Ceres, the only object in the asteroid belt large enough to be a dwarf planet, is about 950 km in diameter, whereas Vesta, Pallas, and Hygiea have mean diameters of less than 600 km. The remaining bodies range down to the size of a dust particle. The asteroid material is so thinly distributed that numerous unmanned spacecraft have traversed it without incident. Nonetheless, collisions between large asteroids do occur, and these can produce an asteroid family whose members have similar orbital characteristics and compositions. Individual asteroids within the asteroid belt are categorized by their spectra, with most falling into three basic groups: carbonaceous (C-type), silicate (S-type), and metal-rich (M-type).
Introduction
Asteroid belt
Asteroid belt | Introduction
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large objects ( 10 m) in space originating from a region between jupiter and mars
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Most of the rocky impactors of the Late Heavy Bombardment originate from an inner extension of the asteroid belt yielding a smaller but longer lasting bombardment. The innermost region of the asteroid belt is currently sparsely populated due to the presence of the ν6 secular resonance. In the early Solar System, however, this resonance was located elsewhere and the asteroid belt extended farther inward, ending at Mars-crossing orbits. During the giant planet migration the ν6 secular resonance first rapidly traversed the asteroid belt removing roughly half of its mass, much less than in the original Nice model. When the planets reached their current positions the ν6 secular resonance destabilized the orbits of the innermost asteroids.
Jumping-Jupiter scenario | Late Heavy Bombardment
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 in diameter accreted during that early era, whereas smaller bodies are fragments from collisions between asteroids during or after the Jovian disruption. Ceres and Vesta grew large enough to melt and differentiate, with heavy metallic elements sinking to the core, leaving rocky minerals in the crust.
Asteroid | Formation
Asteroids except for the largest, Ceres, are classified as small Solar System bodies and are composed mainly of refractory rocky and metallic minerals, with some ice. They range from a few metres to hundreds of kilometres in size. Asteroids smaller than one meter are usually called meteoroids and micrometeoroids (grain-sized), depending on different, somewhat arbitrary definitions. The asteroid belt occupies the orbit between Mars and Jupiter, between from the Sun. It is thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter. The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometre in diameter.
Solar System | Asteroid belt
Once the clumps reached sufficient mass, they could draw in other bodies through gravitational attraction and become planetesimals. This gravitational accretion led to the formation of the planets. Planetesimals within the region which would become the asteroid belt were too strongly perturbed by Jupiter's gravity to form a planet. Instead, they continued to orbit the Sun as before, occasionally colliding. In regions where the average velocity of the collisions was too high, the shattering of planetesimals tended to dominate over accretion, 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 different orbit; the region lying between the orbits of Mars and Jupiter contains many such orbital resonances.
Asteroid belt | Formation
The asteroid belt is a torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars, that is occupied by a great many solid, irregularly shaped bodies, of many sizes but much smaller than planets, called asteroids or minor planets. This asteroid belt is also called the main asteroid belt or main belt to distinguish it from other asteroid populations in the Solar System such as near-Earth asteroids and trojan asteroids. About half the mass of the belt is contained in the four largest asteroids: Ceres, Vesta, Pallas, and Hygiea. The total mass of the asteroid belt is approximately 4% that of the Moon.
Asteroid belt | Introduction
Ceres, the only object in the asteroid belt large enough to be a dwarf planet, is about 950 km in diameter, whereas Vesta, Pallas, and Hygiea have mean diameters of less than 600 km. The remaining bodies range down to the size of a dust particle. The asteroid material is so thinly distributed that numerous unmanned spacecraft have traversed it without incident. Nonetheless, collisions between large asteroids do occur, and these can produce an asteroid family whose members have similar orbital characteristics and compositions. Individual asteroids within the asteroid belt are categorized by their spectra, with most falling into three basic groups: carbonaceous (C-type), silicate (S-type), and metal-rich (M-type).
Asteroid belt | Introduction
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 in diameter, 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.
Asteroid | Asteroid belt
In 2018, a study from researchers at the University of Florida found the asteroid belt was created from the remnants of several ancient planets instead of a single planet. A hypothesis to the asteroid belt creation is that in general, in the Solar System, a planetary formation is thought to have occurred via a process comparable to the long-standing nebular hypothesis: a cloud of interstellar dust and gas collapsed under the influence of gravity to form a rotating disc of material that then further condensed to form the Sun and planets. During the first few million years of the Solar System's history, an accretion process of sticky collisions caused the clumping of small particles, which gradually increased in size.
Asteroid belt | Formation
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.
Asteroid | Formation
Crater counts using topographic data from the Lunar Reconnaissance Orbiter find an excess of small craters relative to large impact-basins when compared to the size distribution of the asteroid belt. However, if the E-belt was the product of collisions among a small number of large asteroids, it may have had a size distribution that differed from that of the asteroid belt with a larger fraction of small bodies. A recent work has found that the bombardment originating from the inner band of asteroids would yield only two lunar basins and would be insufficient to explain ancient impact spherule beds. It suggests instead that debris from a massive impact was the source, noting that this would better match the size distribution of impact craters.
