Lost minor planet

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 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.

Overview

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. There are also more than a thousand near-Earth objects (NEOs) with an observation arc of one or two days only.

Designation Year of discovery recovery 132 Aethra 1873 1922 1892 X (330 Adalberta) 1892 false positive  452 Hamiltonia 1899 1987 473 Nolli 1901 1987 719 Albert 1911 2000 724 Hapag 1911 1988 843 Nicolaia 1916 1981 878 Mildred 1916 1991 1009 Sirene 1923 1982 1026 Ingrid 1923 1986 1179 Mally 1931 1986

Name Year of discovery recovery 1537 Transylvania 1940 1981 1862 Apollo 1932 1973 1916 Boreas 1953 1976 1922 Zulu 1949 1974 2101 Adonis 1936 1977 3494 Purple Mountain 1962 1980 3789 Zhongguo 1928 1986 7796 Járacimrman 1973 1996 (29075) 1950 DA 1950 2000 69230 Hermes 1937 2003

Designation Year of Notes discovery recovery 1927 LA  1927 still lost Observed 4 times between June 1, 1927 and July 5, 1927 1991 BA 1991 still lost Passed within a lunar distance of Earth 1993 HD 1993 still lost Near-Earth asteroid 1995 SN55 1995 still lost May be the largest centaur 2007 WD5 2007 still lost Passed close to Mars 6344 P–L 1960 2007 Potentially hazardous object; probably a dormant comet

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.

1970s

Recovered body	Description
1862 Apollo	Apollo is a Q-type asteroid, discovered by Karl Reinmuth in 1932, but lost and not recovered until 1973. Another Apollo asteroid is 2101 Adonis, discovered by Eugene Delporte in 1936 and lost until 1977 when it was rediscovered by Charles T. Kowal. It was also one of the first near-Earth asteroids to be discovered.
1916 Boreas	The Amor asteroid Boreas, provisionally designated 1953 RA, was discovered on 1 September 1953 by Sylvain Julien Victor Arend at the Royal Observatory of Belgium, and rediscovered in 1974 by Richard Eugene McCrosky, G. Schwartz and JH Bulger based on a predicted position by Brian G. Marsden.
1922 Zulu	The outer main-belt asteroid, provisionally designated 1949 HC, was discovered on 25 April 1949 by Ernest Leonard Johnson at Johannesburg (UO). It is one of very few asteroids located in the 2:1 mean-motion resonance with Jupiter. This asteroid was lost shortly after discovery and only rediscovered in 1974 by Richard Eugene McCrosky, Cheng-yuan Shao and JH Bulger based on a predicted position by C. M. Bardwell of the Cincinnati Observatory.

1980s and 1990s

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:

Recovered body	Description
330 Adalberta	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.
843 Nicolaia	Nicolaia, provisionally designated 1916 AN, was rediscovered at the Heidelberg Astronomisches Rechen-Institut in 1981.
473 Nolli	Nolli, provisionally designated 1901 GC, was discovered by Max Wolf on 13 February 1901, but it remained lost for many decades until it was recovered finally in 1987, 86 years later.
724 Hapag	Hapag had first been found by Johann Palisa in 1911. It was given the provisional name 1911 NC, but was lost until it was rediscovered in 1988.
719 Albert	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).
878 Mildred	Mildred, provisionally designated 1916 f, was originally discovered in 1916 using the 60-inch Hale telescope at the Californian Mount Wilson Observatory, but was subsequently lost until it was again observed on single nights in 1985 and 1991.
1009 Sirene	Sirene, provisionally designated 1923 PE, was recovered in 1982 by J. Gibson using exposures form the Samuel Oschin Telescope at Palomar Observatory, and he revised its ephemeris.
1026 Ingrid	Ingrid was discovered by Karl Reinmuth on 13 August 1923 and given the provisional designation 1923 NY. It was reidentified in 1986 by Syuichi Nakano.
1179 Mally	Mally was discovered by Max Wolf on 19 March 1931 and given the provisional designation 1931 FD. It was rediscovered in 1986 by Lutz Schmadel, Richard Martin West and Hans-Emil Schuster.

Other notable recoveries

• 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.
• 7796 Járacimrman was discovered at the Czech Kleť Observatory on 16 January 1996 by Zdeněk Moravec and was designated 1996 BG. It was observed until April 1996 and then in June and July 1997. It was revealed, by precovery, to be a lost asteroid which had previously been observed twice: at the Brera-Merate Observatory in northern Italy on 12 December 1973 and at the Australian Mount Stromlo Observatory near Canberra, on 8 and 9 July 1990.

21st century

Recently lost minor planets

• 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.

• In the search for various types of near-Earth object, such as quasi-satellites and Earth-crossers, objects that may correspond to some lost sightings include 2006 RH₁₂₀ or 3753 Cruithne, among others.

• In 2007, the object 2007 RR₉ was found to be the near-Earth asteroid 6344 P–L, lost since 1960. It is a potentially hazardous object and probably a dormant comet, although it was not visibly outgassing at that time.

See also

• Aten asteroid
• Earth-grazing fireballs
• Lost comet
• Precovery

External links

• Minor Planet Center: Asteroid Hazards, Part 2: The Challenge of Detection on YouTube (min. 7:14)
• Minor Planet Center: Asteroid Hazards, Part 3: Finding the Path on YouTube (min. 5:38)