Apparently, 2004 YD5 passed by the Earth at 0.093 LD (Lunar Distance).
This is within geostationary orbit.
It was a very small asteroid, but it wasn't seen until it passed us
because it came towards us from the sunward direction.
To read more, see:
http://www.space.com/scienceastronomy/asteroid_close_041222.html
-Paul
