Enigmatic bursts of high-energy gamma rays produced in Earth's atmosphere are surprisingly strong and frequent, satellite data suggest.
In the early 1990s, Earth-orbiting sensors originally designed to monitor sporadic flares of gamma rays from exotic sources such as black holes and neutron stars also detected the high-energy photons coming from a more mundane source—Earth's atmosphere. These terrestrial gamma-ray flashes (TGFs) were seen once every few weeks and lasted around a millisecond, says physicist David M. Smith of the University of California, Santa Cruz.
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