We're in a cloudy spell this week in my part of the world. Last night you could barely see the outline of the moon through snow and near overcast. My older daughter and I made for a sad sight as we stood on the deck trying to determine the moon's phase for her class project as snowflakes fell on our eyelashes.
Winter clouds are often sheets of solid gray that stay in place the entire day. I'll always check at night for openings or sucker holes that might provide the opportunity to bring out the telescope or go for a walk in the moonlight with the only companion in the immediate family who doesn't mind the cold - my dog.
Not all clouds are featureless backdrops to gray days. Just look at Andrew Kirk's photo of the sculpted lenticular clouds that appear regularly over the Sierras. Some of the most exciting clouds and one of my favorites are the towering cumulonimbus thunderheads that sizzle with lightning. At any given time, there are some 1800 thunderstorms happening around the planet.
This week Michael Briggs, a University of Alabama-Huntsville researcher, announced his team had detected beams of antimatter above thunderstorms using NASA's orbiting Fermi Gamma-ray telescope . First some background. Gamma rays are the most energetic form of light known to exist. They're produced in nuclear explosions, solar flares, supernovas, black holes and neutron stars and can kill living cells. Lucky for life, our atmosphere absorbs all those nasty gamma ray photons, protecting us from certain electromagnetic death.
But wait. It turns out that lightning can produce gamma rays too called terrestrial gamma ray flashes or TGFs. Scientists estimate 500 TGFs occur in storms every day. Fermi was designed to study cosmic sources but its detectors have picked up 130 TGFs since 2008.
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Now here's where the antimatter comes in. According to Einstein's famous 'E=mc squared' equation, matter is nothing more than a highly condensed form of energy. Gamma rays of high enough energy can transform into pairs of particles. One of them is the electron , familiar to most of us as electricity. Rub your stocking feet on the floor and touch a doorknob and you'll know just what electrons feel like.
The other particle is a positron, identical to the electron but having a positive instead of a negative charge. Positrons are the antimatter counterpart of the electron. Put an electron and a positron together and they annihilate one another in a burst of pure energy, gamma ray energy to be exact. There are lots of antiparticles, all identical to their regular matter counterparts but having the opposite charge.
Strong electric fields at the tops of thunderstorms can send a burst of electrons at nearly the speed of light high into the atmosphere. When they're deflected by air molecules there, they give off gamma rays and we see a TGF. Occasionally the cascading electrons can produce so many gamma rays that they convert into a swarm of electrons and positrons and follow the Earth's magnetic field right out into space. There the positrons slam against electrons in the Fermi scope and annihilate in a burst of gamma rays that the detector can "see".
All of this goes to show you never know what you might discover when you build an instrument made for a particular purpose. Fermi, designed to peer into the most violent events in the depths of space, found something just as bizarre right here at home. Who'd a thunk?
To learn more about the antimatter process discovered by Fermi, check out this step-by-step illustrated pdf . And the next time you go out in a storm, don't forget to wear your tin hat. On second thought ...
