NationMaster - Encyclopedia: 2006 redefinition of planet

The 2006 redefinition of "planet" by the International Astronomical Union (IAU) states that, in the solar system, a planet is a celestial body that is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes the shape of a body in hydrostatic equilibrium (that is, it is nearly round), and has "cleared the neighborhood" around its orbit. A non-satellite body fulfilling only the first two criteria is classified as a "dwarf planet", whilst a non-satellite body fulfilling only the first criterion is termed a "small solar system body" (SSSB). The redefinition has been criticized and remains controversial. Wikipedia does not have an article with this exact name. ... Logo of the IAU The International Astronomical Union (French: Union astronomique internationale) unites national astronomical societies from around the world. ... Major features of the solar system (not to scale) The solar system comprises the Sun and the retinue of celestial objects gravitationally bound to it: nine planets and their 158 currently known moons, as well as asteroids, meteoroids, planetoids, comets, and interplanetary dust. ... See lists of astronomical objects for a list of the various lists of astronomical objects in Wikipedia. ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... The Sun is the star at the center of our solar system. ... Hydrostatic equilibrium occurs when compression due to gravity is balanced by outward pressure. ... A satellite is any object that orbits another object (which is known as its primary). ...

According to the definition, there are currently eight planets and three dwarf planets in the solar system. The definition does not apply outside the solar system, and so does not include provision for extrasolar planets. A planet is generally considered to be a relatively large mass of accreted matter in orbit around a star. ... Major features of the solar system (not to scale) The solar system comprises the Sun and the retinue of celestial objects gravitationally bound to it: nine planets and their 158 currently known moons, as well as asteroids, meteoroids, planetoids, comets, and interplanetary dust. ... Infrared Image of a possible extrasolar planet (lower left) in the Constellation Taurus, taken by the Hubble Space Telescope. ...

Reasons for the debate

Since the discovery of Pluto in 1930 astronomers had considered the solar system to have nine planets and assorted other bodies. However, since 2000 the discovery of at least three bodies (Quaoar, Sedna and 2003 UB₃₁₃), all comparable to Pluto in terms of size and orbit, had led to a situation where either the minor bodies would have to be added to the list of officially recognized planets or older ones would need to be removed in order to ensure consistency in definition. There were also concerns surrounding the classification of planets in other solar systems. In 2006 the matter came to a head with the need to categorize and name the recently-discovered trans-Plutonic object 2003 UB₃₁₃, which, being larger than Pluto, was thought to be at least equally deserving of the status of 'planet'. Adjective Plutonian Atmospheric characteristics Atmospheric pressure 0. ... 1930 (MCMXXX) is a common year starting on Wednesday. ... Major features of the solar system (not to scale) The solar system comprises the Sun and the retinue of celestial objects gravitationally bound to it: nine planets and their 158 currently known moons, as well as asteroids, meteoroids, planetoids, comets, and interplanetary dust. ... A planet is generally considered to be a relatively large mass of accreted matter in orbit around a star. ... This article is about the year 2000. ... Artists impression by G. Bacon of STScI / NASA 50000 Quaoar (pronounced kwahÂ·war, kwahÂ·wor, or kwowÂ·ur, Tongva ) [1] is a Trans-Neptunian object orbiting the Sun in the Edgeworth-Kuiper belt. ... 90377 Sedna is a trans-Neptunian object, discovered by Michael Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale University) on November 14, 2003. ... 2003 UB313 is a trans-Neptunian object (TNO) believed to be larger than the planet Pluto. ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... 2003 UB313 is a trans-Neptunian object (TNO) believed to be larger than the planet Pluto. ...

