Asteroids are minor planets, especially those originating from the inner Solar System. Larger ones have also been called planetoids . These terms have historically been applied to any astronomical object that orbits the Sun that shows no planetary disk and is not observed to have the characteristics of an active comet. As small planets outside the Solar System are found and found to have comet-like volatile based surfaces, they are often distinguished from asteroid belt asteroids. In this article, the term "asteroid" refers to the minor planets of the inner Solar System including the orbitals with Jupiter.
There are millions of asteroids, many of which are thought to be devastated planetesimal remains, bodies in the Sun's young solar nebula that never grow big enough to become planets. Most asteroids are known to orbit in the asteroid belt between the orbits of Mars and Jupiter, or co-orbital with Jupiter (Jupiter Trojan). However, other orbital families exist with significant populations, including near-Earth objects. Individual asteroids are classified by their characteristic spectrum, with the majority falling into three major groups: C-type, M-type, and S-type. These are named and are generally identified with carbon-metal, metal, and silicate (rocky) compositions, respectively. The size of the asteroid varies greatly; the largest of nearly 1,000 km (625 miles).
Asteroids are distinguished from comets and meteoroids. In the case of comets, the difference is one of the compositions: while the asteroid consists primarily of minerals and rocks, the comet consists of dust and ice. In addition, asteroids form closer to the sun, preventing the development of the previously mentioned ice comet. The difference between asteroids and meteoroids is mainly one measure: meteoroids have a diameter of less than one meter, while asteroids have a diameter of more than one meter. Finally, meteoroids can consist of comet materials or asteroids.
Only one asteroid, 4 Vesta, has a relatively reflective surface, usually visible to the naked eye, and this is only in a very dark sky when positioned properly. Rarely, small asteroids passing near the Earth can be seen with the naked eye for a short time. As of October 2017, the Minor Planet Center has data on nearly 745,000 objects in the inner and outer Solar System, of which nearly 504,000 have enough information to be numbered.
The United Nations declared June 30 as International Asteroid Day to educate the public about asteroids. International Day Date Asteroid commemorates the anniversary of the impact of Tunguska asteroid over Siberia, Russian Federation, on 30 June 1908.
If a small asteroid collides with Earth, it can still destroy a city. If the middle size (the size of one that killed the dinosaurs) collided, it could destroy humans. If the big ones (like Ceres) collide with the Earth, it could destroy the planet's surface.
Video Asteroid
Discovery
The first discovered asteroid, Ceres, was originally regarded as a new planet. This is followed by the discovery of other similar objects, which, with the equipment of the time, appear as dots of light, such as stars, indicating little or no planetary disk, although it is easily distinguished from the stars because of its movements looks. This prompted astronomer Sir William Herschel to propose the term "asteroid", created in Greek as ??????????, or asteroeids? S , which means a star like a star. -formed ', and derived from the Ancient Greek ????? ast? r 'star, planet'. In the second half of the early nineteenth century, the terms "asteroids" and "planets" (not always qualifies as "minor") are still used interchangeably.
Historical method
Asteroid discovery methods have increased dramatically over the last two centuries.
In the later years of the 18th century, Baron Franz Xaver von Zach organized a group of 24 astronomers to search the skies for the lost planet predicted by about 2.8 AU of the Sun by the Titius-Bode law, partly because of the discovery, by Sir William Herschel on 1781, of the planet Uranus at a distance predicted by law. This task requires that the hand-drawn sky ladders be prepared for all stars in the zodiac ribbon to the limits of the agreed upon forgetfulness. In the next nights, the sky will be mapped again and the moving object will, hopefully, be seen. The expected movement of the lost planet is about 30 arcsec hour per hour, easily seen by observers.
The first object, Ceres, was not discovered by group members, but accidentally in 1801 by Giuseppe Piazzi, director of the Palermo observatory in Sicily. He found an object like a new star in Taurus and followed the displacement of this object for several nights. Later that year, Carl Friedrich Gauss used this observation to calculate the orbits of this unknown object, found between Mars and Jupiter planets. Piazzi named it after Ceres, the goddess of Roman agriculture.
