Dwarf_planet by zzzmarcus


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Dwarf planet

Dwarf planet
been both praised and criticized, and remains disputed by some scientists. The IAU currently recognizes five dwarf planets—Ceres, Pluto, Haumea, Makemake, and Eris.[5] However, only two of these bodies, Ceres and Pluto, have been observed in enough detail to demonstrate that they fit the definition. Eris has been accepted as a dwarf planet because it is more massive than Pluto. The IAU subsequently decided that unnamed trans-Neptunian objects with an absolute magnitude less than +1 (and hence a mathematically delimited minimum diameter of 838 km[6]) are to be named under the assumption that they are dwarf planets. The only two such objects known at the time, Makemake and Haumea, went through this naming procedure and were declared to be dwarf planets. It is suspected that at least another 40 known objects in the Solar System are dwarf planets,[7] and estimates are that up to 200 dwarf planets may be found when the entire region known as the Kuiper belt is explored, and that the number might be as high as 2,000 when objects scattered outside the Kuiper belt are considered.[7] The classification of bodies in other planetary systems with the characteristics of dwarf planets has not been addressed,[8] although if they were detectable they would not be considered planets.[9]

Artist’s impression of Pluto (background) and Charon (foreground). Pluto, considered a planet for 76 years, was reclassified as a dwarf planet in 2006. A dwarf planet, as defined by the International Astronomical Union (IAU), is a celestial body orbiting the Sun that is massive enough to be rounded by its own gravity but has not cleared its neighbouring region of planetesimals and is not a satellite.[1][2] More explicitly, it has to have sufficient mass to overcome its compressive strength and achieve hydrostatic equilibrium. It should not be confused with minor planet. The term dwarf planet was adopted in 2006 as part of a three-way categorization of bodies orbiting the Sun,[3] brought about by an increase in discoveries of trans-Neptunian objects that rivaled Pluto in size, and finally precipitated by the discovery of an even larger object, Eris.[4] This classification states that bodies large enough to have cleared the neighbourhood of their orbit are defined as planets, while those that are not massive enough to be rounded by their own gravity are defined as small solar system bodies. Dwarf planets come in between. The definition officially adopted by the IAU in 2006 has

History of the concept
Before the discoveries of the early 21st century, astronomers had no strong need for a formal definition of a planet. With the discovery of Pluto in 1930, astronomers considered the Solar System to have nine planets, along with thousands of significantly smaller bodies such as asteroids and comets. For almost 50 years Pluto was thought to be larger than Mercury,[10][11] but with the discovery in 1978 of Pluto’s moon Charon, it became possible to measure the mass of Pluto accurately and it was noticed that actual mass was much smaller than the initial estimates.[12] It was roughly one-twentieth the mass of Mercury, which made Pluto by far the smallest


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planet. Although it was still more than ten times as massive as the largest object in the asteroid belt, Ceres, it was one-fifth that of Earth’s Moon.[13] Furthermore, having some unusual characteristics such as large orbital eccentricity and a high orbital inclination, it became evident it was a completely different kind of body from any of the other planets.[14] In the 1990s, astronomers began to find objects in the same region of space as Pluto (now known as the Kuiper belt), and some even farther away.[15] Many of these shared some of the key orbital characteristics of Pluto, and Pluto started being seen as the largest member of a new class of objects, plutinos. This led some astronomers to stop referring to Pluto as a planet. Several terms including minor planet, subplanet, and planetoid started to be used for the bodies now known as dwarf planets.[16][17] By 2005, three other bodies comparable to Pluto in terms of size and orbit (Quaoar, Sedna, and Eris) had been reported in the scientific literature.[18] It became clear that either they would also have to be classified as planets, or Pluto would have to be reclassified.[19] Astronomers were also confident that more objects as large as Pluto would be discovered, and the number of planets would start growing quickly if Pluto were to remain a planet.[20] In 2006, Eris (then known as 2003 UB313) was determined to be slightly larger than Pluto, and some reports unofficially referred to it as the tenth planet.[21] As a consequence, the issue became a matter of intense debate during the IAU General Assembly in August 2006.[22] IAU’s initial draft proposal included Charon, Eris, and Ceres in the list of planets. After many astronomers objected to this proposal, an alternative was drawn up by Uruguayan astronomer Julio Ángel Fernández, in which he created a median classification for objects large enough to be round but that had not cleared their orbits of planetesimals. Dropping Charon from the list, the new proposal also removed Pluto, Ceres, and Eris, since they have not cleared their orbits.[23] The IAU’s final resolution preserved this three-category system for the celestial bodies orbiting the Sun. Fernández suggested calling these median objects planetoids,[24][25] but the IAU’s division III plenary session voted unanimously to call them dwarf planets.[3] The resolution read, in full: “

