253 Mathilde, a C-type asteroid measuring about 50 km (30 mi) across, covered in craters half that size. Photograph taken in 1997 by the NEAR Shoemaker probe.
Diagram of the Solar System's asteroid belt
2014 JO25 imaged by radar during its 2017 Earth flyby

An asteroid is a minor planet of the inner Solar System. Historically, these terms have been applied to any astronomical object orbiting the Sun that did not resolve into a disc in a telescope and was not observed to have characteristics of an active comet such as a tail. As minor planets in the outer Solar System were discovered that were found to have volatile-rich surfaces similar to comets, these came to be distinguished from the objects found in the main asteroid belt.[1] Thus the term "asteroid" now generally refers to the minor planets of the inner Solar System, including those co-orbital with Jupiter. Larger asteroids are often called planetoids.


Millions of asteroids exist: many are shattered remnants of planetesimals, bodies within the young Sun's solar nebula that never grew large enough to become planets.[2] The vast majority of known asteroids orbit within the main asteroid belt located between the orbits of Mars and Jupiter, or are co-orbital with Jupiter (the Jupiter trojans). However, other orbital families exist with significant populations, including the near-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 sizes of asteroids varies greatly; the largest, Ceres, is almost 1,000 km (600 mi) across and massive enough to qualify as a dwarf planet.

Asteroids are somewhat arbitrarily 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 primarily composed of dust and ice. Furthermore, asteroids formed closer to the sun, preventing the development of cometary ice.[3] The difference between asteroids and meteoroids is mainly one of size: meteoroids have a diameter of one meter or less, 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 is only in very dark skies when it is favorably positioned. Rarely, small asteroids passing close to Earth may be visible to the naked eye for a short time.[6] As of March 2020, the Minor Planet Center had data on 930,000 minor planets in the inner and outer Solar System, of which about 545,000 had enough information to be given numbered designations.[7]

The United Nations declared 30 June as International 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]

In April 2018, the B612 Foundation reported "It is 100 percent certain we'll be hit [by a devastating asteroid], but we're not 100 percent sure when."[10] Also in 2018, physicist Stephen Hawking, in his final book Brief Answers to the Big Questions, considered an asteroid collision to be the biggest threat to the planet.[11][12][13] In June 2018, the US National Science and Technology Council warned that America is unprepared for an asteroid impact event, and has developed and released the "National Near-Earth Object Preparedness Strategy Action Plan" to better prepare.[14][15][16][17][18] According to expert testimony in the United States Congress in 2013, NASA would require at least five years of preparation before a mission to intercept an asteroid could be launched.[19]


Sizes of the first ten asteroids to be discovered, compared to the Moon
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.[a] 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 to propose the term "asteroid",[b] 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.[c]

Discovery timeline:

  • 10 by 1849
    • 1 Ceres, 1801
    • 2 Pallas – 1802
    • 3 Juno – 1804
    • 4 Vesta – 1807
    • 5 Astraea – 1845
    • in 1846, planet Neptune was discovered[23]
    • 6 Hebe – July 1847
    • 7 Iris – August 1847
    • 8 Flora – October 1847
    • 9 Metis – 25 April 1848
    • 10 Hygiea – 12 April 1849 tenth asteroid discovered
  • 100 asteroids by 1868
  • 1,000 by 1921
  • 10,000 by 1989
  • 100,000 by 2005[24]
  • 1,000,000 by 2020[7]

Historical methods

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 by the Titius-Bode law, partly because of the discovery, by Sir William Herschel in 1781, of the planet Uranus at the distance predicted by the law.[25] 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 – 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 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 used these observations to calculate the orbit of this unknown object, which was found to be between the planets Mars and Jupiter. Piazzi named it after Ceres, the Roman goddess of agriculture.[25]

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 J.R. Hind, A. de Gasparis, R. Luther, H.M.S. Goldschmidt, J. Chacornac, J. Ferguson, N.R. Pogson, E.W. Tempel, J.C. Watson, C.H.F. Peters, A. Borrelly, J. Palisa, the Henry brothers and A. 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, some calling them "vermin of the skies",[26] a phrase variously attributed to E. Suess[27] and E. Weiss.[28] Even a century later, only a few thousand asteroids were identified, numbered and named.

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 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 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.[29]

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 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

2004 FH is the center dot being followed by the sequence; the object that flashes by during the clip is an artificial satellite.
Cumulative discoveries of just the near-Earth asteroids known by size, 1980–2017

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 asteroids are the Apollos, Amors, and Atens. Various asteroid deflection strategies have been proposed, as early as the 1960s.

The 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 AU of Earth in 1937. Astronomers began to realize the possibilities of Earth impact.

Two events in later decades increased the alarm: the increasing acceptance of the Alvarez hypothesis that an impact event resulted in the Cretaceous–Paleogene extinction, and the 1994 observation of 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, it was estimated that 89% to 96% of near-Earth asteroids one kilometer or larger in diameter had been discovered.[30] A list of teams using such systems includes:[31] [32]

As of 29 October 2018, the LINEAR system alone has discovered 147,132 asteroids.[33] Among all the surveys, 19,266 near-Earth asteroids have been discovered[34] including almost 900 more than 1 km (0.6 mi) in diameter.[35]


Euler diagram showing the types of bodies in the Solar System. (see Small Solar System body)
A composite image, to the same scale, of the asteroids imaged at high resolution prior to 2012. They are, from largest to smallest: 4 Vesta, 21 Lutetia, 253 Mathilde, 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 (right) shown to scale.

Traditionally, small bodies orbiting the Sun were classified as comets, asteroids, or meteoroids, with anything smaller than one meter across being called a meteoroid. Beech and Steel's 1995 paper proposed a meteoroid definition including size limits.[36][37] 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.[38]

In 2006, the term "small Solar System body" was also introduced to cover both most minor planets and comets.[39][d] 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.[40] The word "planetesimal" has a similar meaning, but refers specifically to the small building blocks of the planets that existed when the Solar System was forming. The term "planetule" was coined by the geologist William Daniel Conybeare to describe minor planets,[41] 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.[42]

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 for part of their orbit. Those located between the orbits of Mars and Jupiter were known for many years simply as The Asteroids.[43] 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 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.[44] They are thought to be predominantly comet-like in composition, though some may be more akin to asteroids.[45] 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 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,[46] suggesting "a continuum between asteroids and comets" rather than a sharp dividing line.[47]

The minor planets beyond Jupiter's orbit are sometimes also called "asteroids", especially in popular presentations.[e] However, it is becoming increasingly common for the term "asteroid" to be restricted to minor planets of the inner Solar System.[44] Therefore, this article will restrict itself for the most part to the classical asteroids: objects of the asteroid belt, Jupiter trojans, and near-Earth objects.

When the IAU introduced the class small 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 Body' will be preferred."[49] 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.

Artist's impression shows how an asteroid is torn apart by the strong gravity of a white dwarf.[50]


It is thought that planetesimals in the asteroid belt evolved much like the rest of the solar nebula until 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.[51] Ceres and Vesta grew large enough to melt and differentiate, with heavy metallic elements sinking to the core, leaving rocky minerals in the crust.[52]

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.[53]

Distribution within the Solar System

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 and by the Yarkovsky effect. Significant populations include:

Asteroid belt

The majority of known asteroids orbit within the asteroid belt between the orbits of 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,[54] 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 was prevented by large gravitational perturbations by Jupiter.


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 trojans. Although fewer Jupiter trojans have been discovered (as of 2010), 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 asteroids

Known Near-Earth objects as of January 2018
Frequency of bolides, small asteroids roughly 1 to 20 meters in diameter impacting Earth's atmosphere

Near-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, 14,464 near-Earth asteroids are known[30] and approximately 900–1,000 have a diameter of over one kilometer.


Size distribution

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

Asteroids vary greatly in size, from almost 1000 km for the largest down to rocks just 1 meter across.[f] The three largest are very much like miniature planets: they are roughly spherical, have at least partly differentiated interiors,[55] and are thought to be surviving protoplanets. The vast majority, however, are much smaller and are irregularly shaped; they are thought to be either battered planetesimals or fragments of larger bodies.

The dwarf planet Ceres is by far the largest asteroid, with a diameter of 940 km (580 mi). The next largest are 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 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 and Jupiter, is estimated to be in the range of (2.8–3.2)×1021 kg, about 4% of the mass of the Moon. Of this, Ceres comprises 0.938×1021 kg, about a third of the total. Adding in the next three most massive objects, Vesta (9%), Pallas (7%), and Hygiea (3%), brings this figure up to half, whereas the three most-massive asteroids after that, 511 Davida (1.2%), 704 Interamnia (1.0%), and 52 Europa (0.9%), constitute only another 3%. The number of asteroids 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 5 km and 100 km, where more asteroids than expected from a logarithmic distribution are found.[56]

Approximate number of asteroids (N) larger than a certain diameter (D)
D0.1 km0.3 km0.5 km1 km3 km5 km10 km30 km50 km100 km200 km300 km500 km900 km

Largest asteroids

The four largest asteroids: 1 Ceres, 4 Vesta, 2 Pallas, and 10 Hygiea

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 irregularly shaped asteroids. The fourth-largest asteroid, Hygiea, appears nearly spherical although it may have an undifferentiated interior,[57] like the majority of asteroids. Between them, the four largest asteroids constitute half the mass of the asteroid belt.

Ceres is the only asteroid that appears to be plastic shape under its own gravity and hence the only one that is a likely dwarf planet.[39] It has a much higher absolute magnitude than the other asteroids, of around 3.32,[58] and may possess a surface layer of ice.[59] Like the planets, Ceres is differentiated: it has a crust, a mantle and a core.[59] 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;[60][61] its composition is mainly of basaltic rock with minerals such as olivine.[62] 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 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.[64] Its composition is similar to that of Ceres: high in carbon and silicon, and perhaps partially differentiated.[65] Pallas is the parent body of the Palladian family of asteroids.

