A NASA space telescope hunting for the most powerful explosions in the universe is turning its eye on Earth to hunt for tiny flashes of radiation to determine if they pose a rare, but deadly, threat to high-flying commercial airliners. NASA's Fermi Gamma-Ray Space Telescope has joined the search for mysterious gamma-ray flashes above thunderstorms which are ultra-brief, but could be a concern for air travelers, researchers said. Just one millisecond blast of the so-called terrestrial gamma-ray flashes (TGFs) could expose passengers and crew aboard a nearby jet airliner to the same level of radiation as 400 chest X-rays, according...