's origin and identity had long puzzled astronomers.One early hypothesis was that Pluto was an escaped moonof Neptune, knocked out of orbit by its largest currentmoon, Triton. This idea was eventually rejected after dy-

9Plot of the known Kuiper belt objects, set against the four giantplanets

namical studies of the two planets' orbits showed it to beimpossible.*[138]*[139]Pluto's true place in the Solar System began to reveal it-self only in 1992, when astronomers began to nd smallicy objects beyond Neptune that were similar to Plutonot only in orbit but also in size and composition. Thistrans-Neptunian population is believed to be the sourceof many short-period comets. Astronomers now believePluto to be the largest*[lower-alpha 10] member of theKuiper belt, a stable belt of objects located between 30and 50 AU from the Sun. As of 2011, surveys of theKuiper belt to magnitude 21 were nearly complete andany remaining Pluto-sized objects are expected to be be-yond 100 AU from the Sun.*[140] Like other Kuiper-beltobjects (KBOs), Pluto shares features with comets; forexample, the solar wind is gradually blowing Pluto's sur-face into space, in the manner of a comet.*[141] It hasbeen claimed that if Pluto were placed as near to the Sunas Earth, it would develop a tail, as comets do.*[142] Thisclaim has been disputed with the argument that Pluto'sescape velocity is too high for this to happen.*[143]Though Pluto is the largest Kuiper belt object discov-ered,*[110] Neptune's moon Triton, which is slightlylarger than Pluto, is similar to it both geologically andatmospherically and is believed to be a captured Kuiperbelt object.*[144] Eris (see above) is about the same sizeas Pluto (though more massive) but is not strictly consid-ered a member of the Kuiper belt population. Rather, itis considered a member of a linked population called thescattered disc.A large number of Kuiper belt objects, like Pluto, are ina 2:3 orbital resonance with Neptune. KBOs with thisorbital resonance are called "plutinos", after Pluto.*[145]Like other members of the Kuiper belt, Pluto is thoughtto be a residual planetesimal; a component of the original

protoplanetary disc around the Sun that failed to fully co-alesce into a full-edged planet. Most astronomers agreethat Pluto owes its current position to a sudden migra-tion undergone by Neptune early in the Solar System'sformation. As Neptune migrated outward, it approachedthe objects in the proto-Kuiper belt, setting one in orbitaround itself (Triton), locking others into resonances, andknocking others into chaotic orbits. The objects in thescattered disc, a dynamically unstable region overlappingthe Kuiper belt, are believed to have been placed in theircurrent positions by interactions with Neptune's migrat-ing resonances.*[146] A computer model created in 2004by Alessandro Morbidelli of the Observatoire de la Cted'Azur in Nice suggested that the migration of Neptuneinto the Kuiper belt may have been triggered by the for-mation of a 1:2 resonance between Jupiter and Saturn,which created a gravitational push that propelled bothUranus and Neptune into higher orbits and caused themto switch places, ultimately doubling Neptune's distancefrom the Sun. The resultant expulsion of objects fromthe proto-Kuiper belt could also explain the Late HeavyBombardment 600 million years after the Solar System'sformation and the origin of the Jupiter trojans.*[147] Itis possible that Pluto had a near-circular orbit about 33AU from the Sun before Neptune's migration perturbedit into a resonant capture.*[148] The Nice model requiresthat there were about a thousand Pluto-sized bodies inthe original planetesimal disk, which included Triton andEris.*[147]

8 Observation and explorationPluto's distance from Earth makes in-depth study fromEarth dicult. On 14 July 2015, NASA's New Hori-zons space probe ew through the Pluto system, whichwill provide much information about it.*[25]

8.1 Observation

Pluto's visual apparent magnitude averages 15.1, bright-ening to 13.65 at perihelion.*[3] To see it, a telescopeis required; around 30 cm (12 in) aperture being desir-able.*[149] It looks star-like and without a visible diskeven in large telescopes, because its angular diameter isonly 0.11.The earliest maps of Pluto, made in the late 1980s,were brightness maps created from close observations ofeclipses by its largest moon, Charon. Observations weremade of the change in the total average brightness ofthe PlutoCharon system during the eclipses. For exam-ple, eclipsing a bright spot on Pluto makes a bigger totalbrightness change than eclipsing a dark spot. Computerprocessing of many such observations can be used to cre-ate a brightness map. This method can also track changesin brightness over time.*[150]*[151]

10 8 OBSERVATION AND EXPLORATION

Computer-generated rotating image of Pluto based on observa-tions by the Hubble Space Telescope in 20022003

Better maps were produced from images taken by theHubble Space Telescope (HST), which oered higherresolution, and showed considerably more detail,*[105]resolving variations several hundred kilometers across,including polar regions and large bright spots.*[107]These maps were produced by complex computer pro-cessing, which nds the best-t projected maps for thefew pixels of the Hubble images.*[152] These remainedthe most detailed maps of Pluto until the yby of NewHorizons in July 2015, because the two cameras on theHST used for these maps were no longer in service.*[152]

8.2 Exploration

Further information: New HorizonsPluto presents signicant challenges for spacecraft be-

cause of its small mass and great distance from Earth.Voyager 1 could have visited Pluto, but controllers optedinstead for a close yby of Saturn's moon Titan, resultingin a trajectory incompatible with a Pluto yby. Voyager 2never had a plausible trajectory for reaching Pluto.*[153]No serious attempt to explore Pluto by spacecraft oc-curred until the last decade of the 20th century. In August1992, JPL scientist Robert Staehle telephoned Pluto'sdiscoverer, Clyde Tombaugh, requesting permission tovisit his planet. I told him he was welcome to it,Tombaugh later remembered,though he's got to go onelong, cold trip.*[154] Despite this early momentum, in2000, NASA cancelled the Pluto Kuiper Expressmission,citing increasing costs and launch vehicle delays.*[155]After an intense political battle, a revised mission toPluto, dubbed New Horizons, was granted funding fromthe US government in 2003.*[156] New Horizons waslaunched successfully on 19 January 2006. The missionleader, S. Alan Stern, conrmed that some of the ashes

New Horizons, launched on 19 January 2006

The hemisphere of Pluto that will be imaged at closest approachby New Horizons

of Clyde Tombaugh, who died in 1997, had been placedaboard the spacecraft.*[157]In early 2007 the craft made use of a gravity assist fromJupiter. Its closest approach to Pluto will be on 14 July2015; scientic observations of Pluto have begun vemonths before the closest approach and will continue forat least a month after the encounter. New Horizons cap-tured its rst (distant) images of Pluto in late September2006, during a test of the Long Range ReconnaissanceImager (LORRI).*[158] The images, taken from a dis-tance of approximately 4.2 billion kilometers, conrm thespacecraft's ability to track distant targets, critical for ma-neuvering toward Pluto and other Kuiper belt objects.

8.3 Proposed exploration 11

First Pluto sighting from New Horizons

New Horizons will use a remote sensing package that in-cludes imaging instruments and a radio science investi-gation tool, as well as spectroscopic and other experi-ments, to characterize the global geology andmorphologyof Pluto and its moonCharon, map their surface composi-tion and analyze Pluto's neutral atmosphere and its escaperate. New Horizons will also photograph the surfaces ofPluto and Charon.Pluto's small moons, discovered shortly before and afterthe probe's launch, may present it with unforeseen chal-lenges. Debris from collisions between Kuiper belt ob-jects and the smaller moons, with their relatively low es-cape velocities, may produce a tenuous dusty ring. IfNewHorizons ies through such a ring system, there would bean increased potential for micrometeoroid damage thatcould disable the probe.*[159]On 4 February 2015, NASA released new images ofPluto (taken on 25 and 27 January) from the approachingprobe.*[160] New Horizons was more than 203,000,000km (126,000,000mi) away from Pluto when it began tak-ing the photos, which showed Pluto and its largest moon,Charon.On 20 March 2015, NASA invited the general public tosuggest names for surface features that will be discoveredon Pluto and Charon.*[161]On 15 April 2015, Pluto was imaged showing a possiblepolar cap.*[162]Between April and June 2015, New Horizons began re-turning images of Pluto that exceeded the quality that theHubble Space Telescope could produce.*[163]*[164]

8.3 Proposed explorationA Pluto orbiter/lander/sample return mission was pro-posed in 2003. The plan included a twelve-year trip fromEarth to Pluto, mapping from orbit, multiple landings, awarm water probe, and possible in situ propellant produc-tion for another twelve-year trip back to Earth with sam-ples. Power and propulsion would come from the bimodalMITEE nuclear reactor system.*[165]

9 Gallery

10 See also How I Killed Pluto and Why It Had It Coming Pluto in astrology Pluto in ction Solar eclipses on Pluto

11 Notes[1] Orbital elements refer to the barycenter of the Pluto sys-

tem, and are the instantaneous osculating values at theprecise J2000 epoch. Barycenter quantities are given be-cause, in contrast to the planetary center, they do not ex-perience appreciable changes on a day-to-day basis fromthe motion of the moons. The orbital period of Pluto islisted as 248 years because most references use the morestable barycenter of the Solar System (Sun+Jupiter) to listthe orbital period of the Pluto-Charon system. A J2000heliocentric solution would give a value of 246 years.

