Liquid water is known to exist in abundance on Earth’s surface. Detailed studies of Mars over the past decade have shown tantalizing evidence that liquid water exists there underground, and occasionally spurts out through canyon walls and other geologic events on the Martian surface. Salty water may also flow for short distances across the surface of Mars during the cool Martian summers. Studies made with the Galileo spacecraft show that Europa and probably Ganymede, two of Jupiter’s moons, likely contain liquid water deep beneath their surfaces; and studies done with the Cassini spacecraft show that Saturn’s moon Enceladus blows geysers of liquid water into deep space, through fissures on its icy surface.