How to fight an asteroid
Posted: Friday, February 16, 2007 7:19 PM by Alan Boyle
Today there are more than 100 entries on NASA's list of asteroids that just might possibly hit Earth, even if it's less than a one-in-a-million chance. One of them, called Apophis, currently has a risk rating of 1 in 45,000 - serious enough to get people thinking about how to avoid a "cosmic Katrina." Chances are that Apophis will soon no longer be considered a threat, but what about those others? And what about the thousands of space rocks that are expected to be added to the list over the next few years?
NASA |
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A massive asteroid strike would
have a catastrophic effect.
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Somewhere out there is a killer asteroid with our name on it, and scientists, astronauts, diplomats and space law experts are just starting to draw up a plan for dealing with it - that is, once we figure out which asteroid it is.
Experts on near-Earth asteroids laid out their current thinking on impact threats today during a news briefing in San Francisco at the annual meeting of the American Association for the Advancement of Science. They broke the issue down into three key questions:
- How do we find potentially threatening asteroids and assess whether the threat is real?
- What can we do if we determine there's a threat?
- Who decides what to do?
The first question is likely to get a lot more interesting: In 1998, just around the time that "Armageddon" and "Deep Impact" hit the movie theaters, Congress told NASA to find 90 percent of all near-Earth objects, or NEOs, bigger than a half-mile (1 kilometer) in diameter. So far, the Spaceguard Survey has cataloged more than 800 asteroids of that size, out of a projected population of 1,100.
A couple of years ago, Congress revised the goal, calling on NASA to find 90 percent of the NEOs that are at least 460 feet (140 meters) wide. If one of that smaller class of asteroids were to hit Earth, it probably wouldn't wipe out civilization, as the 1-kilometer variety might - but it would devastate an area the size of, say, England or Northern California, said David Morrison of NASA's Ames Research Center.
NASA is still working on its response to the new mandate, said Doug Cooke, the agency's deputy associate administrator for exploration systems. "The report is actually overdue," but it should be ready for release in the "pretty near term," he told me today.
"NASA does have some work under way, at least in terms of the first steps for doing it," he said. Five NASA-supported search teams are currently involved in the first phase of the Spaceguard Survey, he said. To move into the next phase, the agency is considering plans to augment those efforts, as well as potential space-based missions to look for asteroids, Cooke said.
NASA |
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This chart shows how additional observations have
reduced the likelihood that Apophis will pass through
a "keyhole" in space leading to a collision with Earth
in 2036. The risk may be reduced to zero in 2007.
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Apophis has emerged as the "poster child" for the assessment of asteroid collision threats, said Steven Chesley of NASA's Jet Propulsion Laboratory. Initially, the uncertainties surrounding observations of Apophis' orbital path were so great that experts gave it a 1-in-40 chance of hitting Earth in 2029. Since then, more observations have reduced the risk in 2029 to zero, but that 1-in-45,000 chance remains for a later encounter in 2036.
Chesley said that astronomers have been swarming to make more detailed observations of Apophis over the past couple of months. Those observations - which have not been fully analyzed yet - just might rule out an impact in 2036. "Stay tuned for that," he said.
Even if it turns out that Apophis isn't a threat, it will still be remembered as an "incredibly valuable asteroid" because it raised global awareness about potential impact threats, said former astronaut Russell Schweickart, chairman of the B612 Foundation.
Under the auspices of the Association of Space Explorers, Schweickart has organized a series of four workshops aimed at producing the language for an international protocol on asteroid deflection by mid-2009. The first workshop is scheduled this May in Strasbourg, France.
Schweickart said Apophis is just "an example of thousands of things we're going to have over the next 10 or 12 years," due to the expanded Spaceguard Survey. He pointed to a wavy line going over a map of the earth, representing the places where Apophis could hit in a worst-case scenario for 2036. By 2020, he said, "we're going to find a hundred or more lines across the planet like that."
Chesley estimated that there were about 20,000 medium-size, potentially threatening asteroids out there, waiting to be found, and a chart he showed during today's presentation indicated that more than 3,000 of them could be cataloged during just one year, 2011. The trick, he said, is to "find them as early as possible" so that there's plenty of time to come up with a strategy in case something has to be done.
NASA |
This chart shows the estimates for annual detections of asteroids more than 140
meters wide, based on planning for an expanded Spaceguard Survey.
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So what would be done? NASA astronaut Ed Lu said setting off a nuclear bomb or smashing a spacecraft into an asteroid wouldn't be the best course, because "you don't quite know what the results are going to be." For some time now, he's been fleshing out a scheme for sending a space tractor to hover right next to an asteroid - without touching it at all. In an Apophis-style scenario, the tractor's faint gravitational pull would shift the asteroid in its orbit just enough to avoid a collision.
Schweickart agreed that the space tractor appeared to be the best tool to use, but he emphasized that someone would have to be responsible for deciding when to use it. "You can know something's coming at you, and have something to do about it, but unless somebody's ready to make a decision, nothing's going to happen," he said. "The question is, who is the decision maker?"
That's where the U.N. protocol would have to play a part, he said. The United Nations probably wouldn't take on the job itself, but set up a contract with NASA, or the European Space Agency, or whichever entity was judged most competent. There would also have to be provisions for risk tradeoffs and indemnification - because it turns out that moving an asteroid can be a risky proposition.
"When you start to deflect an asteroid, certain nations are going to have to accept an increase in risk to their populations, in order to take the risk to zero for everybody," he said.
Schweickart and others involved in the asteroid-watching business aren't too crazy about the scaremongering they see in the media when it comes to potential deep impacts, but they also know it's hard to hold the public's interest unless there's an imminent threat.
It could take tens of millions of dollars, or even hundreds of millions, to get a good fix on potentially threatening asteroids. Governments and taxpayers will no doubt have to debate how much to spend, over how long a time frame. But unlike hurricanes or earthquakes, an asteroid armageddon is one natural catastrophe that can be stopped before it starts, Schweickart said.
"We can prevent an asteroid impact, and we do it by reshaping the solar system, ever so slightly," he said. "Literally, we have the human capability today to slightly reshape the solar system to enhance the survival of life on Earth. Now, if we don't do that, we're not that far past the dinosaurs."
