In a new study, scientists have found that airplane passengers flying near thunderstorms could be exposed to dangerously high levels of radiation in the form of terrestrial gamma ray flashes, which is equal to 400 chest x-rays.
In space gamma rays-the most energetic forms of light-are created by violent events, such as supernovae, and powerful objects, such as neutron stars.
Scientists have known for decades that thunderstorms on Earth can also create gamma rays, possibly during lightning production.
Storms that make gamma rays usually hover about 9 miles (15 kilometers) above Earth, about the same altitude at which many commercial planes fly.
According to a report in National Geographic News, the new study shows that just one of these terrestrial gamma ray flashes, or TGFs, can equal the radiation dosage of about 400 chest x-rays-creating potential hazards for frequent flyers.
Terrestrial gamma ray flashes were accidentally discovered in the 1990s, when space telescopes designed to study cosmic gamma ray sources began detecting unexpected gamma rays coming from the direction of Earth.
Unlike cosmic gamma ray bursts, which typically last a few seconds, TFGs last only about one to two milliseconds.
"That's how you can recognize them immediately" as Earth-based, rather than cosmic, gamma rays, said study co-author Joseph Dwyer, a space scientist at the Florida Institute of Technology.
"You can think of a cosmic gamma ray burst as someone switching on a light, leaving it on for a bit, and turning it off. A terrestrial gamma ray flash is more like a strobe light-very brief and very bright," he added.
The amount of danger TGFs pose to airplane travelers is still unknown, because scientists aren't sure exactly where TGFs originate inside a thundercloud or how big the TGF formation regions are.
"If (the source region) is big, it's more diffuse, and you don't get as many gamma rays hitting you," Dwyer said. "If it's compact, the dose is more concentrated," he added.
Also, if TGFs originate near the tops of thunderclouds and propagate upward, airline passengers cruising below the clouds should be safe.
If further research proves that terrestrial gamma ray flashes are a threat, there's very little airlines can do to protect passengers.
"These things are so penetrating that you would need quite a bit of lead to have any chance of stopping them," Dwyer said.