NASA’s space-based Fermi Gama Ray Telescope has provided evidence that thunderstorms on Earth generate antimatter streams. The team at the University of Alabama in Huntsville reported the results this past Monday during the American Astronomical Society meeting in Seattle.
Antimatter can be created in particle accelerators and occurs naturally in places like the Van Allen Belts around the Earth, and the similar belts around other planets like Jupiter, as well as being generated by radioactive beta-decay — all in extremely small quantities. This is the first time there’s been evidence that terrestrial lightning generates antimatter.
According to a story on NASA.gov:
Scientists think the antimatter particles were formed in a terrestrial gamma-ray flash (TGF), a brief burst produced inside thunderstorms and shown to be associated with lightning. It is estimated that about 500 TGFs occur daily worldwide, but most go undetected.
The way it works is this:
Fermi is designed to monitor gamma rays, and orbits along the Earth’s magnetic field.
High-altitude lightning in thunderstorms drive electrons upwards at almost the speed of light.
Sometimes these electrons collide with atoms, which then emit high-energy photons.
Rarely, these photons then strike a second atom that emits two particles — an electron and its antimatter counterpart, the positron.
Because both of these particles are charged, they are drawn along the magnetic field, which in this case led them straight into the maw of the Fermi telescope even though they’re not at all what Fermi was looking for.
In this case, the positrons then encountered electrons — that is to say, “normal matter” — within the Fermi telescope itself.
When antimatter particles hit their normal-matter counterparts, the particles annihilate each other, emitting gamma rays, and that’s what Fermi detected.
Or, as the sort of mind-bending video accompanying the NASA story puts it, “For an instant Fermi became a gamma ray source and set off its own detectors.”
Said video is short and well worth watching, as it makes the events clearer than I ever could. Plus there’s cool spaceship animations and stuffs.
The incident described in the video occurred in December, 2009 when Fermi was over Egypt, but the storm producing the positrons was over Zambia, and thus over the horizon. Though lightning strikes can produce gamma rays, they travel line-of-sight. Therefore, the great distance between Fermi and the storm means that the detected gamma rays couldn’t have come directly from the storm