Cosmic impact probabilities

Cosmic impact probabilities

. A hail of cosmic objects continually pelts the Earth from space. This plot shows the likelihood (vertical axis) that a member of the current population of Earth-crossing asteroids and comets will hit our planet. An object two kilometers in diameter, capable of producing certain worldwide damage, hits the Earth every million years on average. An impact like the one that wiped out the dinosaurs, giving rise to the Chicxulub crater, is estimated to occur every 100 million years. Since smaller asteroids and comets are much more numerous than larger ones, the smaller objects strike our planet more often. An impact like the Tunguska event, which occurred on 30 June 1908, might occur every 700 centuries or so. The explosive energy of the impact is also given (horizontal axis) in units of megatons of exploded trinitrotoluene, or TNT for short. One hundred megatons (1011 kilograms) of TNT is equivalent to about 4 x 1017 joules of energy, the amount released by a typical nuclear bomb on Earth.

Copyright 2010, Professor Kenneth R. Lang, Tufts University