Abstract: A 10-metre object on a heliocentric orbit, now catalogued as 1991 VG, made a close approach to the Earth in 1991 December, and was discovered a month before perigee with the Spacewatch telescope at Kitt Peak. Its very Earth-like orbit and observations of rapid brightness fluctuations argued for it being an artificial body rather than an asteroid. None of the handful of man-made rocket bodies left in heliocentric orbits during the space age have purely gravitational orbits returning to the Earth at that time. In addition, the small perigee distance observed might be interpreted as an indicator of a controlled rather than a random encounter with the Earth, and thus it might be argued that 1991 VG is a candidate as an alien probe observed in the vicinity of our planet.
The approach taken in this paper is to investigate the different probabilities regarding the nature of the near-earth pass of the object designated 1991 VG.
Three distinct possibilities are apparent. The first is that it was a natural asteroid, to which we assign a probability P(n), that is, Probability natural. The second is that it was a man-made spacecraft, probability P(s), or Probability spacecraft. The third is that it was an alien artifact, probability P(a), Probability artifact. If we assume that there are no other possible explanations then the three taken together and written in formula P(n) + P(s) + P(a) = 1. The scepticism of a scientist (myself included) leads one to assume that P(a) = 0, but that assumption, it will be seen, is not supported by our knowledge of 1991 VG and its discovery circumstances. I show below that these indicate both P(n) and P(s) to be small, implying that P(a) , Probability artifact, is significant.
Chapman-Rietschi 1 has noted, following Arkhipov2, that much work and discussion of SETI tends to overlook the possibility of discovering alien artifacts within the Solar System. Such a pursuit is normally known as SETA (Search for Extra-Terrestrial Artifacts3,4). Over the past two decades various authors have debated whether the best place to look for such artifacts is in the asteroid belt5, in the outer Solar System6 on planetary surfaces7, or as extraterrestrial probes in the inner Solar System8-10, whereas the famous Fermi Paradox argument is based upon the understanding that such probes have not been detected, and thus extraterrestrial intelligent beings do not exist11,12. The aim of this communication is to point out (very tentativeIy) that an extraterrestrial spaceprobe may have been detected in late 1991 in near-Earth space.
The 0.91-m Spacewatch telescope of the University of Arizona commenced operation in 1989, since when it has been used to detect asteroids of an unprecedentedly small size in the Earth's vicinity13, On 1991 November 6 Spacewatch observer Jim Scotti discovered a body initially described as being a "fast-moving asteroidal object" at a geocentric distance of 0.022 AU, a month before its closest approach (at 0.0031 AU) to the Earth14. Its heliocentric orbital elements at discovery were a = 1.04AU, e = 0.065, i = 0°.39, so that the suggestion was soon made that "this might be a returning spacecraft" (ref. 14). The fly-by of the Earth-Moon system resulted in slight changes in its osculating elements15-17. Assuming the albedo of an S-type asteroid is appropriate its spectral reflectivity was not dissimilar to main-belt S-type asteroids13 it would be about 9 m in size, or 19 m with the albedo of a C-type. However, observations by Richard West and Olivier Hainaut from ESO, close to the time of nearest approach, indicated a non-asteroidal nature for the object, with strong, rapid brightness variations which can be interpreted as transient specular reflections from the surfaces of a rotating spacecraft18,19. Contrary to this, Wieslaw Wisniewski at Kitt Peak found only a slowly-varying brightness18 but under poor observing conditions. The question of the nature of this object might have been answered by radar observations, but radar sounding attempts failed16,20 1991 VG was also observed in 1992 April with larger telescopes at Kitt Peak21, but it is unlikely to be observed again soon (see below). However, that recovery allowed an improvement of the ephemeris (in both cartesian and frequency space) for the time of the radar observations, which may make identification of 1991 VG in those data possible when they are fully analyzed20.
As outlined in the opening quote at the top of the page, the approach taken here is to investigate the different probabilities for the nature of this object, given our incomplete knowledge. Three distinct possibilities are considered apparent. The first is that it was a man-made spacecraft. The second is that it was a natural asteroid. The third is that it was an alien artifact.