Dwarf planet
The IAU ... resolves that planets and ” other bodies, except satellites, in our Solar System be defined into three distinct categories in the following way: (1) A planet1 is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit. (2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape2, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite. (3) All other objects3, except satellites, orbiting the Sun shall be referred to collectively as “Small Solar System Bodies.”

The eight planets are: Mercury,

Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

An IAU process will be established to

assign borderline objects either dwarf planet or other status.

These currently include most of the

Solar System asteroids, most TransNeptunian Objects (TNOs), comets, and other small bodies.

Although there were concerns about the classification of planets in other solar systems,[8] this issue was not resolved; it was proposed instead to decide this only when such objects will start being observed.[23] The 2006 IAU’s Resolution 6a[26] recognizes Pluto as "the prototype of a new category of trans-Neptunian objects". The name and precise nature of this category were not specified but left for the IAU to establish at a later date; in the debate leading up to the resolution, the members of the category were variously referred to as plutons and plutonian objects but neither name was carried forward.[3] On June 11, 2008, the IAU Executive


From Wikipedia, the free encyclopedia
Planetary discriminants[28] Body Mercury Venus Earth Mars Ceres Jupiter Saturn Uranus Neptune Pluto Haumea Makemake Eris Mass (ME*) 0.055 0.815 1.00 0.107 0.000 15 317.7 95.2 14.5 17.1 0.002 2 0.000 67 0.000 67 0.002 8 Λ/ΛE** 0.012 6 1.08 1.00 0.006 1 8.7 × 10−9 8 510 308 2.51 1.79 1.95 × 10−8 1.72 × 10–9 1.45 × 10–9 3.5 × 10−8 µ***

Dwarf planet

9.1 × 104 1.35 × 106 1.7 × 106 1.8 × 105 0.33 6.25 × 105 1.9 × 105 2.9 × 104 2.4 × 104 0.077 0.02 0.02[29] 0.10

Committee announced a name, plutoid, and a definition: all trans-Neptunian dwarf planets are plutoids.[27] On July 11, 2008, the Working Group for Planetary System Nomenclature reclassified the object then known as (136472) 2005 FY9 as a dwarf planet, and renamed it Makemake.[5]

*ME in Earth masses. **Λ/ΛE = M²/P × PE/M2E. ***µ = M/m, where M is the mass of the body, and m is the aggregate mass of all the other bodies that share its orbital zone.

Orbital dominance
Alan Stern and Harold F. Levison introduced a parameter Λ (lambda), expressing the probability of an encounter resulting in a given deflection of orbit.[30] The value of this parameter in Stern’s model is proportional to the square of the mass and inversely proportional to the period. Following the authors, this value can be used to estimate the capacity of a body to clear the neighbourhood of its orbit. A gap of five orders of magnitude in Λ was found between the smallest terrestrial planets and the largest asteroids and Kuiper belt objects (third column of the planetary discriminants table to the right).[28] Using this parameter, Steven Soter and other astronomers argued for a distinction between dwarf planets and the other eight planets based on their inability to "clear the

neighbourhood around their orbits": planets are able to remove smaller bodies near their orbits by collision, capture, or gravitational disturbance, while dwarf planets lack the mass to do so.[30] In other words, Soter went on to propose a parameter he called the planetary discriminant, designated with the symbol µ (mu), that represents an experimental measure of the actual degree of cleanliness of the orbital zone (where µ is calculated by dividing the mass of the candidate body by the total mass of the other objects that share its orbital zone).[28] There are several other schemes that try to differentiate between planets and dwarf planets,[30] but the 2006 definition uses this concept.[3]

Size and mass
When an object achieves hydrostatic equilibrium, also known as gravitational relaxation, there are no gravitational imbalances in its surface. A global layer of liquid placed on this surface (assuming for argument’s sake it would remain a liquid) would form a liquid surface of the same shape, apart from smallscale surface features such as craters and fissures. This does not mean the body is a sphere; the faster a body rotates, the more oblate or even scalene it becomes, but such forces affect a liquid surface as well. The extreme example of a non-spherical body in hydrostatic equilibrium is Haumea, which is twice as long along its major axis as it is at the poles.


