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[[File:Ceres-Vesta-Eros compared to Pluto-Charon.jpg|300px|thumb|By far the largest object within the belt is the dwarf planet [[Ceres (dwarf planet)|Ceres]]. The total mass of the asteroid belt is significantly less than [[Pluto]]'s, and roughly twice that of Pluto's moon, [[Charon (moon)|Charon]].]]
The '''asteroid belt''' is a [[torus]]-shaped region in the [[Solar System]], centered on the [[Sun]] and roughly spanning the space between the orbits of the planets [[Jupiter]] and [[Mars]]. It contains a great many solid, irregularly shaped bodies called [[asteroid]]s or [[minor planet]]s. The identified objects are of many sizes
The asteroid belt is the smallest and innermost known [[circumstellar disc]] in the Solar System. Classes of [[Small Solar System body|small Solar System bodies]] in other regions are the [[near-Earth objects]], the [[Centaur (minor planet)|centaurs]], the [[Kuiper belt]] objects, the [[scattered disc]] objects, the [[sednoid]]s, and the [[Oort cloud]] objects. About 60% of the main belt mass is contained in the four largest asteroids: [[Ceres (dwarf planet)|Ceres]], [[4 Vesta|Vesta]], [[2 Pallas|Pallas]], and [[10 Hygiea|Hygiea]]. The total mass of the asteroid belt is estimated to be 3% that of the [[Moon]].<ref name="Pitjeva2018">{{cite journal|last=Pitjeva|first=E. V.|author-link=Elena V. Pitjeva|title=Masses of the Main Asteroid Belt and the Kuiper Belt from the Motions of Planets and Spacecraft|journal=Solar System Research|volume=44|issue=8–9|pages=554–566|year=2018|arxiv=1811.05191|doi=10.1134/S1063773718090050|bibcode=2018AstL...44..554P|s2cid=119404378}}</ref>
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Ceres, the only object in the asteroid belt large enough to be a [[dwarf planet]], is about 950 km in diameter, whereas Vesta, Pallas, and Hygiea have mean diameters less than 600 km.<ref name="Krasinskyetal2002">{{cite journal |author-link = Georgij A. Krasinsky |first1=G. A. |last1= Krasinsky | last2=Pitjeva | first2=E. V. | last3=Vasilyev | first3=M. V. | last4=Yagudina | first4=E. I. |bibcode=2002Icar..158...98K |title=Hidden Mass in the Asteroid Belt |journal=Icarus |volume=158 |issue=1 |pages=98–105 |date=July 2002 |doi=10.1006/icar.2002.6837 |author2-link=Elena V. Pitjeva}}</ref><ref name="Pitjeva2005">{{cite journal |last=Pitjeva |first=E. V. |author-link=Elena V. Pitjeva |title=High-Precision Ephemerides of Planets—EPM and Determination of Some Astronomical Constants |journal=Solar System Research |year=2005 |volume=39 |issue=3 |pages=176–186 |url=http://iau-comm4.jpl.nasa.gov/EPM2004.pdf |doi=10.1007/s11208-005-0033-2 |bibcode=2005SoSyR..39..176P |s2cid=120467483 |url-status=dead |archive-url=https://web.archive.org/web/20140703074335/http://iau-comm4.jpl.nasa.gov/EPM2004.pdf|archive-date=July 3, 2014 }}</ref><ref name="halfmass" /><ref name="jplsbdb">{{cite web|first=Donald K.|last=Yeomans|date = July 13, 2006|url = http://ssd.jpl.nasa.gov/sbdb.cgi|title = JPL Small-Body Database Browser|publisher = NASA JPL|access-date = 2010-09-27|archive-url= https://web.archive.org/web/20100929043420/http://ssd.jpl.nasa.gov/sbdb.cgi| archive-date= 29 September 2010 |url-status= live}}</ref> The remaining bodies range down to the size of a dust particle. The asteroid material is so thinly distributed that numerous uncrewed spacecraft have traversed it without incident.<ref>{{cite news |url=http://www.universetoday.com/110276/why-the-asteroid-belt-doesnt-threaten-spacecraft/ |title=Why the Asteroid Belt Doesn't Threaten Spacecraft | first=Brian | last=Koberlein |work=Universe Today |date=2014-03-12 |access-date=2016-01-30}}</ref> Nonetheless, collisions between large asteroids occur and can produce an [[asteroid family]], whose members have similar orbital characteristics and compositions. Individual asteroids within the belt are categorized by their [[spectrum|spectra]], with most falling into three basic groups: [[carbon]]aceous ([[C-type asteroid|C-type]]), [[silicate]] ([[S-type asteroid|S-type]]), and metal-rich ([[M-type asteroid|M-type]]).
