Supporting evidence for the theory that Earth’s oceans may have been brought here by cometary collisions has emerged. Astronomers from the University of Hawaii have located three icy asteroids that give off a ‘tail’ of volatile materials, which have flat, circular orbits in the ‘main belt’ between Mars and Jupiter. This will add fuel to the ongoing debate about how to distinguish between an asteroid and a comet, and indeed what those two words can be defined as meaning.