21
November 2002
Planetary Science: Impact Factor
In the past eight years, US Department of Defense satellites scanning the Earth for evidence of nuclear explosions have detected nearly 300 optical flashes caused by small (50–100 m) asteroids exploding in the atmosphere. This has provided a new estimate of the flux of near-Earth objects colliding with the Earth. The result is of particular interest as the body that exploded above Tunguska in June 1908 was a ‘small’ asteroid, yet big enough to flatten 2,000 square kilometres of Siberian forest. The revised estimate suggests that Earth is hit once a year by objects that release energy equivalent to 5 kilotons of TNT, and that Tunguska-like (10-megaton) events will occur about once every 1,000 years. This is more encouraging than the old estimate, from ground-based observations, of once every 300 years.
The flux of small near-Earth objects colliding with the Earth
P. BROWN, R. E. SPALDING, D. O. REVELLE, E. TAGLIAFERRI & S. P. WORDEN
Nature
420, 294–296 (2002); doi:10.1038/nature01238
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Intermediate Impact Factors
R. JEDICKE
Nature
420, 273–274 (2002); doi:10.1038/420273a
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