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Dwarf planet
is the only object known to presently be selfrounded (though Vesta may once have been). Therefore, it has been suggested that the limit where other rocky-ice bodies like Ceres become rounded might be somewhere around 900 km.[7] More icy bodies like trans-Neptunian objects have less rigid interiors and therefore more easily relax under their selfgravity into a rounded shape.[7] The smallest icy body known to have achieved hydrostatic equilibrium is Mimas, while the largest irregular one is Proteus; both average slightly more than 400 km (250 mi) in diameter. Mike Brown (a leading researcher in this field and discoverer of Eris) suggests that the lower limit for an icy dwarf planet is therefore likely to be somewhere under 400 km.[7] It is also not clear to what extent deviations from perfect equilibrium are to be tolerated, or whether having achieved equilibrium is sufficient for inclusion. All solid bodies in the solar system, such as Iapetus with its equatorial ridge and Mars with its shield volcanoes, deviate to some extent. This may be a critical for the consideration of the asteroid 4 Vesta, which may deviate from equilibrium due to a large impact that removed part of one hemisphere.

The relative masses of the five known dwarf planets, plus Charon. The mass of Makemake is a rough estimate.

Current members
Relative masses including the Earth’s Moon. The upper and lower size and mass limits of dwarf planets have not been specified by the IAU. There is no defined upper limit, and an object larger or more massive than Mercury that has not "cleared the neighbourhood around its orbit" would be classified as a dwarf planet.[31] The lower limit is determined by the requirements of achieving a hydrostatic equilibrium shape, but the size or mass at which an object attains this shape depends on its composition and thermal history. The original draft of the 2006 IAU resolution redefined hydrostatic equilibrium shape as applying "to objects with mass above 5 × 1020 kg and diameter greater than 800 km",[8] but this was not retained in the final draft.[3] Empirical observations suggest that the lower limit may vary according to the composition of the object. For example, in the asteroid belt, Ceres, with a diameter of 975 km, Haumea with its moons, Hiʻiaka and Namaka (artist’s conception)

Makemake (artist’s conception) As of 2008, the IAU has classified five celestial bodies as dwarf planets. Two of these, Ceres and Pluto, are known to qualify as


From Wikipedia, the free encyclopedia
Orbital attributes of dwarf planets[34] Name Region of Solar System Asteroid belt Kuiper belt Kuiper belt Orbital Orbital radius period (AU) (years) 2.77 39.48 43.34 45.79 4.60 248.09 285.4 309.9 557 Mean orbital speed (km/s) 17.882 4.666 4.484 4.419 3.436

Dwarf planet

Inclination Orbital Planetary to ecliptic eccentricity discriminant (°) 10.59 17.14 28.19 28.96 44.19 0.080 0.249 0.189 0.159 0.442 0.33 0.077 ? ? 0.10

Ceres Pluto Haumea

Makemake Kuiper belt Eris

Scattered 67.67 disc

Eris (through the Hubble Space Telescope) dwarf planets through direct observation. The other three, Eris, Haumea, and Makemake, are thought to be dwarf planets from mathematical modeling—or in the case of Eris, because it is larger than Pluto—and qualify for the classification under IAU naming rules based on their magnitudes.[5][26] 1. Ceres – discovered on January 1, 1801 (45 years before Neptune), considered a planet for half a century before reclassification as an asteroid. Classified as a dwarf planet on September 13, 2006. 2. Pluto – discovered on February 18, 1930, classified as a planet for 76 years. Reclassified as a dwarf planet on August 24, 2006.

Ceres (through the Hubble Space Telescope) 3. Eris – discovered on January 5, 2005. Called the "tenth planet" in media reports. Accepted as a dwarf planet on September 13, 2006. 4. Makemake – discovered on March 31, 2005. Accepted as a dwarf planet on July 11, 2008. 5. Haumea – discovered on December 28, 2004. Accepted as a dwarf planet on September 17, 2008. No space probes have visited any of the dwarf planets. This will change if NASA’s Dawn and New Horizons missions reach Ceres and Pluto, respectively, as planned in 2015.[32][33] Dawn is also slated to orbit and observe another potential dwarf planet, Vesta, in 2011.


