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92-517: Minor planets include asteroids ( near-Earth objects , Earth trojans , Mars trojans , Mars-crossers , main-belt asteroids and Jupiter trojans ), as well as distant minor planets ( Uranus trojans , Neptune trojans , centaurs and trans-Neptunian objects ), most of which reside in the Kuiper belt and the scattered disc . As of October 2024, there are 1,392,085 known objects, divided into 740,000 numbered , with only one of them recognized as

184-455: A dwarf planet almost 1000 km in diameter. A body is classified as a comet, not an asteroid, if it shows a coma (tail) when warmed by solar radiation, although recent observations suggest a continuum between these types of bodies. Of the roughly one million known asteroids, the greatest number are located between the orbits of Mars and Jupiter , approximately 2 to 4 AU from the Sun, in

276-445: A Data Base of Physical and Dynamical Properties of Near Earth Asteroids. Environmental characteristics have three aspects: space environment, surface environment and internal environment, including geological, optical, thermal and radiological environmental properties, etc., which are the basis for understanding the basic properties of minor planets, carrying out scientific research, and are also an important reference basis for designing

368-450: A comet. Objects are called dwarf planets if their own gravity is sufficient to achieve hydrostatic equilibrium and form an ellipsoidal shape. All other minor planets and comets are called small Solar System bodies . The IAU stated that the term minor planet may still be used, but the term small Solar System body will be preferred. However, for purposes of numbering and naming, the traditional distinction between minor planet and comet

460-478: A crust, a mantle and a core. 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; its composition is mainly of basaltic rock with minerals such as olivine. Aside from the large crater at its southern pole, Rheasilvia , Vesta also has an ellipsoidal shape. Vesta is the parent body of

552-644: A diameter of one kilometer or larger. A small number of NEAs are extinct comets that have lost their volatile surface materials, although having a faint or intermittent comet-like tail does not necessarily result in a classification as a near-Earth comet, making the boundaries somewhat fuzzy. The rest of the near-Earth asteroids are driven out of the asteroid belt by gravitational interactions with Jupiter . Many asteroids have natural satellites ( minor-planet moons ). As of October 2021 , there were 85 NEAs known to have at least one moon, including three known to have two moons. The asteroid 3122 Florence , one of

644-487: A distance of 0.4192  AU (62,710,000  km ; 38,970,000  mi ), peaking in brightness at an apparent magnitude of 17.0. In opposition on 23 November 2012, it brightened to magnitude 16.0. It is a member of the Alinda group of asteroids with a 3:1 resonance with Jupiter that has excited the eccentricity of the orbit over the eons. As an Alinda asteroid it makes approaches to Jupiter, Earth, and Venus. For

736-488: A dwarf planet (secured discoveries) and 652,085 unnumbered minor planets, with only five of those officially recognized as a dwarf planet . The first minor planet to be discovered was Ceres in 1801, though it was called a 'planet' at the time and an 'asteroid' soon after; the term minor planet was not introduced until 1841, and was considered a subcategory of 'planet' until 1932. The term planetoid has also been used, especially for larger, planetary objects such as those

828-460: A false positive or become lost later on —called a provisionally designated minor planet . After the observation arc is accurate enough to predict its future location, a minor planet is formally designated and receives a number. It is then a numbered minor planet . Finally, in the third step, it may be named by its discoverers. However, only a small fraction of all minor planets have been named. The vast majority are either numbered or have still only

920-407: A few other asteroids discovered over the next few years. 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 . Many asteroids are the shattered remnants of planetesimals , bodies within the young Sun's solar nebula that never grew large enough to become planets . It is thought that planetesimals in

1012-487: A group headed by Franz Xaver von Zach , editor of the German astronomical journal Monatliche Correspondenz (Monthly Correspondence), sent requests to 24 experienced astronomers (whom he dubbed the " celestial police "), asking that they combine their efforts and begin a methodical search for the expected planet. Although they did not discover Ceres, they later found the asteroids 2 Pallas , 3 Juno and 4 Vesta . One of

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1104-555: A name (e.g. 433 Eros ). The formal naming convention uses parentheses around the number, 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. Minor planets that have been given a number but not a name keep their provisional designation, e.g. (29075) 1950 DA . Because modern discovery techniques are finding vast numbers of new asteroids, they are increasingly being left unnamed. The earliest discovered to be left unnamed