The asteroid belt formed from the primordial [[solar nebula]] as a group of [[planetesimal]]s,<ref name=CosmosUp>{{cite web |url=http://www.cosmosup.com/how-did-the-asteroid-belt-form/ |title=How Did The Asteroid Belt Form? Was There A Planet There? |publisher=CosmosUp |date=2016-01-17 |access-date=2016-01-30 |archive-date=December 6, 2018 |archive-url=https://web.archive.org/web/20181206114730/http://www.cosmosup.com/how-did-the-asteroid-belt-form/ |url-status=dead }}</ref> the smaller precursors of the [[protoplanet]]s. Between Mars and Jupiter, however, [[gravity|gravitational]] perturbations from Jupiter disrupted their [[accretion (astrophysics)|accretion]] into a planet,<ref name=CosmosUp/><ref>{{cite web |url=http://www.space.com/16105-asteroid-belt.html |title=Asteroid Belt: Facts & Information | first=Nola Taylor | last=Redd |work=Space.com |date=2012-06-11 |access-date=2016-01-30}}</ref> imparting excess kinetic energy
==History of observation==
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[[File:Costanzo Angelini, L'astronomo Piazzi 1825 ca.jpg|thumb|upright|[[Giuseppe Piazzi]], discoverer of Ceres, the largest object in the asteroid belt: Ceres was known as a planet, but later reclassified as an asteroid and
On January 1, 1801, [[Giuseppe Piazzi]], chairman of astronomy at the [[University of Palermo]], Sicily, found a tiny moving object in an orbit with exactly the radius predicted by this pattern. He dubbed it "Ceres", after the [[Ceres (Roman mythology)|Roman goddess]] of the harvest and patron of Sicily. Piazzi initially believed it to be a comet, but its lack of a [[Coma (cometary)|coma]] suggested it was a planet.<ref name="police">{{cite journal|title=Call the police! The story behind the discovery of the asteroids|journal=[[Astronomy Now]]|issue=June 2007|pages=60–61}}</ref>
Thus, the aforementioned pattern predicted the [[Semi-major axis|semimajor axes]] of all eight planets of the time (Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, and Uranus). Concurrent with the discovery of Ceres, an informal group of 24 astronomers dubbed the "[[celestial police]]" was formed under the invitation of [[Franz Xaver von Zach]] with the express purpose of finding additional planets; they focused their search for them in the region between Mars and Jupiter, where the [[Titius–Bode law]] predicted there should be a planet.<ref>{{cite web |last1=Winterburn |first1=Emily |title=Discovering asteroid Vesta: the story of the Celestial Police |url=https://www.skyatnightmagazine.com/space-science/asteroid-vesta-discovery-celestial-police/ |website=Sky at Night Magazine |publisher=BBC |access-date=18 October 2022|date = 10 March 2021}}</ref><ref>{{cite news |last1=McWilliams |first1=Brendan |title=Fruitless search of the Celestial Police |url=https://www.irishtimes.com/news/fruitless-search-of-the-celestial-police-1.320465 |access-date=18 October 2022 |work=Irish Times |date=31 July 2001}}</ref>
About 15 months later, [[Heinrich Wilhelm Matthias Olbers|Heinrich Olbers]], a member of the celestial police, discovered a second object in the same region, Pallas. Unlike the other known planets, Ceres and Pallas remained points of light even under the highest telescope magnifications instead of resolving into discs. Apart from their rapid movement, they appeared indistinguishable from [[star]]s.<ref name="serendipity"/>
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