A _____ Family of Asteroids Is a Group of Asteroids That Have Nearly Identical Orbits.

Circumstellar disk (accumulation of matter) in an orbit between those of Mars and Jupiter

The asteroids of the inner Solar System and Jupiter: The belt is located between the orbits of Jupiter and Mars.

The relative masses of the acme 12 asteroids known compared to the remaining mass of all the other asteroids in the chugalug

By far the largest object within the belt is the dwarf planet Ceres. The total mass of the asteroid belt is significantly less than Pluto's, and roughly twice that of Pluto's moon Charon.

The asteroid belt is a torus-shaped region in the Solar System, located roughly betwixt the orbits of the planets Jupiter and Mars. It contains a great many solid, irregularly shaped bodies, of many sizes, simply much smaller than planets, called asteroids or minor planets. This asteroid chugalug is too called the chief asteroid chugalug or main belt to distinguish information technology from other asteroid populations in the Solar System such equally near-Earth asteroids and trojan asteroids.^[1]

The asteroid belt is the smallest and innermost known circumstellar disc in the Solar System. About half its mass is independent in the iv largest asteroids: Ceres, Vesta, Pallas, and Hygiea.^[i] The total mass of the asteroid belt is nigh 4% that of the Moon.

Ceres, the only object in the asteroid chugalug large enough to exist a dwarf planet, is virtually 950 km in diameter, whereas Vesta, Pallas, and Hygiea take mean diameters less than 600 km.^{[2] [3] [four] [5]} The remaining bodies range downwardly to the size of a dust particle. The asteroid material is and then thinly distributed that numerous unmanned spacecraft have traversed it without incident.^[6] Yet, collisions between large asteroids practise occur, and these can produce an asteroid family whose members accept similar orbital characteristics and compositions. Individual asteroids within the asteroid belt are categorized past their spectra, with most falling into three basic groups - carbonaceous (C-blazon), silicate (S-type), and metal-rich (M-type).

The asteroid chugalug formed from the primordial solar nebula every bit a grouping of planetesimals.^[7] Planetesimals are the smaller precursors of the protoplanets. Between Mars and Jupiter, however, gravitational perturbations from Jupiter imbued the protoplanets with too much orbital energy for them to accrete into a planet.^{[seven] [viii]} Collisions became as well violent, and instead of fusing together, the planetesimals and most of the protoplanets shattered. As a result, 99.ix% of the asteroid chugalug'due south original mass was lost in the first 100 million years of the Solar Organization's history.^[ix] Some fragments eventually found their way into the inner Solar System, leading to meteorite impacts with the inner planets. Asteroid orbits continue to be appreciably perturbed whenever their period of revolution about the Sun forms an orbital resonance with Jupiter. At these orbital distances, a Kirkwood gap occurs equally they are swept into other orbits.^[10]

Classes of small Solar System bodies in other regions are the about-World objects, the centaurs, the Kuiper belt objects, the scattered disc objects, the sednoids, and the Oort cloud objects.

On 22 January 2014, European Infinite Bureau (ESA) scientists reported the detection, for the first definitive fourth dimension, of water vapor on Ceres, the largest object in the asteroid chugalug.^[eleven] The detection was made by using the far-infrared abilities of the Herschel Space Observatory.^[12] The finding was unexpected considering comets, not asteroids, are typically considered to "sprout jets and plumes". According to 1 of the scientists, "The lines are becoming more and more blurred between comets and asteroids".^[12]

History of observation [edit]

Johannes Kepler noticed in 1596 irregularities in the orbits of Mars and Jupiter, which were later explained past the gravity from the asteroids.