[2] Surface area derived from the radius r: 4r2 .

[3] Volume v derived from the radius r: 4r3/3 .

[4] Surface gravity derived from the massM, the gravitationalconstant G and the radius r: GM/r2 .

[5] Escape velocity derived from themassM, the gravitationalconstant G and the radius r:

p2GM/r .

[6] Based on the orientation of Charon's orbit, which is as-sumed the same as Pluto's spin axis due to the mutual tidallocking.

[7] Based on geometry of minimum and maximum distancefrom Earth and Pluto radius in the factsheet

[8] The equivalence is less close in languages whosephonology diers widely from Greek's, such as SomaliBuluuto and Navajo Totoo.

[9] The discovery of Charon in 1978 allowed astronomers toaccurately calculate the mass of the Plutonian system. Butit did not indicate the two bodies' individual masses, whichcould only be estimated after other moons of Pluto's werediscovered in late 2005. As a result, because Pluto came

12 12 REFERENCES

to perihelion in 1989, most Pluto perihelion date esti-mates are based on the PlutoCharon barycenter. Charoncame to perihelion 4 September 1989. The PlutoCharonbarycenter came to perihelion 5 September 1989. Plutocame to perihelion 8 September 1989.

[10] The dwarf planet Eris is roughly the same size as Pluto,about 2330 km; Eris is, however, 28% more massive thanPluto. Eris is a scattered-disc object, often considereda distinct population from Kuiper-belt objects like Pluto;Pluto is the largest body in the Kuiper belt proper, whichexcludes the scattered-disc objects.

}}-->

12 References[1] HORIZONS Web-Interface for Pluto Barycenter (Ma-

jor Body=9)". JPL Horizons On-Line Ephemeris System.Retrieved 11 October 2012. SelectEphemeris Type: El-ements,Target Body: Pluto BarycenterandCenter:@Sun.

[2]HorizonOnline Ephemeris System for Pluto Barycenter. JPL Horizons On-Line Ephemeris System @ Solar Sys-tem Dynamics Group. Retrieved 16 January 2011. (setObserver Location to @sun to place the observer at thecenter of the sun)

[3] Williams, David R. (7 September 2006). Pluto FactSheet. NASA. Retrieved 24 March 2007.

[4] Seligman, Courtney.Rotation Period and Day Length. Retrieved 13 August 2009.

[5]How Big Is Pluto? New Horizons Settles Decades-LongDebate. NASA. 13 July 2015. Retrieved 13 July 2015.

[6] Lakdawalla, Emily.Pluto minus one day: Very rst NewHorizons Pluto encounter science results. The PlanetarySociety. Retrieved 13 July 2015.

[7] Buie, Marc W.; Grundy, William M.; Young, Eliot F. etal. (2006). Orbits and photometry of Pluto's satel-lites: Charon, S/2005 P1, and S/2005 P2. Astro-nomical Journal 132 (1): 290. arXiv:astro-ph/0512491.Bibcode:2006AJ....132..290B. doi:10.1086/504422.

[8] Archinal, B. A.; aHearn, M. F.; Bowell, E.; Conrad,A.; Consolmagno, G. J.; Courtin, R.; Fukushima, T.; He-stroer, D.; Hilton, J. L.; Krasinsky, G. A.; Neumann,G.; Oberst, J.; Seidelmann, P. K.; Stooke, P.; Tholen, D.J.; Thomas, P. C.; Williams, I. P. (2010). Report ofthe IAUWorkingGroup onCartographic Coordinates andRotational Elements: 2009. Celestial Mechanics and Dy-namical Astronomy 109 (2): 101. doi:10.1007/s10569-010-9320-4.

[9] Hamilton, Calvin J. (12 February 2006). Dwarf PlanetPluto. Views of the Solar System. Retrieved 10 January2007.

[10] AstDys (134340) Pluto Ephemerides. Department ofMathematics, University of Pisa, Italy. Retrieved 27 June2010.

[11] JPL Small-Body Database Browser: 134340 Pluto.Retrieved 12 June 2008.

[12] Pluto has carbon monoxide in its atmosphere.Physorg.com. 19 April 2011. Retrieved 22 November2011.

[13] Stern, S. Alan; Mitton, Jacqueline (2005). Pluto andCharon: ice worlds on the ragged edge of the solar sys-tem. Weinheim:Wiley-VCH. ISBN3-527-40556-9. Re-trieved 3 July 2013.

[14] NASA: How fast does light travel from the Sun to each ofthe planets?

[15] Astronomers Measure Mass of Largest Dwarf Planet. hubblesite. 2007. Retrieved 3 November 2007.

[16] Akwagyiram, Alexis (2 August 2005).Farewell Pluto?".BBC News. Retrieved 5 March 2006.

[17] Gray, Richard (10 August 2008).Pluto should get backplanet status, say astronomers. The Telegraph. Retrieved9 August 2008.

[18] Gorwyn, Adam; Alan Stern:dA Chihuahua is still a dog,and Pluto is still a planet , EarthSky interview, 18 Febru-ary 2010

[19] Should Large Moons Be Called 'Satellite Planets'?".News.discovery.com. 14 May 2010. Retrieved 4 Novem-ber 2011.

[20] Showalter, Mark R. (11 July 2012). Hubble Discoversa Fifth Moon Orbiting Pluto (News Release STScI-2012-32)". HubbleSite NewsCenter. Retrieved 11 July 2012.

[21] Olkin, Catherine B.; Wasserman, Lawrence H.; Franz,Otto G. (2003). The mass ratio of Charon toPluto from Hubble Space Telescope astrometry with thene guidance sensors (PDF). Icarus (Lowell Observa-tory) 164 (1): 254259. Bibcode:2003Icar..164..254O.doi:10.1016/S0019-1035(03)00136-2. Retrieved 13March 2007.

[22] Pluto and the Developing Landscape of Our Solar Sys-temInternational Astronomical Union. Retrieved on 27October 2010.

[23] Dunn, Marcia (14 July 2015). Pluto close-up: Space-craft makes yby of icy, mystery world. AP News. Re-trieved 14 July 2015.

[24] Chang, Kenneth (13 July 2015). A Close-Up for PlutoAfter Spacecraft s 3-Billion-MileTrip. The New YorkTimes. Retrieved 13 July 2015.

[25] Brown, Dwayne; Buckley, Michael; Stotho, Maria (15January 2015). January 15, 2015 Release 15-011 NASA's New Horizons Spacecraft Begins First Stages ofPluto Encounter. NASA. Retrieved 15 January 2015.

[26] Overbye, Dennis (6 July 2015).Reaching Pluto, and theEnd of an Era of Planetary Exploration. The New YorkTimes. Retrieved 7 July 2015.

[27] About New Horizons. nasa.gov. NASA. Retrieved 3May 2014.

13

[28] Chang, Kenneth (6 July 2015).Almost Time for Pluto sClose-Up. The New York Times. Retrieved 6 July 2015.

[29] Croswell, Ken (1997). Planet Quest: The Epic Discoveryof Alien Solar Systems. New York: The Free Press. p. 43.ISBN 978-0-684-83252-4.

[30] Tombaugh, Clyde W. (1946).The Search for the NinthPlanet, Pluto. Astronomical Society of the Pacic Leaets5: 7380. Bibcode:1946ASPL....5...73T.

[31] Hoyt, William G. (1976). W. H. Pickering's PlanetaryPredictions and the Discovery of Pluto. Isis 67 (4): 551564. doi:10.1086/351668. JSTOR 230561.

[32] Littman, Mark (1990). Planets Beyond: Discovering theOuter Solar System. Wiley. p. 70. ISBN 0-471-51053-X.

[33] Buchwald, Greg; Dimario, Michael; Wild, Walter (2000).Pluto is Discovered Back in Time. AmateurPro-fessional Partnerships in Astronomy (San Francisco: SanFrancisco: Astronomical Society of the Pacic) 220: 335.Bibcode:2000ASPC..220..355B. ISBN 1-58381-052-8.

[34] Croswell 1997, p. 50.

[35] Croswell 1997, p. 52.

[36] Rao, Joe (11 March 2005).Finding Pluto: Tough Task,Even 75 Years Later. Space.com. Retrieved 8 Septem-ber 2006.

[37] Mager, Brad.The Search Continues. Pluto: The Dis-covery of Planet X. Retrieved 29 November 2011.

[38] Rincon, Paul (13 January 2006).The girl who named aplanet. Pluto: The Discovery of Planet X. Retrieved 12April 2007.

[39]The Trans-Neptunian Body: Decision to call it Pluto.The Times. 27 May 1930. p. 15.

[40] Name Pluto Given to Body Believed to Be Planet X.The New York Times. Associated Press. 25 May 1930. p.1. ISSN 0362-4331. Pluto, the title of the Roman godsof the region of darkness, was announced tonight at Low-ell Observatory here as the name chosen for the recentlydiscovered trans-Neptunian body, which is believed to bethe long-sought Planet X.

[41] Croswell 1997, pp. 5455.

