{{Merge|Minor planet|date=January 2008}}
{{otheruses}}
{{wiktionary|asteroid}}
[[Image:(253) mathilde.jpg|thumb|260px|right|[[253 Mathilde]], a [[C-type asteroid]].]]
'''Asteroids''', also called minor planets or planetoids, are a class of [[astronomical objects]]. The term asteroid is generally used to indicate a diverse group of small celestial bodies in the [[solar system]] that orbit around the [[Sun]]. 'Asteroid' (Greek for "star-like") is the most commonly used word in the English literature for [[minor planets]], which has been the term preferred by the [[International Astronomical Union]]; some other languages prefer ''planetoid'' (Greek: "planet-like"), because it more or less describes what they are. In late [[2006 redefinition of planet|August 2006]], the IAU introduced the term "[[small solar system body|small solar system bodies]]" (SSSB), which includes most objects thus far classified as minor planets, as well as [[comets]]. At the same time they introduced the term '[[dwarf planet]]' for the largest minor planets. This article deals specifically with the minor planets that orbit in the inner solar system (roughly up to the orbit of [[Jupiter (planet)|Jupiter]]). For information on other types of objects, such as [[comets]], [[Trans-Neptunian objects]], and [[Centaur (planetoid)|centaurs]], see [[Small solar system body]].

The first asteroid to be discovered, [[Ceres (dwarf planet)|Ceres]], is the largest asteroid known to date and is now classified as a [[dwarf planet]]. All others are currently classified as [[small solar system bodies]]. The vast majority of asteroids are found within the main [[asteroid belt]], with [[ellipse|elliptical]] orbits between those of [[Mars (planet)|Mars]] and [[Jupiter]]. It is thought that these asteroids are remnants of the [[protoplanetary disc]], and in this region the [[accretion (astronomy)|accretion]] of [[planetesimals]] into a larger planet or planets during the formative period of the solar system was prevented by large gravitational perturbations by [[Jupiter]]. Some asteroids have [[Asteroid moon|moons]] or are found in co-orbiting pairs known as [[binary asteroids|binary systems]].

==Asteroids in the solar system==

[[Image:InnerSolarSystem-en.png|250px|thumb|left|The [[Asteroid belt|Main asteroid belt]] (white) and the [[Trojan asteroids]] (green)]]
Hundreds of thousands of asteroids have been discovered within the solar system and the present rate of discovery is about 5000 per month. As of [[December 19]], [[2007]], from a total of 395,305 registered minor planets, 173,116 have orbits known well enough to be given [[astronomical naming conventions|permanent official numbers]].<ref>{{cite web|title=Minor Planet Statistics|accessdate=2007-12-19|url=http://www.cfa.harvard.edu/iau/lists/ArchiveStatistics.html}}</ref> Of these, 14,226<ref>{{cite web|title=Minor Planet Names|accessdate=2007-12-19|url=http://www.cfa.harvard.edu/iau/lists/MPNames.html}}</ref> have official names.<ref>trivia: about 650<!--- Give or take two or so, as the Schmadel and IPA lists disagree a little ---> of these names require [[diacritic]]s</ref> The lowest-numbered but unnamed minor planet is {{mpl|(3708) 1974 FV|1}};<ref>{{cite web|title=Discovery Circumstances: Numbered Minor Planets (1)-(5000)
|accessdate=2006-10-11|url=http://www.cfa.harvard.edu/iau/lists/NumberedMPs000001.html}}</ref> the highest-numbered named minor planet is [[164215 Doloreshill]].<ref>{{cite web|title=Discovery Circumstances: Numbered Minor Planets (160001)-(165000)
|accessdate=2007-11-25|url=http://www.cfa.harvard.edu/iau/lists/NumberedMPs160001.html}}</ref>
Current estimates put the total number of asteroids above 1 km in diameter in the solar system to be between 1.1 and 1.9 million.<ref>{{cite web|title=New study reveals twice as many asteroids as previously believed|accessdate=2006-03-28|url=http://www.spaceref.com/news/viewpr.html?pid=7925}}</ref> The largest asteroid in the inner solar system is [[1 Ceres]], with diameters of 975×909 km. Two other large inner solar system belt asteroids are [[2 Pallas]] and [[4 Vesta]]; both have diameters of ~500 km. Vesta is the only main belt asteroid that is sometimes visible to the naked eye (in some very rare occasions, a near-Earth asteroid may be visible without technical aid; see [[99942 Apophis]]).
[[Image:4 Vesta 1 Ceres Moon at 20 km per px.png|thumb|300px|right|Left to right: [[4 Vesta]], [[1 Ceres]], Earth's [[Moon]]]]
The mass of all the asteroids of the Main Belt is estimated to be about 3.0-3.6{{e|21}}&nbsp;kg,<ref>{{cite journal| authorlink= Georgij A. Krasinsky | first=G. A. | last= Krasinsky | coauthors=[[Elena V. Pitjeva|Pitjeva, E. V.]]; Vasilyev, M. V.; Yagudina, E. I. | url=http://adsabs.harvard.edu/abs/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><ref>{{cite conference | first=E. V. | last= Pitjeva | authorlink= Elena V. Pitjeva | title= Estimations of masses of the largest asteroids and the main asteroid belt from ranging to planets, Mars orbiters and landers | booktitle= 35th COSPAR Scientific Assembly. Held 18 - 25 July 2004, in [[Paris, France]] | pages= 2014 | year= 2004 | url= http://adsabs.harvard.edu/abs/2004cosp.meet.2014P}}</ref> or about 4% of the mass of our moon. Of this, [[Ceres (dwarf planet)|Ceres]] comprises 0.95{{e|21}}&nbsp;kg, some 32% of the total. Adding in the next three most massive asteroids, [[4 Vesta]] (9%), [[2 Pallas]] (7%), and [[10 Hygiea]] (3%), brings this figure up to 51%; while the three after that, [[511 Davida]] (1.2%), [[704 Interamnia]] (1.0%), and [[3 Juno]] (0.9%), only add another 3% to the total mass. The number of asteroids then increases rapidly as their individual masses decrease.

