Asteroids whose orbits are not known accurately enough to find them again
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.[2] 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.[3]
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.[2] 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.[5][a] There are also more than a thousand
near-Earth objects (NEOs) with an
observation arc of one or two days only.[6]
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.[7]
Leif Kahl Kristensen at the
University of Aarhus rediscovered
452 Hamiltonia and
1537 Transylvania, along with numerous other small objects, in 1981.[16] 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:[16]
The object originally named Adalberta, provisionally designated 1892 X, turned out to be an erroneous observation. The designation was later reassigned to A910 CB.[17]
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.[19]
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.[20][21]
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).[21]
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.[21][22]
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.[8]
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.[25]
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.[26]
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.[27] 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.[28] 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.[29]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".[28][30] The best fit trajectory had the asteroid passing within 21,000 km of Mars and only 16,000 km from its moon
Deimos.[29][31]
2010 AU118 is a kilometer-sized
Amor-class NEO and Mars-crosser discovered on 27 May 2010, by the
Wide-field Infrared Survey Explorer (WISE) spacecraft. The asteroid was only observed 19 times during 13–15 January 2010, and has not since been observed.[32] Virtual clones of the asteroid that fit the uncertainty region in the known trajectory, showed a 1 in 770 million chance that the asteroid could have impacted the Earth on 2020 October 20.[33] However,
NEODyS lists the nominal 20 October 2020 Earth distance as 3 AU (450,000,000 km; 280,000,000 mi).[34]
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.[13]
^Note: this query at JPL's Small-Body Database lists all unnamed asteroids with an orbital uncertainty of 9, which also includes recently discovered bodies. The lost minor planets appear first, since the table is sorted by the body's first observation date.
^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.
^Wiley Interscience Recovery of the Long Lost Minor Planet (843) Nicolaia after 65 Years (Astronomisches Rechen-Institut Heidelberg – Mitteilungen Serie B)
L. D. Schmadel 1 *, L. Kohoutek 2 * Heidelberg Astronomisches Rechen-Institut