Antimatter seems impossibly exotic, something that exists only in particle accelerators or in cosmic events many light-years away. But the next time there's a big thunderstorm, look up at the sky: you're looking at the creation of natural antimatter bursts.
NASA's Fermi Gamma-ray Space Telescope picked up on the antimatter by monitoring several recent thunderstorms. Lightning is known to produce what's known as a terrestrial gamma-ray flash, or TGF, which is basically a brief burst of gamma-rays. There are a few different ways to create gamma-rays, including the collision of an electron and its antimatter counterpart, the positron.
When these two particles annihilate each other, they create gamma-rays with energies of precisely 511,000 electron volts. Fermi can pick up on the specific energies of the gamma-rays, and it was able to find at least four of the 130 observed TGFs with that particular energy signature. This isn't a common phenomenon, then, but neither is it particularly rare, considering Fermi has only been watching the storms for about a year.
So how is the antimatter created in the first place? Thunderstorms possess electric fields at the tops of their systems, and particularly powerful storms are able to funnel huge swaths of electrons upwards at great speed. These electrons run into molecules, which alter their course and cause the electrons to emit gamma-rays.
Some of these gamma-rays, traveling at near the speed of light, then pass near an atomic nucleus, which cause the ray to turn into an electron and positron. The matter and antimatter pair then travel out into space along Earth's magnetic field. The entire process only takes a couple of milliseconds. Here's a handy guide to the entire process, courtesy of NASA. Click the image for a closer look:
Amazingly, we've only known that thunderstorms can create gamma-rays (not to mention x-rays) for about a year, so the realization that they can create antimatter as well would have been unimaginable as recently as 2009. Duke researcher Steven Cummer puts it simply:
"I think this is one of the most exciting discoveries in geoscience in a very long time. [It] seems like something straight out of science fiction."