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104-681: Originally entitled Up! , it offers a futuristic story of social outcasts living on an asteroid in outer space in the year 2972. Among them is Gabriel Finn, a space sanitation man who collects trash in a clamshell-shaped garbage ship called the Helen of Troy . The storyline was so incomprehensible that at the last moment producers decided to insert a plot synopsis in the Playbill , but audiences were still baffled by what they were witnessing unfold on stage. Pyrotechnic displays, trampolines to portray weightlessness, and other special effects did little to enhance

208-640: A revised version of the Nice model Jupiter trojans are captured when Jupiter encounters an ice giant during the instability. In this version of the Nice model one of the ice giants (Uranus, Neptune, or a lost fifth planet ) is scattered inward onto a Jupiter-crossing orbit and is scattered outward by Jupiter causing the orbits of Jupiter and Saturn to quickly separate. When Jupiter's semi-major axis jumps during these encounters existing Jupiter trojans can escape and new objects with semi-major axes similar to Jupiter's new semi-major axis are captured. Following its last encounter

312-472: 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

416-568: A deficit of periods in the range 8–10 hours. The Maxwellian distribution of the rotational periods of Jupiter trojans may indicate that they have undergone a stronger collisional evolution compared to the asteroid belt. In 2008 a team from Calvin College examined the light curves of a debiased sample of ten Jupiter trojans, and found a median spin period of 18.9 hours. This value was significantly higher than that for main-belt asteroids of similar size (11.5 hours). The difference could mean that

520-644: 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

624-417: A factor of 2 if small Jupiter trojans are more reflective than large ones. The number of Jupiter trojans observed in the L 4 swarm is slightly larger than that observed in L 5 . Because the brightest Jupiter trojans show little variation in numbers between the two populations, this disparity is probably due to observational bias. Some models indicate that the L 4 swarm may be slightly more stable than

728-407: 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

832-512: A figure of the Trojan War , hence the name "trojan". The total number of Jupiter trojans larger than 1 km in diameter is believed to be about 1 million , approximately equal to the number of asteroids larger than 1 km in the asteroid belt . Like main-belt asteroids, Jupiter trojans form families . As of 2004 , many Jupiter trojans showed to observational instruments as dark bodies with reddish, featureless spectra . No firm evidence of

936-742: A fixed separation from Jupiter. They slowly librate around their respective equilibrium points, periodically moving closer to Jupiter or farther from it. Jupiter trojans generally follow paths called tadpole orbits around the Lagrangian points; the average period of their libration is about 150 years. The amplitude of the libration (along the Jovian orbit) varies from 0.6° to 88°, with the average being about 33°. Simulations show that Jupiter trojans can follow even more complicated trajectories when moving from one Lagrangian point to another—these are called horseshoe orbits (currently no Jupiter Trojan with such an orbit

1040-483: 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

1144-455: A kilometer across and larger than meteoroids , to Ceres , 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

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1248-465: 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

1352-564: 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

1456-401: 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

1560-578: 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:

1664-541: 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

1768-417: 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

1872-452: A variation of this theory Jupiter captures trojans during its initial growth then migrates as it continues to grow. During Jupiter's migration the orbits of objects in horseshoe orbits are distorted causing the L4 side of these orbits to be over occupied. As a result, an excess of trojans is trapped on the L4 side when the horseshoe orbits shift to tadpole orbits as Jupiter grows. This model also leaves

1976-477: Is 0.056 ± 0.003 for the objects larger than 57 km, and 0.121 ± 0.003 (R-band) for those smaller than 25 km. The asteroid 4709 Ennomos has the highest albedo (0.18) of all known Jupiter trojans. Little is known about the masses, chemical composition, rotation or other physical properties of the Jupiter trojans. The rotational properties of Jupiter trojans are not well known. Analysis of

2080-410: 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

2184-427: 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

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2288-465: Is caused by (1) the assumption that all Jupiter trojans have a low albedo of about 0.04, whereas small bodies may have an average albedo as high as 0.12; (2) an incorrect assumption about the distribution of Jupiter trojans in the sky. According to the new estimates, the total number of Jupiter trojans with a diameter larger than 2 km is 6,300 ± 1,000 and 3,400 ± 500 in the L 4 and L 5 swarms, respectively. These numbers would be reduced by

2392-461: Is known, though one is known for Neptune ). Discerning dynamical families within the Jupiter trojan population is more difficult than it is in the asteroid belt, because the Jupiter trojans are locked within a far narrower range of possible positions. This means that clusters tend to overlap and merge with the overall swarm. By 2003 roughly a dozen dynamical families were identified. Jupiter-trojan families are much smaller in size than families in