Hygiea is the largest carbonaceous asteroid[66] and, unlike the other largest asteroids, lies relatively close to the plane of the ecliptic.[67] It is the largest member and presumed parent body of the Hygiean family of asteroids. Because there is no sufficiently large crater on the surface to be the source of that family, as there is on Vesta, it is thought that Hygiea may have been completely disrupted in the collision that formed the Hygiean family and recoalesced after losing a bit less than 2% of its mass. Observations taken with the Very Large Telescope's SPHERE imager in 2017 and 2018, and announced in late 2019, revealed that Hygiea has a nearly spherical shape, which is consistent both with it being in hydrostatic equilibrium (and thus a dwarf planet), or formerly being in hydrostatic equilibrium, or with being disrupted and recoalescing.[68][69]

Attributes of largest asteroids

to ecliptic
(% of Moon)
(×1018 kg)
(% of Ceres)
(mean 939.4)
(mean 525.4)
15%25928%3.46 ± 0.045.34
(mean 511±4)
(mean 433±8)


Measurements of the rotation rates of large asteroids in the asteroid belt show that there is an upper limit. Very few asteroids with a diameter larger than 100 meters have a rotation period smaller than 2.2 hours.[70] 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 the accumulation of debris after collisions between asteroids.[71]


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.[72] 10 Hygiea, however, which appears to have a uniformly primitive composition of carbonaceous chondrite, is thought to be the largest undifferentiated asteroid, though it may be a differentiated asteroid that was globally disrupted by an impact and then reassembled. Other asteroids appear to be the remnant cores or mantles of proto-planets, high in rock and metal. Most small 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.[73]

In the main asteroid belt, there appear to be two primary populations of asteroid: a dark, volatile-rich population, consisting of the C-type and P-type asteroids, with albedos less that 0.10 and densities under 2.2 g/cm3, and a dense, volatile-poor population, consisting of the S-type and M-type asteroids, with albedos over 0.15 and densities greater than 2.7. Within these populations, larger asteroids are denser, presumably due to compression. There appears to be minimal macro-porosity (interstitial vacuum) in the score of asteroids with masses greater than 10×1018 kg.[74]

Asteroids contain traces of amino acids and other organic compounds, and some speculate that asteroid impacts may have seeded the early Earth with the chemicals necessary to initiate life, or may have even brought life itself to Earth (also see panspermia).[75][76] In August 2011, a report, based on NASA studies with meteorites found on Earth, was published suggesting DNA and RNA components (adenine, guanine and related organic molecules) may have been formed on asteroids and comets in outer space.[77][78][79]

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 (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. The fact that such large asteroids as Sylvia may 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.[80]

On 7 October 2009, the presence of water ice was confirmed on the surface of 24 Themis using NASA's Infrared Telescope Facility. The surface of the asteroid appears completely covered in ice. As this ice layer is sublimating, it may be getting replenished by a reservoir of ice under the surface. Organic compounds were also detected on the surface.[81][82][83][84] Scientists hypothesize that some of the first water brought to Earth was delivered by asteroid impacts after the collision that produced the Moon. The presence of ice on 24 Themis supports this theory.[83]

In October 2013, water was detected on an extrasolar body for the first time, on an asteroid orbiting the white dwarf GD 61.[85] On 22 January 2014, 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.[86] The detection was made by using the far-infrared abilities of the Herschel Space Observatory.[87] 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."[87]

In May 2016, significant asteroid data arising from the Wide-field Infrared Survey Explorer and NEOWISE missions have been questioned.[88][89][90] Although the early original criticism had not undergone peer review,[91] a more recent peer-reviewed study was subsequently published.[92][18]

In November 2019, scientists reported detecting, for the first time, sugar molecules, including ribose, in meteorites, suggesting that chemical processes on asteroids can produce some fundamentally essential bio-ingredients important to life, and supporting the notion of an RNA world prior to a DNA-based origin of life on Earth, and possibly, as well, the notion of panspermia.[93][94]

Acfer 049, a meteorite discovered in Algeria in 1990, was shown in 2019 to have ice fossils inside it – the first direct evidence of water ice in the composition of asteroids.[95]

Findings have shown that solar winds can react with the oxygen in the upper layer of the asteroids and create water. It has been estimated that every cubic metre of irradiated rock could contain up to 20 litres.[96]

Surface features

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 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.[97] Medium-sized asteroids such as Mathilde and 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.[98]


Asteroids become darker and redder with age due to space weathering.[99] However evidence suggests most of the color change occurs rapidly, in the first hundred thousand years, limiting the usefulness of spectral measurement for determining the age of asteroids.[100]


Showing Kirkwood gaps, by showing positions based on their semi-major axis

Asteroids are commonly categorized according to two criteria: the characteristics of their orbits, and features of their reflectance spectrum.

Orbital classification

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.[101] Families are more common and easier to identify within the main asteroid belt, but several small families have been reported among the Jupiter trojans.[102] 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

Some asteroids have unusual horseshoe orbits that are co-orbital with Earth or some other planet. Examples are 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 and Venus are known to have quasi-satellites.

Such objects, if associated with Earth or 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

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 (115 ft) across can be seen.

In 1975, an asteroid taxonomic system based on color, albedo, and spectral shape was developed by Chapman, Morrison, and Zellner.[103] 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.[104] 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.[105]

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.


Originally, spectral designations were based on inferences of an asteroid's composition.[106] 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 the same (or similar) materials.


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.[107] In addition, names can be proposed by the asteroid's discoverer, within guidelines established by the International Astronomical Union.[108]


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.[109]

1 CeresOld planetary symbol of Ceres Other sickle variant symbol of CeresCeres' scythe, reversed to double as the letter C1801
2 PallasOld symbol of Pallas Variant symbol of PallasAthena's (Pallas') spear1801
3 JunoOld symbol of Juno Old symbol of JunoA star mounted on a scepter, for Juno, the Queen of Heaven1804
4 VestaOld planetary symbol of Vesta Old planetary symbol of VestaThe altar and sacred fire of Vesta1807
5 AstraeaAstraea symbol (fixed width).svg Astraea scales symbol (fixed width).svgA scale, rendered as an inverted anchor, symbol of justice1845
6 HebeHebe symbol (simple, fixed width).svg 6 Hebe symbol (fixed width).svgHebe's cup1847
7 IrisIris symbol (simple, fixed width).svg Iris symbol (fixed width).svgA rainbow (iris) and a star1847
8 Flora8 Flora symbol (1852).svg Flora symbol (fixed width).svgA flower (flora)1847
9 Metis9 Metis symbol.svgThe eye of wisdom and a star1848
10 HygieaHygiea symbol (original, fixed width).svg Rod of Asclepius (fixed width).svgHygiea's serpent and a star, or the Rod of Asclepius1849
11 ParthenopeParthenope symbol (fixed width).svg Parthenope lyre symbol (fixed width).svga fish and a star, or a lyre; symbols of the sirens1850
12 VictoriaVictoria symbol (fixed width).svgThe laurels of victory and a star1850
13 EgeriaAstronomical symbol of 13 Egeria Astronomical symbol of 13 EgeriaA shield, symbol of Egeria's protection, and a star1850
14 IreneIrene symbol (fixed width).svgA dove carrying an olive branch (symbol of irene 'peace')
with a star on its head,[110] or an olive branch, a flag of truce, and a star
15 EunomiaEunomia symbol (fixed width).svgA heart, symbol of good order (eunomia), and a star1851
16 PsychePsyche symbol (fixed width).svg Psyche symbol (elaborate, fixed width).svgA butterfly's wing, symbol of the soul (psyche), and a star1852
17 ThetisThetis symbol (fixed width).svgA dolphin, symbol of Thetis, and a star1852
18 MelpomeneMelpomene symbol (fixed width).svgThe dagger of Melpomene, and a star1852
19 FortunaFortuna symbol (fixed width).svgThe wheel of fortune and a star1852
26 ProserpinaProserpina symbol (fixed width).svgProserpina's pomegranate1853
28 BellonaBellona symbol (fixed width).svgBellona's whip / morning star and lance[111]1854
29 AmphitriteAmphitrite symbol (fixed width).svgThe shell of Amphitrite and a star1854
35 LeukotheaLeukothea symbol (fixed width).svgA lighthouse beacon, symbol of Leucothea[112]1855
37 Fides37 Fides symbol.svgThe cross of faith (fides)[113]1855

In 1851,[114] after the fifteenth asteroid (Eunomia) had been discovered, 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 was the first asteroid that was not assigned an iconic symbol, and no iconic symbols were created after the 1855 discovery of 37 Fides.[h] 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.[110]


Eros as seen by visiting spacecraft

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 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 occultations (when an asteroid passes directly in front of a star). Radar imaging can yield good information about asteroid shapes and orbital and rotational parameters, especially for near-Earth asteroids. In terms of delta-v and propellant requirements, NEOs are more easily accessible than the Moon.[115]

The first close-up photographs of asteroid-like objects were taken in 1971, when the 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 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 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 in 2002).

From September to November 2005, the Japanese Hayabusa probe studied 25143 Itokawa in detail and was plagued with difficulties, but returned samples of its surface to Earth on 13 June 2010.

The European Rosetta probe (launched in 2004) flew by 2867 Šteins in 2008 and 21 Lutetia, the third-largest asteroid visited to date, in 2010.

In September 2007, 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 is the second-largest asteroid visited to date.

On 13 December 2012, China's lunar orbiter Chang'e 2 flew within 3.2 km (2 mi) of the asteroid 4179 Toutatis on an extended mission.

The Japan Aerospace Exploration Agency (JAXA) launched the Hayabusa2 probe in December 2014, and plans to return samples from 162173 Ryugu in December 2020.

