Russell Schweickart, the former Apollo astronaut, runs the B612 Foundation (B612 is the asteroid home of Saint-Exupéry’s Little Prince). The foundation’s goal is to get NASA officials, Congress, and ultimately the international community to take the space-rock threat seriously; it advocates testing a means of precise asteroid tracking, then trying to change the course of a near-Earth object.
Current telescopes cannot track asteroids or comets accurately enough for researchers to be sure of their courses. When 99942 Apophis was spotted, for example, some calculations suggested it would strike Earth in April 2029, but further study indicates it won’t—instead, Apophis should pass between Earth and the moon, during which time it may be visible to the naked eye. The Pan-STARRS telescope complex will greatly improve astronomers’ ability to find and track space rocks, and it may be joined by the Large Synoptic Survey Telescope, which would similarly scan the entire sky. Earlier this year, the software billionaires Bill Gates and Charles Simonyi pledged $30 million for work on the LSST, which proponents hope to erect in the mountains of Chile. If it is built, it will be the first major telescope to broadcast its data live over the Web, allowing countless professional and amateur astronomers to look for undiscovered asteroids.
Schweickart thinks, however, that even these instruments will not be able to plot the courses of space rocks with absolute precision. NASA has said that an infrared telescope launched into an orbit near Venus could provide detailed information on the exact courses of space rocks. Such a telescope would look outward from the inner solar system toward Earth, detect the slight warmth of asteroids and comets against the cold background of the cosmos, and track their movements with precision. Congress would need to fund a near-Venus telescope, though, and NASA would need to build it—neither of which is happening.
Another means of gathering data about a potentially threatening near-Earth object would be to launch a space probe toward it and attach a transponder, similar to the transponders used by civilian airliners to report their exact locations and speed; this could give researchers extremely precise information on the object’s course. There is no doubt that a probe can rendezvous with a space rock: in 2005, NASA smashed a probe called Deep Impact into the nucleus of comet 9P/Tempel in order to vaporize some of the material on the comet’s surface and make a detailed analysis of it. Schweickart estimates that a mission to attach a transponder to an impact-risk asteroid could be staged for about $400 million—far less than the $11.7 billion cost to NASA of the 2003 Columbia disaster.
Then what? In the movies, nuclear bombs are used to destroy space rocks. In NASA’s 2007 report to Congress, the agency suggested a similar approach. But nukes are a brute-force solution, and because an international treaty bans nuclear warheads in space, any proposal to use them against an asteroid would require complex diplomatic agreements. Fortunately, it’s likely that just causing a slight change in course would avert a strike. The reason is the mechanics of orbits. Many people think of a planet as a vacuum cleaner whose gravity sucks in everything in its vicinity. It’s true that a free-falling body will plummet toward the nearest source of gravity—but in space, free-falling bodies are rare. Earth does not plummet into the sun, because the angular momentum of Earth’s orbit is in equilibrium with the sun’s gravity. And asteroids and comets swirl around the sun with tremendous angular momentum, which prevents them from falling toward most of the bodies they pass, including Earth.
For any space object approaching a planet, there exists a “keyhole”—a patch in space where the planet’s gravity and the object’s momentum align, causing the asteroid or comet to hurtle toward the planet. Researchers have calculated the keyholes for a few space objects and found that they are tiny, only a few hundred meters across—pinpoints in the immensity of the solar system. You might think of a keyhole as the win-a-free-game opening on the 18th tee of a cheesy, incredibly elaborate miniature-golf course. All around the opening are rotating windmills, giants stomping their feet, dragons walking past, and other obstacles. If your golf ball hits the opening precisely, it will roll down a pipe for a hole in one. Miss by even a bit, and the ball caroms away.
