It goes something like this: Thousands of asteroids, some weighing millions of tons, are whizzing about in space. One of these orbiting menaces is eventually destined to crash into earth, ending life as we know it. If scientists can detect the destructive mass in time, they can deflect it with a Herculean assault of lasers and nuclear weapons and save the world.The trouble, says Gehrels, a planetary scientist at the University of Arizona, is that hardly anyone is taking the threat seriously. Only a handful of astronomers are trying to track the errant asteroids. And no plan exists for dealing with any that might be on a collision course. The theory that deadly asteroids may smash into the earth is far from science fiction. "It's absolutely feasible to believe it could happen," says David Morrison, chief of the Space Science Division at the NASA Ames Research Center in California. "And it's not overstating the case to say an asteroid impact threatens civilization." The scenario is that a collision with earth by an asteroid one kilometer or greater in diameter would send a cloud of dust particles into the stratosphere large enough to spread out like a thin film over the planet and block the sun. The whole earth would turn to darkness, surface temperatures would fall drastically, and most plant and animal life would die. Many believe this phenomenon has occurred at least once before. In 1980, the father and son team of Luis and Walter Alvarez at the University of California at Berkeley, studied geographic layers of the earth and found high levels of minerals known to be common in meteors but uncommon to earth. Their hypothesis, that an asteroid or shower of asteroids was responsible for the extinction of dinosaurs 66 million years ago, is now widely accepted. According to Richard Binzel, associate professor of earth, atmospheric, and planetary sciences at MIT, some 5,000 objects in space pose a collision threat to earth. Of those, about 2,000 are large enough to wreak global havoc, while the smaller ones might knock out a city or even level an entire country. Most asteroids are contained in the asteroid belt between Mars and Jupiter. But over the millennia, a number of asteroids began to oscillate in their orbit around the sun because of the countervailing gravitation forces of nearby Jupiter. Some eventually broke free and took off on new orbits that now intersect with that of earth. At present, only 200 of these objects, or about 5 percent, have been identified and charted. When Binzel generates a diagram superimposing the orbits of near-earth asteroids over the orbit of the earth for any given month, he finds the number of intersections remarkable. "Then when you look at this diagram and realize the paths charted represent only a small percentage of the near-earth asteroids out there," he says, "the reality sets in that impacts are a natural, inevitable process in planetary evolution." After a year-long study headed by Morrison, NASA recently urged Congress to spearhead an international effort, dubbed "Space Guard," to set up a worldwide network of six telescopes dedicated to discovering and tracing near-earth objects. Two of the telescopes would be located in the United States, with the others in Russia, India, Australia, and France. Morrison estimates the network would cost $50 million to build and $10 million a year to operate, for the 20 to 25 years he estimates would be required to track the remaining near-earth objects and determine if and when a collision might occur.
Detection Key To Deflection
Once NASA detects an Asteroid, it has years to plan an effective response. There are other ways to deflect an asteroid, not just nuclear weapons.
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In "Star Warriors on Sky Patrol" (Op-Ed, March 25), Robert L. Park makes the error of tarring good and important science with the same brush he applies to an overenthusiastic emphasis on nuclear weapons. There may or may not be merit in using nuclear weapons to deflect asteroids or comets that we someday might find to be on a collision course with Earth. But that isn't the point. According to David Morrison, an astronomer who headed the first National Aeronautics and Space Administration workshop on this subject: "You take a complete census, track their orbits and calculate whether they are a danger. If you find one that is, then you have decades or even centuries to plan a response. You don't have to rush out and build missiles and arsenals." But there are proper, effective and low-cost efforts we can conduct now. One of these, recommended by Mr. Morrison's workshop, is to accelerate detection of earth-crossing asteroids at a cost of about $10 million a year. Even Mr. Park calls this "a reasonable price for peace of mind." Another such program is the integrated sensor test program, nicknamed Clementine. Its goal is to test and demonstrate, by flying past an asteroid named Geographos, which will cross Earth's orbit in August 1994, the sensors and autonomous navigation techniques needed by a device to deflect an asteroid aimed at the earth. NASA requested the mission and strongly supports it because it will generate, at no cost to NASA, comprehensive and accurate topographical and mineralogical data on both the asteroid and the moon, which Clementine will orbit on its way to meet Geographos. Moreover, Clementine is projected to cost less than $50 million spread over the next three years, and that money has been budgeted. So what's the problem? The mission is financed by the Defense Department's Strategic Defense Initiative Organization, which sees Clementine as an ideal mechanism for testing sensors and guidance systems developed for military needs on a mission that can also meet nonmilitary scientific goals. But because S.D.I. is involved in antimissile weapon technologies, there is danger that Clementine -- as well as the much-needed asteroid detection program proposed by Mr. Morrison's workshop -- may be lumped together with the highly controversial nuclear weapon issue that has so inflamed Mr. Park, even though neither Clementine nor asteroid detection has anything to do with nuclear weapons or their designers .A position paper by my organization on the potential hazards of Earth approaching asteroids motivated Congress to request the two NASA workshops, the second of which so incensed Mr. Park. We believe that the first workshop's recommendation for accelerating asteroid detection is an ideal outcome of our paper. But we are particularly pleased by the Clementine mission, which not only takes the first rational step toward preventing an ultimate catastrophe, but also delivers much-needed scientific data, affords an opportunity to learn how to do truly low-cost space missions, and, best of all, shows that we really can beat swords into plowshares.JERRY GREY Director, Science and Technology Policy, American Institute of Aeronautics and Astronautics Washington, April 2, 1992