2496-470: Is normally understood to specifically mean the Jupiter trojans because the first Trojans were discovered near Jupiter's orbit and Jupiter currently has by far the most known Trojans. In 1772, Italian-born mathematician Joseph-Louis Lagrange , in studying the restricted three-body problem , predicted that a small body sharing an orbit with a planet but lying 60° ahead or behind it will be trapped near these points. The trapped body will librate slowly around

2600-409: Is open to question, because multiple weak resonances with Jupiter and Saturn cause them to behave chaotically over time. Collisional shattering slowly depletes the Jupiter trojan population as fragments are ejected. Ejected Jupiter trojans could become temporary satellites of Jupiter or Jupiter-family comets . Simulations show that the orbits of up to 17% of Jupiter trojans are unstable over the age of

2704-535: Is significantly higher than that of 617 Patroclus. Such a difference in densities suggests that density may not be a good indicator of asteroid origin. Two main theories have emerged to explain the formation and evolution of the Jupiter trojans. The first suggests that the Jupiter trojans formed in the same part of the Solar System as Jupiter and entered their orbits while it was forming. The last stage of Jupiter's formation involved runaway growth of its mass through

2808-529: 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

2912-480: 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

3016-439: 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

3120-640: 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

3224-402: 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

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3328-548: The Solar System's formation or slightly later, during the migration of giant planets. The term "Trojan Asteroid" specifically refers to the asteroids co-orbital with Jupiter, but the general term " trojan " is sometimes more generally applied to other small Solar System bodies with similar relationships to larger bodies: Mars trojans , Neptune trojans , Uranus trojans and Earth trojans are known to exist. Temporary Venus trojans and Saturn trojans exist, as well as for 1 Ceres and 4 Vesta . The term "Trojan asteroid"

3432-415: The Trojan War was suggested by Johann Palisa of Vienna , who was the first to accurately calculate their orbits. Asteroids in the leading (L 4 ) orbit are named after Greek heroes (the "Greek node or camp" or " Achilles group"), and those at the trailing (L 5 ) orbit are named after the heroes of Troy (the "Trojan node or camp"). The asteroids 617 Patroclus and 624 Hektor were named before

3536-614: The Vestian family and other V-type asteroids , and is the source of the HED meteorites , which constitute 5% of all meteorites on Earth. Jupiter trojan The Jupiter trojans , commonly called trojan asteroids or simply trojans , are a large group of asteroids that share the planet Jupiter 's orbit around the Sun . Relative to Jupiter, each trojan librates around one of Jupiter's stable Lagrange points : either L 4 , existing 60° ahead of

3640-467: 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

3744-471: 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

3848-486: The 4.4–40 km range the Jupiter trojans' size distribution resembles that of the main-belt asteroids. Nothing is known about the masses of the smaller Jupiter trojans. The size distribution suggests that the smaller Trojans may be the products of collisions by larger Jupiter trojans. Jupiter trojans have orbits with radii between 5.05 and 5.35 AU (the mean semi-major axis is 5.2 ± 0.15 AU), and are distributed throughout elongated, curved regions around

3952-552: 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

4056-792: The Greece/Troy rule was devised, resulting in a "Greek spy", Patroclus , in the Trojan node and a "Trojan spy", Hector , in the Greek node. In 2018, at its 30th General Assembly in Vienna, the International Astronomical Union amended the naming convention for Jupiter trojans, allowing for asteroids with H larger than 12 (that is, a mean diameter smaller than approximately 22 kilometers, for an assumed albedo of 0.057) to be named after Olympic athletes, because there are now far more known Jupiter trojans than available names of Greek and Trojan warriors that fought in

4160-591: 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

4264-537: The Jupiter trojan population 3–4 orders of magnitude too large. The second theory proposes that the Jupiter trojans were captured during the migration of the giant planets described in the Nice model . In the Nice model the orbits of the giant planets became unstable 500–600 million years after the Solar System's formation when Jupiter and Saturn crossed their 1:2 mean-motion resonance . Encounters between planets resulted in Uranus and Neptune being scattered outward into

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4368-622: The Jupiter trojans possess a lower average density, which may imply that they formed in the Kuiper belt (see below). Spectroscopically , the Jupiter trojans mostly are D-type asteroids , which predominate in the outer regions of the asteroid belt. A small number are classified as P or C-type asteroids . Their spectra are red (meaning that they reflect more light at longer wavelengths) or neutral and featureless. No firm evidence of water, organics or other chemical compounds has been obtained as of 2007 . 4709 Ennomos has an albedo slightly higher than

4472-494: The Jupiter-trojan average, which may indicate the presence of water ice. Some other Jupiter Trojans, such as 911 Agamemnon and 617 Patroclus , have shown very weak absorptions at 1.7 and 2.3 μm, which might indicate the presence of organics. The Jupiter trojans' spectra are similar to those of the irregular moons of Jupiter and, to a certain extent, comet nuclei , though Jupiter trojans are spectrally very different from