Debate within the IAU led Julio Fernández and Gonzalo Tancredi of Uruguay^[1] to suggest proposals to redefine the term "planet" so as to include other objects beyond the traditional nine planets that had been historically considered part of the solar system.^[2] In its final form the proposal was denoted as Resolutions 5A, 5B, 6A and 6B for GA-XXVI. Members of the IAU's General Assembly voted on the proposal on August 24, 2006 in Prague, Czech Republic, with the vote removing Pluto's status as a planet and reclassifying it as a dwarf planet.^[3] Pluto had long been exceptional among the planets, being small, distant, and eccentric in orbit. The planet Neptune and its moon Triton, taken by Voyager 2 as it entered the outer solar system The definition of planet has proven elusive despite the term being one of the best-known astronomical words. ... A planet is generally considered to be a relatively large mass of accreted matter in orbit around a star. ... Overview of the Planets in the Solar System. ... Major features of the solar system (not to scale) The solar system comprises the Sun and the retinue of celestial objects gravitationally bound to it: nine planets and their 158 currently known moons, as well as asteroids, meteoroids, planetoids, comets, and interplanetary dust. ... August 24 is the 236th day of the year in the Gregorian Calendar (237th in leap years), with 129 days remaining. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... Prague (Czech: Praha (IPA: ), see also other names) is the capital and largest city of the Czech Republic. ...

In its original form the redefinition would have kept Pluto as a planet and recognized three new planets: Ceres, Charon, and 2003 UB₃₁₃. It was presumed that, after more observation and discussion, astronomers would accept more objects in the solar system as meeting the new definition. On August 22, however, the original redefinition (which recognized twelve solar system planets, including Pluto), was dealt a fatal blow in two open IAU meetings. Jay Pasachoff of Williams College, who attended both meetings, was quoted as saying, "I think that today can go down as 'the day we lost Pluto' ".^[4] 1 Ceres (seer-eez (key), IPA , Latin CerÄ“s) was the first asteroid to be discovered (indicated by the 1 in its name). ... Media:Example. ... 2003 UB313 is a trans-Neptunian object (TNO) believed to be larger than the planet Pluto. ... Major features of the solar system (not to scale) The solar system comprises the Sun and the retinue of celestial objects gravitationally bound to it: nine planets and their 158 currently known moons, as well as asteroids, meteoroids, planetoids, comets, and interplanetary dust. ... August 22 is the 234th day of the year in the Gregorian calendar (235th in leap years), with 131 days remaining. ... Williams College is a private, coeducational liberal arts college located in Williamstown, Massachusetts. ...

August 16

Draft proposal

The IAU published the original definition proposal on August 16, 2006. Its form followed loosely the second of three options considered by a 19-member IAU-appointed panel in 2005. Its form was: Earth (often referred to as the Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth in order of size. ... August 16 is the 228th day of the year (229th in leap years) in the Gregorian Calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ...

This definition would have led to three celestial bodies being recognized as planets: Image File history File links Cquote1. ... Hydrostatic equilibrium occurs when compression due to gravity is balanced by outward pressure. ... Image File history File links Cquote2. ...

A further twelve bodies, pending refinements of knowledge regarding their physical properties, were possible candidates to join the list under this definition. Some objects in this second list were more likely eventually to be adopted as 'planets' than others. Despite what had been claimed in the media,^[5] the proposal did not necessarily leave the solar system with only twelve planets. Mike Brown, the discoverer of Sedna and 2003 UB₃₁₃, has said that at least 53 known bodies in the solar system probably fit the definition, and that a complete survey would probably reveal more than 200.^[6] 1 Ceres (seer-eez (key), IPA , Latin CerÄ“s) was the first asteroid to be discovered (indicated by the 1 in its name). ... Media:Example. ... The term double planet has several accepted usages. ... 2003 UB313 is a trans-Neptunian object (TNO) believed to be larger than the planet Pluto. ... For the name see Xenia. ... Dr. Michael (Mike) E. Brown has been an associate professor of planetary astronomy at the California Institute of Technology (Caltech) since 2002. ... 90377 Sedna is a trans-Neptunian object, discovered by Michael Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale University) on November 14, 2003. ...

