This might kill more than a city. Maybe a whole state or province or prefecture.

Astronaut Tom Jones: Flight Notes

July 3, 2012

The B612 Foundation announced last week that it will raise funds to launch and operate a space-based telescope to search for dangerous near-Earth asteroids (NEAs). The hazard from these bodies is real. The Tunguska impact in Siberia, in 1908, was caused by Earth’s collision with a small asteroid, about 40 meters across, which exploded with the force of 3 to 5 Megatons of TNT, enough to level a major city. There are about a million near-Earth asteroids big enough to penetrate Earth’s atmosphere and cause city-wide or regional destruction; Tunguska-sized impacts occur every few centuries. Each year, about thirty explosions as powerful as the Hiroshima A-bomb occur in the high atmosphere from small asteroid impacts.

Today, we know of less than 10,000 of these objects. The number of detections is growing rapidly, thanks to NASA’s search program. The agency spends $20M per year on asteroid detection…

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