Owen and his fellow planetary scientists are used to picturing Titan in their imaginations. Now they've visited, if only by remote control. For the past two-and-a-half years, a space probe called Cassini has hobnobbed with the moons and rings of Saturn and gazed down on the giant planet. Soon after arriving, Cassini even launched a second, smaller probe called Huygens, which touched down on Titan's surface.
The Titan encounter was a high point in what has amounted to a voyage back in time. From the exotic metallic hydrogen in its interior to the ﬁne rubble of its rings, on moons that range from the icy oddball Phoebe to Enceladus, which spurts warm geysers, Saturn carries clues to how the solar system took shape 4.6 billion years ago and gave rise to life. The planet and its orbiting retinue, says planetary scientist Jeff Cuzzi of NASA's Ames Research Center, "connects us to solar system structure and evolution on the grandest scale."
Saturn has been slow to give up its secrets. In 1610 Galileo discovered what turned out to be its most amazing feature, the rings, but through his primitive telescope, he mistook them for two smaller bodies flanking Saturn. Only in 1656 did Dutch astronomer Christiaan Huygens (the namesake of the Titan probe) recognize what they were. Huygens also discerned a faint spark outside the rings—a moon later named Titan, after the Titans of Greek mythology, who reigned during Earth's early days.
Since then, decade by decade, astronomers have picked out smaller moons, 56 at last count. In the 1940s, as telescopes improved, they discerned a haze around Titan, the ﬁrst sign that, unlike any other moon in the solar system, it has a dense atmosphere. Finally, the ﬁrst space probes flew past Saturn—Pioneer 11 in 1979 and Voyagers 1 and 2 in 1980 and 1981. Speeding by, they snapped close-ups of the planet, rings, and moons and gleaned the ﬁrst hints that Titan is a frozen time capsule of conditions similar to those found on the very early Earth.