An asteroid is going to pass so close to Earth in 2029 that it will be closer to us than many communication satellites are. Depending on how our own Gravity affects it will depend on whether it hits us on its next pass. Possible strike dates are 2034-37 (a stirke is possible in any of those years depending on gravity), 2046, 2048, 2054 and 2055.
The asteroid is estimated to be 300m in diameter and capable of wiping out a large city or worse, causing a large tsunami.
Dont belive it - look up 2004 MN4
Wiki on it, pay attention to the bit which mentions what happens AFTER it passes us the first time.
Annnd just in case you think this is some sort of internet wind up - next time you pass the news shelves in the next week - have a look for New Scientist - its the cover story.