4576-406: The L 4 Lagrangian point of the Sun – Jupiter system, later named 588 Achilles . In 1906–1907 two more Jupiter trojans were found by fellow German astronomer August Kopff ( 624 Hektor and 617 Patroclus ). Hektor, like Achilles, belonged to the L 4 swarm ("ahead" of the planet in its orbit), whereas Patroclus was the first asteroid known to reside at the L 5 Lagrangian point ("behind"

4680-438: The L 5 swarm. The largest Jupiter trojan is 624 Hektor , which has a mean diameter of 203 ± 3.6 km. There are few large Jupiter trojans in comparison to the overall population. With decreasing size, the number of Jupiter trojans grows very quickly down to 84 km, much more so than in the asteroid belt. A diameter of 84 km corresponds to an absolute magnitude of 9.5, assuming an albedo of 0.04. Within

4784-463: The Solar System. Levison et al. believe that roughly 200 ejected Jupiter trojans greater than 1 km in diameter might be travelling the Solar System, with a few possibly on Earth-crossing orbits. Some of the escaped Jupiter trojans may become Jupiter-family comets as they approach the Sun and their surface ice begins evaporating. On 4 January 2017 NASA announced that Lucy was selected as one of their next two Discovery Program missions. Lucy

4888-532: 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

4992-452: 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

5096-484: The Sun, in 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

5200-401: 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

5304-484: 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

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5408-435: The Trojan war. Estimates of the total number of Jupiter trojans are based on deep surveys of limited areas of the sky. The L 4 swarm is believed to hold between 160,000 and 240,000 asteroids with diameters larger than 2 km and about 600,000 with diameters larger than 1 km. If the L 5 swarm contains a comparable number of objects, there are more than 1 million Jupiter trojans 1 km in size or larger. For

5512-544: 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

5616-460: The accretion of large amounts of hydrogen and helium from the protoplanetary disk ; during this growth, which lasted for only about 10,000 years, the mass of Jupiter increased by a factor of ten. The planetesimals that had approximately the same orbits as Jupiter were caught by the increased gravity of the planet. The capture mechanism was very efficient—about 50% of all remaining planetesimals were trapped. This hypothesis has two major problems:

5720-502: 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

5824-551: 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

5928-591: The asteroid belt; the largest identified family, the Menelaus group, consists of only eight members. In 2001, 617 Patroclus was the first Jupiter trojan to be identified as a binary asteroid . The binary's orbit is extremely close, at 650 km, compared to 35,000 km for the primary's Hill sphere . The largest Jupiter trojan— 624 Hektor — is probably a contact binary with a moonlet. Jupiter trojans are dark bodies of irregular shape. Their geometric albedos generally vary between 3 and 10%. The average value

6032-494: 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 ,

6136-595: 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

6240-428: The density of the binary Jupiter trojan 617 Patroclus as being less than that of water ice (0.8 g/cm ), suggesting that the pair, and possibly many other Trojan objects, more closely resemble comets or Kuiper belt objects in composition—water ice with a layer of dust—than they do the main-belt asteroids. Countering this argument, the density of Hektor as determined from its rotational lightcurve (2.480 g/cm )

6344-414: 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

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6448-406: 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,

6552-578: The first Broadway shows to lose more than $ 1 million, was MacDermot's second flop of the season. His Dude had closed after 16 performances five weeks earlier. Asteroid An asteroid 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

6656-468: 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

6760-408: The ice giant can pass through one of the libration points and perturb their orbits leaving this libration point depleted relative to the other. After the encounters end some of these Jupiter trojans are lost and others captured when Jupiter and Saturn are near weak mean motion resonances such as the 3:7 resonance via the mechanism of the original Nice model. The long-term future of the Jupiter trojans

6864-594: 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

6968-404: 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

7072-720: 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

7176-512: 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

7280-416: 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

7384-514: 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

7488-451: The number of trapped bodies exceeds the observed population of Jupiter trojans by four orders of magnitude , and the present Jupiter trojan asteroids have larger orbital inclinations than are predicted by the capture model. Simulations of this scenario show that such a mode of formation also would inhibit the creation of similar trojans for Saturn , and this has been borne out by observation: to date no trojans have been found near Saturn. In

7592-503: 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

7696-439: The objects brighter than absolute magnitude 9.0 the population is probably complete. These numbers are similar to that of comparable asteroids in the asteroid belt. The total mass of the Jupiter trojans is estimated at 0.0001 of the mass of Earth or one-fifth of the mass of the asteroid belt. Two more recent studies indicate that the above numbers may overestimate the number of Jupiter trojans by several-fold. This overestimate

