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IAU Technical Review Team Assessment on Asteroid 2000 SG344

Issue date: Nov 3, 2000

Recognizing the public interest and concern over possible impacts from small Near-Earth Asteroids (NEAs), the International Astronomical Union has established a process to provide international expert review of any discoveries or calculations that predict a close encounter with a non-neglibible chance of future impact. This review process has been exercised to confirm the calculations, based on current observations, of a close encounter with a low probability of impact on 21 September 2030 by a very small asteroid-like object, designated 2000 SG344.

Computations made earlier this week by a group of international experts suggest that the object 2000 SG344, has a remote 1 in 500 chance of impacting the Earth in 2030. These results have been verified over the course of the past 72 hours by a Technical Review Team of the International Astronomical Union. The greatest likelihood is that future observations of the object will yield higher precision orbit computations that will show with certainty that it will miss the Earth entirely. The unusual nature of the orbit of 2000 SG344 suggests the possibility that it might simply be a man-made rocket booster from the Apollo era.

Object 2000 SG344 was discovered on September 29, 2000 by David J. Tholen and Robert J. Whiteley using the Canada-France-Hawaii 3.6-meter aperture telescope on the island of Hawaii. Shortly thereafter, pre-discovery observations taken in May 1999 by MIT's LINEAR observatory team were also identified. Given the observed brightness of the object and its assumed reflectivity, an estimate can be made for its diameter. While the reflectivity of this object is not known, values typical for near-Earth asteroids imply this object's extent is about 30 - 70 meters.

Orbital calculations in late October by Andrea Milani (University of Pisa, Italy) first indicated the possibility of a future impact. Paul Chodas of the Near-Earth Object Program Office at NASA's Jet Propulsion Laboratory estimates a one in 500 chance of the object hitting the Earth on September 21, 2030. The possibility of an Earth impacting orbit was confirmed by Steven Chesley (NASA/JPL), Giovanni Valsecchi (Italian National Research Center in Rome, Italy) and Karri Muinonen (University of Helsinki). If the object is near the large end of the estimated size range for an asteroid, it would be classified as category 1 within the 10 point Torino Scale, meaning the object is one that merits careful monitoring. If the object's size is closer to the lower limit of 30 meters, it would be classified as Torino Scale 0 and hence not of immediate concern.

Because the orbital period of this object about the sun is 354 days, it moves a bit faster than the Earth about the Sun so it is drifting slowly away and will not return to the Earth's neighborhood until nearly three decades. It was last in the Earth's neighborhood in 1971. As yet undiscovered pre-discovery observations made in 1971 and additional observations made in the coming months would provide the data for further refining this object's orbit and the circumstances of its close Earth approach in 2030. During the 2030 close approach, the perturbative effects of the Earth upon the object could change its orbital period so that numerous encounters might be possible after 2030. The likelihood of this situation is also under study.

Because of its Earth-like orbit, this object is an obvious candidate for being a left-over space probe or rocket stage. For example, the S-IVB stages of the five Apollo rockets (Apollo 8-12) entered into heliocentric orbits that are similar to the orbit of object 2000 SG344. If this object is a man-made rocket booster, it would have a higher reflectivity than a natural asteroid and hence it would have to be smaller (about 15 meters) to reflect as much light as a much darker asteroid. While object 2000 SG344 seems too bright to be an Apollo rocket booster, the possibility of its being man-made has not been completely ruled out.

While object 2000 SG344 will likely pass close to the Earth in 2030, it should be made clear that the probability of the object missing the Earth is at least 500 to 1. If the ongoing studies determine that this object is likely to be a relatively small man-made booster then such a lightweight object would pose no hazard. It is interesting to note the chance of object 2000 SG344 striking the Earth in 2030 is actually somewhat less than the chance of an undiscovered object of the same size striking the Earth in any given year. Thus object 2000 SG344 is more interesting than threatening but the international efforts to characterize the nature and future motion of this object will continue.

In line with its policy decisions, the IAU does not intend to make any further statements on the eventuality of an impact by 2000 SG344, leaving that to the individual scientists who are observing this interesting small asteroid and computing its orbit.

Contacts:

NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory
      Steve Chesley
      Paul Chodas
      Don Yeomans, Manager
       
Chair, International Astronomical Union Working Group for Near-Earth Objects 
      David Morrison, NASA/Ames

University of Pisa, Italy
      Andrea Milani

University of Helsinki, Finland    
      Karri Muinonen 

Italian Space Research Center, Rome Italy
      Giovanni Valsecchi

Torino Scale
      Richard Binzel, MIT

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