In 1596, Johannes Kepler wrote, "Between Mars and Jupiter, I place a planet," in his Mysterium Cosmographicum, stating his prediction that a planet would be found there.^[thirteen] While analyzing Tycho Brahe's data, Kepler thought that too large a gap existed between the orbits of Mars and Jupiter to fit Kepler'southward then-current model of where planetary orbits should be found.^[xiv]

In an bearding footnote to his 1766 translation of Charles Bonnet's Contemplation de la Nature,^[15] the astronomer Johann Daniel Titius of Wittenberg^{[16] [17]} noted an apparent blueprint in the layout of the planets, at present known as the Titius-Bode Police. If one began a numerical sequence at 0, and then included 3, 6, 12, 24, 48, etc., doubling each time, and added four to each number and divided past 10, this produced a remarkably shut approximation to the radii of the orbits of the known planets as measured in astronomical units, provided ane allowed for a "missing planet" (equivalent to 24 in the sequence) between the orbits of Mars (12) and Jupiter (48). In his footnote, Titius alleged, "But should the Lord Builder have left that infinite empty? Not at all."^[16]

When William Herschel discovered Uranus in 1781, the planet'south orbit matched the law almost perfectly, leading astronomers to conclude that a planet had to be between the orbits of Mars and Jupiter.

Giuseppe Piazzi, discoverer of Ceres, the largest object in the asteroid chugalug: Ceres was known as a planet, merely after reclassified as an asteroid and from 2006 as a dwarf planet.

On Jan 1, 1801, Giuseppe Piazzi, chairman of astronomy at the University of Palermo, Sicily, found a tiny moving object in an orbit with exactly the radius predicted past this pattern. He dubbed information technology "Ceres", later on the Roman goddess of the harvest and patron of Sicily. Piazzi initially believed information technology to be a comet, but its lack of a blackout suggested information technology was a planet.^[xviii] Thus, the aforementioned pattern predicted the semimajor axes of all eight planets of the fourth dimension (Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, and Uranus).

Almost 15 months later, Heinrich Olbers discovered a second object in the same region, Pallas. Unlike the other known planets, Ceres and Pallas remained points of lite even under the highest telescope magnifications instead of resolving into discs. Apart from their rapid movement, they appeared indistinguishable from stars.

Appropriately, in 1802, William Herschel suggested they exist placed into a dissever category, named "asteroids", afterwards the Greek asteroeides, meaning "star-like".^{[19] [twenty]} Upon completing a series of observations of Ceres and Pallas, he concluded,^[21]

Neither the appellation of planets nor that of comets tin can with any propriety of language exist given to these two stars ... They resemble small stars then much as hardly to exist distinguished from them. From this, their asteroidal appearance, if I take my proper name, and call them Asteroids; reserving for myself, however, the liberty of changing that proper noun, if another, more expressive of their nature, should occur.

By 1807, further investigation revealed two new objects in the region: Juno and Vesta.^[22] The burning of Lilienthal in the Napoleonic wars, where the main body of piece of work had been done,^[23] brought this starting time menstruation of discovery to a close.^[22]

Despite Herschel's coinage, for several decades it remained common practice to refer to these objects as planets^[xv] and to prefix their names with numbers representing their sequence of discovery: ane Ceres, 2 Pallas, 3 Juno, 4 Vesta. In 1845, though, astronomers detected a fifth object (5 Astraea) and, presently thereafter, new objects were found at an accelerating rate. Counting them among the planets became increasingly cumbersome. Eventually, they were dropped from the planet list (equally first suggested by Alexander von Humboldt in the early 1850s) and Herschel's choice of nomenclature, "asteroids", gradually came into common use.^[15]

The discovery of Neptune in 1846 led to the discrediting of the Titius–Bode law in the optics of scientists because its orbit was nowhere most the predicted position. To date, no scientific caption for the law has been given, and astronomers' consensus regards it every bit a coincidence.^[24]

The expression "asteroid belt" came into utilise in the early on 1850s, although pinpointing who coined the term is difficult. The commencement English use seems to exist in the 1850 translation (past Elise Otté) of Alexander von Humboldt'south Cosmos:^[25] "[...] and the regular appearance, about the 13th of November and the 11th of August, of shooting stars, which probably form role of a belt of asteroids intersecting the Earth'southward orbit and moving with planetary velocity". Another early appearance occurred in Robert James Isle of man's A Guide to the Cognition of the Heavens:^[26] "The orbits of the asteroids are placed in a wide belt of infinite, extending between the extremes of [...]". The American astronomer Benjamin Peirce seems to have adopted that terminology and to have been one of its promoters.^[27]

