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Asteroids are minor planets, especially those of the inner Solar System. The larger ones have also been called planetoids. These terms have historically been applied to any astronomical object orbiting the Sun
Sun
that did not show the disc of a planet and was not observed to have the characteristics of an active comet. As minor planets in the outer Solar System
Solar System
were discovered and found to have volatile-based surfaces that resemble those of comets, they were often distinguished from asteroids of the asteroid belt.[1] In this article, the term "asteroid" refers to the minor planets of the inner Solar System including those co-orbital with Jupiter. There are millions of asteroids, many thought to be the shattered remnants of planetesimals, bodies within the young Sun's solar nebula that never grew large enough to become planets.[2] The large majority of known asteroids orbit in the asteroid belt between the orbits of Mars
Mars
and Jupiter, or are co-orbital with Jupiter
Jupiter
(the Jupiter trojans). However, other orbital families exist with significant populations, including the near- Earth
Earth
objects. Individual asteroids are classified by their characteristic spectra, with the majority falling into three main groups: C-type, M-type, and S-type. These were named after and are generally identified with carbon-rich, metallic, and silicate (stony) compositions, respectively. The size of asteroids varies greatly, the largest is almost 1,000 km (625 mi) across. Asteroids are differentiated from comets and meteoroids. In the case of comets, the difference is one of composition: while asteroids are mainly composed of mineral and rock, comets are composed of dust and ice. In addition, asteroids formed closer to the sun, preventing the development of the aforementioned cometary ice.[3] The difference between asteroids and meteoroids is mainly one of size: meteoroids have a diameter of less than one meter, whereas asteroids have a diameter of greater than one meter.[4] Finally, meteoroids can be composed of either cometary or asteroidal materials.[5] Only one asteroid, 4 Vesta, which has a relatively reflective surface, is normally visible to the naked eye, and this only in very dark skies when it is favorably positioned. Rarely, small asteroids passing close to Earth
Earth
may be visible to the naked eye for a short time.[6] As of October 2017[update], the Minor Planet
Planet
Center had data on almost 745,000 objects in the inner and outer Solar System, of which almost 504,000 had enough information to be given numbered designations.[7] The United Nations
United Nations
declared June 30 as International Asteroid Day
Asteroid Day
to educate the public about asteroids. The date of International Asteroid Day commemorates the anniversary of the Tunguska asteroid impact over Siberia, Russian Federation, on 30 June 1908.[8][9]

Contents

1 Discovery

1.1 Historical methods 1.2 Manual methods of the 1900s and modern reporting 1.3 Computerized methods

2 Terminology 3 Formation 4 Distribution within the Solar System

4.1 Asteroid
Asteroid
belt 4.2 Trojans 4.3 Near- Earth
Earth
asteroids

5 Characteristics

5.1 Size distribution

5.1.1 Largest asteroids

5.2 Rotation 5.3 Composition 5.4 Surface features 5.5 Color

6 Classification

6.1 Orbital classification

6.1.1 Quasi-satellites and horseshoe objects

6.2 Spectral classification

6.2.1 Problems

7 Naming

7.1 Symbols

8 Exploration

8.1 Planned and future missions

9 Fiction 10 Gallery 11 See also 12 Notes 13 References 14 External links

Discovery[edit]

Sizes of the first ten asteroids to be discovered, compared to the Moon

243 Ida
243 Ida
and its moon Dactyl. Dactyl is the first satellite of an asteroid to be discovered.

The first asteroid to be discovered, Ceres, was originally considered to be a new planet.[note 1] This was followed by the discovery of other similar bodies, which, with the equipment of the time, appeared to be points of light, like stars, showing little or no planetary disc, though readily distinguishable from stars due to their apparent motions. This prompted the astronomer Sir William Herschel
William Herschel
to propose the term "asteroid",[note 2] coined in Greek as ἀστεροειδής, or asteroeidēs, meaning 'star-like, star-shaped', and derived from the Ancient Greek ἀστήρ astēr 'star, planet'. In the early second half of the nineteenth century, the terms "asteroid" and "planet" (not always qualified as "minor") were still used interchangeably. [note 3] Historical methods[edit]

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Asteroid
Asteroid
discovery methods have dramatically 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 AU from the Sun
Sun
by the Titius-Bode law, partly because of the discovery, by Sir William Herschel
William Herschel
in 1781, of the planet Uranus
Uranus
at the distance predicted by the law. This task required that hand-drawn sky charts be prepared for all stars in the zodiacal 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.

First asteroid image (Ceres and Vesta) from Mars
Mars
– viewed by Curiosity (20 April 2014).

The first object, 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
Palermo
in Sicily. He discovered a new star-like object in Taurus and followed the displacement of this object during several nights. Later that year, Carl Friedrich Gauss
Carl Friedrich Gauss
used these observations to calculate the orbit of this unknown object, which was found to be between the planets Mars
Mars
and Jupiter. Piazzi named it after 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.[citation needed] However, Karl Ludwig Hencke
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
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 J. R. Hind, Annibale de Gasparis, Robert Luther, H. M. S. Goldschmidt, Jean Chacornac, James Ferguson, Norman Robert Pogson, E. W. Tempel, J. C. Watson, C. H. F. Peters, A. Borrelly, J. Palisa, the Henry brothers and Auguste Charlois. In 1891, Max Wolf pioneered the use of astrophotography to detect asteroids, which appeared as short streaks on long-exposure photographic plates. This dramatically increased the rate of detection compared with earlier visual methods: Wolf alone discovered 248 asteroids, beginning with 323 Brucia, whereas only slightly more than 300 had been discovered up to that point. It was known that there were many more, but most astronomers did not bother with them, calling them "vermin of the skies",[13] a phrase variously attributed to Eduard Suess[14] and Edmund Weiss.[15] Even a century later, only a few thousand asteroids were identified, numbered and named. Manual methods of the 1900s and modern reporting[edit] Until 1998, asteroids were discovered by a four-step process. First, a region of the sky was photographed by a wide-field telescope, or astrograph. Pairs of photographs were taken, typically one hour apart. Multiple pairs could be taken over a series of days. Second, the two films or plates of the same region were viewed under a stereoscope. Any body in orbit around the Sun
Sun
would move slightly between the pair of films. Under the stereoscope, the image of the body would seem 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.[16] These first three steps do not constitute asteroid discovery: the observer has only found an apparition, which gets a provisional designation, made up of the year of discovery, a letter representing the half-month of discovery, and finally a letter and a number indicating the discovery's sequential number (example: 1998 FJ74). The last step of discovery is to send the locations and time of observations to the Minor Planet
Planet
Center, where computer programs determine whether an apparition ties together earlier apparitions into a single orbit. If so, the object receives a catalogue number and the observer of the first apparition with a calculated orbit is declared the discoverer, and granted the honor of naming the object subject to the approval of the International Astronomical Union. Computerized methods[edit]

2004 FH
2004 FH
is the center dot being followed by the sequence; the object that flashes by during the clip is an 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 asteroids). The three most important groups of near- Earth
Earth
asteroids are the Apollos, Amors, and Atens. Various asteroid deflection strategies have been proposed, as early as the 1960s. The near- Earth
Earth
asteroid 433 Eros
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 AU of Earth
Earth
in 1937. Astronomers began to realize the possibilities of Earth
Earth
impact. Two events in later decades increased the alarm: the increasing acceptance of the Alvarez hypothesis
Alvarez hypothesis
that an impact event resulted in the Cretaceous–Paleogene extinction, and the 1994 observation of Comet
Comet
Shoemaker-Levy 9 crashing into 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 ten meters across. All these considerations helped spur the launch of highly efficient surveys that consist of charge-coupled device (CCD) cameras and computers directly connected to telescopes. As of 2011[update], it was estimated that 89% to 96% of near- Earth
Earth
asteroids one kilometer or larger in diameter had been discovered.[17] A list of teams using such systems includes:[18]

Lincoln Near- Earth
Earth
Asteroid
Asteroid
Research (LINEAR) Near- Earth
Earth
Asteroid
Asteroid
Tracking (NEAT) Spacewatch Lowell Observatory Near-Earth-Object Search
Lowell Observatory Near-Earth-Object Search
(LONEOS) Catalina Sky Survey
Catalina Sky Survey
(CSS) Campo Imperatore Near- Earth
Earth
Object Survey (CINEOS) Japanese Spaceguard
Spaceguard
Association Asiago-DLR Asteroid Survey (ADAS) Pan-STARRS

As of 20 September 2013[update], the LINEAR system alone has discovered 138,393 asteroids.[19] Among all the surveys, 4711 near- Earth
Earth
asteroids have been discovered[20] including over 600 more than 1 km (0.6 mi) in diameter. Terminology[edit]

Euler diagram
Euler diagram
showing the types of bodies in the Solar System. (see Small Solar System
Solar System
body)

A composite image, to scale, of the asteroids that have been imaged at high resolution except Ceres. As of 2011[update], they are, from largest to smallest: 4 Vesta, 21 Lutetia, 253 Mathilde, 243 Ida
243 Ida
and its moon Dactyl, 433 Eros, 951 Gaspra, 2867 Šteins, 25143 Itokawa.

