Thunderstorms have been caught producing one of the most mysterious substances in the universe: antimatter. The discovery could further our understanding of the murky physics of lightning production.

NASA’s Fermi spacecraft seems to have been hit by the antimatter counterpart to electrons – positrons – emanating from thunderstorms on Earth.

Thunderstorms emit gamma rays, known as terrestrial gamma ray flashes (TGFs), although what causes them is still a mystery. While observing these flashes, Fermi also detected a separate set of gamma rays with an energy of 511 kiloelectronvolts. These rays were produced when a barrage of positrons struck the spacecraft’s detectors and were annihilated by making contact with electrons there.

“These signals are the first direct evidence that thunderstorms make antimatter particle beams,” said Michael Briggs, a member of the Fermi team at the University of Alabama in Huntsville.


Antimatter source

Where does the antimatter come from? The Fermi scientists believe that gamma rays produced in thunderstorms may spawn positrons and electrons when they hit atoms in Earth’s atmosphere.

Lightning and TGFs are both thought to be connected to strong electric fields in storm clouds, but the exact processes that trigger these phenomena are not well understood, nor is their relationship with each other.

“It’s a little bit premature to say exactly what the implications of this [discovery] are going to be going forward, but I’m very confident that it’s an important piece of the puzzle,” says Steven Cummer of Duke University in Durham, North Carolina, who was not involved in the work.

Briggs presented the discovery yesterday at a meeting of the American Astronomical Society in Seattle, Washington. The research will be published in Geophysical Research Letters.

When this article was first posted, the second sentence of the fifth paragraph read: “The Fermi scientists believe that TGFs produced in thunderstorms may convert atoms in Earth’s atmosphere into positrons and electrons.”