Antimatter particles beamed into space by thunderstorms

Thunderstorms on Earth are creating antimatter particles that are beamed into space. The antimatter is in the form of positrons, the anti equivalent of electrons, and has been detected by the NASA gamma ray telescope, Fermi, which orbits the Earth 550 km above the surface.

The phenomenon were first noticed in 1994, using Fermi’s predecessor, the Compton Gamma Ray Observatory. Known as terrestrial gamma ray flashes, or TGFs, the origin of these mysterious gamma rays was previously unknown.

Normally, gamma rays originate from the most energetic objects in the Universe, such as a supernova, so it was quite unexpected to discover them being beamed from the Earth.

However, it turns out the telescope was picking up gamma rays that were not actually originating from the Earth, but were being created inside the detector itself. It all revolves around the anti-matter particles, positrons. They are identical to electrons but have the opposite charge. When a positron and electron meet, they combine to produce a high-energy burst of gamma rays, and destroy themselves completely in the process. This is what was happening inside the telescope, which was the perfect place to detect the characteristic gamma rays this annihilation produced. Positrons were entering the detector and being annihilated with the electrons from inside the satellite. This annihilation releases photons with a specific energy – 511keV – in the form of gamma rays, which were then detected.

It would appear that lightning within the Earth’s atmosphere was producing the positrons, but exactly how is still unknown. Michael Briggs, from the Gamma Ray Astronomy Group at the University of Alabama in Huntsville, said: “We really don’t know what’s special about the lightning, how it’s different, or if it is different from other lightning.”

The emitted positrons are channelled by the Earth’s magnetic field several thousands of kilometres away from the original storm shooting them out of the Earth’s atmosphere.

A good example of this occurred on December 14^th 2009. Fermi was positioned above the Sahara Desert in Africa, an area not well known for its thunderstorms, and yet the satellite detected gamma rays coming from a storm. In fact, the detector was picking up the signature of a lightning storm in Zambia - 4000km away. “The positrons followed the magnetic field lines of the Earth to Fermi,” explained Briggs. “Zambia was over the horizon, so there is no way that Fermi could have seen gamma rays from the TGF.”

Remarkably little is known about the lightning we see on Earth. There are hundreds of storms every day all over the globe, and yet the processes that create these positrons are completely unknown. It is astonishing to think that there is enough energy in a flash of lightning to create and accelerate beams of antimatter particles several hundred kilometres into near-Earth space. And even more astonishing to think we only just found out.