Asteroid is largest to pass Earth since 1985

The Baltimore Sun

If you're reading this Tuesday morning (or any time thereafter), then scientists were right: An asteroid the size of a city block did not crash into the Earth as we slept.

OK, there was never any danger of that. Asteroid 2007 TU24 swept by the planet at 3:33 a.m. EST at a safe distance of 334,000 miles - roughly one-and-a-half times the distance from Earth to the moon. But it was the closest an asteroid this size has come since 1985, and the closest one we know about until 2027.

Had Earth been in the bulls-eye, TU24 would not have burned up harmlessly.

"This one would punch right through the atmosphere with no trouble," said Donald Yeomans, manager of NASA's Near Earth Object Program.

Its impact at a velocity of 6 miles per second would have released energy equivalent to 1,500 megatons of TNT, about 60 times the force of the largest hydrogen bomb in the U.S. arsenal during the Cold War.

While it would not have sent us all the way of the dinosaurs, Yeomans said, "this would be a regionally destructive event. Or, if it hit in the ocean, there would most likely be a substantial tsunami."

NASA has four full-time sky surveys to find and track every space rock orbiting the sun that could threaten the Earth. So far, Yeomans said, they've found about 900 at least a kilometer in size - big enough to cause global "problems." They think that's 90 percent of the total. None, so far, is projected to hit us.

frank.roylance@baltsun.com

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