An artist's illustration of a massive asteroid impact on earth. Some single-celled organisms may be able to survive extreme impacts such as these, scientists say.

The toughest part about defending Earth against hazardous space rocks may be overcoming human nature.

Our species tends to tackle problems as they come up, defusing dangers deemed immediate and extreme. But effectively protecting the planet from asteroids will require constant vigilance over the long haul, experts say, since the threat of a major cosmic impact will never go away.

"It's a long-term, ongoing type of situation," Bill Ailor, principal engineer with the Center for Orbital and Re-entry Debris Studies at The Aerospace Corporation, said last Wednesday (March 12) during a presentation with NASA's Future In-Space Operations working group. "And I don't think humanity has a particularly good track record of being able to deal with a problem that's more than, say, a generation long." [Potentially Dangerous Asteroids (Images)]

A very real threat

Earth has been pummeled by asteroids and comets continuously over the eons, sometimes with catastrophic results. A strike by a 6-mile-wide (10 kilometers) body, for example, wiped out the dinosaurs 65 million years ago.

The danger of death from above will never disappear. Scientists think 1 million or more asteroids cruise through space in Earth's neighborhood, and some of these rocks doubtless have our planet in their crosshairs.

Adding to the threat is the fact that scientists have so far identified and tracked just 10,700 or so of these near-Earth asteroids.

There is some good news: About 95 percent of the 980 potential civilization-enders — rocks at least 0.6 miles (1 km) wide — have been found, and none of them pose a threat to Earth in the near future. But that still leaves many thousands of unseen, unknown asteroids that could devastate an area the size of a state if they hit Earth.

The world got a reminder of the potential danger on Feb. 15, 2013, when a 65-foot-wide (20 meters) object exploded without warning over the Russian city of Chelyabinsk, injuring about 1,500 people. [Photos: Russian Meteor Explosion of Feb. 15, 2013]

In an eerie cosmic coincidence, the surprise Russian meteor blast occurred on the same day that a 100-foot-wide (30 m) asteroid called 2012 DA14 gave Earth a close shave, missing our planet by just 17,200 miles (27,000 km). (For comparison, the moon orbits at an average distance of 239,000 miles, or 385,000 km).

Always ready

Humanity doesn't have to go the way of the dinosaurs, Ailor and other experts stress; our species has the ability to deflect or destroy an incoming asteroid, provided we know about the potential impact in advance.

Given a lead time of years or decades, for example, we could launch a robotic probe to rendezvous with and fly alongside a threatening space rock, nudging it off course via a subtle but constant gravitational tug.

And if the asteroid popped up on the radar just a month or so out, we could potentially blast it to smithereens with a nuclear bomb as a last resort.

But the design and implementation of such strategies must begin as soon as possible to maximize the chance of success, Ailor said.

"The technologies that you need must be available when you need them," he said. "For example, if you've got about five years out, that's not very much time to go off and develop new techniques."

Further, humanity must keep its asteroid-deflecting skills fresh far into the future — a task that runs counter to our species' short-term mindset.

"We might not need to do this for 100 years or something, but sometime we will need to do it," Ailor said. "So how do we maintain the capabilities and the technologies available over a long period of time to do a mission which may not occur for years or decades? That'll be a challenge as well."

A global effort

Mounting an effective asteroid-deflection mission will also require global cooperation, posing another potential difficulty.

For instance, the cost will be quite high, since multiple missions will probably be launched to guard against failure. (The probability of a launch failure is around 1 percent, Ailor said, and the chances of a spacecraft failure are likely somewhat higher than that.)

"Deflection/disruption campaigns may involve a substantial percentage of the planet's space-launch resources," Ailor said.

And planetary defense is, of course, an inherently global issue, since every nation around the world is susceptible to an asteroid or comet strike. Deflection efforts would have to be coordinated internationally, and not just for financial reasons: Nudging an incoming asteroid could move it away from one country and — if not done completely or correctly — toward another one.

Indeed, the United Nations is currently developing a framework for international cooperation to help prevent strikes by dangerous asteroids and/or mitigate their worst consequences. This framework should help decision-makers answer difficult questions, such as when action is required, how a deflection campaign will be organized and who will pay for it, advocates say.

"I think these kinds of challenges are almost harder than the technical parts of it," Ailor said.

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