In June 2018, the US National Science and Technology Council warned that America is unprepared for an asteroid impact event, and has developed and released the "National Near-Earth Object Preparedness Strategy Action Plan" to better prepare.[14][15][16][18]


In September 2016, NASA launched the OSIRIS-REx sample return mission to asteroid 101955 Bennu, which it reached in December 2018. On May 10 2021, the probe departed the asteroid with a sample from its surface, and is expected to return to Earth on September 24 2023.[116]

Planned and future missions

Planned Lucy spacecraft

In early 2013, NASA announced the planning stages of a mission to capture a near-Earth asteroid and move it into lunar orbit where it could possibly be visited by astronauts and later impacted into the Moon.[117] On 19 June 2014, NASA reported that asteroid 2011 MD was a prime candidate for capture by a robotic mission, perhaps in the early 2020s.[118]

It has been suggested that asteroids might be used as a source of materials that 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.

In the U.S. Discovery program the Psyche proposal to 16 Psyche and Lucy spacecraft to Jupiter trojans made it to the semi-finalist stage of mission selection.

In January 2017, Lucy and Psyche were both selected as NASA's Discovery Program missions 13 and 14 respectively.[119]

In November 2021, NASA launched its Double Asteroid Redirection Test (DART), a mission to test technology for defending Earth against potential asteroids or comets.[120]

Location of Ceres (within asteroid belt) compared to other bodies of the Solar System

Astronomical unitAstronomical unitAstronomical unitAstronomical unitAstronomical unitAstronomical unitAstronomical unitAstronomical unitAstronomical unitAstronomical unitHalley's CometSunEris (dwarf planet)Makemake (dwarf planet)Haumea (dwarf planet)PlutoCeres (dwarf planet)NeptuneUranusSaturnJupiterMarsEarthVenusMercury (planet)Astronomical unitAstronomical unitDwarf planetDwarf planetCometPlanet

Distances of selected bodies of the Solar System from the Sun. The left and right edges of each bar correspond to the perihelion and aphelion of the body, respectively, hence long bars denote high orbital eccentricity. The radius of the Sun is 0.7 million km, and the radius of Jupiter (the largest planet) is 0.07 million km, both too small to resolve on this image.


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 or other inhabited planets, dwarf planets, and natural satellites by potential impact.


See also

Explanatory notes

  1. ^ 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.
  2. ^ In an oral presentation,[20] Clifford Cunningham presented his finding that the word was coined by Charles Burney, Jr., the son of a friend of Herschel,[21][22]
  3. ^ For example, theAnnual of Scientific Discovery. 1871. p. 316 – via Google Books.: "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 and Jupiter".
    The Universal English Dictionary (John Craig, 1869) lists the asteroids (and gives their pronunciations) up to 64 Angelina, along with the definition "one of the recently-discovered planets." At this time it was common to anglicize the spellings of the names, e.g. "Aglaia" for 47 Aglaja and "Atalanta" for 36 Atalante.
  4. ^ The definition of "small Solar System bodies" says that they "include most of the Solar System asteroids, most trans-Neptunian objects, comets, and other small bodies".
  5. ^ For instance, a joint NASAJPL public-outreach website states:

    We include Trojans (bodies captured in Jupiter's 4th and 5th Lagrange points), Centaurs (bodies in orbit between 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.[48]

  6. ^ 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.
  7. ^ The order of arrangement in the chart will certainly change with new data. The value of Interamnia, for example, has an uncertainty of 30%, though most estimates are more precise than that.
  8. ^ Except for Pluto and, in the astrological community, for a few outer bodies such as 2060 Chiron.