The definition would have considered a pair of objects to be a double planet system if each component independently satisfied the planetary criteria and the common center of gravity of the system (known as the barycenter) was located outside of both bodies.^[7] Pluto and Charon would have been the only known double planet in the solar system. Other planetary satellites (for example, Earth's moon) might be in hydrostatic equilibrium, but would still not have been defined as a double planet since the barycenter of the system lies within the more massive celestial body (that is, Earth). The term double planet has several accepted usages. ... In physics, the center of mass (or centre of mass) of a system of particles is a specific point at which, for many purposes, the systems mass behaves as if it were concentrated. ... Adjective Plutonian Atmospheric characteristics Atmospheric pressure 0. ... Earth (often referred to as the Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth in order of size. ... Bulk composition of the moons mantle and crust estimated, weight percent Oxygen 42. ... Hydrostatic equilibrium occurs when compression due to gravity is balanced by outward pressure. ... It has been suggested that Center of gravity be merged into this article or section. ...

The term "minor planet" would have been abandoned, replaced by the categories "Small Solar System Body" (SSSB) and a new classification of "pluton". The former would have described those objects underneath the "spherical" threshold. The latter would have been applied to those planets with highly inclined orbits, large eccentricities and an orbital period of more than 200 years (that is, those orbiting beyond Neptune). Pluto would have been the prototype for this class. The term "dwarf planet" would have been available to describe all planets smaller than the eight "classical planets" in orbit around the Sun, though would not have been an official IAU classification.^[8] The IAU did not make recommendations in the draft resolution on what separated a planet from a brown dwarf.^[9] A vote on the proposal was scheduled for August 24, 2006.^[10] This brown dwarf (smaller object) orbits the star Gliese 229, which is located in the constellation Lepus about 19 light years from Earth. ... August 24 is the 236th day of the year in the Gregorian Calendar (237th in leap years), with 129 days remaining. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ...

Such a redefinition of the term 'planet' could also have led to changes in classification for the trans-Neptunian objects 2003 EL₆₁, 2005 FY₉, Sedna, Orcus, Quaoar, Varuna, 2002 TX₃₀₀, Ixion, 2002 AW₁₉₇, and the asteroids Vesta, Pallas, and Hygiea. 2003 EL61 (also written 2003 EL61), nicknamed Santa (non-official designation), is a large and very unusual Kuiper belt object discovered by Mike Brown at Caltech in the United States. ... 2005 FY9 (also written 2005 FY9), codenamed Easterbunny by its discoverers, is a very large Kuiper belt object discovered on March 31, 2005 by the team led by Michael Brown. ... 90377 Sedna is a trans-Neptunian object, discovered by Michael Brown (Caltech), Chad Trujillo (Gemini Observatory) and David Rabinowitz (Yale University) on November 14, 2003. ... 90482 Orcus (originally known by the provisional designation 2004 DW) is a Kuiper Belt object (KBO) that was discovered by Michael Brown of Caltech, Chad Trujillo of the Gemini Observatory, and David Rabinowitz of Yale University. ... Artists impression by G. Bacon of STScI / NASA 50000 Quaoar (pronounced kwahÂ·war, kwahÂ·wor, or kwowÂ·ur, Tongva ) [1] is a Trans-Neptunian object orbiting the Sun in the Edgeworth-Kuiper belt. ... 20000 Varuna (VAR oo na) is a Kuiper Belt object about 1060 km in diameter, estimated from a combination of thermal and optical measurements. ... (55636) 2002 TX300 (Also written as (55636) 2002 TX300) is a large Trans-Neptunian object discovered in October 15, 2002 by the NEAT program. ... (28978) Ixion (ikÂ·syeÂ·un) is a Kuiper belt object discovered on May 22, 2001 with a diameter of < 822 km and a semimajor axis of about 39. ... (55565) 2002 AW197 is a trans-Neptunian object. ... 4 Vesta (ves-ta) is the second most massive asteroid in the asteroid belt, with a mean diameter of about 530 km and an estimated mass 12% the mass of the entire asteroid belt. ... 2 Pallas (pal-us, Greek Î Î±Î»Î»Î¬Ï‚) was the first asteroid discovered after 1 Ceres. ... 10 Hygiea (hye-jee-a or hi-jee-a) is the fourth largest Main belt asteroid with a diameter of 407 km. ...

On 18 August the Division of Planetary Sciences of the American Astronomical Society, the world's largest international professional society of planetary scientists, endorsed the draft proposal.^[11] August 18 is the 230th day of the year (231st in leap years) in the Gregorian calendar. ...

