AsteroidAn asteroid is a small, solid object in our Solar System, orbiting the Sun. An asteroid is an example of a minor planet (or planetoid), which are much smaller than planets.\nThe asteroids are believed to be remnants of the protoplanetary disc which were not incorporated into planets during the system's formation. Some asteroids have moonss.\nThe vast majority of the asteroids are within the asteroid belt, with elliptical orbits between those of Mars and Jupiter.\n
Problems with spectral classificationOriginally, spectral designations were based on inferences of an asteroid's composition:
Asteroid discoveryAsteroid discovery proceeded in several phases. The first asteroid 1 Ceres was discovered by accident in 1801, and then three others (2 Pallas, 3 Juno, 4 Vesta) over the next few years, with Vesta found in 1807. After eight more years of fruitless searches, most astronomers assumed that there were no more and abandoned any further searches. However, Karl Ludwig Hencke persisted, and began searching for more asteroids in 1830. Fifteen years later, he found 5 Astraea, the first new asteroid in 38 years. He also found 6 Hebe less than two years later. After this, other astronomers joined in the search and at least one new asteroid was discovered every year after that (except the wartime year 1945). Notable asteroid hunters of this early era were J. R. Hind, Annibale de Gasparis, Robert Luther, H. M. S. Goldschmidt, Jean Chacornac, James Ferguson, Norman Robert Pogson, E. W. Tempel, J. C. Watson, C. H. F. Peters, A. Borrelly, J. Palisa, Paul Henry and Prosper Henry and Auguste Charlois. In 1891, however, Max Wolf pioneered the use of astrophotography to detect asteroids, which appeared as short streaks on long-exposure photographic plates. This drastically increased the rate of detection compared with previous visual methods: Wolf alone discovered 248 asteroids, beginning with 323 Brucia, whereas only slightly more than 300 had been discovered up to that point. Still, a century later, only a few thousand asteroids were identified, numbered and named. It was known that there were many more, but most astronomers did not bother with them, calling them "vermin of the skies". Until 1998, asteroids were discovered by a four-step process. First, a region of the sky was photographed by a wide-field telescope. Pairs of photographs were taken, typically one hour apart. Multiple pairs could be taken over a series of days. Second, the two films of the same region were viewed under a stereoscope. Any body in orbit around the sun would move slightly between the pair of films. Under the stereoscope, the image of the body would appear 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: the observer has only found an apparition. The final step of discovery was to send\nthe locations and time of observations to Brian Marsden of the Minor Planet Center. Dr. Marsden has computer programs that compute whether an apparition tied together previous apparitions into a single orbit. If so, then the observer of the final apparition is declared a discoverer, and the discoverer got the honour of naming the asteroid (subject to the approval of the International Astronomical Union). When the orbit of an asteroid is confirmed, it is given a number, and later it may also be given a name (e.g. 1 Ceres). The first few are named after figures from Graeco-Roman mythology, but as such names started to run out, others were also used —famous people, the names of the discoverer's wives, even television characters. A few groups have names with a common theme —for instance Centaurs are all named after legendary Centaurs, and Trojans after heroes from the Trojan War. The Centaurs are of special interest; many of them are massive comets, such as 2060 Chiron. Since 1998, a large majority of the asteroids have been discovered with automated systems that comprise Charge-Coupled Device (CCD) cameras and computers directly connected to telescopes. A list of teams using such automated systems include [1]:
Asteroid deflectionThere is increasing interest in identifying asteroids whose orbits cross Earth's orbit, and that could, given enough time, collide with Earth. The three most important groups of near-Earth asteroids are the Apollos, Amors and the Atens. Various asteroid deflection strategies have been proposed. The near-Earth asteroid 433 Eros had been discovered as long ago as 1898, and the 1930s brought a flurry of similar objects. In order of discovery, these were: 1221 Amor, 1862 Apollo, 2101 Adonis and finally 69230 Hermes, which approached within 0.005 AU of the Earth in 1937. Astronomers began to realize the possibilities of Earth impact. Two events in later decades increased the level of alarm: the increasing acceptance of Walter Alvarez's theory of dinosaur extinction being due to an impact event, and the 1994 observation of Comet Shoemaker-Levy 9 crashing into Jupiter. The U.S. military also declassified the information that its military satellites, built to detect nuclear explosions, had detected hundreds of upper-atmosphere impacts by objects ranging from one to 10 meters across. All of these considerations helped spur the launch of highly-efficient programs such as LINEAR, NEAT and LONEOS, which have drastically increased the rate of asteroid detection.Asteroid explorationThe first "nearby" photos of an asteroid were taken by the Galileo spacecraft of 951 Gaspra and 243 Ida (1991), while NEAR Shoemaker landed on 433 Eros (2001). Galileo also discovered the first known asteroid moon Dactyl which orbits 243 Ida.See alsoExternal linksCategory:Asteroids simple:Asteroid |
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