In August 1972, large numbers of US magnetic mines in the oceans surrounding North Vietnam began spontaneously exploding. The mines were strategically placed to detonate when in close proximity to a ship, but it was not ships causing the mines to activate. The US reported dozens of mines exploding, but the amount is estimated to be as high as 4,000.
What could have possibly set off these explosives? Surprisingly, the Sun.
Solar storm of August 1972
In August 1972 one of the most powerful solar storms ever recorded struck Earth. That month, the Sun had displayed increased solar activity before unleashing a series of extremely powerful solar flares.
A solar flare is an intense eruption of radiation from the surface of the Sun caused by the interactions of powerful magnetic fields within the Sun. The burst of energy from a solar flare can be followed by a coronal mass ejection (CME). A CME is a magnetic cloud of radioactive particles that are expelled from the Sun into the cold expanse of interplanetary space at unfathomably high speeds. Although the Sun is almost 93 million miles away from the Earth, normal CMEs can make the journey in just one or two days.
During the 1972 storm, the most powerful flare occurred on August 4th, sending a magnetized and radioactive cloud hurtling towards the Earth. The ejection reached Earth in just 14.6 hours, a record that still stands today as the shortest coronal mass ejection travel time on record.
Upon its arrival, sensors and monitoring devices all over the Earth were doused with charged particles that sent their displays off the scales. Similarly, magnetometers were overloaded. The ejection’s interaction with the Earth’s magnetosphere caused bright auroras much further south than normal, observed as low as Spain.
Dangers from storms of this power are not limited to the ground though. Satellites and other spacecraft can be seriously damaged by coronal mass ejections, with one satellite receiving approximately two years of wear from the storm.
Worryingly, the storm occurred between Apollo 16 and Apollo 17, the latter of which would lift off just a few months later. Had the astronauts been on a mission during the event, they would have received a dangerous dose of radiation even inside the Apollo command module. If they were caught while performing a moonwalk, they would have likely received a dose of radiation enough to guarantee death.
Mine detonation
US mines positioned around North Vietnam were magnetically triggered. Sensors within the mines constantly monitored the magnetic fields around the device, which would be altered when a ship enters its proximity. The sheer power of the 1972 solar storm was enough to distort the Earth’s magnetic field and was also powerful enough to trigger the mines around North Vietnam.
At the time the military already knew solar storms could interfere with systems on Earth, but they did not understand to what extent this could happen.
New appreciation for the 1972 event
In 1972, the strange happenings caused by the enormous CME were seen as unremarkable and mostly fell under the radar of researchers at the time. It wasn’t until Delores Knipp, a research professor at the University of Colorado Boulder, began looking into the event that the true scale of the Sun’s activities back in the 1970s was realized.
Knipp’s research began after a chance conversation with a colleague who at the time was working at what would later become the Space Weather Prediction Center. Here, the colleague witnessed US Navy officials enter a meeting with his boss. While he did not hear the details of the meeting, he knew it was about a then-recent solar storm and its impacts on the military.
After learning about this, Knipp dived into military archives. She found a document that had been declassified in the 1990s that contained information about the spontaneous detonation of sea mines in Asia.
With some more digging, Knipp realized that estimates made at the time significantly low-balled the power of the storm. She believes the storm is actually much closer in severity to the 1859 Carrington event, the largest geomagnetic storm ever recorded.
Despite this, many have failed to recognize its significance.
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“I think people forgot about it,” Knipp said. “They didn’t know about the sea mine problem and the effect on the power grids got published in engineering journals, not science journals.”
Knipp regards the 1972 solar storm as a warning about how vulnerable we are to the mind-boggling power of the Sun.