[42] UK CPI ination numbers based on data available fromGregory Clark (2015), "The Annual RPI and AverageEarnings for Britain, 1209 to Present (New Series)" Mea-suringWorth.

[43] NASA's Solar System Exploration: Multimedia:Gallery: Pluto's Symbol. NASA. Retrieved 29 Novem-ber 2011.

[44] Heinrichs, Allison M. (2006).Dwarfed by comparison. Pittsburgh Tribune-Review. Retrieved 26 March 2007.

[45] Clark, David L.; Hobart, David E. (2000). Reectionson the Legacy of a Legend(PDF). Retrieved 29 Novem-ber 2011.

[46] Renshaw, Steve; Ihara, Saori (2000).ATribute to HoueiNojiri. Retrieved 29 November 2011.

[47] Planetary Linguistics. Archived from the original on17 December 2007. Retrieved 12 June 2007.

[48] 'Bathrobe'. Uranus, Neptune, and Pluto in Chinese,Japanese, and Vietnamese. cjvlang.com. Retrieved 29November 2011.

[49] Stern, Alan; Tholen, David James (1997). Pluto andCharon. University of Arizona Press. pp. 206208.ISBN 9780816518401.

[50] Crommelin, Andrew Claude de la Cherois(1931). The Discovery of Pluto. MonthlyNotices of the Royal Astronomical Society 91:380385. Bibcode:1931MNRAS..91..380..doi:10.1093/mnras/91.4.380.

[51] Nicholson, Seth B.; Mayall, Nicholas U. (December1930). The Probable Value of the Mass of Pluto. Publications of the Astronomical Society of the Pa-cic 42 (250): 350. Bibcode:1930PASP...42..350N.doi:10.1086/124071.

[52] Nicholson, Seth B.; Mayall, Nicholas U. (January1931). Positions, Orbit, and Mass of Pluto. As-trophysical Journal 73: 1. Bibcode:1931ApJ....73....1N.doi:10.1086/143288.

[53] Kuiper, Gerard P. (1950). The Diameter of Pluto. Publications of the Astronomical Society of the Pa-cic 62 (366): 133137. Bibcode:1950PASP...62..133K.doi:10.1086/126255.

[54] Croswell 1997, p. 57.

[55] Christy, James W.; Harrington, Robert Sutton (1978).The Satellite of Pluto. Astronomical Journal83 (8): 10051008. Bibcode:1978AJ.....83.1005C.doi:10.1086/112284.

[56] Seidelmann, P. Kenneth; Harrington, Robert Sut-ton (1988). Planet X The current status. Celestial Mechanics and Dynamical Astron-omy 43: 5568. Bibcode:1987CeMec..43...55S.doi:10.1007/BF01234554. Retrieved 29 November2011.

[57] Standish, E. Myles (1993).Planet XNo dynamical ev-idence in the optical observations. Astronomical Jour-nal 105 (5): 2002006. Bibcode:1993AJ....105.2000S.doi:10.1086/116575.

[58] Standage, Tom (2000). The Neptune File. Penguin. p.168. ISBN 0-8027-1363-7.

[59] History I: The Lowell Observatory in 20th century As-tronomy. The Astronomical Society of the Pacic. 28June 1994. Retrieved 29 November 2011.

[60] Tyson, Neil deGrasse (2 February 2001). AstronomerResponds to Pluto-Not-a-Planet Claim. Space.com. Re-trieved 30 November 2011.

[61] NASA-Funded Scientists Discover Tenth Planet.NASA press releases. 29 July 2005. Retrieved 22 February2007.

14 12 REFERENCES

[62] Soter, Steven (2007). What is a Planet?". The As-tronomical Journal (Department of Astrophysics, Amer-ican Museum of Natural History) 132 (6): 2513.arXiv:astro-ph/0608359. Bibcode:2006AJ....132.2513S.doi:10.1086/508861.

[63] IAU 2006 General Assembly: Resolutions 5 and 6(PDF). IAU. 24 August 2006.

[64] IAU 2006 General Assembly: Result of the IAU Res-olution votes. International Astronomical Union (NewsRelease IAU0603). 24 August 2006. Retrieved 15 June2008.

[65] Green, Daniel W. E. (13 September 2006). "(134340)Pluto, (136199) Eris, and (136199) Eris I (Dysnomia)"(PDF). IAU Circular 8747. Archived from the original on5 February 2007. Retrieved 1 December 2011.

[66] Britt, Robert Roy (24 August 2006). Pluto Demoted:No Longer a Planet in Highly Controversial Denition.Space.com. Retrieved 8 September 2006.

[67] Ruibal, Sal (6 January 1999). Astronomers question ifPluto is real planet. USA Today.

[68] Britt, Robert Roy (21 November 2006). Why PlanetsWill Never Be Dened. Space.com. Retrieved 1 De-cember 2006.

[69] Britt, Robert Roy (24 August 2006). Scientists de-cide Pluto's no longer a planet. MSNBC. Retrieved 8September 2006.

[70] Shiga, David (25 August 2006). New planet denitionsparks furore. NewScientist.com. Retrieved 8 Septem-ber 2006.

[71] Buie, MarcW. (September 2006).My response to 2006IAU Resolutions 5a and 6a. Southwest Research Insti-tute. Archived from the original on 3 June 2007. Re-trieved 1 December 2011.

[72] Overbye, Dennis (24 August 2006). Pluto Is Demotedto 'Dwarf Planet'". The New York Times. Retrieved 1 De-cember 2011.

[73] DeVore, Edna (7 September 2006). Planetary Politics:Protecting Pluto. Space.com. Retrieved 1 December2011.

[74] Holden, Constance (23 March 2007). Reha-bilitating Pluto. Science 315 (5819): 1643.doi:10.1126/science.315.5819.1643c.

[75] Gutierrez, JoniMarie (2007).A jointmemorial. Declar-ing Pluto a planet and declaring March 13, 2007, 'Plutoplanet day' at the legislature. Legislature of New Mex-ico. Retrieved 5 September 2009.

[76] Illinois General Assembly: Bill Status of SR0046, 96thGeneral Assembly. ilga.gov. Illinois General Assembly.Retrieved 16 March 2011.

[77] Pluto's still the same Pluto. Independent Newspa-pers. Associated Press. 21 October 2006. Retrieved 29November 2011. Mickey Mouse has a cute dog.

[78] "'Plutoed' chosen as '06 Word of the Year. AssociatedPress. 8 January 2007. Retrieved 10 January 2007.

[79] Minkel, J. R. (10 April 2008). Is Rekindling the PlutoPlanet Debate a Good Idea?". Scientic American. Re-trieved 1 December 2011.

[80] The Great Planet Debate: Science as Process.A Scientic Conference and Educator Workshop.gpd.jhuapl.edu. Johns Hopkins University AppliedPhysics Laboratory. 27 June 2008. Retrieved 1 Decem-ber 2011.

[81]Scientists Debate Planet Denition and Agree to Dis-agree, Planetary Science Institute press release of 19September 2008, PSI.edu

[82] Plutoid chosen as name for Solar System objects likePluto. Paris: International Astronomical Union (NewsRelease IAU0804). 11 June 2008. Retrieved 1 Decem-ber 2011.

[83]Plutoids Join the Solar Family, DiscoverMagazine, Jan-uary 2009, p. 76

[84] Science News, 5 July 2008, p. 7

[85] Pluto to become most distant planet. JPL/NASA. 28January 1999. Retrieved 16 January 2011.

[86] Sussman, Gerald Jay; Wisdom, Jack (1988). Numeri-cal evidence that the motion of Pluto is chaotic. Science241 (4864): 433437. Bibcode:1988Sci...241..433S.doi:10.1126/science.241.4864.433. PMID 17792606.

[87] Wisdom, Jack; Holman, Matthew (1991). Symplec-tic maps for the n-body problem. Astronomical Jour-nal 102: 15281538. Bibcode:1991AJ....102.1528W.doi:10.1086/115978.

[88] Wan, Xiao-Sheng; Huang, Tian-Yi; Innanen, Kim A.(2001). The 1:1 Superresonance in Pluto's Mo-tion. The Astronomical Journal 121 (2): 11551162.Bibcode:2001AJ....121.1155W. doi:10.1086/318733.

[89] Hunter, Maxwell W. (2004). Unmanned scienticexploration throughout the Solar System. Space Sci-ence Reviews 6 (5): 501. Bibcode:1967SSRv....6..601H.doi:10.1007/BF00168793.

[90] Malhotra, Renu (1997). Pluto's Orbit. Retrieved 26March 2007.

[91] Williams, David R. (17November 2010).Planetary FactSheet Metric. NASA Goddard Space Flight Center.Retrieved 29 November 2011.

[92] Alfvn, Hannes; Arrhenius, Gustaf (1976).SP-345 Evo-lution of the Solar System. Retrieved 28 March 2007.

[93] Williams, James G.; Benson, G. S. (1971). Res-onances in the Neptune-Pluto System. Astronom-ical Journal 76: 167. Bibcode:1971AJ.....76..167W.doi:10.1086/111100.