Three other asteroids (2 Pallas, 3 Juno, and 4 Vesta) were discovered over the next few years, with Vesta invented in 1807. After eight more years of unsuccessful searches, most astronomers assume that there is no more and left out further searches.
However, Karl Ludwig Hencke survived, and began searching for more asteroids in 1830. Fifteen years later, he discovered 5 Astraea, the first new asteroid in 38 years. He also found 6 Hebe less than two years later. After this, other astronomers join the search and at least one new asteroid is discovered every year after that (except for the war of 1944 and 1945). The leading asteroid hunters of this early era are JR Hind, Annibale de Gasparis, Robert Luther, HMS Goldschmidt, Jean Chacornac, James Ferguson, Norman Robert Pogson, EW Tempel, JC Watson, CHF Peters, A. Borrelly, J. Palisa, Henry Brothers and Auguste Charlois.
In 1891, Max Wolf pioneered the use of astrophotography to detect asteroids, which appear as short lines on long exposure photographic plates. This dramatically increases the detection rate compared to previous visual methods: Wolf itself found 248 asteroids, beginning with 323 Brucia, while only slightly more than 300 were found up to that point. It is known that there are many more, but most astronomers do not care about them, calling them "celestial pests", a phrase many associated with Eduard Suess and Edmund Weiss. Even a century later, only a few thousand asteroids were identified, numbered and named.
The 1900s manual and modern reporting methods
Until 1998, the asteroid was discovered by a four-step process. First, the sky area is photographed by a wide field telescope, or astrograph. Paired photo taken, usually one hour apart. Some couples can be taken for several days. Secondly, two films or plates of the same region are seen under the stereoscope. Any object in orbit around the Sun will move slightly between a pair of films. Under the stereoscope, the body image will appear to be slightly hovering over the background of the star. Third, once a moving body is identified, its location will be measured appropriately using a digitalization microscope. Locations will be measured relative to the location of known stars.
These first three steps are not an asteroid discovery: the observer finds only a sighting, which gets a temporary title, consisting of years of discovery, a letter representing a half-month of discovery, and finally a letter and number indicating the sequence number of the present invention (eg 1998 FJ 74 ).
The final step of the discovery is to send the location and time of observation to the Minor Planet Center, where the computer program determines whether a sighting ties the previous sighting into one orbit. If so, the object receives the catalog number and the observer of the first sighting by countless orbits declared as inventors, and is given the honor of naming objects subject to the approval of the International Astronomical Union.
Computerized method
There is an increasing interest in identifying asteroids whose orbits cross the Earth, and that can, with sufficient time, collide with Earth (see Earth-crosser asteroids) . The three most important groups of asteroids near the Earth are Apollos, Amors, and Atens. Various asteroid deflection strategies have been proposed, since the 1960s.
Esteroids 433 Eros that approached the Earth have been discovered since 1898, and the 1930s brought the activity of similar objects. In the order of discovery, these are: 1221 Amor, 1862 Apollo, 2101 Adonis, and finally 69230 Hermes, which approached in 0.005 AU Earth in 1937. Astronomers are beginning to realize the possible impact of Earth.
Two events in decades later increased alarm: increased acceptance of Alvarez's hypothesis that impact events resulted in Cretaceous-Paleogene extinction, and 1994 Comet Shoemaker-Levy 9's observations hit Jupiter. The US military also announced information that its military satellites, built to detect nuclear explosions, have detected hundreds of top atmospheric impacts by objects ranging from one to ten meters.
All of these considerations help spur the launch of a highly efficient survey consisting of a charge-coupled device (CCD) camera and a computer connected directly to a telescope. As of 2011, it is estimated that 89% to 96% of near-Earth asteroids one kilometer or greater in diameter have been found. The list of teams using the system includes:
- Near Lincoln Earth Asteroid Research (LINEAR)
- Near Earth Asteroid Tracking (NEAT)
- Spacewatch
- Lowell Observatory Near-Earth-Object Search (LONEOS)
- Catalina Sky Survey (CSS)
- Campo Imperatore Near-Earth Object Survey (CINEOS)
- Japan Spaceguard Association
- Asiago-DLR Asteroid Survey (ADAS)
- Pan-STARRS
On September 20, 2013, the LINEAR system itself has found 138,393 asteroids. Among all the surveys, 4711 near-Earth asteroids have been found including over 600 more than 1 km (0.6 mi) in diameter.
