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Planetary science

Planetary science

Deep Impact may be more than a movie

05 Jun 1998

In the movie Deep Impact astronauts use atomic bombs to try to deflect or destroy a comet on collision with Earth. Now US scientists have calculated the effect of such nuclear tipped missiles as part of a research project to study asteroid formation. They found that the effects of such an explosion vary depending on the structure of the asteroid. They believe many asteroids that suffer collisions have gravitational fields strong enough to stay together as piles of 'rubble'. They found that porous asteroids 'damp down' the effect of the blast, and the first explosion is vital in defining whether the rock will disintegrate or not (Nature 393 437).

The researchers constructed a mathematical representation of the irregularly spaced near Earth asteroid Castalia for their calculations. They assumed it would be made of solid rock, a pair of solid rocks separated by rubble, or a 50% porous agglomeration of large boulders. To simulate a collision they imagined a 8m diameter basalt sphere travelling at 5 kms-1 hitting the asteroid. This would impart a explosive force equivalent to a 17 kiloton nuclear device. They found that in most cases only 10 percent of the asteroid’s mass reached escape velocity, the rest of the material stayed loosely bound in the area. A hard rock object on the otherhand was more likely to simply split into two. As well as suggesting that deflecting or destroying asteroids may not be as easy as first thought, it also suggests that most binary asteroids were formed in collisions this way.

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