A minor planet is "lost" when today's observers cannot find it, because its location is too uncertain to target observations. This happens if the orbital elements of a minor planet are not known accurately enough, typically because the observation arc for the object is too short, or too few observations were made before the object became unobservable (e.g. too faint due to increasing distance, or too close to the Sun to view at night).
By some definitions thousands, if not tens of thousands, of mostly small observed minor planets are lost. Some lost minor planets discovered in decades past cannot be found because the available observational data is insufficient for reliable orbit determination. With limited information astronomers cannot know where to look for the object at future dates.
Lost objects are sometimes recovered when serendipitously re-observed by a later astronomical survey. If the orbital elements of the newly found object are sufficiently close to those of the earlier lost object, the two may be equated. This can be established by calculating backwards the "new" object's orbit (once it is firmly known) and checking past positions against those previously recorded for the lost object. This usually greatly extends the object's arc length, thus fixing the orbit much more precisely. The back-orbit calculations are especially tricky for lost comets because their orbits can be affected by non-gravitational forces, such as emission of jets of gas from the comet nucleus. Many previously lost asteroids (a type of minor planet) were rediscovered in the 1980s and 1990s, but many minor planets are still lost.[1]
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.
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.
| 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. |
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 (below) had remained unobserved since their discoveries:
| Recovered body | Description | |
|---|---|---|
| 330 Adalberta | The object originally named Adalberta, provisionally designated 1892 X, turned out to be an erroneous observation. The designation was later reassigned to A910 CB. | |
| 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.[2] | |
| 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.[3] | |
| 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
Recently lost minor planets