An asteroid, headed our way

"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."