Norbert Schörghofer of the University of Hawaii at Manoa has proposed a new Martian climate theory, which suggests the planet has gone through at least 40 ice ages during the past five million years. These regularly send the planet's permanent ice sheets toward the equator before melting backward. These cyclical fluctuations are likely caused by shifts in the planet's orbit that alter the amount of sunlight reaching the planet's surface. The large volumes of ice found across the planet has puzzled scientists, with the prevailing theory being that the ice was laid down some 5 million years previously as snowfalls, but explaining how the ice water has survived so long has proven difficult. Schörghofer's theory explains the presence of the ice by suggesting it was laid down much later than thought, some perhaps only half a million years ago. National Geographic has the full story.