Over 100 asteroids had been located past mid-1868, and in 1891, the introduction of astrophotography by Max Wolf accelerated the rate of discovery nonetheless further.^[28] A total of ane,000 asteroids had been constitute by 1921,^[29] ten,000 past 1981,^[thirty] and 100,000 by 2000.^[31] Modern asteroid survey systems now employ automated means to locate new minor planets in always-increasing numbers.

Origin [edit]

The asteroid belt showing the orbital inclinations versus distances from the Dominicus, with asteroids in the core region of the asteroid belt in cerise and other asteroids in blue

Germination [edit]

In 1802, shortly after discovering Pallas, Olbers suggested to Herschel that Ceres and Pallas were fragments of a much larger planet that once occupied the Mars–Jupiter region, with this planet having suffered an internal explosion or a cometary bear on many million years before^[32] (Odessan astronomer K. N. Savchenko suggested that Ceres, Pallas, Juno, and Vesta were escaped moons rather than fragments of the exploded planet).^[33] The large amount of energy required to destroy a planet, combined with the belt's depression combined mass, which is just nearly 4% of the mass of Earth's Moon,^[2] does not support the hypothesis. Further, the significant chemical differences betwixt the asteroids become difficult to explicate if they come up from the aforementioned planet.^[34] In 2018, a study from researchers at the University of Florida concluded the asteroid belt was created from the remnants of several ancient planets instead of a single planet.^[35]

A hypothesis for the asteroid belt'southward creation relates to how, in general for the Solar Organisation, planetary formation is thought to have occurred via a process comparable to the long-standing nebular hypothesis; a cloud of interstellar dust and gas complanate under the influence of gravity to form a rotating disc of material that then further condensed to form the Sun and planets.^[36] During the get-go few meg years of the Solar Organisation's history, an accession process of sticky collisions caused the clumping of small particles, which gradually increased in size. One time the clumps reached sufficient mass, they could describe in other bodies through gravitational attraction and become planetesimals. This gravitational accretion led to the formation of the planets.

Planetesimals within the region that would go the asteroid belt were besides strongly perturbed past Jupiter'south gravity to form a planet. Instead, they continued to orbit the Dominicus as before, occasionally colliding.^[37] In regions where the boilerplate velocity of the collisions was also loftier, the shattering of planetesimals tended to dominate over accession,^[38] preventing the formation of planet-sized bodies. Orbital resonances occurred where the orbital period of an object in the belt formed an integer fraction of the orbital period of Jupiter, perturbing the object into a unlike orbit; the region lying between the orbits of Mars and Jupiter contains many such orbital resonances. Equally Jupiter migrated inward following its formation, these resonances would have swept across the asteroid belt, dynamically heady the region'due south population and increasing their velocities relative to each other.^[39]

During the early on history of the Solar Arrangement, the asteroids melted to some caste, allowing elements within them to be partially or completely differentiated by mass. Some of the progenitor bodies may even accept undergone periods of explosive volcanism and formed magma oceans. Because of the relatively small size of the bodies, though, the menstruum of melting was necessarily brief (compared to the much larger planets), and had generally ended about 4.5 billion years ago, in the offset tens of millions of years of germination.^[40] In August 2007, a study of zircon crystals in an Antarctic meteorite believed to take originated from Vesta suggested that information technology, and by extension the residual of the asteroid belt, had formed rather apace, inside 10 1000000 years of the Solar System'southward origin.^[41]

Evolution [edit]

The asteroids are not samples of the primordial Solar System. They have undergone considerable evolution since their formation, including internal heating (in the commencement few tens of millions of years), surface melting from impacts, space weathering from radiation, and bombardment by micrometeorites.^[42] Although some scientists refer to the asteroids as residual planetesimals,^[43] other scientists consider them distinct.^[44]

