On September 22, 1979, the American surveillance satellite Vela 6911 detected two intense flashes of light in the South Atlantic, between Africa and Antarctica. The readings from the satellite's optical sensors were not entirely clear, but it was determined that the power required to produce something of that magnitude was in the range of two to three kilotons. Experts speculated that these could have been clandestine nuclear tests by Israel or South Africa, or an event similar to the one that devastated Tunguska a century ago. What caused the Vela Incident?
The Vela Project
The United States launched Project Vela to monitor nuclear tests taking place on the surface or in the atmosphere of our planet. In 1963, the Partial Test Ban Treaty had been signed by 130 countries and prohibited all nuclear explosions except underground ones, in order to avoid radioactive fallout. Developed by DARPA (Defense Advanced Research Projects Agency) and supervised by the US Air Force, Project Vela rested on three pillars: Vela Uniform, which would attempt to detect underground nuclear explosions through related seismic events; Vela Sierra, several satellites designed to detect signals of nuclear explosions in the atmosphere; and Vela Hotel, other satellites conceived to detect nuclear signals coming from space. Initially the program was supposed to operate for a few years, but the robustness of the Vela satellites—designed to work for six months—caused it to last 26 years.
There were 12 satellites in total, six of the Vela Hotel type and six of the Vela Sierra type, orbiting at altitudes between 100,000 and 113,000 kilometers, above the Van Allen belts. They were equipped with 12 external X-ray detectors and 18 internal neutron and gamma-ray detectors, powered by their solar panels. They also had two special sensors capable of detecting flashes with durations shorter than a millisecond, necessary because atmospheric nuclear explosions that they would eventually have to report produce a single short-duration signal.
Indeed, an explosion of this type emits a flash that lasts about 1 millisecond, followed by a second, longer but less intense light that lasts a few seconds. This occurs because the first flash is quickly overtaken by the atmospheric shock wave—composed of ionized gas—which, although it emits quite a bit of light, quickly becomes opaque and hides the explosion. No known natural phenomenon can produce this effect, so the Vela satellites had no trouble detecting these explosions.
A Double Flash in the Atlantic
On September 22, 1979, after having successfully reported 41 nuclear explosions corresponding to as many tests conducted by the superpowers of the time, the Vela 6911 satellite recorded two strange flashes with its optical sensors. Although they had the usual characteristics of atmospheric nuclear explosions, they had occurred in a region of the planet—the South Atlantic, between Africa and Antarctica (47°S, 40°E)—where something like this was not expected. The power was estimated at between 2 and 3 kilotons, 10 to 20 times less than that of the Hiroshima bomb.
The press quickly called these flashes "Vela Incident". Intelligence agencies began to work, and two main hypotheses were considered. The first, which was assigned a higher probability, was that these flashes were the result of two secret nuclear detonations belonging to Israel or South Africa. The second, that an object from outer space—possibly a comet or a meteorite—had detonated due to the overheating suffered upon entering our atmosphere, giving rise to something similar to the "Tunguska Event" but over the sea.
Although the press quickly forgot the incident, intelligence agencies wanted to know at all costs what had happened, and they followed every lead. At that time, South Africa had begun a nuclear weapons development program, and when Vela 6911 captured the flashes, several ships of the South African navy were conducting maneuvers in that area. When everything seemed to indicate that this nation was responsible, Mordechai Vanunu, an Israeli nuclear engineer, revealed that his country had been developing its own nuclear program in the Negev desert for about 10 years, and had collaborated closely with the South Africans.
These statements led many to assume that both nations, jointly, had carried out the tests. However, and although an initial report from the United States government attributed the flashes to a South African nuclear explosion, a special commission composed of experts appointed by the Carter administration concluded that, "since no radiation was found near the event", it could not be assured that this was the cause of the phenomenon.
In the midst of the confusion, the voices of those responsible for the Arecibo radio telescope ("we have detected an unusual event in the ionosphere"), the Australian government ("we have recorded abnormal radioactivity levels in the area"), and the scientists in charge of designing and supervising the Vela satellites ("the satellite has functioned correctly, and its reliability is demonstrated by having already detected 41 nuclear tests.") Time passed, and it seemed we would never know what happened.
Confession and Retraction
But in February 1994, Commodore Dieter Gerhardt, whose résumé included activities as diverse as "Soviet spy", "convict", and "commander of the Simon's Town Naval Base in South Africa", surprised everyone by publicly declaring that "although not directly involved, I can affirm that the flash was the product of an Israeli-South African atomic test, whose code name was Operation Phenix. It was supposed not to be detected, but the weather changed and the Americans discovered it." Gerhardt's reputation was not the best, and the incident continued without an officially recognized cause.
Three years later, in 1997, an Israeli newspaper quoted the former South African Foreign Minister who confirmed that Vela had been a South African nuclear test. However, and again sowing doubt, shortly after, the official declared that his words had been "taken out of context."
Even today, many of the documents related to the incident remain "classified" by various governments, which does little to clarify what happened. The hypothesis that attributes the event to an extraterrestrial object seems to have lost strength, especially after what the Australians expressed regarding the presence of radiation in the area. It is much more likely that it was some clandestine nuclear test produced during the Cold War, although we still do not know for sure.
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