Jumping-Jupiter scenario | Late Heavy Bombardment
On its way to Jupiter, "Juno" traversed the asteroid belt without collecting science data. Due to the low density of materials within the belt, the odds of a probe running into an asteroid are now estimated at less than 1 in 1 billion. Most belt asteroids imaged to date have come from brief flyby opportunities by probes headed for other targets. Only the Dawn, NEAR Shoemaker and Hayabusa missions have studied asteroids for a protracted period in orbit and at the surface.
Asteroid belt | Exploration
The outer edge of the terrestrial region, between 2 and 4 AU from the Sun, is called the asteroid belt. The asteroid belt initially contained more than enough matter to form 2–3 Earth-like planets, and, indeed, a large number of planetesimals formed there. As with the terrestrials, planetesimals in this region later coalesced and formed 20–30 Moon- to Mars-sized planetary embryos; however, the proximity of Jupiter meant that after this planet formed, 3 million years after the Sun, the region's history changed dramatically. Orbital resonances with Jupiter and Saturn are particularly strong in the asteroid belt, and gravitational interactions with more massive embryos scattered many planetesimals into those resonances.
Formation and evolution of the Solar System | Asteroid belt
Jupiter and Saturn drive most asteroids from their initial orbits during their migrations, leaving behind an excited remnant derived from both inside and outside Jupiter's original location. Before Jupiter's migrations the surrounding regions contained asteroids which varied in composition with their distance from the Sun. Rocky asteroids dominated the inner region, while more primitive and icy asteroids dominated the outer region beyond the ice line. As Jupiter and Saturn migrate inward, ~15% of the inner asteroids are scattered outward onto orbits beyond Saturn. After reversing course, Jupiter and Saturn first encounter these objects, scattering about 0.5% of the original population back inward onto stable orbits.
Grand tack hypothesis | Asteroid belt
The sweeping of resonances and the penetration of the ice giant into the asteroid belt results in the dispersal of asteroid collisional families formed during or before the Late Heavy Bombardment. A collisional family's inclinations and eccentricities are dispersed due to the sweeping secular resonances, including those inside mean motion resonances, with the eccentricities being most affected. Perturbations by close encounters with the ice giant result in the spreading of a family's semi-major axes. Most collisional families would thus become unidentifiable by techniques such as the hierarchical clustering method, and V-type asteroids originating from impacts on Vesta could be scattered to the middle and outer asteroid belt.
Jumping-Jupiter scenario | Asteroid belt
It may have been originated within the Venus–Earth–Mars region or in the main asteroid belt like other near-Earth objects, then transition to Amor-class asteroid before entering Earth's co-orbital region.
2006 JY26 | Origin
Later, as Jupiter and Saturn migrate into the outer region, about 0.5% of the primitive asteroids are scattered onto orbits in the outer asteroid belt. The encounters with Jupiter and Saturn leave many of the captured asteroids with large eccentricities and inclinations. These may be reduced during the giant planet instability described in the Nice model so that the eccentricity distribution resembles that of the current asteroid belt. Some of the icy asteroids are also left in orbits crossing the region where the terrestrial planets later formed, allowing water to be delivered to the accreting planets as when the icy asteroids collide with them.
Grand tack hypothesis | Asteroid belt
The asteroid belt is located between Mars and Jupiter. It is made of thousands of rocky planetesimals from to a few meters across. These are thought to be debris of the formation of the Solar System that could not form a planet due to Jupiter's gravity. When asteroids collide they produce small fragments that occasionally fall on Earth. These rocks are called meteorites and provide information about the primordial solar nebula. Most of these fragments have the size of sand grains. They burn up in the Earth's atmosphere, causing them to glow like meteors.
Geology of solar terrestrial planets | Asteroid belt
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 , about 4% of the mass of the Moon. Of this, Ceres comprises , 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%.
Asteroid | Size distribution
The rapid traverse of resonances through the asteroid belt can leave its population and the overall distribution of its orbital elements largely preserved. In this case the asteroid belt's depletion, the mixing of its taxonomical classes, and the excitation of its orbits, yielding a distribution of inclinations peaked near 10° and eccentricities peaked near 0.1, must have occurred earlier. These may be the product of Jupiter's Grand Tack, provided that an excess of higher eccentricity asteroids is removed due to interactions with the terrestrial planets. Gravitational stirring by planetary embryos embedded in the asteroid belt could also produce its depletion, mixing, and excitation.
Jumping-Jupiter scenario | Asteroid belt
The total mass of the asteroid belt is estimated to be kilograms, which is just 3% of the mass of the Moon. The four largest objects, Ceres, 4 Vesta, 2 Pallas, and 10 Hygiea, account for maybe 40% of the belt's total mass, with 25% accounted for by Ceres alone.
Asteroid belt | Characteristics
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, this planet having suffered an internal explosion or a cometary impact many million years before (Odessan astronomer K. N. Savchenko suggested that Ceres, Pallas, Juno, and Vesta were escaped moons rather than fragments of the exploded planet). The large amount of energy required to destroy a planet, combined with the belt's low combined mass, which is only about 4% of the mass of Earth's Moon, does not support the hypothesis. Further, the significant chemical differences between the asteroids become difficult to explain if they come from the same planet.
Asteroid belt | Formation
Asteroids that become located in the gap orbits (either primordially because of the migration of Jupiter's orbit, or due to prior perturbations or collisions) are gradually nudged into different, random orbits with a larger or smaller semi-major axis.