The current asteroid chugalug is believed to contain only a small fraction of the mass of the primordial belt. Computer simulations suggest that the original asteroid chugalug may accept contained mass equivalent to the Earth'southward.^[45] Primarily because of gravitational perturbations, most of the textile was ejected from the belt within about i 1000000 years of formation, leaving behind less than 0.1% of the original mass.^[37] Since their formation, the size distribution of the asteroid chugalug has remained relatively stable; no significant increase or decrease in the typical dimensions of the principal-belt asteroids has occcurred.^[46]

The 4:1 orbital resonance with Jupiter, at a radius 2.06 astronomical units (AUs), tin can be considered the inner boundary of the asteroid belt. Perturbations by Jupiter send bodies straying there into unstable orbits. Nigh bodies formed within the radius of this gap were swept upwardly by Mars (which has an aphelion at 1.67 AU) or ejected by its gravitational perturbations in the early history of the Solar Organisation.^[47] The Hungaria asteroids prevarication closer to the Sun than the 4:1 resonance, simply are protected from disruption by their high inclination.^[48]

When the asteroid belt was start formed, the temperatures at a altitude of 2.7 AU from the Sun formed a "snowfall line" below the freezing bespeak of water. Planetesimals formed across this radius were able to accumulate ice.^{[49] [l]} In 2006, a population of comets had been discovered inside the asteroid belt beyond the snow line, which may have provided a source of water for Globe's oceans. Co-ordinate to some models, outgassing of water during the Globe's determinative period was insufficient to grade the oceans, requiring an external source such as a cometary bombardment.^[51]

Characteristics [edit]

951 Gaspra, the first asteroid imaged by a spacecraft, as viewed during Galileo's 1991 flyby; colors are exaggerated

Fragment of the Allende meteorite, a carbonaceous chondrite that fell to Earth in Mexico in 1969

Reverse to popular imagery, the asteroid belt is by and large empty. The asteroids are spread over such a big book that reaching an asteroid without aiming carefully would be improbable. Nonetheless, hundreds of thousands of asteroids are currently known, and the total number ranges in the millions or more, depending on the lower size cutoff. Over 200 asteroids are known to be larger than 100 km,^[52] and a survey in the infrared wavelengths has shown that the asteroid chugalug has between 700,000 and one.7 million asteroids with a diameter of 1 km or more.^[53] The absolute magnitudes of nigh of the known asteroids are between 11 and 19, with the median at virtually sixteen.^[54]

The full mass of the asteroid belt is estimated to be 2.39×ten²¹ kg, which is but three% of the mass of the Moon.^[55] The 4 largest objects, Ceres, Vesta, Pallas, and Hygiea, account for maybe 62% of the belt's total mass, with 39% accounted for by Ceres alone.^{[56] [4]}

Limerick [edit]

The current chugalug consists primarily of three categories of asteroids: C-type or carbonaceous asteroids, S-blazon or silicate asteroids, and Thou-blazon or metal asteroids.

Carbonaceous asteroids, as their name suggests, are carbon-rich. They boss the asteroid belt's outer regions.^[57] Together they comprise over 75% of the visible asteroids. They are redder in hue than the other asteroids and have a very low albedo. Their surface compositions are similar to carbonaceous chondrite meteorites. Chemically, their spectra match the primordial composition of the early Solar Arrangement, with just the lighter elements and volatiles removed.

Due south-blazon (silicate-rich) asteroids are more than common toward the inner region of the belt, within two.v AU of the Sun.^{[57] [58]} The spectra of their surfaces reveal the presence of silicates and some metallic, but no significant carbonaceous compounds. This indicates that their materials accept been significantly modified from their primordial composition, probably through melting and reformation. They have a relatively loftier albedo and form virtually 17% of the total asteroid population.