{{see also|list of noteworthy asteroids|list of asteroids|comets}}

==Asteroid classification==
Asteroids are commonly classified according to two criteria: the characteristics of their orbits, and features of their reflectance [[visible spectrum|spectrum]].

===Orbit groups and families===
{{main|Asteroid family|Minor planet}}

Many asteroids have been placed in groups and families based on their orbital characteristics. It is customary to name a group of asteroids after the first member of that group to be discovered. Groups are relatively loose dynamical associations, whereas families are much "tighter" and result from the catastrophic break-up of a large parent asteroid sometime in the past.<ref>V. Zappalà et al ''Asteroid Families: Search of a 12,487-Asteroid Sample Using Two Different Clustering Techniques'', Icarus, Vol. 116, p. 291 (1995.)</ref>

For a full listing of known asteroid groups and families, see [[minor planet]] and [[asteroid family]].

===Spectral classification===<!-- This section is linked from [[4769 Castalia]] -->
{{sync|Asteroid spectral types}}
[[Image:433eros.jpg|thumb|right|This picture of [[433 Eros]] shows the view looking from one end of the asteroid across the gouge on its underside and toward the opposite end. Features as small as 35 m across can be seen.]]

In 1975, an asteroid [[taxonomy|taxonomic]] system based on [[colour]], [[albedo]], and [[spectral line|spectral shape]] was developed by [[Clark R. Chapman]], [[David Morrison]], and [[Ben Zellner]].<ref>{{cite journal|author=Chapman, C. R., Morrison, D., & Zellner, B.|title=Surface properties of asteroids: A synthesis of polarimetry, radiometry, and spectrophotometry|journal=Icarus|volume=25|pages=104-130|year=1975}}</ref> These properties are thought to correspond to the composition of the asteroid's surface material. Originally, they classified only three types of asteroids, based on meteoroid types:

*[[C-type asteroid]]s - carbonaceous, 75% of known asteroids
*[[S-type asteroid]]s - silicaceous, 17% of known asteroids
*[[M-type asteroid]]s - metallic, 8% of known asteroids

This list has since been expanded to include a number of other asteroid types. The number of types continues to grow as more asteroids are studied. See [[Asteroid spectral types]] for more detail or [[:Category:Asteroid spectral classes]] for a list.

Note that the proportion of known asteroids falling into the various spectral types does not necessarily reflect the proportion of all asteroids that are of that type; some types are easier to detect than others, biasing the totals.

====Problems with spectral classification====
Originally, spectral designations were based on inferences of an asteroid's composition:<ref>{{cite book|last=McSween Jr., Harry Y.|title=Meteorites and Their Parent Planets|id=ISBN 0-521-58751-4}}</ref>

* C - [[carbonate|Carbonaceous]]
* S - [[silicate|Silicaceous]]
* M - [[Metallic]]

However, the correspondence between spectral class and composition is not always very good, and there are a variety of classifications in use. This has led to significant confusion. While asteroids of different spectral classifications are likely to be composed of different materials, there are no assurances that asteroids within the same taxonomic class are composed of similar materials.

