THE world is unprepared for an asteroid strike, and we should be planning now to protect ourselves. That鈥檚 the frightening conclusion of an international group of experts who met last week at a NASA workshop on the asteroid threat.
After nearly five years of intensive surveys, researchers are calling for an urgent shift of emphasis. There is now an estimated 1 in 5 chance that an asteroid big enough to destroy a city will hit the Earth in the next 100 years. Yet the long-term orbits of most dangerous asteroids are proving hard to pin down. 鈥淚 feel a lot less safe today than I did,鈥� says Mike Belton, who worked on comet observations at the National Optical Astronomy Observatory in Tucson, Arizona, before founding NASA contractor Belton Space Exploration Initiatives, also in Tucson.
So instead of just scanning the skies for asteroids on a collision course, many researchers are backing a $3 billion programme to develop ways to deflect an object found to be heading our way.
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Over the past five years, most researchers have been happy to not worry about how to protect ourselves unless we found a rock with our name on it. The LINEAR (Lincoln Near Earth Asteroid Research) telescopes in Socorro, New Mexico, and other optical surveys have so far logged more than half of the 1000 or so asteroids over 1 kilometre across which are in orbits that could cross Earth鈥檚 (see Graphic). But although none so far is on target to collide with us, that view has changed, and the people thinking up schemes to deflect asteroids or blow them up are no longer fringe figures.
One reason for the change of heart is that the more we find out about the composition of asteroids, the more difficult the task of deflecting them appears. For example, follow-up radar images of asteroids found by LINEAR show that almost all of them rotate more slowly than 10 times per day. This cut-off suggests that what we thought of as rocks are actually rubble piles that would fly apart if they rotated any faster, Alan Harris of the German Aerospace Centre in Berlin told the workshop, held near Washington DC.
Such objects would be extremely difficult to move or deflect in a predictable way. What鈥檚 more, radar studies published earlier this year show that around 1 in 6 known asteroids are actually binary systems, making them even harder to approach and land on than previously thought. Belton now fears that the knowledge required to intercept and deflect an asteroid could take centuries to collect.
And it鈥檚 not just the big ones we need to worry about. A growing concern is the large number of smaller asteroids, between 300 and 1000 metres across, that are being detected by current surveys. These bodies are not being carefully tracked or studied because they are probably too small to cause a global catastrophe. But they could easily wipe out a city if they landed nearby. Researchers now estimate there is a 1 in 5 chance of an asteroid in this size range hitting Earth in the next 100 years. 鈥淭hat is precisely why I decided to change my life and get into asteroids,鈥� says Belton.
Worse, it鈥檚 becoming clear that we can鈥檛 be sure about the orbits of these smaller asteroids, however carefully we track them. At the workshop, Duncan Steele of Salford University near Manchester showed how radiation pressure from the Sun can make smaller asteroids drift from their predicted orbit.
Findings like this have convinced researchers that it鈥檚 time to look into methods of dealing with dangerous asteroids. 鈥淲e should pick a concrete goal of, say, moving an asteroid of 150 metres across by 5 to 10 centimetres per second by 2015, and work up,鈥� says Ed Lu of NASA Johnson Space Center in Maryland. At the workshop, Belton outlined a 25-year strategy for this work that would cost $3 billion 鈥� a vast investment compared with the $4 million a year the US now spends on asteroid studies.
Those with the money, however, are busy passing the buck. One obvious source of funding is NASA, but it is still focusing on basic science. Ed Weiler of NASA headquarters in Washington DC said the agency would not be responsible if an asteroid destroyed the Earth. 鈥淚 can鈥檛 take responsibility unless I have H-bombs in my desk,鈥� he says. And Pete Worden of the US Air Force headquarters in Washington DC told the workshop that the US military will not be a major source of funding unless there is a clearer chain of command within the US government of who is responsible for defining asteroid risks.
With no other international organisations spending significant amounts of money on asteroid deflection, the task of saving the planet may yet fall to private institutions or charities. For example, Apollo 9 astronaut Rusty Schweickart and Clark Chapman of Southwest Research Institute in Boulder, Colorado, are tired of waiting for funds to appear. They aim to use charitable funds to develop the technology needed to move an asteroid. 鈥淚f you find someone with a few tens of millions of dollars and name the mission after them, maybe that鈥檚 the way to go,鈥� says Erik Asphaug of the University of California, Santa Cruz, who organised the workshop.
If governments won鈥檛 stump up the cash to protect the planet, they won鈥檛 get the credit either.