Grand-blazon (metallic-rich) asteroids form about 10% of the full population; their spectra resemble that of iron-nickel. Some are believed to have formed from the metallic cores of differentiated progenitor bodies that were disrupted through collision. However, some silicate compounds besides can produce a similar appearance. For example, the large Thou-type asteroid 22 Kalliope does not appear to be primarily equanimous of metal.^[59] Within the asteroid belt, the number distribution of Chiliad-type asteroids peaks at a semimajor axis of near two.7 AU.^[60] Whether all M-types are compositionally similar, or whether information technology is a label for several varieties which practice not fit neatly into the main C and South classes is non yet clear.^[61]

I mystery of the asteroid belt is the relative rarity of V-type or basaltic asteroids.^[63] Theories of asteroid formation predict that objects the size of Vesta or larger should form crusts and mantles, which would exist composed mainly of basaltic rock, resulting in more than than half of all asteroids being equanimous either of basalt or olivine. Observations, however, suggest that 99% of the predicted basaltic material is missing.^[64] Until 2001, most basaltic bodies discovered in the asteroid belt were believed to originate from the asteroid Vesta (hence their proper name V-blazon), but the discovery of the asteroid 1459 Magnya revealed a slightly unlike chemical composition from the other basaltic asteroids discovered until then, suggesting a unlike origin.^[64] This hypothesis was reinforced by the further discovery in 2007 of two asteroids in the outer chugalug, 7472 Kumakiri and (10537) 1991 RY xvi , with a differing basaltic limerick that could not have originated from Vesta. These latter 2 are the only V-type asteroids discovered in the outer belt to engagement.^[63]

The temperature of the asteroid belt varies with the distance from the Lord's day. For grit particles inside the chugalug, typical temperatures range from 200 M (−73 °C) at 2.ii AU downward to 165 M (−108 °C) at 3.two AU^[65] However, due to rotation, the surface temperature of an asteroid can vary considerably as the sides are alternately exposed to solar radiation and then to the stellar background.

Main-belt comets [edit]

Several otherwise unremarkable bodies in the outer belt testify cometary activity. Considering their orbits cannot be explained through the capture of classical comets, many of the outer asteroids are thought to be icy, with the water ice occasionally exposed to sublimation through small impacts. Main-chugalug comets may accept been a major source of the Earth's oceans because the deuterium-hydrogen ratio is too low for classical comets to take been the principal source.^[66]

Orbits [edit]

The asteroid chugalug (showing eccentricities), with the asteroid belt in ruby-red and blue ("core" region in red)

About asteroids inside the asteroid belt accept orbital eccentricities less than 0.4, and an inclination of less than 30°. The orbital distribution of the asteroids reaches a maximum at an eccentricity around 0.07 and an inclination below 4°.^[54] Thus, although a typical asteroid has a relatively circular orbit and lies almost the plane of the ecliptic, some asteroid orbits tin can exist highly eccentric or travel well outside the ecliptic plane.

Sometimes, the term "primary belt" is used to refer just to the more than compact "core" region where the greatest concentration of bodies is found. This lies between the strong 4:1 and 2:1 Kirkwood gaps at 2.06 and 3.27 AU, and at orbital eccentricities less than roughly 0.33, forth with orbital inclinations below about 20°. Every bit of 2006^[update], this "cadre" region contained 93% of all discovered and numbered minor planets inside the Solar System.^[67] The JPL Pocket-size-Torso Database lists over 700,000 known main-belt asteroids.^[68]

Kirkwood gaps [edit]

Number of asteroids in the asteroid chugalug as a function of their semimajor centrality: The dashed lines point the Kirkwood gaps, where orbital resonances with Jupiter destabilize orbits. The color gives a possible division into three zones:

 Zone I: inner main-chugalug ( a < 2.5 AU)

 Zone II: heart main-belt (ii.5 AU < a < two.82 AU)

 Zone III: outer main-belt ( a > 2.82 AU)