From Wikipedia, the free encyclopedia
Physical attributes of dwarf planets Name Equatorial Equatorial diameter diameter relative to (km) the Moon 28.0% 68.7% 33.1% 74.8% 974.6±3.2 2306±30

Dwarf planet

Mass Mass Density Surface Escape Axial relative ( × 1021 ( × 103g/m³) gravity velocity incli to kg) (m/s2) (km/s) the Moon 1.3% 17.8% 0.95 13.05 ~4? 16.7 2.08 2.0 ~2? 2.3 0.27 0.58 ~0.44 ~0.5 ~0.8 0.51 1.2 ~0.84 ~0.8 1.3 ~3°

Ceres[35][36] Pluto[37][38] Haumea[39][40] Eris[42][43]


1150+250−100 5.7% 1500+400−200 ~5%? 2400±100 22.7%

4.2 ± 0.1 2.6–3.3

Makemake[39][41] 43.2%

resolution (5)[8] presented to the IAU stated that Charon could be considered a planet because: 1. Charon independently would satisfy the size and shape criteria for a dwarf planet status (in the terms of the final resolution); 2. Charon revolves with Pluto around a common barycentre located between the two bodies (rather than within one of the bodies) because Charon’s mass is not insignificant relative to that of Pluto.[47] This definition, however, was not preserved in the IAU’s final resolution and it is unknown if it will be included in future debates.

Plutoid candidates
See also: List of plutoid candidates Pluto (approximate true color)

As with Ceres, the next three largest objects in the main asteroid belt – Vesta, Pallas, and Hygiea[44] – could eventually be classified as dwarf planets if it is shown that their shape is determined by hydrostatic equilibrium.[45] While uncertain, the present data suggests that it is unlikely for Pallas and Hygiea. Vesta, however, appears to deviate from hydrostatic equilibrium only because of a large impact that occurred after it solidified;[46] the definition of dwarf planet does not specifically address this issue. The Dawn probe scheduled to enter orbit around Vesta in 2011 may help clarify matters.[32] The status of Charon (currently regarded as a satellite of Pluto) remains uncertain, as there is currently no clear definition of what distinguishes a satellite system from a binary (double planet) system. The original draft

Illustration of the relative sizes, albedos, and colours of the largest Trans-Neptunian objects Many Trans-Neptunian objects (TNOs) are thought to have icy cores and therefore would require a diameter of perhaps 400 km (250 mi) – only about 3% of that of Earth – to relax into gravitational equilibrium, making them dwarf planets of the plutoid class.[7] Although only rough estimates of the diameters of these objects are available, as of August 2006, it was believed that another 42 bodies


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Prime plutoid candidates[50] Name Category Estimated diameter (km)
by [7] by

Dwarf planet

Magnitude Mass
(H) ( × 1020 kg)

by [52]

by [53]

Orbital radius

Orcus Pluto Ixion Huya Varuna

plutino (1 moon) plutino plutino cubewano

1,100 909




39.12 39.48

980 480 780 800

570 480 874 709

650 — 500 —

1,065 — 900 —

~5.8 0.8–1.6? ~5.9 1.6–3.7

39.65 39.76 42.90 43.11 43.34

2002 TX300 Haumean cubewano Haumea Quaoar Makemake 2002 AW197 Eris 1996 TL66 Sedna SDO detached object cubewano cubewano (1 moon)

1,290 1,260 844


10–26 45.79


940 710 —



890 —

~5.2 0.78 2.6? 17–61

47.30 55.02 67.67 82.90 486.0

2002 TC302 5:2 SDO

1,200 1,150 632

460–690 —

1,800 1,500 < 1,600 < 1,500

beyond Neptune (besides Pluto and Eris) were likely dwarf planets.[7][48] A team is investigating another 30 such objects, and believe that the total number will eventually prove to be about 200 in the Kuiper belt, and many more beyond it.[7] Tancredi & Favre (2008) attempt to estimate which TNOs are likely to qualify, based on both direct measurements and lightcurve data. They propose that nine of the candidates be considered dwarf planets.[49] Six of these have been estimated by one researcher or another to be at least 900 km in diameter, the size of the smallest known dwarf planet, Ceres, as has a tenth candidate, 2002 AW197. These ten prime candidates are:

the four Galilean moons of Jupiter (Io, Europa, Ganymede, and Callisto), seven moons of Saturn (Mimas, Enceladus, Tethys, Dione, Rhea, Titan, and Iapetus), five moons of Uranus (Miranda, Ariel, Umbriel, Titania, and Oberon), one moon of Neptune (Triton), and one moon of Pluto (Charon).

