Starfish Prime: The First Accidental Geomagnetic Storm

July 9, 2022: Sixty years ago today, one of the biggest geomagnetic storms of the Space Age struck Earth. It didn’t come from the sun.

“We made it ourselves,” recalls Clive Dyer of the University of Surrey Space Centre in Guildford UK. “It was the first anthropogenic space weather event.”

On July 9, 1962, the US military detonated a thermonuclear warhead 250 miles above the Pacific Ocean–a test called “Starfish Prime.” What happened next surprised everyone. Witnesses from Hawaii to New Zealand reported auroras overhead, magnificent midnight “rainbow stripes” that tropical sky watchers had never seen before. Radios fell silent, then suddenly became noisy as streetlights went dark in Honolulu.

Above: ‘Nuclear auroras’ viewed from Honolulu (left) and from a surveillance aircraft (right) on July 9, 1962.

Essentially, Starfish Prime created an artificial solar storm complete with auroras, geomagnetic activity, and blackouts. Much of the chaos that night was caused by the electromagnetic pulse (EMP)–a ferocious burst of radiation that ionized the upper atmosphere. Ionized air over the Pacific pinned down Earth’s magnetic field, then let it go again when the ionization subsided. The rebound created a manmade geomagnetic storm for hundreds of miles around the blast zone.

Dyer, who is widely known for his studies of extreme space weather events, was still in school when the bomb exploded. “In 1962 the Cold War was red hot, and we all thought the end was nigh,” he says. “Starfish Prime was a defining event.”

“The explosion led to the early demise of all the spacecraft in orbit at the time. These included Ariel-1, the UK’s first spacecraft, and Telstar-1, a US communications satellite which had the bad luck to be launched the very next day.”

Credit: R.E. Fischell, “ANNA-1B Solar Cell Damage Experiment,” Transcript of the Photovoltaic Specialists Conference, April 10, 1963, Washington DC.

Normally, geomagnetic storms bring down satellites via orbital decay. The upper atmosphere heats up and expands to the point where it can pull satellites down toward Earth. Starfish Prime was different.

“The explosion filled Earth’s magnetosphere with energetic electrons,” explains Dyer. “Electrons were injected by the gradual beta decay of fission products and added to our planet’s natural radiation belts. There were increased fluxes of trapped electrons for many years after the blast.”

These artificial electrons hit satellites hard, degrading their electronics and solar arrays.

“Ariel-1 became almost unusable after 4 days due to power degradation and tape recorder failure,” recalls Dyer. “The Telstar satellite lasted until November 1962 when its command decoder failed. It still managed to provide the first transatlantic TV feed, synchronize UK/US time to 1 microsecond and inspired the Tornado’s rock classic ‘Telstar,’ which used recordings of a flushing toilet played backwards.”

Starfish Prime serves as a warning of what could happen if Earth is blasted by high doses of radiation. Sixty years later, researchers are still learning what it can teach us about the vulnerability of power grids. An even scarier atmospheric explosion may have been Soviet test 184 (also designated K3) on October 22, 1962, which set fires and knocked out hundreds of miles of power lines in Kazakhstan. That, however, is a different anniversary.

7 thoughts on “Starfish Prime: The First Accidental Geomagnetic Storm

  1. Sixty years ago today the Cosmic Ray Research group at the University of Tasmania launched a balloon borne geiger counter from Hobart which detected an intense burst of gamma radiation from Starfish Prime fission product debris. The expanding radioactive plasma bubble temporarily breached the geomagnetic field above Johnston Island and injected electrically charged fission products along magnetic field lines into the Southern hemisphere atmosphere. (See Edwards and Reid, Journal of Geophysical Research 69(17):3607-3612 Sept. 1964). (Abstract on ResearchGate: Effects of nuclear explosion Starfish prime observed at Hobart Tasmania July 9 1962.). Also Nature: October 1962 Edwards et alia: Radiation enhancement following Johnston island thermonuclear explosion. (Abstract on ResearchGate).


  2. This is fascinating. I am a very amateur astronomy hobbyist whose main focus (pardon the pun) is astro photography. I am excited to learn of such events and phenomena. In 1962 I was 14 years old, just beginning my enchantment with space. I wish such events and discussion of them were more widely disseminated to the general public. As a psychologist, I work with many adolescents who have great interest in such things. I frequently refer them to Spaceweather to inspire them. Thank you for publishing this. I look forward to an article about the Russian November 1962 event anniversary.


  3. Find a copy of the documentary film, Nukes in Space. Excellent footage of Starfish Prime.
    Also research the early 80’s magazine article, The Chaos Factor, about the EMP effects of a nuclear blast in near space. This was long before our current home computer and cell phone culture. The effects on the electricity power grids would be catastrophic.


  4. Actually, measures are being quietly taken to mitigate the damage to the grid of an EMP event. Consider that there are three classes of EMP, low, medium, and high frequency. Low frequency events include solar storms. Medium frequency events are mostly lightning strikes and are local. High frequency events are what you get out of a nuclear weapon. The first two of these are standard material in electrical engineering colleges. Military aircraft are immunized against the high frequency events by such technologies as the MIL-STD-1553 and 1753 data bus. And gradually, our grid is being hardened against such an assault as well. True, an attack could be very destructive… but maybe not as catastrophic as some fearmongers claim.


    • Agreed. As an electrical engineer, I owned a company that provided engineering services to TV and radio broadcasters. The possibility of damage and lost air time by EMP’s has been studied in depth.
      The general conclusion was that equipment that can take a direct lightning hit and keep on going had nothing to fear from EMP’s. Broadcast equipment often takes multiple lightning hits in a single storm to no ill effect. It is built to take it.
      Airplanes, cars, electronic equipment in metal enclosures are in what is termed a Faraday Cage and are not usually susceptible to damage from EMP’s Also, modern satellites are radiation hardened.
      In an extremely bad CME (Coronal Mass Ejection) from the Sun, aimed at the Earth, there will be damage but it will not a doomsday scenario. If someone sends a nuke your way, you’ll have more things to worry about than the EMP!
      Professional journalism with integrity is a thing of the past. Many a time, I have been in a studio, only to have a news “star” ask me for details on technical subjects only to interrupt me and say “it needs to be more spectacular. Just a part of the “if it bleeds, it leads” reality of “news organizations” today.


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