On May 10, 2024, the strongest solar storm in 20 years sparked auroras on Earth that were visible as far south as Florida. It also created two new bands of radiation around the planet, researchers report in the February JGR Space Physics.
Earth is encircled by two donut-shaped bands of particles called the Van Allen belts, where energetic protons and electrons from the sun are trapped by the planet’s magnetic field. These permanent belts are split into an inner one between about 6,000 and 12,000 kilometers above Earth’s surface, and an outer one between 25,000 and 45,000 kilometers.
Between the bands is a zone called a slot region. This region is usually empty, but a temporary third belt formed there for about four weeks in 2012, also triggered by a solar storm.
The bands in 2024 formed in the same region but were surprisingly persistent.
“These stayed for months, until another even smaller storm perturbed them,” says space scientist Xinlin Li of the University of Colorado Boulder.
One band, made mostly of electrons, lasted about three months. The other, primarily composed of protons, could last for close to a year, Li says.
Li and colleagues had launched a tiny satellite in April 2023 to investigate how the inner radiation belt forms and behaves. The satellite worked well for a year, then suddenly went quiet in April 2024.
“We still can’t identify exactly what caused it,” Li says. “It just went to sleep.”
When the solar storm happened a month later, Li was distraught. “I thought, ‘Oh, why?’” he says. “People were excited to see the aurora in Boulder, and I didn’t care.” He just wished the satellite had been there to capture it.
But as suddenly as it shut off, the satellite came back to life in June. The new belts were clearly present. “It was very obvious there was something so different,” Li says.
Long-lived belts of radiation could be dangerous to satellites and astronauts. Many satellites bound for geostationary orbits spend some time in the slot zone first and could be exposed to more charged particles than they were designed to handle. Engineers will have to account for the possibility of extra radiation belts in the future, Li says.