According to the IAU, the roundness condition generally results in the need for a mass of at least 5 x 10²⁰ kg, or diameter of at least 800 km.^[8] However, Mike Brown claims that these numbers are only right for rocky bodies like asteroids, and that icy bodies like Kuiper Belt objects reach hydrostatic equilibrium at much smaller sizes, probably somewhere between 200 and 400 km in diameter.^[12]

Advantages

The proposed definition found support among many astronomers as it used the presence of a physical qualitative factor (the object being round) as its defining feature. Most other potential definitions depended on a limiting quantity (e.g. a minimum size or maximum orbital inclination) tailored for the solar system. According to members of the IAU committee this definition did not use man-made limits but instead deferred to "nature" in deciding whether or not an object was a planet.^[13] Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ...

It also had the advantage of measuring an observable quality. Suggested criteria involving the nature of formation would have been more likely to see accepted planets later declassified as scientific understanding improved.

Additionally, the definition kept Pluto as a planet. Pluto's planetary status was and is fondly thought of by many, and the general public could have been alienated from professional astronomers; there was considerable uproar when the media last suggested, in 1999, that Pluto might be demoted, which was a misunderstanding of a proposal to catalog all trans-Neptunian objects uniformly. ^[14]

Criticism of proposal

The proposed redefinition was criticized as ambiguous: Astronomer Phil Plait^[15] and NCSE writer Nick Matzke^[16] had both written about why they thought the redefinition was not, in general, a good one. It defined a planet as orbiting a star, which would have meant that any planet ejected from its star system or formed outside of one (a rogue planet or interstellar planet) could not have been called a planet, even if it fit all other definitions. A similar situation already applied to the term 'moon', such bodies ceasing to be moons on being ejected from planetary orbit; this usage had widespread acceptance. Dr. Philip Plait (a. ... The NCSEs logo The National Center for Science Education (NCSE) is a non-profit organization affiliated with the American Association for the Advancement of Science. ... A rogue planet is a planet that either has an extremely elongated orbit around its star so that it is not on the same orbital plane as the other planets in the system, or it is an interstellar planet, a planet that drifts freely through space and doesnt orbit... An interstellar planet is a hypothetical type of rogue planet that has been ejected from its solar system by a proto-gas giant to become an outcast, drifting in interstellar space. ...

Similarly the redefinition did not differentiate between planets and brown dwarf stars. Any attempt to clarify this differentiation was to be left until a later date. This brown dwarf (smaller object) orbits the star Gliese 229, which is located in the constellation Lepus about 19 light years from Earth. ...

There had also been criticism of the definition of double planet: at present the Moon is defined as a satellite of the Earth, but over time the Earth-Moon barycenter will drift outwards (see Tidal acceleration) and could eventually become situated outside of both bodies. This development would then upgrade the Moon to planetary status at that time, according to the redefinition. The time taken for this to occur, however, would be billions of years, long after many astronomers expect the Sun to expand into a red giant and destroy both Earth and Moon.^[17] The term double planet has several accepted usages. ... It has been suggested that Center of gravity be merged into this article or section. ... It has been suggested that Tidal friction be merged into this article or section. ... According to the Hertzsprung-Russell diagram, a red giant is a large non-main sequence star of stellar classification K or M; so-named because of the reddish appearance of the cooler giant stars. ...

In an 18 August Science Friday interview, Mike Brown expressed doubt that a scientific definition was even necessary: August 18 is the 230th day of the year (231st in leap years) in the Gregorian calendar. ... Science Friday is a call-in talk show that is part of National Public Radios Talk of the Nation radio program hosted by Ira Flatow every Friday. ...

On 18 August, Owen Gingerich, a historian and astronomer emeritus at Harvard who led the committee which generated the original definition, said that correspondence he had received had been evenly divided for and against the proposal.^[19] To meet Wikipedias quality standards, this article or section may require cleanup. ... August 18 is the 230th day of the year (231st in leap years) in the Gregorian calendar. ... Harvard University is a private university in Cambridge, Massachusetts, USA, and a member of the Ivy League. ...