The largest asteroid in the previous image, Vesta (left), with Ceres (center) and the Moon
Moon
(right) shown to scale.

Traditionally, small bodies orbiting the Sun
Sun
were classified as comets, asteroids, or meteoroids, with anything smaller than ten meters across being called a meteoroid. Beech and Steel's 1995 paper proposed a meteoroid definition including size limits.[21][22] The term "asteroid", from the Greek word for "star-like", never had a formal definition, with the broader term minor planet being preferred by the International Astronomical Union. However, following the discovery of asteroids below ten meters in size, Rubin and Grossman's 2010 paper revised the previous definition of meteoroid to objects between 10 µm and 1 meter in size in order to maintain the distinction between asteroids and meteoroids.[4] The smallest asteroids discovered (based on absolute magnitude H) are 2008 TS26 with H = 33.2 and 2011 CQ1 with H = 32.1 both with an estimated size of about 1 meter.[23] In 2006, the term "small Solar System
Solar System
body" was also introduced to cover both most minor planets and comets.[note 4][24] Other languages prefer "planetoid" (Greek for "planet-like"), and this term is occasionally used in English especially for larger minor planets such as the dwarf planets as well as an alternative for asteroids since they are not star-like.[25] The word "planetesimal" has a similar meaning, but refers specifically to the small building blocks of the planets that existed when the Solar System
Solar System
was forming. The term "planetule" was coined by the geologist William Daniel Conybeare
William Daniel Conybeare
to describe minor planets,[26] but is not in common use. The three largest objects in the asteroid belt, Ceres, Pallas, and Vesta, grew to the stage of protoplanets. Ceres is a dwarf planet, the only one in the inner Solar System. When found, asteroids were seen as a class of objects distinct from comets, and there was no unified term for the two until "small Solar System body" was coined in 2006. The main difference between an asteroid and a comet is that a comet shows a coma due to sublimation of near surface ices by solar radiation. A few objects have ended up being dual-listed because they were first classified as minor planets but later showed evidence of cometary activity. Conversely, some (perhaps all) comets are eventually depleted of their surface volatile ices and become asteroid-like. A further distinction is that comets typically have more eccentric orbits than most asteroids; most "asteroids" with notably eccentric orbits are probably dormant or extinct comets.[27] For almost two centuries, from the discovery of Ceres in 1801 until the discovery of the first centaur, Chiron in 1977, all known asteroids spent most of their time at or within the orbit of Jupiter, though a few such as Hidalgo ventured far beyond Jupiter
Jupiter
for part of their orbit. When astronomers started finding more small bodies that permanently resided further out than Jupiter, now called centaurs, they numbered them among the traditional asteroids, though there was debate over whether they should be considered asteroids or as a new type of object. Then, when the first trans-Neptunian object (other than Pluto), Albion, was discovered in 1992, and especially when large numbers of similar objects started turning up, new terms were invented to sidestep the issue: Kuiper-belt object, trans-Neptunian object, scattered-disc object, and so on. These inhabit the cold outer reaches of the Solar System
Solar System
where ices remain solid and comet-like bodies are not expected to exhibit much cometary activity; if centaurs or trans-Neptunian objects were to venture close to the Sun, their volatile ices would sublimate, and traditional approaches would classify them as comets and not asteroids. The innermost of these are the Kuiper-belt objects, called "objects" partly to avoid the need to classify them as asteroids or comets.[28] They are thought to be predominantly comet-like in composition, though some may be more akin to asteroids.[29] Furthermore, most do not have the highly eccentric orbits associated with comets, and the ones so far discovered are larger than traditional comet nuclei. (The much more distant Oort cloud
Oort cloud
is hypothesized to be the main reservoir of dormant comets.) Other recent observations, such as the analysis of the cometary dust collected by the Stardust probe, are increasingly blurring the distinction between comets and asteroids,[30] suggesting "a continuum between asteroids and comets" rather than a sharp dividing line.[31] The minor planets beyond Jupiter's orbit are sometimes also called "asteroids", especially in popular presentations.[note 5] However, it is becoming increasingly common for the term "asteroid" to be restricted to minor planets of the inner Solar System.[28] Therefore, this article will restrict itself for the most part to the classical asteroids: objects of the asteroid belt, Jupiter
Jupiter
trojans, and near- Earth
Earth
objects. When the IAU introduced the class small Solar System
Solar System
bodies in 2006 to include most objects previously classified as minor planets and comets, they created the class of dwarf planets for the largest minor planets—those that have enough mass to have become ellipsoidal under their own gravity. According to the IAU, "the term 'minor planet' may still be used, but generally the term 'Small Solar System
Solar System
Body' will be preferred."[32] Currently only the largest object in the asteroid belt, Ceres, at about 975 km (606 mi) across, has been placed in the dwarf planet category. Formation[edit]

Artist’s impression shows how an asteroid is torn apart by the strong gravity of a white dwarf.[33]

It is thought that planetesimals in the asteroid belt evolved much like the rest of the solar nebula until Jupiter
Jupiter
neared its current mass, at which point excitation from orbital resonances with Jupiter ejected over 99% of planetesimals in the belt. Simulations and a discontinuity in spin rate and spectral properties suggest that asteroids larger than approximately 120 km (75 mi) in diameter accreted during that early era, whereas smaller bodies are fragments from collisions between asteroids during or after the Jovian disruption.[34] Ceres and Vesta grew large enough to melt and differentiate, with heavy metallic elements sinking to the core, leaving rocky minerals in the crust.[35] In the Nice model, many Kuiper-belt objects are captured in the outer asteroid belt, at distances greater than 2.6 AU. Most were later ejected by Jupiter, but those that remained may be the D-type asteroids, and possibly include Ceres.[36] Distribution within the Solar System[edit] See also: List of minor-planet groups, List of notable asteroids, and List of minor planets

The asteroid belt (white) and Jupiter's trojan asteroids (green)

Various dynamical groups of asteroids have been discovered orbiting in the inner Solar System. Their orbits are perturbed by the gravity of other bodies in the Solar System
Solar System
and by the Yarkovsky effect. Significant populations include: Asteroid
Asteroid
belt[edit] Main article: Asteroid
Asteroid
belt The majority of known asteroids orbit within the asteroid belt between the orbits of Mars
Mars
and Jupiter, generally in relatively low-eccentricity (i.e. not very elongated) orbits. This belt is now estimated to contain between 1.1 and 1.9 million asteroids larger than 1 km (0.6 mi) in diameter,[37] and millions of smaller ones. These asteroids may be remnants of the protoplanetary disk, and in this region the accretion of planetesimals into planets during the formative period of the Solar System
Solar System
was prevented by large gravitational perturbations by Jupiter. Trojans[edit] Main article: Trojan (astronomy) Trojans are populations that share an orbit with a larger planet or moon, but do not collide with it because they orbit in one of the two Lagrangian points of stability, L4 and L5, which lie 60° ahead of and behind the larger body. The most significant population of trojans are the Jupiter
Jupiter
trojans. Although fewer Jupiter
Jupiter
trojans have been discovered (As of 2010[update]), it is thought that they are as numerous as the asteroids in the asteroid belt. Trojans have been found in the orbits of other planets, including Venus, Earth, Mars, Uranus, and Neptune. Near- Earth
Earth
asteroids[edit] Main article: Near- Earth
Earth
asteroids Near- Earth
Earth
asteroids, or NEAs, are asteroids that have orbits that pass close to that of Earth. Asteroids that actually cross Earth's orbital path are known as Earth-crossers. As of June 2016[update], 14,464 near- Earth
Earth
asteroids are known[17] and the number over one kilometer in diameter is estimated to be 900–1,000.

Frequency of bolides, small asteroids roughly 1 to 20 meters in diameter impacting Earth's atmosphere.

