Thunderstorms generate what may be nature’s most impressive displays: lightning. And there’s plenty of it; lightning strikes Earth millions of times every day.

Although lightning is common, it’s also mysterious. The electric fields inside clouds don’t appear to be strong enough to power lightning. So for the past 90 years, scientists have pondered whether it might have a cosmic origin – cosmic rays – particles that ram into Earth’s atmosphere at almost the speed of light. Many of them come from the Sun. But the most powerful come from exploding stars, the gas around black holes, and other powerful objects in deep space.

When a cosmic-ray particle hits an atom or molecule in the upper atmosphere, it creates a shower of other particles. And it’s these particles that might then zip through clouds, creating lightning.

A study published earlier this year seems to affirm this idea. Scientists studied a thunderstorm over New Mexico with a sophisticated array of radio antennas. They traced more than 300 strikes from beginning to end, at intervals of less than a thousandth of a second.

Among other things, the radio waves revealed that the bolts weren’t moving the way they should if they’d been sparked by the clouds themselves. Instead, the lightning seemed to be triggered by something coming from beyond Earth: cosmic rays.

Script by Damond Benningfield