Astrobiologists searching the heavens for extraterrestrial life have a simple motto: “Follow the water, ”says The Washington Post. Water is an essential ingredient in all earthly biochemistry, so scientists believe it’s logical to look for life first on planets and moons with liquid water.New data from NASA’s Cassini spacecraft indicate that Enceladus, a tiny, ice-encrusted moon orbiting Saturn, may be home to an underground body of water roughly the size of Lake Superior. The existence of the reservoir was first suggested in 2005, when Cassini detected the moon’s south pole emitting plumes of water vapor. Further observation revealed additional factors, such as gravitational asymmetry and surface contours, indicative of a subterranean ocean. The new data also point to a rocky sea floor, where the chemical interplay between minerals and water could be a catalyst for the development of life. Cassini, which was launched in 1997, is not equipped to search for life, so Enceladus, along with one of Jupiter’s ice-covered moons, Europa, is now in the running to be the target of a future robotic space mission. “The two of them provide the highest probability of finding extant life,” says NASA astrobiologist Mary Voytek.