Maps Asteroid
Terminology
Traditionally, small bodies orbiting the Sun are classified as comets, asteroids, or meteoroids, with anything smaller than ten meters across are called meteoroids. Beech and Steel's 1995 paper proposes meteoroid definitions including size limits. The term "asteroid", from the Greek word for "star-like", has never had a formal definition, with minor minor minor planets favored by the International Astronomical Union.
However, after the discovery of asteroids below ten meters, Rubin and Grossman 2010 papers revised the previous definition of meteoroids into objects between 10 Ã,Âμm and 1 meter in size to keep the difference between asteroids and meteoroids. The smallest asteroid found (based on absolute quantity H ) is 2008 TS 26 with H = 33.2 and < span> CQ 2011 1 with H = 32.1 both with an approximate size of about 1 meter.
In 2006, the term "small Solar System" was also introduced to cover the smallest planets and comets. Other languages ​​prefer "planetoid" (Greek for "planets"), and the term is sometimes used in English especially for larger minor planets such as dwarf planets as well as alternatives to asteroids because they are not like stars. The word "planetesimal" has the same meaning, but specifically refers to the small building blocks of the planets that existed when the Solar System was formed. The term "planetule" was coined by geologist William Daniel Conybeare to describe a minor planet, but it is not commonly used. The three largest objects in the asteroid belt, Ceres, Pallas, and Vesta, grew onto the protoplanet stage. Ceres is a dwarf planet, the only one in the inner Solar System.
When found, the asteroid is seen as a different object class of comets, and there is no integrated term for two until the "small Solar System" was created in 2006. The main difference between asteroids and comets is that comets show coma because of sublimation of surface ice near by radiation sun. Some objects are finally listed double because they were first classified as minor planets but then show evidence of comet activity. Conversely, some (possibly all) comets eventually dissipate the surface of the surface and become like asteroids. The further difference is that comets usually have more eccentric orbits than most asteroids; most "asteroids" with very eccentric orbits may be dead or extinct comets.
For nearly two centuries, from the discovery of Ceres in 1801 to the discovery of the first centaur, Chiron in 1977, all known asteroids spend most of their time in or in Jupiter's orbit, although some like Hidalgo ventured far beyond Jupiter for parts of its orbit. When astronomers began to find more small objects that were permanently farther away from Jupiter, now called centaurs, they number them among traditional asteroids, though there is debate over whether they should be considered asteroids or as new types of objects. Then, when the first trans-Neptunian object (other than Pluto), Albion, was discovered in 1992, and especially when a large number of similar objects began to spin, a new term was created to avoid problems: Kuiper-belt objects, Neptune Objects, disc-scattered objects, etc. It inhabs the cold outer part of the Solar System where ice remains solid and comet-like bodies are not expected to show much comet activity; if the centaur or trans-Neptunus object makes close efforts with the Sun, the volatile ice will be sublimated, and the traditional approach will classify it as a comet rather than an asteroid.
The deepest of these are the Kuiper-belt objects, called "objects" partially to avoid the need to classify them as asteroids or comets. They are suspected of having a comet-like composition, although some may be more akin to asteroids. In addition, most do not have the eccentric orbits associated with comets, and which have so far been found to be larger than traditional cometary cores. (The Oort Cloud is much further hypothesized to be the main reservoir of inactive comets.) Other recent observations, such as comet dust analysis collected by the Stardust probe, further obscure the differences between comets and asteroids, suggesting "the continuum between asteroids and comets "rather than the sharp dividing line.
