When a huge solar storm hit Earth in May 2024, the material that fed the surge of electrically charged particles around the planet came mostly from Earth itself. That is the finding of a Nagoya University-led team, which analyzed data from a Japanese satellite as the storm unfolded.
The researchers report that about 85% of the ions in the storm’s “ring current,” a doughnut of charged particles circling Earth, were oxygen that had escaped from the upper atmosphere. The study appears in Science Advances.
What They Found
The storm was one of the strongest on record. The team’s measure of the disturbance, an index called SYM-H, dropped to a minimum of −518 nanoteslas, the second-largest since 1981, according to the university’s summary. Near the storm’s peak, Earth’s magnetic field weakened by about 40% at an altitude of roughly 16,000 kilometers (about 10,000 miles).
Japan’s Arase satellite measured the mass and energy of individual ions during the event. Lead author Naritoshi Kitamura said it was “the first simultaneous observation of ring current ions and solar wind during a storm this large.”
Why It Matters
Big geomagnetic storms can disturb satellites, radio communications and power grids. Knowing what the ring current is made of helps scientists model how a storm builds and how Earth’s own atmosphere may feed it. The authors suggest the findings could eventually help forecasting, though they do not claim to have shown that yet.
For readers who follow space weather, the takeaway is that Earth is not just a target. Oxygen is lifted from the ionosphere during a storm and ends up among the particles that circle the planet, which is a feedback loop forecasters have long suspected but rarely caught in such detail. The same ring current is what weakens the magnetic field measured at the ground, which is why storms like this can light up auroras far from the poles.
The Catch
This is one storm, observed by one satellite. The team said it has not determined whether the deformation of the magnetic field directly caused the drop in energetic electrons, and more research is needed. A proposed Japanese mission mentioned in the release is still a proposal.
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