The search for extraterrestrial intelligence (SETI) has seen a great deal of publicity, from television programs interviewing involved scientists to blockbuster movies like Contact. But the idea that there might be signs of extraterrestrial life closer to home has received relatively short shrift. Nonetheless, SETA (the search for extraterrestrial artifacts) has spawned interesting work, from Gregory Matloff’s examinations of anomalous Kuiper Belt objects to Robert Freitas’ surveys of ‘halo orbits’ around the Lagrangian points.

So far both kinds of search — SETI and SETA — have come up short, but a few curious things have been observed on each side. One interesting SETA investigation involved an object called 1991 VG, which made a close approach to Earth in 1991 (thanks to Adam Crowl for bringing this one to my attention). Discovered by Jim Scotti using the University of Arizona’s Spacewatch telescope (normally used to detect small asteroids near the Earth), 1991 VG seemed to be about 10 meters in size, but did not appear to be an asteroid. In a 1995 paper on 1991 VG, astronomer Duncan Steel (Anglo-Australian Observatory and University of Adelaide) noted “…strong, rapid brightness variations which can be interpreted as transient specular reflections from the surfaces of a rotating spacecraft.”

Fair enough — various man-made spacecraft have left rocket parts behind that could account for the object (and the thought that this could be leftover Apollo hardware immediately sprang to mind). But 1991 VG gets more interesting still given Steel’s finding that none of these known rocket bodies seem to have orbits returning to Earth at the time of the observation. That and the extremely close pass by the Earth suggested to Steel the possibility that 1991 VG could be an alien probe on a controlled reconnaissance mission.

Note this: Steel is hardly advocating the alien probe conclusion. What he is doing is to point out the interesting aspects of 1991 VG and examining it as an object of SETA interest. Studies like this are unlikely to turn up alien artifacts, but if we never investigate anomalies, we’ll sharply limit our understanding of what happens in space near the Earth. So how should such a study be followed up?

“It will be of interest,” says Steel, “to see whether sky-surveillance programmes reveal asteroids with similar orbital and light-curve properties as 1991 VG.” Steel reports that his personal bias is that this is a manmade artificial object; he calls for detailed investigation of rocket bodies left in heliocentric orbits that could account for the sighting. “If 1991 VG is a returned man-made rocket body,” he concludes, “it was very much a fluke that it was observed, and the normal process of science then requires that we consider the possibility of some other origin for it.”

Steel’s paper is “SETA and 1991 VG,” in The Observatory Vol. 115 (April, 1995), pp. 78-83. Also, see Jim Scotti’s recollections of the discovery, written in 1996. From Scotti’s posting:

“…the debate is still alive, and may continue to be so until someone can recover it next time it comes back around and then someday we can go out and take a close look. Does it have a regolith or a rocky surface or does it have “USA” or “CCCP” painted on the side? My guess is that it is indeed a natural object, but if it is manmade, perhaps it is a Saturn IVB stage from one of the early Apollo missions. As I recall, at least one left the 3rd stage in a high Earth orbit that would have eventually been perturbed into solar orbit.”

On SETA itself, one early Freitas paper is “A Search for Natural or Artificial Objects Located at the Earth-Moon Libration Points,” Icarus 42 (1980), pp. 442–47. Freitas argues in the paper that the Earth/Moon Lagrangian points are not in fact stable, being disturbed by solar gravity, but that large, stable orbits around these points do exist. Matloff’s recent work, discussed here, includes “Suggested Targets for an Infrared Search for Artificial Kuiper Belt Objects,” JBIS 58 (January/February 2005), pp. 51-61, written in collaboration with Anthony R. Martin (of Project Daedalus fame).