Massive dunes, some of them 100 meters tall and a kilometer or more wide at their base, cover about one-eighth of Titan’s surface. And they take an exceptionally long time to form, according to a new study. Using radar data gleaned by the Cassini probe when it occasionally swooped past Saturn’s haze-shrouded moon, researchers mapped the orientation of about 10,000 crests of linear dunes in Titan’s four largest dune fields. (The dunes, artist’s depiction shown, are likely made of tiny sand-sized particles of frozen hydrocarbons produced by light-driven chemical reactions within the dense orange clouds that swaddle the moon.) Single dunes in those fields, like frozen waves, often stretch unbroken for dozens of kilometers. The new analysis also spotted, for the first time, areas where dunes weren’t so sharply defined. In many of those regions, smaller features superimposed on the larger dunes had been sculpted by winds that blew, on average, at a 23° angle from those that had formed the older features. Computer simulations suggest that it would take about 3000 Saturn years (or 88,200 Earth years) to shift Titan’s dunes to the extent seen in the images, the researchers report online today in Nature Geoscience. That interval is far longer than any daily or seasonal cycles in weather the satellite might experience, the researchers say. Therefore, they contend, the shifts in winds must result from long-term climate cycles associated with variations in Saturn’s orbit. A similar phenomenon has taken place on Earth, the researchers note: The overall patterns in many large dune fields in the southwestern Sahara and the southwestern United States, shaped by the winds that blew during the most recent ice age more than 10,000 years ago, remain largely unaffected by modern winds that now blow in a different direction.