1196-465: A numerical procession known as the Titius–Bode law (now discredited). Except for an unexplained gap between Mars and Jupiter, Bode's formula seemed to predict the orbits of the known planets. He wrote the following explanation for the existence of a "missing planet": This latter point seems in particular to follow from the astonishing relation which the known six planets observe in their distances from

1288-427: A provisional designation. Example of the naming process: A newly discovered minor planet is given a provisional designation . For example, the provisional designation 2002 AT 4 consists of the year of discovery (2002) 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

1380-476: A region known as the main asteroid belt . The total mass of all the asteroids combined is only 3% that of Earth's Moon . The majority of main belt asteroids follow slightly elliptical, stable orbits, revolving in the same direction as the Earth and taking from three to six years to complete a full circuit of the Sun. Asteroids have historically been observed from Earth. The first close-up observation of an asteroid

1472-573: A relatively reflective surface , is normally visible to the naked eye in dark skies when it is favorably positioned. Rarely, small asteroids passing close to Earth may be briefly visible to the naked eye. As of April 2022 , the Minor Planet Center had data on 1,199,224 minor planets in the inner and outer Solar System, of which about 614,690 had enough information to be given numbered designations. In 1772, German astronomer Johann Elert Bode , citing Johann Daniel Titius , published

1564-401: A sample in 2020 which was delivered back to Earth in 2023. NASA's Lucy , launched in 2021, is tasked with studying ten different asteroids, two from the main belt and eight Jupiter trojans . Psyche , launched October 2023, aims to study the metallic asteroid Psyche . Near-Earth asteroids have the potential for catastrophic consequences if they strike Earth, with a notable example being

1656-532: A series of days. Second, the two films or plates of the same region were viewed under a stereoscope . A 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. These first three steps do not constitute asteroid discovery:

1748-565: 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 . By 1851, the Royal Astronomical Society decided that asteroids were being discovered at such a rapid rate that a different system

1840-645: A somewhat larger surface soil layer size. Soil layers are inevitably subject to intense space weathering that alters their physical and chemical properties due to direct exposure to the surrounding space environment. In silicate-rich soils, the outer layers of Fe are reduced to nano-phase Fe (np-Fe), which is the main product of space weathering . For some small planets, their surfaces are more exposed as boulders of varying sizes, up to 100 metres in diameter, due to their weaker gravitational pull. These boulders are of high scientific interest, as they may be either deeply buried material excavated by impact action or fragments of

1932-417: 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. 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

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2024-429: A variety of other rich geological effects on the surface of minor planets, such as mass wasting on slopes and impact crater walls, large-scale linear features associated with graben , and electrostatic transport of dust. By analysing the various geological processes on the surface of minor planets, it is possible to learn about the possible internal activity at this stage and some of the key evolutionary information about

2116-437: Is a minor planet —an object that is neither a true planet nor an identified comet — that orbits within the inner Solar System . They are rocky, metallic, or icy bodies with no atmosphere, classified as C-type ( carbonaceous ), M-type ( metallic ), or S-type ( silicaceous ). The size and shape of asteroids vary significantly, ranging from small rubble piles under a kilometer across and larger than meteoroids , to Ceres ,

2208-410: Is also known. Numerical orbital dynamics stability simulations indicate that Saturn and Uranus probably do not have any primordial trojans. 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 April 2022 , a total of 28,772 near-Earth asteroids were known; 878 have

2300-427: 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 brightest of the four main-belt asteroids 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

2392-505: Is similar to that of carbon- or iron-bearing meteorites, the interaction between the minor planets and the solar wind is likely to be unipolar induction , resulting in an external magnetic field for the minor planet. In addition, the magnetic fields of minor planets are not static; impact events, weathering in space and changes in the thermal environment can alter the existing magnetic fields of minor planets. At present, there are not many direct observations of minor planet magnetic fields, and

2484-544: Is so slow and rather uniform, it has occurred to me several times that it might be something better than a comet". In April, Piazzi sent his complete observations to Oriani, Bode, and French astronomer Jérôme Lalande . The information was published in the September 1801 issue of the Monatliche Correspondenz . By this time, the apparent position of Ceres had changed (mostly due to Earth's motion around

2576-407: Is still used. Hundreds of thousands of minor planets have been discovered within the Solar System and thousands more are discovered each month. The Minor Planet Center has documented over 213 million observations and 794,832 minor planets, of which 541,128 have orbits known well enough to be assigned permanent official numbers . Of these, 21,922 have official names. As of 8 November 2021,