[94] Faure, Gunter; Mensing, Teresa M. (2007). Pluto andCharon: The Odd Couple. Introduction to Planetary Sci-ence (Springer). pp. 401408. doi:10.1007/978-1-4020-5544-7. ISBN 978-1-4020-5544-7.

15

[95] Schombert, Jim; University of Oregon Astronomy 121Lecture notes, Pluto Orientation diagram

[96] Pluto Time. NASA Solar System Exploration. Re-trieved 13 July 2015.

[97] NASA Lets You ExperiencePluto Timewith NewCustom Tool. NASA. 5 June 2015.

[98] NOAA Solar Calculator. NOAA Earth System Re-search Laboratory Global Monitoring Division. Retrieved13 July 2015.

[99] de la Fuente Marcos, Carlos; de la Fuente Marcos, Ral(2012).Plutino 15810 (1994 JR1), an accidental quasi-satellite of Pluto. Monthly Notices of the Royal As-tronomical Society Letters 427: L85. arXiv:1209.3116.Bibcode:2012MNRAS.427L..85D. doi:10.1111/j.1745-3933.2012.01350.x.

[100] Pluto's fake moon. Retrieved 24 September 2012.[101] Hussmann, Hauke; Sohl, Frank; Spohn, Tilman

(November 2006). Subsurface oceans and deepinteriors of medium-sized outer planet satellitesand large trans-neptunian objects (PDF). Icarus185 (1): 258273. Bibcode:2006Icar..185..258H.doi:10.1016/j.icarus.2006.06.005.

[102] Owen, Tobias C.; Roush, Ted L.; Cruikshank, DaleP. et al. (1993). Surface Ices and the At-mospheric Composition of Pluto. Science 261(5122): 745748. Bibcode:1993Sci...261..745O.doi:10.1126/science.261.5122.745. PMID 17757212.

[103] Boyle, Alan (11 February 1999).Pluto regains its placeon the fringe. MSNBC. Retrieved 20 March 2007.

[104] Buie, Marc W.; Grundy, William M.; Young, Eliot F. etal. (2010). Pluto and Charon with the Hubble SpaceTelescope: I. Monitoring global change and improved sur-face properties from light curves. Astronomical Jour-nal 139 (3): 11171127. Bibcode:2010AJ....139.1117B.doi:10.1088/0004-6256/139/3/1117.

[105] Buie, Marc W.Pluto map information. Retrieved 10February 2010.

[106] Villard, Ray; Buie, Marc W. (4 February 2010). NewHubble Maps of Pluto Show Surface Changes. NewsRelease Number: STScI-2010-06. Retrieved 10 February2010.

[107] Buie, Marc W.; Grundy, William M.; Young, Eliot F. etal. (2010). Pluto and Charon with the Hubble SpaceTelescope: II. Resolving changes on Pluto's surface and amap for Charon. Astronomical Journal 139 (3): 11281143. Bibcode:2010AJ....139.1128B. doi:10.1088/0004-6256/139/3/1128.

[108] The Inside Story. pluto.jhuapl.edu NASA NewHorizons mission site. Johns Hopkins University AppliedPhysics Laboratory. 2007. Retrieved 15 February 2014.

[109] Millis, Robert L.; Wasserman, Lawrence H.; Franz, OttoG. et al. (1993). Pluto's radius and atmosphere Re-sults from the entire 9 June 1988 occultation data set. Icarus 105 (2): 282. Bibcode:1993Icar..105..282M.doi:10.1006/icar.1993.1126.

[110] Brown, Michael E. (22 November 2010). How big isPluto, anyway?". Mike Brown's Planets. Retrieved 9 June2015. (Franck Marchis on 8 November 2010)

[111] Young, Eliot F.; Binzel, Richard P. (1994). Anew determination of radii and limb parameters forPluto and Charon from mutual event lightcurves.Icarus 108 (2): 219224. Bibcode:1994Icar..108..219Y.doi:10.1006/icar.1994.1056.

[112] Young, Eliot F.; Young, Leslie A.; Buie, MarcW. (2007).Pluto's Radius. American Astronomical Society, DPSmeeting No. 39, #62.05; Bulletin of the American Astro-nomical Society 39: 541. Bibcode:2007DPS....39.6205Y.

[113] Zalucha, Angela M.; Gulbis, Amanda A. S.; Zhu, Xunet al. (2011). An analysis of Pluto occultationlight curves using an atmospheric radiative-conductivemodel. Icarus 211 (1). Bibcode:2011Icar..211..804Z.doi:10.1016/j.icarus.2010.08.018.

[114] Lellouch, Emmanuel; de Bergh, Catherine; Sicardy,Bruno et al. (13 March 2014). Exploringthe spatial, temporal, and vertical distributionof methane in Pluto's atmosphere. Icarus.arXiv:1403.3208. Bibcode:2015Icar..246..268L.doi:10.1016/j.icarus.2014.03.027.

[115] Davies, John (2001). Beyond Pluto (extract)" (PDF).Royal Observatory, Edinburgh. Retrieved 26March 2007.

[116] Close, Laird M.; Merline, William J.; Tholen, DavidJ. et al. (2000). Adaptive optics imaging of PlutoCharon and the discovery of a moon around the Aster-oid 45 Eugenia: the potential of adaptive optics in plan-etary astronomy. Proceedings of the International So-ciety for Optical Engineering (European Southern Obser-vatory) 4007: 787795. Bibcode:2000SPIE.4007..787C.doi:10.1117/12.390379.

[117] Croswell, Ken (1992).Nitrogen in Pluto's Atmosphere. Retrieved 27 April 2007.

[118] Lellouch, Emmanuel; Sicardy, Bruno; de Bergh,Catherine et al. (2009). Pluto's lower atmospherestructure and methane abundance from high-resolutionspectroscopy and stellar occultations. Astronomyand Astrophysics 495 (3): L17L21. arXiv:0901.4882.Bibcode:2009A&A...495L..17L. doi:10.1051/0004-6361/200911633.

[119] Than, Ker (2006). Astronomers: Pluto colder thanexpected. Space.com (via CNN.com). Retrieved 30November 2011.

[120] Lellouch, Emmanuel; Sicardy, Bruno; de Bergh, Cather-ine (2009). Pluto's lower atmosphere structure andmethane abundance from high-resolution spectroscopyand stellar occultations. Astronomy & Astrophysics.

[121] Britt, Robert Roy (2003). Puzzling Seasons and SignsofWind Found on Pluto. Space.com. Archived from theoriginal on 9 January 2009. Retrieved 26 March 2007.

[122] Gugliotta, Guy (1 November 2005). Possible NewMoons for Pluto. Washington Post. Retrieved 10 Octo-ber 2006.

16 12 REFERENCES

[123] NASA's Hubble Discovers Another Moon AroundPluto. NASA. 20 July 2011. Retrieved 20 July 2011.

[124] Wall, Mike (11 July 2012). Pluto Has a Fifth Moon,Hubble Telescope Reveals. Space.com. Retrieved 11July 2012.

[125] Buie, M.; Tholen, D.; Grundy, W. (2012). The Orbitof Charon is Circular. The Astronomical Journal 144:15. Bibcode:2012AJ....144...15B. doi:10.1088/0004-6256/144/1/15.

[126] Showalter, M. R.; Hamilton, D. P. (3 June 2015).Resonant interactions and chaotic rotation of Plutos small moons. Nature 522 (7554): 4549.doi:10.1038/nature14469.

[127] Stern, S. Alan; Weaver, Harold A., Jr.; Ste, Andrew J.et al. (2006).Characteristics and Origin of the Quadru-ple System at Pluto. Nature 439 (7079): 946948.arXiv:astro-ph/0512599. Bibcode:2006Natur.439..946S.doi:10.1038/nature04548. PMID 16495992.

[128] Witze, Alexandra (2015).Pluto s moons move in syn-chrony. Nature. doi:10.1038/nature.2015.17681.

[129] Matson, J. (11 July 2012). New Moon for Pluto: Hub-ble Telescope Spots a 5th Plutonian Satellite. ScienticAmerican web site. Retrieved 12 July 2012.

[130] Richardson, Derek C.; Walsh, Kevin J. (2005). BinaryMinor Planets. Annual Review of Earth and PlanetarySciences 34 (1): 4781. Bibcode:2006AREPS..34...47R.doi:10.1146/annurev.earth.32.101802.120208.

[131] Sicardy, Bruno; Bellucci, Aurlie; Gendron, ric etal. (2006). Charon's size and an upper limiton its atmosphere from a stellar occultation. Na-ture 439 (7072): 524. Bibcode:2006Natur.439...52S.doi:10.1038/nature04351. PMID 16397493.

[132] Young, Leslie A. (1997). The Once and Future Pluto. Southwest Research Institute, Boulder, Colorado. Re-trieved 26 March 2007.

[133] Charon: An ice machine in the ultimate deep freeze. Gemini Observatory News Release. 2007. Retrieved 18July 2007.

[134] NASA's Hubble Finds Pluto s Moons Tumbling in Ab-solute Chaos. Retrieved 3 June 2015.

[135]Pluto's moons are even weirder than thought. Retrieved20 June 2015.