  1. ^ "Asteroids". Jet Propulsion Laboratory. NASA. Retrieved 13 September 2010.
  2. ^ "What are asteroids and comets?". CNEOS. Frequently Asked Questions (FAQs). Archived from the original on 9 September 2010. Retrieved 13 September 2010.
  3. ^ "What is the difference between an asteroid and a comet?". Infrared Processing and Analysis Center. Cool Cosmos. Pasadena, CA: California Institute of Technology. Retrieved 13 August 2016.
  4. ^ a b Rubin, Alan E.; Grossman, Jeffrey N. (January 2010). "Meteorite and meteoroid: New comprehensive definitions". Meteoritics and Planetary Science. 45 (1): 114–122. Bibcode:2010M&PS...45..114R. doi:10.1111/j.1945-5100.2009.01009.x.
  5. ^ Atkinson, Nancy (2 June 2015). "What is the difference between asteroids and meteorites?". Universe Today. Retrieved 13 August 2016.
  6. ^ Britt, Robert Roy (4 February 2005). "Closest flyby of large asteroid to be naked-eye visible".
  7. ^ a b "Latest Published Data". Minor Planet Center. International Astronomical Union. Retrieved 11 March 2020.
  8. ^ "United Nations General Assembly proclaims 30 June as International Asteroid Day". Office for Outer Space Affairs (Press release). United Nations. 7 December 2016. UNIS/OS/478.
  9. ^ "International cooperation in the peaceful uses of outer space". United Nations. Rapporteur: Awale Ali Kullane. 25 October 2016. Retrieved 6 December 2016.{{cite web}}: CS1 maint: others (link)
  10. ^ Homer, Aaron (28 April 2018). "Earth will be hit by an asteroid with 100 percent certainty, says space-watching group B612". Inquisitr. Retrieved 26 November 2018. The group of scientists and former astronauts is devoted to defending the planet from a space apocalypse.
  11. ^ Stanley-Becker, Isaac (15 October 2018). "Stephen Hawking feared race of 'superhumans' able to manipulate their own DNA". The Washington Post. Retrieved 26 November 2018.
  12. ^ Haldevang, Max de (14 October 2018). "Stephen Hawking left us bold predictions on AI, superhumans, and aliens". Quartz. Retrieved 26 November 2018.
  13. ^ Bogdan, Dennis (18 June 2018). "Better Way To Avoid Devastating Asteroids Needed?". The New York Times. Retrieved 26 November 2018.
  14. ^ a b National Near-Earth Object Preparedness Strategy Action Plan (PDF). (Report). 21 June 2018. Retrieved 22 June 2018 – via National Archives.
  15. ^ a b Mandelbaum, Ryan F. (21 June 2018). "America isn't ready to handle a catastrophic asteroid impact, new report warns". Gizmodo. Retrieved 22 June 2018.
  16. ^ a b Myhrvold, Nathan (22 May 2018). "An empirical examination of WISE/NEOWISE asteroid analysis and results". Icarus. 314: 64–97. Bibcode:2018Icar..314...64M. doi:10.1016/j.icarus.2018.05.004.
  17. ^ Chang, Kenneth (14 June 2018). "Asteroids and adversaries: Challenging what NASA knows about space rocks". The New York Times. Retrieved 26 November 2018. Two years ago, NASA dismissed and mocked an amateur's criticisms of its asteroids database. Now Nathan Myhrvold is back, and his papers have passed peer review.
  18. ^ a b c Chang, Kenneth (14 June 2018). "Asteroids and adversaries: Challenging what NASA knows about space rocks". The New York Times. Retrieved 22 June 2018.
  19. ^ Threats from Space: A review of U.S. Government efforts to track and mitigate asteroids and meteors (PDF) (Report). Hearing before the Committee on Science, Space, and Technology. Vol. Part I and Part II. House of Representatives. 19 March 2013. p. 147. Retrieved 26 November 2018.
  20. ^ HADII Abstracts. HAD Meeting with DPS. Denver, CO. October 2013. Archived from the original on 1 September 2014. Retrieved 14 October 2013.
  21. ^ Nolin, Robert (8 October 2013). "Local expert reveals who really coined the word 'asteroid'". Sun-Sentinel. Archived from the original on 30 November 2014. Retrieved 10 October 2013.
  22. ^ Wall, Mike (10 January 2011). "Who really invented the word 'Asteroid' for space rocks?". Retrieved 10 October 2013.
  23. ^ "Discovery of Neptune". Today in Science. 23 September 2016. Retrieved 13 November 2018.
  24. ^ Tichá, Jana; Marsden, Brian G.; Bowell, Edward L.G.; Williams, Iwan P.; Marsden, Brian G.; Green, Daniel W.E.; et al. (2009). "Division III / Working Group Committee on Small Bodies Nomenclature". Proceedings of the International Astronomical Union. 4 (T27A): 187–189. Bibcode:2009IAUTA..27..187T. doi:10.1017/S1743921308025489. ISSN 1743-9213.
  25. ^ a b McCall, Gerald J.H.; Bowden, A.J.; Howarth, Richard J. (2006). The History of Meteoritics and Key Meteorite Collections: Fireballs, Falls and Finds. Geological Society of London. ISBN 978-1-86239-194-9 – via Google Books.
  26. ^ Friedman, Lou. "Vermin of the Sky". The Planetary Society.
  27. ^ Hale, George E. (1916). "Some Reflections on the Progress of Astrophysics". Popular Astronomy. Address at the semi-centennial of the Dearborn Observatory. Vol. 24. pp. 550–558 [555]. Bibcode:1916PA.....24..550H.
  28. ^ Seares, Frederick H. (1930). "Address of the Retiring President of the Society in Awarding the Bruce Medal to Professor Max Wolf". Publications of the Astronomical Society of the Pacific. 42 (245): 5–22 [10]. Bibcode:1930PASP...42....5S. doi:10.1086/123986.
  29. ^ Chapman, Mary G. (17 May 1992). "Carolyn Shoemaker, planetary astronomer and most successful 'comet hunter' to date". Astrogeology. USGS. Retrieved 15 April 2008.
  30. ^ a b "Discovery Statistics". CNEOS. Archived from the original on 13 May 2004. Retrieved 15 June 2016.
  31. ^ Yeomans, Don. "Near Earth Object Search Programs". NASA. Archived from the original on 24 April 2008. Retrieved 15 April 2008.
  32. ^ "Statistics by Survey (all)". Jet Propulsion Laboratory. Discovery Statistics. NASA. 27 December 2018. Archived from the original on 28 December 2018. Retrieved 27 December 2018.
  33. ^ "Minor Planet Discover Sites". Minor Planet Center. International Astronomical Union. Retrieved 27 December 2018.
  34. ^ "Unusual Minor Planets". Minor Planet Center. International Astronomical Union. Retrieved 27 December 2018.
  35. ^ "Cumulative Totals". Jet Propulsion Laboratory. Discovery Statistics. NASA. 20 December 2018. Retrieved 27 December 2018.
  36. ^ Beech, M.; Steel, D. (September 1995). "On the definition of the term meteoroid". Quarterly Journal of the Royal Astronomical Society. 36 (3): 281–284. Bibcode:1995QJRAS..36..281B. Meteoroid: A solid object moving in space, with a size less than 10 m, but larger than 100 μm.
  37. ^ Czechowski, L. (2006). "Planetology and classification of the solar system bodies". Adv. Space Res. 38 (9): 2054–2059. Bibcode:2006AdSpR..38.2054C. doi:10.1016/j.asr.2006.09.004.
  38. ^ "2011 CQ1". Jet Propulsion Laboratory. JPL Small-Body Database browser (2011-02-04 last obs). NASA.
  39. ^ a b "The final IAU resolution on the definition of "planet" ready for voting" (Press release). International Astronomical Union. 24 August 2006. Retrieved 2 March 2007.
  40. ^ Chaisson, E.J. "Solar System modeling". Center for Astronomy. Harvard University. Retrieved 9 April 2016.
  41. ^ "Meaning of Planetule". Hyper-dictionary. Retrieved 15 April 2008.
  42. ^ Weissman, Paul R.; Bottke, William F. Jr.; Levinson, Harold F. (2002). "Evolution of Comets into Asteroids" (PDF). Planetary Science Directorate. Southwest Research Institute. Retrieved 3 August 2010.
  43. ^ Eglinton, D.; Eglinton, A.C. (16 June 1932). "The Asteroids". The Queenslander. Astronomy (column). Retrieved 25 June 2018.
  44. ^ a b "Are Kuiper Belt objects asteroids?". Ask an astronomer. Cornell University. Archived from the original on 3 January 2009.
  45. ^ Short, Nicholas M., Sr. "Asteroids and Comets". Goddard Space Flight Center. NASA. Archived from the original on 25 September 2008.
  46. ^ Comet dust seems more ‘asteroidy’. Scientific American (audio podcast). 25 January 2008.
  47. ^ "Comet samples are surprisingly asteroid-like". New Scientist. 24 January 2008.
  48. ^ "Asteroids". Solar System Dynamics. Jet Propulsion Laboratory. Archived from the original on 14 June 2006. Retrieved 8 December 2021.
  49. ^ "Pluto". Questions and Answers on Planets. International Astrophysical Union.
  50. ^ "The glowing halo of a zombie star". European Southern Observatory. Retrieved 16 November 2015.
  51. ^ Bottke, William F., Jr.; Durda, Daniel D.; Nesvorny, David; Jedicke, Robert; Morbidelli, Alessandro; Vokrouhlicky, David; Levison, Hal (2005). "The fossilized size distribution of the main asteroid belt" (PDF). Icarus. 175 (1): 111. Bibcode:2005Icar..175..111B. doi:10.1016/j.icarus.2004.10.026.
  52. ^ Kerrod, Robin (2000). Asteroids, Comets, and Meteors. Lerner Publications Co. ISBN 978-0-585-31763-2.
  53. ^ McKinnon, William; McKinnon, B. (2008). "On The Possibility of Large KBOs Being Injected into The Outer Asteroid Belt". Bulletin of the American Astronomical Society. 40: 464. Bibcode:2008DPS....40.3803M.
  54. ^ Tedesco, Edward; Metcalfe, Leo (4 April 2002). "New study reveals twice as many asteroids as previously believed" (Press release). European Space Agency. Retrieved 21 February 2008.
  55. ^ Schmidt, B.; Russell, C.T.; Bauer, J.M.; Li, J.; McFadden, L.A.; Mutchler, M.; et al. (2007). "Hubble Space Telescope Observations of 2 Pallas". Bulletin of the American Astronomical Society. 39: 485. Bibcode:2007DPS....39.3519S.
  56. ^ Davis, ed. (2002). Asteroids III. cited byIvezić, Željko (2004). "Lecture 4: Moving objects detected by SDSS" (PDF). Astronomy Department. Lecture notes for ASTR 598. University of Washington. Archived from the original (PDF) on 20 July 2011.
  57. ^ "Asteroids | Imaging the Universe". Retrieved 31 August 2021.
  58. ^ Parker, J.W.; Stern, S.A.; Thomas, P.C.; Festou, M.C.; Merline, W.J.; Young, E.F.; Binzel, R.P.; Lebofsky, L.A. (2002). "Analysis of the First Disk-resolved Images of Ceres from Ultraviolet Observations with the Hubble Space Telescope". The Astronomical Journal. 123 (1): 549–557. arXiv:astro-ph/0110258. Bibcode:2002AJ....123..549P. doi:10.1086/338093.
  59. ^ a b "Asteroid 1 Ceres". The Planetary Society. Archived from the original on 29 September 2007. Retrieved 20 October 2007.
  60. ^ "Asteroid or mini-planet? Hubble maps the ancient surface of Vesta". Hubble Space Telescope (Press release). Space Telescope Science Institute. 19 April 1995. STScI-1995-20. Retrieved 16 December 2017.
    "Key stages in the evolution of the asteroid Vesta". Hubble Space Telescope (Press release). Space Telescope Science Institute. 19 April 1995. Archived from the original on 7 September 2008. Retrieved 20 October 2007.
  61. ^ Russel, C.; Raymond, C.; Fraschetti, T.; Rayman, M.; Polanskey, C.; Schimmels, K.; Joy, S. (2005). "Dawn mission and operations". Proceedings of the International Astronomical Union. 1 (S229): 97–119. Bibcode:2006IAUS..229...97R. doi:10.1017/S1743921305006691.
  62. ^ Burbine, T.H. (July 1994). "Where are the olivine asteroids in the main belt?". Meteoritics. 29 (4): 453. Bibcode:1994Metic..29..453B.
  63. ^ Pitjeva, E.V. (2005). "High-Precision Ephemerides of Planets – EPM and Determination of Some Astronomical Constants" (PDF). Solar System Research. 39 (3): 184. Bibcode:2005SoSyR..39..176P. doi:10.1007/s11208-005-0033-2. S2CID 120467483. Archived from the original (PDF) on 3 July 2014.
  64. ^ Torppa, J.; Kaasalainen, M.; Michałowski, T.; Kwiatkowski, T.; Kryszczyńska, A.; Denchev, P.; Kowalski, R. (1996). "Shapes and rotational properties of thirty asteroids from photometric data". Icarus. 164 (2): 346–383. Bibcode:2003Icar..164..346T. doi:10.1016/S0019-1035(03)00146-5.
  65. ^ Larson, H.P.; Feierberg, M.A. & Lebofsky, L.A. (1983). "The composition of asteroid 2 Pallas and its relation to primitive meteorites". Icarus. 56 (3): 398. Bibcode:1983Icar...56..398L. doi:10.1016/0019-1035(83)90161-6.
  66. ^ Barucci, M.A.; et al. (2002). "10 Hygiea: ISO Infrared Observations" (PDF). Icarus. 156 (1): 202–210. Bibcode:2002Icar..156..202B. doi:10.1006/icar.2001.6775. Archived from the original (PDF) on 28 November 2007. Retrieved 21 October 2007.
  67. ^ "Ceres the Planet". Archived from the original on 11 October 2007. Retrieved 20 October 2007.
  68. ^ Vernazza, P.; Jorda, L.; Ševeček, P.; Brož, M.; Viikinkoski, M.; Hanuš, J.; et al. (28 October 2019). "A basin-free spherical shape as an outcome of a giant impact on asteroid Hygiea, Supplementary Information" (PDF). Nature Astronomy. doi:10.1038/s41550-019-0915-8. hdl:10045/103308. S2CID 209938346. Retrieved 30 October 2019.
  69. ^ Strickland, A. (28 October 2019). "It's an asteroid! No, it's the new smallest dwarf planet in our solar system". CNN. Retrieved 28 October 2019.
  70. ^ "About Lightcurves". ALCDEF. Asteroid Lightcurve Photometry Database. 4 December 2018. Retrieved 27 December 2018.
  71. ^ Rossi, Alessandro (20 May 2004). "The mysteries of the asteroid rotation day". The Spaceguard Foundation. Archived from the original on 12 May 2006. Retrieved 9 April 2007.
  72. ^ "Asteroid or mini-planet? Hubble maps the ancient surface of Vesta". HubbleSite (Press release). News Center / Release Images. Space Telescope Science Institute. 19 April 1995. Retrieved 27 January 2015.
  73. ^ Soter, Steven (16 August 2006). "What is a Planet?" (PDF). Retrieved 25 December 2017. {{cite journal}}: Cite journal requires |journal= (help)
  74. ^ P. Vernazza et al. (2021) VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis. Astronomy & Astrophysics 54, A56
  75. ^ "Life is sweet: Sugar-packing asteroids may have seeded life on Earth". 19 December 2001. Archived from the original on 24 January 2002.
  76. ^ Reuell, Peter (8 July 2019). "Harvard study suggests asteroids might play key role in spreading life". Harvard Gazette. Retrieved 26 September 2019.
  77. ^ Callahan, M.P.; Smith, K.E.; Cleaves, H.J.; Ruzica, J.; Stern, J.C.; Glavin, D.P.; House, C.H.; Dworkin, J.P. (11 August 2011). "Carbonaceous meteorites contain a wide range of extraterrestrial nucleobases". PNAS. 108 (34): 13995–13998. Bibcode:2011PNAS..10813995C. doi:10.1073/pnas.1106493108. PMC 3161613. PMID 21836052.
  78. ^ Steigerwald, John (8 August 2011). "NASA researchers: DNA building blocks can be made in space" (Press release). NASA. Retrieved 10 August 2011.
  79. ^ "DNA building blocks can be made in space, NASA evidence suggests". ScienceDaily. 9 August 2011. Retrieved 9 August 2011.
  80. ^ Descamps, P.; Marchis, F.; Berthier, J.; Emery, J.P.; Duchêne, G.; de Pater, I.; et al. (February 2011). "Triplicity and physical characteristics of asteroid (216) Kleopatra". Icarus. 211 (2): 1022–1033. arXiv:1011.5263. Bibcode:2011Icar..211.1022D. doi:10.1016/j.icarus.2010.11.016. S2CID 119286272.
  81. ^ Cowen, Ron (8 October 2009). "Ice confirmed on an asteroid". Science News. Archived from the original on 12 October 2009. Retrieved 9 October 2009.
  82. ^ Atkinson, Nancy (8 October 2009). "More water out there, ice found on an asteroid". International Space Fellowship. Archived from the original on 11 October 2009. Retrieved 11 October 2009.
  83. ^ a b Campins, H.; Hargrove, K; Pinilla-Alonso, N.; Howell, E.S.; Kelley, M.S.; Licandro, J.; et al. (2010). "Water ice and organics on the surface of the asteroid 24 Themis". Nature. 464 (7293): 1320–132. Bibcode:2010Natur.464.1320C. doi:10.1038/nature09029. PMID 20428164. S2CID 4334032.
  84. ^ Rivkin, Andrew S.; Emery, Joshua P. (2010). "Detection of ice and organics on an asteroidal surface". Nature. 464 (7293): 1322–1323. Bibcode:2010Natur.464.1322R. doi:10.1038/nature09028. PMID 20428165. S2CID 4368093.
  85. ^ Mack, Eric. "Newly spotted wet asteroids point to far-flung Earth-like planets". CNET.
  86. ^ Küppers, Michael; O'Rourke, Laurence; Bockelée-Morvan, Dominique; Zakharov, Vladimir; Lee, Seungwon; von Allmen, Paul; et al. (2014). "Localized sources of water vapour on the dwarf planet (1) Ceres". Nature. 505 (7484): 525–527. Bibcode:2014Natur.505..525K. doi:10.1038/nature12918. PMID 24451541. S2CID 4448395.
  87. ^ a b Harrington, J.D. (22 January 2014). "Herschel Telescope Detects Water on Dwarf Planet" (Press release). NASA. Release 14-021. Retrieved 22 January 2014.
  88. ^ Myhrvold, Nathan (23 May 2016). "Asteroid thermal modeling in the presence of reflected sunlight with an application to WISE/NEOWISE observational data". Icarus. 303: 91–113. arXiv:1605.06490. Bibcode:2018Icar..303...91M. doi:10.1016/j.icarus.2017.12.024. S2CID 118511665.
  89. ^ Chang, Kenneth (23 May 2016). "How big are those killer asteroids? A critic says NASA doesn't know". The New York Times. Archived from the original on 1 January 2022. Retrieved 24 May 2016.
  90. ^ Billings, Lee (27 May 2016). "For asteroid-hunting astronomers, Nathan Myhrvold says the sky is falling". Scientific American. Retrieved 28 May 2016.
  91. ^ NASA Response to Recent Paper on NEOWISE Asteroid Size Results. NASA Administrator (Report). NASA. 25 May 2016. Retrieved 29 May 2016.
  92. ^ Myhrvold, Nathan (22 May 2018). "An empirical examination of WISE/NEOWISE asteroid analysis and results". Icarus. 314: 64–97. Bibcode:2018Icar..314...64M. doi:10.1016/j.icarus.2018.05.004.
  93. ^ Steigerwald, Bill; Jones, Nancy; Furukawa, Yoshihiro (18 November 2019). "First detection of sugars in meteorites gives clues to origin of life" (Press release). NASA. Retrieved 18 November 2019.
  94. ^ Furukawa, Yoshihiro; et al. (18 November 2019). "Extraterrestrial ribose and other sugars in primitive meteorites". Proceedings of the National Academy of Sciences of the United States of America. 116 (49): 24440–24445. Bibcode:2019PNAS..11624440F. doi:10.1073/pnas.1907169116. PMC 6900709. PMID 31740594.
  95. ^ "Ice fossils found in 4.6 billion-year-old meteorite reveal building blocks of our solar system".
  96. ^ Earth's water may have been formed by solar winds
  97. ^ Conrad, A.R.; Dumas, C.; Merline, W.J.; Drummonf, J.D.; Campbell, R.D.; Goodrich, R.W.; et al. (2007). "Direct measurement of the size, shape, and pole of 511 Davida with Keck AO in a single night" (PDF). Icarus. 191 (2): 616–627. Bibcode:2007Icar..191..616C. doi:10.1016/j.icarus.2007.05.004. Archived from the original (PDF) on 11 August 2007.
  98. ^ Boyle, Alan (6 March 2015). "Dawn spacecraft slips quietly into orbit around dwarf planet Ceres". NBC Universal Media, LLC. Retrieved 11 March 2015.
  99. ^ "University of Hawaii astronomer and colleagues find evidence that asteroids change color as they age". Institute for Astronomy (Press release). University of Hawaii. 19 May 2005. Retrieved 27 February 2013.
  100. ^ Courtland, Rachel (30 April 2009). "Sun damage conceals asteroids' true ages". New Scientist. Retrieved 27 February 2013.
  101. ^ Zappalà, V.; Bendjoya, Ph.; Cellino, A.; Farinella, P.; Froeschlé, C. (1995). "Asteroid families: Search of a 12,487 asteroid sample using two different clustering techniques". Icarus. 116 (2): 291–314. Bibcode:1995Icar..116..291Z. doi:10.1006/icar.1995.1127.
  102. ^ Jewitt, David C.; Sheppard, Scott; Porco, Carolyn (2004). "Jupiter's outer satellites and Trojans" (PDF). In Bagenal, Fran; Dowling, Timothy E.; McKinnon, William B. (eds.). Jupiter: The Planet, Satellites and Magnetosphere. Cambridge University Press.
  103. ^ Chapman, C.R.; Morrison, David; Zellner, Ben (1975). "Surface properties of asteroids: A synthesis of polarimetry, radiometry, and spectrophotometry". Icarus. 25 (1): 104–130. Bibcode:1975Icar...25..104C. doi:10.1016/0019-1035(75)90191-8.
  104. ^ Tholen, D.J. (1989). "Asteroid taxonomic classifications". Asteroids II; Proceedings of the Conference. University of Arizona Press. pp. 1139–1150. Bibcode:1989aste.conf.1139T.
  105. ^ 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. S2CID 4880578.
  106. ^ McSween, Harry Y., Jr. (1999). Meteorites and their Parent Planets (2nd ed.). Oxford University Press. ISBN 978-0-521-58751-8.
  107. ^ "The Naming of Asteroids". Open Learn. London, UK: The Open University. Retrieved 14 August 2016.
  108. ^ "Asteroid naming guidelines". The Planetary Society. Retrieved 14 August 2016.
  109. ^ Gould, B.A. (1852). "On the symbolic notation of the asteroids". Astronomical Journal. 2: 80. Bibcode:1852AJ......2...80G. doi:10.1086/100212.
  110. ^ a b Hilton, James L. (17 September 2001). "When did the asteroids become minor planets?". Archived from the original on 6 November 2007. Retrieved 26 March 2006.
  111. ^ 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.
  112. ^ 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.
  113. ^ 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.
  114. ^ Hilton, James L. "When did the asteroids become minor planets?". U.S. Naval Observatory. Washington, DC: Naval Meteorology and Oceanography Command. Archived from the original on 6 April 2012. Retrieved 6 November 2011.
  115. ^ Rob R. Landis; David J. Korsmeyer; Paul A. Abell; Daniel R. Adamo. A piloted Orion flight to a near-Earth object: A feasibility study (PDF). American Institute of Aeronautics and Astronautics (Report).
  116. ^ Chang, Kenneth (10 May 2021). "Bye-Bye, Bennu: NASA Heads Back to Earth With Asteroid Stash in Tow". The New York Times. ISSN 0362-4331. Retrieved 31 October 2021.
  117. ^ Wall, Mike (30 September 2013). "NASA may slam captured asteroid into Moon (eventually)".
  118. ^ Borenstein, Seth (19 June 2014). "Rock that whizzed by Earth may be grabbed by NASA". AP News. Retrieved 20 June 2014.
  119. ^ Northon, Karen (4 January 2017). "NASA Selects Two Missions to Explore the Early Solar System" (Press release). NASA.
  120. ^ Potter, Sean (23 November 2021). "NASA, SpaceX Launch DART: First Test Mission to Defend Planet Earth". NASA. Retrieved 4 December 2021.