2668-484: Is that both moons may be captured main-belt asteroids . Both moons have very circular orbits which lie almost exactly in Mars's equatorial plane , and hence a capture origin requires a mechanism for circularizing the initially highly eccentric orbit, and adjusting its inclination into the equatorial plane, most probably by a combination of atmospheric drag and tidal forces , although it is not clear whether sufficient time

2760-439: Is that comets typically have more eccentric orbits than most asteroids; highly eccentric asteroids are probably dormant or extinct comets. The minor planets beyond Jupiter's orbit are sometimes also called "asteroids", especially in popular presentations. However, it is becoming increasingly common for the term asteroid to be restricted to minor planets of the inner Solar System. Therefore, this article will restrict itself for

2852-658: The Chicxulub impact , widely thought to have induced the Cretaceous–Paleogene mass extinction . As an experiment to meet this danger, in September 2022 the Double Asteroid Redirection Test spacecraft successfully altered the orbit of the non-threatening asteroid Dimorphos by crashing into it. In 2006, the International Astronomical Union (IAU) introduced the currently preferred broad term small Solar System body , defined as an object in

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2944-738: The International Astronomical Union is dedicated to the Physical Study of Comets & Minor Planets. Archival data on the physical properties of comets and minor planets are found in the PDS Asteroid/Dust Archive. This includes standard asteroid physical characteristics such as the properties of binary systems, occultation timings and diameters, masses, densities, rotation periods, surface temperatures, albedoes, spin vectors, taxonomy, and absolute magnitudes and slopes. In addition, European Asteroid Research Node (E.A.R.N.), an association of asteroid research groups, maintains

3036-462: The Solar System that is neither a planet , a dwarf planet , nor a natural satellite ; this includes asteroids, comets, and more recently discovered classes. According to IAU, "the term 'minor planet' may still be used, but generally, 'Small Solar System Body' will be preferred." Historically, the first discovered asteroid, Ceres , was at first considered a new planet. It was followed by

3128-580: The Vestian family and other V-type asteroids , and is the source of the HED meteorites , which constitute 5% of all meteorites on Earth. 3360 Syrinx 3360 Syrinx (originally designated 1981 VA ) is an Apollo and Mars crosser asteroid discovered in 1981. It approaches Earth to within 40  Gm three times in the 21st century: 33 Gm in 2039, 40 Gm in 2070, and 24 Gm in 2085. On 20 September 2012, it closely encountered Earth at

3220-467: 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 . Contrary to popular imagery, the asteroid belt is mostly empty. The asteroids are spread over such a large volume that reaching an asteroid without aiming carefully would be improbable. Nonetheless, hundreds of thousands of asteroids are currently known, and

3312-476: The thermal infrared suggest a composition containing mainly phyllosilicates , which are well known from the surface of Mars. The spectra are distinct from those of all classes of chondrite meteorites, again pointing away from an asteroidal origin. Both sets of findings support an origin of Phobos from material ejected by an impact on Mars that reaccreted in Martian orbit, similar to the prevailing theory for

3404-559: The Ancient Greek ἀστήρ astēr 'star, planet'. In the early second half of the 19th century, the terms asteroid and planet (not always qualified as "minor") were still used interchangeably. Traditionally, small bodies orbiting the Sun were classified as comets , asteroids, or meteoroids , with anything smaller than one meter across being called a meteoroid. The term asteroid, never officially defined, can be informally used to mean "an irregularly shaped rocky body orbiting

3496-459: The IAU has called dwarf planets since 2006. Historically, the terms asteroid , minor planet , and planetoid have been more or less synonymous. This terminology has become more complicated by the discovery of numerous minor planets beyond the orbit of Jupiter , especially trans-Neptunian objects that are generally not considered asteroids. A minor planet seen releasing gas may be dually classified as

3588-652: 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. 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. Various dynamical groups of asteroids have been discovered orbiting in

3680-486: The Sun that does not qualify as a planet or a dwarf planet under the IAU definitions". The main difference between an asteroid and a comet is that a comet shows a coma (tail) due to sublimation of its near-surface ices by solar radiation. A few objects 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

