1991 VG
Encyclopedia
1991 VG is a Near-Earth object
discovered by James Scotti
. Due to its unusual orbit and rapid variation in brightness, there was early speculation that it could be a man-made spacecraft or rocket. In recent years, however, it has been discovered that most small objects with diameters less than about 100-200 meters are fast rotators. Also, more objects with very Earth-like orbits have been discovered.
having been suggested. More recently, the first Earth Trojan asteroid
- 2010 TK7
has been identified and such objects could well be a source for objects like 1991 VG.
, because its orbital path did not closely match any known man-made spacecraft or rocket bodies. Author D. Steele suggested the extraterrestrial origin in a "tongue in cheek" article in The Observatory.
Near-Earth object
A near-Earth object is a Solar System object whose orbit brings it into close proximity with the Earth. All NEOs have a perihelion distance less than 1.3 AU. They include a few thousand near-Earth asteroids , near-Earth comets, a number of solar-orbiting spacecraft, and meteoroids large enough to...
discovered by James Scotti
James V. Scotti
James Vernon Scotti is an American astronomer. He was born in Bandon, Oregon and graduated from Woodway Senior High in Edmonds, Washington in 1978. He received his B.Sc. in Astronomy from the University of Arizona in Tucson in 1983. Ever since that time, he has worked on the Spacewatch project,...
. Due to its unusual orbit and rapid variation in brightness, there was early speculation that it could be a man-made spacecraft or rocket. In recent years, however, it has been discovered that most small objects with diameters less than about 100-200 meters are fast rotators. Also, more objects with very Earth-like orbits have been discovered.
Earth-like Orbit
On November 6, 1991, Scotti discovered a faint object which was designated 1991 VG soon after discovery. The object's heliocentric orbit was found to be very similar to Earth's orbit and it was found that it would make a close approach to Earth just a month after discovery. Given such an Earth-like orbit, the dynamical lifetime of such an object is relatively short with the object quickly either impacting Earth or being perturbed by Earth onto a different orbit. The similarity of its orbit with Earth is also very difficult to explain from natural sources, with ejecta from a recent Lunar impact or non-gravitational perturbations such as the Yarkovsky effectYarkovsky effect
The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum...
having been suggested. More recently, the first Earth Trojan asteroid
Earth Trojan asteroid
Earth trojans are asteroids that orbit in the vicinity of the Earth-Sun Lagrangian points and . They are named after the Trojan asteroids that are associated with the analogous Lagrangian points of Jupiter....
- 2010 TK7
2010 TK7
2010 TK7 is the first Earth trojan asteroid to be discovered; it precedes Earth in its orbit around the Sun. Trojan objects are most easily conceived as orbiting at a Lagrangian point, a dynamically stable location 60 degrees ahead of or behind a massive orbiting body, in a type of 1:1 orbital...
has been identified and such objects could well be a source for objects like 1991 VG.
Probable monolithic structure
Since the discovery of 1991 VG, about 80% of small asteroids with absolute magnitudes (H) fainter than 22.0 (corresponding to sizes smaller than about 200 meters) which have had their lightcurve measured have rotation periods under 2 hours. Such rapid rotation would cause objects that are rubble piles - i.e. conglomerates of debris held together only by their gravitational attraction - to disrupt due to centripetal acceleration. Most such objects, therefore, are thought to be monolithic bodies or conglomerates which are held together by forces other than gravity (monolithic rocks, groups of debris held together by impact melt or welded by some other natural process). The unusual rapid lightcurve variation seen on the long trailed images of 1991 VG during its 1991 December close flyby of Earth is thus no longer considered unique or unexpected.Possible artificial origin
The uncertainty of the object's origin, combined with rapid variation in the object's brightness in images obtained during its close passage with Earth in early December 1991, led to some speculation that 1991 VG might be artificial in origin. There was much speculation that it could be a rocket body from a satellite launched in the early 1970s when 1991 VG made its previous close approach with Earth. Earlier close approaches to Earth were before the start of the space age. Some even went so far as to suggest the possibility that it might be an extraterrestrial object such as a Bracewell probeBracewell probe
A Bracewell probe is a hypothetical concept for an autonomous interstellar space probe dispatched for the express purpose of communication with one or more alien civilizations. It was proposed by Ronald N...
, because its orbital path did not closely match any known man-made spacecraft or rocket bodies. Author D. Steele suggested the extraterrestrial origin in a "tongue in cheek" article in The Observatory.