|Radar image of 2005 YU55 in April 2010|
According to Jay Melosh at Purdue, the asteroid would create a crater 6.3 km across, 518 m deep, and deposit the energy equivalent to a magnitude 7 eartquake. YU will pass close to Venus in 2029 and the exact details of that encounter will determine how close to the earth it will come in 2041.
JPL has a small-body database browser here that allows you to visualize the orbit, but the site is, at this time a few hours before the encounter, overloaded. We're not going to see it in gray, rainy Urbana tonight, but amateur observers in Europe and on the East Coast have a great chance. This is the first near asteroid for which observers have had advance warning and been gearing up to make radar, visual and infrared observations. With 5-meter radar observation, they are hoping to create a detailed 3-D image of its shape and surface.
I'll update the photos as they are released after the encounter.