ASTEROID 243 IDA, about 35 miles long, and its moon
(Image courtesy of NASA/NSSDC)
Until recently, nearly all the thinking about the risks of space-rock strikes has focused on counting craters. But what if most impacts don’t leave craters? This is the prospect that troubles Boslough. Exploding in the air, the Tunguska rock did plenty of damage, but if people had not seen the flashes, heard the detonation, and traveled to the remote area to photograph the scorched, flattened wasteland, we’d never know the Tunguska event had happened. Perhaps a comet or two exploding above Canada 12,900 years ago spelled the end for saber-toothed cats and Clovis society. But no obvious crater resulted; clues to the calamity were subtle and hard to come by.
Comets, asteroids, and the little meteors that form pleasant shooting stars approach Earth at great speeds—at least 25,000 miles per hour. As they enter the atmosphere they heat up, from friction, and compress, because they decelerate rapidly. Many space rocks explode under this stress, especially small ones; large objects are more likely to reach Earth’s surface. The angle at which objects enter the atmosphere also matters: an asteroid or comet approaching straight down has a better chance of hitting the surface than one entering the atmosphere at a shallow angle, as the latter would have to plow through more air, heating up and compressing as it descended. The object or objects that may have detonated above Canada 12,900 years ago would probably have approached at a shallow angle.
If, as Boslough thinks, most asteroids and comets explode before reaching the ground, then this is another reason to fear that the conventional thinking seriously underestimates the frequency of space-rock strikes—the small number of craters may be lulling us into complacency. After all, if a space rock were hurtling toward a city, whether it would leave a crater would not be the issue—the explosion would be the issue.
A generation ago, the standard assumption was that a dangerous object would strike Earth perhaps once in a million years. By the mid-1990s, researchers began to say that the threat was greater: perhaps a strike every 300,000 years. This winter, I asked William Ailor, an asteroid specialist at The Aerospace Corporation, a think tank for the Air Force, what he thought the risk was. Ailor’s answer: a one-in-10 chance per century of a dangerous space-object strike.
Regardless of which estimate is correct, the likelihood of an event is, of course, no predictor. Even if space strikes are likely only once every million years, that doesn’t mean a million years will pass before the next impact—the sky could suddenly darken tomorrow. Equally important, improbable but cataclysmic dangers ought to command attention because of their scope. A tornado is far more likely than an asteroid strike, but humanity is sure to survive the former. The chances that any one person will die in an airline crash are minute, but this does not prevent us from caring about aviation safety. And as Nathan Myhrvold, the former chief technology officer of Microsoft, put it, “The odds of a space-object strike during your lifetime may be no more than the odds you will die in a plane crash—but with space rocks, it’s like the entire human race is riding on the plane.”
Given the scientific findings, shouldn’t space rocks be one of NASA’s priorities? You’d think so, but Dallas Abbott says NASA has shown no interest in her group’s work: “The NASA people don’t want to believe me. They won’t even listen.”
NASA supports some astronomy to search for near-Earth objects, but the agency’s efforts have been piecemeal and underfunded, backed by less than a tenth of a percent of the NASA budget. And though altering the course of space objects approaching Earth appears technically feasible, NASA possesses no hardware specifically for this purpose, has nearly nothing in development, and has resisted calls to begin work on protection against space strikes. Instead, NASA is enthusiastically preparing to spend hundreds of billions of taxpayers’ dollars on a manned moon base that has little apparent justification. “What is in the best interest of the country is never even mentioned in current NASA planning,” says Russell Schweickart, one of the Apollo astronauts who went into space in 1969, who is leading a campaign to raise awareness of the threat posed by space rocks. “Are we going to let a space strike kill millions of people before we get serious about this?” he asks.
In January, I attended an internal NASA conference, held at agency headquarters, during which NASA’s core goals were presented in a PowerPoint slideshow. Nothing was said about protecting Earth from space strikes—not even researching what sorts of spacecraft might be used in an approaching-rock emergency. Goals that were listed included “sustained human presence on the moon for national preeminence” and “extend the human presence across the solar system and beyond.” Achieving national preeminence—isn’t the United States pretty well-known already? As for extending our presence, a manned mission to Mars is at least decades away, and human travel to the outer planets is not seriously discussed by even the most zealous advocates of space exploration. Sending people “beyond” the solar system is inconceivable with any technology that can reasonably be foreseen; an interstellar spaceship traveling at the fastest speed ever achieved in space flight would take 60,000 years to reach the next-closest star system.
After the presentation, NASA’s administrator, Michael Griffin, came into the room. I asked him why there had been no discussion of space rocks. He said, “We don’t make up our goals. Congress has not instructed us to provide Earth defense. I administer the policy set by Congress and the White House, and that policy calls for a focus on return to the moon. Congress and the White House do not ask me what I think.” I asked what NASA’s priorities would be if he did set the goals. “The same. Our priorities are correct now,” he answered. “We are on the right path. We need to go back to the moon. We don’t need a near-Earth-objects program.” In a public address about a month later, Griffin said that the moon-base plan was “the finest policy framework for United States civil space activities that I have seen in 40 years.”
