Thousands of Threats

But Schweickart is still worried: "Don't relax; there's more where that one comes from." He says that one must assume that large asteroids exist in the thousands. Astronomers estimate that there are at least 1,000 near-earth objects of one kilometer or more and perhaps a million larger than 50 meters. "The estimate is that every month one that size [100 meters] not only passes between Earth and the moon, but has passed between Earth and the moon for billions of years. The difference is now we can see them because we¿re looking."

Adds Schweickart: "It¿s like Las Vegas: the odds are the odds. We are going to get whacked at some point, and we should know it in advance. We probably will have decades of warning." Enough time, perhaps, to do something about the threat.

Toward that end, he says that work on the detection side needs to continue beyond the congressional mandate to identify 90 percent of near-earth objects over one kilometer. "Once we get those catalogued, there are many more in small sizes that are still very dangerous to life on Earth," he explains. "We need to go from the program we have now to a program that picks up things down to 300 meters in diameter. Even though they won¿t cause extinction, they could cause serious global disturbances--wipe out regions, let alone cities. And because there are a lot more [of the smaller-size asteroids], the probability is higher we¿re going to find one that¿s going to hit us."

Stopping the Impact

Then the task will be to prevent the impact. Right now, says Schweickart, the only known technology for the purpose is "the wrong thing--a nuclear weapon that you send out there to blow it up." The result, he says: "You turn a rifle bullet into a shotgun blast."

Instead, "I'm interested in going beyond detection by using technology which is or will shortly become available to actively change the orbits of these potentially threatening asteroids in a controlled way, so that they no longer threaten life on Earth," he says. "You have to go out and meet it with a 'tugboat,' a space vehicle that would allow us to push it around for years at a time. You change the orbit by very small velocities, which causes it to miss, rather than hit, Earth."

The process would be based on developing rocket technology, but Schweickart declined to be more specific, explaining, "We¿re talking about things that have existed, but haven¿t been put to use for this purpose."

He is discussing the problem in a small, private international group that includes astronomers, biologists, engineers and others. He says he will reveal more about the group in six months to a year, when it is ready to publish the results of its work. Some of the group members met in October 2001 at NASA Johnson Space Flight Center in a workshop organized by Piet Hut and Ed Lu. It was called Project B612, after the name of the small asteroid that was home to the Little Prince in the novel "Le Petit Prince," by Antoine de Saint-Exupery. Among the ideas discussed during the workshop was using a plasma-drive system such as nuclear-electric propulsion for controlled flight near an problem asteroid.

In the meantime, understanding of the issue is not at a point where the government could address it--that is, get a Congressional budget item and spend money, says Schweickart. "The problem, partly--as far as the general public is concerned--is that it would be a laugher," he says of the idea of "somebody talk[ing] about spending a few billion dollars to push the next asteroid out of the way." For the moment, he says, the matter should be studied and analyzed quietly. "It¿s one of those things which you want to keep people¿s attention on and at the same time not panic. If we keep on with the detection program, we should know [about a problem asteroid] ahead of time, and that will give us, with developing technology, the opportunity to deflect it."

Lucy Komisar is New York journalist who writes on international issues.

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