The Strongest Solar Storm in 20 Years Was Mostly Harmless, but We May Not Be So Lucky Next Time

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For years, we have been warned about impending doom from the sun. If pointed in our direction, powerful eruptions of radiation and plasma from our star can strike our planet to supercharge Earth's atmosphere and magnetic field, effectively hitting a global "reset" button on much of our modern technology. A sufficiently intense bombardment could raise a geomagnetic storm that would push satellites out of orbit, short out submarine cables that suture together the Internet and plunge the world into darkness with massive blackouts from collapsed power grids. Yet this past weekend, when one of the strongest solar outbursts in 20 years blasted our planet, we managed to emerge unscathed thanks to years of careful public and private planning. The storm has ebbed, although the solar region that sparked it has since spat out additional monstrous flares—fortunately no longer targeted at Earth because of the sun's spin. But while we've passed our biggest test yet, experts say now is not the time to let down our guard: the question of more cataclysmic solar activity isn't a matter of "if" but "when."

"This is a success story," says Shawn Dahl, a space weather forecaster at the National Oceanic and Atmospheric Administration's Space Weather Prediction Center (SWPC) in Boulder, Colo., but the weekend's storm was "nowhere close" to the strength of more powerful known historical events. Is it time to put our feet up? "Heck no," he says.

On May 8, after ground- and space-based telescopes detected multiple explosive outbursts from the sun headed for Earth, the SWPC issued a warning of an imminent severe space weather event. At least seven of these outbursts, known as coronal mass ejections, or CMEs, walloped our planet with billions of tons of solar plasma—an interplanetary punch that left Earth's magnetic field ringing and made the upper atmosphere swell, almost as if bruised. The resulting geomagnetic storm was the most severe since 2003. It posed potentially grave dangers to global infrastructure while also bathing much of the world in achingly beautiful auroral displays.

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At present, it's difficult to say just how close we came to catastrophe because many companies—from grid controllers to satellite operators—do not like to reveal information on how a geomagnetic storm affected them, says Daniel Welling, a climate and space scientist at the University of Michigan. "They don't want to look like they're vulnerable," he says. "Satellite operators have to insure their spacecraft, and that can be very expensive." Yet various scattered reports are already offering some insight into the storm's disruptive effects. Flight trackers showed airlines rerouting planes to avoid Earth's poles, where crews and passengers would have been exposed to worrisome spikes in cosmic radiation from the storm. Transpower, New Zealand's state-owned enterprise running that nation's electric power, said in a statement that it had preemptively "switched off some circuits across the country on Saturday [May 11]," and as a result, there was "no impact on New Zealand's electricity supply." In Minnesota, the firm Minnesota Power opened capacitor banks to deal with possible effects from the storm. Similar precautions were likely taken at other power grids around the world, too, although the lack of information makes it "tremendously" difficult to know how effective those measures were, Welling says.

Geomagnetic storms can also play havoc with signals from GPS satellites, and multiple farmers reported issues with GPS-guided farming equipment over the weekend. In South Dakota, one farmer's tractor started driving in circles during the storm, and multiple farmers reported outages on social media. "Our GPS on both the planter and the strip tiller were absolutely bonkers today," one commenter wrote on Reddit. "I saw this post and looked ... no GPS," said another. LandMark Implement, a John Deere dealership based in Nebraska and Kansas, texted its customers an advisory to "turn off" GPS devices on their farming equipment. "The base stations were sending out corrections that have been affected by the geomagnetic storm and were causing drastic shifts in the field," the company noted in an online post. LandMark declined to comment further when contacted.

The storm posed hazards in space as well. Seven astronauts on the International Space Station were mostly safe from the storm's effects, NASA said, but did have to take some precautions. "The crew was told to avoid lower-shielded areas of the space station out of an abundance of caution," says Sandra Jones, a spokesperson for NASA's Johnson Space Center. "Certain areas provide less protection from radiation, such as the air lock, while other areas, such as crew quarters, provide enhanced protection. The crew was never in any danger, and the energy levels have since decreased." Other satellite operators experienced greater difficulties. One company in the U.K., Sen, which streams 4K video from a satellite in low-Earth orbit, chose to power down its spacecraft for four days to prevent any damage from the storm, such as fried circuit boards or electronic failures. "It was in an idle mode," says Marcin Bujar, spacecraft operations lead at Sen. "We just kept the bare minimum on—the flight computer and radio receiver." This prevented the satellite from carrying out some tasks, including planned observations of flooding in South America and wildfires in Canada. "It definitely had an impact," Bujar says.

