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[[File:Planets2008.jpg|400px|thumb|right|The [[Sun]], [[planet]]s and [[dwarf planet]]s of the Solar System. Compared with each other, the sizes are correct but the distances are not.]]
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Eris (68 AU) is the largest known scattered disc object. There has been a debate on weather or not it should be described as a planet. This is because it is 25% larger than Pluto and it is around the same distance across. It is the largest known dwarf planet in the Solar System. It has one moon, [[Dysnomia (moon)|Dysnomia]]. Eris and Pluto have a similar orbit.
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===Asteroid belt===
{{Main|Asteroid belt}}
[[File:InnerSolarSystem-en.png|300px|thumb|Image of the [[asteroid belt]] and the [[Trojan asteroids]]]]

[[Asteroid]]s are [[Small Solar System body|small Solar System bodies]] that are made up of mainly [[refractory (astronomy)|refractory]] rocky and [[metallic]] [[mineral]]s, with some ice.<ref>{{cite web|title=Are Kuiper Belt Objects asteroids? Are large Kuiper Belt Objects planets?
|publisher=[[Cornell University]]|url=http://curious.astro.cornell.edu/question.php?number=601|accessdate=2009-03-01}}</ref>

The asteroid belt is located between Mars and Jupiter. It is 2.3 and 3.3&nbsp;AU from the Sun. It is thought to be objects from when the Solar System was formed and failed to form into larger objects because of the gravitational pull of Jupiter.<ref>{{cite journal
 | author=Petit, J.-M.; Morbidelli, A.; Chambers, J.
 | title=The Primordial Excitation and Clearing of the Asteroid Belt
 | journal=Icarus
 | year=2001
 | volume=153
 | issue=2
 | pages=338–347
 | url=http://www.gps.caltech.edu/classes/ge133/reading/asteroids.pdf
 | format=PDF
 | accessdate=2007-03-22 | doi = 10.1006/icar.2001.6702
| bibcode=2001Icar..153..338P
}}</ref>

Asteroids range in size from hundreds of kilometers across to [[micro]]scopic. All asteroids except the largest, Ceres, are classified as small Solar System bodies, but some asteroids such as [[4 Vesta|Vesta]] and [[10 Hygiea|Hygiea]] may be reclassed as [[dwarf planet]]s if they are shown to have [[hydrostatic equilibrium]].<ref>{{cite web|title=IAU Planet Definition Committee|publisher=International Astronomical Union|year=2006|url=http://www.iau.org/public_press/news/release/iau0601/newspaper/|accessdate=2009-03-01}}</ref>

The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometre in diameter.<ref>{{cite web |year=2002 |title=New study reveals twice as many asteroids as previously believed |work=ESA |url=http://www.esa.int/esaCP/ESAASPF18ZC_index_0.html|accessdate=2006-06-23}}</ref> Despite this, the total mass of the asteroid belt is unlikely to be more than a thousandth of that of the Earth.<ref name=Krasinsky2002>{{cite journal |authorlink=Georgij A. Krasinsky |first=G. A. |last=Krasinsky |coauthors=[[Elena V. Pitjeva|Pitjeva, E. V.]]; Vasilyev, M. V.; Yagudina, E. I. |bibcode=2002Icar..158...98K |title=Hidden Mass in the Asteroid Belt |journal=Icarus |volume=158 |issue=1 |pages=98–105 |month=July |year=2002 |doi=10.1006/icar.2002.6837}}</ref> The asteroid belt is scattered, which allows [[spacecraft]]s to pass through without any damage. Asteroids with diameters between 10 and 10<sup>−4</sup>&nbsp;m are called [[meteoroid]]s.<ref>{{cite journal |author=Beech, M. |coauthors=Duncan I. Steel |year=1995 |month=September |title=On the Definition of the Term Meteoroid |journal=[[Quarterly Journal of the Royal Astronomical Society]] |volume=36 |issue=3 |pages=281–284 |bibcode=1995QJRAS..36..281B |last2=Steel}}</ref>

====Ceres====
[[Ceres (dwarf planet)|Ceres]] (2.77&nbsp;AU) is the largest asteroid, a [[protoplanet]], and a dwarf planet. It has a diameter of under 1000&nbsp;km, and a mass large enough for its own gravity to pull it into a [[sphere|spherical shape]]. Ceres was considered a planet when it was discovered in the 19th century, but was reclassified as an asteroid in the 1850s as further observations revealed additional asteroids.<ref>{{cite web |title=History and Discovery of Asteroids |format=DOC |work=NASA |url=http://dawn.jpl.nasa.gov/DawnClassrooms/1_hist_dawn/history_discovery/Development/a_modeling_scale.doc |accessdate=2006-08-29}}</ref> It was classified in 2006 as a dwarf planet.

====Asteroid groups====
Asteroids in the asteroid belt are divided into [[asteroid group]]s and families. These are based on how they orbit. [[Asteroid moon]]s are asteroids that orbit larger asteroids. They are not like planetary moons, but are larger than smaller asteroids that orbits them. The asteroid belt also contains [[main-belt comet]]s, which is thought to have been the reason why Earth has liquid water.<ref>{{cite web |year=2006 |author=Phil Berardelli |title=Main-Belt Comets May Have Been Source Of Earths Water |work=SpaceDaily |url=http://www.spacedaily.com/reports/Main_Belt_Comets_May_Have_Been_Source_Of_Earths_Water.html |accessdate=2006-06-23}}</ref>

[[Trojan asteroid]]s are located in either of Jupiter's [[L5 point|L<sub>4</sub> or L<sub>5</sub> points]]. The term "Trojan" is also used for small bodies in any other planetary or satellite Lagrange point. [[Hilda family|Hilda asteroids]] are in a 2:3 [[Orbital resonance|resonance]] with Jupiter. They go around the Sun three times for every two Jupiter orbits.<ref name=Barucci>{{cite book|last=Barucci|first=M. A.|coauthors=Kruikshank, D.P.; Mottola S.; Lazzarin M.|year=2002 |chapter=Physical Properties of Trojan and Centaur Asteroids|title=Asteroids III|publisher=University of Arizona Press|pages=273–87|location=Tucson, Arizona}}</ref>

[[Near-Earth asteroid]]s are asteroids that are near planet Earth. They sometimes will cross the orbit of other inner planets.<ref name = "MorbidelliAstIII">{{cite journal|url = http://www.boulder.swri.edu/~bottke/Reprints/Morbidelli-etal_2002_AstIII_NEOs.pdf|title = Origin and Evolution of Near-Earth Objects|author = A. Morbidelli, W. F. Bottke Jr., Ch. Froeschlé, P. Michel|journal = Asteroids III|editor = W. F. Bottke Jr., A. Cellino, P. Paolicchi, and R. P. Binzel|pages = 409–422|month = January | year = 2002|publisher = University of Arizona Press|format=PDF|bibcode = 2002aste.conf..409M|last2 = Bottke|last3 = Froeschlé|last4 = Michel}}</ref>

== References ==
{{reflist|2}}