Humans live in a vast solar system where 2,000 feet seems a razor-thin distance.

Yet it's just wide enough to trigger concerns that an asteroid due to buzz Earth on April 13, 2029 may shift its orbit enough to return and strike the planet seven years later.

The concern: Within the object's range of possible fly-by distances lie a handful of gravitational "sweet spots," areas some 2,000 feet across that are also known as keyholes.

The physics may sound complex, but the potential ramifications are plain enough. If the asteroid passes through the most probable keyhole, its new orbit would send it slamming into Earth in 2036. It's unclear to some experts whether ground-based observatories alone will be able to provide enough accurate information in time to mount a mission to divert the asteroid, if that becomes necessary.

So NASA researchers have begun considering whether the US needs to tag the asteroid, known as 99942 Apophis, with a radio beacon before 2013.

Timing is everything, astronomers say. If officials attempt to divert the asteroid before 2029, they need to nudge the space rock's position by roughly half a mile - something well within the range of existing technology. After 2029, they would need to shove the asteroid by a distance as least as large as Earth's diameter. That feat would tax humanity's current capabilities.

NASA's review of the issue was triggered by a letter from the B612 Foundation. The foundation's handful of specialists hope to demonstrate controlled asteroid-diversion techniques by 2015.

Last Wednesday, representatives from the foundation met with colleagues at NASA's Jet Propulsion Laboratory (JPL) to review the issue. The foundation's letter marks the first time specialists in the asteroid-hazard field have called for a scouting mission to assess such a threat.

"We understand the risk from this object, and while it's small, it's not zero," says David Morrison, the senior scientist at NASA's Astrobiology Institute at the Ames Research Center at Moffett Field, Calif.
The call for a reconnaissance mission also illustrates how far the field of asteroid-hazard assessment has come.

"Ten years ago, we would have been blissfully ignorant," says Donald Yeomans, who heads NASA's near-Earth object project at JPL. Today, at least five programs worldwide are hunting down near-Earth objects. NASA is well on its way toward achieving its goal of cataloging 90 percent of the near-Earth objects larger than 0.6 miles across by 2008. And it is devising ways to ensure that information about potential hazards reaches top decisionmakers throughout the government.

Based on available data, astronomers give Apophis - a 1,000-foot wide chunk of space debris - a 1-in-15,000 chance of a 2036 strike. Yet if the asteroid hits, they add, damage to infrastructure alone could exceed $400 billion.

I think this is quite worrying, though, hopefully, scientists will make the right decision in time for the right action !