What is the Risk of Asteroid Impact?
The smallest asteroid impacts occur about twice a year. Only about 3 m (10 ft) in diameter, these rocks, moving at an average of 17 km/sec, have enough energy to cause an airburst twice the size of the Hiroshima bomb at an altitude of 43 km. Originally, there was concern that atmospheric asteroid impacts would be mistaken as nuclear explosions by sky satellites and initiate a nuclear war, but modern satellites are able to distinguish the characteristic double-flash of nuclear bombs. The Royal Astronomical Society considers anything smaller than 50 meters across to be a “meteoroid”. Meteoroids are what are commonly known as “falling stars”. Larger asteroid impacts, more than 50 m (164 ft) across, occur about every 500 years. Similar to smaller asteroids, asteroids around this size usually lack the kinetic energy to make it to the surface, and explode in an airburst at an altitude of about 7 km. The energy of the airburst is about 6 megatons of TNT, equivalent to a small hydrogen bomb. A
