When you buy through links on our articles, Future and its syndication partners may earn a commission.A powerful solar flare erupted from the sun on Nov. 11, unleashing a stream of super-charged protons that increased radiation levels around Earth to a bi-decadal high. | Credit: NOAA Space Weather Prediction CenterRadiation levels in Earth’s atmosphere rose to the highest level in nearly two decades in November after a rare solar super-flare pummeled the planet with high-speed particles from the sun. The solar flare, an extremely bright flash of light, erupted from the AR4274 sunspot on Nov. 11. Classified as a powerful X5.1, the flare followed a series of milder flares and coronal mass ejections (CMEs) that treated skywatchers to mesmerizing aurora displays as far south as Florida.Apart from being the most intense solar flare of 2025 to date, the X-class flare also unleashed a stream of high-speed protons and other energetic particles toward our planet, something very few solar flares do. This year, about 20 X-flares hit Earth — but only the one from Nov. 11 was accompanied by the high-speed proton stream. That day, when Earth-based monitors began showing elevated radiation levels, researchers released several stratospheric balloons with sensors to see how radiation levels evolved throughout the atmosphere.AdvertisementAdvertisementAdvertisementAdvertisementThey found that at altitudes where most commercial aircraft travel — around 40,000 feet (12 kilometers) — radiation briefly rose to levels ten times higher than the normal cosmic-ray-related background. If a pregnant woman were to be exposed to such radiation levels for more than 12 hours, she would have exceeded a limit officially considered as safe for a fetus. Fortunately in this case, the worst was over in about two hours, according to Benjamin Clewer, a space weather researcher at the University of Surrey in the U.K. “Typically, these events peak right at the beginning and that might only last about half an hour,” Clewer told Space.com. “In this case, the event officially finished in 15 hours, but only the first two hours were significant.”CMEs also expel clouds of energetic particles into interplanetary space. Those particles, contained in clouds of magnetized plasma, take days to reach the planet. The protons unleashed by a solar flare, however, travel at nearly the speed of light and arrive within minutes, Clewer said.When those energetic protons hit the top of Earth’s atmosphere, they interact with molecules of air, triggering showers of secondary, less energetic particles including neutrons, muons and electrons. Such particles constantly trickle down onto Earth’s surface as a result of the battering our planet experiences due to cosmic rays that arrive from the most distant parts of the ga …