Characteristics[edit] Size distribution[edit]

The asteroids of the Solar System, categorized by size and number

Asteroids vary greatly in size, from almost 7006100000000000000♠1000 km for the largest down to rocks just 1 meter across.[note 6] The three largest are very much like miniature planets: they are roughly spherical, have at least partly differentiated interiors,[38] and are thought to be surviving protoplanets. The vast majority, however, are much smaller and are irregularly shaped; they are thought to be either surviving planetesimals or fragments of larger bodies. The dwarf planet Ceres is by far the largest asteroid, with a diameter of 975 km (606 mi). The next largest are 4 Vesta
4 Vesta
and 2 Pallas, both with diameters of just over 500 km (300 mi). Vesta is the only main-belt asteroid that can, on occasion, be visible to the naked eye. On some rare occasions, a near- Earth
Earth
asteroid may briefly become visible without technical aid; see 99942 Apophis. The mass of all the objects of the asteroid belt, lying between the orbits of Mars
Mars
and Jupiter, is estimated to be about 2.8–7021320000000000000♠3.2×1021 kg, or about 4% of the mass of the Moon. Of this, Ceres comprises 7020950000000000000♠0.95×1021 kg, a third of the total.[39] Adding in the next three most massive objects, Vesta (9%), Pallas (7%), and Hygiea (3%), brings this figure up to 51%; whereas the three after that, 511 Davida
511 Davida
(1.2%), 704 Interamnia
704 Interamnia
(1.0%), and 52 Europa (0.9%), only add another 3% to the total mass. The number of asteroids then increases rapidly as their individual masses decrease. The number of asteroids decreases markedly with size. Although this generally follows a power law, there are 'bumps' at 7003500000000000000♠5 km and 7005100000000000000♠100 km, where more asteroids than expected from a logarithmic distribution are found.[40]

Approximate number of asteroids (N) larger than a certain diameter (D)

D 0.1 km 0.3 km 0.5 km 1 km 3 km 5 km 10 km 30 km 50 km 100 km 200 km 300 km 500 km 900 km

N 7007250000000000000♠25000000 7006400000000000000♠4000000 7006200000000000000♠2000000 7005750000000000000♠750000 7005200000000000000♠200000 7004900000000000000♠90000 7004100000000000000♠10000 7003110000000000000♠1100 600 200 30 5 3 1

Largest asteroids[edit] See also: Largest asteroids

The relative masses of the twelve largest asteroids known,[41][note 7] compared to the remaining mass of the asteroid belt.[42]

  1 Ceres   4 Vesta   2 Pallas   10 Hygiea   31 Euphrosyne   704 Interamnia   511 Davida   532 Herculina   15 Eunomia   3 Juno   16 Psyche   52 Europa   all others

Although their location in the asteroid belt excludes them from planet status, the three largest objects, Ceres, Vesta, and Pallas, are intact protoplanets that share many characteristics common to planets, and are atypical compared to the majority of "potato"-shaped asteroids. The fourth largest asteroid, Hygiea, has an undifferentiated interior, like the majority of asteroids. Between them, the four largest asteroids constitute half the mass of the asteroid belt. Ceres is the only asteroid with a fully ellipsoidal shape and hence the only one that is a dwarf planet.[24] It has a much higher absolute magnitude than the other asteroids, of around 3.32,[43] and may possess a surface layer of ice.[44] Like the planets, Ceres is differentiated: it has a crust, a mantle and a core.[44] No meteorites from Ceres have been found on Earth. Vesta, too, has a differentiated interior, though it formed inside the Solar System's frost line, and so is devoid of water;[45][46] its composition is mainly of basaltic rock such as olivine.[47] Aside from the large crater at its southern pole, Rheasilvia, Vesta also has an ellipsoidal shape. Vesta is the parent body of the Vestian family
Vestian family
and other V-type asteroids, and is the source of the HED meteorites, which constitute 5% of all meteorites on Earth. Pallas is unusual in that, like Uranus, it rotates on its side, with its axis of rotation tilted at high angles to its orbital plane.[48] Its composition is similar to that of Ceres: high in carbon and silicon, and perhaps partially differentiated.[49] Pallas is the parent body of the Palladian family
Palladian family
of asteroids. Hygiea is the largest carbonaceous asteroid[50] and, unlike the other largest asteroids, lies relatively close to the plane of the ecliptic.[51] It is the largest member and presumed parent body of the Hygiean family
Hygiean family
of asteroids.

Attributes of largest asteroids

Name Orbital radius (AU) Orbital period (years) Inclination to ecliptic Orbital eccentricity Diameter (km) Diameter (% of Moon) Mass (×1018 kg) Mass (% of Ceres) Density[52] (g/cm3) Rotation period (hr) Axial tilt Surface temperature

Vesta 2.36 3.63 7.1° 0.089 573×557×446 (mean 525) 15% 260 28% 3.44 ± 0.12 5.34 29° 85–270 K

Ceres 2.77 4.60 10.6° 0.079 975×975×909 (mean 953) 28% 940 100% 2.12 ± 0.04 9.07 ≈ 3° 167 K

Pallas 2.77 4.62 34.8° 0.231 580×555×500 (mean 545) 16% 210 22% 2.71 ± 0.11 7.81 ≈ 80° 164 K

Hygiea 3.14 5.56 3.8° 0.117 530×407×370 (mean 435) 12% 87 9% 2.76 ± 1.2 27.6 ≈ 60° 164 K

Rotation[edit] Measurements of the rotation rates of large asteroids in the asteroid belt show that there is an upper limit. No asteroid with a diameter larger than 100 meters has a rotation period smaller than 2.2 hours. For asteroids rotating faster than approximately this rate, the inertial force at the surface is greater than the gravitational force, so any loose surface material would be flung out. However, a solid object should be able to rotate much more rapidly. This suggests that most asteroids with a diameter over 100 meters are rubble piles formed through accumulation of debris after collisions between asteroids.[53] Composition[edit]

Cratered terrain on 4 Vesta

The physical composition of asteroids is varied and in most cases poorly understood. Ceres appears to be composed of a rocky core covered by an icy mantle, where Vesta is thought to have a nickel-iron core, olivine mantle, and basaltic crust.[54] 10 Hygiea, however, which appears to have a uniformly primitive composition of carbonaceous chondrite, is thought to be the largest undifferentiated asteroid. Most of the smaller asteroids are thought to be piles of rubble held together loosely by gravity, though the largest are probably solid. Some asteroids have moons or are co-orbiting binaries: Rubble piles, moons, binaries, and scattered asteroid families are thought to be the results of collisions that disrupted a parent asteroid, or, possibly, a planet.[55] Asteroids contain traces of amino acids and other organic compounds, and some speculate that asteroid impacts may have seeded the early Earth
Earth
with the chemicals necessary to initiate life, or may have even brought life itself to Earth
Earth
(also see panspermia).[56] In August 2011, a report, based on NASA
NASA
studies with meteorites found on Earth, was published suggesting DNA
DNA
and RNA
RNA
components (adenine, guanine and related organic molecules) may have been formed on asteroids and comets in outer space.[57][58][59]

Asteroid
Asteroid
collision – building planets (artist concept).