3772-455: The Sun), and was too close to the Sun's glare for other astronomers to confirm Piazzi's observations. Toward the end of the year, Ceres should have been visible again, but after such a long time it was difficult to predict its exact position. To recover Ceres, mathematician Carl Friedrich Gauss , then 24 years old, developed an efficient method of orbit determination . In a few weeks, he predicted

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3864-401: The Sun, their volatile ices would sublimate , and traditional approaches would classify them as comets. The Kuiper-belt bodies are called "objects" partly to avoid the need to classify them as asteroids or comets. They are thought to be predominantly comet-like in composition, though some may be more akin to asteroids. Most do not have the highly eccentric orbits associated with comets, and

3956-489: The Sun. Let the distance from the Sun to Saturn be taken as 100, then Mercury is separated by 4 such parts from the Sun. Venus is 4 + 3 = 7. The Earth 4 + 6 = 10. Mars 4 + 12 = 16. Now comes a gap in this so orderly progression. After Mars there follows a space of 4 + 24 = 28 parts, in which no planet has yet been seen. Can one believe that the Founder of the universe had left this space empty? Certainly not. From here we come to

4048-544: The accretion epoch), whereas most smaller asteroids are products of fragmentation of primordial asteroids. The primordial population of the main belt was probably 200 times what it is today. Three largest objects in the asteroid belt, 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, like

4140-502: The asteroid belt evolved much like the rest of objects in 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

4232-561: The asteroid belt is estimated to be 2.39 × 10 kg, which is just 3% of the mass of the Moon; the mass of the Kuiper Belt and Scattered Disk is over 100 times as large. The four largest objects, Ceres, Vesta, Pallas, and Hygiea, account for maybe 62% of the belt's total mass, with 39% accounted for by Ceres alone. 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

4324-501: The asteroid later named 5 Astraea . It was the first new asteroid discovery in 38 years. Carl Friedrich Gauss was given the honor of naming the asteroid. After this, other astronomers joined; 15 asteroids were found by the end of 1851. In 1868, when James Craig Watson discovered the 100th asteroid, the French Academy of Sciences engraved the faces of Karl Theodor Robert Luther , John Russell Hind , and Hermann Goldschmidt ,

4416-610: The astronomers selected for the search was Giuseppe Piazzi , a Catholic priest at the Academy of Palermo, Sicily. Before receiving his invitation to join the group, Piazzi discovered Ceres on 1 January 1801. He was searching for "the 87th [star] of the Catalogue of the Zodiacal stars of Mr la Caille ", but found that "it was preceded by another". Instead of a star, Piazzi had found a moving star-like object, which he first thought

4508-458: The convection of the conductive fluid will generate a large and strong magnetic field . However, the size of a minor planet is generally small and most of the minor planets have a "crushed stone pile" structure, and there is basically no "dynamo" structure inside, so it will not generate a self-generated dipole magnetic field like the Earth. But some minor planets do have magnetic fields—on the one hand, some minor planets have remanent magnetism : if

4600-466: 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 , coined in Greek as ἀστεροειδής, or asteroeidēs , meaning 'star-like, star-shaped', and derived from

4692-406: The distance of Jupiter by 4 + 48 = 52 parts, and finally to that of Saturn by 4 + 96 = 100 parts. Bode's formula predicted another planet would be found with an orbital radius near 2.8 astronomical units (AU), or 420 million km, from the Sun. The Titius–Bode law got a boost with William Herschel 's discovery of Uranus near the predicted distance for a planet beyond Saturn . In 1800,

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4784-399: The fact that most minor planets are rubble pile structures, which are loose and porous, gives the impact action on the surface of minor planets its unique characteristics. On highly porous minor planets, small impact events produce spatter blankets similar to common impact events: whereas large impact events are dominated by compaction and spatter blankets are difficult to form, and the longer

4876-666: The few existing planets detection projects generally carry magnetometers, with some targets such as Gaspra and Braille measured to have strong magnetic fields nearby, while others such as Lutetia have no magnetic field. Solar System   → Local Interstellar Cloud   → Local Bubble   → Gould Belt   → Orion Arm   → Milky Way   → Milky Way subgroup   → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster   → Local Hole   → Observable universe   → Universe Each arrow ( → ) may be read as "within" or "part of". Asteroid An asteroid

4968-472: The fourth, when I had the satisfaction to see it had moved at the same rate as on the preceding days. Piazzi observed Ceres a total of 24 times, the final time on 11 February 1801, when illness interrupted his work. He announced his discovery on 24 January 1801 in letters to only two fellow astronomers, his compatriot Barnaba Oriani of Milan and Bode in Berlin. He reported it as a comet but "since its movement

