Space / Meteors, Asteroids, & Comets

Across the continent at JPL, Steven Chesley began to fine-tune the orbit (pdf). On December 20, he placed the odds of a collision at 1 in 5,000. Three days later, with more data, those odds grew to 1 in 250. “We kind of missed Christmas that year,” he says. The odds kept getting higher as he analyzed the trajectory more thoroughly. By the day after Christmas—the day of the Indonesian tsunami—the odds reached an alarming 1 in 37. The researchers quietly plotted the likely plane along which the asteroid would pass but did not release the information to the media. If that plane intersected Earth, then the impact area would lie somewhere along a narrow band crossing the North Atlantic, Europe, and southern Asia. “We know there is an asteroid out there with our name on it,” adds Chesley. “We just didn’t expect to find one so soon.”

Then researchers poking around in the University of Arizona’s Spacewatch survey archives came to the rescue. An observation made earlier in the year shifted the asteroid’s projected path just enough to one side to spare Earth. “That ruled out the possibility of an impact conclusively,” Chesley says. He and the handful of other scientists breathed a sigh of relief. But like every near-Earth asteroid, Apophis will keep orbiting, so the risk will not go away. Although the next pass has only a 1-in-45,000 chance of colliding, future encounters could pose a greater risk. Calculating odds farther ahead is extremely difficult, though, because so many slight gravitational influences change an asteroid’s path over time.

Schweickart was deeply shaken by the Apophis experience. “I don’t know how to transmit to you the emotion, the level of intensity of a group of people you could name on two hands during those days in December 2004,” he says. His interest in the asteroid threat extended back to 2001, when he and a few colleagues sat down at NASA’s Johnson Space Center in Houston just six weeks after the terrorist attacks on New York and Washington to discuss ways to deflect an incoming asteroid. That led to his founding an organization named for the asteroid that was the home of Saint-Exupéry’s Little Prince—the B612 foundation. Its goal is to alter an asteroid’s orbit in a controlled manner by the year 2015.

Since the first serious asteroid scare in 1996, astronomers have pondered a multitude of ways to deflect an incoming rock. Some researchers suggest sending nuclear weapons, Hollywood-style, to blow up the asteroid; others propose a simple crash landing that would shove the body into a slightly new orbit. Another method would unfurl mirrors that would vaporize part of the rock. Two spacecraft—NEAR-Shoemaker and Hayabusa—have already played tag with asteroids, while another has experimented with shooting a projectile into a comet. Most of the proposed defense methods would require careful study of an asteroid’s composition—you might simply create a rocky doughnut by trying to blast one apart.

The European Space Agency recently took these ideas into a more concrete direction by releasing a concept for a spacecraft called Don Quixote that could push at an asteroid while another spacecraft (called Sancho, of course) hovers nearby to monitor any change in its orbit. Schweickart and his colleagues propose instead that a space tug could rendezvous with an asteroid and change its trajectory simply by using the probe’s gravitational pull. The advantage to this approach, he says, is that you don’t need to touch the asteroid or ascertain its makeup to move it out of a dangerous trajectory. The disadvantage is that the tug lacks muscle and could make only small adjustments to the orbit. The former astronaut has so far made little headway within NASA—which is focused instead on returning men to the moon—or even among many scientists who prefer to spend precious funds on asteroid detection.

So what would we have done if Apophis were on a collision course with Earth in 2029? Once Schweickart plotted the asteroid’s potential landfall, he suddenly realized the threat’s political and legal implications. If a city-busting rock were heading toward Iran, would the United States take the lead and spend billions of dollars to stop it? By nudging an asteroid off course, a probe would send it on a new trajectory. What if the probe could not complete the maneuver and shifted the threat elsewhere?

Such concerns led the ex-astronaut and Air Force pilot to tap members of an exclusive club he founded called the Association of Space Explorers—men and women who have, briefly, been near-Earth objects themselves. “This group of people can get the attention of national leaders all over the world,” Schweickart says. This January, the group wined and dined donors at a fund-raiser in Oakland, California, and they recently held a workshop in France, the first in a series to hash out a draft United Nations treaty to cope with the asteroid threat. To Schweickart, a matter of life and death trumps space science: “Do we really need to know more about a moon of Jupiter compared with being prepared to protect life on Earth?”

That attitude is bound to irritate a lot of space scientists. Yeomans, for example, insists that the three most important things to do are “find ’em early, find ’em early, and find ’em early.” NASA researchers have their own plan, the Near-Earth Object Program—the agency’s program to spot 90 percent of all potentially hazardous asteroids more than two-thirds of a mile wide that might hit Earth in the foreseeable future. Amateur astronomers, long major players in ascertaining the exact orbits of asteroids, are likely to play less and less of a role as professionals turn their powerful telescopes to the objects once considered too mundane for academics to study at all. One way or another, astronomers say they intend to find every sizable rock that might be rushing at Earth. By 2020, we should know whether we need to save ourselves from going the way of the dinosaurs. “We take our snapshot now,” Spahr says, “and we’ll be good for centuries.”