Wednesday, March 09, 2005

Mystery of Arizona's Meteor Crater Solved



By Robert Roy Britt
Senior Science Writer
Space.com
3-9-05

The space rock that carved Meteor Crater in Arizona hit the planet much more slowly than astronomers once figured, but still 10 times faster than a rifle bullet.

The new analysis, announced today, explains why there's a lot less melted rock in the crater than expected. The mystery has dogged researchers for years.

The big hole in the ground -- 570 feet deep and 4,100 feet (1.25 kilometers) across -- was blown into existence 50,000 years ago by an asteroid roughly 130 feet (40 meters) wide.

Previous calculations had the rock slamming into the ground at no less than 34,000 mph (15 km/sec), based in part on the expected speeds of large meteors in relation to Earth. Such an impact ought to have generated more melted rock in and around the crater than what's been found.

A new computer model, reported in the March 10 issue of the journal Nature, shows the incoming object would have slowed considerably during its plunge through the atmosphere, part of it breaking into a pancake-shaped cloud of iron fragments prior to impact.

About half the original 300,000-ton bulk remained intact, smacking the planet at about 26,800 mph (12 km/sec), said the study's lead researcher, Jay Melosh of the University of Arizona.

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