Number 162 (Story #2), January 31, 1994 by Phillip F. Schewe and Ben Stein ATOM-BOMB SIZED METEOROID EXPLOSIONS in the Earth's atmosphere occur many times a year. In general, meteors will fragment upon entering the upper atmosphere because of friction. Smaller fragments will burn up but the larger ones may actually explode, at altitudes of 20 miles or so. Data from military satellites being made public for the first time reveal the scope of these meteoroid blasts: an average of 8 events a year were observed to have an energy equivalent to a small nuclear bomb, although the true occurrence may be 10 times larger. Scientists estimate that every 10 million years we should receive a catastrophic hit that would devastate life forms over much of the planet, much like the dinosaur-killing impact 65 million years ago. Much of the military data were originally gathered in an attempt to discriminate between meteoroid blasts and manmade nuclear explosions. (The New York Times, 25 Jan; Sky & Telescope, Feb 1994.)