Composition is calculated from three primary sources: albedo, surface spectrum, and density. The last can only be determined accurately by observing the orbits of moons the asteroid might have. So far, every asteroid with moons has turned out to be a rubble pile, a loose conglomeration of rock and metal that may be half empty space by volume. The investigated asteroids are as large as 280 km in diameter, and include 121 Hermione
121 Hermione
(268×186×183 km), and 87 Sylvia (384×262×232 km). Only half a dozen asteroids are larger than 87 Sylvia, though none of them have moons; however, some smaller asteroids are thought to be more massive, suggesting they may not have been disrupted, and indeed 511 Davida, the same size as Sylvia to within measurement error, is estimated to be two and a half times as massive, though this is highly uncertain. The fact that such large asteroids as Sylvia can be rubble piles, presumably due to disruptive impacts, has important consequences for the formation of the Solar System: Computer simulations of collisions involving solid bodies show them destroying each other as often as merging, but colliding rubble piles are more likely to merge. This means that the cores of the planets could have formed relatively quickly.[60] On 7 October 2009, the presence of water ice was confirmed on the surface of 24 Themis
24 Themis
using NASA’s Infrared Telescope
Telescope
Facility. The surface of the asteroid appears completely covered in ice. As this ice layer is sublimated, it may be getting replenished by a reservoir of ice under the surface. Organic compounds were also detected on the surface.[61][62][63][64] Scientists hypothesize that some of the first water brought to Earth
Earth
was delivered by asteroid impacts after the collision that produced the Moon. The presence of ice on 24 Themis supports this theory.[63] In October 2013, water was detected on an extrasolar body for the first time, on an asteroid orbiting the white dwarf GD 61.[65] On 22 January 2014, European Space Agency
European Space Agency
(ESA) scientists reported the detection, for the first definitive time, of water vapor on Ceres, the largest object in the asteroid belt.[66] The detection was made by using the far-infrared abilities of the Herschel Space Observatory.[67] The finding is unexpected because comets, not asteroids, are typically considered to "sprout jets and plumes". According to one of the scientists, "The lines are becoming more and more blurred between comets and asteroids."[67] In May 2016, significant asteroid data arising from the Wide-field Infrared Survey Explorer and NEOWISE missions have been questioned,[68][69][70] but the criticism has yet to undergo peer review.[71] Surface features[edit] Most asteroids outside the "big four" (Ceres, Pallas, Vesta, and Hygiea) are likely to be broadly similar in appearance, if irregular in shape. 50-km (31-mi) 253 Mathilde
253 Mathilde
is a rubble pile saturated with craters with diameters the size of the asteroid's radius, and Earth-based observations of 300-km (186-mi) 511 Davida, one of the largest asteroids after the big four, reveal a similarly angular profile, suggesting it is also saturated with radius-size craters.[72] Medium-sized asteroids such as Mathilde and 243 Ida
243 Ida
that have been observed up close also reveal a deep regolith covering the surface. Of the big four, Pallas and Hygiea are practically unknown. Vesta has compression fractures encircling a radius-size crater at its south pole but is otherwise a spheroid. Ceres seems quite different in the glimpses Hubble has provided, with surface features that are unlikely to be due to simple craters and impact basins, but details will be expanded with the Dawn spacecraft, which entered Ceres orbit on 6 March 2015.[73] Color[edit] Asteroids become darker and redder with age due to space weathering.[74] However evidence suggests most of the color change occurs rapidly, in the first hundred thousands years, limiting the usefulness of spectral measurement for determining the age of asteroids.[75] Classification[edit] Asteroids are commonly classified according to two criteria: the characteristics of their orbits, and features of their reflectance spectrum. Orbital classification[edit] Main articles: Asteroid group
Asteroid group
and Asteroid
Asteroid
family Many asteroids have been placed in groups and families based on their orbital characteristics. Apart from the broadest divisions, 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 tighter and result from the catastrophic break-up of a large parent asteroid sometime in the past.[76] Families are more common and easier to identify within the main asteroid belt, but several small families have been reported among the Jupiter
Jupiter
trojans.[77] Main belt families were first recognized by Kiyotsugu Hirayama in 1918 and are often called Hirayama families in his honor. About 30–35% of the bodies in the asteroid belt belong to dynamical families each thought to have a common origin in a past collision between asteroids. A family has also been associated with the plutoid dwarf planet Haumea. Quasi-satellites and horseshoe objects[edit] Some asteroids have unusual horseshoe orbits that are co-orbital with Earth
Earth
or some other planet. Examples are 3753 Cruithne
3753 Cruithne
and 2002 AA29. The first instance of this type of orbital arrangement was discovered between Saturn's moons Epimetheus and Janus. Sometimes these horseshoe objects temporarily become quasi-satellites for a few decades or a few hundred years, before returning to their earlier status. Both Earth
Earth
and Venus
Venus
are known to have quasi-satellites. Such objects, if associated with Earth
Earth
or Venus
Venus
or even hypothetically Mercury, are a special class of Aten asteroids. However, such objects could be associated with outer planets as well. Spectral classification[edit] Main article: Asteroid
Asteroid
spectral types

This picture of 433 Eros
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 (115 ft) across can be seen.

In 1975, an asteroid taxonomic system based on color, albedo, and spectral shape was developed by Clark R. Chapman, David Morrison, and Ben Zellner.[78] These properties are thought to correspond to the composition of the asteroid's surface material. The original classification system had three categories: C-types for dark carbonaceous objects (75% of known asteroids), S-types for stony (silicaceous) objects (17% of known asteroids) and U for those that did not fit into either C or S. This classification has since been expanded to include many other asteroid types. The number of types continues to grow as more asteroids are studied. The two most widely used taxonomies now used are the Tholen classification and SMASS classification. The former was proposed in 1984 by David J. Tholen, and was based on data collected from an eight-color asteroid survey performed in the 1980s. This resulted in 14 asteroid categories.[79] In 2002, the Small Main-Belt Asteroid Spectroscopic Survey resulted in a modified version of the Tholen taxonomy with 24 different types. Both systems have three broad categories of C, S, and X asteroids, where X consists of mostly metallic asteroids, such as the M-type. There are also several smaller classes.[80] 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[edit] Originally, spectral designations were based on inferences of an asteroid's composition.[81] However, the correspondence between spectral class and composition is not always very good, and a variety of classifications are in use. This has led to significant confusion. Although 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. Naming[edit] Main article: Minor planet
Minor planet
§ Naming

2013 EC, shown here in radar images, has a provisional designation

A newly discovered asteroid is given a provisional designation (such as 2002 AT4) consisting of the year of discovery and an alphanumeric code indicating the half-month of discovery and the sequence within that half-month. Once an asteroid's 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.[82] In addition, names can be proposed by the asteroid's discoverer, within guidelines established by the International Astronomical Union.[83] Symbols[edit] Main article: Astronomical symbols The first asteroids to be discovered were assigned iconic symbols like the ones traditionally used to designate the planets. By 1855 there were two dozen asteroid symbols, which often occurred in multiple variants.[84]

Asteroid Symbol Year

1 Ceres ⚳ Ceres' scythe, reversed to double as the letter C 1801

2 Pallas ⚴ Athena's (Pallas') spear 1801

3 Juno ⚵ A star mounted on a scepter, for Juno, the Queen of Heaven 1804

4 Vesta ⚶ The altar and sacred fire of Vesta 1807

5 Astraea

A scale, or an inverted anchor, symbols of justice 1845

6 Hebe

Hebe's cup 1847

7 Iris

A rainbow (iris) and a star 1847

8 Flora

A flower (flora), specifically the Rose of England 1847

9 Metis

The eye of wisdom and a star 1848

10 Hygiea

Hygiea's serpent and a star, or the Rod of Asclepius 1849

11 Parthenope

A harp, or a fish and a star; symbols of the sirens 1850

12 Victoria

The laurels of victory and a star 1850

13 Egeria

A shield, symbol of Egeria's protection, and a star 1850

14 Irene

A dove carrying an olive branch (symbol of irene 'peace') with a star on its head,[85] or an olive branch, a flag of truce, and a star 1851