Tiny alterations might be enough to deflect a space rock headed toward a keyhole. “The reason I am optimistic about stopping near-Earth-object impacts is that it looks like we won’t need to use fantastic levels of force,” Schweickart says. He envisions a “gravitational tractor,” a spacecraft weighing only a few tons—enough to have a slight gravitational field. If an asteroid’s movements were precisely understood, placing a gravitational tractor in exactly the right place should, ever so slowly, alter the rock’s course, because low levels of gravity from the tractor would tug at the asteroid. The rock’s course would change only by a minuscule amount, but it would miss the hole-in-one pipe to Earth.
Will the gravitational-tractor idea work? The B612 Foundation recommends testing the technology on an asteroid that has no chance of approaching Earth. If the gravitational tractor should prove impractical or ineffective, other solutions could be considered. Attaching a rocket motor to the side of an asteroid might change its course. So might firing a laser: as materials boiled off the asteroid, the expanding gases would serve as a natural jet engine, pushing it in the opposite direction.
But when it comes to killer comets, you’ll just have to lose sleep over the possibility of their approach; there are no proposals for what to do about them. Comets are easy to see when they are near the sun and glowing but are difficult to detect at other times. Many have “eccentric” orbits, spending centuries at tremendous distances from the sun, then falling toward the inner solar system, then slingshotting away again. If you were to add comets to one of those classroom models of the solar system, many would need to come from other floors of the building, or from another school district, in order to be to scale. Advanced telescopes will probably do a good job of detecting most asteroids that pass near Earth, but an unknown comet suddenly headed our way would be a nasty surprise. And because many comets change course when the sun heats their sides and causes their frozen gases to expand, deflecting or destroying them poses technical problems to which there are no ready solutions. The logical first step, then, seems to be to determine how to prevent an asteroid from striking Earth and hope that some future advance, perhaps one building on the asteroid work, proves useful against comets.
None of this will be easy, of course. Unlike in the movies, where impossibly good-looking, wisecracking men and women grab space suits and race to the launchpad immediately after receiving a warning that something is approaching from space, in real life preparations to defend against a space object would take many years. First the necessary hardware must be built—quite possibly a range of space probes and rockets. An asteroid that appeared to pose a serious risk would require extensive study, and a transponder mission could take years to reach it. International debate and consensus would be needed: the possibility of one nation acting alone against a space threat or of, say, competing U.S. and Chinese missions to the same object, is more than a little worrisome. And suppose Asteroid X appeared to threaten Earth. A mission by, say, the United States to deflect or destroy it might fail, or even backfire, by nudging the rock toward a gravitational keyhole rather than away from it. Asteroid X then hits Costa Rica; is the U.S. to blame? In all likelihood, researchers will be unable to estimate where on Earth a space rock will hit. Effectively, then, everyone would be threatened, another reason nations would need to act cooperatively—and achieving international cooperation could be a greater impediment than designing the technology.
We will soon have a new president, and thus an opportunity to reassess NASA’s priorities. Whoever takes office will decide whether the nation commits to spending hundreds of billions of dollars on a motel on the moon, or invests in space projects of tangible benefit—space science, environmental studies of Earth, and readying the world for protection against a space-object strike. Although the moon-base initiative has been NASA’s focus for four years, almost nothing has yet been built for the project, and comparatively little money has been spent; current plans don’t call for substantial funding until the space-shuttle program ends, in 2010. This suggests that NASA could back off from the moon base without having wasted many resources. Further, the new Ares rocket NASA is designing for moon missions might be just the ticket for an asteroid-deflection initiative.
Congress, too, ought to look more sensibly at space priorities. Because it controls federal funding, Congress holds the trump cards. In 2005, it passively approved the moon-base idea, seemingly just as budgetary log-rolling to maintain spending in the congressional districts favored under NASA’s current budget hierarchy. The House and Senate ought to demand that the space program have as its first priority returning benefits to taxpayers. It’s hard to imagine how taxpayers could benefit from a moon base. It’s easy to imagine them benefiting from an effort to protect our world from the ultimate calamity.