Minor planets outside Jupiter's orbit are sometimes also called "asteroids", especially in popular presentations. However, it is becoming increasingly common for the term "asteroid" to be confined to the minor planets of the inner Solar System. Therefore, this article will limit itself to most classic asteroids: asteroid belt objects, Jupiter trojans, and near-Earth objects.
When the IAU introduced a small class of Solar System in 2006 to include most of the objects previously classified as planets and small comets, they created the dwarf planet class for the largest minor planet - which has enough mass to be ellipsoidal under their own. gravity. According to the IAU, "the term 'minor planet' may still be usable, but generally the term 'Little Solar System' will be preferred." Currently only the largest object in the asteroid belt, Ceres, about 975 km (606 mi), has been placed in the dwarf planet category.
Formation
It is thought that the planets in the asteroid belt evolved like the rest of the solar nebula until Jupiter approached the current mass, where the excitation point of the orbital resonance with Jupiter spouted more than 99% planetesimal in the belt. Simulations and discontinuities in spin rates and spectral properties show that asteroids are larger than about 120 km (75 mi) in diameter increased during the early era, while smaller bodies are fragments of collisions between asteroids during or after Jovian interference. Ceres and Vesta grow large enough to melt and differentiate, with heavy metal elements sinking to the core, leaving rock minerals in the earth's crust.
In the Nice model, many Kuiper-belt objects are captured in the outer asteroid belt, at a distance of more than 2.6 AU. Most are later released by Jupiter, but the remaining ones may be D-type asteroids, and may include Ceres. Distribution
in the Solar System
Various groups of dynamic asteroids have been found orbiting in the inner Solar System. Their orbits are disturbed by the gravity of other objects in the Solar System and by the effects of Yarkovsky. Significant populations include:
Asteroid belt
The majority of asteroids are known to orbit within the asteroid belt between the orbits of Mars and Jupiter, generally in relatively low-eccentricity orbits (ie not very elongated). This belt is now estimated to contain between 1.1 and 1.9 million asteroids larger than 1 km (0.6 mi) in diameter, and millions smaller. This asteroid may be a remnant of the protoplanet disk, and in this region the planet's planetesimal increase during the formative period of the Solar System is prevented by major gravitational disturbances by Jupiter.
Trojan
Trojans are populations that share orbits with larger planets or moons, but do not collide with them as they orbit at any of the two Lagrangian, L4 and L5 stability points, located 60 ° in front and behind the larger body.
The most significant trojan population is the Jupiter trojan. Although fewer Jupiter trojans have been discovered (In 2010), it is estimated that they are as much asteroids in the asteroid belt. Trojans have been found in the orbit of other planets, including Venus, Earth, Mars, Uranus, and Neptune.
Near Earth Asteroids
Near-Earth asteroids, or NEA, are asteroids that have orbits passing near Earth. An asteroid that actually crosses the Earth's orbital path is known as the Earth-passer . As of June 2016, 14,464 asteroids near the Earth are known and its diameter is more than one kilometer estimated at 900-1000.
Characteristics
Size distribution
Asteroids vary greatly in size, from nearly 1000Ã, km to the largest decrease to the rocks only 1 meter. The three greatest are very similar to miniature planets: they are roughly round, at least have partially differentiated interiors, and are considered protoplanets that survive. Mostly, however, are much smaller and irregularly shaped; they are considered as living planets or larger body fragments.
Ceres' dwarf planet is by far the largest asteroid, with a diameter of 975 km (606 mi). The next largest ones are the 4 Vesta and 2 Pallas, both with a diameter of more than 500 km (300 mi). Vesta is the only main belt asteroid that can sometimes be seen with the naked eye. On some rare occasions, near-Earth asteroids can be seen briefly without technical assistance; see 99942 Apophis.