15 Eunomia

A heart, symbol of good order (eunomia), and a star 1851

16 Psyche

A butterfly's wing, symbol of the soul (psyche), and a star 1852

17 Thetis

A dolphin, symbol of Thetis, and a star 1852

18 Melpomene

The dagger of Melpomene, and a star 1852

19 Fortuna

The wheel of fortune and a star 1852

26 Proserpina

Proserpina's pomegranate 1853

28 Bellona

Bellona's whip and lance[86] 1854

29 Amphitrite

The shell of Amphitrite
Amphitrite
and a star 1854

35 Leukothea

A lighthouse beacon, symbol of Leucothea[87] 1855

37 Fides

The cross of faith (fides)[88] 1855

In 1851,[89] after the fifteenth asteroid (Eunomia) had been discovered, Johann Franz Encke
Johann Franz Encke
made a major change in the upcoming 1854 edition of the Berliner Astronomisches Jahrbuch (BAJ, Berlin Astronomical Yearbook). He introduced a disk (circle), a traditional symbol for a star, as the generic symbol for an asteroid. The circle was then numbered in order of discovery to indicate a specific asteroid (although he assigned ① to the fifth, Astraea, while continuing to designate the first four only with their existing iconic symbols). The numbered-circle convention was quickly adopted by astronomers, and the next asteroid to be discovered (16 Psyche, in 1852) was the first to be designated in that way at the time of its discovery. However, Psyche was given an iconic symbol as well, as were a few other asteroids discovered over the next few years (see chart above). 20 Massalia
20 Massalia
was the first asteroid that was not assigned an iconic symbol, and no iconic symbols were created after the 1855 discovery of 37 Fides.[note 8] That year Astraea's number was increased to ⑤, but the first four asteroids, Ceres to Vesta, were not listed by their numbers until the 1867 edition. The circle was soon abbreviated to a pair of parentheses, which were easier to typeset and sometimes omitted altogether over the next few decades, leading to the modern convention.[85] Exploration[edit] See also: Sample return mission, Asteroid
Asteroid
mining, and Colonization of the asteroids Until the age of space travel, objects in the asteroid belt were merely pinpricks of light in even the largest telescopes and their shapes and terrain remained a mystery. The best modern ground-based telescopes and the Earth-orbiting Hubble Space Telescope
Telescope
can resolve a small amount of detail on the surfaces of the largest asteroids, but even these mostly remain little more than fuzzy blobs. Limited information about the shapes and compositions of asteroids can be inferred from their light curves (their variation in brightness as they rotate) and their spectral properties, and asteroid sizes can be estimated by timing the lengths of star occulations (when an asteroid passes directly in front of a star). Radar
Radar
imaging can yield good information about asteroid shapes and orbital and rotational parameters, especially for near- Earth
Earth
asteroids. In terms of delta-v and propellant requirements, NEOs are more easily accessible than the Moon.[90] The first close-up photographs of asteroid-like objects were taken in 1971, when the Mariner 9
Mariner 9
probe imaged Phobos and Deimos, the two small moons of Mars, which are probably captured asteroids. These images revealed the irregular, potato-like shapes of most asteroids, as did later images from the Voyager probes of the small moons of the gas giants. The first true asteroid to be photographed in close-up was 951 Gaspra in 1991, followed in 1993 by 243 Ida
243 Ida
and its moon Dactyl, all of which were imaged by the Galileo probe en route to Jupiter. The first dedicated asteroid probe was NEAR Shoemaker, which photographed 253 Mathilde
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
9969 Braille
(by Deep Space 1
Deep Space 1
in 1999), and 5535 Annefrank (by Stardust in 2002). In September 2005, the Japanese Hayabusa
Hayabusa
probe started studying 25143 Itokawa in detail and was plagued with difficulties, but returned samples of its surface to Earth
Earth
on 13 June 2010. The European Rosetta probe (launched in 2004) flew by 2867 Šteins
2867 Šteins
in 2008 and 21 Lutetia, the third-largest asteroid visited to date, in 2010. In September 2007, NASA
NASA
launched the Dawn spacecraft, which orbited 4 Vesta from July 2011 to September 2012, and has been orbiting the dwarf planet 1 Ceres since 2015. 4 Vesta
4 Vesta
is the second-largest asteroid visited to date. On 13 December 2012, China's lunar orbiter Chang'e 2
Chang'e 2
flew within 3.2 km (2 mi) of the asteroid 4179 Toutatis
4179 Toutatis
on an extended mission. Planned and future missions[edit] The Japan Aerospace Exploration Agency (JAXA) launched the Hayabusa
Hayabusa
2 probe in December 2014, and plans to return samples from 162173 Ryugu in December 2020. In May 2011, NASA
NASA
selected the OSIRIS-REx
OSIRIS-REx
sample return mission to asteroid 101955 Bennu; it launched on September 8, 2016. In early 2013, NASA
NASA
announced the planning stages of a mission to capture a near- Earth
Earth
asteroid and move it into lunar orbit where it could possibly be visited by astronauts and later impacted into the Moon.[91] On 19 June 2014, NASA
NASA
reported that asteroid 2011 MD
2011 MD
was a prime candidate for capture by a robotic mission, perhaps in the early 2020s.[92] It has been suggested that asteroids might be used as a source of materials that may be rare or exhausted on Earth
Earth
(asteroid mining), or materials for constructing space habitats (see Colonization of the asteroids). Materials that are heavy and expensive to launch from Earth
Earth
may someday be mined from asteroids and used for space manufacturing and construction. In the U.S. Discovery program
Discovery program
the Psyche spacecraft proposal to 16 Psyche and Lucy spacecraft to Jupiter
Jupiter
trojans made it to the semifinalist stage of mission selection. Fiction[edit] Main article: Asteroids in fiction Asteroids and the asteroid belt are a staple of science fiction stories. Asteroids play several potential roles in science fiction: as places human beings might colonize, resources for extracting minerals, hazards encountered by spacecraft traveling between two other points, and as a threat to life on Earth
Earth
or other inhabited planets, dwarf planets and natural satellites by potential impact. Gallery[edit]

951 Gaspra
951 Gaspra
is the first asteroid to be imaged in close-up, imaged by Galileo on 29 October 1991 (enhanced color)

Several views of 433 Eros
433 Eros
in natural color, imaged by NEAR on 12 February 2000

Vesta imaged by Dawn on 9 July 2011

Ceres imaged by Dawn on 4 February 2015

See also[edit]

Amor asteroid Apollo asteroid Asteroid
Asteroid
Day Asteroid
Asteroid
impact avoidance Aten asteroid Atira asteroid BOOTES
BOOTES
(Burst Observer and Optical Transient Exploring System) Category:Asteroids Category: Asteroid
Asteroid
groups and families Category:Binary asteroids Centaur (minor planet) Chang'e 2
Chang'e 2
lunar orbiter Constellation program Dawn spacecraft Dwarf planet Impact event List of asteroid close approaches to Earth List of minor planets
List of minor planets
named after people List of minor planets
List of minor planets
named after places List of minor planets List of notable asteroids List of impact craters on Earth List of unconfirmed impact craters on Earth Lost asteroid Marco Polo (spacecraft) Meanings of minor planet names Mesoplanet Minor planet Near- Earth
Earth
object NEOShield NEOSSat (Near Earth
Earth
Object Surveillance Satellite) Canada's new satellite Pioneer 10
Pioneer 10
spacecraft Rosetta spacecraft

Space portal Astronomy
Astronomy
portal

Notes[edit]

^ Ceres is the largest asteroid and is now classified as a dwarf planet. All other asteroids are now classified as small Solar System bodies along with comets, centaurs, and the smaller trans-Neptunian objects. ^ In an oral presentation,[10] Clifford Cunningham presented his finding that the word was coined by Charles Burney, Jr., the son of a friend of Herschel,[11][12] ^ For example, the Annual of Scientific Discovery for 1871, page 316, reads "Professor J. Watson has been awarded by the Paris Academy of Sciences, the astronomical prize, Lalande foundation, for the discovery of eight new asteroids in one year. The planet Lydia (No. 110), discovered by M. Borelly at the Marseilles Observatory [...] M. Borelly had previously discovered two planets bearing the numbers 91 and 99 in the system of asteroids revolving between Mars
Mars
and Jupiter". ^ The definition of "small Solar System
Solar System
bodies" says that they "include most of the Solar System
Solar System
asteroids, most trans-Neptunian objects, comets, and other small bodies". ^ For instance, a joint NASA– JPL
JPL
public-outreach website states:

"We include Trojans (bodies captured in Jupiter's 4th and 5th Lagrange points), Centaurs (bodies in orbit between Jupiter
Jupiter
and Neptune), and trans-Neptunian objects (orbiting beyond Neptune) in our definition of "asteroid" as used on this site, even though they may more correctly be called "minor planets" instead of asteroids."

^ Below 1 meter, these are considered to be meteoroids. The definition in the 1995 paper (Beech and Steel) has been updated by a 2010 paper (Rubin and Grossman) and the discovery of 1-meter asteroids. ^ The values of Juno and Herculina may be off by as much as 16%, and Euphrosyne by a third. The order of the lower eight may change as better data is acquired, but the values do not overlap with any known asteroid outside these twelve. ^ Except for Pluto
Pluto
and, in the astrological community, for a few outer bodies such as 2060 Chiron

References[edit]

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taxonomic classifications". Asteroids II; Proceedings of the Conference. University of Arizona Press. pp. 1139–1150. Bibcode:1989aste.conf.1139T.  ^ Bus, S. J. (2002). "Phase II of the Small Main-belt Asteroid Spectroscopy Survey: A feature-based taxonomy". Icarus. 158 (1): 146. Bibcode:2002Icar..158..146B. doi:10.1006/icar.2002.6856.  ^ McSween Jr., Harry Y. (1999). Meteorites and their Parent Planets (2nd ed.). Oxford University Press. ISBN 0-521-58751-4.  ^ "The Naming of Asteroids". Open Learn. The Open University. Retrieved 14 August 2016.  ^ " Asteroid
Asteroid
Naming Guidelines". The Planetary Society. The Planetary Society. Retrieved 14 August 2016.  ^ Gould, B. A. (1852). "On the Symbolic Notation of the Asteroids". Astronomical Journal. 2: 80. Bibcode:1852AJ......2...80G . doi:10.1086/100212 .  ^ a b Hilton, James L. (17 September 2001). "When Did the Asteroids Become Minor Planets". Archived from the original on 2007-11-06. Retrieved 26 March 2006.  ^ Encke, J. F. (1854). "Beobachtung der Bellona, nebst Nachrichten über die Bilker Sternwarte". Astronomische Nachrichten. 38 (9): 143. Bibcode:1854AN.....38..143. . doi:10.1002/asna.18540380907 .  ^ Luther, R (1855). "Name und Zeichen des von Herrn R. Luther zu Bilk am 19. April entdeckten Planeten". Astronomische Nachrichten. 40 (24): 373. Bibcode:1855AN.....40Q.373L . doi:10.1002/asna.18550402405 .  ^ Luther, R. (1855). "Schreiben des Herrn Dr. R. Luther, Directors der Sternwarte zu Bilk, an den Herausgeber". Astronomische Nachrichten. 42 (7): 107. Bibcode:1855AN.....42..107L . doi:10.1002/asna.18550420705 .  ^ "When did the asteroids become minor planets?". Naval Meteorology and Oceanography Command. Archived from the original on 6 April 2012. Retrieved 6 November 2011.  ^ Rob R. Landis; David J. Korsmeyer; Paul A. Abell; et al. "A Piloted Orion Flight to a Near- Earth
Earth
Object: A Feasibility Study" (PDF). American Institute of Aeronautics and Astronautics.  ^ Wall, Mike (30 September 2013). " NASA
NASA
May Slam Captured Asteroid Into Moon
Moon
(Eventually)". SPACE.com.  ^ Borenstein, Seth (19 June 2014). "Rock that whizzed by Earth
Earth
may be grabbed by NASA". AP News. Retrieved 20 June 2014. 

