Among Saturn’s substantial posse of moons—61 have been discovered so far—two particularly odd ones are capturing the imagination of planetary scientists. A torrent of findings has shown that giant Titan (3,200 miles wide, larger than the planet Mercury) and tiny Enceladus (just one-tenth as big) are worlds of unexpected complexity, placing them among the most promising extraterrestrial sites in our solar system to look for prebiotic chemistry or even for life itself. Research in the past several months has further fueled the excitement, yielding new hints of liquid water on Enceladus and revealing ethane lakes and methane rain on Titan.
In 2005, while exploring the Saturn system, the Cassini spacecraft made a startling discovery: Cryovolcanoes on Enceladus were spewing jets of water vapor and ice into space, possibly from a liquid water source beneath the surface. This past July researchers examining data from Cassini’s mass spectrometer announced that the icy debris contains ammonia, a potent antifreeze that could keep water in a liquid state even at the deep-freeze temperatures (–136 degrees Fahrenheit) measured near the vents. A month earlier, astronomers in Germany and the U.K. reported that sodium salts make up as much as 2 percent of the ice grains in the jets. Such a high salt concentration suggests the presence of a buried reservoir of liquid water. (Long-frozen ice would include little sodium, but a lingering underground lake would turn salty from dissolved minerals, just as the oceans have on Earth.)