In the immediate aftermath of the IAU definition of dwarf planet, a number of scientists expressed their disagreement with the IAU resolution.[54] Campaigns included car bumper stickers and T-shirts.[55] Mike Brown (the discoverer of Eris) agrees with the reduction of the number of planets to eight.[56] NASA has announced that it will use the new guidelines established by the IAU.[57] However, Alan Stern, the director of the NASA’s mission to Pluto, rejects the current IAU definition of planet, both in terms of defining dwarf planets as something other than a type of planet, and in using orbital characteristics (rather than intrinsic characteristics) of objects to define them as dwarf

Ellipsoidal moons
A total of 19 known moons are massive enough to have relaxed into a rounded shape under their own gravity. These bodies have no significant physical differences from the dwarf planets, but are not considered members of that class because they do not directly orbit the Sun. They are Earth’s moon,


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planets.[58] Thus, as of January 2008, he and his team still refer to Pluto as the ninth planet,[59] while accepting the characterization of dwarf planet for Ceres and Eris.

Dwarf planet

~mbrown/dwarfplanets/. Retrieved on 2008-01-26. [8] ^ "The IAU draft definition of "planet" and "plutons"". International Astronomical Union. 2006-08-16. http://www.iau.org/public_press/news/ release/iau0601/. • List of Solar System bodies formerly [9] "Working Group on Extrasolar Planets of regarded as planets the International Astronomical Union". • Table of planets and dwarf planets in the International Astronomical Union. 2001. Solar System http://www.dtm.ciw.edu/boss/ • Ice dwarf definition.html. Retrieved on • Mesoplanet 2008-01-26. • List of planetary bodies [10] Mager, Brad. "Pluto Revealed". discoveryofpluto.com. http://www.discoveryofpluto.com/ pluto06.html. Retrieved on 2008-01-26. [1] "IAU 2006 General Assembly: Result of [11] Cuk, Matija; Masters, Karen the IAU Resolution votes". International (2007-09-14). "Is Pluto a planet?". Astronomical Union. 2006. Cornell University, Astronomy http://www.iau.org/iau0603.414.0.html. Department. Retrieved on 2008-01-26. http://curious.astro.cornell.edu/ [2] "Dwarf Planets". NASA. question.php?number=624. Retrieved on http://solarsystem.nasa.gov/planets/ 2008-01-26. profile.cfm?Object=Dwarf&Display=OverviewLong. Marc W.; William M. Grundy, Eliot [12] Buie, Retrieved on 2008-01-22. F. Young, Leslie A. Young and S. Alan [3] ^ "Definition of a Planet in the Solar Stern (2006). "Orbits and Photometry of System: Resolutions 5 and 6" (PDF). IAU Pluto’s Satellites: Charon, S/2005 P1, 2006 General Assembly (International and S/2005 P2" (abstract page). The Astronomical Union). 2006-08-24. Astronomical Journal 132 (132): 290–98. http://www.iau.org/static/resolutions/ doi:10.1086/504422. http://www.iop.org/ Resolution_GA26-5-6.pdf. Retrieved on EJ/abstract/1538-3881/132/1/290. 2008-01-26. Retrieved on 2008-02-10. [4] "The Outer Planets", 2007, The Universe [13] Jewitt, David; Delsanti, Audrey (2006) program (rebroadcast 2008-09-29, (PDF). The Solar System Beyond The 18-19:00 hrs EDST) The History Planets in Solar System Update : Topical Channel. and Timely Reviews in Solar System [5] ^ "Dwarf Planets and their Systems". Sciences (PDF). Springer. doi:10.1007/ Working Group for Planetary System 3-540-37683-6. ISBN 978-3-540-37683-5. Nomenclature (WGPSN). 2008-07-11. http://www.ifa.hawaii.edu/faculty/jewitt/ http://planetarynames.wr.usgs.gov/ papers/2006/DJ06.pdf. Retrieved on append7.html#DwarfPlanets. Retrieved 2008-02-10. on 2008-07-13. [14] Weintraub, David A. (2006). Is Pluto a [6] Dan Bruton. "Conversion of Absolute Planet? A Historical Journey through the Magnitude to Diameter for Minor Solar System. Princeton, N.J.: Princeton Planets". Department of Physics & Univ. Press. pp. 1–272. ISBN Astronomy (Stephen F. Austin State 978-0-691-12348-6. University). [15] Phillips, Tony; Phillips, Amelia http://www.physics.sfasu.edu/astro/ (2006-09-04). "Much Ado about Pluto". asteroids/sizemagnitude.html. Retrieved PlutoPetition.com. on 2008-06-13. http://www.plutopetition.com/ [7] ^ Brown, Michael E.. "The Dwarf unplanet.php. Retrieved on 2008-01-26. Planets". California Institute of [16] "Planetoids Beyond Pluto". Astrobiology Technology, Department of Geological Magazine. 2004-12-30. Sciences. http://web.gps.caltech.edu/ http://www.astrobio.net/news/