5060-599: 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: 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 estimated to contain between 1.1 and 1.9 million asteroids larger than 1 km (0.6 mi) in diameter, and millions of smaller ones. These asteroids may be remnants of

5152-404: The largest minor planets—those massive enough to have become ellipsoidal under their own gravity. Only the largest object in the asteroid belt has been placed in this category: Ceres , at about 975 km (606 mi) across. Despite their large numbers, asteroids are a relatively recent discovery, with the first one—Ceres—only being identified in 1801. Only one asteroid, 4 Vesta , which has

5244-720: The largest potentially hazardous asteroids with a diameter of 4.5 km (2.8 mi), has two moons measuring 100–300 m (330–980 ft) across, which were discovered by radar imaging during the asteroid's 2017 approach to Earth. Near-Earth asteroids are divided into groups based on their semi-major axis (a), perihelion distance (q), and aphelion distance (Q): It is unclear whether Martian moons Phobos and Deimos are captured asteroids or were formed due to impact event on Mars. Phobos and Deimos both have much in common with carbonaceous C-type asteroids , with spectra , albedo , and density very similar to those of C- or D-type asteroids. Based on their similarity, one hypothesis

5336-512: The law was a coincidence. Piazzi named the newly discovered object Ceres Ferdinandea, "in honor of the patron goddess of Sicily and of King Ferdinand of Bourbon ". Three other asteroids ( 2 Pallas , 3 Juno , and 4 Vesta ) were discovered by von Zach's group over the next few years, with Vesta found in 1807. No new asteroids were discovered until 1845. Amateur astronomer Karl Ludwig Hencke started his searches of new asteroids in 1830, and fifteen years later, while looking for Vesta, he found

5428-473: The long-term interaction with the external environment, which may lead to some indication of the nature of the parent body's origin. Many of the larger planets are often covered by a layer of soil ( regolith ) of unknown thickness. Compared to other atmosphere-free bodies in the solar system (e.g. the Moon ), minor planets have weaker gravity fields and are less capable of retaining fine-grained material, resulting in

5520-429: The lowest-numbered unnamed minor planet is (4596) 1981 QB , and the highest-numbered named minor planet is 594913 ꞌAylóꞌchaxnim . There are various broad minor-planet populations: All astronomical bodies in the Solar System need a distinct designation. The naming of minor planets runs through a three-step process. First, a provisional designation is given upon discovery—because the object still may turn out to be

5612-416: The majority of asteroids. The four largest asteroids constitute half the mass of the asteroid belt. Ceres is the only asteroid that appears to have a plastic shape under its own gravity and hence the only one that is a dwarf planet . It has a much higher absolute magnitude than the other asteroids, of around 3.32, and may possess a surface layer of ice. Like the planets, Ceres is differentiated: it has

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5704-419: The minor planet exploration mission, measuring the albedo and color changes of the planet surface is also the most basic method to directly know the difference in the material composition of the planet surface. The geological environment on the surface of minor planets is similar to that of other unprotected celestial bodies, with the most widespread geomorphological feature present being impact craters: however,

5796-514: The most part to the classical asteroids: objects of the asteroid belt , Jupiter trojans , and near-Earth objects . For almost two centuries after the discovery of Ceres in 1801, all known asteroids spent most of their time at or within the orbit of Jupiter, though a few, such as 944 Hidalgo , ventured farther for part of their orbit. Starting in 1977 with 2060 Chiron , astronomers discovered small bodies that permanently resided further out than Jupiter, now called centaurs . In 1992, 15760 Albion

5888-516: The number—e.g. (433) Eros—but dropping the parentheses is quite common. Informally, it is also common to drop the number altogether, or to drop it after the first mention when a name is repeated in running text. In addition, names can be proposed by the asteroid's discoverer, within guidelines established by the International Astronomical Union. The first asteroids to be discovered were assigned iconic symbols like

5980-436: The objects of the asteroid belt , lying between the orbits of Mars and Jupiter , is estimated to be (2394 ± 6) × 10  kg , ≈ 3.25% of the mass of the Moon. Of this, Ceres comprises 938 × 10  kg , about 40% of the total. Adding in the next three most massive objects, Vesta (11%), Pallas (8.5%), and Hygiea (3–4%), brings this figure up to a bit over 60%, whereas the next seven most-massive asteroids bring