[136] Pluto's moons dance to a random beat. Retrieved 20June 2015.

[137] HubbleSite NewsCenter Hubble Finds Two Chaot-ically Tumbling Pluto Moons (06/03/2015) Introduc-tion. hubblesite.org. Retrieved 3 June 2015.

[138]Much ado about Pluto. 1999. Retrieved 24 June 2015.

[139] The Michigan Technic Volumes 7879. University ofMichigan. 1959. p. =101. Retrieved 23 June 2015.

[140] Sheppard, Scott S.; Trujillo, Chadwick A.; Udalski,Andrzej et al. (2011). A Southern Sky and Galac-tic Plane Survey for Bright Kuiper Belt Objects. Astronomical Journal 142 (4). arXiv:1107.5309.Bibcode:2011AJ....142...98S. doi:10.1088/0004-6256/142/4/98.

[141]Colossal Cousin to a Comet?". pluto.jhuapl.edu NASANew Horizons mission site. Johns Hopkins University Ap-plied Physics Laboratory. Archived from the original on13 November 2014. Retrieved 15 February 2014.

[142] Tyson, Neil deGrasse (1999). Pluto Is Not a Planet.The Planetary Society. Archived from the original on 27September 2011. Retrieved 30 November 2011.

[143]Nine ReasonsWhy Pluto Is a Planetby Philip Metzger[144] Neptune's Moon Triton. The Planetary Society.

Archived from the original on 10 December 2011. Re-trieved 30 November 2011.

[145] Jewitt, David C. (2004). The Plutinos. Universityof Hawaii. Archived from the original on 19 April 2007.Retrieved 26 March 2007.

[146] Hahn, Joseph M. (2005). Neptune's Migration into aStirredUp Kuiper Belt: A Detailed Comparison of Sim-ulations to Observations(PDF). Saint Mary's University.Retrieved 5 March 2008.

[147] Levison, Harold F.; Morbidelli, Alessandro; Van Laer-hoven, Christa et al. (2007). Origin of the Struc-ture of the Kuiper Belt during a Dynamical Instabilityin the Orbits of Uranus and Neptune. Icarus 196 (1):258. arXiv:0712.0553. Bibcode:2008Icar..196..258L.doi:10.1016/j.icarus.2007.11.035.

[148] Malhotra, Renu (1995). The Origin of Pluto's Orbit:Implications for the Solar System Beyond Neptune. As-tronomical Journal 110: 420. arXiv:astro-ph/9504036.Bibcode:1995AJ....110..420M. doi:10.1086/117532.

[149] This month Pluto's apparent magnitude is m=14.1.Could we see it with an 11reector of focal length 3400mm?". Singapore Science Centre. 2002. Archived fromthe original on 11 November 2005. Retrieved 29 Novem-ber 2011.

[150] Young, Eliot F.; Binzel, Richard P.; Crane, Keenan(2000). A Two-Color Map of Pluto Based on MutualEvent Lightcurves. Bulletin of the American Astronom-ical Society (AA(SwRI), AB(M.I.T.), AC (Boulder HighSchool)) 32: 1083. Bibcode:2000DPS....32.4601Y.

[151] Buie, Marc W.; Tholen, David J.; Horne, Keith(1992). Albedo maps of Pluto and Charon: Ini-tial mutual event results. Icarus 97 (2): 221227. Bibcode:1992Icar...97..211B. doi:10.1016/0019-1035(92)90129-U.

[152] Buie, Marc W.How the Pluto maps were made. Re-trieved 10 February 2010.

[153] Voyager Frequently Asked Questions. Jet PropulsionLaboratory. 14 January 2003. Retrieved 8 September2006.

17

[154] Sobel, Dava (1993).The last world. Discover maga-zine. Retrieved 13 April 2007.

[155] Williams, David R. (2005). Pluto Kuiper Express.NASA Goddard Space Flight Center. Retrieved 26 March2007.

[156] Britt, Robert Roy (2003). Pluto Mission a Go! InitialFunding Secured. space.com. Archived from the originalon 23 August 2010. Retrieved 13 April 2007.

[157] Stern, S. Alan (2006). Happy 100th Birthday, ClydeTombaugh. Southwest Research Institute. Retrieved 13April 2007.

[158] New Horizons, Not Quite to Jupiter, Makes First PlutoSighting. pluto.jhuapl.edu NASANewHorizons missionsite. Johns Hopkins University Applied Physics Labora-tory. 28 November 2006. Retrieved 29 November 2011.

[159] Ste, Andrew J.; Stern, S. Alan (2007). First Con-straints on Rings in the Pluto System. The AstronomicalJournal 133 (4): 14851489. arXiv:astro-ph/0608036.Bibcode:2007AJ....133.1485S. doi:10.1086/511770.

[160] Happy Birthday Clyde Tombaugh: New Horizons Re-turns New Images of Pluto. pluto.jhuapl.edu NASANew Horizons mission site. Johns Hopkins University Ap-plied Physics Laboratory. 4 February 2015. Retrieved 14July 2015.

[161] Help us put names on the maps of Pluto and Charon!

[162] Brown, Dwayne; Buckley, Michael (29 April 2015).NASA s NewHorizons Detects Surface Features, Possi-ble Polar Cap on Pluto. National Aeronautics and SpaceAdministration. Retrieved 30 April 2015.

[163] NASA (2015).Timeline. New Horizons News Center,Johns Hopkins Applied Physics Laboratory. Retrieved 14July 2015.

[164] Morring, Jr., Frank (29 April 2015).NewHorizons De-livering Pluto Imagery With Better Resolution Than Hub-ble. aviationweek.com. Retrieved 14 July 2015.

[165] Powell, James; Maise, George; Paniagua, John (815March 2003). Pluto Orbiter/lander/sample returnmissions using the MITEE nuclear engine. 2003IEEE Aerospace Conference (Ieeexplore.ieee.org).doi:10.1109/AERO.2003.1235077. ISBN 0-7803-7651-X. Retrieved 22 November 2011.

[166] Dierent Faces of Pluto Emerging in New Images fromNew Horizons. JPL Johns Hopkins Applied PhysicsLaboratory. 12 June 2015.

13 External links New Horizons homepage Pluto Prole at NASA's Solar System Explorationsite

NASA Pluto factsheet

Website of the observatory that discovered Pluto Earth telescope image of Pluto system Keck infrared with AO of Pluto system Gray, Meghan (2009). Pluto. Sixty Symbols.Brady Haran for the University of Nottingham.

