Space + Flight

26
Mar

Why Can’t We Prevent An Asteroid Strike?

When a meteor streaked over Russia last month and exploded in the sky above Chelyabinsk, shattering windows and injuring nearly 1,500 people, it was a reminder that the Earth moves blithely through a curtain of speeding asteroids, some of which occasionally pay a visit. Star gazers, of course, see these reminders many times a night in the shape of shooting stars—the glowing trails created by small specks of rock burning up as they enter the atmosphere. But when an object is large enough to make it through most of the atmosphere intact and strike—or nearly strike—the surface, “oohs” and “aahs” are not the first things on people’s lips.

It was an asteroid, after all, whose impact—with resulting mega-tsunamis, super-heated dust clouds, and years-long dusk—contributed to the doom of the dinosaurs. A far smaller one in 1908 leveled 80 million trees with a force a thousand times more powerful than the Hiroshima bomb in remote Tunguska, Siberia. And on the very same day that the Chelyabinsk meteor made its presence known, a roughly Tunguska-sized asteroid known as 2012 DA14 skimmed between the Earth and some of our own satellites, a one-two punch that has people asking just what, exactly, we are doing to protect ourselves.

Asteroid Ida
Asteroid 243 Ida is a massive resident of the asteroid belt. Large asteroids are easily spotted. But it's smaller, still potentially devestating, objects that worry scientists more because we cannote easily detect them.

In fact, “mind the asteroids” has been on the to-do list of the world’s spacefaring nations for some time. Scientists have long had a general portrait of the solar system’s historical population of asteroids, from keeping a tally of the craters on Earth, the Moon, and neighboring planets. Watching fragments of the Shoemaker-Levy 9 comet slam into Jupiter in 1994, the largest piece hitting with a force of 600 times the world’s nuclear arsenal, added a bit of urgency to the task of discovering the locations of asteroids whizzing about our system, recalls planetary scientist Don Yeomans, manager of the Near Earth Objects Program at NASA’s Jet Propulsion Laboratory. In 1998, NASA committed to finding and tracking 90% of asteroids greater than 1 km in size in ten years, which they finished slightly behind schedule. Though none of those are on track to hit us in the next 100 years, they are far from the whole population of asteroids that could harm us—the Tunguska object is thought to have been around 30 meters wide, less than 1/30th the size of the smallest asteroid tracked by the 1-km survey.

Given the recent scare from the Chelyabinsk meteor, you’d think rallying further support to find, track, and defend against asteroids would be relatively easy. But as a Congressional hearing last week on the topic showed, it’s not. Over and over again, Congress tried to wrap their heads around how much was reasonable to spend on the issue. It’s not a simple calculation for humans to make. Asteroid strikes are rare yet stupendously destructive—something they have in common with terrorist attacks and nuclear power plant accidents—but, says David Ropeik, a consultant and journalist who writes about risk perception, they are missing something that makes preparing for those disasters an easy sell—personal experience.

“When we think about risk, we’re not using our ‘rational,’ just-the-facts, analytical brain—we’re using our instinctual, feeling brain,” he says. And because none of these policymakers, or most of the public, have actually witnessed the destruction wrought by an incoming asteroid themselves, asteroid strikes don’t feel real.

Weighing the Odds

On the face of it, the numbers are pretty straightforward. An asteroid strike the size of the one linked to the dinosaur extinction is calculated to happen only once every 100 million years. But “civilization-destroying” impacts are estimated to happen every 500,000 years or so. Tunguska-sized asteroids, capable of destroying whole cities, are thought to hit every 300 years. They may not strike in populated areas—the interval for that, as estimated by a landmark 1992 NASA report requested by Congress, is once every 3,000 years, and for specifically urban areas 100,000 years. But even if they hit in the oceans, they could cause enormous tsunamis on the coasts. At any rate, asteroids of various sizes will certainly strike us—perhaps not in the next few decades or even in the next hundred years, but within the foreseeable human future.

Here’s the thing about asteroid strikes that makes them different from many other natural disasters—they are preventable. If we know about an asteroid’s collision course ahead of time, we can nudge the object, changing its course so it whizzes by without hitting us. There are a variety of ideas on how best to do this, ranging from using a nuclear bomb to painting the incoming object white (or black) so photons will push it off track. But the technique that NASA officials say will likely make the most sense, depending on the situation, involves ramming it with a spaceship, similar to what NASA’s Deep Impact mission did to the comet 9P/Tempel in 2005. It’s a process that has to be carefully engineered: you have to know the asteroid’s size, shape, speed, projected orbit, and composition to calculate the effect of the impact.

