Andrew Masterson
Andrew Masterson is a former editor of Cosmos.
Nup, still not an alien craft. That’s the central finding of a review of a near-Earth asteroid first sighted in 1991 and which has been sparking stories of extraterrestrial fly-bys ever since.
The 20 metre-diameter object, dubbed 1991 VG, was first spotted by US astronomer James Scotti in November of that year. It immediately attracted a lot of attention for two reasons. First, it was awfully close to Earth – astronomers calculated that within a few weeks of discovery it would pass just 450,000 kilometres from the planet.
Second, it exhibited a heliocentric orbit very similar to that of Earth, which was unusual, not to say unprecedented.
At the time, these observations led to a flurry of theories attempting to explain its appearance and behaviour. Some astronomers considered that 1991 VG was simply a newly discovered type of small asteroid, but others weren’t convinced.
Scotti himself suggested that based on its orbital pattern it might be a spacecraft returning to Earth. Other researchers looked at its light curve – the way light reflected off it in multiple images – and concluded that it may well possess reflective side panels. It was possibly a tumbling satellite, they suggested.
From there, it was only a short narrative distance from the possibility of a human-made satellite to an alien-made one, and theories that 1991 VG was an extraterrestrial probe emerged. They have proven remarkably resilient.
The object disappeared from earth orbit in 1992. Based on its trajectory, however, astronomers were confident it would return at some point in 2017. When news of its expected arrival surfaced in 2015, all the old alien theories were dusted off and received a surprising amount of coverage in rather a lot of publications, some wackier than others.
It did return, as predicted, in August, passing by an order of magnitude further away from Earth.
By then, however, astronomical understanding of the behaviour and frequency of small asteroids had moved on considerably.
In a paper published in the journal Monthly Notices of the Royal Astronomical Society, astronomers Carlos and Raul de la Fuente Marcos of the Universidad Complutense de Madrid in Spain revisit the rumour-laden history of 1991 VG and filter it through present day research.
They confirm that the object “was briefly captured by Earth’s gravity as a mini-moon during its previous fly-by in 1991-1992”, a phenomenon that has almost certainly happened in the past and will very probably happen again in the future.
The asteroid, however, “is not a present-day co-orbital companion of the Earth”.
Far from being unique, the astronomers say, any realistic modelling for the orbits of near-Earth objects predicts that asteroids such as VG 1991 must exist. Indeed, they point out that so far three other similar ones have been observed, in 2001, 2008, and 2014 (none of them prompting speculation about alien origins).
The paper comes to a conclusion that is either reassuring or dispiriting, depending on one’s point of view: “All this evidence confirms that there is no compelling reason to believe that 1991 VG is not natural.”