18 14 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

14 Text and image sources, contributors, and licenses14.1 Text

Pluto Source: https://en.wikipedia.org/wiki/Pluto?oldid=671432968 Contributors: Brion VIBBER, Vicki Rosenzweig, Mav, Bryan Derk-sen, The Anome, Malcolm Farmer, Gareth Owen, -- April, Ed Poor, Eob, Jkominek, Danny, Shsilver, XJaM, Rmhermen, Gianfranco,Roadrunner, SimonP, Ben-Zin~enwiki, Merphant, Caltrop, Zoe, Kst, Ewen, Rickyrab, Twilsonb, Rbrwr, Spi~enwiki, Patrick, JohnOwens,Kinnerc, Michael Hardy, Tim Starling, Alan Peakall, Oliver Pereira, DopeshJustin, Lousyd, SGBailey, Ixfd64, Cyde, TakuyaMurata, GT-Bacchus, Minesweeper, Egil, Looxix~enwiki, Ahoerstemeier, EasilyAmused, Angela, Salsa Shark, Glenn, Kylet, Poor Yorick, Netsnipe,Evercat, Mxn, Darkonc, Schneelocke, Hike395, Jengod, The Tom, Timwi, Wikiborg, RickK, Stone, Xanthine, Darac, Fuzheado, Doradus,WhisperToMe, Zoicon5, Polaris999, Haukurth, Tpbradbury, Regulus, Ed g2s, Head, Traroth, Nickshanks, AnonMoos, FlyByPC, Secret-london, Jerzy, Jusjih, Johnleemk, Flockmeal, Jeq, Jni, ChamPro, Robbot, ChrisO~enwiki, Fredrik, Zandperl, Korath, Moncrief, StephanSchulz, Naddy, Postdlf, Merovingian, PedroPVZ, Academic Challenger, SchmuckyTheCat, Ktotam, Joelwest, Diderot, Timrollpickering,DHN, Davodd, Btljs, Bkell, Hadal, UtherSRG, JackofOz, Umlautbob, Mushroom, Anthony, Jor, SoLando, HaeB, Rizzoj, Dina, File-mon, Jsan, Robert Happelberg, Fabiform, Nephelin~enwiki, Centrx, Giftlite, DocWatson42, Awolf002, Jyril, TOttenville8, Eran, Harp,Wolfkeeper, Tom harrison, Wighson, Herbee, Dissident, Obli, Karn, Everyking, P.T. Aufrette, Curps, Henry Flower, David Johnson, JoeKress, Jdavidb, Cantus, Fjarlq, Avsa, Dmmaus, Pascal666, Siroxo, Luigi30, Python eggs, Pne, Mckaysalisbury, Edcolins, Cam, Mateusz-ica, Mooquackwooftweetmeow, Gyrofrog, Heysup420, Electrawn, Utcursch, 159753, SoWhy, Alexf, Sonjaaa, GeneralPatton, Antandrus,The Singing Badger, HorsePunchKid, Beland, Joeblakesley, Ctachme, MistToys, Piotrus, Vanished user 1234567890, FelineAvenger,Kaldari, Armaced, Khaosworks, Rdsmith4, Kesac, DragonySixtyseven, Gauss, Mozzie, Thincat, Tomruen, Pmanderson, Icairns, Ge-oGreg, DenisMoskowitz, Boojum, Gscshoyru, TonyW, Asbestos, Iantresman, Urhixidur, Edsanville, Joyous!, Tomwalden, JohnArmagh,M1ss1ontomars2k4, Kasreyn, Adashiel, Trevor MacInnis, Gcanyon, Lacrimosus, Fiveof15, Talkstosocks, Mike Rosoft, Scottk, Kmccoy,D6, Freakofnurture, Astronouth7303, AliveFreeHappy, O'Dea, Spiy sperry, Jiy, JTN, Moverton, Discospinster, Rich Farmbrough, Gua-nabot, Supercoop, Jaedza, Naive cynic, ArnoldReinhold, YUL89YYZ, Ionesco, Roo72, Xezbeth, Ponder, Ibagli, Wadewitz, MuDavid,Pavel Vozenilek, Paul August, SpookyMulder, Bender235, ESkog, Flapdragon, Zaslav, Neurophyre, Kjoonlee, FrankCostanza, Jnesto-rius, Wilgamesh, Brian0918, Tompw, RJHall, Zscout370, JustPhil, El C, Huntster, Rgdboer, Lankiveil, Bletch, Bluap, Kwamikagami,Worldtraveller, Tverbeek, PhilHibbs, Shanes, Tom, Remember, SS~enwiki, Sietse Snel, Art LaPella, RoyBoy, Femto, Kaveh, Iridia,Bobo192, Circeus, WCityMike, TomStar81, JesseBHolmes, 23skidoo, Jemedke, Smalljim, Redlentil, Dreish, BrokenSegue, Tronno,Phidauex, Apyule, Reuben, Redquark, The shaggy one, La goutte de pluie, Jojit fb, Scotthatton, TheProject, Famousdog, Larry V, MrIni-tialMan, BillCook, Sam Korn, Krellis, Crust, Gsklee, Jonathunder, Mareino, Ehurtley, Merope, Jumbuck, Danski14, Bob rulz, Gary,Vandalism~enwiki, Q0, Hektor, Qwe, Nik42, Richard Harvey, J.Voss, Typobox, Inky, Penwhale, Doopokko, Andrew Gray, Riana, Aza-Toth, Axl, Ekko, Ferrierd, Water Bottle, Hu, Snowolf, Mbimmler, Ross Burgess, Burwellian, Ravenhull, Schaefer, Dhartung, Malber,Andrew Norman, ClockworkSoul, RPH, Deacon of Pndapetzim, Suruena, Evil Monkey, Omphaloscope, Amorymeltzer, Inge-Lyubov,Juhtolv, Vuo, BlastOButter42, Pauli133, Gene Nygaard, Axeman89, Nick Mks, RickDeNatale, New Age Retro Hippie, Bookandcof-fee, Kazvorpal, Kitch, Dan100, Harvestdancer, The Reection, RyanGerbil10, Duke33, Tariqabjotu, Starks, Supercool Dude, Bobrayner,WilliamKF, Thryduulf, Bacteria, DrDaveHPP, Rorschach, Firsfron, Reinoutr, DavidK93, FeanorStar7, JarlaxleArtemis, Spamguy, Haver-mayer, Justinlebar, Etacar11, LOL, Aza~enwiki, Asteron, PoccilScript, Risyphon1024, Volcanopele, Benhocking, Jacobolus, Madch-ester, Joeyconnick, Benbest, Pol098, Before My Ken, Lincher, Direwolf, Duncan.france, Tckma, MONGO, Nakos2208~enwiki, Ele-assar777, Hbdragon88, Sygmoral, Dglynch, Sengkang, GregorB, Andromeda321, Eyreland, JamesH, Frankie1969, Smartech~enwiki,Karam.Anthony.K, Pfalstad, Dysepsion, Thirty-seven, John Kenneth Fisher, Siqbal, Rnt20, Ashmoo, Graham87, Marskell, Ryoung122,Chupon, Magister Mathematicae, A Train, Cuchullain, Chun-hian, Lasunncty, David Levy, FreplySpang, Alvinying, Bardnet, JIP, Pmj,Pentawing, Timsj, Search4Lancer, Canderson7, Drbogdan, Sjakkalle, Rjwilmsi, Seidenstud, Nightscream, Koavf, Loginnow, Wikibofh,Strait, Marasama, BlueMoonlet, Tangotango, Trypsin, Joz3d, MZMcBride, Mike s, Mitul0520, Mred64, Mike Peel, XLerate, Kazrak,HappyCamper, Ligulem, NeonMerlin, Bubba73, Brighterorange, The wub, Bhadani, Sango123, Yamamoto Ichiro, SNIyer12, Kevmitch,RainR, Titoxd, FlaBot, Eyas, SchuminWeb, RobertG, Winhunter, Brusselsshrek, Nihiltres, Crazycomputers, Rbonvall, RexNL, Gurch,Slowpokeiv, Arctic.gnome, Magbatz, DevastatorIIC, Enon, Fosnez, TeaDrinker, Joedeshon, Srleer, Ahkilinc, Wrightbus, OpenTopped-Bus, Glenn L, Phoenix2~enwiki, WhyBeNormal, Mstroeck, Chobot, Bornhj, Mhking, Jpkotta, Gwernol, Wjfox2005, EamonnPKeane, TheRambling Man, Satanael, GreyWyvern, YurikBot, Wavelength, TexasAndroid, Hawaiian717, RobotE, Jcam, Sceptre, Wester, Hairy Dude,Jachin, 281186, Jimp, Alethiareg, Adam1213, Xoloz, Red Slash, Anonymous editor, Ericorbit, Splash, Pigman, Epolk, KSmrq, DanMS,Chaser, CanadianCaesar, Shawn81, RadioFan, Hydrargyrum, Stephenb, Mithridates, Gaius Cornelius, Theoemrys, Eleassar, Kyorosuke,Cryptic, Doctorsundar, Kimchi.sg, Wimt, TopAce~enwiki, MarcK, Daveswagon, Anomalocaris, NawlinWiki, DragonHawk, SEWilcoBot,Wiki alf, DERAMOZ, Pagrashtak, Msikma, RattleMan, Grafen, WAS, Itisan, Dugosz, Howcheng, Joelr31, LiamE, Sleeker, Bmdavll, Lex-icon, Irishguy, Nick, Peligro~enwiki, Anetode, Dooky, Chal7ds, Rmky87, EverettColdwell, Raven4x4x, Moe Epsilon, RUL3R, Misza13,Lomn, CKHideki, Tony1, Ospalh, Aaron Schulz, Mysid, Gadget850, T-rex, Darkfred, Derek.cashman, Dddstone, Rcinda1, Woling, Caer-wine, Brisvegas, Asams10, Dna-webmaster, Edwartica, Wknight94, Smoove K, Sierra 1, Tetracube, FF2010, Rickspawn96, Zero1328, Cal-cwatch, Paul Magnussen, Theodolite, Zzuuzz, PTSE, RMeier, Ninly, Chesnok, Joshmaul, Kandrey89, Ageekgal, Lily moonsilver, Moogsi,Pietdesomere, Th1rt3en, Reyk, CapitalLetterBeginning, Careax, Colin, De Administrando Imperio, Aeon1006, Plankhead, JoanneB, RedJay, Erasmocbc, Wechselstrom, Hurricane Devon, JLaTondre, Jaranda, Nixer, GoodSirJava, Ilmari Karonen, Kaicarver, Poulpy, Bart l, Yb-bor, Stuhacking, Kungfuadam, Eamon03, Sethie, Carlosguitar, Tomtab, Iago Dali, NYo FACE,Mardus, SkerHawx, Serendipodous,Wallie,DVD R W, One, Uren, West Virginian, Luk, The Wookieepedian, Deuar, Sardanaphalus, Sintonak.X, A bit iy, SmackBot, Scorpiona,Unschool, Ipodpeter35, Ashill, Moeron, Malkinann, Bravo-Alpha, Prodego, Jeppesn, KnowledgeOfSelf, Royalguard11, Martin.Budden,Melchoir, The Monster, Unyoyega, Pgk, Kilo-Lima, KocjoBot~enwiki, Midway, Nickst, RlyehRising, Alex mayorga, EncycloPetey, Jrock-ley, Monz, Richard B, Frymaster, Lucohami, Alsandro, Trystan, Master Deusoma, Mjolnir1984, Xaosux, Cool3, Aksi great, Richmeister,KYN, Mre5765, Gilliam, Betacommand, Skizzik, Psiphiorg, Marc Kupper, Anika7, Teemu08, Mirokado, Saros136, Amatulic, Izehar,GoneAwayNowAndRetired, Chris the speller, Bluebot, Keegan, Geneb1955, Tigah, Sirex98, Darth Sidious, MalafayaBot, Silly rabbit,SchftyThree, Hibernian, Moshe Constantine Hassan Al-Silverburg, Stevage, Stickyfox, DoctorW, EdgeOfEpsilon, Tweet, Farry, DHN-bot~enwiki, Methnor, Colonies Chris, Hongooi, Chr.K., GWatson, Springeragh, WDGraham, Zsinj, Can't sleep, clown will eat me, JohnHyams, Scott3, Tamfang, Pasacho, Tglaisyer, Mrwuggs, Skillet~enwiki, Poopoobutt, Writtenright, Squilibob, Zone46, Onorem, Bill shan-non 2001, Chvredansante, Astrobhadauria~enwiki, Morton devonshire, The Fading Light, GeorgeMoney, Electrolite, Addshore, Gmcole,SundarBot, JSmith9579, Insanity666, HeteroZellous, BIL, Weirdy, Earlfando, Ahodes1, Cybercobra, Hopquick, Nakon, Savidan, Michael-Billington, EVula, Aeln, Metebelis, Thunk, Faz90, Nbrosch, Cutejoe, Gregwmay, Mini-Geek, KdogDS, Sg1guy253, Jan.Kamenicek,Occultations, Polonium, Hammer1980, Gildir, PaulMison, Zonk43, Hunter2005, Henning Makholm, Kendrick7, Ericl, Daniel.Cardenas,DDima, Pilotguy, Tesseran, CIS, Bosola, ChadScott, SashatoBot, Nishkid64, MusicMaker5376, ArglebargleIV, Technocratic, Harryboyles,

