Asteroid hunters have good news – and a challenge – for the rest of us.After an extensive search for asteroids a kilometer or more across, engineer Steve Chesley says that "we can now say with confidence that no asteroids large enough to cause such a global calamity [as killing off the dinosaurs] are headed our way."

But if one of them – or even a smaller, city-destroying rock – were detected on a collision course, would the world community be prepared to handle it? A conference of legal experts that discussed this question at the University of Nebraska in Lincoln last month answered it with a resounding "No."

Scientists and engineers who have studied the problem of deflecting a dangerous asteroid believe the technical issues are difficult but solvable. The challenge now is figuring out the legal issues of who takes action on behalf of humankind and of what their responsibilities and liabilities will be.

Asteroid hunters believe they can give us plenty of warning. There is "a fair chance that the next Earth impactor will actually be identified with many decades and perhaps centuries of warning time," explains Mr. Chesley of the NASA Jet Propulsion Laboratory in Pasadena, Calif., in the March/April issue of the Planetary Report.

That's plenty of time to develop a spacecraft whose gravitational attraction might nudge an asteroid aside – or a rocket or some application of nuclear explosives to do the job.

However, if a single country – or small group of nations – tries to take the initiative on its own, the international reaction could stall any action at all.

"The international political reactions to the US shooting down one of its own satellites a year ago to prevent presumably dangerous and toxic rocket fuel from reaching Earth only foreshadows what would happen if the US would detonate nukes claiming to destroy an incoming asteroid," said Frans von der Dunk, a University of Nebraska space law expert, at the Nebraska conference, according to Space News.

Overlooking the hype about nuclear weapons, which engineers consider an unlikely, extreme measure, Professor von der Dunk has pointed out the main issue. Averting a regional or global asteroid threat may involve unforeseen collateral damage – such as splintered chunks making their way to Earth or worse. Therefore, the world community has to have a say in how that threat is handled.

Right now, to use von der Dunk's word, that community is "underorganized" to meet this challenge.

Getting organized for possible future action is less urgent than coping with global warming. But like any good insurance planning, it should not languish on the back burner of global politics.

This need will come into sharper focus as the new Pan-STARRS 1 telescope in Hawaii goes into action this spring. Its mission to catalogue objects across the entire sky will pick out many more asteroids, large and small.

Someday those facts may foretell a future impact. The world community should make sure that it has its response plan in order with the legal mechanism for assigning responsibilities in place.