Asteroid belt | Kirkwood gaps
It may have been originated within the Venus-Earth-Mars region or in the main asteroid belt like other Near-Earth Objects, then transitioned to an Amor-class asteroid before entering Earth's co-orbital region.
2012 FC71 | Origin
Despite this, the total mass of the asteroid belt is unlikely to be more than a thousandth of that of Earth. The asteroid belt is very sparsely populated; spacecraft routinely pass through without incident.
Solar System | Asteroid belt
Other recent cluster formations, such as the Iannini cluster ( million years ago), may have provided additional sources of this asteroid dust.
Asteroid belt | New families
Crossing the asteroid belt is possible, because although there are over a million asteroids larger than in diameter, the distance between them is so large spacecraft pass through empty space. This was established in the early 1970s when "Pioneer 10" and "Pioneer 11" traversed the belt for the first time. There is some increased probability of encountering dust, but otherwise it takes special planning to actually pass very close to an asteroid as was done with "Galileo" spacecraft. When it passed through the belt on its way to orbit Jupiter in the 1990s, it did a flyby of asteroid 243 Ida.
132524 APL | Traversing the asteroid belt
, is an asteroid from the central region of the asteroid belt, approximately 1.2 kilometers in diameter. It was first observed at Paranal Observatory in the Atacama desert of Chile on 20 January 2004. missed the virtual impactor date of 29 August 2009. The asteroid was removed from the Sentry Risk Table in April 2014 as a result of precovery images establishing it is a harmless main belt asteroid.
2004 BX159 | Introduction
Some of these quickly entered planet crossing orbit initiating the Late Heavy Bombardment. Others entered quasi-stable higher inclination orbits, later producing an extended tail of impacts, with a small remnant surviving as the Hungarias. The increase in the orbital eccentricities and inclinations of the destabilized objects also raised impact velocities, resulting in a change the size distribution of lunar craters, and in the production of impact melt in the asteroid belt. The innermost (or E-belt) asteroids are estimated to have produced nine basin-forming impacts on the Moon between 4.1 and 3.7 billion years ago with three more originating from the core of the asteroid belt.
Jumping-Jupiter scenario | Late Heavy Bombardment
The precise origins of the Kuiper belt and its complex structure are still unclear, and astronomers are awaiting the completion of several wide-field survey telescopes such as Pan-STARRS and the future LSST, which should reveal many currently unknown KBOs. These surveys will provide data that will help determine answers to these questions. The Kuiper belt is thought to consist of planetesimals, fragments from the original protoplanetary disc around the Sun that failed to fully coalesce into planets and instead formed into smaller bodies, the largest less than in diameter. Studies of the crater counts on Pluto and Charon revealed a scarcity of small craters suggesting that such objects formed directly as sizeable objects in the range of tens of kilometers in diameter rather than being accreted from much smaller, roughly kilometer scale bodies.
Kuiper belt | Origin
As Jupiter migrated inward following its formation, these resonances would have swept across the asteroid belt, dynamically exciting the region's population and increasing their velocities relative to each other.
Asteroid belt | Formation
Since their formation, the size distribution of the asteroid belt has remained relatively stable: there has been no significant increase or decrease in the typical dimensions of the main-belt asteroids. The 4:1 orbital resonance with Jupiter, at a radius 2.06 AU, can be considered the inner boundary of the asteroid belt. Perturbations by Jupiter send bodies straying there into unstable orbits. Most bodies formed within the radius of this gap were swept up by Mars (which has an aphelion at 1.67 AU) or ejected by its gravitational perturbations in the early history of the Solar System. The Hungaria asteroids lie closer to the Sun than the 4:1 resonance, but are protected from disruption by their high inclination.
Asteroid belt | Evolution
In contrast, objects in the asteroid belt have essentially circular orbits and are expected to be mostly baked dry of ice by their confinement to the inner Solar System (see extinct comet). It is suggested that these main-belt asteroid-comets are evidence of a recent impact exposing an icy interior to solar radiation. It is estimated short-period comets remain active for about 10,000 years before having most of their ice sublimated away and going dormant.
118401 LINEAR | Introduction
The extended-belt asteroids were located between the current inner boundary of the asteroid belt and the orbit of Mars with semi-major axis ranging from 1.7 to 2.1 astronomical units (AU). In the current Solar System most orbits in this region are unstable due to the presence of the ν secular resonance. However, prior to the giant planet migration described in the Nice model the outer planets would have been in a more compact configuration with nearly circular orbits. With the planets in this configuration the ν secular resonance would be located outside the asteroid belt. Stable orbits would have existed inside 2.1 AU and the inner edge of the primordial asteroid belt would have been defined by Mars-crossing orbits.
E-belt asteroids | Location and stability
The Kuiper belt (), occasionally called the Edgeworth–Kuiper belt, is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger – 20 times as wide and 20–200 times as massive. Like the asteroid belt, it consists mainly of small bodies or remnants from when the Solar System formed. While many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia and water.
Kuiper belt | Introduction
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 .
Asteroid | Orbital classification
Skirting the inner edge of the belt (ranging between 1.78 and 2.0 AU, with a mean semi-major axis of 1.9 AU) is the Hungaria family of minor planets. They are named after the main member, 434 Hungaria; the group contains at least 52 named asteroids. The Hungaria group is separated from the main body by the 4:1 Kirkwood gap and their orbits have a high inclination. Some members belong to the Mars-crossing category of asteroids, and gravitational perturbations by Mars are likely a factor in reducing the total population of this group. Another high-inclination group in the inner part of the asteroid belt is the Phocaea family.
