### Discovery Links Lightning to Space Weather, Unveils Radiation Threat to Satellites

Researchers from the University of Colorado Boulder have unearthed a fascinating relationship between lightning storms on Earth and space weather. The discovery, led by undergraduate aerospace engineering student Max Feinland, has revealed that lightning can release exceptionally high-energy electrons, dubbed "extra-hot" electrons, from Earth's inner radiation belt. This breakthrough could prove critical in shielding satellites and astronauts from potentially hazardous radiation in space.

These "killer electrons," as described by Feinland, are particularly concerning because they can penetrate satellite metal, damage circuitry, and pose carcinogenic risks to humans in space. "This is one kind of downpour you don't want to get caught in," Feinland remarked. His team's findings were published on October 8 in the journal *Nature Communications*.

Earth is surrounded by radiation belts that are formed by its magnetic field, explained Lauren Blum, an assistant professor at CU Boulder's Laboratory for Atmospheric and Space Physics (LASP). The belts consist of an inner belt starting 600 miles from Earth and an outer belt beginning around 12,000 miles away. These regions act as barriers, capturing charged particles from the sun and protecting our planet. While scientists have known about electrons falling from the outer belt, this study marks the first observation of similar activity from the inner belt.

When a lightning bolt occurs on Earth, it emits radio waves that travel into space. These waves can collide with electrons in the belts, knocking them free and causing what is known as "lightning-induced electron precipitation." This process, much like shaking an umbrella to remove rain, can influence our atmosphere's chemistry.

Prior to this study, only lower-energy "colder" electrons were directly measured falling from the inner belt. Unexpectedly, Feinland discovered clumps of high-energy electrons while analyzing data from NASA’s decommissioned Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite. “Some literature suggests that there aren’t any high-energy electrons in the inner belt at all,” Feinland noted.

Over a decade of data from 1996 to 2006 provided 45 instances of these high-energy electron surges. Feinland then compared these events with lightning strike records in North America and found a correlation — some electron spikes occurred less than a second after lightning strikes.

The phenomenon appears akin to a cosmic pinball game: radio waves from a lightning strike send electrons bouncing between Earth’s hemispheres within 0.2 seconds, causing some to drop into the atmosphere. This newfound knowledge opens avenues for predicting these events, potentially safeguarding people and technology in orbit during high solar activity periods.

Other contributors to this groundbreaking study include Robert Marshall at CU Boulder, Longzhi Gan from Boston University, Mykhaylo Shumko from Johns Hopkins University Applied Physics Laboratory, and Mark Looper from The Aerospace Corporation. More insights can be found in their publication in *Nature Communications*.