: Hole from on high

25-07-2010, 10:09 PM

Researchers poring over Google Earth images have discovered one of Earths freshest impact craters a 45-meter-wide pock in southwestern Egypt that probably was excavated by a fast-moving iron meteorite no more than a few thousand years ago.
Although the crater was first noticed in autumn 2008, researchers have since spotted the blemish on satellite images taken as far back as 1972, says Luigi Folco, a cosmochemist at the University of Siena in Italy. He and his colleagues report their find online July 22 in Science.
The rim of the Egyptian crater stands about 3 meters above the surrounding plain, which is partially covered with distinct swaths of light-colored material blasted from the crater by the impact. These rays, which emanate from the impact site like spokes from the hub of a wheel, are what drew researchers attention to the crater, says Folco. While such rayed craters are common on the moon and other airless bodies of the solar system, they are exceedingly rare on Earth because erosion and other geological processes quickly erase such evidence.
During expeditions to the site early in 2009 and again this year, scientists found more than 5,000 iron meteorites that together weigh more than 1.7 tons. The team estimates that the original lump of iron weighed between 5 and 10 metric tons when it slammed into the ground at a speed of around 3.5 kilometers per second, with most of the material vaporizing during the collision.
Analyses of soil samples from the site and of sand fused into glass by the impacts intense heat and pressure may help the team estimate when the event occurred. Preliminary analyses suggest that it happened sometime during the last 10,000 years, probably no more than 5,000 years ago, Folco says.