The mystery of Earth companion 1991 VG

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A space object of unknown origin called 1991 VG is floating around the heavens above. Its Earth-like orbit and fast fluctuations in brightness suggest that the 30-foot entity isn’t simply an asteroid or remnant from the space age, as was initially assumed (Image via

About 20 years ago, a mysterious object made a close approach to Earth that some believe was indicative of a controlled encounter. In 2017, the object is due to swing pass Earth again. Ross Jones reports.

IT CAN BE a depressing world. ISIS, earthquakes, species extinction, the Liberal Party.

Let’s, just for a moment, take a break and amuse ourselves with a little light mystery, Friday night ABC style. The denouement should be early 2017, just after the next election. It’s not a murder mystery, it’s a science mystery, but it does have suspects.

Back in the 1940’s, a small object, less than 20 metres across, slipped into earth’s heliocentric orbit. 

Earth has a few companion asteroids, mostly harmless, but, if things go along as they are, this new companion will impact the planet in 2110. That’s a few generations down the track, so no worries you’d think.

The thing is, it shouldn’t be there.

Jim Scotti was senior research specialist at the Lunar and Planetary Lab of the University of Arizona. Back in December 1991, he was at the lab’s Kitts Peak (Arizona) telescope when, in the course of playing with various settings beyond the usual range, he noticed an odd thing. He named this thing 1991 VG.

In 1996, Scotti wrote:

It was a magnitude V=20.7 object moving with rates typical of a Near-Earth Asteroid.

V is a measure of the brightness of the object. From there it’s a complex formula to determine the object’s size.

Scotti wrote:

From the photometry we did we can say that if the objects' albedo is low, around 5%, it is about 19 meters in diameter.  If it is around 20%, then it is about 9 meters in diameter.  If it were a perfect mirror it could be as small as about 4 meters in diameter.

Albedo is the reflection coefficient.

So what did Scotti think 1991 VG was?

We were immediately suspicious that the object might be manmade. On November 8, I already suggested to Brian Marsden that perhaps it might be a Saturn IVB stage, but it was only a wild guess at trying to explain the Earth-like orbit.

Saturn IVB is the upper stage of an Apollo moon rocket. The stage is not that big, measuring just 16.8 metres x 6.6 metres, so about the right size for 1991 VG. Some IVBs were crashed into the moon and some sent into decaying earth orbit, but four were sent into orbits around the sun.

1991 VG orbital diagram (Source:

Needless to say, these helioecentric orbits were not intended to coincide with Earth’s, but one, Apollo 12, launched in November 1969, ran out of fuel prematurely somewhere past the moon and went into a weird orbit around the earth and moon. It sailed by earth in 1971 and 2003 and is not due back until 2041. That is, at the time Scotti logged 1991 VG, the Apollo 12 IVB was somewhere on the other side of the moon.

The disconcerting thing is that an object in such an orbit would not last very long — how could it be natural?

….Marsden integrated the orbit backwards, hoping to improve the predictions for an attempt to observe 1991 VG with radar by linking it to a manmade spacecraft.  He found that it had been in the vicinity of Earth last in about 1973 or 1974, but only got within about 0.07AU.  That suggested the Helios A spacecraft booster, a Centaur upper stage. Jonathan McDowell contacted General Dynamics and found out that that booster was put back into a Geocentric orbit after dumping the Helios Spacecraft.

So, 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.

Duncan Steel, BSc, Fellow of the Royal Astronomical Society, has discovered a dozen asteroids and was well-enough placed to introduce the Sex Pistols at their first "completed" concert. TV, books, radio, professional articles — a science dude.

Between 1990 and 1995, Steel was in Coonabarabran directing the Anglo-Australian Observatory program for the discovery and tracking of near-Earth asteroids. Steel took an interest in 1991 VG and, towards the end of his tenure, The Observatory magazine published his take on Scotti’s data.

Duncan opened with:

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 argue 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, and the a priori probability of discovery for 1991 VG was very small, of order one in 100,000 per annum. 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.

Now, them’s fightin’ words!

Steel works his way through the possibilities.

Excerpt from Duncan Steel's article in Observatory magazine

Is it space junk? Probably not.

Identification with any of the above would require the action of nongravitational forces, such as radiation pressure or leaking fuel, but these agencies are not known to have acted; in any case, it does not seem to be possible to definitely to identify 1991 VG as having originated on the Earth….

…If 1991 VG is indeed a man-made rocket body, then its return to our vicinity and its accidental detection by Spacewatch was a very unlikely event.

Is it a natural body? Probably not.

Attention is now turned to Pn, the probability that 1991 VG was a natural body. There are two factors which argue against such an identification. The first is the light variations mentioned earlier; the balance of evidence (e.g,, see the image presented in ref. 19, which is distinctly similar to rotating artificial satellite trails frequently seen in wide-field photographs) supports the idea that 1991 VG is an artificial object. Second, the pre-encounter orbit of 1991 VG was so similar to that of the Earth that it was unstable under close approaches to our planet on a time-scale measured in millennia at most. This is obvious from the above discussion of the frequency of close approaches. The dynamics therefore would require 1991 VG to have recently arrived in that orbit (perhaps as ejecta from a lunar impact?), which is unlikely if it is an asteroid.

