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The impact of small asteroids with the Earth could be mistaken for a nuclear first strike and trigger a nuclear war reports BBC Online from the panel discussion that took place in the U.S. Senate last week. U. S. Air Force Brigadier General Simon Worden, who took part but was not speaking on behalf of the U.S. Air Force, voiced concerns that the detonation of small Near Earth Objects in the atmosphere could be misinterpreted as a nuclear explosion by countries lacking sophisticated detection systems. General Worden said that he would like to see a new warning centre established to monitor such events and provide information to governments worldwide.
Several Near Earth Objects break-up explosively in the Earth's atmosphere every year but do not cause any damage on the ground since the explosions occur at high altitude. Five or six objects 10 m in size detonate each year with an energy of around 20 kilotons, equivalent to the Hiroshima bomb, and around 30 objects 1 m in diameter at 1 kiloton. Occasionally these events are witnessed by observers on the ground as a flash of light in the sky, although usually the sound of the explosion in not heard. Such events are, however, observed by satellites but are not associated with the radiation produced by nuclear explosions.
Near Earth Objects larger than around 50 m in size penetrate our planet's protective atmosphere to low enough altitude to cause damage on the ground when they detonate. Such events, which can devastate thousands of square kilometres and could easily be mistaken for a nuclear explosions, are thought to occur once every 100 to 300 years. Despite their frequency, however, they are still unlikely to occur over an inhabited area.
More info: BBC Online
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