See also



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Dwarf planet

modules.php?op=modload&name=News&file=article&sid=1366. ...&Anotaciones de planetas de 9 a 8 Retrieved on 2008-01-26. Tancredi" (in Spanish). Science and [17] "Hubble Observes Planetoid Sedna, Research Institute, Mercedes, Uruguay. Mystery Deepens". NASA’s Hubble http://www.ici.edu.uy/perfilASTRO.htm. Space Telescope home site. 2004-04-14. Retrieved on 2008-02-11. http://hubblesite.org/newscenter/archive/ [26] ^ "IAU 2006 General Assembly: Result of releases/2004/14/. Retrieved on the IAU Resolution votes". 2008-01-26. http://www.iau.org/public_press/news/ [18] Brown, Michael E.. "The Discovery of release/iau0603. Eris, the Largest Known Dwarf Planet". [27] Plutoid chosen as name for Solar System California Institute of Technology, objects like Pluto. Press release. Department of Geological Sciences. http://www.iau.org/public_press/news/ http://www.gps.caltech.edu/~mbrown/ release/iau0804/. planetlila/. Retrieved on 2008-01-26. [28] ^ Soter, Steven (2006-08-16). "What is a [19] Brown, Michael E. (2004). "What is the Planet?". The Astronomical Journal 132: definition of a planet?". California 2513–19. doi:10.1086/508861. Institute of Technology, Department of http://arxiv.org/abs/astro-ph/0608359. Geological Sciences. Retrieved on 2008-01-22. http://web.gps.caltech.edu/~mbrown/ [29] Calculated using the estimate for the sedna/index.html#planets. Retrieved on mass of the Kuiper belt found in Iorio, 2008-01-26. 2007 of 0.033 Earth masses [20] Brown, Mike (2006-08-16). "War of the [30] ^ Stern, S. Alan; Levison, Harold F. Worlds". New York Times. (2002). "Regarding the criteria for http://www.nytimes.com/2006/08/16/ planethood and proposed planetary opinion/16brown.html. Retrieved on classification schemes" (PDF). Highlights 2008-02-20. of Astronomy 12: 205–13, as presented [21] "Astronomers Measure Mass of Largest at the XXIVth General Assembly of the Dwarf Planet". NASA’s Hubble Space IAU–2000 Manchester, UK, 7–18 August Telescope home site. 2007-06-14. 2000. http://www.boulder.swri.edu/~hal/ http://hubblesite.org/newscenter/archive/ PDF/planet_def.pdf. Retrieved on releases/2007/24/full/. Retrieved on 2008-01-22. 2008-01-26. [31] Indeed, Mike Brown has set out to find [22] Brown, Michael E.. "What makes a such an object. ("Julia Sweeney and planet?". California Institute of Michael E. Brown". Hammer Technology, Department of Geological Conversations: KCET podcast. 2007. Sciences. http://www.gps.caltech.edu/ http://www.pluggd.tv/audio/channels/ ~mbrown/whatsaplanet/. Retrieved on kcet_podcast__hammer_conversations/ 2008-01-26. episodes/2h10l. Retrieved on [23] ^ Britt, Robert Roy (2006-08-19). 2008-06-28. ) "Details Emerge on Plan to Demote [32] ^ Russel, C.T.; Capaccioni, F.; Coradini, Pluto". Space.com. A.; et al. (2006). "Dawn Discovery http://www.space.com/scienceastronomy/ mission to Vesta and Ceres: Present 060819_new_proposal.html. Retrieved on status". Advances in Space Research 38: 2006-08-18. 2043–48. doi:10.1016/j.asr.2004.12.041. [24] Bailey, Mark E.. "Comments & http://adsabs.harvard.edu/abs/ discussions on Resolution 5: The 2006AdSpR..38.2043R. Retrieved on definition of a planet - Planets Galore". 2007-12-08. Dissertatio cum Nuncio Sidereo, Series [33] Britt, Robert Roy (2003). "Pluto Mission Tertia - official newspaper of the IAU a Go! Initial Funding Secured". General Assembly 2006. Astronomical Space.com. http://www.space.com/ Institute Prague. http://astro.cas.cz/ scienceastronomy/ nuncius/appendix.html. Retrieved on pluto_horizons_030225.html. Retrieved 2008-02-09. on 2007-04-13. [25] "Dos uruguayos, Julio Fernández y [34] Bowell, Ted. "The Asteroid Orbital Gonzalo Tancredi en la historia de la Elements Database". Lowell Observatory. astronomía:reducen la cantidad de


