For many people, asteroids are big rocks that drift menacingly through space and are great places to have a laser cannon dogfight. Conventional scientific wisdom holds that they are the leftover scraps of planet formation. Their full story, though, is rather more complex and still only dimly glimpsed. What planetary scientists lump together as asteroids are far too diverse—from boulders to floating heaps of gravel to mini planets with signs of past volcanic activity and even liquid water—to have a single common origin.