Further reading

Further information about asteroids

External links

Media files used on this page

Solar System Template Final.png
Major Solar System objects. Sizes of planets and Sun are roughly to scale, but distances are not. This is not a diagram of all known moons – small gas giants' moons and Pluto's S/2011 P 1 moon are not shown.
243 ida.jpg
This color picture is made from images taken by the imaging system on the Galileo spacecraft about 14 minutes before its closest approach to asteroid 243 Ida on August 28, 1993, at a distance of about 10,500 kilometers (6,500 miles). The images used are from the sequence in which Ida's moon was originally discovered; the moon is visible to the right of the asteroid. This picture is made from images through the 4100-ångström (violet), 7560 Å (infrared) and 9680 Å (infrared) filters. The color is 'enhanced' in the sense that the CCD camera is sensitive to near-infrared wavelengths of light beyond human vision; a 'natural' color picture of this asteroid would appear mostly gray. Shadings in the image indicate changes in illumination angle on the many steep slopes of this irregular body as well as subtle color variations due to differences in the physical state and composition of the soil (regolith). There are brighter areas, appearing bluish in the picture, around craters on the upper left end of Ida, around the small bright crater near the center of the asteroid, and near the upper right-hand edge (the limb). This is a combination of more reflected blue light and greater absorption of near infrared light, suggesting a difference in the abundance or composition of iron-bearing minerals in these areas. Ida's moon also has a deeper near-infrared absorption and a different color in the violet than any area on this side of Ida. The moon is not identical in spectral properties to any area of Ida in view here, though its overall similarity in reflectance and general spectral type suggests that it is made of the same rock types basically. These data, combined with study of further imaging data and more detailed spectra from the Near Infrared Mapping Spectrometer, may allow scientists to determine whether the larger parent body of which Ida, its moon, and some other asteroids are fragments was a heated, differentiated object or made of relatively unaltered primitive chondritic material.
Euler diagram of solar system bodies.svg
Author/Creator: SounderBruce (translated version), Ariel Provost (French version), Tahc (original version), Licence: CC BY-SA 3.0
An Euler diagram showing the relationship between objects in the Solar System.
The central star has been excluded. Also excluded are artificial satellites.

