Researchers have long wondered why there is not more melted rock at Arizona's Barringer Meteorite Crater between Flagstaff and Winslow.At an impact speed of 34,000 to 44,000 mph, the massive space rock should have melted substantial quantities of the white Coconino geological formation. One possible explanation has been that the meteor contained large amounts of water, which would have lessened the force of the impact that created the 570-foot-deep, 4,100-foot-wide crater.
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But new calculations suggest the rock, after it was broken up in the atmosphere, was going slower than previously believed.
The Barringer site "is probably the most studied impact crater on Earth," said astronomer H. Jay Melosh of the University of Arizona. "We were astonished to discover something entirely unexpected about how it was formed."
Using computer models for how such objects would interact with the atmosphere, Melosh and astronomer Gareth Collins of Imperial College London concluded that the 300,000-ton, 130-foot-diameter meteor fractured before it hit the ground, with about half of it dispersing into small fragments.
The remaining half struck the ground at a speed of 26,800 mph, about 10 times the velocity of a bullet fired from a high-powered rifle, but not fast enough to melt large quantities of rock, the scientists reported this week in the journal Nature.
The intact fragment exploded with the energy of at least 2.5 megatons of TNT, they said.