Incoming!

Also possible is a dock-and-push approach, in which a spacecraft parks on the asteroid's surface, fires its thrusters, and alters the trajectory. Robert Gold of the Applied Physics Laboratory at Johns Hopkins University says the probe he designed for NASA's Near Earth Asteroid Rendezvous mission—the first to land on an asteroid—could divert a hundred-meter-wide object, which is large enough to wipe out the Washington Beltway. "If you found [the asteroid] 30 years in advance, that little 6-foot by 6-foot spacecraft could provide enough impulse to make it miss Earth," he says.



Still, as Yeomans warns, none of this will work without advance notice. Currently, NASA expects to find only about 90 percent of the NEOs large enough to cause global catastrophes. The remaining 10 percent are too dark for today's telescopes, or too difficult to distinguish from the many asteroids that orbit harmlessly in the solar system's main asteroid belt between Mars and Jupiter. Andrea Milani, of the Space Mechanics group at the University of Pisa in Italy, wants to find the hidden large NEOs and extend the survey down to objects as small as 300 meters across. Both goals require a new generation of ground-based telescopes capable of detecting fainter objects, and possibly space-based observatories to peer into obscure areas of the solar system. The ground-based, 8.4-meter Large-aperture Synoptic Survey Telescope is one possibility, but its $120 million price is the equivalent of 40 years of the current search budget.



As the search expands, at least one group is recommending a practice deflection. The B612 Foundation, which takes its name from the asteroid in Antoine de Saint-Exupéry's The Little Prince, is designing a mission to alter an asteroid's orbit using a low-thrust, possibly nuclear-electric spacecraft. The Houston-based organization, a group of scientists and astronauts that includes space station crewmember Ed Lu, won't be able to fund the mission on its own, so B612 plans to present the plan to NASA and other space agencies, and push for a test by 2015. Clark Chapman of B612 won't name an exact price for the mission, but he estimates it will fall somewhere between the cost of a typi-cal interplanetary probe mission and NASA's several-billion-dollar Jupiter Icy Moons Orbiter project.



Morrison applauds the civilian effort, but also calls for more from NASA. "We need an actual program, even if it's a modest beginning, to demonstrate that we can do some of this," he says. Morrison doubts that any concerted effort will be made until a specific threat is discovered—something like 1950DA but closer to home. In the meantime, he and fellow asteroid spotters will keep at it.



"It's one of the few areas where astronomy can actually have a practical impact on us, on Earth," he says. "Saving the world, that's not such a bad idea."



Gregory Mone, a PopSci assistant editor, is the author of The Wages of Genius.