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Dwarf planet

ftp://ftp.lowell.edu/pub/elgb/astorb.html. (2007). "Physical Properties of Kuiper Retrieved on 2008-02-12. Belt and Centaur Objects: Constraints [35] Thomas, P.C; Parker J.Wm.; McFadden, from Spitzer Space Telescope". L.A.; et al. (2005). "Differentiation of the University of Arizona, Lowell asteroid Ceres as revealed by its shape". Observatory, California Institute of Technology, NASA Ames Research Nature 437: 224–26. doi:10.1038/ Center, Southwest Research Institute, nature03938. http://adsabs.harvard.edu/ Cornell University. http://arxiv.org/abs/ abs/2005Natur.437..224T. Retrieved on astro-ph/0702538v1. Retrieved on 2008-02-16. 2007-05-18. [36] Calculated based on the known [43] Brown, Michael E.; Schaller, Emily L. parameters. APmag and AngSize (2007). "The Mass of Dwarf Planet Eris". generated with Horizons (Ephemeris: Observer Table: Quantities = 9,13,20,29) Science 316 (5831): 1585. doi:10.1126/ [37] Williams, D.R. (2006-09-07). "Pluto Fact science.1139415. PMID 17569855. Sheet". NASA. http://www.sciencemag.org/cgi/content/ http://nssdc.gsfc.nasa.gov/planetary/ full/316/5831/1585. factsheet/plutofact.html. Retrieved on [44] Rincon, Paul (2006-08-16). "Planets plan 2007-03-24. boosts tally to 12". BBC News. [38] Buie, M. W.; Grundy, W.M.; Young, E.F.; http://news.bbc.co.uk/1/hi/sci/tech/ Young, L.A.; Stern, S.A. (2006). "Orbits 4795755.stm. Retrieved on 2007-03-17. and photometry of Pluto’s satellites: [45] Battersby, Stephen (2006-08-16). "Three Charon, S/2005 P1, and S/2005 P2". new planets may join solar system". New Scientist.com. Astronomical Journal 132: 290. http://www.newscientistspace.com/ doi:10.1086/504422. arΧiv:astro-ph/ article.ns?id=dn9761&feedId=online0512491. http://adsabs.harvard.edu/cginews_rss20F53. Retrieved on bin/nph2008-01-26. bib_query?bibcode=2006AJ....132..290B&db_key=AST&data_type=HTML&format=&high=444b66a4 [46] Thomas, Peter C.; Binzelb, Richard P.; [39] ^ Stansberry, J.; Grundy, W.; Brown, M.; Gaffeyc, Michael J.; Zellnerd, Benjamin et al. (2007) (abstract). Physical H.; Storrse, Alex D.; Wells, Eddie (1997). Properties of Kuiper Belt and Centaur "Vesta: Spin Pole, Size, and Shape from Objects: Constraints from Spitzer Space Telescope. http://arxiv.org/abs/astro-ph/ HST Images". Icarus 128 (1): 88–94. 0702538v1. doi:10.1006/icar.1997.5736. [40] Rabinowitz, David L.; Barkume, K.M.; [47] the footnote in the original text reads: Brown, E.M. et al. (2006). "Photometric For two or more objects comprising a Observations Constraining the Size, multiple object system.... A secondary Shape, and Albedo of 2003 EL61, a object satisfying these conditions i.e. Rapidly Rotating, Pluto-Sized Object in that of mass, shape is also designated a the Kuiper Belt". The Astrophysical planet if the system barycentre resides outside the primary. Secondary objects Journal 639 (2): 1238–1251. doi:10.1086/ not satisfying these criteria are 499575. http://arxiv.org/abs/astro-ph/ "satellites". Under this definition, Pluto’s 0509401. companion Charon is a planet, making [41] J. Licandro, N. Pinilla-Alonso, M. Pedani, Pluto-Charon a double planet. et al. (2006). "The methane ice rich [48] Britt, Robert Roy (2006-08-16). "Nine surface of large TNO 2005 FY9: a PlutoPlanets Become 12 with Controversial twin in the trans-neptunian belt?". New Definition". Space.com. Astronomy and Astrophysics 445 http://www.space.com/scienceastronomy/ (L35-L38): L35. doi:10.1051/ 060816_planet_definition.html. Retrieved 0004-6361:200500219. on 2008-01-26. http://www.aanda.org/ [49] Tancredi & Favre. "Which are the dwarfs index.php?option=article&access=doi&doi=10.1051/ in the Solar system?". Asteroids, Comets, 0004-6361:200500219. Retrieved on Meteors. http://www.lpi.usra.edu/ 2008-07-14. meetings/acm2008/pdf/8261.pdf/. [42] Stansberry, John; Grundy, Will; Brown, Retrieved on 2008-09-20. Mike; Spencer, John; Trilling, David; Cruikshank, Dale; Margot, Jean-Luc