Asteroid belt | Periphery
This list includes few examples since there are about 589 asteroids in the asteroid belt with a measured radius between 20 and 49 km. Many thousands of objects of this size range have yet to be discovered in the trans-Neptunian region. The number of digits is not an endorsement of significant figures. The table switches from kg to kg (Eg). Most mass values of asteroids are assumed.
List of Solar System objects by size | From 20 to 49 km
2013 BS45 may have originated within the Venus-Earth-Mars region; alternatively, it may have come from the main asteroid belt like other Near-Earth Objects, then transitioned to an Amor-class asteroid before entering Earth's co-orbital region.
2013 BS45 | Origin
Some of the debris from collisions can form meteoroids that enter the Earth's atmosphere. Of the 50,000 meteorites found on Earth to date, 99.8 percent are believed to have originated in the asteroid belt.
Asteroid belt | Meteorites
These processes remove more than 90% of the origin mass implanted into the asteroid belt according to Bottke and colleagues. The size frequency distribution of this simulated population following this erosion are in excellent agreement with observations. This suggests that the Jupiter Trojans, Hildas, and some of the outer asteroid belt, all spectral D-type asteroids, are the remnant planetesimals from this capture and erosion process. It has also been suggested that the dwarf planet was captured via this process. A few D-type asteroids have been recently discovered with semi-major axes less than 2.5 AU, closer than those that would be captured in the original Nice model.
Nice model | Trojans and the asteroid belt
A large number of Pluto-massed objects would requires the Kuiper belt's size distribution to have multiple deviations from a constant slope.
Jumping-Jupiter scenario | Kuiper belt
The asteroids are not samples of the primordial Solar System. They have undergone considerable evolution since their formation, including internal heating (in the first few tens of millions of years), surface melting from impacts, space weathering from radiation, and bombardment by micrometeorites. Although some scientists refer to the asteroids as residual planetesimals, other scientists consider them distinct. The current asteroid belt is believed to contain only a small fraction of the mass of the primordial belt. Computer simulations suggest that the original asteroid belt may have contained the mass equivalent to the Earth. Primarily because of gravitational perturbations, most of the material was ejected from the belt within about 1 million years of formation, leaving behind less than 0.1% of the original mass.
Asteroid belt | Evolution
"New Horizons" passed through the asteroid belt during the summer of 2006, and the test helped prepare the team and spacecraft for the future flybys of Jupiter and Pluto. The asteroid belt is a feature of the Solar System, consisting of a large number asteroids that orbit the sun primarily between (Earth-Sun distance) which is between the orbits of planets Mars and Jupiter.
132524 APL | Ralph instrument
The Vesta family is believed to have formed as the result of a crater-forming impact on Vesta. Likewise, the HED meteorites may also have originated from Vesta as a result of this collision.
Asteroid belt | Families and groups
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 hazard to the spacecraft, but it has since been safely traversed by 12 spacecraft without incident. "Pioneer 11", "Voyagers 1" and "2" and "Ulysses" passed through the belt without imaging any asteroids. "Galileo" imaged 951 Gaspra in 1991 and 243 Ida in 1993, NEAR 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 between July 2011 and September 2012 and has orbited Ceres since March 2015.
Asteroid belt | Exploration
, provisionally known as , is a resonant trans-Neptunian object in the Kuiper belt located in the outermost regions of the Solar System. It measures approximately 291 kilometers in diameter. It has more carbon than typical of KBOs, and the first to be confirmed as having this composition in this region of space. It is thought that it had originated closer to the Sun, maybe even the main asteroid belt.
(120216) 2004 EW95 | Introduction
This main-belt asteroid measures approximately 12 kilometers in diameter and belongs to the main belt's background population.
Víctor Manuel Blanco | Honors
In planetary astronomy, the grand tack hypothesis proposes that after its formation at 3.5 AU, Jupiter migrated inward to 1.5 AU, before reversing course due to capturing Saturn in an orbital resonance, eventually halting near its current orbit at 5.2 AU. The reversal of Jupiter's migration is likened to the path of a sailboat changing directions (tacking) as it travels against the wind. The planetesimal disk is truncated at 1.0 AU by Jupiter's migration, limiting the material available to form Mars. Jupiter twice crosses the asteroid belt, scattering asteroids outward then inward. The resulting asteroid belt has a small mass, a wide range of inclinations and eccentricities, and a population originating from both inside and outside Jupiter's original orbit.
Grand tack hypothesis | Introduction
Such small asteroids then become subject to perturbations such as the Yarkovsky effect that can push them towards orbital resonances with Jupiter over time. Once there, they are relatively rapidly ejected from the asteroid belt. Tentative age estimates have been obtained for some families, ranging from hundreds of millions of years to less than several million years as for the compact Karin family. Old families are thought to contain few small members, and this is the basis of the age determinations.
