Closest Known Approach by a Large Asteroid

2005 YU-55 is going to make a very close approach to the Earth on the night of November 8, 2011. At that time, its distance from Earth will be just under nine-tenths of the moon's distance away from us. 2005 YU-55 cannot hit Earth at least over the interval that we can compute the motion reliably which extends for several hundred years.
It's going to be moving very rapidly as it traverses the sky near the Earth on November 7, 8, 9 and 10th. In affect it'll be moving straight at us from one direction and then it will go whizzing by and straight away from us in the other direction. So its motion across the sky will be close to degrees over the course of less than two days. It made a close approach to Earth about eighteen months ago in April of 2010. Colleagues of ours at Arecibo Observatory where able to observe this asteroid using the radar facility at Arecibo and they were able to obtain radar images that showed that this object is about 400 meters across. On November 8, 9, 10 we'll be observing it again.
This time with both the Arecibo telescope and with the Goldstone telescope here in California. This is the closest approach by an asteroid that large that we've ever known about in advance. The radar telescopes that we use to observe asteroids are very large radio dishes. The Goldstone telescope is 70 meters, which is 240 feet across so it's truly enormous, and Arecibo is even larger still. The Goldstone telescope has a new radar imaging capability which has just become available that will enable us to see much finer detail than has previously been possible. And depending on how we transmit the signal we can get different types of data.
It shows us how big it is, it can show us features on the asteroid, it can tell us information about the asteroids rotation period. We should be able to tell much better with these new observations that we're going to do. NASA Jet Propulsion Laboratory, California Institute of Technology