4 June 1998
Asteroid Deflections May Be Impossible
As though to challenge the far-fetched heroics of Deep Impact star Robert Duvall, a study of asteroid collisions published today in Nature has raised serious doubts about the feasibility of deflecting an asteroid hell-bent on hitting the Earth. Using computer simulations to analyze the effects of impacts on asteroids with various internal structures, astronomer Erik Asphaug has come up with some alarming findings. Powerful blasts - including nuclear explosions - could have little or no effect in defending our planet from catastrophe.
"It's a lot more difficult to nudge these asteroids around than we had thought," says Asphaug, a research associate at the University of California, Santa Cruz. "More work needs to be done before we can decide whether nuclear warheads provide a viable deterrent."
Starting with a computer model of the near-Earth asteroid Castalia - a peanut-shaped lump about a mile across - Asphaug and his team generated three internal structures: solid rock, a pair of close-contact solid rocks, and "rubble pile" (with pore space accounting for half the volume). Each of the models was then subjected to simulated impacts. For the sake of the study, the researchers simulated a house-sized rock travelling at 5 kilometres per second, which would create an impact more devastating than the Hiroshima atomic bomb.
Disturbingly, the porous nature of the "rubble pile" asteroid was shown to dampen the shock waves and limit the effects of the impact. The twin-lobed "contact binary" asteroid also looked resilient, with one side likely to be blasted apart and the other left almost unaffected. Only the solid rock model could be blown to smithereens - though at the risk of creating large pieces of debris.
Hundreds of thousands of asteroids currently swarm about near-Earth space, says Asphaug. An impact with any one of them would dwarf even the largest thermonuclear device ever exploded.
"Asteroids are not an imminent threat," he adds, "and I am far more concerned about what humans are doing to the planet. But in case we ever identify an asteroid or comet on a collision course, it would be best to know our enemy so that we can get it before it gets us."
GoGo Further - Asteroid Impact Simulations