Asteroid family | Origin and evolution
The overwhelming majority of known asteroids have orbits lying between the orbits of Mars and Jupiter, roughly between 2 and 4 AU. These could not form a planet due to the gravitational influence of Jupiter. Jupiter's gravitational influence, through orbital resonance, clears Kirkwood gaps in the asteroid belt, first recognised by Daniel Kirkwood in 1874. The region with the densest concentration (lying between the Kirkwood gaps at 2.06 and 3.27 AU, with eccentricities below about 0.3, and inclinations smaller than 30°) is called the asteroid belt. It can be further subdivided by the Kirkwood Gaps into the:
List of minor-planet groups | The asteroid belt
These are composed primarily of S-type asteroids, whereas the neighboring Hungaria family includes some E-types. The Phocaea family orbit between 2.25 and 2.5 AU from the Sun. Skirting the outer edge of the asteroid belt is the Cybele group, orbiting between 3.3 and 3.5 AU. These have a 7:4 orbital resonance with Jupiter. The Hilda family orbit between 3.5 and 4.2 AU, and have relatively circular orbits and a stable 3:2 orbital resonance with Jupiter. There are few asteroids beyond 4.2 AU, until Jupiter's orbit. Here the two families of Trojan asteroids can be found, which, at least for objects larger than 1 km, are approximately as numerous as the asteroids of the asteroid belt.
Asteroid belt | Periphery
, this "core" region contained 93% of all discovered and numbered minor planets within the Solar System. The JPL Small-Body Database lists over 700,000 known main belt asteroids.
Asteroid belt | Orbits
The forcing exerted by Jupiter on the orbits of the asteroids and the semi-major axes where it was strongest, would also vary, causing a chaotic excitation of the asteroids orbits that could reach or exceed their present level. The highest eccentricity asteroids would be later be removed by encounters with the terrestrial planets. The eccentricities of the terrestrial planets are excited beyond the current values during this process, however, requiring that the instability occur before their formation in this case. Gravitational stirring by embryos during the instability could increase the number of asteroids entered unstable orbits, resulting in the loss of 99-99.9% of its mass.
Jumping-Jupiter scenario | Asteroid belt
Additional groupings have been found that are less certain. Asteroid families can be confirmed when the members display common spectral features. 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. The Flora family, one of the largest with more than 800 known members, may have formed from a collision less than 1 billion years ago. The largest asteroid to be a true member of a family (as opposed to an interloper in the case of Ceres with the Gefion family) is 4 Vesta.
Asteroid belt | Families and groups
A rapid alteration of Jupiter's and Saturn's orbits is necessary to reproduce the current orbital distribution. This scenario removes only 50% of the asteroids from the main belt producing 2–3 basins on the Moon.
E-belt asteroids | Problems with alternative sources of LHB
The spectra of their surfaces reveal the presence of silicates and some metal, but no significant carbonaceous compounds. This indicates that their materials have been significantly modified from their primordial composition, probably through melting and reformation. They have a relatively high albedo and form about 17% of the total asteroid population.
Asteroid belt | Composition
In 1918, the Japanese astronomer Kiyotsugu Hirayama noticed that the orbits of some of the asteroids had similar parameters, forming families or groups. Approximately one-third 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 as similar spectral features, all of which indicate a common origin in the breakup of a larger body. Graphical displays of these elements, for members of the asteroid belt, show concentrations indicating the presence of an asteroid family. There are about 20 to 30 associations that are almost certainly asteroid families.
Asteroid belt | Families and groups
Contrary to popular imagery, the asteroid belt is mostly empty. The asteroids are spread over such a large volume that it would be improbable to reach an asteroid without aiming carefully. 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, and a survey in the infrared wavelengths has shown that the asteroid belt has between 700,000 and 1.7 million asteroids with a diameter of 1 km or more. The apparent magnitudes of most of the known asteroids are between 11 and 19, with the median at about 16.
Asteroid belt | Characteristics
However, most if not all of the embryos must have been lost before the instability. A mixing of asteroids types could be the product of asteroids being scattered into the belt during the formation of the planets. An initially small mass asteroid belt could have its inclinations and eccentricities excited by secular resonances that hopped across the asteroid belt if Jupiter's and Saturn's orbits became chaotic while in resonance. The orbits of the asteroids could be excited during the instability if the ice giant spent hundreds of thousands of years on a Jupiter crossing orbit. Numerous gravitational encounters between the ice giant and Jupiter during this period would cause frequent variations in Jupiter's semi-major axis, eccentricity and inclination.
Jumping-Jupiter scenario | Asteroid belt
The belt's age is estimated to be years.
Zeta Leporis | Asteroid belt
373 Melusina (prov. designation: "or" ) is a large Main belt asteroid. It is classified as a C-type asteroid and is probably composed of carbonaceous material. It was discovered by Auguste Charlois on 15 September 1893 in Nice.
373 Melusina | Introduction
" is a non-family asteroid from the main belt's background population when applying the hierarchical clustering method to its proper orbital elements. Based on osculating Keplerian orbital elements, the asteroid has also been classified as a member of the Flora family (), a giant asteroid family and the largest family of stony asteroids in the main-belt. It orbits the Sun in the inner asteroid belt at a distance of 1.7–2.6 AU once every 3 years and 2 months (1,164 days; semi-major axis of 2.17 AU). Its orbit has an eccentricity of 0.19 and an inclination of 4° with respect to the ecliptic.