Steel concluded:

The above has been intended to provide prima facie evidence that 1991 VG is a candidate alien artifact. The alternative explanations – that it was a peculiar asteroid, or a man-made body – are both estimated to be unlikely, but require further investigation. In connection with the former, it will be of interest to see whether sky-surveillance programmes reveal asteroids with similar orbital and light-curve properties as 1991 VG. For the latter, each of the handful of rocket bodies which mankind has left in heliocentric orbits in the plausible launch windows requires detailed investigation: are their initial heliocentric orbits known, was fuel left on board any of them, are their physical parameters such that non-gravitational forces could plausibly bring them back to the Earth within a few decades, could they fit the observed spectral reflectivity of 1991 VG? My personal bias is that 1991 VG was indeed an artificial object, but an anthropogenic one.

The point is that such an interpretation, which will likely be favoured by most, requires: (i) the action of non-gravitational forces which are not known to have occurred; (ii) the chance return of one of a very small number of man-made objects left on heliocentric orbits in acceptable epochs; (iii) that return to have been unusually close, given its geocentric distance at discovery; and (iv) the object to have been spotted despite long odds against such discovery. If 1991 VG is a returned man-made rocket body, 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 says his bias is toward an anthropogenic explanation, but then demolishes this possibility. Is he saying 1991 VG is an alien probe but covering himself against unprofessionalism?

IA readers are aware just how much bullshit there is on the internet, particularly when the word alien crops up.

Hoax? Is Steel real? Did he really write that article?

The answer is yes and yes.

I sent an email to Steel and he replied:

Dear Ross:

(a) The paper was published in 'The Observatory' magazine; and you should see follow-up papers there.

(b) The (asteroidal) designation is "1991 VG".

(c) The up-to-date version is that the object in question is/was most likely the upper stage of the Apollo 12 launch, which is known to have been inserted into a luni-terrestrial orbit in 1969 from which it seems it must have 'leaked' into heliocentric orbit in 1975 (if 1991 VG is/was indeed that upper stage: everything fits OK). There is a good theoretical basis for this, but the object in question was not tracked (or indeed trackable) between 1969 and 1975, so that it is not possible to prove this to be the case. Perhaps new observations at some stage will demonstrate the veracity of the proposed identification.

(d) A web search will show many discussions of the above, mostly by people who 'want' it to be an alien probe.


Duncan Steel

So, it is conformed Steel did write the article, but he isn’t giving much away — at least not to an unknown correspondent of unknown integrity. It’s a delicate issue.

One problem is the Apollo 12 IVB has already been identified and tracked, and it’s not 1991 VG.

It is another former asteroid called, enchantingly, JOO2E3.

According to a 2003 paper published by the American Astronomical Society:

Through the modeling of common spacecraft materials, the observations of J002E3 show a strong correlation of absorption features to a combination of human-made materials including white paint, black paint, and aluminum. Absorption features in the near IR show a strong correlation with paint containing a titanium-oxide semiconductor. Using the material model and the orbital information, it was concluded that J002E3 is a human-made object from an Apollo rocket upperstage, most likely Apollo 12.

Other theories for 1991 VG were canvassed in a 2008 paper published by the Royal Astronomical Society:

Its origin has been speculated to be a returning spacecraft, lunar ejecta or a low-inclination Amor- or Apollo-class object. The latter is arguably the more likely source…

Amor and Apollo are classes of Near Earth Asteroids. No mention of Steel’s fourth possibility.

The paper continues:

It has been speculated that 1991 VG might be a returning spacecraft because of its very Earth-like orbit and its peculiar spectrum, yet this hypothesis was rejected because it is unlikely that a heliocentric orbit was reached by a spacecraft with such a large projected area (Tancredi 1997). Another possibility is that 1991 VG and companions are lunar ejecta. Tancredi favours this as the most likely explanation because the alternative – dynamical evolution from the asteroid belt – has a very low probability.

Lunar ejecta occur when a body strikes the moon and various-sized bits are ejected into the solar system. After a long discussion, the authors dismissed this possibility:

Hence the lunar ejecta hypothesis can be rejected.


Since one can most likely rule out spacecraft (Tancredi 1997) or lunar ejecta as the origin of these bodies, the most likely source is low-eccentricity Apollo and Amor asteroids.

But Scotti had dismissed the idea of an NEA 12 years earlier and the quoted Tancredi apparently thought it a highly unlikely explanation.

And that brings us back to where we started. A mystery.

Stay tuned for 2017. Will Labor be in power? Will Tony Abbott have been deported? Will Arthur Sinodinos be in gaol? Or, will other events overwhelm them all?

You never know, 1991 VG might be quite spacious inside.

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