On May 10 and 11, 2024, skies that rarely witness the aurora lit up with vivid ribbons of green and pink as far south as parts of the United States and Europe. The source of that celestial display was a super geomagnetic storm so powerful that scientists are still reckoning with what it revealed. Now, new research published in Science Advances shows that this storm—formally known as the "Gannon storm" or "Mother's Day storm"—gave humanity its first direct glimpse inside the charged particle belt encircling Earth, and what they found upended decades of scientific assumption.
The storm struck after a large sunspot fired a rapid series of powerful solar eruptions, with clouds of magnetized plasma merging as they hurtled toward Earth. It reached a minimum SYM-H index of −518 nanotesla, making it the second-largest geomagnetic storm recorded since 1981. The last comparable event was the November 2004 superstorm. But what made May 2024 truly historic was not just its size—it was the unprecedented data captured by Japan's Arase satellite.
Launched in 2016 and operated by the Japan Aerospace Exploration Agency (JAXA), Arase had been waiting more than seven years for an opportunity like this. The spacecraft carried specialized instruments designed to identify the mass and energy of detected ions, and when it crossed through the ring current—a vast belt of energized particles drifting thousands of kilometers above the equator—it finally delivered what scientists had long sought: direct measurements of ring current composition during a superstorm.
The findings were striking. "The data were clear—approximately 85% of ions were oxygen from Earth's own ionosphere," said Naritoshi Kitamura, lead author and designated assistant professor from the Institute for Space-Earth Environmental Research at Nagoya University. Scientists had debated whether the ring current primarily drew from solar wind or from Earth's own ionosphere, the electrically charged upper layer of our atmosphere. This storm proved that Earth was the dominant supplier by a landslide.
The dominance of these heavier ionospheric ions may have intensified the storm's magnetic disturbance and concentrated the ring current peak unusually close to our planet. Arase detected a 40% decrease in magnetic field intensity roughly 16,000 kilometers above Earth. Kitamura emphasized that understanding this ionospheric contribution could be essential for predicting future superstorms—events with real consequences beyond their beauty. "Some super or extreme geomagnetic storms are not just impressive light shows," he noted. "They pose radiation risks to spacecraft, disturb GPS signals and communications, and cause power outages."
The research team is now making a case for a proposed Japanese multisatellite mission to further investigate how ion supply processes work. For now, the May 2024 storm stands as both a reminder of the sun's formidable power and a milestone in humanity's ability to understand it—transforming a moment of cosmic upheaval into a breakthrough that could one day help protect the infrastructure our lives depend on.