The mass of all objects of the asteroid belt, which lies between the orbits of Mars and Jupiter, is estimated at about 2.8 - 3.2 ÃÆ' - 10 21 kg , or about 4% of the mass of the Moon. Of this amount, Ceres consists of 0.95 ÃÆ' - 10 21 Ã, kg , one third of the total. Adding in the next three largest objects, Vesta (9%), Pallas (7%), and Hygiea (3%), carry this number up to 51%; while three afterwards, 511 Davida (1.2%), 704 Interamnia (1.0%), and 52 Europa (0.9%), only add 3% of the total mass. The number of asteroids then increases rapidly as the individual mass decreases.
The number of asteroids decreases sharply by size. Although this generally follows the law of force, there are 'bumps' in 5 km and 100 km , where more asteroids than expected from logarithmic distributions are found.
Biggest asteroid
Although their location in the asteroid belt does not include them from planetary status, the three largest objects, Ceres, Vesta, and Pallas, are intact protoplanets that share many common characteristics for the planet, and are unusual compared to the majority of "potato" asteroids. The fourth largest asteroid, Hygiea, has no different interior, like the majority of asteroids. Among them, the four largest asteroids form half the mass of the asteroid belt.
Ceres is the only asteroid with a full ellipsoidal shape and hence the only one that is a dwarf planet. It has an absolute magnitude that is much higher than the other asteroids, about 3.32, and may have an ice surface layer. Like the planets, Ceres is distinguished: it has a crust, a mantle and a core. There are no meteorites from Ceres found on Earth.
Vesta also has different interiors, although it is formed inside the frozen solar system, and so is waterless; Its composition is mainly from basaltic rocks such as olivine. Apart from the large crater at the south pole, Rheasilvia, Vesta also has an ellipsoidal shape. Vesta is the parent body of the Vestian family and other V-type asteroids, and is the source of the HED meteorite, which accounts for 5% of all meteorites on Earth.
Pallas is unusual in that case, like Uranus, it spins on its side, with its rotational axis tilted at a high angle to its orbital plane. Its composition is similar to Ceres: high in carbon and silicon, and may be partly differentiated. Pallas is the parent body of the Palladian asteroid family.
Hygiea is the largest carbon asteroid and, unlike the other largest asteroid, lies relatively close to the plane of the ecliptic. It is the largest and supposedly parent member of the Hygiean asteroid family.
Rotation
The measurement of large asteroid rotation rates in the asteroid belt suggests that there is an upper limit. No asteroid with a diameter of more than 100 meters has a rotation period smaller than 2.2 hours. For asteroids to spin faster than approximately this level, the inertia force on the surface is greater than the force of gravity, so any loose surface material will be thrown out. However, solid objects must be able to spin much faster. This suggests that most of the asteroids with a diameter of more than 100 meters are piles of debris formed through the accumulation of debris after a collision between asteroids.
Composition
The physical composition of asteroids varies and in many cases is poorly understood. Ceres appears to consist of a rocky core covered by a cold mantle, where Vesta is thought to have a nickel iron core, olivine coat, and basaltic crust. 10 Hygiea, however, which seems to have a primitive composition of carbon chondrite, is considered the largest undifferentiated asteroid. Most of the smaller asteroids are considered piles of debris held together loosely by gravity, although the largest may be solid. Some asteroids have moon or binary orbiting together: Piles of debris, moon, binaries, and scattered asteroid families are thought to be the result of a collision that disrupts the parent's asteroid, or, perhaps, the planet.
Asteroids contain traces of amino acids and other organic compounds, and some speculate that asteroid impacts may have sowed the Earth early with the chemicals needed to start life, or perhaps even bring life itself to Earth (also see panspermia) > me. In August 2011, a report, based on a NASA study with meteorites found on Earth, was published showing DNA and RNA components (adenine, guanine and related organic molecules) may have formed on asteroids and comets in outer space.
