Scientists believe heat from radioactive decay inside a tiny, icy Saturn moon shortly after it formed billions of years ago may explain why geysers are erupting from the surface today. The Cassini spacecraft last year beamed back dazzling images of Yellowstone-like geysers spewing from a warm section on Enceladus, raising the possibility that the moon, which has an overall surface temperature of about minus-330 degrees, may have an internal environment suitable for primitive life. However, scientists have been stumped by the origin of Enceladus' interior heat. Now a new model suggests ancient radioactive decay played a key role in shaping the moon's warm south pole region, where plumes of water vapor and ice crystals periodically vent. According to the theory, Enceladus formed some 4.5 billion years ago by the mixing of ice and rock containing radioactive isotopes of aluminum and iron. Over a period of several million years, the rapid decay of the isotopes produced a burst of heat that resulted in a rocky core enclosed by an ice sheet. Over time, the remaining decomposition in the core further warmed and melted the moon's interior. If confirmed, the model suggests Enceladus possesses the necessary ingredients to support life - a stable heat source, organic materials and liquid water.