(6265) 1985 TW3 | Orbit and classification
The dusty material in the system was analyzed in 2007 by a group led by Dr. Carey Lisse, of the Johns Hopkins University Applied Physics Laboratory in Laurel, MD, USA. Observations were made using the infrared spectrometer on board the Spitzer Space Telescope, and interpreted using the results of the NASA "Deep Impact" and "STARDUST" missions. Analysis of the atomic and mineral composition, dust temperature, and dust mass show a huge amount of warm material similar to metal rich S-type asteroids in a narrow belt at 1.8 ± 0.2 AU from the HD 113766 A. The group found at least a Mars' mass worth of warm dust in particles of size 10 m or less, and very likely as much as a few Earth masses of dust if one adds in the contribution of material in bodies up to 1 km in radius which are currently thought to be the basic building blocks of rocky planet formation.
HD 113766 | Rocky accretion belt
The slope for the cold objects is q = 8.2 at large diameters and q = 2.9 at small diameters with a change in slope at 140 km. The size distributions of the scattering objects, the plutinos, and the Neptune trojans have slopes similar to the other dynamically hot populations, but may instead have a divot, a sharp decrease in the number of objects below a specific size. This divot is hypothesized to be due to either the collisional evolution of the population, or to be due to the population having formed with no objects below this size, with the smaller objects being fragments of the original objects.
Kuiper belt | Mass and size distribution
For this to have occurred on in its current orbit and at temperatures of ~35K, significant quantities of thermal energy would have been required. While this energy could have been delivered by a very large chance collision, the strong overall similarity between the modern C-type asteroids in the outer asteroid belt and suggests that these objects formed in the same region of the early Sun's protoplanetary disk, much closer to the Sun and at higher temperatures. The Grand tack hypothesis predicts that the primitive C-type asteroids were dispersed from their formation location by the migrations of Jupiter and Saturn and many were injected into the outer asteroid belt where we find them today.
(120216) 2004 EW95 | Physical characteristics
" is non-family asteroid of the main belt's background population. It orbits the Sun in the central asteroid belt at a distance of 2.1–3.3 AU once every 4 years and 5 months (1,602 days; semi-major axis of 2.68 AU). Its orbit has an eccentricity of 0.23 and an inclination of 13° with respect to the ecliptic.
(7563) 1988 BC | Classification and orbit
For a more complete list, see List of Solar System objects by size. The inner asteroid belt (defined as the region interior to the 3:1 Kirkwood gap at 2.50 AU) has few large asteroids. Of those in the above list, only 4 Vesta, 19 Fortuna, 6 Hebe, 7 Iris and 9 Metis orbit there. (Sort table by mean distance.)
List of exceptional asteroids | Largest by diameter
When this occurs the trojan co-orbital region is "dynamically open" and objects can both escape and enter the region. Primordial trojans escape and a fraction of the numerous objects from the disrupted planetesimal disk temporarily inhabit it. Later when Jupiter and Saturn orbits are farther apart the Trojan region becomes "dynamically closed", and the planetesimals in the trojan region are captured, with many remaining today. The captured trojans have a wide range of inclinations, which had not previously been understood, due to their repeated encounters with the giant planets. The libration angle and eccentricity of the simulated population also matches observations of the orbits of the Jupiter trojans.
Nice model | Trojans and the asteroid belt
In 1596, Johannes Kepler predicted “Between Mars and Jupiter, I place a planet” in his "Mysterium Cosmographicum". While analyzing Tycho Brahe's data, Kepler thought that there was too large a gap between the orbits of Mars and Jupiter. In an anonymous footnote to his 1766 translation of Charles Bonnet's "Contemplation de la Nature", the astronomer Johann Daniel Titius of Wittenberg noted an apparent pattern in the layout of the planets, now known as the Titius-Bode Law. If one began a numerical sequence at 0, then included 3, 6, 12, 24, 48, etc., doubling each time, and added four to each number and divided by 10, this produced a remarkably close approximation to the radii of the orbits of the known planets as measured in astronomical units "provided" one allowed for a "missing planet" (equivalent to 24 in the sequence) between the orbits of Mars (12) and Jupiter (48).
Asteroid belt | History of observation
, is a sub-kilometer asteroid and near-Earth object of the Amor group, that is on a low-eccentricity and low-inclination orbit between the orbits of Earth and Mars. It was discovered by the Spacewatch survey at Kitt Peak National Observatory on 22 May 1998.
(350462) 1998 KG3 | Introduction
The E-belt asteroids were the population of a hypothetical extension of the primordial asteroid belt proposed as the source of most of the basin-forming lunar impacts during the Late Heavy Bombardment.
E-belt asteroids | Introduction
started its existence as part of a much larger body in the asteroid belt, with a likely diameter greater than 100 kilometers. 's immediate history likely started when its parent body experienced a large cratering event or, more likely, a catastrophic disruption event that resulted in a highly fractured, shattered, or reaccumulated object (rubble pile). As a result, may have been produced as a reassembly of ejected fragments. The location of what is now within this parent body is unknown. Given the available modeling work and data, the most plausible source family candidates for are Eulalia, New Polana, and Erigone.
(341843) 2008 EV5 | Origin and orbital history
A theme related to that of the Fifth Planet is the generation of a new asteroid belt, via the demolition of a planet, sometimes the Earth. The energy required to reduce a planet such as Earth to loose rubble is truly enormous: about 2 J, equivalent to the Sun's entire luminous energy output for about a week!