At present, the spectral classification based on several coarse resolution spectroscopic surveys in the 1990s is still the standard. Scientists have been unable to agree on a better taxonomic system, largely due to the difficulty of obtaining detailed measurements consistently for a large sample of asteroids (e.g. finer resolution spectra, or non-spectral data such as densities would be very useful).

==Asteroid discovery==
[[Image:243 ida.jpg|thumb|right|[[243 Ida]] and its moon Dactyl, the first satellite of an asteroid to be discovered.]]

===Historical methods===
Asteroid discovery methods have drastically improved over the past two centuries.

In the last years of the 18th century, Baron [[Franz Xaver von Zach]] organized a group of 24 astronomers to search the sky for the "missing planet" predicted at about 2.8 [[Astronomical unit|AU]] from the [[Sun]] by the [[Titius-Bode law]], partly as a consequence of the discovery, by Sir [[William Herschel]] in 1781, of the planet [[Uranus (planet)|Uranus]] at the distance "predicted" by the law. This task required that hand-drawn sky charts be prepared for all stars in the [[zodiac]]al band down to an agreed-upon limit of faintness. On subsequent nights, the sky would be charted again and any moving object would, hopefully, be spotted. The expected motion of the missing planet was about 30 seconds of arc per hour, readily discernible by observers.

Ironically, the first asteroid, [[1 Ceres]], was not discovered by a member of the group, but rather by accident in 1801 by [[Giuseppe Piazzi]], director of the observatory of [[Palermo]] in [[Sicily]]. He discovered a new star-like object in [[Taurus (constellation)|Taurus]] and followed the displacement of this object during several nights. His colleague, [[Carl Friedrich Gauss]], used these observations to determine the exact distance from this unknown object to the Earth. Gauss' calculations placed the object between the planets [[Mars (planet)|Mars]] and [[Jupiter (planet)|Jupiter]]. Piazzi named it after [[Ceres (mythology)|Ceres]], the Roman goddess of agriculture.

Three other asteroids ([[2 Pallas]], [[3 Juno]], and [[4 Vesta]]) were discovered over the next few years, with Vesta found in 1807. After eight more years of fruitless searches, most astronomers assumed that there were no more and abandoned any further searches.

However, [[Karl Ludwig Hencke]] persisted, and began searching for more asteroids in 1830. Fifteen years later, he found [[5 Astraea]], the first new asteroid in 38 years. He also found [[6 Hebe]] less than two years later. After this, other astronomers joined in the search and at least one new asteroid was discovered every year after that (except the wartime year 1945). Notable asteroid hunters of this early era were [[John Russell Hind|J. R. Hind]], [[Annibale de Gasparis]], [[Karl Theodor Robert Luther|Robert Luther]], [[Hermann Mayer Salomon Goldschmidt|H. M. S. Goldschmidt]], [[Jean Chacornac]], [[James Ferguson (astronomer)|James Ferguson]], [[Norman Robert Pogson]], [[Ernst Wilhelm Leberecht Tempel|E. W. Tempel]], [[James Craig Watson|J. C. Watson]], [[Christian Heinrich Friedrich Peters|C. H. F. Peters]], [[Alphonse Louis Nicolas Borrelly|A. Borrelly]], [[Johann Palisa|J. Palisa]], the [[Paul Henry and Prosper Henry|Henry brothers]] and [[Auguste Charlois]].

In 1891, however, [[Maximilian Franz Joseph Cornelius Wolf|Max Wolf]] pioneered the use of [[astrophotography]] to detect asteroids, which appeared as short streaks on long-exposure photographic plates. This drastically increased the rate of detection compared with previous visual methods: Wolf alone discovered 248 asteroids, beginning with [[323 Brucia]], whereas only slightly more than 300 had been discovered up to that point. Still, a century later, only a few thousand asteroids were identified, numbered and named. It was known that there were many more, but most astronomers did not bother with them, calling them "vermin of the skies".

===Manual methods of the 1900s and modern reporting===
Until 1998, asteroids were discovered by a four-step process. First, a region of the sky was [[photograph]]ed by a wide-field [[telescope]] (usually an [[Astrograph]]). Pairs of photographs were taken, typically one hour apart. Multiple pairs could be taken over a series of days. Second, the two [[film]]s of the same region were viewed under a [[stereoscope]]. Any body in orbit around the Sun would move slightly between the pair of films. Under the stereoscope, the image of the body would appear to float slightly above the background of stars. Third, once a moving body was identified, its location would be measured precisely using a digitizing microscope. The location would be measured relative to known star locations.<ref>{{cite web|title=Carolyn Shoemaker|accessdate=2003-06-23|url=http://astrogeology.usgs.gov/About/People/CarolynShoemaker/}}</ref>

These first three steps do not constitute asteroid discovery: the observer has only found an apparition, which gets a [[provisional designation in astronomy|provisional designation]], made up of the year of discovery, a letter representing the week of discovery, and finally a letter and a number indicating the discovery's sequential number (example: {{mp|1998 FJ|74}}).

