The ‘nuclear test’ spotted by a satellite nobody’s owning up to 45 years later

45 years ago to the day, an American satellite spotted something unusual in the Indian Ocean.

A Vela satellite was in orbit near South Africa’s Prince Edward Islands, about halfway between the southern point of Africa and Antarctica, when it detected a double flash of bright light just before 1am UTC.

The Vela satellites were designed to spot nuclear explosions which broke the Partial Nuclear Test Ban Treaty – signed by 126 countries in 1963 to ban all test detonations of nuclear weapons, unless carried out underground.

To this day, most experts think an unauthorised nuclear test is the most likely explanation for the double flash.

But nearly half a century later, nobody has owned up to it – so Metro is taking a look at some of the expert opinions, facts and theories behind those mysterious flashes.

So what actually happened?

The American Vela satellite detected the ‘double flash’, then named the South Atlantic flash, just before 1am UTC on September 22, 1979.

The double flash could have been characteristic of an atmospheric nuclear explosion of two to three kilotonnes – equivalent to 2-3,000 tonnes of TNT.

Acoustic sound data, previously used to help the US detect Soviet submarines, was then used to try and figure out if a nuclear detonation had taken place. However this data didn’t come back with any substantial evidence.

US Air Force surveillance craft flew over that area of the Indian Ocean for more than a month after, until October 29, to carry out atmospheric sampling and analyse wind patterns.

They figured out that fallout from a nuclear explosion in that area would have been carried to south-west Australia – and low levels of iodine, a short-half-life product of nuclear fission, was found in sheep in the southeastern Australian states of Victoria and Tasmania.

The immediate fall-out

After reports of the double flash were made public, the US Defence Department said it was either a bomb blast or a combination of natural occurrences, such as lightning, a meteor, or a glint from the sun.

The US National Security Council’s initial assessment was that it had ‘high confidence’ the flashes were a low-yield nuclear explosion, even though there were ‘no corroborating seismic or hydro-acoustic data’.

A later report revised the Security Council’s verdict to ‘inconclusive’ as to whether a nuclear test had happened – but if it had, South Africa’s weapons programme was probably responsible.

The American Office of Science and Technology Police was asked by then-US president Jimmy Carter to re-examine the data in the 1980s, as part of his re-election campaign which included themes of nuclear disarmament and nonproliferation.

A panel of independent scientific and engineering experts re-analysed the Vela satellite data, as well as other data collected during the subsequent investigation.

They concluded that while they couldn’t rule out a nuclear blast, ‘based on our experience in related scientific assessments, it is our collective judgment that the September 22 signal was probably not from a nuclear explosion’.

Who could be the culprit?

As discussed above, there’s no consensus that the double flashes were definitely a nuclear explosion. But if they were, who could have been responsible for it?

One of the main suspects was South Africa, which at the time had a clandestine nuclear weapons programme despite having signed the Partial Test Ban Treaty.

The location of the double flashes, between the southern tip of Africa and Antarctica, also raised suspicion.

But the International Atomic Energy Agency believes South Africa couldn’t have constructed such a nuclear bomb until November 1979 – two months after the incident. Plus, they believed that all possible South African nuclear bombs had been accounted for.

Israel was also considered a prime suspect – and in fact some experts believe the double flashes could have been an Israeli test conducted in cooperation with South Africa.

It was believed at the time that Israel had its own nuclear weapons, and some journalists believed that this was one of several joint tests with South Africa in the Indian Ocean.

One journalist, Seymour Hersh, believed the IDF sent two ships and ‘a contingent of Israeli military men and nuclear experts’ for the test, while author Richard Rhodes suggested the US covered up the cooperation between Israel and South Africa to avoid complicating their relations.

Leonard Weiss, of the Center for International Security and Cooperation at Stanford University, said in 2011: ‘The weight of the evidence that the Vela event was an Israeli nuclear test assisted by South Africa appears overwhelming.’

The Soviet Union was also a suspect, because 20 years earlier the USSR carried out underwater tests in the Pacific, in violation of a moratorium between the Soviets and the US.

Nuclear testing was also carried out by India in 1974, casting suspicion on them as it could have been possible for the Indian Navy to operate in such southern waters.

However, India was fairly quickly ruled out as a potential culprit, as India was not hiding its nuclear weapons capability at the time.

Pakistan was considered as a suspect, as the country might have wanted to prove its nuclear technology in secret.

And as the double flash happened not far from the French-owned Kerguelen Islands, it was considered that France might have been testing a small neutron or other tactical nuclear bomb.

What’s the situation now?

Not much new information has come to light since the double flashes 45 years ago.

Most questions remain unanswered, and no country has come forward to officially claim responsibility for the flashes, nor explain what caused them.

But a convicted Soviet spy turned commander of South Africa’s Simon’s Town naval base shone new light on the incident in 1995.

He said: ‘Although I was not directly involved in planning or carrying out the operation, I learned unofficially that the flash was produced by an Israeli-South African test, code-named Operation Phenix [sic].

‘The explosion was clean and was not supposed to be detected. But they were not as smart as they thought, and the weather changed—so the Americans were able to pick it up.’

Some US documents relating to the incident were declassified and published on the National Security Archive in 2006.

Analysis of those newly available documents led to a report which concluded: ‘A Central Intelligence Agency-sponsored panel of well-respected scientists concluded that a mysterious flash detected by a U.S. Vela satellite over the South Atlantic on the night of 22 September 1979 was likely a nuclear test.’

In 2017, a new study demonstrated how unlikely it was that the Vela satellite’s reading was caused by a meteor collision.

And as recently as 2022, another study examining readings from a Nasa satellite taken just under 17 minutes after the double flashes found evidence of a trace left by the blast’s shockwave in the ozone layer.

So while the scientific consensus strongly suggests that this was a nuclear test, and the political consensus leans towards it being carried out by both South Africa and Israel, there is still no concrete answer nearly half a decade later.

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