6072-463: 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 FJ 74 ). The last step is sending the locations and time of observations to the Minor Planet Center , where computer programs determine whether an apparition ties together earlier apparitions into

6164-453: The ones so far discovered are larger than traditional comet nuclei . 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, suggesting "a continuum between asteroids and comets" rather than a sharp dividing line. In 2006, the IAU created the class of dwarf planets for

6256-560: The ones traditionally used to designate the planets. By 1852 there were two dozen asteroid symbols, which often occurred in multiple variants. In 1851, 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),

6348-566: The origin of Earth's moon. Asteroids vary greatly in size, from almost 1000 km for the largest down to rocks just 1 meter across, below which an object is classified as a meteoroid . The three largest are very much like miniature planets: they are roughly spherical, have at least partly differentiated interiors, 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

6440-460: The parent body had a magnetic field or if the nearby planetary body has a strong magnetic field, the rocks on the parent body will be magnetised during the cooling process and the planet formed by the fission of the parent body will still retain remanence, which can also be detected in extraterrestrial meteorites from the minor planets; on the other hand, if the minor planets are composed of electrically conductive material and their internal conductivity

6532-455: The path of Ceres and sent his results to von Zach. On 31 December 1801, von Zach and fellow celestial policeman Heinrich W. M. Olbers found Ceres near the predicted position and thus recovered it. At 2.8 AU from the Sun, Ceres appeared to fit the Titius–Bode law almost perfectly; however, Neptune, once discovered in 1846, was 8 AU closer than predicted, leading most astronomers to conclude that

6624-428: The payload of exploration missions Without the protection of an atmosphere and its own strong magnetic field, the minor planet's surface is directly exposed to the surrounding radiation environment. In the cosmic space where minor planets are located, the radiation on the surface of the planets can be divided into two categories according to their sources: one comes from the sun, including electromagnetic radiation from

6716-443: The periodic change of the planet's light curve, which can be observed by ground-based equipment, so as to obtain the planet's magnitude , rotation period , rotation axis orientation, shape, albedo distribution, and scattering properties. Generally speaking, the albedo of minor planets is usually low, and the overall statistical distribution is bimodal, corresponding to C-type (average 0.035) and S-type (average 0.15) minor planets. In

6808-399: The planet's parent body that have survived. The rocks provide more direct and primitive information about the material inside the minor planet and the nature of its parent body than the soil layer, and the different colours and forms of the rocks indicate different sources of material on the surface of the minor planet or different evolutionary processes. Usually in the interior of the planet,

6900-576: The planets receive such large impacts, the greater the overall density. In addition, statistical analysis of impact craters is an important means of obtaining information on the age of a planet surface. Although the Crater Size-Frequency Distribution (CSFD) method of dating commonly used on minor planet surfaces does not allow absolute ages to be obtained, it can be used to determine the relative ages of different geological bodies for comparison. In addition to impact, there are

6992-494: The publication of the Minor Planet Circular (MPC) of October 19, 2005, which saw the highest-numbered minor planet jump from 99947 to 118161. The first few asteroids were named after figures from Greek and Roman mythology , but as such names started to dwindle the names of famous people, literary characters, discoverers' spouses, children, colleagues, and even television characters were used. Commission 15 of

7084-427: The same birth cloud as Mars. Another hypothesis is that Mars was once surrounded by many Phobos- and Deimos-sized bodies, perhaps ejected into orbit around it by a collision with a large planetesimal . The high porosity of the interior of Phobos (based on the density of 1.88 g/cm , voids are estimated to comprise 25 to 35 percent of Phobos's volume) is inconsistent with an asteroidal origin. Observations of Phobos in

7176-399: The sun, and ionizing radiation from the solar wind and solar energy particles; the other comes from the sun outside the solar system, that is, galactic cosmic rays , etc. Usually during one rotation period of a minor planet, the albedo of a minor planet will change slightly due to its irregular shape and uneven distribution of material composition. This small change will be reflected in

7268-496: The three most successful asteroid-hunters at that time, on a commemorative medallion marking the event. 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

7360-439: 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 absolute magnitudes of most of the known asteroids are between 11 and 19, with the median at about 16. The total mass of