At this point, Yeomans estimates, we would need 10-20 years of advance notice to prepare—to build a ship, launch it, hit the asteroid, and allow time for the spacecraft’s small nudge to sufficiently skew the object’s trajectory so it misses Earth. “If you find one that’s going to hit tomorrow morning or within three weeks, or even within a few months, there’s not a whole lot you can do about it except evacuate the affected areas,” he says. “The search is the most important.”

Hunting for Asteroids

In 2005, as a follow-up to the survey begun in 1998, Congress asked NASA to find 90% of all asteroids 140 meters or larger by 2020. That phase is going slowly enough, however, that it won’t meet Congress’s goal in time. “We’ve done the best we could with the money that’s appropriated for us,” says Lindley Johnson, the NASA executive in charge of the Near-Earth Object Program. “The systems we have are for larger objects…We could do it with the assets we have available given enough time. But if you want to accomplish it on the order of a decade or two, you of course have to have more capable systems in order to do that.”

The fact that such surveys exist is an improvement on earlier eras, but the pace of asteroid discovery and its dependence on public funding has some people worried. Not that an optimally supported search program would be that expensive: the National Academies of Science estimates $100 million a year. By comparison, that’s the same amount the Federal Highways Administration is authorized to give a state to rebuild roads after a single natural disaster. If building and testing a mitigation program are factored in, an asteroid defense system would cost something like $2 billion between now and 2025. That’s just under $200 million per year.

But a program to prevent something that feels as distant as an asteroid strike, while relatively cheap compared to other government endeavors, may not always get the support it needs from elected officials, or the general public.

Last week, construction and staff jobs at the Pan-STARRS telescope system in Hawaii, which is used for near-Earth-object observation, among other purposes, had to be rescued by an anonymous $3 million donation after federal funding was cut. Corey Powell, editor-at-large at Discover Magazine, recently estimated that the federal budget for asteroid detection is 1/20,000th of what we spend on homeland security, and about one-fifth of Congress’s yearly budget for free postage. From the public’s point of view, maybe that’s enough: a recent headline at NowThisNews quipped, “Congress Holds Asteroid Hearings, Because There Are No Other Problems.”

Despite this apathy, the urgency in some quarters is such that the nonprofit B612 Foundation is planning to build and, in 2018, launch an asteroid-spotting infrared space telescope to pick up where NASA has slowed down.

“There’s no sense in us trying to beat on the federal government to do it. Private initiatives in space are where things are heading these days,” says Rusty Schweickart, a former astronaut who co-founded B612. “When you really look at it, this is no bigger than a community putting in a performing arts center or a new wing on a hospital…you’re talking $400 million, so let’s just do it!” He estimates that in the six and a half years the telescope is expected to operate, it will find about 95% of the 140-meter asteroids NASA has been tasked with finding.

Political Hurdles

While B612’s telescope may speed detection along, ultimately it is governments that must decide what we should do when an incoming asteroid is sighted. Once an asteroid is found, space agencies will be able to determine approximately where on Earth it will strike, and it’s not hard to see how tensions might rise quickly, and how difficult it might be to hold a calm, reasoned discussion about which spacefaring nation should do what and who is responsible if things go wrong. Currently, a UN subcommittee is working to put together a protocol to address the issue before it becomes a crisis. But how much attention the problem gets will depend on how palpable policymakers feel it is.

At a House hearing on March 19, with mentions of sequester bouncing around, one representative asked John Holdren, the president’s science advisor, to estimate the cost-effectiveness of an asteroid-strike-prevention program. Holdren answered with the facts—that when you consider the amount of human life that would be lost and amortize that over a reasonable number of years, you get something like 100 deaths per year due to asteroids. It’s relatively small compared to 1 million deaths annually from malaria and 5 million from tobacco, Holdren admitted.

But that sort of accounting does not accurately reflect the possible devastation of a large strike. “What is the value of all civilization?” Holdren asked. “It is a very big number. We just can’t get at it that way.”

That exchange illustrates the intractable nature of the problem, Ropeik says. “We haven’t evolved to have instincts for some risks that require a little more careful, rational thought, like this one.” Asteroid strikes occupy a tragic blind spot in the human mind. Like climate change, they are potentially avoidable but extremely difficult for us to confront. “It doesn’t feel real,” Ropeik says. “It feels just not-real enough to be able to ignore.”

Perhaps to help things feel more real, it might help to revisit one of the only known accounts of the last time a major object struck the Earth: Tunguska, 1908. According to S.B. Semenov, who was sitting on the porch of a Siberian trading post that June evening, he first saw what looked like a fire above the trees before him. Then a shockwave blew him off the porch. His shirt was so hot, he said, that it felt like it was on fire. He was more than 40 miles away from the spot where the asteroid crashed into the Earth.