7800-436: 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

7904-463: 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

8008-448: 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

8112-538: 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),

8216-566: 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

8320-455: 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

8424-448: The planet in its orbit, or L 5 , 60° behind. Jupiter trojans are distributed in two elongated, curved regions around these Lagrangian points with an average semi-major axis of about 5.2  AU . The first Jupiter trojan discovered, 588 Achilles , was spotted in 1906 by German astronomer Max Wolf . More than 9,800 Jupiter trojans have been found as of May 2021 . By convention, they are each named from Greek mythology after

8528-457: The planet). By 1938, 11 Jupiter trojans had been detected. This number increased to 14 only in 1961. As instruments improved, the rate of discovery grew rapidly: by January 2000, a total of 257 had been discovered; by May 2003, the number had grown to 1,600. As of October 2018 there are 4,601 known Jupiter trojans at L 4 and 2,439 at L 5 . The custom of naming all asteroids in Jupiter's L 4 and L 5 points after famous heroes of

8632-493: The point of equilibrium in a tadpole or horseshoe orbit . These leading and trailing points are called the L 4 and L 5 Lagrange points . The first asteroids trapped in Lagrange points were observed more than a century after Lagrange's hypothesis. Those associated with Jupiter were the first to be discovered. E. E. Barnard made the first recorded observation of a trojan, (12126) 1999 RM 11 (identified as A904 RD at

8736-414: The presence of water, or any other specific compound on their surface has been obtained, but it is thought that they are coated in tholins , organic polymers formed by the Sun's radiation. The Jupiter trojans' densities (as measured by studying binaries or rotational lightcurves) vary from 0.8 to 2.5 g·cm . Jupiter trojans are thought to have been captured into their orbits during the early stages of

8840-469: The primordial Kuiper belt , disrupting it and throwing millions of objects inward. When Jupiter and Saturn were near their 1:2 resonance the orbits of pre-existing Jupiter trojans became unstable during a secondary resonance with Jupiter and Saturn. This occurred when the period of the trojans' libration about their Lagrangian point had a 3:1 ratio to the period at which the position where Jupiter passes Saturn circulated relative to its perihelion. This process

8944-556: The project. After fifteen previews, the Broadway production, directed by Peter Hall , produced by George W. George and choreographed by George Faison , opened on November 28, 1972, the first production at the brand-new Uris Theatre where, unable to withstand a universal assault by the critics, it ran for only seven performances. The cast included Raul Julia , Irene Cara , Keene Curtis , Chuck Cissel , Ralph Carter , Melanie Chartoff , and Virginia Vestoff . Via Galactica , one of

9048-534: The redder Kuiper belt objects. A Jupiter trojan's spectrum can be matched to a mixture of water ice, a large amount of carbon-rich material ( charcoal ), and possibly magnesium -rich silicates . The composition of the Jupiter trojan population appears to be markedly uniform, with little or no differentiation between the two swarms. A team from the Keck Observatory in Hawaii announced in 2006 that it had measured

9152-426: The rotational light curves of 72 Jupiter trojans gave an average rotational period of about 11.2 hours, whereas the average period of the control sample of asteroids in the asteroid belt was 10.6 hours. The distribution of the rotational periods of Jupiter trojans appeared to be well approximated by a Maxwellian function , whereas the distribution for main-belt asteroids was found to be non-Maxwellian, with

9256-427: 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

9360-496: 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

9464-563: The time), in 1904, but neither he nor others appreciated its significance at the time. Barnard believed he had seen the recently discovered Saturnian satellite Phoebe , which was only two arc-minutes away in the sky at the time, or possibly an asteroid. The object's identity was not understood until its orbit was calculated in 1999. The first accepted discovery of a trojan occurred in February 1906, when astronomer Max Wolf of Heidelberg-Königstuhl State Observatory discovered an asteroid at

9568-439: 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

9672-449: 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

9776-706: 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

9880-408: The two Lagrangian points; each swarm stretches for about 26° along the orbit of Jupiter, amounting to a total distance of about 2.5 AU. The width of the swarms approximately equals two Hill's radii , which in the case of Jupiter amounts to about 0.6 AU. Many of Jupiter trojans have large orbital inclinations relative to Jupiter's orbital plane—up to 40°. Jupiter trojans do not maintain

9984-407: 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

10088-405: Was also reversible allowing a fraction of the numerous objects scattered inward by Uranus and Neptune to enter this region and be captured as Jupiter's and Saturn's orbits separated. These new trojans had a wide range of inclinations, the result of multiple encounters with the giant planets before being captured. This process can also occur later when Jupiter and Saturn cross weaker resonances. In

10192-489: 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

10296-438: 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

10400-534: 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

10504-450: 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

10608-534: 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

10712-460: 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

10816-447: 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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