SAN FRANCISCO – In the movie version of stopping an asteroid from hitting Earth popularized by Armageddon, a few brave Americans quickly head out to the near-Earth object and blow it up.

The reality will be far less dramatic, former astronaut Rusty Schweickart told scientists at the American Geophysical Union meeting here Wednesday. Asteroid-deflection efforts will have to start years before a prospective impact and will have to be essentially international.

"Whether or not the international community, within or outside the United Nations, can rise to the demands of such a challenge in advance of an impact … is problematic," Schweickart summarized.

Two general strategies for deflecting asteroids are currently on the table. The first is some type of impactor or blast, possibly nuclear, that would knock the asteroid off the collision course. The second is a longer-term "shepherding" operation that would slowly morph the asteroid's trajectory in space so that it misses Earth. Both schemes would have major international implications.

Nuclear weapons have been explicitly outlawed in space since the Partial Test Ban Treaty was negotiated in 1963. Sending a nuclear weapon into space to hit an asteroid would require modifying the treaty, which could have unforeseen negative repercussions.

"Many of us have expressed our concern about nuclear effects because of political options," said David Morrison, an astronomer at NASA Ames Research Center who organized a session at the AGU meeting about near-Earth objects.

Schweickart's group, The B612 Foundation, has advocated a different approach to asteroid deflection, but one that will require an equally difficult international negotiation. They propose to bump or tow an asteroid "in a controlled manner" so that it misses Earth. The only problem is that such a process would take time and as the asteroid's trajectory changed, it would be "pointed" at different places along a horizontal plane on Earth called the risk corridor.

That's a major geopolitical problem, Schweickart said, because it requires temporarily increasing the risk to one population — in the example above, Venezuela, or Russia — to eventually eliminate the risk for the entire Earth.

"It's going to be slowly dragged across the Earth. That is a binary decision," Schweickart said. "You don't have the option of dragging it down through the Antarctic."

Who gets to decide which way the asteroid is dragged away from an impact with Earth? The United Nations? The United States? Russia? Some independent body of astronomers and space agencies?

"What deflection technologies are OK and who says they are OK?" Schweickart asked. "Who accepts liability? How do you decide that it's OK to endanger the people of Venezuela or the people of Kazakhstan?"

He called figuring such questions out a "geopolitical decision of the first order." Earlier this year, the Association of Space Explorers presented a report to the U.N. Committee on the Peaceful Uses of Outer Space recommending that some international decision-making bodies be created to evaluate and respond to near-Earth object hazards.

The U.N. committee could bring some options before the General Assembly by 2012, although Schweickart has some doubts that people are politically prepared to deal with the tough decisions that humanity could face to deflect an asteroid.

"You're going to have to make that decision when the probability is less than one, 10 or 20 years ahead of time," he said. "That's not easy for anyone, let alone the United Nations."

Images: 1) A gravity tug./NASA.

2) Association of Space Explorers.

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