The semimajor axis of an asteroid is used to draw the dimensions of its orbit effectually the Lord's day, and its value determines the pocket-size planet's orbital period. In 1866, Daniel Kirkwood announced the discovery of gaps in the distances of these bodies' orbits from the Sun. They were located in positions where their catamenia of revolution about the Lord's day was an integer fraction of Jupiter's orbital period. Kirkwood proposed that the gravitational perturbations of the planet led to the removal of asteroids from these orbits.^[69]

When the mean orbital period of an asteroid is an integer fraction of the orbital menses of Jupiter, a mean-movement resonance with the gas giant is created that is sufficient to perturb an asteroid to new orbital elements. Asteroids that become located in the gap orbits (either primordially because of the migration of Jupiter'south orbit,^[70] or due to prior perturbations or collisions) are gradually nudged into different, random orbits with a larger or smaller semimajor axis.

Collisions [edit]

The zodiacal light, a minor part of which is created by dust from collisions in the asteroid belt

The loftier population of the asteroid belt makes for a very agile surround, where collisions between asteroids occur frequently (on astronomical time scales). Collisions between master-chugalug bodies with a mean radius of ten km are expected to occur about once every 10 million years.^[71] A standoff may fragment an asteroid into numerous smaller pieces (leading to the formation of a new asteroid family).^[72] Conversely, collisions that occur at low relative speeds may also join ii asteroids. After more than four billion years of such processes, the members of the asteroid belt now conduct little resemblance to the original population.

Along with the asteroid bodies, the asteroid belt also contains bands of dust with particle radii of up to a few hundred micrometres. This fine material is produced, at least in function, from collisions between asteroids, and by the touch of micrometeorites upon the asteroids. Due to the Poynting–Robertson consequence, the pressure of solar radiation causes this dust to slowly spiral inwards toward the Dominicus.^[73]

The combination of this fine asteroid dust, besides equally ejected cometary material, produces the zodiacal light. This faint auroral glow can be viewed at nighttime extending from the direction of the Lord's day along the aeroplane of the ecliptic. Asteroid particles that produce the visible zodiacal calorie-free boilerplate almost 40 μm in radius. The typical lifetimes of main-belt zodiacal cloud particles are well-nigh 700,000 years. Thus, to maintain the bands of dust, new particles must be steadily produced within the asteroid chugalug.^[73] Information technology was once thought that collisions of asteroids form a major component of the zodiacal light. However, computer simulations by Nesvorný and colleagues attributed 85 pct of the zodiacal-calorie-free dust to fragmentations of Jupiter-family comets, rather than to comets and collisions between asteroids in the asteroid belt. At well-nigh x per centum of the dust is attributed to the asteroid belt.^[74]

Meteorites [edit]

Some of the debris from collisions can form meteoroids that enter the Earth's atmosphere.^[75] Of the 50,000 meteorites found on Earth to engagement, 99.8 percent are believed to have originated in the asteroid belt.^[76]

Families and groups [edit]

This plot of orbital inclination (i_p ) versus eccentricity (e_p ) for the numbered primary-belt asteroids clearly shows clumpings representing asteroid families.

In 1918, the Japanese astronomer Kiyotsugu Hirayama noticed that the orbits of some of the asteroids had similar parameters, forming families or groups.^[77]

Approximately i-tertiary of the asteroids in the asteroid belt are members of an asteroid family. These share similar orbital elements, such as semi-major axis, eccentricity, and orbital inclination as well equally similar spectral features, all of which indicate a common origin in the breakup of a larger trunk. Graphical displays of these elements, for members of the asteroid belt, show concentrations indicating the presence of an asteroid family. At that place are about 20 to 30 associations that are almost certainly asteroid families. Additional groupings have been found that are less certain. Asteroid families can be confirmed when the members display spectral features.^[78] Smaller associations of asteroids are called groups or clusters.

