A powerful solar storm in May 2024 compressed Earth's plasmasphere and allowed high-energy electrons to cross a region that normally acts as a radiation barrier, according to a study published in Geophysical Research Letters on October 26, 2026. Researchers found that electron levels inside the planet's inner radiation belt rose to more than 5,000 times their pre-storm levels, reaching energies of around three megaelectronvolts.
The findings challenge previous scientific understanding of Earth's magnetic environment and highlight potential risks to satellites, spacecraft and astronauts.
Earth is surrounded by two doughnut-shaped regions of electrically charged particles known as the Van Allen radiation belts, which are held in place by the planet's magnetic field.
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For years, scientists believed that the inner radiation belt acted as an almost impenetrable barrier, preventing highly energetic electrons, commonly called 'killer electrons', from entering the region closer to Earth.
May 2024 Solar Storm Breached the Radiation Barrier
This finding traces back to a May 2024 G5 geomagnetic storm, the most extreme rating for space weather. Erupted from powerful solar flares and coronal mass ejections, the storm streamed energetic charged particles straight toward Earth.
Japan's Arase satellite, which has monitored Earth's radiation belts since 2017, detected the findings.
The increase occurred gradually over approximately 24 hours, with lower-energy particles appearing first, followed by increasingly energetic electrons. This suggested that the particles were accelerated locally within the inner radiation belt rather than simply moving inwards from the outer belt.
How Did the Solar Storm Accelerate Electrons?
The reduction in cold plasma within the plasmasphere created favourable conditions for electromagnetic waves known as 'chorus waves' to accelerate electrons to extremely high energies.
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These highly energetic electrons can travel at speeds close to that of light and penetrate satellite shielding, potentially damaging sensitive electronic equipment and shortening spacecraft lifespans. They can also increase radiation exposure risks for astronauts.