The final step of discovery is to send the locations and time of observations to [[Brian Marsden]] of the [[Minor Planet Center]]. Dr. Marsden has computer programs that compute whether an apparition ties together previous apparitions into a single orbit. If so, the object gets a number. The observer of the first apparition with a calculated orbit is declared the discoverer, and he gets the honor of naming the asteroid (subject to the approval of the [[International Astronomical Union]]) once it is numbered.

===Computerized methods ===
[[Image:Asteroid 2004 FH.gif|framed|right|
[[2004 FH]] is the centre dot being followed by the sequence; the object that flashes by during the clip is an [[satellite|artificial satellite]].]]
There is increasing interest in identifying asteroids whose orbits cross [[Earth]]'s, and that could, given enough time, collide with Earth (see [[Earth-crosser asteroid]]s). The three most important groups of [[near-Earth asteroid]]s are the [[Apollo asteroid|Apollos]], [[Amor asteroid|Amors]], and [[Aten asteroid|Atens]]. Various [[asteroid deflection strategies]] have been proposed, as early as the 1960s<!--- ''Project Icarus'' --->.

The [[near-Earth object|near-Earth]] asteroid [[433 Eros]] had been discovered as long ago as [[1898]], and the [[1930s]] brought a flurry of similar objects. In order of discovery, these were: [[1221 Amor]], [[1862 Apollo]], [[2101 Adonis]], and finally [[69230 Hermes]], which approached within 0.005 [[Astronomical Unit|AU]] of the [[Earth]] in [[1937]]. Astronomers began to realize the possibilities of Earth impact.

Two events in later decades increased the level of alarm: the increasing acceptance of [[Walter Alvarez]]' hypothesis that an [[impact event]] resulted in the [[Cretaceous–Tertiary extinction event|Cretaceous–Tertiary extinction]], and the [[1994]] observation of [[Comet Shoemaker-Levy 9]] crashing into [[Jupiter (planet)|Jupiter]]. The U.S. military also declassified the information that its military satellites, built to detect nuclear explosions, had detected hundreds of upper-atmosphere impacts by objects ranging from one to 10 metres across.

All of these considerations helped spur the launch of highly efficient automated systems that consist of Charge-Coupled Device ([[Charge-coupled device|CCD]]) cameras and computers directly connected to telescopes. Since 1998, a large majority of the asteroids have been discovered by such automated systems. A list of teams using such automated systems includes:<ref>{{cite web|title=Near Earth Object Program|accessdate=2004-06-23|url=http://neo.jpl.nasa.gov/programs}}</ref>

* The [[Lincoln Near-Earth Asteroid Research]] (LINEAR) team
* The [[Near-Earth Asteroid Tracking]] (NEAT) team
* [[Spacewatch]]
* The [[LONEOS|Lowell Observatory Near-Earth-Object Search]] (LONEOS) team
* The [[Catalina Sky Survey]] (CSS)
* The [[Campo Imperatore Near-Earth Objects Survey]] (CINEOS) team
* The [[Japanese Spaceguard Association]]
* The [[Asiago-DLR Asteroid Survey]] (ADAS)

The LINEAR system alone has discovered 84,764 asteroids, as of [[August 28]], [[2007]].<ref>{{cite web|title=Minor Planet Discover Sites|accessdate=2007-08-31|url=http://www.cfa.harvard.edu/iau/lists/MPDiscSites.html}}</ref> Between all of the automated systems, 4711 near-Earth asteroids have been discovered<ref>{{cite web|title=Unusual Minor Planets|accessdate=2007-08-31|url=http://www.cfa.harvard.edu/iau/lists/Unusual.html}}<!--- using the "close approach" quote ---></ref> including over 600 more than 1 km in diameter.

==Naming asteroids==
===Overview: naming conventions===
A newly discovered asteroid is given a [[Provisional designation in astronomy|provisional designation]] consisting of the year of discovery and an alphanumeric code (such as {{mpl|2002 AT|4}}). Once its orbit has been confirmed, it is given a number, and later may also be given a name (e.g. [[433 Eros]]). The formal naming convention uses parentheses around the number (e.g. ''(433) Eros''), but dropping the parentheses is quite common. Informally, it is common to drop the number altogether, or to drop it after the first mention when a name is repeated in running text.