The composition is calculated from three main sources: albedo, surface spectrum, and density. The latter can only be determined accurately by observing the moon's orbits that may be possessed by asteroids. So far, every asteroid with a moon has turned into a pile of rubble, a loose conglomerate of stones and metals that may be half an empty space with volume. The investigated asteroid has a diameter of 280 km, and includes 121 Hermione (268ÃÆ'â € "186ÃÆ'â €" 183Ã, km), and 87 Sylvia (384ÃÆ'â € "262ÃÆ'â €" 232Ã, km). Only half a dozen asteroids are bigger than 87 Sylvia, though no one has a moon; However, some of the smaller asteroids are considered more massive, suggesting they may not be disturbed, and indeed Davida, the same size as Sylvia in measurement error, is estimated to be two and a half times larger, though this is highly uncertain. The fact that large asteroids such as Sylvia can be a pile of debris, perhaps because of its disturbing impact, has important consequences for the formation of the Solar System: Simulated computer collisions involving solid objects show they destroy each other as often as fused, but crash into heap debris more likely to join. This means the planet's core can form relatively quickly.
On October 7, 2009, the presence of water ice was confirmed on the 24th Themis surface using NASA's Infrared Telescope Facility. The surface of the asteroid appears to be covered with ice. Because the ice sheet is sublimated, it may be replenished by an ice reservoir beneath the surface. Organic compounds are also detectable on the surface. The scientists hypothesized that some of the first water brought to Earth was delivered by the impact of asteroids after the collisions that produced the Moon. The presence of ice in 24 Themis supports this theory.
In October 2013, water was detected on the extrasolar body for the first time, on an asteroid orbiting white dwarf GD 61. On January 22, 2014, European Space Agency (ESA) scientists reported detection, for the first definitive time, the steam water at Ceres, the largest object in asteroid belt. The detection was performed using the far-infrared capabilities of the Herschel Space Observatory. This finding is unexpected because comets, not asteroids, are usually considered "raging jets and plumes". According to one scientist, "Lines become increasingly blurred between comets and asteroids." In May 2016, significant asteroid data arising from the Wide-field Infrared Survey Explorer and NEOWISE missions have been questioned. Although initial original criticisms have not yet experienced peer review, a more recent peer-reviewed study was then published.
Surface Features
Most of the asteroids outside the "big four" (Ceres, Pallas, Vesta, and Hygiea) tend to be very similar in appearance, if not regularly shaped. 50-km (31-mi) 253 Mathilde is a pile of saturated debris with a crater with an asteroid radius size diameter, and 300-km (186-mi) Earth-based observations 511 Davida, one of the largest asteroids after the big four, revealing the angular profile the same, indicating it is also saturated with the size of the crater radius. Medium-sized asteroids such as Mathilde and 243 Ida that have been observed closely also reveal deep regoliths that cover the surface. Of the top four, Pallas and Hygiea are practically unknown. Vesta has a compression fracture encircling a radius-sized crater at the south pole, but instead is a spheroid. Ceres seems to be very different from Hubble's glance, with surface features that are unlikely to be caused by simple craters and impact basins, but the details will be expanded with the Dawn spacecraft, which enters ceres orbits on March 6, 2015. Color
Asteroids become darker and red from age because of weathering. But evidence suggests that most color changes occur quickly, within the first hundred thousand years, limiting the usefulness of spectral measurements to determine the age of the asteroid.
Classification
Asteroids are generally classified according to two criteria: their orbital characteristics, and their spectrum of reflectance features.
Orbital classification
Many asteroids have been placed in groups and families based on their orbital characteristics. Regardless of the widest distribution, it is common to name a group of asteroids after the first member of the group is found. The group is a relatively loose dynamic association, while the family is tighter and results from the outbreak of major parental asteroid disasters in the past. Families are more common and easier to identify in the main asteroid belt, but some small families have been reported among Jupiter trojans. The family of the main belt was first recognized by Kiyotsugu Hirayama in 1918 and is often called the Hirayama family in his honor.
About 30-35% of the body in the asteroid belt belonging to each dynamic family is considered to have the same origin in the past collision between the asteroids. A family is also linked to the Haumea plutoid dwarf planet.
Quasi-satellite and horseshoe objects
Some asteroids have an unusual horseshoe orbit which is a common orbital with the Earth or some other planet. Examples are 3753 Cruithne and 2002 AA 29 . The first example of this type of orbital arrangement is found between the moons of Saturn, Epimetheus and Janus.