14.1 Text 19

Thanatosimii, Attys, Kuru, John, Forestfughting, Shumway, J 1982, Jan.Smolik, BurnDownBabylon, Heimstern, Rejax, Pomakis, JoshuaZ,JorisvS, Coredesat, Temple, Ulaire, Manchot~enwiki, Heran et Sang'gres, Mr. Lefty, Jess Mars, Keber, Zzzzzzzzzzz, Vamoose, Ck-atz, Basilbrushleo, RandomCritic, Comicist, JHunterJ, Footballplayr69, Slakr, Werdan7, Muadd, Noah Salzman, Turbo da cat, Suraj vas,Dwayne Stange, Kyoko, Rock4arolla, DevAnubis, Eurocommuter, Afogarty, Mets501, Ace Class Shadow, Doczilla, JCScaliger, Artman40,Ryulong, UKintheUS, RichardF, Novangelis, Jose77, Atakdoug, JohnnyBGood, Norm mit, PaulGS, Marshall Stax, Hetar, Vanished user,Iridescent, Michaelbusch, Jachim, LeyteWolfer, Joseph Solis in Australia, Shoeofdeath, In limestone, Kevinmooney, Kinst, Red, GregoryBenoit, J Di, Meka11218, Igoldste, S0me l0ser, Amakuru, Evilbatman, DavidOaks, Blehfu, LadyofShalott, Bobamnertiopsis, Bigboy6,Az1568, Cherry Cotton, Suekientz55, Rattatosk, Tawkerbot2, Bubbha, Ouishoebean, Acom, Spiderboy12, Poolkris, Albertod4, Mrma-roon25, Orangutan, Eelyworm, PhoenixSeraph, Chnv, Vitriden, J Milburn, Spacini, JForget, LordAndrew, InvisibleK, CRGreathouse,CmdrObot, Rambam rashi, Ale jrb, Deathbob, TimothyHorrigan, Zarex, Iuio, Kevin McE, Jibal, Vortek1, Vyznev Xnebara, Banedon,ThreeBlindMice, Ruslik0, Benwildeboer, Aquirata, CuriousEric, Aussiepete, McVities, Rain74, Shizane, LCpl, St Fan~enwiki, NE Ent,Neo-bender, Karenjc, Warhammer40kguy, MrFish, RagingR2, Safalra, RoddyYoung, Pewwer42, Jowan2005, Arrenlex, Ufviper, Mat-tyh190, Md84419, Grenno, Cydebot, Derek Balsam, Ejke47, Squizz48, Nbound, Peripitus, Douglsmith, Bkessler23, Nebular110, Van-ished user 2340rujowierfj08234irjwfw4, ChristTrekker, Reywas92, Mike Christie, Dominicanpapi82, CovenantD, Gogo Dodo, Daakun,Travelbird, TicketMan, Flowerpotman, Deseavers, Dsf, Llort, ST47, Darklinkskywalker, Wikipediarules2221, Daniel J. Leivick, Lucky-herb, Delta Spartan, Q43, Tawkerbot4, Bernard the Varanid, Phydend, Thenewestdoctorwho, BhaiSaab, Optimist on the run, Ssilvers, Lee,Pilcrow, JayW, Mfko, Ike-bana, Omicronpersei8, Nicoisgreat111, Daniel Olsen, Unnatural20, Satori Son, Casliber, EvocativeIntrigue,CieloEstrellado, Lid, Thijs!bot, Sow, Wikid77, SchutteGod, X2turkey2x, King Bee, Felix Portier~enwiki, Ante Aikio, Blowski, Bear475,Sagaciousuk, Chinmaypatel, Intotherush, Headbomb, Dtgriscom, John254, WillMak050389, Crzycheetah, Bobblehead, Bad Astronomer,NorwegianBlue, Bulldogsully, ChristineD95132, Lars Lindberg Christensen, PJtP, Torax2, Leon7, CharlotteWebb, Ludde23, BlytheG,Post Falls Man, DeusMP, Deipnosophista, Tiasusnmt, TarkusAB, Geckzilla, Escarbot, Mentisto, Sidasta, AntiVandalBot, Wang ty87916,RobotG, Majorly, Babylone, Wainson, Luna Santin, Mwhiz, Emeraldcityserendipity, Opelio, Thejetset1, Aprogressivist, Liquid-aim-bot,Uwaga budowa~enwiki, Quintote, Voortle, Fashionslide, David136a, Jadelmann, Tmopkisn, Mctoomer, Scepia, Spangs, Manushand, Dr.Submillimeter, LibLord, Pixelface, NJW494, Carolc91, Pasteman, TorynHill, KingArthur10, Boxjam, Cbrodersen, PresN, Canadian-Bacon, Ingolfson, DOSGuy, MelaLitho, JAnDbot, Valtasarus, Deective, Abyssoft, Meinsla, MER-C, Planetary, Caracaskid, Something14,Instinct, M.C., QuantumEngineer, Keithkesslerexp, Natantus, Rearete, Db099221, Legolost, Plzdontblock, Sophie means wisdom, An-donic, Coolhandscot, Raknapid, Hut 8.5, Dr Croubie, Verger~enwiki, Hardee67, Calculusfreak, Rothorpe, Lindaige, Joebengo, Doom777,Pablothegreat85, Ruthfulbarbarity, Magioladitis, Clausewitz01, Connormah, WolfmanSF, Kimbalee1, Markwalters79, Nieed, Scholar-iusx, Pedro, Murgh, Bongwarrior, VoABot II, MiguelMunoz, Carlwev, Indie.Bones, Xn4, Finnsmark, David Cat, Selshjeans, Swpb,Niksor, Ajste, Sethhater123, BudMann9, Bigdan201, Alandbrown, CTF83!, The Enlightened, Thexlemonxdemon, Nyttend, Roadsoap,Rugops, Ggariepy, Remdabest, Shador5529, Astrazoic, Cat-ve, Bangabalunga, Al1as, JMBryant, KConWiki, Leks81, Martinkb, Indon,Dragfyre, Animum, Richardneish, Pausch, Cyktsui, Miss Mondegreen, Homo cosmosicus, Winterus, BatteryIncluded, ArthurWeasley,Arce, Allstarecho, Meadow Soprano Wheels!, Larry nyc, LorenzoB, Chivista~enwiki, Plum pie, Bevo873, Wonton, Adistinguishedhis-torian, Eliesheva, Robivy64, Bugtrio, Heliac, Sick night re, TomPower, ArmadilloFromHell, NJR ZA, The venue, RHCPJedi, Cuspla,JoergenB, Glen, DerHexer, Alphabetagamma, PatPeter, Megalodon99, Esanchez7587, CCS81, Khalid Mahmood, Monicaacinom, Dizzy-izzy, TheRanger, Figures&Puck, ExNoctem, MBarry, Madonna Can, Retaliation.Vocals, Sharanique, IvoShandor, Kheider, Never Mystic,Darkside5001, Viewport, Gjd001, Don jennings, Soccerrocker1977, Mai Ling, Kiminatheguardian, Kornfan71, Ab humayun, Kmhe-bert, Hdt83, MartinBot, Albireo3000~enwiki, Apc123, Sly Marbro 03, RP88, Ebellii, Arjun01, Poeloq, Jim.henderson, GrzegorzWu,Rettetast, KirshSritharan, Anaxial, Billiamkarr, Azalea pomp, Doodledoo, Daguerio, AlexiusHoratius, Brainster 101, ItsProgrammable,Dinkytown, RockMFR, Omega34, Huzzlet the bot, Zukanator, Watch37264, J.delanoy, Captain panda, Areeshie, Hu Totya, Child ofAlbion, DrKiernan, Ehritzaa, Planemo, Skeptic2, AstroHurricane001, AltiusBimm, UBeR, Lizrael, Flowie-sama, Hans Dunkelberg, Edue-moni, Piercetheorganist, All Is One, VAcharon, Nigholith, Blaccjesus, Yonidebot, KrAtul, Eliz81, Jonsett, WarthogDemon, Piotrowskired,Maproom, Acalamari, SeanJ220, Rufous-crowned Sparrow, ADouBTor, Ben dude56, IdLoveOne, Hutchin hutchi, Ashmin2006, Dr. F.Roy Dean Schlipp, Dfoofnik, Homereblue, Jer10 95, Eric Christiansen, Supuhstar, (jarbarf), Comp25, Poeticmuse, HiLo48, Plasticup,Achtung5, Spoxjox, Belovedfreak, Antony-22, Nwbeeson, Mr-Dollaz, SJP, Malerin, Brandon 0104, Potatoswatter, Slipknoter57, Comet-styles, WJBscribe, Que-Can, Burzmali, Takhtar8, Spiral Wave, Mikeyg2000, Mike V, Stukie, Redrocket, Serph, Sds6065, Arvind Vyas,Devholyjoke, Qoou.Anonimu, Samus098, Enwortmann, KGV, P.J. Garnham, Bob bronx, CardinalDan, Idioma-bot, Spellcast, DidierMisson, Highelds, Lrdwhyt, Stewader, Tripacer99, ACSE, Lights, VolkovBot, CWii, Sethant, Craigheinke, TheUltimateHistorian, Al-noktaBOT, Toddles29, Katydidit, Wakoworld, Barneca, Goltz20707, Philip Trueman, Amos Han, Linkman424, TXiKiBoT, D4S, Gune,ANNAfoxlover, Roshanmelwani, Malinaccier, Frit, Roberto walrus, Technopat, Qaletaqa, Aquzenn, Rei-bot, Anonymous Dissident, Har-ryAla, Norn Guy, Qxz, Someguy1221, Zimbardo Cookie Experiment, Farazars, Plandr, JhsBot, Leafyplant, Dlae, Fbs. 13, Byakuya 999,Markp93, Sc0ttkclark, Seb az86556, Kangaru 28, ZookPS3, Guest9999, KennyRogerz, Wikiisawesome, Papercut 2008, Jessecarllane, Cul-veyhouse, Shade-hedgehog, TupacisGod, Milan Kerlger, 88wolfmaster, Pious7, Brianrusso, Calltheroofer, Synthebot, Ccol7280, Envi-roboy, Sai2020, Sevela.p, Pafcool2, Humbalinga, Bob Man Lot, Gunnville, AlleborgoBot, RomanPolach, TheNewHubris, Planet-man828,Sfmammamia, Vsst, Resurgent insurgent, EmxBot, Ali mcmc, Aborigine, SieBot, TJRC, Jim77742, Tiddly Tom, Graham Beards, Caulde,Scarian, Panicattdfan, Rob.bastholm, Caltas, Iduee, God Emperor, DitzyNizzy, Egizm0, Triwbe, Shinpachi222, Letter 7, Keithnoll, Jer-ryobject, Purbo T, Keilana, Atanasio, PookeyMaster, Chromaticity, Radon210, Soccergeek43, Jc-S0CO, Yerpo, Oxymoron83, Nuttyco-conut, Kosack, Steven Zhang, Lightmouse, Murlough23, KathrynLybarger, Alex.muller, RedCoat1510, OKBot, LonelyMarble, The Stick-ler, Bake hi, Jacob.jose, Sean.hoyland, AllHailZeppelin, Nergaal, TracySurya, Randy Kryn, Starcluster, Hibsch, Asher196, Freewayguy,Gr8opinionater, Faithlessthewonderboy, MBK004, Darthprime99, ClueBot, Ddstwins, Wildie, Peteriscoo, Cmoney8, Rumping, Shruti14,Jackollie, Snigbrook, Bobathon71, Unknown Interval, Foxj, The Thing That Should Not Be, Majestic122, Plastikspork, Ribbon Salminen,KusanagiTsuragi, Unbuttered Parsnip, Frmorrison, VQuakr, Laudak, Rafaelgarcia, Aria1561, Youngie345, Foofbun, Methychroma, Piled-higheranddeeper, Neverquick, ChandlerMapBot, Solar-Wind, Fulmer7, Rockfang, Paulcmnt, Ant133, Pastazdude, Failure.exe, DragonBot,BuShWaCkErS, McMarcoP, ThisPageOwns, Chrisruhr, Ktr101, Excirial, Johnnyboi89, Jakeandtd11, Redhouse948298945389, Urban-fabio, RUGBY13, Gostkowski, Concordbandgeek, Jusdafax, Alexkraegen, Nicholaske, Mspear, Thispagedoesown, Goon Noot, Rytoruin,Winston365, Hobson.michael, Cookies1245, Muhandes, RM2DL, Vivio Testarossa, 500cake, Showdon, Emo dylen, Patricius Augustus,Jotterbot, Njardarlogar, Nvvchar, Enoch Wong, Cal2391, Whereiswally, CowboySpartan, Nadimzo, Toligalanis, Callum859, Thortveitite,Bleubeatle, Dekisugi, Titch46, Kr3man, JasonAQuest, Ditkafan1909, AbJ32, John Paul Parks, Boombasha, Robfbms, InsanityBringer,Zanark12, CowAteMe, Thingg, Aitias, R98563256, Icwnr, Gotcan, Nabs2597, Umomma321, Socks 01, Soho shorty, BetoCG, Nik2007,Caboose117, RedSox2008, Mikey0194, HumphreyW,Wnt, Upstatelaxer22, Miami33139, DumZiBoT, Novjunulo, Lawngnome633, John-hofman123, Against the current, Nishanigreen, XLinkBot, Lvoegtline, Wertuose, BodhisattvaBot, Tryagain711, Bballandrea38, Bradv,Steve erwIN, Katanablade99, Dora-bobba, Rreagan007, Theyoyoyo, WikHead, SilvonenBot, Greengal17, Badgernet, Noctibus, WikiDao,Navy Blue, Cl3rkenwell, Freedom1234, 0pulse, MystBot, Erynnwasloved, Gglee, Frog luva96, Keaton 417, Primarypenguin, D.M. from