Some of the most prominent families in the asteroid belt (in order of increasing semi-major axes) are the Flora, Eunoma, Koronis, Eos, and Themis families.^[60] The Flora family unit, one of the largest with more 800 known members, may take formed from a collision less than 1 billion years agone.^[79] The largest asteroid to be a true fellow member of a family (as opposed to an interloper in the case of Ceres with the Gefion family) is iv Vesta. The Vesta family is believed to have formed as the result of a crater-forming impact on Vesta. Likewise, the HED meteorites may also accept originated from Vesta as a result of this standoff.^[80]

Three prominent bands of dust have been establish within the asteroid belt. These have like orbital inclinations every bit the Eos, Koronis, and Themis asteroid families, and and so are perchance associated with those groupings.^[81]

The main belt evolution afterward the Late Heavy Battery was very likely afflicted by the passages of large Centaurs and trans-Neptunian objects (TNOs). Centaurs and TNOs that accomplish the inner Solar Arrangement tin modify the orbits of chief belt asteroids, though only if their mass is of the order of ten^−nineM _☉ for single encounters or, one order less in case of multiple shut encounters. However Centaurs and TNOs are unlikely to have significantly dispersed young asteroid families in the main belt, but they can have perturbed some old asteroid families. Current master belt asteroids that originated every bit Centaurs or trans-Neptunian objects may lie in the outer belt with short lifetime of less than 4 1000000 years, about probable betwixt two.viii and 3.2 AU at larger eccentricities than typical of main belt asteroid.^[82]

Periphery [edit]

Skirting the inner border of the belt (ranging between 1.78 and two.0 AU, with a mean semi-major axis of 1.9 AU) is the Hungaria family of modest planets. They are named subsequently the main member, 434 Hungaria; the grouping contains at least 52 named asteroids. The Hungaria group is separated from the main trunk by the 4:ane Kirkwood gap and their orbits take a loftier inclination. Some members belong to the Mars-crossing category of asteroids, and gravitational perturbations by Mars are probable a factor in reducing the total population of this group.^[83]

Another high-inclination group in the inner part of the asteroid belt is the Phocaea family. These are composed primarily of Due south-type asteroids, whereas the neighboring Hungaria family includes some E-types.^[84] The Phocaea family orbit betwixt 2.25 and 2.5 AU from the Sun.

Skirting the outer border of the asteroid chugalug is the Cybele group, orbiting between 3.3 and iii.v AU. These have a 7:4 orbital resonance with Jupiter. The Hilda family orbit between 3.5 and 4.two AU, and have relatively round orbits and a stable iii:ii orbital resonance with Jupiter. There are few asteroids beyond 4.ii AU, until Jupiter's orbit. Here the ii families of Trojan asteroids tin can be establish, which, at least for objects larger than 1 km, are approximately as numerous equally the asteroids of the asteroid chugalug.^[85]

New families [edit]

Some asteroid families have formed recently, in astronomical terms. The Karin Cluster apparently formed almost five.7 meg years ago from a standoff with a progenitor asteroid 33 km in radius.^[86] The Veritas family formed about eight.iii million years ago; evidence includes interplanetary dust recovered from ocean sediment.^[87]

More than recently, the Datura cluster appears to have formed about 530,000 years ago from a collision with a main-belt asteroid. The age estimate is based on the probability of the members having their current orbits, rather than from any physical prove. However, this cluster may accept been a source for some zodiacal dust material.^{[88] [89]} Other recent cluster formations, such equally the Iannini cluster (c.  i–5 meg years agone), may have provided additional sources of this asteroid grit.^[90]

Exploration [edit]

The first spacecraft to traverse the asteroid belt was Pioneer 10, which entered the region on 16 July 1972. At the time there was some concern that the debris in the belt would pose a risk to the spacecraft, but it has since been safely traversed past 12 spacecraft without incident. Pioneer xi, Voyagers i and 2 and Ulysses passed through the chugalug without imaging whatsoever asteroids. Galileo imaged 951 Gaspra in 1991 and 243 Ida in 1993, Most imaged 253 Mathilde in 1997 and landed on 433 Eros in February 2001, Cassini imaged 2685 Masursky in 2000, Stardust imaged 5535 Annefrank in 2002, New Horizons imaged 132524 APL in 2006, Rosetta imaged 2867 Šteins in September 2008 and 21 Lutetia in July 2010, and Dawn orbited Vesta betwixt July 2011 and September 2012 and has orbited Ceres since March 2015.^[91] On its way to Jupiter, Juno traversed the asteroid belt without collecting science data.^[92] Due to the low density of materials inside the chugalug, the odds of a probe running into an asteroid are at present estimated at less than i in 1 billion.^[93]