Sometimes these horseshoe things temporarily become quasi-satellites for decades or several hundred years, before returning to previous status. Both Earth and Venus are known to have quasi-satellites.
Such objects, when associated with Earth or Venus or even hypothetically Mercury, are special classes of the Aten asteroid. However, such objects can be attributed to the outer planets as well.
Spectral classification
In 1975, the asteroid taxonomy system based on color, albedo, and spectral form was developed by Clark R. Chapman, David Morrison, and Ben Zellner. These properties are considered in accordance with the asteroid surface material composition. The original classification system has three categories: the C-type for dark-carbon objects (75% of known asteroids), S-type for silicaceous (17% of known asteroids) and U for non-C or S This classification has been extended to include many other types of asteroids. The number of species continues to grow as the asteroid increases.
The two most widely used taxonomies now used are the Tholen classification and SMASS classification. The first was proposed in 1984 by David J. Tholen, and is based on data collected from an eight-color asteroid survey conducted in the 1980s. This produces 14 categories of asteroids. In 2002, the Large-Belt Asteroid Spectroscopy Survey produced a modified version of Tholen's taxonomy with 24 different types. Both systems have three broad categories of asteroids C, S, and X, where X consists of most metallic asteroids, such as M-type. There are also some smaller classes.
The proportion of asteroids known to fall into various spectral types does not necessarily reflect the proportion of all asteroids belonging to that type; some types are more easily detected than others, get used to the total.
Problems
Initially, the spectral designation is based on the conclusion of asteroid composition. However, the correspondence between the spectral class and the composition is not always very good, and various classifications are in use. This has caused significant confusion. Although asteroids of different spectral classifications tend to consist of different materials, there is no guarantee that asteroids in the same taxonomic class are composed of the same material.
Naming
Newly discovered asteroids are given temporary titles (such as 2002 AT 4 ) consisting of years of invention and alphanumeric code showing half the findings and sequence in half of that month. Once the orbit of the asteroid has been confirmed, it is numbered, and then may also be named (eg 433 Eros). Formal naming conventions use parentheses around the numbers (eg (433) Eros), but dropping the parentheses is quite common. Informally, it is common to drop a number altogether, or to drop it after the first mention when the name is repeated in the run of the text. In addition, the name may be proposed by the asteroid inventor, in the guidelines established by the International Astronomical Union. Symbol
The first discovered asteroid was assigned an iconic symbol as traditionally used to designate planets. In 1855 there were two dozen asteroid symbols, which often occurred in several variants.
In 1851, after the fifteenth (Eunomia) asteroid was discovered, Johann Franz Encke made major changes in the upcoming 1854 edition of Berlin Astronomisches Jahrbuch (BAJ, Berlin Astronomical Yearbook). He introduced the disc (circle), the traditional symbol for the star, as a generic symbol for asteroids. The circle is then numbered to find a particular asteroid (though it assigns (1) to the fifth, Astraea, while continuing to designate the first four only with existing iconic symbols). The circular-numbered convention was quickly adopted by astronomers, and the next asteroid to be found (16 Psyche, in 1852) was first designated that way at the time of its discovery. However, Psyche is also given an iconic symbol, as are some of the other asteroids found over the next few years (see chart above). 20 Massalia is the first asteroid not given the iconic symbol, and no iconic symbol was created after the discovery of 1855 of the 37 Fides. That year the number of Astraas increased to (5), but the first four asteroids, Ceres to Vesta, were not listed by their numbers until the 1867 edition. The circle was shortened to a pair of parentheses, which were easier to set and sometimes removed completely the next few decades, leading to a modern convention.
Exploration
Until the age of space travel, objects in the asteroid belt are only a bright spot of light even the largest telescope and its shape and plain remains a mystery. The best modern ground-based telescopes and Hubble Space Telescope that orbit the Earth can complete a small amount of detail on the largest asteroid surface, but even this remains largely more than a fuzzy blob. Limited information about the shape and composition of asteroids can be inferred from their light curves (their variation in brightness as they rotate) and their spectral properties, and the size of the asteroids can be estimated by the long time of star grafting (when the asteroids pass directly in front of the star). Radar imagery can produce good information about asteroids and orbital and rotational parameters, especially for near-Earth asteroids. In terms of the delta-v and propellant requirements, NEO is more accessible than the Moon.
