* Astronomy

Northern Arizona's Meteor Crater, also known as the Barringer Meteorite Crater, is a 174 metres deep, 1250 metre-wide hole in the ground that was created by nickel-iron meteorite crashing into Earth almost 50,000 years ago.
Scientists at the University of Arizona recently announced that the meteor was travelling at 11.16 km/s when it smashed into the Earth, significantly slower than the original estimation of 18.33 km/s.
The meteors estimated diameter was 45-50 m with a mass of 300,000 - 400,000 tons



New analysis explains why there's a lot less melted rock in the crater than expected. The mystery has dogged researchers for years.
Previous calculations had the rock slamming into the ground at no less than 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 2005 issue of the journal Nature, shows the incoming object would have slowed considerably during its plunge through the atmosphere, a shock wave, at an altitude of about 14 km, just ahead of the incoming body would break it apart; and at an altitude of 5 km, into a pancake-shaped cloud roughly 200 meters across, of iron fragments prior to impact.
About half the original 300,000-ton bulk remained intact, smacking the planet at about 12 km/sec, roughly 10 times faster than a rifle bullet.
Meteor Crater was the first scar on Earth confirmed to have been created by a space rock.

"It's probably the most studied impact crater on Earth. We were astonished to discover something entirely unexpected about how it formed."

The modelling is based in part on investigations by Daniel Barringer. Barringer and others found chunks of the iron space rock weighing from a pound up to 1,000 pounds in a 9.6 km diameter circle around the crater. The new work also draws from an improved understanding of how Earth's atmosphere cushions extraterrestrial blows.

"Earth's atmosphere is an effective but selective screen that prevents smaller meteoroids from hitting Earth's surface".

The effect of hitting the Earth’s atmosphere, even for an iron-heavy meteorite like the one that struck Arizona, is a lot like hitting a wall. And many space rocks are already cracked before they arrive.

"Even though iron is very strong, the meteorite had probably been cracked from collisions in space. The weakened pieces began to come apart and shower down from about 14 kilometres high. And as they came apart, atmospheric drag slowed them down, increasing the forces that crushed them so that they crumbled and slowed more."

The Meteor Crater Visitor Centre shows a 10-minute movie called "Collisions and Impacts" twice each hour, and the Interactive Learning Centre includes exhibits such as an Apollo space test capsule, an Astronaut Hall of Fame, meteorite fragments and Create-a-Crater, where you can digitally design your own crater by plugging in the elements, density, angle of descent and velocity of a meteorite.

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