From Wikipedia, the free encyclopedia
[50] All bodies with estimated diameters of 900 km or more, with 3 additional prime suspects (Huya, 2002 TX300, 1996 TL66) cited in Tancredi & Favre. "Which are the dwarfs in the Solar system?". Asteroids, Comets, Meteors. http://www.lpi.usra.edu/meetings/ acm2008/pdf/8261.pdf. Retrieved on 2008-09-20. [51] Johnston, Robert (2007-11-24). "List of Known Trans-Neptunian Objects". Johnston’s Archive.net. http://www.johnstonsarchive.net/astro/ tnoslist.html. Retrieved on 2008-01-26. [52] Barucci, M.A.; Stansberry, John; Grundy, Will; Brown, Mike; Cruikshank, Dale; Spencer, John; Trilling, David; Margot, Jean-Luc (2007). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope". The Solar System beyond Neptune (University of Arizona Press). http://arxiv.org/pdf/astro-ph/0702538. Retrieved on 2008-01-26. [53] David C. Jewitt. "Kuiper Belt: The 1000 km Scale KBOs". University of Hawaii, Institute for Astronomy. http://www.ifa.hawaii.edu/faculty/jewitt/ kb.html. Retrieved on 2008-02-10. [54] Rincon, Paul (2006-08-25). "Pluto vote ’hijacked’ in revolt". BBC News. http://news.bbc.co.uk/2/hi/science/ nature/5283956.stm. Retrieved on 2008-01-26. [55] Chang, Alicia (2006-08-25). "Online merchants see green in Pluto news". Associated Press (USA Today). http://www.usatoday.com/tech/science/ space/2006-08-25-pluto-

Dwarf planet
memorabilia_x.htm. Retrieved on 2008-01-25. [56] Brown, Michael E.. "The Eight Planets". California Institute of Technology, Department of Geological Sciences. http://web.gps.caltech.edu/~mbrown/ eightplanets/. Retrieved on 2008-01-26. [57] "Hotly-Debated Solar System Object Gets a Name". NASA press release. 2006-09-14. http://www.nasa.gov/vision/ universe/solarsystem/ erisf-20060914.html. Retrieved on 2008-01-26. [58] Stern, Alan (2006-09-06). "Unabashedly Onward to the Ninth Planet". New Horizons Web Site. http://pluto.jhuapl.edu/overview/ piPerspectives/ piPerspective_09_06_2006.php. Retrieved on 2008-01-26. [59] Stern, Alan (2008-01-17). "Happy Birthday New Horizons! Two Years on the Road to the Ninth Planet". New Horizons Web Site. http://pluto.jhuapl.edu/overview/ piPerspectives/ piPerspective_01_17_2008.php. Retrieved on 2008-01-26.

External links
• NPR: Dwarf Planets May Finally Get Respect (David Kestenbaum) • BBC News: Q&A New planets proposal, August 16, 2006 • Ottawa Citizen: The case against Pluto (P. Surdas Mohit) August 24, 2006 • James L. Hilton, When Did the asteroids Become Minor Planets?

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