Linda Billings and JPL personnel report that it happens all the time, i.e., small asteroids impact Earth atmosphere weekly or so. Small asteroids near Earth, with sizes of only about a meter, hit the atmosphere and disintegrate with surprising frequency - around every other week, new data show. Data gathered by U.S. government sensors and released to NASA for use by the science community reveal that these small impact events are frequent and random. A map of these small impact events - known as fireballs or bolides - recently released by NASA shows the frequency and approximate energy released by bolide events detected from 1994 through 2013. It dwarfs a data-base of small impacts based on infrasound detections released last fall, but it does not contain all fireballs - objects less than a meter in size - that impacted the Earth during this period. The largest impact energy recorded during this 20-year interval was the recent daytime Chelyabinsk event - 440,000 - 500,000 tons of TNT - recorded over central Russia on February 15, 2013. This small asteroid that exploded in the atmosphere near Chelyabinsk, Russia was about 20 meters in size before it hit the Earth. While that impact focused public attention on the potential hazards of NEO impacts with Earth, space scientists have long known that such events are just a part of geologic history of Earth. Meteor Crater near Winslow, Arizona, is evidence of the impact with surface of a 50-meter asteroid about 50,000 years ago. Impact of the metal-rich object released energy equivalent to a 10-megaton explosion and formed a 1.2 kilometer-diameter crater. Scientists have identified several dozen impact craters in North America alone, most masked by erosion and vegetation.
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