Actually, Congress has asked NASA to pay more attention to space rocks. In 2005, Congress instructed the agency to mount a sophisticated search of the proximate heavens for asteroids and comets, specifically requesting that NASA locate all near-Earth objects 140 meters or larger that are less than 1.3 astronomical units from the sun—roughly out to the orbit of Mars. Last year, NASA gave Congress its reply: an advanced search of the sort Congress was requesting would cost about $1 billion, and the agency had no intention of diverting funds from existing projects, especially the moon-base initiative.
How did the moon-base idea arise? In 2003, after the shuttle Columbia was lost, manned space operations were temporarily shut down, and the White House spent a year studying possible new missions for NASA. George W. Bush wanted to announce a voyage to Mars. Every Oval Office occupant since John F. Kennedy knows how warmly history has praised him for the success of his pledge to put men on the moon; it’s only natural that subsequent presidents would dream about securing their own place in history by sending people to the Red Planet. But the technical barriers and even the most optimistic cost projections for a manned mission to Mars are prohibitive. So in 2004, Bush unveiled a compromise plan: a permanent moon base that would be promoted as a stepping-stone for a Mars mission at some unspecified future date. As anyone with an aerospace engineering background well knows, stopping at the moon, as Bush was suggesting, actually would be an impediment to Mars travel, because huge amounts of fuel would be wasted landing on the moon and then blasting off again. Perhaps something useful to a Mars expedition would be learned in the course of building a moon base; but if the goal is the Red Planet, then spending vast sums on lunar living would only divert that money from the research and development needed for Mars hardware. However, saying that a moon base would one day support a Mars mission allowed Bush to create the impression that his plan would not merely be restaging an effort that had already been completed more than 30 years before. For NASA, a decades-long project to build a moon base would ensure a continuing flow of money to its favorite contractors and to the congressional districts where manned-space-program centers are located. So NASA signed on to the proposal, which Congress approved the following year.
It is instructive, in this context, to consider the agency’s rhetoric about China. The Chinese manned space program has been improving and is now about where the U.S. program was in the mid-1960s. Stung by criticism that the moon-base project has no real justification—37 years ago, President Richard Nixon cancelled the final planned Apollo moon missions because the program was accomplishing little at great expense; as early as 1964, the communitarian theorist Amitai Etzioni was calling lunar obsession a “moondoggle”—NASA is selling the new plan as a second moon race, this time against Beijing. “I’ll be surprised if the Chinese don’t reach the moon before we return,” Griffin said. “China is now a strategic peer competitor to the United States in space. China is drawing national prestige from achievements in space, and there will be a tremendous shift in national prestige toward Beijing if the Chinese are operating on the moon and we are not. Great nations have always operated on the frontiers of their era. The moon is the frontier of our era, and we must outperform the Chinese there.”
Wouldn’t shifting NASA’s focus away from wasting money on the moon and toward something of clear benefit for the entire world—identifying and deflecting dangerous space objects—be a surer route to enhancing national prestige? But NASA’s institutional instinct is not to ask, “What can we do in space that makes sense?” Rather, it is to ask, “What can we do in space that requires lots of astronauts?” That finding and stopping space rocks would be an expensive mission with little role for the astronaut corps is, in all likelihood, the principal reason NASA doesn’t want to talk about the asteroid threat.
NASA’s lack of interest in defending against space objects leaves a void the Air Force seems eager to fill. The Air Force has the world’s second-largest space program, with a budget of about $11 billion—$6 billion less than NASA’s. The tension between the two entities is long-standing. Many in the Air Force believe the service could achieve U.S. space objectives faster and more effectively than NASA. And the Air Force simply wants flyboys in orbit: several times in the past, it has asked Congress to fund its own space station, its own space plane, and its own space-shuttle program. Now, with NASA all but ignoring the space-object threat, the Air Force appears to be seizing an opportunity.
All known space rocks have been discovered using telescopes designed for traditional “soda straw” astronomy—that is, focusing on a small patch of sky. Now the Air Force is funding the first research installation designed to conduct panoramic scans of the sky, a telescope complex called Pan-STARRS, being built by the University of Hawaii. By continuously panning the entire sky, Pan-STARRS should be able to spot many near-Earth objects that so far have gone undetected. The telescope also will have substantially better resolving power and sensitivity than existing survey instruments, enabling it to find small space rocks that have gone undetected because of their faintness.
The Pan-STARRS project has no military utility, so why is the Air Force the sponsor? One speculation is that Pan-STARRS is the Air Force’s foot in the door for the Earth-defense mission. If the Air Force won funding to build high-tech devices to fire at asteroids, this would be a major milestone in its goal of an expanded space presence. But space rocks are a natural hazard, not a military threat, and an Air Force Earth-protection initiative, however gallant, would probably cause intense international opposition. Imagine how other governments would react if the Pentagon announced, “Don’t worry about those explosions in space—we’re protecting you.”
Thus, the task of defending Earth from objects falling from the skies seems most fitting for NASA, or perhaps for a multinational civilian agency that might be created. Which raises the question: What could NASA, or anyone else, actually do to provide a defense?