Killer Asteroids: A Real But Remote Risk?

By John Roach
for National Geographic News
June 19, 2003

It is almost certain that Earth will be hit by an asteroid large enough to exterminate a large percentage of our planet's life, including possibly over a billion people, according to researchers. But as such cataclysmic collisions occur on average only once in a million years or so, are they really worth worrying about?

At some point in the geological future a large chunk of rock and ice will smack into Earth and destroy life as we know it. This is a cold, sober, scientific fact, according to Andrea Milani, a researcher at the University of Pisa in Italy.

"A future impact from, say, a 1-kilometer [0.62 mile]-diameter asteroid is, rather than just probable, almost certain over a time span of a million years," he said.

Wolf Reimold, a geoscientist at the University of Witwatersrand in Johannesburg, South Africa, said a 1-kilometer-wide asteroid would produce an impact crater of about 12 miles (20 kilometers) in diameter and wipe out an area the size of the United Kingdom. The human toll would depend on where such an impact occurs.

"Estimates may range from 500,000 to 1.5 billion casualties," he said. "This latter number certainly smells of global nuclear war. Such an event would in all likelihood not wipe out mankind, but it would cause a global economic crisis."

Given the real threat of impact by a so-called near Earth object (NEO) and the consequences for human life, Milani and Reimold are urging the worldwide scientific community, and the agencies that fund their research, to take the field of impact mitigation seriously.

In separate papers appearing in the June 20 issue of the journal Science, Milani and Reimold outline what is known about the impact threat and how impacts have shaped the geologic and life history of Earth.

They agree that the developed world has made great strides over the past few decades in NEO research, but say that more funding is required to raise public awareness of the impact risk and to determine how to thwart an incoming object.

"Governments have the responsibility to deal with a lot of problems afflicting humankind. But these same governments must realize that large asteroid or comet impact has the potential to wipe out all other problems, including mankind," said Reimold.

Impact Science

Impacts of meteorites, asteroids, and comets are frequent events on a geological time scale, said Milani. They have shaped the surface of the Earth and altered the course of life that thrives upon it.

For example, 65 million years ago a 6.2-mile (10 kilometer)-diameter asteroid impact resulted in a 100-million-megaton explosion that excavated a 112-mile (180 kilometer)-wide crater on the Yucatán Peninsula in Mexico and brought the dinosaur era to an end.

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