The Bad Astronomer writes: "The asteroid 2011 AG5 is 140 meters across: football-stadium-sized. Its orbit isn't nailed down well enough to say yet, but using what's currently known, there's a 1 in 625 chance it will impact the Earth in 2040. It's behind the Sun until September 2013, and more observations taken then will probably reduce the odds of impact to something close to 0. But does it make sense to wait until then to start investigating a mission to deflect it away our planet? Astronomers are debating this right now, and what they conclude may pave the way for how we deal with an asteroid threat in the future."