Asteroids that have been given a number but not a name keep their provisional designation, ''e.g''. [[(29075) 1950 DA]]. As modern discovery techniques are discovering vast numbers of new asteroids, they are increasingly being left unnamed. The first asteroid to be left unnamed was for a long time [[(3360) 1981 VA]], now [[3360 Syrinx]]; as of November 2006, this distinction is now held by {{mpl|(3708) 1974 FV|1}}. On rare occasions, a small body's [[Provisional designation in astronomy|provisional designation]] may become used as a name in itself: the still unnamed {{mpl|(15760) 1992 QB|1}} gave its name to a group of [[Kuiper belt]] objects which became known as [[cubewano]]s.

===Numbering asteroids===
Asteroids are awarded with an official number once their orbits are confirmed. With the increasing rapidity of asteroid discovery, asteroids are currently being awarded six-figure numbers. The switch from five figures to six figures arrived with the publication of the [[Minor Planet Circular]] (MPC) of [[October 19]], [[2005]], which saw the highest numbered asteroid jump from 99947 to 118161. This change caused a small "[[Y2k]]"-like crisis for various automated data services, since only five digits were allowed in most data formats for the asteroid number. Most services have now widened the asteroid number field. For those which did not, the problem has been addressed in some cases by having the leftmost digit (the ten-thousands place) use the alphabet as a digit extension. A=10, B=11,…, Z=35, a=36,…, z=61. A high number such as 120437 is thus cross-referenced as C0437 on some lists.

===Sources for names===
{{main|Meanings of asteroid names}}

The first few asteroids were named after figures from [[Graeco-Roman mythology]], but as such names started to run out, others were used &mdash;famous people, literary characters, the names of the discoverer's wives, children, and even television characters.

The first asteroid to be given a non-mythological name was [[20 Massalia]], named after the city of [[Marseille]]s. For some time only female (or feminized) names were used; [[Alexander von Humboldt]] was the first man to have an asteroid named after him, but his name was feminized to [[54 Alexandra]]. This unspoken tradition lasted until [[334 Chicago]] was named; even then, oddly feminised names show up in the list for years afterward.

As the number of asteroids began to run into the hundreds, and eventually the thousands, discoverers began to give them increasingly frivolous names. The first hints of this were [[482 Petrina]] and [[483 Seppina]], named after the discoverer's pet dogs. However, there was little controversy about this until 1971, upon the naming of [[2309 Mr. Spock]] (which was not even named after the ''[[Star Trek]]'' character, but after the discoverer's cat who supposedly bore a resemblance to him). Although the [[International Astronomical Union|IAU]] subsequently banned pet names as sources, eccentric asteroid names are still being proposed and accepted, such as [[4321 Zero]], [[6042 Cheshirecat]], [[9007 James Bond]], [[13579 Allodd]], [[24680 Alleven]], [[128036 Rafaelnadal]] or [[26858 Misterrogers]].

===Special naming rules===
Asteroid naming is not always a free-for-all: there are some types of asteroid for which rules have developed about the sources of names. For instance [[Centaur (planetoid)|Centaurs]] (asteroids orbiting between Saturn and Neptune) are all named after mythological [[centaur]]s, [[Trojan asteroid|Trojans]] after heroes from the [[Trojan War]], and [[trans-Neptunian objects]] after underworld spirits.

Another well-established rule is that comets are named after their discoverer(s), whereas asteroids are not. One way to "circumvent" this rule has been for astronomers to exchange the courtesy of naming their discoveries after each other. A particular exception to this rule is [[96747 Crespodasilva]], which was named after its discoverer, [[Lucy d'Escoffier Crespo da Silva]], because she died shortly after the discovery, at age 22.<ref>{{cite web|title=Citation from MPC 55988|accessdate=2006-06-05|url=http://scully.cfa.harvard.edu/~cgi/ShowCitation.COM?num=96747}}</ref><ref>{{cite web|title=MIT News Office: Lucy Crespo da Silva, 22, a senior, dies in fall|accessdate=2006-06-05|url=http://web.mit.edu/newsoffice/2000/dasilva.html}}</ref> A few objects are also cross-listed as both comets and asteroids, such as [[4015 Wilson-Harrington]] = [[107P/Wilson-Harrington]].