Cosmic dust found within the Solar System falls under two categories depicted here: Small Solar System bodies and natural satellites. If the dust is orbiting the Sun, as with zodiacal dust, then it fits with small solar system bodies, which have no lower limit defined. And if the dust is orbiting a body other than the Sun, as with the countless particles of Saturn's rings, then these fit with natural satellites, which also have no lower limit defined. This diagram could be further refined to show how moonlets and dust fall within the category of natural satellites, with a separate set of cosmic dust orbiting the Sun falling within the category of small Solar System bodies.
W3C grn.svg The SVG code is valid.
Building Planets Through Collisions (Artist's Concept)

Planets, including those like our own Earth, form from epic collisions between asteroids and even bigger bodies, called proto-planets. Sometimes the colliding bodies are ground to dust, and sometimes they stick together to ultimately form larger, mature planets.

This artist's conception shows one such smash-up, the evidence for which was collected by NASA's Spitzer Space Telescope. Spitzer's infrared vision detected a huge eruption around the star NGC 2547-ID8 between August 2012 and 2013. Scientists think the dust was kicked up by a massive collision between two large asteroids. They say the smashup took place in the star's "terrestrial zone," the region around stars where rocky planets like Earth take shape.

NGC 2547-ID8 is a sun-like star located about 1,200 light-years from Earth in the constellation Vela. It is about 35 million years old, the same age our young sun was when its rocky planets were finally assembled via massive collisions -- including the giant impact on proto-Earth that led to the formation of the moon. The recent impact witnessed by Spitzer may be a sign of similar terrestrial planet building. Near-real-time studies like these help astronomers understand how the chaotic process works.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

For more information about Spitzer, visit and
Ceres symbol (fixed width).svg
Author/Creator: Denis Moskowitz, Licence: CC BY-SA 4.0
Planetary symbol for 1 Ceres (U+26B3 ⚳). 0.8px lines, capped.
Pallas symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
U+26B4 ⚴: symbol for asteroid (2) Pallas. 0.8px line weight
Juno symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
Symbol for asteroid 3 Juno, U+26B5 ⚵. 0.8px line weight.
Vesta symbol (original, fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
The earliest symbol for asteroid (4) Vesta, dating from at least 1807. Stylized to match other fixed-width astronomical symbols.
67P Churyumov-Gerasimenko - Rosetta (32755885495).png
Author/Creator: Justin Cowart, Licence: CC BY 2.0

Approximate true color image of comet 67P taken by the Rosetta spacecraft's OSIRIS Narrow Angle Camera on March 17, 2015. This image is a four frame mosaic, with each color frame imaged through VIS_BLUE, VIS_GREEN, and VIS_RED filters. At the time this image was taken, Rosetta was located roughly 82 km (51 mi) from the comet's centre.

Image Credit: ESA / Rosetta / MPS for OSIRIS Team (MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA) / Justin Cowart
Solar system.jpg
This is a montage of planetary images taken by spacecraft managed by the Jet Propulsion Laboratory in Pasadena, CA. Included are (from top to bottom) images of Mercury, Venus, Earth (and Moon), Mars, Jupiter, Saturn, Uranus and Neptune. The spacecraft responsible for these images are as follows:
  • the Mercury image was taken by Mariner 10,
  • the Venus image by Magellan,
  • the Earth and Moon images by Galileo,
  • the Mars image by Mars Global Surveyor,
  • the Jupiter image by Cassini, and
  • the Saturn, Uranus and Neptune images by Voyager.
  • Pluto is not shown as it is no longer a planet. The inner planets (Mercury, Venus, Earth, Moon, and Mars) are roughly to scale to each other; the outer planets (Jupiter, Saturn, Uranus, and Neptune) are roughly to scale to each other. PIA 00545 is the same montage with Neptune shown larger in the foreground. Actual diameters are given below:
  • Sun (to photosphere) 1,392,684 km
  • Mercury 4,879.4 km
  • Venus 12,103.7 km
  • Earth 12,756.28 km
  • Moon 3,476.2 km
  • Mars 6,804.9 km
  • Jupiter 142,984 km
  • Saturn 120,536 km
  • Uranus 51,118 km
  • Neptune 49,528 km
Crab Nebula.jpg
This is a mosaic image, one of the largest ever taken by NASA's Hubble Space Telescope, of the Crab Nebula, a six-light-year-wide expanding remnant of a star's supernova explosion. Japanese and Chinese astronomers recorded this violent event in 1054 CE, as did, almost certainly, Native Americans.

The orange filaments are the tattered remains of the star and consist mostly of hydrogen. The rapidly spinning neutron star embedded in the center of the nebula is the dynamo powering the nebula's eerie interior bluish glow. The blue light comes from electrons whirling at nearly the speed of light around magnetic field lines from the neutron star. The neutron star, like a lighthouse, ejects twin beams of radiation that appear to pulse 30 times a second due to the neutron star's rotation. A neutron star is the crushed ultra-dense core of the exploded star.

The Crab Nebula derived its name from its appearance in a drawing made by Irish astronomer Lord Rosse in 1844, using a 36-inch telescope. When viewed by Hubble, as well as by large ground-based telescopes such as the European Southern Observatory's Very Large Telescope, the Crab Nebula takes on a more detailed appearance that yields clues into the spectacular demise of a star, 6,500 light-years away.

The newly composed image was assembled from 24 individual Wide Field and Planetary Camera 2 exposures taken in October 1999, January 2000, and December 2000. The colors in the image indicate the different elements that were expelled during the explosion. Blue in the filaments in the outer part of the nebula represents neutral oxygen, green is singly-ionized sulfur, and red indicates doubly-ionized oxygen.
The Earth seen from Apollo 17 with transparent background.png
"The Blue Marble" is a famous photograph of the Earth taken on December 7, 1972 by the crew of the Apollo 17 spacecraft en route to the Moon at a distance of about 29,000 kilometers (18,000 statute miles). It shows Africa, Antarctica, and the Arabian Peninsula.
Eros, Vesta and Ceres size comparison.jpg
The size comparison of the asteroids are Ceres, Vesta, and Eros.
Author/Creator: ESO, European Southern Observatory, Licence: CC BY 4.0
Artist's impression of "the oldest star of our Galaxy": HE 1523-0901
  • About 13.2 billion years old
  • Approximately 7500 light years far from Earth
  • Published as part of Hamburg/ESO Survey in the May 10 2007 issue of The Astrophysical Journal
Author/Creator: Me, Licence: Copyrighted free use
SVG replacement for File:Spaceship and the Sun.jpg. A stylized illustration of a spaceship and the sun, based on the description of the emblem of the fictional Galactic Empire in Isaac Asimov's Foundation series ("The golden globe with its conventionalized rays, and the oblique cigar shape that was a space vessel"). This image could be used as a icon for science-fiction related articles.
This view of the rising Earth greeted the Apollo 8 astronauts as they came from behind the Moon after the fourth nearside orbit. Earth is about five degrees above the horizon in the photo. The unnamed surface features in the foreground are near the eastern limb of the Moon as viewed from Earth. The lunar horizon is approximately 780 kilometers from the spacecraft. Width of the photographed area at the horizon is about 175 kilometers. On the Earth 240,000 miles away, the sunset terminator bisects Africa.
Ceres processed.jpg
Obraz Ceres ze zdjęć zrobionych 5 i 6 Maja 2015. Dystans 13 600 km.
VLT asteroid images aa41781-21 (Figure 1a).pdf
Author/Creator: VSO Very Large Telescope SPHERE/ZIMPOL team, Licence: CC BY-SA 4.0
VLT/SPHERE images of asteroids > 210 km in diameter, deconvolved with the MISTRAL algorithm
Parthenope symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
simplified symbol
Rod of Asclepius (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
alternate symbol for Ophiuchus by Dennis Moskowitz, essentially a rod of Asclepius
Egeria symbol (fixed width).svg
Author/Creator: Hind, John Russell, Licence: CC BY-SA 4.0
J. R. Hind's design for the symbol of asteroid 13 Egeria.
The inner Solar System, from the Sun to Jupiter. Also includes the asteroid belt (the white donut-shaped cloud), the Hildas (the orange "triangle" just inside the orbit of Jupiter), the Jupiter trojans (green), and the near-Earth asteroids. The group that leads Jupiter are called the "Greeks" and the trailing group are called the "Trojans" (Murray and Dermott, Solar System Dynamics, pg. 107)
This image is based on data found in the en:JPL DE-405 ephemeris, and the en:Minor Planet Center database of asteroids (etc) published 2006 Jul 6. The image is looking down on the en:ecliptic plane as would have been seen on 2006 August 14. It was rendered by custom software written for Wikipedia. The same image without labels is also available at File:InnerSolarSystem.png.
Bennu 330km 181029.jpg
This “super-resolution” view of asteroid Bennu was created using eight images obtained by NASA’s OSIRIS-REx spacecraft on Oct. 29, 2018 from a distance of about 205 miles (330 km). The spacecraft was moving as it captured the images with the PolyCam camera, and Bennu rotated 1.2 degrees during the nearly one minute that elapsed between the first and the last snapshot. The team used a super-resolution algorithm to combine the eight images and produce a higher resolution view of the asteroid. Bennu occupies about 100 pixels and is oriented with its north pole at the top of the image.
Hyakutake Color.jpg
Author/Creator: E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz, Austria (, Licence: CC BY-SA 3.0
Image of comet C/1996 B2 (Hyakutake), taken on 1996 March 25, with a 225mm f/2.0 Schmidt Camera (focal length 450mm) on Kodak Panther 400 color slide film. Exposure 0:56 to 1:06 UT (10 minutes). The field shown is about 6.5°x4.8°. Note the prominent disconnection event in the comet's ion tail. Stars in the image appear trailed, as the camera tracked the comet during the exposure.
Victoria symbol (fixed width).svg
Author/Creator: , Licence: CC BY-SA 4.0
Versione del simbolo dell'asteroide 12
Egeria symbol (original, fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
original design of the symbol for asteroid (13) Egeria: a buckler and a star
PIA19547: Ceres RC3 Animation - Still Frame 25

UPLOADER NOTE: Frame 25 of the original GIF animation (16.096KB) - via JASC Animation Shop v 2.02.

