Unveiling Titan.

It rains liquid methane there, and the atmosphere is a dense orange that has been compared to Los Angeles smog. But space scientists today are excited to be closer than ever to solving the great mysteries of Titan, the largest of the many moons that orbit the planet Saturn. In January, the space probe Huygens (HOY-gens) parachuted through the orange murk to take the first close-up photographs of Titan. In the short time it had left before its batteries died, Huygens transmitted enough data to keep scientists busy for years.

Titan is the second-largest moon in our solar system--about a third larger than Earth's moon. (Only Ganymede, one of Jupiter's moons, is larger.) Until now, Titan has been hidden from view by its atmosphere, which is about 1 1/2 times as thick as Earth's.

Like a Mystery Novel

At first, scientists hoped that Titan might offer some clues about the origins of life on Earth. What they've found so far is a puzzle. Titan is too cold--about 300 degrees below zero Fahrenheit--to support life as we know it. But deep-cut riverbeds and lakes and a turbulent atmosphere suggest that the moon has an active geology that is still changing it.

"Unveiling Titan is like reading a mystery novel," said Charles Elachi, director of NASA's Jet Propulsion Laboratory. "Each time you flip the page, you learn something new, but you don't know the whole story until you've read the whole book."

Huygens was released from the Cassini spacecraft, which was launched in 1997 with a mission to explore Saturn, its distinctive rings, and its moons. In July 2004, Cassini settled into Saturn's orbit and began transmitting amazing images of the rings. The first images suggested that other tiny moons in the gaps between rings may help the rings keep their shape.

Cassini and Huygens are products of NASA's historic collaboration with the European Space Agency and the Italian Space Agency. Cassini is scheduled to make 74 complete revolutions of Saturn in a mission that will last until 2008.