November 6, 1991 began as a relatively routine night for astronomer James Scotti. Working at the University of Arizona's Kitt Peak observatory, Scotti was scanning the cosmos for asteroids when he discovered a small, fast moving object with highly unusual features. Only about 10 meters in diameter, the object exhibited an anomalous rate of rotation, fluctuations in brightness and speed for its size, suggesting to Scotti that it was something other than your "run-of-the-mill" main belt asteroid. Stranger still, the object was in a heliocentric orbit remarkably similar to that of Earth.
Scotti tracked the object, now known as 1991 VG, for the next two nights and once he had enough data to plot a preliminary orbit, he was surprised to find that the object would be passing within approximately .003 au (280,000 miles) of Earth the following month. While asteroids passing through Earth's neighborhood are certainly no rarity, they also tend not to last very long since they are likely to impact the planet or be thrown into a different orbit when they pass by.
Yet as Scotti continued to gather data on 1991 VG, it became clear that this was at least the object's second Earth flyby. The previous close pass occurred around March of 1975.
The object's longevity immediately aroused Scotti's suspicion, leading him to speculate that it might have been constructed by someone or something.
"We looked into all the possibilities for it being man-made," Scotti told Motherboard. "There were a few possible spacecraft and rocket bodies that might be 1991 VG, but when we looked into each, we were able to eliminate each of them."
In 1995, Duncan Steel, an astronomer then affiliated with the University of Adelaide, published an article in The Observatory speculating on the nature of this mysterious object, including the possibility that it was alien in origin. He noted that the fact that "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 [in November of 1991]" meant that "it might be argued that 1991 VG is a candidate as an alien probe observed in the vicinity of our planet."
"There were a few possible spacecraft and rocket bodies that might be 1991 VG, but when we looked into each, we were able to eliminate each of them."
Ironically, while Steel was raising this theory of 1991 VG as alien object in order to ultimately disqualify it as an explanation, it was this paper that would ultimately establish the connection between the object and the Search for Extraterrestrial Artefacts (SETA) in the minds of internet denizens everywhere.
"I do not think [VG 1991] is of extraterrestrial origin," Steel said in an email. "I do think that we should take seriously the possibility that there are alien artefacts in the solar system, although I very much doubt that there are any, based on what we know so far."
While the likelihood of 1991 VG being an alien probe is minute, the debate about just what the object might be is far from settled. Steel maintains that based on what we know about the object it is likely man-made, perhaps from the Apollo 12 rocket.
Scotti, on the other hand, has not entirely ruled out a natural origin for this mystery object. According to him, 1991 VG exhibited unusual variations in brightness, which suggested that the object was rotating very quickly with just a few minutes from peak to peak. At the time there was a general consensus that such a fast rotation was likely to make the asteroid fly apart from the centrifugal force generated by the rotation.
Yet according to Scotti, in the years since he spotted 1991 VG, it was discovered that a significant portion of asteroids under 100 meters have remarkably fast rotation periods. Thus for an object as small as 1991 VG, a rotation period of a few minutes, while rare, is not impossible. It would simply mean that the object is a monolithic structure, a small boulder, rather than a rubble pile.
"My question is where did 1991 VG come from and how did it get into its present orbit?" said Scotti. "One possibility would be that it is ejecta from a lunar impact. Another possibility is that the Yarkovsky force, caused by the thermal emissions of a rotating object, systematically pushed the object around over long times. It's still a puzzle!"
Luckily, we may not have to wait very long to solve the mystery of 1991 VG. The object is due for another close pass in the summer of 2017, but it will be farther from Earth than in 1991 and only viewable from the Southern Hemisphere.
Then again, there's always the possibility that it's a sentient alien probe, in which case we should probably start getting ready for the invasion.
True Mysteries... from Space! is part of All in Your Head, a series that takes a scientific look at all things spooky and scary. Follow along here.