===Asteroid symbols===
The first few asteroids discovered were assigned symbols like the ones traditionally used to designate Earth, the Moon, the Sun and planets. The symbols quickly became ungainly, hard to draw and recognise. By the end of 1851 there were 15 known asteroids, each (except one) with its own symbol(s).<ref>{{cite journal| last=Gould| first=B. A.| authorlink=Benjamin Apthorp Gould | year=1852| title= On the Symbolic Notation of the Asteroids| journal= Astronomical Journal| volume= 2| pages= 80}}</ref>

{| class="wikitable"
|- align="center" style="align:center; background:#ffc0c0"
! Asteroid || Symbol
|-
| [[Ceres (dwarf planet)|Ceres]] || [[Image:Ceres symbol.svg|30x20px|Old planetary symbol of Ceres]] [[Image:Ceres2.svg|30x20px|Variant symbol of Ceres]] [[Image:Ceres symbol.svg|30x20px|Sickle variant symbol of Ceres]] [[Image:Ceres3.svg|30x20px|Other sickle variant symbol of Ceres]]
|-
| [[2 Pallas]] || [[Image:2Pallas symbol.svg|30x20px|Old symbol of Pallas]] [[Image:2 Pallas.svg|30x20px|Variant symbol of Pallas]]
|-
| [[3 Juno]] || [[Image:Juno symbol.svg|30x20px|Old symbol of Juno]] [[Image:3 Juno (1).png|30x20px|Other symbol of Juno]] [[Image:Symbol 3.jpg|30x20px]]
|-
| [[4 Vesta]] || [[Image:4 Vesta (0).svg|30x20px|Old symbol of Vesta]] [[Image:Simbolo di Vesta.svg|30x20px|Old planetary symbol of Vesta]] [[Image:Vesta symbol.svg|30x20px|Modern astrological symbol of Vesta]][[Image:4 Vesta Unsimplified Symbol.svg|30x20px]]
|-
| [[5 Astraea]] || [[Image:5 Astraea Symbol.svg|30x20px]]
|-
| [[6 Hebe]] || [[Image:6 Hebe Astronomical Symbol.svg|30x20px]]
|-
| [[7 Iris]] || [[Image:7 Iris Astronomical Symbol.svg|30x20px]]
|-
| [[8 Flora]] || [[Image:8 Flora Astronomical Symbol.svg|30x20px]]
|-
| [[9 Metis]] || [[Image:9 Metis symbol.svg|30x20px]]
|-
| [[10 Hygiea]] || [[Image:10 Hygiea Astronomical Symbol.svg|30x20px]]
|-
| [[11 Parthenope]] || [[Image:11 Parthenope symbol.svg|30x20px]]
|-
| [[12 Victoria]] || [[Image:12 Victoria symbol.svg|30x20px]]
|-
| [[13 Egeria]] || <small>Never assigned.
|-
| [[14 Irene]] || <small>"A dove carrying an olive-branch, with a star on its head," never drawn.</small><ref name="hilton">{{cite web|title=When Did the Asteroids Become Minor Planets|authorlink=James L. Hilton| first=James L.| last=Hilton |accessdate=2006-03-26|url=http://aa.usno.navy.mil/faq/docs/minorplanets.php| date=September 17, 2001}}</ref>
|-
| [[15 Eunomia]] || [[Image:15 Eunomia symbol.svg|30x20px]]
|-
| [[28 Bellona]] || [[Image:28 Bellona symbol.svg|30x20px]]
|-
| [[35 Leukothea]] || [[Image:35 Leukothea symbol.png|30x20px]]
|-
| [[37 Fides]] || [[Image:37 Fides symbol.svg|30x20px]]
|}
[[Johann Franz Encke]] made a major change in the ''Berliner Astronomisches Jahrbuch'' (BAJ, "Berlin Astronomical Yearbook") for 1854. He introduced encircled numbers instead of symbols, although his numbering began with [[5 Astraea|Astraea]], the first four asteroids continuing to be denoted by their traditional symbols. This symbolic innovation was adopted very quickly by the astronomical community. The following year (1855), Astraea's number was bumped up to 5, but Ceres through Vesta would be listed by their numbers only in the 1867 edition. A few more asteroids ([[28 Bellona]],<ref>{{cite journal| last=Encke| first= J. F.| year= 1854| title=Beobachtung der Bellona, nebst Nachrichten über die Bilker Sternwarte| journal= Astronomische Nachrichten| volume= 38| pages=143}}</ref> [[35 Leukothea]],<ref>{{cite journal| last=Rümker| first= G.| coauthors= Peters, C. A. F.| year= 1855| title=Name und Zeichen des von Herrn R. Luther zu Bilk am 19. April entdeckten Planeten| journal= Astronomische Nachrichten| volume= 40| pages= 373}}</ref> and [[37 Fides]]<ref>{{cite journal| last=Luther| first= R.| year= 1856| title=Schreiben des Herrn Dr. R. Luther, Directors der Sternwarte zu Bilk, an den Herausgeber| journal= Astronomische Nachrichten| volume= 42| pages= 107}}</ref>) would be given symbols as well as using the numbering scheme. The circle would become a pair of parentheses, and the parentheses sometimes omitted altogether over the next few decades.<ref name="hilton">{{cite web|title=When Did the Asteroids Become Minor Planets|authorlink=James L. Hilton| first=James L.| last=Hilton |accessdate=2006-03-26|url=http://aa.usno.navy.mil/hilton/AsteroidHistory/minorplanets.html| date=September 17, 2001}}</ref>

