IAU Technical Review Team Assessment on Asteroid 2000 SG344

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.

Primary IAU contact persons are: