, provisional designation , is an asteroid, classified as a near-Earth object and potentially hazardous asteroid of the Apollo group, approximately in diameter. It once had the highest known probability of impacting Earth. In 2002, it had the highest Palermo rating with a value of 0.17 for a possible collision in 2880. 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 with a Palermo rating of −1.42. As of 2018, It is listed on the Sentry Risk Table with the highest cumulative Palermo rating. is not assigned a Torino scale rating, because the 2880 date is over 100 years in the future.
Discovery and nomenclature
was first discovered on 23 February 1950 by Carl A. Wirtanen at Lick Observatory. It was observed for seventeen days and then lost because the 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 on 4 January 2001. Just two hours later it was recognized as.
Observations
On 5 March 2001, ' made a close approach to Earth at a distance of. It was studied by radar at the Goldstone and Arecibo observatories from March 3 to 7, 2001. The studies showed that the asteroid has a mean diameter of 1.1 km, assuming that ' is a retrograde rotator. Optical lightcurve analysis by Lenka Sarounova and Petr Pravec shows that its rotation period is hours. Due to its short rotation period and high radar albedo, ' is thought to be fairly dense and likely composed of nickel–iron. In August 2014, scientists from the University of Tennessee determined that ' is a rubble pile that is kept together by van der Waals forces. The next close approach to Earth by 1950 DA is scheduled to occur on 5 February 2021. However, at that time it will still be nearly half an AU away from Earth making reacquisition observations impractical. The next close approach that presents a good opportunity to observe the asteroid will be the one that occurs on 2 March 2032, when it will only be 0.075 AU from Earth. The following table lists next five close approaches nearer than 0.10 AU.
Main-belt asteroid78 Diana will pass about from ' on 5 August 2150. At that distance and size, Diana will perturb ' enough so that the change in trajectory is notable by 2880. In addition, over the intervening time, ' rotation will cause its orbit to slightly change as a result of the Yarkovsky effect. If ' 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 ' does not have a significant chance of impacting Earth. As of the 7 December 2015 solution, the probability of an impact in 2880 is 1 in 8,300. The energy released by a collision with an object the size of 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.
