A computer generated “aridity index” that maps out the dry places (yellow-brown) and the wet places (green) of an Earth-like planet that rotates on its axis much more slowly than Earth. The slowly rotating version of Earth has climate zones very different from actual Earth – the Sahara desert has turned into a rain forest, and the northern U.S. and Canada have become more arid like Los Angeles. Overall, slowing the rotation produces a rocky planet with rain and possibly habitable conditions on more of the surface of the planet. (NASA GISS-Columbia University)