In this closest-yet view of Ceres, the brightest spots within a crater in the northern hemisphere are revealed to be composed of many smaller spots. This frame is from an animation of sequences taken by NASA's Dawn spacecraft on May 4, 2015.

This animation shows a sequence of images taken by NASA's Dawn spacecraft on May 4, 2015, from a distance of 8,400 miles (13,600 kilometers), in its RC3 mapping orbit. The image resolution is 0.8 mile (1.3 kilometers) per pixel.

In this closest-yet view, the brightest spots within a crater in the northern hemisphere are revealed to be composed of many smaller spots. However, their exact nature remains unknown.

Dawn's mission is managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a project of the directorate's Discovery Program, managed by NASA's Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK, Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, the Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute are international partners on the mission team. For a complete list of acknowledgements, visit

For more information about the Dawn mission, visit
(253) mathilde.jpg
a Photo of Asteroid (253) Mathilde taken by the space probe NEAR Shoemaker on 27 June 1997 from a distance of 2400 km. It is lit up by the sun from the top right. The part of the Asteroid visible in the picture has Dimensions of 59 km x 47 km, whereas the picture resolution is 380px. On the surface, numerous large craters are visible, like the Large Crater in the Center, named Karoo [1], which is more than 30 km wide. Most of it is shaded in the picture.
This composite image shows the comparative sizes of eight asteroids.
Astraea scales symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
simplified variant of scales symbol for asteroid (5) Astraea
VLT asteroid images aa41781-21 (Figure 1b).pdf
Author/Creator: VSO Very Large Telescope SPHERE/ZIMPOL team, Licence: CC BY-SA 4.0
VLT/SPHERE images of asteroids < 210 km in diameter, deconvolved with the MISTRAL algorithm
8 Flora symbol (1852).svg
The traditional astronomical symbol for 8 Flora, after Gould, B.A. 1852, On the Symbolic Notation of the Asteroids, Astron. J., 2, 80. As the number of asteroids grew, the symbols got more and more complex, leading to the creation of Minor Planet Numbers. This stylised flower is perhaps the most difficult to date, with its fairly complicated curves. Still, 10 Hygiea would get much worse.
Leukothea symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
old symbol for asteroid (35) Leukothea
A plot of inner solar system asteroids and planets as of 2006 May 9, in a manner that exposes the Kirkwood Gaps. Similar to the position plot, planets (with trajectories) are orange, Jupiter being the outer most in this view. Various asteroid classes are colour coded: 'generic' main-belt are white. Inside the main belt, we have the Aten's (red), Apollo (green) and Amor (blue). Outside the main belt, the Hilda (blue) and the Trojan's (green). All object position vectors have been normalized to the length of the object's semi-major axis. The Kirkwood Gaps are visible in the main belt.
Thetis symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
symbol for asteroid (17) Thetis: a dolphin and a star.
243 Ida - August 1993 (16366655925).jpg
Author/Creator: Kevin Gill from Nashua, NH, United States, Licence: CC BY-SA 2.0

Asteroid 243 Ida as seen by the Galileo probe on August 28, 1993.

Image Credit: NASA/JPL/Processed by Kevin M. Gill
6 Hebe symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
semi-decorative variant of the symbol for asteroid 6 Hebe, based on the Berliner Astronomisches Jahrbuch für 1853
Radar imaging of 2013 ET
Iris symbol (simple, fixed width).svg
This is the symbol for the asteroid 7 Iris.
Twenty Years of Planetary Defense - July 23, 2018

Animation depicts a mapping of the positions of known near-Earth objects

The animation depicts a mapping of the positions of known near-Earth objects (NEOs) at points in time over the past 20 years, and finishes with a map of all known asteroids as of January 2018. Asteroid search teams supported by NASA's NEO Observations Program have found over 95 percent of near-Earth asteroids currently known. There are now over 18,000 known NEOs and the discovery rate averages about 40 per week. Image credit: NASA/JPL-Caltech
This picture of Eros, taken on February 14, 2001, shows the view looking from one end of the asteroid across the gouge on its underside and toward the opposite end. In this mosaic, constructed from two images taken after the NEAR spacecraft was inserted into orbit, features as small as 120 feet (35 meters) across can be seen. House-sized boulders are present in several places; one lies on the edge of the giant crater separating the two ends of the asteroid. A bright patch is visible on the asteroid in the top left-hand part of this image, and shallow troughs can be see just below this patch. The troughs run parallel to the asteroid's long dimension. (Mosaic of images 0125971425, 0125971487)
Asteroid 2004 FH.gif

Timelapse of Asteroid 2004 FH's flyby (NASA/JPL Public Domain)

2004 FH is the centre dot being followed by the sequence; the object that flashes by near the end is an artificial satellite.
Known NEAs.png
All known Near Earth Asteroids (NEA), cumulative discoveries over time
A cluster of mysterious bright spots on dwarf planet Ceres can be seen in this image, taken by NASA's Dawn spacecraft from an altitude of 2,700 miles (4,400 kilometers). The image, with a resolution of 1,400 feet (410 meters) per pixel, was taken on June 9, 2015.
Hebe symbol (simple, fixed width).svg
One version of the symbol for the asteroid 6 Hebe. Distinguish Bacchus symbol (fixed width).svgBacchus symbol (fixed width).svg
Melpomene symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
symbol for asteroid 18 Melpomene: a dagger and a star
Bellona symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
symbol for asteroid (28) Bellona, with the Geissel fashioned as a morning star, after Schmadel, Dictionary of Minor Planet Names
Ceres 'C' symbol.svg
Ceres symbol, reversed to resemble the initial 'C'
Flora symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
symbol for asteroid (8) Flora, per the form in Schmadel, Dictionary of Minor Planet Names
PIA21597 - New Radar Images of Asteroid 2014 JO25 (cropped).gif
This movie of asteroid 2014 JO25 was generated using radar data collected by NASA's 230-foot-wide (70-meter) Deep Space Network antenna at Goldstone, California on April 19, 2017.

When the observations began 2014 JO25 was 1.53 million miles (2.47 million kilometers) from Earth. By the time the observations concluded, the asteroid was 1.61 million miles (2.59 million kilometers) away.

The asteroid has a contact binary structure -- two lobes connected by a neck-like region. The largest of the asteroid's two lobes is estimated to be 2,000 feet (610 meters) across.

Asteroid 2014 JO25 approached to within 1.1 million miles (1.8 million kilometers) of Earth on April 19. There are no future flybys by 2014 JO25 as close as this one for more than 400 years.

The resolution of the radar images is about 25 feet (7.5 meters) per pixel. 154 images were used to create the movie shown.

More information regarding asteroid 2014 JO25 can be found at and
Fortuna symbol (fixed width).svg
J. R. Hind's symbol for the asteroid 19 Fortuna.
9 Metis symbol.svg
Symbol for the asteroid en:9 Metis
37 Fides symbol.svg
Symbol for the asteroid en:37 Fides
PIA02475 Eros' Bland Butterscotch Colors.jpg
These color images of Eros was acquired by NEAR on February 12, 2000, at a range of 1800 kilometers (1100 miles) during the final approach imaging sequence prior to orbit insertion. A five and one-half hour long sequence of images covering visible and infrared wavelengths was taken at that time, to provide a global overview of the color and spectral properties of the asteroid. The images show approximately the color that Eros would appear to the unaided human eye.

Eros' subtle butterscotch hue at visible wavelengths is nearly uniform across the surface. Two days after these images were taken, mapping by NEAR's infrared spectrometer showed that Eros exhibits a great deal more variety at longer wavelengths. These variations could be due to differences in texture or composition of the surface. Both NEAR's multispectral imager and infrared spectrometer will be used extensively during the month of March to map Eros' color and spectral properties from an altitude of 200 kilometers (120 miles). The images to be returned will show details as small as 20 meters (68 feet) across, providing a new perspective on the asteroid's many fascinating landforms discovered so far by NEAR.

Built and managed by The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, NEAR was the first spacecraft launched in NASA's Discovery Program of low-cost, small-scale planetary missions. See the NEAR web page at for more details.
Artist’s impression of the glowing disc of material around the white dwarf SDSS J1228+1040.jpg
Author/Creator: Mark Garlick ( and University of Warwick/ESO, Licence: CC BY 4.0
This artist’s impression shows how an asteroid torn apart by the strong gravity of a white dwarf has formed a ring of dust particles and debris orbiting the Earth-sized burnt out stellar core  SDSS J1228+1040. Gas produced by collisions within the disc is detected in observations obtained over twelve years with ESO’s Very Large Telescope, and reveal a narrow glowing arc.
PIA17937: First Asteroid Image from the Surface of Mars

The Mast Camera (Mastcam) on NASA's Curiosity Mars rover has captured the first image of an asteroid taken from the surface of Mars. The night-sky image actually includes two asteroids: Ceres and Vesta, plus one of Mars' two moons, Deimos, which may have been an asteroid before being captured into orbit around Mars. The image was taken after nightfall on the 606th Martian day, or sol, of Curiosity's work on Mars (April 20, 2014, PDT). In other camera pointings the same night, the Mastcam also imaged Mars' larger moon, Phobos, plus the planets Jupiter and Saturn.

