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Rock piles in space

Research suggests asteroids even more hazardous than thought

animation of asteroids colliding
Computer animation of the moment when asteroids collide   

June 3, 1998
Web posted at 5:00 p.m. EDT

(CNN) -- Computer models are causing scientists to rethink their view of asteroids, those ancient rocks scattered throughout space. And the news is not good.

Researcher Erik Asphaug has a model of asteroids that departs from the traditional concept of them as solid chunks of rock. He believes most asteroids are fractured, with lots of loose rock that would absorb the shock of a nuclear bomb.

Should an asteroid show up on a collision course with Earth, using a rocket-borne nuclear device to nudge it off course is one method scientists have proposed to avert catastrophe.

Such a scenario forms the basis for two high-profile summer movies: the recently released "Deep Impact" and the upcoming "Armageddon."

CNN's Don Knapp shows the asteroid model
icon 2 min. 30 sec. VXtreme video

Scientists say the plot isn't far-fetched. They believe it happens once or twice every million years: A comet or asteroid tears through the Earth's atmosphere and smashes into the ground or ocean with enough force to destroy civilization.

For months, Asphaug and other scientists ran a high-powered computer model that simulates the instant one asteroid collides with another -- a key moment in asteroid evolution.

Their conclusion? Most asteroids aren't so solid after all but are cosmic rock piles, held together by gravity.

Deep Impact
Scene from "Deep Impact"   

"We're finding out now that as you impact an asteroid, it's much easier to break it into small pieces than it is to send those pieces on their way," Asphaug says. "And we believe most asteroids are what we call rubble piles."

In other words, if Earth is on a cosmic collision course with an asteroid, nuking it may only bring debris raining down.

Any plan to alter the course of an asteroid should begin with good space reconnaissance, Asphaug says.

Such reconnaissance, through telescopes or space probes, might tell scientists whether the rock is solid, a couple of chunks, or a slew of pieces.

"If your asteroid is solid rock, it responds to an impact, or explosion, in one way," he explains. "If it's a rubble pile, fractured through and through, it's going to respond in a very different way."

There are roughly a million asteroids about the size of football fields whizzing in near-Earth space. At least 2,000 of those large bodies -- known as NEOs (Near-Earth Objects) - - could cross the orbit of Earth and, in theory, could hit us.

But Asphaug says he worries less about asteroids smacking the Earth than he does about nuclear bombs, the devices some believe could be used to blast them out of the sky.

Asphaug's study appears in the June 4 issue of the science journal Nature.

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