http://neo.jpl.nasa.gov/apophis/
2029 it will pas between us and the moon. 2.9% chance of hitting us.
russian space agency says it will pass through a area in space that will sling it back into us in 7 years. Nasa says it won't pass through that area of space referred to as a keyhole.
so by 2020 we better be able to beam shit right out of the skies and obliterate it with our ray guns, or whatever sci fi moniker you want to use