A team of researchers at the University of Colorado Boulder, led by undergraduate Max Feinland, has revealed a surprising link between Earth's lightning storms and space weather. The study found that lightning can eject high-energy "extra-hot" electrons from the inner radiation belt, a region of charged particles surrounding Earth. This new discovery could help protect satellites and astronauts from hazardous radiation exposure.
"These particles are the scary ones or what some people call 'killer electrons,'" said Feinland, who graduated in aerospace engineering at CU Boulder in 2024. "They can penetrate metal on satellites, hit circuit boards and can be carcinogenic if they hit a person in space."
The inner and outer radiation belts, which are formed by Earth's magnetic field, act as barriers trapping charged particles from the sun. The inner belt begins about 600 miles above Earth, while the outer belt starts roughly at 12,000 miles. Researchers have known that electrons can descend from the outer belt toward Earth, but Feinland and his team are the first to detect similar activity in the inner belt.
Lauren Blum, a co-author and assistant professor at CU Boulder's Laboratory for Atmospheric and Space Physics, explained, "Space weather is really driven both from above and below."
When lightning strikes on Earth, it generates radio waves that can travel into space and collide with electrons in the radiation belts, knocking them loose. This phenomenon, called "lightning-induced electron precipitation," was previously only associated with lower-energy electrons, but Feinland's work uncovered evidence of high-energy particles behaving similarly.
Feinland discovered this while analyzing data from NASA's SAMPEX satellite. He identified 45 instances of high-energy electrons in the inner belt between 1996 and 2006, many occurring shortly after lightning strikes in North America.
Blum likened the process to a game of pinball, where radio waves from lightning strikes knock electrons in the inner belt, causing them to bounce between Earth's hemispheres. With each bounce, some electrons fall into the atmosphere.
"You have a big blob of electrons that bounces, and then returns and bounces again," Blum said. "You'll see this initial signal, and it will decay away."
The research team hopes to better understand these events, which may become more common during periods of high solar activity, and develop ways to predict them to safeguard orbiting spacecraft and astronauts.
"I didn't even realize how much I liked research until I got to do this project," Feinland said.
Research Report:Lightning-induced relativistic electron precipitation from the inner radiation belt
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