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Alphabetical list of minor planet names (ASCII) (Minor Planet
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Asteroids

Main

Notable asteroids Physical characteristics

dynamic method

Impact avoidance Tracking Capture Gravitational keyhole Earth-crosser Close approaches Binary

moon contact

P–L

Distribution

Interior to Earth

vulcanoids Mercury-crossers Venus-crossers

Main-belt

Kirkwood gap comets

Trojans

Venus
Venus
trojan Earth Mars Jupiter Uranus
Uranus
trojan Neptune
Neptune
trojan

Near-Earth

Aten Amor Apollo Apohele Earth-crossers

Between Earth
Earth
and the main belt

Mars
Mars
crossers Mars
Mars
trojans

Outer Solar System, does not include distant minor planets

Jupiter-crossers Jupiter
Jupiter
trojan

Classification

Orbital

Group Family (list)

Spectral

Tholen

C-group

B-type F-type G-type C-type

S-type X-group

M-type E-type P-type

small classes

A-type D-type J-type T-type Q-type R-type V-type

SMASS

C-group

B-type C-type Cg Ch Cgh Cb

S-group

A-type Q-type R-type K-type L-type S-type Sa Sq Sr Sk Sl

X-group

X-type Xe Xc Xk

small types

T-type D-type Ld-type O-type V-type

Exploration

Asteroid
Asteroid
Redirect Mission Asteroids visited by spacecraft Human mission Mining

Ceres

Colonization

Lists

Near-Earth Minor planets Lost Discovering observatories Space missions

See also: Asteroids in fiction Asteroids in astrology

occultation

Comet

v t e

Ceres

Geography

General

Geology of Ceres

Craters

Achita Annona Asari Coniraya Dantu Darzamat Ezinu Fejokoo Hamori Haulani Kerwan Mondamin Nawish Occator Urvara Yalode Zadeni

Montes

Ahuna Mons

Other features

Bright spots

Astronomy

Classification

Asteroid Definition of planet Dwarf planet Planet 2006 definition of planet

Discovery

Barnaba Oriani Carl Friedrich Gauss Francis Wollaston Franz Xaver von Zach Giuseppe Piazzi Heinrich Olbers Jérôme Lalande Johann Elert Bode Tobias Mayer

Possible trojans

(185105) 2006 SV23 1372 Haremari

Exploration

Dawn mission Ceres Polar Lander
Ceres Polar Lander
(proposed)

Related

Ceres in fiction Colonization In astrology Solar System
Solar System
bodies formerly considered to be planets

v t e

Comets

Features

Nucleus Coma Tails Antitail Comet
Comet
dust Meteor shower

Types

Periodic

Numbered Lost Halley-type Jupiter-family Encke-type Main-belt

Non-periodic

Hyperbolic Unknown-orbit

Great Comet Sungrazing (Kreutz) Extinct Rock Exocomet Interstellar

Related

Naming of comets Centaur Comet
Comet
discoverers

LINEAR

Extraterrestrial atmosphere Oort cloud Small Solar System
Solar System
body Asteroid

Space missions

Planned and proposed

DESTINY+ CAESAR Comet
Comet
Hopper CONDOR CORSAIR CRAF Hayabusa
Hayabusa
Mk2 Marco Polo Vesta

Past and current

CONTOUR Deep Impact/EPOXI Deep Space 1 Giotto ICE Rosetta

Philae Timeline

Sakigake Stardust/NeXT Suisei Ulysses Vega program

Vega 1 Vega 2

Latest

C/2016 U1 (NEOWISE) C/2015 G2 (MASTER) C/2015 F5 (SWAN-XingMing) C/2015 F3 C/2014 Q2 (Lovejoy) C/2014 E2 (Jacques) C/2013 US10
C/2013 US10
(Catalina) C/2013 A1
C/2013 A1
(Siding Spring) C/2012 S4 (PANSTARRS) C/2012 K1
C/2012 K1
(PANSTARRS)

Culture and speculation

Antimatter comet Comets in fiction

Fictional comets

Comet
Comet
vintages

Lists of comets
Lists of comets
(more)

Periodic comets

Until 1985 (all)

1P/Halley 2P/Encke 3D/Biela 4P/Faye 5D/Brorsen 6P/d'Arrest 7P/Pons–Winnecke 8P/Tuttle 9P/Tempel 10P/Tempel 11P/Tempel–Swift–LINEAR 12P/Pons–Brooks 13P/Olbers 14P/Wolf 15P/Finlay 16P/Brooks 17P/Holmes 18D/Perrine–Mrkos 19P/Borrelly 20D/Westphal 21P/Giacobini–Zinner 22P/Kopff 23P/Brorsen–Metcalf 24P/Schaumasse 25D/Neujmin 26P/Grigg–Skjellerup 27P/Crommelin 28P/Neujmin 29P/Schwassmann–Wachmann 30P/Reinmuth 31P/Schwassmann–Wachmann 32P/Comas Solà 33P/Daniel 34D/Gale 35P/Herschel–Rigollet 36P/Whipple 37P/Forbes 38P/Stephan–Oterma 39P/Oterma 40P/Väisälä 41P/Tuttle–Giacobini–Kresák 42P/Neujmin 43P/Wolf–Harrington 44P/Reinmuth 45P/Honda–Mrkos–Pajdušáková 46P/Wirtanen 47P/Ashbrook–Jackson 48P/Johnson 49P/Arend–Rigaux 50P/Arend 51P/Harrington 52P/Harrington–Abell 53P/Van Biesbroeck 54P/de Vico–Swift–NEAT 55P/Tempel–Tuttle 56P/Slaughter–Burnham 57P/du Toit–Neujmin–Delporte 58P/Jackson–Neujmin 59P/Kearns–Kwee 60P/Tsuchinshan 61P/Shajn–Schaldach 62P/Tsuchinshan 63P/Wild 64P/Swift–Gehrels 65P/Gunn 66P/du Toit 67P/Churyumov–Gerasimenko 68P/Klemola 69P/Taylor 70P/Kojima 71P/Clark 72P/Denning–Fujikawa 73P/Schwassmann–Wachmann 74P/Smirnova–Chernykh 75D/Kohoutek 76P/West–Kohoutek–Ikemura 77P/Longmore 78P/Gehrels 79P/du Toit–Hartley 80P/Peters–Hartley 81P/Wild 82P/Gehrels 83D/Russell 84P/Giclas 85P/Boethin 86P/Wild 87P/Bus 88P/Howell 89P/Russell 90P/Gehrels 91P/Russell 92P/Sanguin 93P/Lovas 94P/Russell 95P/Chiron 96P/Machholz 97P/Metcalf–Brewington 98P/Takamizawa 99P/Kowal 100P/Hartley 101P/Chernykh 102P/Shoemaker

After 1985 (notable)

103P/Hartley 105P/Singer Brewster 107P/Wilson–Harrington 109P/Swift–Tuttle 111P/Helin–Roman–Crockett 114P/Wiseman–Skiff 128P/Shoemaker–Holt 139P/Väisälä–Oterma 144P/Kushida 147P/Kushida–Muramatsu 153P/Ikeya–Zhang 163P/NEAT 168P/Hergenrother 169P/NEAT 177P/Barnard 178P/Hug–Bell 205P/Giacobini 209P/LINEAR 238P/Read 246P/NEAT 252P/LINEAR 255P/Levy 273P/Pons–Gambart 276P/Vorobjov 289P/Blanpain 311P/PANSTARRS 322P/SOHO 332P/Ikeya-Murakami 354P/LINEAR

P/1997 B1 (Kobayashi) P/2010 B2 (WISE) P/2011 NO1 (Elenin)