August 18

According to Alan Boss of the Carnegie Institution of Washington, a subgroup of the IAU met on August 18, 2006 and held a straw poll on the draft proposal: only 18 were in favour of it, with over 50 against. The 50 in opposition preferred an alternative proposal drawn up by Uruguayan astronomer Julio Ángel Fernández.^[19] Alan P. Boss is an American astrophysicist. ... The Carnegie Institution of Washington (CIW) is a foundation established by Andrew Carnegie in 1902 to support scientific research. ... August 18 is the 230th day of the year (231st in leap years) in the Gregorian calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... A straw poll is a type of voting where the results of the poll have little or no direct results, other than to gauge opinion. ...

Under the alternative proposal the current solar system would have remained unchanged, but Pluto would have been demoted to a dwarf planet. Near-Earth objects (NEO) are asteroids, comets and large meteoroids whose orbit intersects Earths orbit and which may therefore pose a collision danger. ... The centaurs are a class of icy planetoids that orbit the Sun between Jupiter and Neptune, named after the mythical race of centaurs. ... A trans-Neptunian object (TNO) is any object in the solar system with all or most of its orbit beyond that of Neptune. ... Comet Hale-Bopp For other uses, see Comet (disambiguation). ... Image File history File links Cquote2. ...

August 22

On 22 August the draft proposal was rewritten with two changes from the previous draft. August 22 is the 234th day of the year in the Gregorian calendar (235th in leap years), with 131 days remaining. ...

The first was a generalisation of the name of the new class of planets (previously the draft resolution had explicitly opted for the term 'pluton'), with a decision on the name to be used postponed.

Many geologists had been critical of the choice of name for Pluto-like planets,^[21] being concerned about the term pluton which has been used for years within the geological community to represent a form of magmatic intrusion; such formations are fairly common hunks of rock.^[22]^[23] Confusion was thought undesirable due to the status of planetology as a field closely allied to geology.^[24] Pluton redirects here. ... Pluton redirects here. ...

Further concerns surrounded use of the word pluton as in many European languages such as French and Spanish, Pluto is itself called Pluton, potentially adding to confusion.

The second change was a redrawing of the planetary definition in the case of a double planet system. There had been a concern that, in extreme cases where a double body had its secondary component in a highly eccentric orbit, there could have been a drift of the barycenter in and out of the primary body, leading to a shift in the classification of the secondary body between satellite and planet depending on where in its orbit the system was. Thus the definition was reformulated so as to consider a double planet system in existence if its barycenter lay outside both bodies for a majority of the system's orbital period. A satellite is any object that orbits another object (which is known as its primary). ...

Later on the 22nd two open meetings were held which ended in an abrupt about-face on the basic planetary definition. The position of astronomer Julio Ángel Fernández gained the upper hand among the members attending and was described as unlikely to lose its hold by the 24th. This position would result in only eight major planets, with Pluto ranking as a "dwarf planet" or "planetoid".^[25] The discussion at the first meeting was heated and lively, with IAU members in vocal disagreement with one another over such issues as the relative merits of static and dynamic physics; the main sticking point was over whether or not to include a body's orbital characteristics among the definition criteria. In an indicative vote members heavily defeated the proposals on Pluto-like objects and double planet systems, and were evenly divided on the question of hydrostatic equilibrium. The debate was said to be "still open", with private meetings being held ahead of a vote scheduled for the following day.^[26] Statics is the branch of physics concerned with physical systems in static equilibrium, that is, in a state where the relative positions of subsystems do not vary over time, or where components and structures are at rest under the action of external forces of equilibrium. ... In physics, dynamics is the branch of classical mechanics that is concerned with the effects of forces on the motion of objects. ...

At the second meeting of the day, following 'secret' negotiations, a compromise began to emerge after the Executive Committee moved explicitly to exclude consideration of extra-solar planets and to bring into the definition a criterion concerning the dominance of a body in its neighbourhood.^[27] Infrared Image of a possible extrasolar planet (lower left) in the Constellation Taurus, taken by the Hubble Space Telescope. ...

