Earth's own upper atmosphere supplied roughly 85% of the charged particles fueling the extreme May 2024 solar superstorm, according to a Nagoya University-led study reported on November 13, 2026. Using direct measurements from Japan's Arase satellite, researchers found heavy oxygen ions from Earth's ionosphere far outnumbered solar wind particles. The findings were published in Science Advances.
On May 10 and 11, 2024, successive solar eruptions slammed into Earth's magnetosphere, triggering the Gannon superstorm. The event drove the SYM-H geomagnetic index down to minus 518 nanotesla, the second-largest disturbance recorded since 1981, and vivid auroras lit night skies closer to the equator than usual. For decades, space physicists debated where ring current ions originate during extreme storms. Both the solar wind and Earth's ionosphere contribute under normal conditions; because dense solar wind streams triggered the May 2024 event, many scientists expected solar particles to dominate.
Launched in 2016 and operated by JAXA, Arase flew directly through Earth's ring current near the storm's onset and peak, and its onboard sensors measured both the mass and energy of individual ions. Lead author Naritoshi Kitamura of Nagoya University said the data showed approximately 85% of ions were oxygen from Earth's own ionosphere and that solar wind protons played only a minor role. Because terrestrial oxygen ions are far heavier than solar wind protons, their surge likely intensified the storm and pulled the peak ring current unusually close to Earth.
Near the storm's height, Arase recorded a 40% drop in magnetic field intensity roughly 16,000 kilometers above the planet. Instruments simultaneously observed a sharp decline in energetic electrons circulating in the same region. Researchers suspect the severely weakened magnetic field pushed those electrons off their normal orbits; further study will be required to confirm that link, as scientists have not yet established direct causation.
