New Scientist: Astronomers continue to be surprised by Saturn’s moon Enceladus. Most of the planets and moons studied so far consist of a core of dense material covered by a large mantle and an outer crust. Based on computer modeling, however, Enceladus’s core can’t be stiff and rocky and also produce the huge watery plumes that have been observed shooting into space as the moon orbits Saturn. In order to generate the heat necessary to melt the icy crust and shoot the jets, the moon’s core may be more like a rubble pile with empty spaces filled with ice or water, similar to a snow cone. The finding has implications for the search for extraterrestrial life because such hydrothermal systems are important to the formation of biological organisms.