Astrophysics

The Sky is Not Falling

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Science  21 May 2004:
Vol. 304, Issue 5674, pp. 1081
DOI: 10.1126/science.304.5674.1081a

Near-Earth asteroids (NEAs) have the potential to hit us, and Chapman reviews what we know about NEA hazards. There are about 170 recognized terrestrial impact craters, and the impact rate has remained relatively constant except for a brief period about 4 billion years ago called the Late Heavy Bombardment, when the rate was a thousand times higher. About 2670 NEAs have been identified, of which about 600 are considered potentially hazardous.

A rare collision (one every 10 to 100 million years) with a 3-km-diameter body would create a 1-million-megaton explosion [about 100 times less energetic than the K-T (cretaceous-tertiary) impact event], whereas a more frequent (once per century) 40-m-diameter object would create a 10-megaton explosion (similar to the Tunguska event in 1908). When the Spaceguard Survey has completed their catalog of all 1-km or larger NEAs in 2008, the worldwide impact event mortality, averaged over a very long time, should be reduced to 100 deaths per year. — LR

Earth Planet. Sci. Lett. 222, 1 (2004).

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