How a solar flare nearly triggered a nuclear war

1967 – more than two decades into the Cold War. Tensions between the US and Soviet Union remained high – and on 23 May, radars designed to detect incoming Soviet missiles appeared to be jammed. This was considered an act of war. Commanders put additional aircraft laden with nuclear weapons in a “ready to launch” status.

But crisis was averted. Luckily, the US Air Force had started monitoring the sun’s activity and realised that a blast of solar weather had probably jammed the radar stations. 

A paper to be published in Space Weather by physicists and retired air force officers in the US describes just how close the US came to launching an attack on the Soviet Union – all because of a blast from the sun.

Today, a fleet of probes and spacecraft are trained on the sun to monitor any outbursts. But none of it existed mid last century.

The US military began monitoring solar activity in the late 1950s using Earth-based telescopes. In the 1960s, the Air Weather Service in the Air Force kept an eye out for solar flares – massive burps of radiation from the sun’s atmosphere that, if they hit Earth, can disrupt radio communications.

By 1967, solar forecasters at the North American Aerospace Defence Command (NORAD) received daily updates on the sun’s activity, delivered via an array of observatories in the US and overseas.

On 18 May, an unusually large group of sunspots – cool, dark patches that indicate atmospheric unrest – appeared in one region of the sun and within a few days, forecasters predicted it was likely to spit out a major flare.

Indeed, observatories in New Mexico and Colorado saw a flare visible to the naked eye while a solar radio observatory in Massachusetts reported the sun was emitting unprecedented levels of radio waves.

Over the next day or so, as the flare unfolded, all three Ballistic Missile Early Warning System sites – one each at Clear Air Force Station in Alaska, Thule Air Base in Greenland and Fylingdales in the UK – stopped working.

But there were a few signs that the culprit was not on Earth. The sites happened to be in full sunlight. And because radar relies on detecting radio waves, the sudden influx of solar radio waves overwhelmed the systems, the study authors write.

And as the solar radio emissions waned, so too did the “jamming”. 

The study authors believe information from NORAD’s forecasters made it to commanders in time to stop military action. Delores Knipp, a space physicist at the University of Colorado in Boulder and lead author of the paper, noted that information about the solar storm was probably relayed to the highest levels of government – possibly even President Johnson.

After the initial flare died down, the effects were felt on Earth for a week. Northern lights, usually only seen near the north pole, were seen as far south as New Mexico.

According to the study authors, it was the military’s correct diagnosis of the solar storm that prevented the event from becoming a disaster.

Ultimately, the storm led the military to recognise space weather as an operational concern and build a stronger space weather forecasting system, says retired Colonel Arnold Snyder, a NORAD solar forecaster who was on duty that day.