==Asteroid exploration==
Until the age of [[space travel]], asteroids were merely pinpricks of light in even the largest telescopes and their shapes and terrain remained a mystery.

The first [[close-up]] photographs of asteroid-like objects were taken in 1971 when the [[Mariner 9]] probe imaged [[Phobos (moon)|Phobos]] and [[Deimos (moon)|Deimos]], the two small moons of [[Mars (planet)|Mars]], which are probably captured asteroids. These images revealed the irregular, potato-like shapes of most asteroids, as did subsequent images from the [[Voyager program|Voyager]] probes of the small moons of the [[gas giant]]s.

[[Image:951 Gaspra.jpg|thumb|right|[[951 Gaspra]], the first asteroid to be imaged in close up.]]
The first true asteroid to be photographed in close-up was [[951 Gaspra]] in 1991, followed in 1993 by [[243 Ida]] and its moon [[Dactyl (asteroid)|Dactyl]], all of which were imaged by the [[Galileo spacecraft|Galileo probe]] ''en route'' to [[Jupiter (planet)|Jupiter]].

The first dedicated asteroid probe was [[NEAR Shoemaker]], which photographed [[253 Mathilde]] in 1997, before entering into orbit around [[433 Eros]], finally landing on its surface in 2001.

Other asteroids briefly visited by spacecraft ''en route'' to other destinations include [[9969 Braille]] (by [[Deep Space 1]] in 1999), and [[5535 Annefrank]] (by [[Stardust (spacecraft)|Stardust]] in 2002).

In September 2005, the Japanese [[Hayabusa]] probe started studying [[25143 Itokawa]] in detail and may return samples of its surface to earth. The Hayabusa mission has been plagued with difficulties, including the failure of two of its three control wheels, rendering it difficult to maintain its orientation to the sun to collect solar energy. Following that, the next asteroid encounters will involve the European [[Rosetta space probe|Rosetta probe]] (launched in 2004), which will study [[2867 Šteins]] and [[21 Lutetia]] in 2008 and 2010.

In September 2007 [[NASA]] launched the [[Dawn Mission]], which will orbit [[1 Ceres]] and [[4 Vesta]] in 2011-2015, with its mission possibly then extended to [[2 Pallas]].

It has been suggested that asteroids might be used in the future as a source of materials which may be rare or exhausted on earth ([[asteroid mining]]), or materials for constructing [[space habitats]] (see [[Colonization of the asteroids]]). Materials that are heavy and expensive to launch from earth may someday be mined from asteroids and used for [[space manufacturing]] and construction.

==Asteroids in fiction==
{{main|Asteroids in fiction}}

Asteroids and asteroid belts are a staple of science fiction stories. Asteroids play several potential roles in science fiction: as places which human beings might colonize; as resources for extracting minerals; as a hazard encountered by spaceships travelling between two other points; and as a threat to life on Earth due to potential impacts.

==References==
<div class="references-small"><references/></div>

==See also==
<div class="references-small" style="-moz-column-count:4; column-count:4;">
* [[Asteroid belt]]
* [[Asteroid mining]]
* [[BOOTES]] (Burst Observer and Optical Transient Exploring System)
* [[:Category:Asteroid groups and families|Category:Asteroid groups and families]]
* [[:Category:Asteroids|Category:Asteroids]]
* [[:Category:Binary asteroids|Category:Binary asteroids]]
* [[Centaur (planetoid)]]
* [[Dwarf planet]]
* [[Impact event]]
* [[List of asteroids]]
* [[List of asteroids named after important people]]
* [[List of asteroids named after places]]
* [[List of noteworthy asteroids]]
* [[Meanings of asteroid names]]
* [[Minor planet]]
* [[Minor Planet Center]]
* [[Near-Earth object]]
* [[Pronunciation of asteroid names]]
* [[Asteroid deflection strategies]]
</div>

