August 29, 2014

23.01.11: A Hail of Anti-Matter?

Lightning (& antimatter?) as seen over Astroguyz HQ…

An anti-matter barrage may be underway high overhead. Recently, NASA scientists have released evidence that antimatter in the form of positron emission may be created right here on Earth during terrestrial thunderstorms. The evidence comes from the Fermi Gamma-ray Space Telescope, designed to monitor extra-galactic gamma-ray bursts. Since its launch in 2008, Fermi’s Gamma-ray Burst Monitor instrument has detected 130 of what are known as Terrestrial Gamma-ray Flashes, (TGF’s) generated by lightning. Occasionally, these gamma-ray bursts of energy strike an atmospheric molecule, ejecting a high energy electron and its antimatter cousin, a positron. These positrons then travel along magnetic field lines striking electrons on Fermi’s detectors and annihilating in a brief flash. These gamma ray annihilations aboard Fermi can reach energies of up to 511,000 electron volts and sometimes strike the spacecraft twice as they return along the magnetic field lines back towards Earth. Fermi can even see these bursts over the horizon, as happened in December 14th, 2009 during an active storm over Zambia. Up to 500 TGF’s are thought to occur each day.

Which begs the question; do these bursts strike other spacecraft in Low Earth Orbit? Will the Alpha Magnetic Spectrometer record similar annihilations once in service later this year aboard the International Space Station? It’s amazing to think that such a phenomenon as lightning is still poorly understood. Until the last decade or so, ghostly apparitions such as elves or sprites associated with lightning were doubted as spurious, and those who have seen them have questioned their sanity.

Positrons may seem exotic, but you have bathed in them if you’ve ever had a PET (Positron Emission Tomography) scan. The reason you do not spontaneously annihilate is that a target radionuclide tracer is used, and the amount of radiation used is non-ionizing… and remember, an electron in relation to the radius of an atom is tiny, and the chance interaction is exceedingly small. Mostly, were made of…nothing!  

It is rather sobering to think that something as mundane as a summer thunderstorm may have a deep cosmic connection, and it will be fascinating to follow the future discoveries by Fermi and the AMS of these elusive beasts. The farther we see out into the cosmos, the more we learn about ourselves and our own planet…     

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