http://blogs.discovermagazine.com/badastronomy/2009/08/10/when-worlds-collide/
n.The Spitzer Space Telescope has detected signs of an interplanetary smashup, and oh, what a colossal event it was… apparently, 100 light years away around the young star HD 172555, an object the size of the Moon slammed into a planet the size of Mercury!