More than 700,000 minor planets have been observed, many of which must be considered lost due to insufficient observational data.
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. 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 the observational data obtained was insufficient 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 (once it is firmly known) backwards and checking its past positions against those previously recorded for the lost object. This may greatly extend the observation arc, thus fixing the orbit much more precisely. For lost comets the back orbit calculations are 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.
This is a small selection of some early lost or notable asteroids with their discovery and rediscovery dates. (A more detailed description for some of these minor planets can be found in the following sections). The true number of lost asteroids may be over 150,000. There are also about 30,000 unnumbered bodies with a condition code of U = 9, indicating the highest possible uncertainty of their orbit determination. Many of these bodies have been observed years if not decades ago and must be considered lost.[a] There are also more than a thousand near-Earth objects (NEOs) with an observation arc of one or two days only.
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.
Leif Kahl Kristensen at the University of Aarhus rediscovered 452 Hamiltonia and 1537 Transylvania, along with numerous other small objects, in 1981. At the time these results were published, only the nine numbered minor planets 330 Adalberta, 473 Nolli, 719 Albert, 724 Hapag, 843 Nicolaia, 878 Mildred, 1009 Sirene, 1026 Ingrid, and 1179 Mally remained unobserved since their discoveries:
Adalberta, provisionally designated 1892 X, was not rediscovered, since it turned out to be an erroneous observation. The designation was later reassigned to A910 CB after 1892 X was determined to be a false positive.2006 HH123 was another lost minor planet that turned out to be a false positive.
Near-Earth asteroid 719 Albert (1911 MT) had also been found by Johann Palisa in 1911. Due to inaccuracies in its computed orbit, Albert was also lost and not recovered until 2000, when Jeffrey A. Larsen located it using data from the Spacewatch asteroid survey project. At the time of its rediscovery, Albert was the last remaining "lost asteroid" among those assigned numbers (since 69230 Hermes was not numbered until 2003).
While studying in Chicago in 1928, Zhang Yuzhe discovered an asteroid that was given the provisional designation 1928 UF, and later the number 1125. He named it "China", or "中華" Zhōnghuá. However, this asteroid was not observed beyond its initial appearance and a precise orbit could not be calculated. In 1957, the Purple Mountain Observatory in China discovered a new asteroid, and with Zhang Yuzhe's agreement the new object 1957 UN1 was reassigned the official designation 1125 China in place of the lost 1928 UF. However, in 1986, the newly discovered object 1986 QK1 was confirmed to be a rediscovery of the original 1928 UF, and this object was named 3789 Zhongguo, which is also a name for China.
The near-Earth asteroid (29075) 1950 DA was discovered on 23 February 1950 by Carl Wirtanen at Lick Observatory. It was observed for 17 days and then lost, since not enough observations were made to allow its orbit to be plotted. It was then rediscovered on 31 December 2000. The chance it will impact Earth on 16 March 2880 is about 1 in 4,000, or 0.025 percent.
2007 WD5 is a 50 m (160 ft) Apollo-class NEO and a Mars-crosser discovered on 20 November 2007, by Andrea Boattini of the Catalina Sky Survey. Early observations of 2007 WD5 caused excitement amongst the scientific community when it was estimated as having as high as a 1 in 25 chance of colliding with Mars on 30 January 2008. However, by 9 January 2008 additional observations allowed NASA's Near Earth Object Program (NEOP) to reduce the uncertainty region resulting in only a 1-in-10,000 chance of impact.2007 WD5 most likely passed Mars at a distance of 6.5 Mars radii. Due to this relatively small distance and the uncertainty level of the prior observations, the gravitational effects of Mars on its trajectory are unknown and, according to Steven Chesley of NASA's JPL-Near Earth Object program, 2007 WD5 is currently considered "lost". The best fit trajectory had the asteroid passing within 21,000 km of Mars and only 16,000 km from its moon Deimos.
^On 18 March 1892, a body discovered by Max Wolf with the provisional designation 1892 X was originally named 330 Adalberta, but was lost and never recovered. In 1982, it was determined that Wolf erroneously measured two images of stars, not asteroids. Because it was a false positive and the body never existed, the named designation 330 Adalberta was reused for another asteroid, A910 CB, discovered in 1910.