Comet-like asteroids

596 Scheila 2060 Chiron
2060 Chiron
(95P) 4015 Wilson–Harrington
4015 Wilson–Harrington
(107P) 7968 Elst–Pizarro
7968 Elst–Pizarro
(133P) 165P/LINEAR 166P/NEAT 167P/CINEOS 60558 Echeclus (174P) 118401 LINEAR (176P) 238P/Read 259P/Garradd 311P/PANSTARRS 324P/La Sagra P/2010 A2 (LINEAR) P/2012 F5 (Gibbs) P/2012 T1 (PANSTARRS) P/2013 R3 (Catalina-PANSTARRS) (300163) 2006 VW139

Lost

Recovered

11P/Tempel–Swift–LINEAR 15P/Finlay 17P/Holmes 27P/Crommelin 54P/de Vico–Swift–NEAT 55P/Tempel–Tuttle 57P/du Toit–Neujmin–Delporte 69P/Taylor 72P/Denning–Fujikawa 80P/Peters–Hartley 97P/Metcalf–Brewington 107P/Wilson–Harrington 109P/Swift–Tuttle 113P/Spitaler 122P/de Vico 157P/Tritton 177P/Barnard 205P/Giacobini 206P/Barnard–Boattini 271P/van Houten–Lemmon 273P/Pons–Gambart 289P/Blanpain

Destroyed

3D/Biela 73P/Schwassmann–Wachmann D/1993 F2 (Shoemaker–Levy 9)

Not found

D/1770 L1 (Lexell) 5D/Brorsen 18D/Perrine–Mrkos 20D/Westphal 25D/Neujmin 34D/Gale 75D/Kohoutek 83D/Russell

Visited by spacecraft

21P/Giacobini–Zinner
21P/Giacobini–Zinner
(1985) 1P/Halley
1P/Halley
(1986) 26P/Grigg–Skjellerup
26P/Grigg–Skjellerup
(1992) 19P/Borrelly
19P/Borrelly
(2001) 81P/Wild
81P/Wild
(2004) 9P/Tempel
9P/Tempel
(2005, 2011) C/2006 P1
C/2006 P1
(2007) 103P/Hartley
103P/Hartley
(2010) 67P/Churyumov–Gerasimenko
67P/Churyumov–Gerasimenko
(2014)

Non-Periodic comets (notable)

Until 1910

C/-43 K1 (Caesar's Comet) X/1106 C1 (Great Comet
Comet
of 1106) C/1577 V1 (Great Comet
Comet
of 1577) C/1652 Y1 C/1680 V1 (Great Comet
Comet
of 1680, Kirsch's Comet, Newton's Comet)) C/1702 H1 ( Comet
Comet
of 1702) C/1729 P1 ( Comet
Comet
of 1729, Comet
Comet
Sarabat) C/1743 X1 (Great Comet
Comet
of 1744, Comet
Comet
Klinkenberg-Chéseaux) C/1760 A1 (Great Comet
Comet
of 1760) C/1769 P1
C/1769 P1
(Great Comet
Comet
of 1769) C/1807 R1
C/1807 R1
(Great Comet
Comet
of 1807) C/1811 F1 (Great Comet
Comet
of 1811) C/1819 N1 (Great Comet
Comet
of 1819) C/1823 Y1 (Great Comet
Comet
of 1823) C/1843 D1 (Great March Comet
Comet
of 1843) C/1847 T1 (Miss Mitchell's Comet) C/1858 L1 ( Comet
Comet
Donati) C/1861 G1 ( Comet
Comet
Thatcher) C/1861 J1
C/1861 J1
(Great Comet
Comet
of 1861) C/1865 B1 (Great Southern Comet
Comet
of 1865) X/1872 X1
X/1872 X1
(Pogson's Comet) C/1874 H1
C/1874 H1
( Comet
Comet
Coggia) C/1881 K1
C/1881 K1
( Comet
Comet
Tebbutt) C/1882 R1 (Great Comet
Comet
of 1882) C/1887 B1 (Great Southern Comet
Comet
of 1887) C/1890 V1 ( Comet
Comet
Zona) C/1901 G1 (Great Comet
Comet
of 1901) C/1910 A1 (Great January Comet
Comet
of 1910)

After 1910

C/1911 O1
C/1911 O1
(Brooks) C/1911 S3 (Beljawsky) C/1927 X1 (Skjellerup–Maristany) C/1931 P1 (Ryves) C/1941 B2 (de Kock-Paraskevopoulos) (de) C/1947 X1 (Southern Comet) (de) C/1948 V1 (Eclipse) C/1956 R1 (Arend–Roland) C/1957 P1 (Mrkos) (de) C/1961 O1 (Wilson-Hubbard) (de) C/1961 R1 (Humason) C/1962 C1 (Seki-Lines) (de) C/1963 R1 (Pereyra) C/1965 S1 (Ikeya-Seki) C/1969 Y1 (Bennett) C/1970 K1 (White–Ortiz–Bolelli) C/1973 E1 (Kohoutek) C/1975 V1 (West) C/1980 E1
C/1980 E1
(Bowell) C/1983 H1 (IRAS–Araki–Alcock) C/1989 X1 (Austin) C/1989 Y1 (Skorichenko–George) C/1992 J1 (Spacewatch–Rabinowitz) C/1993 Y1 (McNaught–Russell) C/1995 O1 (Hale–Bopp) C/1996 B2 (Hyakutake) C/1997 L1 (Zhu–Balam) C/1998 H1 (Stonehouse) C/1998 J1 (SOHO) C/1999 F1 (Catalina) C/1999 S4
C/1999 S4
(LINEAR) C/2000 U5 (LINEAR) C/2000 W1 (Utsunomiya-Jones) C/2001 OG108 (LONEOS) C/2001 Q4 (NEAT) C/2002 T7 (LINEAR) C/2004 F4 (Bradfield) (de) C/2004 Q2 (Machholz) C/2006 A1 (Pojmański) C/2006 M4 (SWAN) C/2006 P1
C/2006 P1
(McNaught) C/2007 E2 (Lovejoy) C/2007 F1 (LONEOS) C/2007 K5 (Lovejoy) C/2007 N3 (Lulin) C/2007 Q3
C/2007 Q3
(Siding Spring) C/2007 W1 (Boattini) C/2008 Q1 (Matičič) C/2009 F6 (Yi–SWAN) C/2009 R1
C/2009 R1
(McNaught) C/2010 X1
C/2010 X1
(Elenin) C/2011 L4
C/2011 L4
(PANSTARRS) C/2011 W3 (Lovejoy) C/2012 E2 (SWAN) C/2012 F6 (Lemmon) C/2012 K1
C/2012 K1
(PANSTARRS) C/2012 S1 (ISON) C/2012 S4 (PANSTARRS) C/2013 A1
C/2013 A1
(Siding Spring) C/2013 R1 (Lovejoy) C/2013 US10
C/2013 US10
(Catalina) C/2013 V5
C/2013 V5
(Oukaimeden) C/2014 E2 (Jacques) C/2014 Q2 (Lovejoy) C/2015 V2
C/2015 V2
(Johnson)

After 1910 (by name)

Arend–Roland Austin Beljawsky Bennett Boattini Bowell Bradfield (de) Brooks Catalina

C/1999 F1 C/2013 US10

de Kock–Paraskevopoulos (de) Eclipse Elenin Hale-Bopp Humason Hyakutake Ikeya-Seki IRAS–Araki–Alcock ISON Jacques Johnson Kohoutek Lemmon LINEAR

C/1999 S4 C/2000 U5 C/2002 T7

LONEOS

C/2001 OG108 C/2007 F1

Lovejoy

C/2007 E2 C/2007 K5 C/2011 W3 C/2013 R1 C/2014 Q2

Lulin Machholz Matičič McNaught

C/2006 P1 C/2009 R1

McNaught–Russell Mrkos (de) NEAT Oukaimeden Pan-STARRS

C/2011 L4 C/2012 K1 C/2012 S4 311P

Pereyra Pojmański Ryves Seki–Lines (de) Siding Spring

C/2007 Q3 C/2013 A1

Skjellerup–Maristany Skorichenko–George SOHO Southern (de) Spacewatch–Rabinowitz Stonehouse SWAN

C/2006 M4 C/2012 E2

Utsunomiya–Jones West White–Ortiz–Bolelli Wilson–Hubbard (de) Yi–SWAN Zhu–Balam

Category Commons Wikinews

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The Solar System

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Planets

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Rings

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Moons

Terrestrial

Moon other near- Earth
Earth
objects

Martian

Phobos Deimos

Jovian

Ganymede Callisto Io Europa all 69

Saturnian

Titan Rhea Iapetus Dione Tethys Enceladus Mimas Hyperion Phoebe all 62

Uranian

Titania Oberon Umbriel Ariel Miranda all 27

Neptunian

Triton Proteus Nereid all 14

Plutonian

Charon Nix Hydra Kerberos Styx

Haumean

Hiʻiaka Namaka

Makemakean

S/2015 (136472) 1

Eridian

Dysnomia

Lists

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objects

By size By discovery date

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Small Solar System bodies

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moons

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Venus
trojans Near- Earth
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objects Earth-crossers Earth
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first discovered: Ceres Pallas Juno Vesta