The first close-up images of asteroid-like objects were taken in 1971, when the Mariner 9 probe imaged Phobos and Deimos, two small moons of Mars, which might have captured the asteroids. These images show the most irregular and potato-shaped form of asteroids, just like the later pictures of the Voyager probe of the gas giant little moons.
The first original asteroid photographed at close range was 951 Gaspra in 1991, followed in 1993 by 243 Ida and its moon Dactyl, all of which were imaged by the Galileo probe on the way to Jupiter.
The first special asteroid probe was NEAR Shoemaker , which photographed 253 Mathilde in 1997, before entering the orbit around 433 Eros, eventually landing on its surface in 2001.
Other asteroids briefly visited by spacecraft on the way to other destinations include 9969 Braille (by Deep Space 1 in 1999), and 5535 Annefrank (by Stardust in 2002).
In September 2005, the Japanese investigation of Hayabusa began studying 25143 Itokawa in detail and faced difficulties, but returned samples from its surface to Earth on June 13, 2010.
The European Probe Rosetta (launched in 2004) flew with 2,867? Teins in 2008 and 21 Lutetia, the third largest asteroid visited to date, in 2010.
In September 2007, NASA launched the Fajar spacecraft, which orbits the 4th Vesta from July 2011 to September 2012, and has orbited the 1 Ceres dwarf planet since 2015. 4 Vesta is the second largest asteroid visited for date.
On December 13, 2012, the Chinese moon orbiter Chang'e 2 flew within 3.2 km (2 mi) of the 4179 Toutatis asteroid on an extended mission.
Planned and upcoming missions
The Japan Space Exploration Agency (JAXA) launched the Hayabusa2 probe in December 2014, and plans to return samples from 162173 Ryugu in December 2020.
In May 2011, NASA selected the OSIRIS-REx sample return mission to Bennu 101955 asteroid; launched on September 8, 2016.
In early 2013, NASA announced a mission planning stage to capture near-Earth asteroids and move them into a moon's orbit where it might be visited by astronauts and then impact on the Moon. On June 19, 2014, NASA reported that the 2011 MD asteroid was a prime candidate to be captured by a robot mission, probably in the early 2020s.
It has been suggested that asteroids may be used as sources of materials that may be scarce or depleted on Earth (asteroid mining), or materials for building a spatial habitat (see Asteroid colonization) . Heavy and expensive materials to be launched from Earth could one day be mined from asteroids and used for the manufacture and construction of space.
In the US Discovery program, the 16th Psyche spacecraft's Psychic spacewalks spacecraft flight to Jupiter trojan successfully reached the semifinal stage of mission selection.
Fiction
Asteroids and asteroid belts are the subject of science fiction. Asteroids play several potential roles in science fiction: as human places may colonize, the resources to extract minerals, the dangers faced by spaceships traveling between two other points, and as threats to life on Earth or other inhabited planets, dwarf planets and natural satellites by potential impacts.
Gallery
See also
Note
References
External links
- List of minor planet names (ASCII) (Minor Planet Center)
- Asteroid article in Discovery of Planet Science Research
- ESA Awareness of Space Situation: Near-Earth Object Segment
- The IAU Committee on Small Body Nomenclature
- JPL Asteroid Watch Site
- NASA Asteroid and Comet Observation Sites
- Near Earth Asteroid Tracking (NEAT)
- Near Dynamic Site Object Earth
- NEO MAP (Armagh Observatory)
- Spaceguard Center
- TECA table from the next close approach to Earth
- When Asteroids Become a Small Planet?
- Asteroids, BBC Radio 4 discussions with Monica Grady, Carolin Crawford & amp; John Zarnecki ( In Our Time , November 3, 2005)
Source of the article : Wikipedia
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