A thunderstorm can do more than make lightning: it can briefly produce antimatter. The particles are positrons, the antimatter counterparts of electrons. They form when powerful electrical fields in a storm set off a chain of high-energy events. Scientists have detected the telltale signals both from orbit and near the ground.
Inside a storm cloud, strong electrical fields can accelerate electrons to extraordinary speeds. As those electrons pass through air, they release gamma rays—an energetic form of light—in bursts called terrestrial gamma-ray flashes. Some gamma rays can then produce a pair of particles: an electron and a positron. NASA’s explanation of thunderstorm gamma rays describes how a familiar weather event can generate something that sounds like science fiction.
How do researchers know the antimatter is there? When a positron meets an ordinary electron, the two annihilate, releasing gamma rays with a distinctive energy. NASA’s Fermi Gamma-ray Space Telescope has detected that signature from beams associated with thunderstorms. Some particles even traveled upward far enough for the spacecraft to encounter them, showing that the process is not confined to the cloud where it begins.
There is evidence from below the clouds, too. During a February 2017 thunderstorm in Japan, ground-based instruments recorded signals after lightning that researchers identified as evidence of positrons. Their published findings on lightning-triggered reactions describe a different route to antimatter: energetic gamma rays struck atoms in the air, creating unstable forms of nitrogen that later emitted positrons.
This does not mean storms leave behind a stash of antimatter. Positrons disappear when they encounter electrons. The surprise is that something as familiar as a thunderstorm can briefly act like a natural particle accelerator. For more unexpected discoveries, explore these science facts.