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Imperial scientist cracks meteor puzzle


External Sites:
-Nature website
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10 March 2005
BY LAURA GALLAGHER

An Imperial scientist has found that the famous Meteor Crater in Arizona was created by a much gentler impact than previously believed. The findings, detailed in this weeks Nature, explain why the crater contains far less rock melted by the impact than suggested by extrapolation from larger craters.

The 1.2 kilometre wide Arizona Meteor Crater is one of the most intensively studied impact craters on Earth, yet the missing melt has puzzled researchers for years.

Dr Gareth Collins, together with Professor H Jay Melosh of the University of Arizona, use a simple model to show that the projectile slowed up enormously on hitting the Earth's atmosphere, breaking up into a pancake-shaped cloud of clustered iron fragments some 200 metres across before it struck.

The 1.2km wide Meteor Crater in Arizona

The researchers conclude that the velocity on impact was just 12 kilometres per second, with the energy released being equivalent to about 2.5 megatonnes of TNT. Their calculations are borne out by the recovery of small, unmelted iron fragments around the crater and by the surprisingly small amount of rock melted by the impact.

"It is very satisfying to discover something new about such a well-studied crater, " said Dr Collins, from the Department of Earth Science and Engineering. "Although still incredibly violent by normal geologic standards, this surface impact velocity is too low for substantial melting of the target rock."

Past estimates of the speed at which the meteor was travelling when it hit the Earth range from 9.4 to 20 kilometres per second, with the faster figures recently considered more likely.

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