==External links==
{{Commonscat|Asteroids}}
* [http://www.cfa.harvard.edu/iau/lists/MPNames.html Alphabetical list of minor planet names (ASCII)] (Minor Planet Center)
* [http://neat.jpl.nasa.gov/ Near Earth Asteroid Tracking (NEAT)]
* [http://solarsystem.nasa.gov/planets/profile.cfm?Object=Asteroids Asteroids Page] at [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [http://aa.usno.navy.mil/faq/docs/minorplanets.php When Did the Asteroids Become Minor Planets?]
*[http://www.colorado.edu/physics/2000/applets/satellites.html Asteroid Simulator with Moon and Earth]
* [http://www.newscientistspace.com/channel/solar-system/comets-asteroids Everything you wanted to know about comets and asteroids] — Provided by ''[[New Scientist]]''.
* [http://www.ipa.nw.ru/PAGE/DEPFUND/LSBSS/englenam.htm Alphabetical and numerical lists of minor planet names (Unicode)] (Institute of Applied Astronomy)
* [http://www.armageddononline.org/content/view/46/67/ Known Asteroid Impacts & Their Effects]
* [http://www.fair-society.org Future Asteroid Interception Research]
* [http://newton.dm.unipi.it/cgi-bin/neodys/neoibo Near Earth Objects Dynamic Site]
* [http://hamilton.dm.unipi.it/cgi-bin/astdys/astibo Asteroids Dynamic Site] Up-to date [[osculating orbit|osculating]] [[orbital elements]] and [[proper orbital elements]]
* [http://quasar.ipa.nw.ru/PAGE/DEPFUND/LSBSS/statmpn.htm Asteroid naming statistics]
* [http://www.spaceguarduk.com/ Spaceguard UK]
*[http://www.astrosurf.com/aude/map/us/AstFamilies2004-05-20.htm Large amount of information on asteroid groups collected by Gérard Faure], translation Richard Miles.
* [http://michaelgr.wordpress.com/2007/04/14/near-earth-objects-are-we-whistling-in-the-dark/ Near Earth Objects and Asteroids: Are We Whistling in the Dark?]

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[[als:Asteroid]]
[[ar:كويكب]]
[[an:Asteroide]]
[[ast:Asteroide]]
[[zh-min-nan:Sió-he̍k-chheⁿ]]
[[be-x-old:Астэроід]]
[[bs:Asteroidi]]
[[bg:Астероид]]
[[ca:Asteroide]]
[[cv:Астероид]]
[[cs:Asteroid]]
[[da:Asteroide]]
[[de:Asteroid]]
[[et:Asteroid]]
[[el:Αστεροειδής]]
[[es:Asteroide]]
[[eo:Asteroido]]
[[eu:Asteroide]]
[[fa:سیارک]]
[[fr:Astéroïde]]
[[gl:Asteroide]]
[[ko:소행성]]
[[hr:Asteroidi]]
[[io:Asteroido-zono]]
[[id:Asteroid]]
[[it:Asteroide]]
[[he:אסטרואיד]]
[[jv:Asteroid]]
[[pam:Asteroid]]
[[kn:ಕ್ಷುದ್ರ ಗ್ರಹ]]
[[ka:მცირე ცთომილები]]
[[la:Asteroides]]
[[lv:Asteroīds]]
[[lb:Asteroid]]
[[lt:Asteroidas]]
[[li:Planetoïed]]
[[hu:Kisbolygó]]
[[mk:Астероид]]
[[mt:Asterojde]]
[[ms:Asteroid]]
[[nl:Planetoïde]]
[[ja:小惑星]]
[[no:Asteroide]]
[[nn:Asteroide]]
[[oc:Asteroïde]]
[[nds:Asteroid]]
[[pl:Planetoida]]
[[pt:Asteróide]]
[[ksh:Asteroid]]
[[ro:Asteroid]]
[[qu:Puriq quyllurcha]]
[[ru:Астероид]]
[[scn:Astiròidi]]
[[simple:Asteroid]]
[[sk:Asteroid]]
[[sl:Asteroid]]
[[sr:Астероид]]
[[sh:Asteroid]]
[[su:Astéroid]]
[[fi:Asteroidi]]
[[sv:Asteroid]]
[[tl:Asteroyd]]
[[ta:சிறுகோள்]]
[[tt:Asteroidlar]]
[[th:ดาวเคราะห์น้อย]]
[[vi:Tiểu hành tinh]]
[[tr:Asteroit]]
[[uk:Астероїд]]
[[ur:سیارچے]]
[[vec:Asteroide]]
[[yi:אסטראוד]]
[[zh:小行星]]