A Moon That Spews Water: The Secret Ocean of Enceladus

Saturn's moon Enceladus is only about 500 kilometers in diameter, a bit longer than Taiwan, and its surface is an ice shell at -200 degrees Celsius. At first glance, it just looks like an ordinary ice ball. Until 2005, when the Cassini probe flew over its south pole and captured an image that made scientists jump out of their chairs: this ice ball was spewing water into space. Its south pole has four giant fissures, nicknamed 'tiger stripes,' constantly erupting with water vapor and ice crystal plumes reaching hundreds of kilometers high. These ejected materials are even abundant enough to form Saturn's E ring—in other words, one of Saturn's rings was 'sprayed' out by this small moon. Where does the water come from? The answer lies beneath the ice shell: an entire global ocean of liquid saltwater. Enceladus is so far from the sun, why hasn't the ocean frozen? Because Saturn's powerful tidal forces constantly knead it, much like repeatedly bending a wire generates heat, friction keeps the ocean liquid. The most exciting part is yet to come. Cassini flew directly through the plumes to sample them, and detected: salinity, silicon dioxide nanoparticles (indicating hydrothermal activity on the seafloor), hydrogen gas, and various organic molecules. Recent analyses have even found phosphorus—a key element for life, almost all the necessary components are there. Beside hydrothermal vents in Earth's deep sea, there's a complete ecosystem, and the environment at the bottom of Enceladus's ocean might be very similar. This means one of the most likely places in the solar system to find extraterrestrial life isn't Mars, but a small moon that sprays 'seawater samples' into space all by itself.