A set of new studies, many of which draw on data from NASA's Cassini spacecraft, reveal fascinating details in the emerging picture of how Saturn's moon Titan shifts with the seasons and even throughout the day. The papers, published in the journal Planetary and Space Science in a special issue titled "Titan through Time", show how this largest moon of Saturn is a cousin – though a very peculiar cousin – of Earth.
"As a whole, these papers give us some new pieces in the jigsaw puzzle that is Titan," said Conor Nixon, a Cassini team scientist at the NASA Goddard Space Flight Center, Greenbelt, Md., who co-edited the special issue with Ralph Lorenz, a Cassini team scientist based at the Johns Hopkins University Applied Physics Laboratory, Laurel, Md. "They show us in detail how Titan's atmosphere and surface behave like Earth's – with clouds, rainfall, river valleys and lakes. They show us that the seasons change, too, on Titan, although in unexpected ways."
A newly published selection of images, shown at bottom of page, made from data collected by Cassini's visual and infrared mapping spectrometer over five years – shows how the cloud thinned out and retreated as winter turned to spring in the northern hemisphere.
"While the temperature difference – 1.5 kelvins – is smaller than what we're used to on Earth, the finding still shows that Titan's surface behaves in ways familiar to us earthlings," Cottini said. "We now see how the long Titan day (about 16 Earth days) reveals itself through the clouds."
Titan is covered in carbon-bearing material — "it's a giant factory of organic chemicals," according to Ralph Lorenz of Johns Hopkins University Applied Physics Laboratory. "We are carbon-based life, and understanding how far along the chain of complexity towards life that chemistry can go in an environment like Titan will be important in understanding the origins of life throughout the universe."
"One of the things that attracts me about Titan is that it has a lot of the same circulation features as Earth, but done with completely different substances that work atdifferent temperatures,"Pierrehumbert said. On Earth, for example, water forms liquid and is relatively active as a vapor in the atmosphere. But on Titan, water is a rock. "It's not more volatile on Titan than sand is on Earth."