Asteroids in fiction | New asteroid belts
Some asteroid families have formed recently, in astronomical terms. The Karin Cluster apparently formed about 5.7 million years ago from a collision with a progenitor asteroid 33 km in radius. The Veritas family formed about 8.3 million years ago; evidence includes interplanetary dust recovered from ocean sediment. More 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 evidence. However, this cluster may have been a source for some zodiacal dust material.
Asteroid belt | New families
The object remained listed as an inner heliospheric asteroid for several years, until identifications with and and a subsequent improvement of the orbital uncertainty completely overturned previous calculations. is now a secured central main-belt asteroid orbiting the Sun at a distance of 2.2–3.1 AU once every 4 years and 3 months (1,555 days; semi-major axis of 2.63 AU). Its orbit has an eccentricity of 0.17 and an inclination of 32° with respect to the ecliptic.
(459883) 2014 JX55 | Orbital determination as main-belt asteroid
The encounters between the ice giant and Jupiter in this model allow Jupiter to acquire its own irregular satellites. Jupiter trojans are also captured following these encounters when Jupiter's semi-major axis jumps and, if the ice giant passes through one of the libration points scattering trojans, one population is depleted relative to the other. The faster traverse of the secular resonances across the asteroid belt limits the loss of asteroids from its core. Most of the rocky impactors of the Late Heavy Bombardment instead originate from an inner extension that is disrupted when the giant planets reach their current positions, with a remnant remaining as the Hungaria asteroids.
Nice model | Modifications
In both the Tholen- and SMASS-like taxonomy of the Small Solar System Objects Spectroscopic Survey (S3OS2), " is a dark D-type asteroid, the dominant spectral type among the larger Jupiter trojans. It has a typical V–I color index of 0.90.
(5648) 1990 VU1 | Physical characteristics
Asteroids in the asteroid belt are divided into asteroid groups and families based on their orbital characteristics. Asteroid moons are asteroids that orbit larger asteroids. They are not as clearly distinguished as planetary moons, sometimes being almost as large as their partners. The asteroid belt also contains main-belt comets, which may have been the source of Earth's water. Jupiter trojans are located in either of Jupiter's L or L points (gravitationally stable regions leading and trailing a planet in its orbit); the term is also used for small bodies in any other planetary or satellite Lagrange point. Hilda asteroids are in a 2:3 resonance with Jupiter; that is, they go around the Sun three times for every two Jupiter orbits.
Solar System | Asteroid groups
With an absolute magnitude of 19.2, the inner main-belt asteroid is approximately 350 meters in diameter, based on an assumed albedo of 0.3 – a typical compromise value between 0.4 and 0.2, corresponding to the Hungaria asteroids both as family and orbital group.
2015 YU9 | Diameter and albedo
, provisional designation , is a Tirela asteroid from the outer regions of the asteroid belt, approximately in diameter. It was discovered on 30 August 2008, by French amateur astronomers Christophe Demeautis and Jean-Marie Lopez at the Pises Observatory in southern France.
(369623) 2011 DY5 | Introduction
The asteroid is an assumed stony S-type asteroid.
(467336) 2002 LT38 | Physical characteristics
During this primary depletion period, the effects of the giant planets and planetary embryos left the asteroid belt with a total mass equivalent to less than 1% that of the Earth, composed mainly of small planetesimals. This is still 10–20 times more than the current mass in the main belt, which is now about . A secondary depletion period that brought the asteroid belt down close to its present mass is thought to have followed when Jupiter and Saturn entered a temporary 2:1 orbital resonance (see below). The inner Solar System's period of giant impacts probably played a role in the Earth acquiring its current water content (~6 kg) from the early asteroid belt.
Formation and evolution of the Solar System | Asteroid belt
The warm dust is very primitive, and definitely not from an asteroidal parent body. A large amount, at least 3 x 10 kg, of 0.1 – 1000 µm warm dust is present, in a roughly collisional equilibrium distribution with dn/da ~ a. This is the equivalent of a 160-kilometer-radius centaur or medium-sized Kuiper belt object of 1.0 g cm density or a "comet" of 260 km radius and 0.40 g cm density. The warm dust mass is much larger than that of a solar system comet (10 – 10 kg), but is very similar to the mass of a Kuiper belt object (10 – 10 kg).
Eta Corvi | Possible Late Heavy Bombardment
The number of objects is inversely proportional to some power of the diameter "D": Early estimates that were based on measurements of the apparent magnitude distribution found a value of q = 4 ±0.5, which implied that there are 8 (=2) times more objects in the 100–200 km range than in the 200–400 km range. Recent research has revealed that the size distributions of the hot classical and cold classical objects have differing slopes. The slope for the hot objects is q = 5.3 at large diameters and q = 2.0 at small diameters with the change in slope at 110 km.
Kuiper belt | Mass and size distribution
A HCM numerical analysis by (Zappala 1995) found a 'core' group of family members, whose proper orbital elements lie in the approximate ranges At the present epoch, the range of osculating orbital elements of these core members is The 1995 analysis by Zappalà found 103 core members, whereas a search of a recent proper element database (AstDys)for 96944 minor planets in 2005 yielded 1043 objects lying within the rectangular-shaped region defined by the first table above. This would give about 1% of all asteroids in the asteroid belt.