August 24

Final draft

The final, third draft definition proposed on 24 August was: August 24 is the 236th day of the year in the Gregorian Calendar (237th in leap years), with 129 days remaining. ...

What exactly it meant to say that a body had "cleared the neighbourhood around its orbit" or that it had a "nearly round" shape was explicitly not defined. These descriptions were used partly to allow for some "common sense" judgement, but primarily to provide language that could readily be used in communicating the definitions to lay audiences. Image File history File links Cquote2. ... Look up Common sense in Wiktionary, the free dictionary. ...

Plenary session debate

Voting on the definition took place at the Assembly plenary session during the afternoon. Following a reversion to the previous rules on 15 August, as a planetary definition is a primarily scientific matter every individual member of the Union attending the Assembly was eligible to vote. The number having registered their attendance at the Assembly at the time of the vote stood at 2411,^[28] but out of the over a thousand who attended the session only 424 members chose to vote or indicate their abstention on Resolution 6A (below). August 15 is the 227th day of the year in the Gregorian Calendar (228th in leap years), with 138 days remaining. ...

The IAU Executive Committee presented four Resolutions to the Assembly, each concerning a different aspect of the debate over the definition.^[29] Minor amendments were made on the floor for the purposes of clarification.

On a literal reading of the Resolution, "dwarf planets" are by implication of paragraph (1) excluded from the status of 'planet'. Use of the word planet in their title may however cause some ambiguity. For other uses, please see Satellite (disambiguation) A satellite is an object that orbits another object (known as its primary). ...

Criticism of final vote

Substance

There continues to be criticism regarding the final draft of the definition. Notably, the lead scientist on NASA's robotic mission to Pluto, Dr Alan Stern, contends that Earth, Mars, Jupiter and Neptune have also not fully cleared their orbital zones either. Earth orbits with 10,000 near-Earth asteroids. Jupiter, meanwhile, is accompanied by 100,000 Trojan asteroids on its orbital path. "If Neptune had cleared its zone, Pluto wouldn't be there," he added.^[30] There is, however, a substantial difference in the extent to which the neighbourhood has been cleared between Pluto and the eight planets. New Horizons is a NASA unmanned mission to fly by Pluto and its moons. ... This page may meet Wikipedias criteria for speedy deletion. ... Earth (often referred to as the Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth in order of size. ... For the Roman god, see Mars (mythology). ... Adjective Jovian Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Adjective Neptunian Atmospheric characteristics Surface pressure â‰«100 MPa Hydrogen - H2 80% Â±3. ... Near-Earth asteroids (NEAs) are asteroids whose orbits are close to Earths orbit. ...

Process

The final vote has come under criticism because of the relatively small percentage of the 9000-strong membership who participated. Besides the fact that most members do not attend the General Assemblies, this lack was also due to the timing of the vote: the final vote was taken on the last day of the 10-day event, after many participants had left or were preparing to leave. Of over 2,700 astronomers attending the conference, probably over a thousand voted on the significant resolutions;^{[citation needed]} on a vote on a subsidiary resolution, the first that required a count, only 424 votes were cast.^[30] There is also the issue of the many astronomers who were unable or who chose not to make the trip to Prague and, thus, cast a vote.

Other

Some astrologers were unhappy that they were left out of the discussion, though astrology has been shown to have no scientific basis and therefore has no relevance or interest to astronomy or astronomers.^[31] Astrology refers to any of several systems, traditions or beliefs in which knowledge of the apparent positions of celestial bodies and related information is held to be useful in understanding, interpreting and organizing knowledge about personality, human affairs and terrestrial events. ...

Final definition

The final definition, as passed on 24 August 2006 is: ^[32]^[33] August 24 is the 236th day of the year in the Gregorian Calendar (237th in leap years), with 129 days remaining. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ...

Impact

It is expected that the decision will have cultural and societal implications. It will affect the “industry of astronomical artifacts and toys”.^[34] Educational books need to be revised. The decision was important enough to prompt the editors of the 2007 edition of the World Book Encyclopedia to hold off printing until a final result had been reached.^[34] The new designation also has repercussion in the astrological world and finds mixed receptions.^[31] World Book Encyclopedia is, according to the publisher, the number-one selling print encyclopedia in the world [1]. The first edition (1917) contained 8 volumes. ...

