I studied geology at university, which means I'm no stranger to an odd-shaped rock. Here on Earth rocks normally get these shapes because of erosion, but out in space erosion doesn't work in the same way.
So I've often wondered how the comet that the Rosetta probe is currently orbiting - called 67P/Churyumov-Gerasimenko - got its rubber-duck-like shape.
Now space scientists think they have the answer. They say the 'head' is actually a small chunk left behind when the 'body' collided with a much larger rock.