Larger groups of satellites, such as SpaceX's 6,000-strong Starlink mega constellation that beams the Internet to Earth from low-Earth orbit, were affected too, although the full impact is unknown. "It's always a scary time for satellite operators when there's a big storm," says Jonathan McDowell, an astronomer at the Center for Astrophysics | Harvard & Smithsonian. Elon Musk, SpaceX's CEO, merely noted on X that the satellites were "under a lot of pressure" but "holding up so far." In February 2022 the company lost 38 freshly launched Starlink satellites after those spacecraft prematurely reentered Earth's suddenly swollen atmosphere because of excess drag from a geomagnetic storm, but such issues seem to have been avoided this time: another Starlink launch proceeded as planned over the weekend, successfully deploying 23 satellites into a higher orbit less susceptible to such effects. Sangeetha Jyothi, a computer scientist at the University of California, Irvine, says the geomagnetic storm does seem to have increased delays in Starlink satellites communicating with the ground, though. "We can see some impact, but it was not disastrous," she says. For ground-based Internet infrastructure supplied through submarine cables, the storm was "not strong enough" to cause any issues, she adds.

Atmospheric swelling caused by the solar storm proved especially notable on the Hubble Space Telescope, which despite orbiting hundreds of kilometers above our planet still descends slowly earthward because of drag. The storm doubled Hubble's rate of orbital decay to "about 80 meters a day instead of 40 meters a day," McDowell says. Claire Andreoli, a spokesperson at NASA's Goddard Space Flight Center, told Scientific American that Hubble is currently estimated to burn up in Earth's atmosphere "in the mid-2030s." Without boosts from other spacecraft, however, further bouts of solar activity could make Hubble's swan song come years earlier, lessening the amount of time that astronomers have with one of the most advanced telescopes ever built. "It's kind of unfortunate to be at the whims of the sun," says JJ Hermes, an astronomer at Boston University.

Overall, however, our planet seems to have mostly survived its latest solar tirade—society, and civilization as a whole, have not come to a premature end. "I was a bit surprised how much of a nothing-burger it was," McDowell says. But don't pop the champagne just yet. While big, this storm is not the extent of what we can expect to face in the coming decades—or perhaps much sooner as the sun heads toward the peak of its 11-year activity cycle in 2025. Measuring the strength of any given geomagnetic storm is difficult because there are many factors at play on Earth and in space, but a crude number can be given. Geomagnetic storm strengths can be expressed in nanoteslas (nT) based on measurements of Earth's magnetic field, which has a baseline of -20 nT. The most powerful recorded geomagnetic storms in history, the Carrington Event of 1859 and the New York Railroad Storm of 1921, both registered at around -900 nT, although the former was potentially as high as -1,750 nT. Last weekend's storm came in at a more sedate -412 nT, Dahl says. "Even though this was historic, it was nowhere close to the level of 1921 and 1859," he says.

Over the past decade, much has been made of the potential threat of solar storms, thanks to work by the SWPC and other organizations. In 2020 the U.S. government passed the Promoting Research and Observations of Space Weather to Improve the Forecasting of Tomorrow (PROSWIFT) Act to "develop formal mechanisms to transition space weather research models and capabilities to operations," NOAA said in a 2023 news release. That has been hugely beneficial, Dahl says, to "make sure that space weather is treated much more respectfully. We are much more prepared than we were 10 years ago." The outcome, in the U.S. and abroad, has bolstered our space weather forecasts, giving us our best warnings yet on the impending danger from a solar barrage. Last weekend's solar storm shows that this diligent preparatory work has not been in vain. This time around, everything went according to plan. But when a much stronger Carrington-esque storm hits, will we be ready? "The sun is a powerful enemy," McDowell says. "We haven't seen the worst it can do."