(29075) 1950 DA (provisional designation1950 DA) is a risk-listed asteroid, classified as a near-Earth object and potentially hazardous asteroid of the Apollo group, approximately 1.3 kilometers (0.81 miles) in diameter.[5] It once had the highest known probability of impacting Earth.[12] In 2002, it had the highest Palermo scale rating with a value of 0.17 and a probability of 1 in 306 (0.33%) for a possible collision in 2880.[13][6] Since that time, the estimated risk has been updated several times. In December 2015, the odds of an Earth impact were revised to 1 in 8,300 (0.012%) with a Palermo scale rating of −1.42.[12]As of February2025[update], it is listed on the Sentry Risk Table with the highest cumulative Palermo scale rating of −0.92.[14][15]1950 DA is not assigned a Torino scale rating, because the 2880 date is over 100 years in the future. As of 2 February 2025, the odds of an Earth impact are 1 in 2,600 (0.039%).[14][12]
1950 DA was first discovered on 23 February 1950 by Carl A. Wirtanen at Lick Observatory.[3] It was observed for seventeen days[6] and then lost because this short observation arc resulted in large uncertainties in Wirtanen's orbital solution. On 31 December 2000, it was recovered at Lowell Observatory and was announced as 2000 YK66 on 4 January 2001.[16] Just two hours later it was recognized as 1950 DA.[6][17]
Arecibo radar movie of 1950 DA obtained during 48 minutes (37% of a rotation) on 4 March 2001
On 5 March 2001, 1950 DA made a close approach to Earth at a distance of 0.05207AU (7.790millionkm; 4.840millionmi; 20.26LD).[18] It was studied by radar at the Goldstone and Arecibo observatories from March 3 to 7, 2001.[6]
The studies showed that the asteroid has a mean diameter of 1.1km, assuming that 1950 DA is a retrograde rotator.[19] Optical lightcurve analysis by Lenka Šarounová and Petr Pravec shows that its rotation period is 2.1216±0.0001 hours. Due to its short rotation period and high radar albedo, 1950 DA is thought to be fairly dense (more than 3.5g/cm3, assuming that it has no internal strength) and likely composed of nickel–iron.[5] In August 2014, scientists from the University of Tennessee determined that 1950 DA is a rubble pile rotating faster than the breakup limit for its density, implying the asteroid is held together by van der Waals forces rather than gravity.[20][21]
1950 DA made distant approaches to Earth on 20 May 2012, 5 February 2021 and 5 February 2023.[18] However, at these times it was a quarter to half an AU away from Earth, preventing more useful astrometrics and timing that occurs when an object is closer to Earth. The next close approach that presents a good opportunity to observe the asteroid will be on 2 March 2032, when it will be 0.076AU (11.4millionkm) from Earth. The following table lists the approaches closer than 0.1AU until the year 2500.[22] By 2136 the close approach solutions are becoming notably more divergent.[citation needed]
Position uncertainty and increasing divergence[22]
Main-belt asteroid 78 Diana (~125km in diameter) will pass about 0.003AU (450,000km; 280,000mi) from 1950 DA on 5 August 2150.[6] At that distance and size, Diana will perturb 1950 DA enough so that the change in trajectory is notable by 2880 (730 years later). In addition, over the intervening time, 1950 DA's rotation will cause its orbit to slightly change as a result of the Yarkovsky effect. If 1950 DA continues on its present orbit, it may approach Earth on 16 March 2880, though the mean trajectory passes many millions of kilometres from Earth, so 1950 DA does not have a significant chance of impacting Earth. As of February2025[update], according to the latest solution dated 2 February 2025, the probability of an impact in 2880 is 1 in 2,600 (0.039%).[12]
The energy released by a collision with an object the size of 1950 DA would cause major effects on the climate and biosphere, which would be devastating to humancivilization. The discovery of the potential impact heightened interest in asteroid deflection strategies.
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