See also

The planet Neptune and its moon Triton, taken by Voyager 2 as it entered the outer solar system The definition of planet has proven elusive despite the term being one of the best-known astronomical words. ... Below is a list of solar system objects with diameter >500km: The Sun, a spectral class G2 star Mercury Venus Earth Moon Mars Jupiter Io Europa Ganymede Callisto complete list of Jupiters natural satellites Saturn Tethys Dione Rhea Titan Iapetus complete list of Saturns natural satellites Uranus Ariel... Minor planets, or planetoids are minor bodies of the Solar system orbiting the Sun (or of other planetary systems orbiting other stars) that are larger than meteoroids (the largest of which might be taken to be around 10 meters or so across) but smaller than major planets (Mercury having a... The scattered disc (or scattered disk) is a distant region of our solar system, thinly populated by icy planetoids known as scattered disk objects (SDOs), a subset of the broader family of trans-Neptunian objects (TNOs). ... Artists rendering of the Kuiper Belt and hypothetical more distant Oort cloud. ... A trans-Neptunian object (TNO) is any object in the solar system that orbits the sun at a greater distance on average than Neptune. ... This article is being considered for deletion in accordance with Wikipedias deletion policy. ... A fusor is a term proposed to the IAU by Gibor Basri, Head of Astronomy at the University of Berkeley, to help clarify the nomenclature of celestial bodies. ... Adjective Plutonian Atmospheric characteristics Atmospheric pressure 0. ...

References

^ "Uruguay celebra salida de Plutón". AFP-EFE. Published by El Nacional (the Venezualn newspaper) on August 26, 2006}}
^ Connor, Steve, "Solar system to welcome three new planets", New Zealand Herald, 2006-08-16.
^ Pluto loses status as a planet. BBC (2006-08-24). Retrieved on 2006-08-24.
^ Overbye, Dennis, "Pluto Seems Poised to Lose Its Planet Status", New York Times, 2006-08-22.
^ Gareth Cook (2006). Nine no longer: Panel declares 12 planets. Boston Globe. Retrieved on 2006-08-16.
^ Mike Brown (2006). How Many Planets Are There?. CalTech. Retrieved on 2006-08-16.
^ Robert Roy Britt (2006). Nine Planets Become 12 with Controversial New Definition. Space.com. Retrieved on 2006-08-16.
^ ^a ^b Draft Resolution 5 for GA-XXVI: Definition of a Planet. International Astronomical Union (2006). Retrieved on 2006-08-16.
^ Planet Definition” Questions & Answers Sheet. International Astronomical Union (2006). Retrieved on 2006-08-16.
^ Gareth Cook (2006). Nine no longer: Panel declares 12 planets. Boston Globe. Retrieved on 2006-08-16.
^ Planetary Scientists Support Proposed Redefinition Of A Planet. SpaceDaily (2006). Retrieved on 2006-08-19.
^ Mike Brown (2006). New Planets. Retrieved on 2006-08-22.
^ Robert Roy Britt (2006). Nine Planets Become 12 with Controversial New Definition. Space.com. Retrieved on 2006-08-19.
^ Pearson education (2006). The Flap over Pluto. infoplease.com. Retrieved on 2006-08-19.
^ Phil Plait (2006). Congratulations! It’s a planet!. Bad Astronomy. Retrieved on 2006-08-18.
^ Nick Matzke (2006). Wherein I argue emotionally about the definition of “planet”. The Panda's Thumb. Retrieved on 2006-08-18.
^ Robert Roy Britt (2006). Earth's moon could become a planet.
^ Ira Flatow and Mike Brown (2006-08-18). Pluto's Planet Status / String Theory. Talk of the Nation - Science Friday. National Public Radio. Retrieved on 2006-08-22.
^ ^a ^b Britt, Robert Roy (2006-08-18). Pluto May Get Demoted After All. Space.com. Retrieved on 2006-08-24.
^ Details Emerge on Plan to Demote Pluto (2006). Retrieved on 2006-08-18.
^ Star-gazers puzzled by Pluto. Independent Online (2006). Retrieved on 2006-08-18.
^ Geologists Force Astronomers To Rethink Pluto Plan (2006). Retrieved on 2006-08-18.
^ Elise Kleeman (2006). Planet, pluton or rock?. Pasadena Star News. Retrieved on 2006-08-20.
^ Geoff Brumfiel (21 August 2006). Plutons, planets and dwarves : Geologists and astronomers wrangle over words.. news@nature.com.
^ Overbye, Dennis, "Pluto Seems Poised to Lose Its Planet Status", New York Times, 2006-08-22.
^ "Astronomers divided over 'planet' definition", Deutsche Presse-Agentur, 2006-08-22.
^ Tresch Fienberg, Richard, ""The Day We Lost Pluto"", Sky & Telescope, 2006-08-22.
^ IAU General Assembly Welcome page 24 August 2006.
^ IAU General Assembly Newspaper, 24 August 2006
^ ^a ^b Pluto vote 'hijacked' in revolt.
^ ^a ^b Jane Spencer (2006-08-25). Pluto's demotion divides astrologers, troubles Scorpios. Wall Street Journal.
^ "IAU 2006 General Assembly: Result of the IAU Resolution votes", IAU, 24 August 2006.
^ Definitions as voted on
^ ^a ^b Dennis Overbye (2006-08-24). Pluto is demoted to ‘dwarf planet’. NYTimes.

