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Lost minor planet
Lost minor planets are minor planets that observers lose track of due to too short an observation arc to accurately predict the future location of the minor planet. Many of the asteroids that were discovered early were lost and rediscovered in the 1980s and 1990s, but a number of minor planets continue to be lost.〔Lost asteroid. (2009). In Encyclopædia Britannica. Retrieved 27 February 2009, from Encyclopædia Britannica Online: http://www.britannica.com/topic/lost-asteroid〕 By some definitions, thousands, if not tens of thousands observed minor planets are lost—they cannot be found by pointing an appropriate telescope at their predicted location, because the uncertainty in their predicted orbit is too large or they are currently too faint to be detected.
Some minor planets and comets discovered in previous decades were "lost" because not enough observational data had been obtained to determine a reliable orbit. Without this information, astronomers would not know where to look for the object at future dates. Occasionally, a "newly discovered" object turns out to be a rediscovery of a previously lost object. This can be determined by calculating the "new" object's orbit backwards and checking its past positions against those previously recorded for the lost object. In the case of lost comets this is especially tricky because of nongravitational forces that can affect their orbits, such as emission of jets of gas from the comet nucleus. However, Brian G. Marsden has specialized in calculating such nongravitational forces. Notably, he successfully predicted the 1992 return of the once-lost periodic comet Swift–Tuttle.
== 20th-century recoveries ==
The number of asteroids that were only observed once and not re-observed grew throughout the 19th and 20th centuries, but improved telescopes, searches, and detection techniques led to resolution of most of these cases between 1970 and 2000. There are earlier examples also, such as 132 Aethra, which was lost between 1873 and 1922.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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