20 14 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

Ukraine, I Love Rainbowness, Swbf2lord, Hawkania, Nickhalavanja, Leenguyen93, Red banana, Mortense, Sandiegospartan18, Bro1990,Roentgenium111, DOI bot, Sachinism, HannahCRichards, FeRD NYC, Kuoadamkuo5, MXVN, Heremod, LaaknorBot, CarsracBot,PFSLAKES1, Roux, Leitmotiv, EvelynFl, Ozzie42, F Notebook, Koliri, Rehman, Lightbot, Potekhin, Zorrobot, Legobot, Luckas-bot, Yobot, Ptbotgourou, Nallimbot, KamikazeBot, YngNorman, JAKoulouris, AnomieBOT, SaiyanEmperor2008, Dah 144 144, Jack-ieBot, Tom87020, Lucas Brown 42, Shadowmorph, Timwether, Materialscientist, Citation bot, ArthurBot, MauritsBot, Xqbot, Baseball-dude12321, , Anna Frodesiak, Mlpearc, Srich32977, Arsia Mons, GrouchoBot, Alumnum, RibotBOT, Nedim Ardoa, SpinachMonster, Spellage, Fotaun, Grinofwales, Friedlad, FrescoBot, Io Herodotus, Lookang, KokkaShinto, RoyGoldsmith, ProfHead, Alxeedo,Endofskull, YouTubeaholic2009, Dhtwiki, John85, Ahmer Jamil Khan, Citation bot 1, Pinethicket, ChrisJBenson, HRoestBot, Jonesey95,Tom.Reding, UnicyclingJugglingGOD, Bmclaughlin9, RedBot, MastiBot, Beao, Saa19952, ShadeofTime09, IVAN3MAN, Keri, Zbayz,Kgrad, FoxBot, Double sharp, TobeBot, Trappist the monk, Jafreen94, Mys 721tx, AHeneen, Lotje, GregKaye, J4V4, Samsamcat, IdS,Earthandmoon, Marcos Elias de Oliveira Jnior, Tbhotch, DARTH SIDIOUS 2, RjwilmsiBot, TjBot, Keyboard mouse, Jmchutchinson,Burmiester, Androstachys, DASHBot, EmausBot, John of Reading, WikitanvirBot, Qurq, Omegaman99, Dewritech, Racerx11, Tinss, Go-ingBatty, Andromedabluesphere440, Ebe123, Luminayre, Jmencisom, AreYou TheCowOf Pain?, Tommy2010, Sonic120, P. S. F. Freitas,Solomonfromnland, JDDJS, AvicBot, HiW-Bot, ZroBo