id="External_links"> El Nacional is a Venezuelan publishing company under the name C.A. Editorial El Nacional that is most widely known for its El Nacional newspaper. ... August 26 is the 238th day of the year in the Gregorian Calendar (239th in leap years). ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 16 is the 228th day of the year (229th in leap years) in the Gregorian Calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 24 is the 236th day of the year in the Gregorian Calendar (237th in leap years), with 129 days remaining. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 22 is the 234th day of the year in the Gregorian calendar (235th in leap years), with 131 days remaining. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 16 is the 228th day of the year (229th in leap years) in the Gregorian Calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 16 is the 228th day of the year (229th in leap years) in the Gregorian Calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 16 is the 228th day of the year (229th in leap years) in the Gregorian Calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 16 is the 228th day of the year (229th in leap years) in the Gregorian Calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 16 is the 228th day of the year (229th in leap years) in the Gregorian Calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 16 is the 228th day of the year (229th in leap years) in the Gregorian Calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 19 is the 231st day of the year (232nd in leap years) in the Gregorian Calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 22 is the 234th day of the year in the Gregorian calendar (235th in leap years), with 131 days remaining. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 19 is the 231st day of the year (232nd in leap years) in the Gregorian Calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 19 is the 231st day of the year (232nd in leap years) in the Gregorian Calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 18 is the 230th day of the year (231st in leap years) in the Gregorian calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 18 is the 230th day of the year (231st in leap years) in the Gregorian calendar. ... Ira Flatow (born March 9, 1949) is a radio and television personality who hosts National Public Radios popular Talk of the Nation - Science Friday. ... Mike Brown can refer to the following people: Michael E. Brown the astronomer. ... Science Friday is a call-in talk show that is part of National Public Radios Talk of the Nation radio program hosted by Ira Flatow every Friday. ... NPR logo NPR redirects here. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 22 is the 234th day of the year in the Gregorian calendar (235th in leap years), with 131 days remaining. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 24 is the 236th day of the year in the Gregorian Calendar (237th in leap years), with 129 days remaining. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 18 is the 230th day of the year (231st in leap years) in the Gregorian calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 18 is the 230th day of the year (231st in leap years) in the Gregorian calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 18 is the 230th day of the year (231st in leap years) in the Gregorian calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 20 is the 232nd day of the year (233rd in leap years) in the Gregorian Calendar. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 22 is the 234th day of the year in the Gregorian calendar (235th in leap years), with 131 days remaining. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 22 is the 234th day of the year in the Gregorian calendar (235th in leap years), with 131 days remaining. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 22 is the 234th day of the year in the Gregorian calendar (235th in leap years), with 131 days remaining. ...

Contents