Asteroids whose orbits are not known accurately enough to find them again
More than 700,000minor planets have been observed, many of which must be considered lost due to insufficient observational data.[1][2]
Aminor planet is "lost" when today's observers cannot find it, because its location is toouncertain to target observations. This happens if theorbital elements of a minor planet are not known accurately enough, typically because theobservation 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 reliableorbit determination. With limited information astronomers cannot know where to look for the object at future dates.
Lost objects are sometimesrecovered when serendipitously re-observed by a laterastronomical 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 forlost comets because their orbits can be affected by non-gravitational forces, such as emission of jets of gas from the comet nucleus. Many previously lostasteroids (a type of minor planet) were rediscovered in the 1980s and 1990s, but many minor planets are still lost.[3]
The orbits of kilometre classNEAs are generally well known, though a few have been lost. However, large numbers of smaller NEAs have highly uncertain orbits[4]
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 thefollowing sections.) The true number of lost asteroids may be over 150,000.[2] There are also about 30,000 unnumbered bodies with acondition 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 thousandnear-Earth objects (NEOs) with anobservation 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 as132 Aethra, which was lost between 1873 and 1922.[7]
Leif Kahl Kristensen at theUniversity of Aarhus rediscovered452 Hamiltonia and1537 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, itself an asteroid first discovered in 1910 and seen again briefly in 1937, 1951, 1974, 1978 (twice) and 1980, receiving a new designation on each occasion, before it was recognised in 1982 that all of these observations were of the same object.[17]
Nolli, provisionally designated 1901 GC, was discovered byMax Wolf on 13 February 1901, but it remained lost for many decades until it was recovered finally in 1987, 86 years later.[19]
Near-Earth asteroid 719 Albert (1911 MT) had also been found byJohann 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 theSpacewatch asteroid survey project. At the time of its rediscovery, Albert was the last remaining "lost asteroid" among those assigned numbers (since69230 Hermes was not numbered until 2003).[21]
Mildred, provisionally designated 1916 f, was originally discovered in 1916 using the60-inch Hale telescope at the CalifornianMount 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 theSamuel Oschin Telescope atPalomar 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, thePurple Mountain Observatory in China discovered a new asteroid, and with Zhang Yuzhe's agreement the new object1957 UN1 was reassigned the official designation1125 China in place of the lost 1928 UF. However, in 1986, the newly discovered object1986 QK1 was confirmed to be a rediscovery of the original 1928 UF, and this object was named3789 Zhongguo, which is also a name for China.[25]
The near-Earth asteroid(29075) 1950 DA was discovered on 23 February 1950 byCarl Wirtanen atLick 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 CzechKleť Observatory on 16 January 1996 byZdeněk Moravec and was designated 1996 BG. It was observed until April 1996 and then in June and July 1997. It was revealed, byprecovery, to be a lost asteroid which had previously been observed twice: at theBrera-Merate Observatory in northern Italy on 12 December 1973 and at the AustralianMount Stromlo Observatory near Canberra, on 8 and 9 July 1990.
Below are some notable asteroids that have been discovered during the 20th century but are still lost as of 2025[update].
1979 XB: this 660-metre (2,170 ft) near-Earth asteroid was observed 18 times over a period of 3.9 days between 11 and 15 December 1979. As of 11 February 2025[update], it has the fourth-highest cumulativePalermo scale rating at −2.70, for possible impacts on Earth during four close approaches in 2056, 2086, 2102 and 2113.[27] Due to the large uncertainty in its orbital parameters,[28] the odds of the most likely impact in 2056 is only 1 in 5.3 million.[27]
6Q0B44E was discovered orbiting Earth in 2006.[29][30] Its properties were consistent with being an artificial piece ofspace debris,[30] so it was not given aminor planet designation. 6Q0B44E was lost in 2007, but another object XL8D89E was discovered on a very similar (but not identical) orbit in 2016. It is likely, though unproven, that both are the same object, which experiences non-gravitational acceleration (such as a slow gas leak) causing slight variations in its orbit.[31] XL8D89E was itself lost in 2018.[31]
2007 WD5 is a 50 m (160 ft)Apollo-class NEO and aMars-crosser discovered on 20 November 2007, byAndrea Boattini of theCatalina Sky Survey.[32] Early observations of2007 WD5 caused excitement amongst the scientific community when it was estimated as having as high as a 1 in 25 chance ofcolliding withMars on 30 January 2008.[33] 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.[34]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'sJPL-Near Earth Object program,2007 WD5 is currently considered "lost".[33][35] The best fit trajectory had the asteroid passing within 21,000 km of Mars and only 16,000 km from its moonDeimos.[34][36]
2010 AU118 is a kilometer-sizedAmor-class NEO and Mars-crosser discovered on 27 May 2010, by theWide-field Infrared Survey Explorer (WISE) spacecraft. The asteroid was only observed 19 times during 13–15 January 2010, and has not since been observed.[37] 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.[38] However,NEODyS lists the nominal 20 October 2020 Earth distance as 3 AU (450,000,000 km; 280,000,000 mi).[39]
In 2007, the object2007 RR9 was found to be the near-Earth asteroid6344 P–L, lost since 1960. It is apotentially hazardous object and probably adormant comet, although it was not visibly outgassing at that time.[13]
2020 MK53 is a losttrans-Neptunian object discovered on 22 June 2020 and announced on 7 April 2023 (MPS 1836391, MPO 735634) by theNew Horizons KBO Search team[40] using the 8.2-meterSubaru Telescope atMauna Kea Observatory in Hawaii.[41] Its orbit is highly uncertain because it was observed for only three days, which is not long enough to determine an orbit accurately.[42][41] Its distance from the Sun might be around 160astronomical units according to orbital calculations, which would make it thefarthest known Solar System object from the Sun.[43] However, the uncertainty in its distance from the Sun ranges from ±4 AU to over ±20,000 AU, depending on the method of calculation.[42]
^Note: thisquery 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 designation330 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