Ceres, with a diameter of about 590 miles (950 kilometers), is the largest object in the asteroid belt, large enough to be classified as a dwarf planet. Vesta is the third-largest object in the asteroid belt, about 350 miles (563 kilometers) wide. These two bodies were the destinations of NASA's Dawn mission, which orbited Vesta in 2011 and 2012 and is currently orbiting Ceres.

This annotated image combines portions of images taken at the same pointing with two different exposure times, plus insets from other camera pointings. In the main portion of the image, Vesta, Ceres and three stars appear as short streaks due to the duration of a 12-second exposure. The background is detector noise, limiting what we can see to magnitude 6 or 7, much like normal human eyesight. The two asteroids and three stars would be visible to someone of normal eyesight standing on Mars. Specks are effects of cosmic rays striking the camera's light detector.

Three square insets at left show Phobos, Jupiter and Saturn at exposures of one-half second each. Deimos was much brighter than the visible stars and asteroids in the same part of the sky, in the main image. The circular inset covers a patch of sky the size that Earth's full moon appears to observers on Earth. At the center of that circular inset, Deimos appears at its correct location in the sky, in a one-quarter-second exposure. In the unannotated version of the 12-second-exposure image, the brightness of Deimos saturates that portion of the image, making the moon appear overly large.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Mars Science Laboratory Project for NASA's Science Mission Directorate, Washington. JPL designed and built the project's Curiosity rover and the rover's Navcam.

More information about Curiosity is online at and
An artist’s conception of the Lucy spacecraft flying by the Trojan Eurybates – one of the six diverse and scientifically important Trojans to be studied. Trojans are fossils of planet formation and so will supply important clues to the earliest history of the solar system.
Irene symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
symbol for asteroid (14) Irene
Juno orb symbol (fixed width).svg
A variant of the astronomical symbol for 3 Juno.[1] There are several such variants, some tilted at a diagonal to give more room for orbs etc. on the scepter.
951 Gaspra.jpg
Asteroid en:951 Gaspra.

Calvin J. Hamilton's website View of the Solar System describes this image as follows:

"This picture Gaspra is a combination of the highest-resolution images and color information obtained by the Galileo spacecraft. The Sun is shining from the right. The subtle color variations on Gaspra's surface have been exaggerated. en:Albedo and color variations are associated with surface en:topography. The bluish areas are regions of slightly higher albedo and tend to be associated with some of the crisper craters and with ridges. The slightly reddish areas, apparently concentrated in low areas, represent regions of somewhat lower albedo. In general, such patterns can be explained in terms of greater exposure of fresher rock in the brighter bluish areas and the accumulation of some en:regolith materials in the darker reddish areas. (Courtesy USGS/NASA/JPL)" [1]
Hygiea symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
zeta-shaped serpent with a star, the original symbol for asteroid (10) Hygiea, as described by the discoverer de Gasparis: "The symbol of Hygeia is a serpent (like a Greek ζ) crowned with a star."[1]
Asteroids by size and number.svg
Author/Creator: , Licence: CC BY-SA 4.0
Asteroids in the solar system, categorized by size and number
NASA's Dawn obtained this image with its framing camera on July 9, 2011. It was taken from a distance of about 26,000 miles (41,000 kilometers) away from the protoplanet Vesta. Each pixel in the image corresponds to roughly 2.4 miles (3.8 kilometers).
Sulphur symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
The alchemical symbol for sulphur, 🜍. Once used as a substitute for 2 Pallas, ⚴.
Astraea symbol (fixed width).svg
The traditional astronomical symbol for 5 Astraea, after Gould, B.A. 1852, On the Symbolic Notation of the Asteroids, Astron. J., 2, 80. As the number of asteroids grew, the symbols got more and more complex, leading to the creation of Minor Planet Numbers. This one, however, is still a relatively simple upside-down anchor, or, possibly, given the mythology, a highly stylised scales of justice.
Psyche symbol (elaborate, fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
Symbol for asteroid 16 Psyche. The butterfly wing is traced from File:Vanessa cardui specimen.jpg, an image of Vanessa cardui, the most cosmopolitan butterfly species.
Moon and Asteroids 1 to 10.svg
Sizes of the first ten Asteroids to be discovered compared to the Earth's Moon, all to scale.

The objects, left to right are: 1 dwarf planet Ceres, 2 Pallas, 3 Juno, 4 Vesta, 5 Astraea, 6 Hebe, 7 Iris, 8 Flora, 9 Metis, and 10 Hygiea.

The scale is 10 km/px on the original image, though not necessarily on the repro here.
Vesta symbol (old elaborate 2).svg
(c) Tooto at English Wikipedia, CC BY 2.5

Based on png version Image:4 Vesta Unsimplified Symbol.png

Early papers for Vesta use a more complicated symbol more-or-less as shown here (at that time, it would have been individually drawn by each person using it). Based on Gould, B.A. 1852, On the Symbolic Notation of the Asteroids, Astron. J., 2, 80, and partially created from Image:Vesta symbol.svg, also released to public domain.
Eunomia symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
asteroid 15 Eunomia
Proserpina symbol (fixed width).svg
This is the symbol for the asteroid 26 Proserpina.
New Map Shows Frequency of Small Asteroid Impacts, Provides Clues on Larger Asteroid Population

This diagram maps the data gathered from 1994-2013 on small asteroids impacting Earth's atmosphere

This diagram maps the data gathered from 1994-2013 on small asteroids impacting Earth's atmosphere to create very bright meteors, technically called "bolides" and commonly referred to as "fireballs". Sizes of red dots (daytime impacts) and blue dots (nighttime impacts) are proportional to the optical radiated energy of impacts measured in billions of Joules (GJ) of energy, and show the location of impacts from objects about 1 meter (3 feet) to almost 20 meters (60 feet) in size.

A map released today by NASA's Near Earth Object (NEO) Program reveals that small asteroids frequently enter and disintegrate in the Earth's atmosphere with random distribution around the globe. Released to the scientific community, the map visualizes data gathered by U.S. government sensors from 1994 to 2013. The data indicate that Earth's atmosphere was impacted by small asteroids, resulting in a bolide (or fireball), on 556 separate occasions in a 20-year period. Almost all asteroids of this size disintegrate in the atmosphere and are usually harmless. The notable exception was the Chelyabinsk event which was the largest asteroid to hit Earth in this period. The new data could help scientists better refine estimates of the distribution of the sizes of NEOs including larger ones that could pose a danger to Earth.

Finding and characterizing hazardous asteroids to protect our home planet is a high priority for NASA. It is one of the reasons NASA has increased by a factor of 10 investments in asteroid detection, characterization and mitigation activities over the last five years. In addition, NASA has aggressively developed strategies and plans with its partners in the U.S. and abroad to detect, track and characterize NEOs. These activities also will help identify NEOs that might pose a risk of Earth impact, and further help inform developing options for planetary defense.

The public can help participate in the hunt for potentially hazardous Near Earth Objects through the Asteroid Grand Challenge, which aims to create a plan to find all asteroid threats to human populations and know what to do about them. NASA is also pursuing an Asteroid Redirect Mission (ARM) which will identify, redirect and send astronauts to explore an asteroid. Among its many exploration goals, the mission could demonstrate basic planetary defense techniques for asteroid deflection.
Parthenope lyre symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
Lyre symbol for asteroid (11) Parthenope
Amphitrite symbol (fixed width).svg
The symbol for the asteroid 29 Amphitrite.
Eros rotation Dec. 3-4 2000.gif

NEAR Shoemaker captured this movie on December 3-4, 2000, while in orbit 200 kilometers (125 miles) from the center of Eros. Covering a full rotation of the 21-mile-long asteroid, the movie opens with a look at one of Eros' battered ends and a sweep over the saddle-shaped depression named Himeros. The sequence then includes a view of Shoemaker Regio - the large boulder patch beside Himeros - before swinging over the opposite end and providing a stunning view of a sunset inside Psyche, the asteroid's large, 5-kilometer (3-mile) impact crater. The movie wraps up with a return to the asteroid's heavily cratered tip.

The last three frames of the original NASA animation have been deleted to improve continuity when looping.
Ceres and Vesta, Moon size comparison.jpg
The asteroid (4) Vesta and the dwarf planet (1) Ceres shown alongside the Earth's Moon. The scale is 20 km/px.
The Four Largest Asteroids.jpg
These are the four largest asteroids (known as "The Big Four"), Ceres (939 km), Vesta (525 km), Pallas (512 km), Hygiea (430 km).
Iris symbol (fixed width).svg
Author/Creator: Kwamikagami, Licence: CC BY-SA 4.0
symbol for asteroid 7 Iris
Nh-pluto-in-true-color 2x JPEG-edit.jpg
PLUTO - NEW HORIZONS - July 14, 2015


Four images from New HorizonsLong Range Reconnaissance Imager (LORRI) were combined with color data from the Ralph instrument to create this global view of Pluto. (The lower right edge of Pluto in this view currently lacks high-resolution color coverage.) The images, taken when the spacecraft was 280,000 miles (450,000 kilometers) away, show features as small as 1.4 miles (2.2 kilometers), twice the resolution of the single-image view taken on July 13 [2015].


The north polar region is at top, with bright Tombaugh Regio to the lower right of center and part of the dark Cthulhu Regio at lower left. Part of the dark Krun Regio is also visible at extreme lower right.

The original NASA image has been modified by doubling the linear pixel density and cropping.
Vesta Cratered terrain with hills and ridges.jpg
An image of cratered terrain with hills and ridges on Vesta taken by Dawn on August 6, 2011. It has a resolution of about 260 meters per pixel.
Psyche symbol (fixed width).svg
Author/Creator: J. R. Hind, Licence: CC BY-SA 4.0
The symbol for the asteroid 16 Psyche.