Asteroid 62412. Credit: Scott Sheppard Comets are often called dirty snowballs by astronomers. However, various investigative missions, such as Giotto and Deep Impact, revealed them to be blackened, cratered, and fractured. No ice fields, reflective crust, or watery clouds were observed. Indeed, the latest pictures from the Rosetta mission of 67P/Churyumov-Gerasimenko indicate that it is a mountain of rock in space.