Well-nigh belt asteroids imaged to engagement take come from brief flyby opportunities by probes headed for other targets. Only the Dawn, About Shoemaker and Hayabusa missions accept studied asteroids for a protracted period in orbit and at the surface.

See also [edit]

• Asteroid mining
• Asteroids in fiction
• Colonization of the asteroids
• Debris disk
• Disrupted planet
• List of asteroids in astrology
• List of exceptional asteroids
• Kuiper belt (The other ring of fabric, at nigh 30–sixty AU)
• 2010 AA15, sub-kilometer asteroid from the inner asteroid chugalug

References [edit]

1. ^ ^{a b} Matt Williams (2015-08-23). "What is the Asteroid Belt?". Universe Today . Retrieved 2016-01-xxx .
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3. ^ Pitjeva, E. Five. (2005). "Loftier-Precision Ephemerides of Planets—EPM and Determination of Some Astronomical Constants" (PDF). Solar System Research. 39 (3): 176–186. Bibcode:2005SoSyR..39..176P. doi:ten.1007/s11208-005-0033-2. S2CID 120467483. Archived from the original (PDF) on July 3, 2014.
4. ^ ^{a b} For recent estimates of the masses of Ceres, Vesta, Pallas and Hygiea, run across the references in the infoboxes of their respective manufactures.
5. ^ Yeomans, Donald K. (July xiii, 2006). "JPL Minor-Body Database Browser". NASA JPL. Archived from the original on 29 September 2010. Retrieved 2010-09-27 .
6. ^ Brian Koberlein (2014-03-12). "Why the Asteroid Belt Doesn't Threaten Spacecraft". Universe Today . Retrieved 2016-01-thirty .
7. ^ ^{a b} "How Did The Asteroid Belt Class? Was In that location A Planet In that location?". CosmosUp. 2016-01-17. Retrieved 2016-01-xxx .
8. ^ Nola Taylor Redd (2012-06-11). "Asteroid Belt: Facts & Information". Space.com . Retrieved 2016-01-30 .
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Farther reading [edit]

• Elkins-Tanton, Linda T. (2006). Asteroids, Meteorites, and Comets (Start ed.). New York: Chelsea House. ISBN978-0-8160-5195-three.

External links [edit]

This audio file was created from a revision of this commodity dated 30 March 2012 (2012-03-thirty), and does not reflect subsequent edits.

• Arnett, William A. (February 26, 2006). "Asteroids". The 9 Planets. Archived from the original on eighteen Apr 2007. Retrieved 2007-04-20 .
• Asteroids Page at NASA'south Solar System Exploration
• Cain, Fraser. "The Asteroid Belt". Universe Today. Archived from the original on vii March 2008. Retrieved 2008-04-01 .
• "Main Asteroid Belt". Sol Company. Archived from the original on 15 May 2007. Retrieved 2007-04-20 .
• Munsell, Kirk (September xvi, 2005). "Asteroids: Overview". NASA's Solar Organization Exploration. Archived from the original on 24 May 2007. Retrieved 2007-05-26 .
• Plots of eccentricity vs. semi-major axis and inclination vs. semi-major axis at Asteroid Dynamic Site
• Staff (October 31, 2006). "Asteroids". NASA. Archived from the original on xi Apr 2007. Retrieved 2007-04-20 .
• Staff (2007). "Space Topics: Asteroids and Comets". The Planetary Society. Archived from the original on 28 April 2007. Retrieved 2007-04-xx .

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Source: https://en.wikipedia.org/wiki/Asteroid_belt

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