Asteroid 1998 QE2 as seen by the Arecibo telescope. Source
Back in 1998, a massive asteroid, dubbed 1998 QE2, was discovered by a team at MIT. This year, the asteroid made a close flyby of Earth, just a little over 6 million kilometers out (that sounds like a very far distance, but in astronomical terms, it's nothing). During that close flyby, it was caught on "camera" by a team manning the Arecibo radio telescope. These researchers bounced radio waves off of the giant floating space rock and were able to map its topography using a technique based on the Doppler effect. What they didn't expect to find, however, was that the asteroid had it's own little moon. That's right, this asteroid is so big that there is an object caught in orbit around it. You can see this moon as the little, white blip towards the bottom left of the picture. We are very fortunate that this asteroid wasn't closer to us.
For more information, check out this article.