Families Notable asteroids Kirkwood gap Main-belt comets Jupiter
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Plutinos Cubewanos

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Hypothetical objects

Vulcan Vulcanoids Phaeton Planet
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Astronomy Timeline

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Outline of the Solar System Portals Solar System Astronomy Earth
Earth
sciences Mars Jupiter Uranus Cosmology

Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way
Milky Way
subgroup → Local Group → Virgo Supercluster → Laniakea Supercluster → Observable universe → Universe Each arrow (→) may be read as "within" or "part of".

v t e

Minor planets navigator

1 Ceres 2 Pallas

v t e

Small Solar System
Solar System
bodies

Minor planets

Designation Groups List Moon Meanings of names

Asteroid

Aten asteroid Asteroid
Asteroid
belt Family Jupiter
Jupiter
trojan Near-Earth Spectral types

Distant minor planet

Centaur Damocloid Neptune
Neptune
trojan Trans-Neptunian object

Detached Kuiper belt Oort cloud Scattered disc

Comets

Extinct Great Halley-type Hyperbolic Long-period Lost Main-belt Near-parabolic Periodic Sungrazing

Other

Meteoroids

v t e

Spacecraft missions to minor planets

including dwarf planets and asteroids

Orbiters

NEAR Shoemaker Hayabusa Dawn Hayabusa2
Hayabusa2
(en route) OSIRIS-REx
OSIRIS-REx
(en route)

Landers

NEAR Shoemaker Hayabusa MASCOT (en route) MINERVA-II 1A, 1B, 2 (en route)

Flybys

Galileo NEAR Shoemaker Cassini–Huygens Deep Space 1 Stardust/NExT Rosetta/Philae New Horizons Chang'e 2

Failed

Clementine MINERVA Deep Impact PROCYON

Planned

NEA Scout (probe, 2019) Lucy (multiple flybys, 2021) DESTINY+ (multiple flybys, 2022) Psyche (orbiter, 2022)

Proposed

DART HAMMER OKEANOS

Cancelled

AGORA AIDA (AIM) Asteroid
Asteroid
Redirect Mission Clementine 2 CRAF Don Quijote Hayabusa
Hayabusa
Mk2 MAOSEP Marco Polo MarcoPolo-R New Horizons
New Horizons
2 Vesta

Related

Asteroid
Asteroid
belt Asteroid
Asteroid
capture Asteroid
Asteroid
mining Human mission to an asteroid Colonization of asteroids Ceres

Colonization

Pluto

Exploration

Vesta Small Solar System
Solar System
bodies

Near- Earth
Earth
object Trans-Neptunian object

Colonization

Trojan

Spacecraft missions to comets List of artificial objects on extra-terrestrial surfaces

Italics indicate active current missions.

v t e

Modern impact events

On Earth

Pre-2000

1490 Ch'ing-yang 1783 Great Meteor 1860 Great Meteor 1908 Tunguska 1913 Great Meteor Procession 1930 Curuçá River 1938 Chicora meteor 1947 Sikhote-Alin meteorite 1969 Murchison meteorite 1972 Great Daylight Fireball 1990 Earth-grazing meteoroid

Post-2000

2002 Eastern Mediterranean 2002 Vitim 2007 Carancas 2008 TC3
2008 TC3
impact 2009 Sulawesi superbolide 2012 Sutter's Mill meteorite 2012 UK meteoroid 2012 Novato meteorite 2013 Chelyabinsk meteor

Chelyabinsk meteorite

2014 AA
2014 AA
impact 2014 Ontario fireball 2015 Kerala meteorite 2015 Thailand bolide WT1190F
WT1190F
impact 2017 China bolide

On Jupiter

1994 Comet
Comet
Shoemaker–Levy 9 2009 Jupiter
Jupiter
impact 2010 Jupiter
Jupiter
impact

Lists

Asteroid
Asteroid
close approaches to Earth Comets Bolides

Meteor air bursts Meteorite
Meteorite
falls

Minor planets

crossing Earth's orbit

See also

Asteroid
Asteroid
impact avoidance Bolide Earth-grazing fireball Meteor procession Meteor shower Meteorite Meteoroid Near- Earth
Earth
object Potentially hazardous object

v t e

Planetary defense

Main topics

Asteroid Bolide Earth-grazing fireball Impact event

List of meteor air bursts

Meteor procession Meteor shower Meteorite Meteoroid Near- Earth
Earth
object Potentially hazardous object

Defense

Asteroid
Asteroid
impact avoidance Asteroid
Asteroid
close approaches Earth-crossing minor planets Gravity tractor Ion Beam Shepherd Damage scales

Palermo
Palermo
scale Torino scale

Space probes

Dawn Deep Impact DART Halley Armada Hayabusa Hayabusa2

MASCOT

NEAR Shoemaker NEA Scout New Horizons OSIRIS-REx PROCYON Rosetta

Philae

Stardust

NEO tracking

ATLAS Catalina Sky Survey LINEAR LONEOS NEAT NEOSSat NEOCam NEODyS OGS Telescope Orbit@home Pan-STARRS SCAP Sentinel Space Telescope Sentry Spacewatch WISE

Organizations

B612 Foundation Japan Spaceguard
Spaceguard
Association Meteoritical Society NEOShield Spaceguard The Spaceguard
Spaceguard
Foundation Space Situational Awareness Programme Planetary Defense Coordination Office

Potential threats

1950 DA 1994 WR12 101955 Bennu 2002 MN (410777) 2009 FD 2010 RF12 99942 Apophis

Films / video

The End of the World (1916) When Worlds Collide (1951) Gorath
Gorath
(1962) The Green Slime
The Green Slime
(1968) The Paradise Syndrome
The Paradise Syndrome
(1968) A Fire in the Sky
A Fire in the Sky
(1978) Meteor (1979) NOVA: Doomsday Asteroid
Asteroid
(1995) Asteroid
Asteroid
(1997) Deep Impact (1998) Armageddon
Armageddon
(1998) Avengers: Age of Ultron (2015) Judgment Day (1999) Post Impact
Post Impact
(2004) Deadly Skies (2006) Super Comet: After the Impact (2007) Impact (2009) NOVA: Last Extinction
Extinction
(2009) Meteor Storm
Meteor Storm
(2010) HORIZON: Asteroids–The Good, the Bad and the Ugly (2010) Melancholia (2011) NOVA: Meteor Strike (2013) NOVA: Asteroid: Doomsday or Payday? (2013) Impact Earth
Earth
(2015)

v t e

Global catastrophic risks

Future of the Earth Ultimate fate of the universe

Technological

Grey goo Kinetic bombardment Mutual assured destruction

Dead Hand Doomsday device

Synthetic intelligence
Synthetic intelligence
/ Artificial intelligence

Existential risk from artificial intelligence

See Template

AI takeover

Technological singularity Transhumanism

Sociological

Malthusian catastrophe New World Order (conspiracy theory) Nuclear holocaust

winter famine cobalt

Societal collapse World War III

Ecological

Climate change

Extinction
Extinction
risk from global warming

Runaway climate change

Global terrestrial stilling Ice
Ice
age Ecocide Human impact on the environment

See Template

Ozone depletion Cascade effect

Earth
Earth
Overshoot Day

Overexploitation Overpopulation

Human overpopulation

Biological

Extinction

Extinction
Extinction
event Human extinction Genetic erosion Genetic pollution

Dysgenics Pandemic

Biological agent

Transhumanism

Physical

Big Crunch Big Rip Coronal mass ejection Gamma-ray burst Hypercane Impact event

Asteroid Comet Potentially hazardous object

Rogue planet Solar flare Supervolcano

winter

Mythological

Eschatology

Buddhist Christian Hindu Islamic Jewish Norse Zoroastrian

2011 end times prediction 2012 phenomenon Apocalypse Armageddon Blood moon prophecy Book of Revelation Doomsday Clock End time Last Judgment List of dates predicted for apocalyptic events Nibiru cataclysm Rapture Revelation 12 sign prophecy Third Temple Year 2000 problem

Fiction

Alien invasion Apocalyptic and post-apocalyptic fiction

List of apocalyptic and post-apocalyptic fiction

Disaster films

List of disaster films

List of fictional doomsday devices Zombie apocalypse

Categories Apocalypticism Future problems Hazards Risk analysis Doomsday scenarios

Authority control

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