7452-449: The total up to 70%. The number of asteroids increases rapidly as their individual masses decrease. The number of asteroids decreases markedly with increasing size. Although the size distribution generally follows a power law , there are 'bumps' at about 5 km and 100 km , where more asteroids than expected from such a curve are found. Most asteroids larger than approximately 120 km in diameter are primordial (surviving from

7544-714: The two Lagrangian points of stability, L 4 and L 5 , which lie 60° ahead of and behind the larger body. In the Solar System, most known trojans share the orbit of Jupiter . They are divided into the Greek camp at L 4 (ahead of Jupiter) and the Trojan camp at L 5 (trailing Jupiter). More than a million Jupiter trojans larger than one kilometer are thought to exist, of which more than 7,000 are currently catalogued. In other planetary orbits only nine Mars trojans , 28 Neptune trojans , two Uranus trojans , and two Earth trojans , have been found to date. A temporary Venus trojan

7636-407: Was a comet: The light was a little faint, and of the colour of Jupiter , but similar to many others which generally are reckoned of the eighth magnitude . Therefore I had no doubt of its being any other than a fixed star. [...] The evening of the third, my suspicion was converted into certainty, being assured it was not a fixed star. Nevertheless before I made it known, I waited till the evening of

7728-489: Was available for this to occur for Deimos. Capture also requires dissipation of energy. The current Martian atmosphere is too thin to capture a Phobos-sized object by atmospheric braking. Geoffrey A. Landis has pointed out that the capture could have occurred if the original body was a binary asteroid that separated under tidal forces. Phobos could be a second-generation Solar System object that coalesced in orbit after Mars formed, rather than forming concurrently out of

7820-438: Was calculated and registered within that specific year. For example, the first two asteroids discovered in 1892 were labeled 1892A and 1892B. However, there were not enough letters in the alphabet for all of the asteroids discovered in 1893, so 1893Z was followed by 1893AA. A number of variations of these methods were tried, including designations that included year plus a Greek letter in 1914. A simple chronological numbering system

7912-534: Was discovered, the first object beyond the orbit of Neptune (other than Pluto ); soon large numbers of similar objects were observed, now called trans-Neptunian object . Further out are Kuiper-belt objects , scattered-disc objects , and the much more distant Oort cloud , hypothesized to be the main reservoir of dormant comets. They inhabit the cold outer reaches of the Solar System where ices remain solid and comet-like bodies exhibit little cometary activity; if centaurs or trans-Neptunian objects were to venture close to

8004-450: Was established in 1925. Currently all newly discovered asteroids receive a provisional designation (such as 2002 AT 4 ) 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

8096-465: Was finally named 15760 Albion in January 2018. A few objects are cross-listed as both comets and asteroids, such as 4015 Wilson–Harrington , which is also listed as 107P/Wilson–Harrington . Minor planets are awarded an official number once their orbits are confirmed. With the increasing rapidity of discovery, these are now six-figure numbers. The switch from five figures to six figures arrived with

8188-520: Was for a long time (3360) 1981 VA , now 3360 Syrinx . In November 2006 its position as the lowest-numbered unnamed asteroid passed to (3708) 1974 FV 1 (now 3708 Socus ), and in May 2021 to (4596) 1981 QB . On rare occasions, a small object's provisional designation may become used as a name in itself: the then-unnamed (15760) 1992 QB 1 gave its "name" to a group of objects that became known as classical Kuiper belt objects ("cubewanos") before it

8280-534: Was known that there were many more, but most astronomers did not bother with them, some calling them "vermin of the skies", a phrase variously attributed to Eduard Suess and Edmund Weiss . Even a century later, only a few thousand asteroids were identified, numbered and named. In the past, 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

8372-465: Was made by the Galileo spacecraft . Several dedicated missions to asteroids were subsequently launched by NASA and JAXA , with plans for other missions in progress. NASA's NEAR Shoemaker studied Eros , and Dawn observed Vesta and Ceres . JAXA's missions Hayabusa and Hayabusa2 studied and returned samples of Itokawa and Ryugu , respectively. OSIRIS-REx studied Bennu , collecting

8464-451: Was needed to categorize or name asteroids. In 1852, when de Gasparis discovered the twentieth asteroid, Benjamin Valz gave it a name and a number designating its rank among asteroid discoveries, 20 Massalia . Sometimes asteroids were discovered and not seen again. So, starting in 1892, new asteroids were listed by the year and a capital letter indicating the order in which the asteroid's orbit

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