WHILE media attention has focused on the dangers of a giant asteroid hitting the Earth, debate is hotting up over the risk from smaller rocks, like the one that exploded above the Tunguska region of Siberia in 1908.
Experts are coming up with dramatically different estimates of the risk from small asteroids, those about 50 or 60 metres across. An astronomer at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, estimates only one impact every 1000 years, but a senior official at the US government’s Space Command says this figure is too low. He claims that during the past century…