Hygiea family | Location and size
Once leaving the inner planets, a visitor to the Planet Walk turns west along Seneca Street to continue towards Jupiter. Between Mars and Jupiter lies the asteroid belt. The obelisk representing the asteroid belt was added several years after the initial installation. Its display contains the only public, unguarded meteorite in the world.
Sagan Planet Walk | The Asteroid Belt
Based on a generic conversion from absolute magnitude, the asteroid measures between 0.6 and 1.4 kilometers in diameter.
(434326) 2004 JG6 | Physical characteristics
Impact craters on the Moon and impact spherule beds found on the Earth dated to this period are consistent with these predictions. The E-belt model predicts a remnant population will remain on Hungaria-like orbits. The initial population of E-belt asteroids was calculated based on the population of potential basin-forming impactors remaining among the Hungaria asteroids. The result was consistent with calculations based on the recent estimates of the orbital density of the main asteroid belt before the planetary migration.
E-belt asteroids | Support for E-belt as source of LHB
This mechanism of the Nice model similarly generates the Neptune trojans. A large number of planetesimals would have also been captured in Jupiter's mean motion resonances as Jupiter migrated inward. Those that remained in a 3:2 resonance with Jupiter form the Hilda family. The eccentricity of other objects declined while they were in a resonance and escaped onto stable orbits in the outer asteroid belt, at distances greater than 2.6 AU as the resonances moved inward. These captured objects would then have undergone collisional erosion, grinding the population away into smaller fragments that can then be acted on by the Yarkovsky effect, causing small objects to drift into unstable resonances, and Poynting–Robertson drag causing smaller grains to drift toward the sun.
Nice model | Trojans and the asteroid belt
The Hungaria asteroids are thought to be the remains of the hypothetical E-belt asteroid population. The dispersal of most of that hypothetical E-belt might have been caused by the outwards migration of the giant planets of the Solar System according to simulations done under the Nice model—and these dispersed E-belt asteroids might in turn have been the impactors of the Late Heavy Bombardment.
Hungaria asteroid | E-belt
"" is an assumed, carbonaceous C-type asteroid. Most Jupiter trojans are D-types, with the reminder being mostly C and P-type asteroids. It has a typical V–I color index of 0.95 and a BR color of 1.23 "(also see table below)".
(32496) 2000 WX182 | Physical characteristics
In his footnote, Titius declared "But should the Lord Architect have left that space empty? Not at all." When William Herschel discovered Uranus in 1781, the planet's orbit matched the law almost perfectly, leading astronomers to conclude that there had to be a planet between the orbits of Mars and Jupiter.
Asteroid belt | History of observation
The orbit of is extremely eccentric, going from the orbit of planet Mercury out into the asteroid belt, located between Mars and Jupiter.
2017 QP1 | Introduction
This object has been characterized as a bright Vestian-like V-type asteroid.
(164121) 2003 YT1 | Physical characteristics
Sweeping secular resonances during the clearing of the gas disk could also excite inclinations and eccentricities, increasing relative velocities so that collisions resulted in fragmentation instead of accretion. A number of these hypotheses could also explain the low mass of the asteroid belt. A number of hypotheses have also been proposed to explain the orbital eccentricities and inclinations of the asteroids and the low mass of the asteroid belt. If the region of the asteroid belt was initially empty due to few planetesimals forming there it could have been populated by icy planetesimals that were scattered inward during Jupiter's and Saturn's gas accretion, and by stony asteroids that were scattered outward by the forming terrestrial planets.
Grand tack hypothesis | Alternatives
Similar processes have been inferred in the debris disks around Fomalhaut and AU Microscopii.
Beta Pictoris | Planetesimal belts
The accepted origin of these asteroids is that main-belt asteroids are moved into the inner Solar System through orbital resonances with Jupiter. The interaction with Jupiter through the resonance perturbs the asteroid's orbit and it comes into the inner Solar System. The asteroid belt has gaps, known as Kirkwood gaps, where these resonances occur as the asteroids in these resonances have been moved onto other orbits. New asteroids migrate into these resonances, due to the Yarkovsky effect that provides a continuing supply of near-Earth asteroids. Compared to the entire mass of the asteroid belt, the mass loss necessary to sustain the NEA population is relatively small; totalling less than 6% over the past 3.5 billion years.
Near-Earth object | Near-Earth asteroids (NEAs)
Based on the asteroids brightness and assumed proximity to Earth, the asteroid was originally estimated to be only 30 meters in diameter.
(444004) 2004 AS1 | Description
"" is an assumed stony S-type asteroid. This asteroid is a typical contact binary, with two distinctive lobes on either end that appear to be in contact, giving it a peanut-like shape.
(388188) 2006 DP14 | Physical characteristics
A second work concurs, finding that the asteroid belt was probably not the source of the Late Heavy Bombardment. Noting the lack of direct evidence of cometary impactors, it proposes that leftover planetesimals were the source of most impacts and that Nice model instability may have occurred early. If a different crater scaling law is used, however, the Nice model is more likely to produce the impacts attributed to the Late Heavy bombardment and more recent impact craters.
Jumping-Jupiter scenario | Late Heavy Bombardment