Flying past Saturn's moon Titan, NASA's Cassini spacecraft has caught a few glimpses of methane clouds speeding over the enormous moon's hydrocarbon seas in its northern polar region.
Clouds developed and dissipated over Ligeia Mare, a roughly 310-mile-wide sea of methane and ethane that ranks as Titan's second-largest lake. Tracked for more than two days in late July, the pale apparitions' movements revealed wind speeds of 7 to 10 mph.
"It was exciting to see them because we have been waiting for a while now," said Elizabeth Turtle, a planetary scientist working with the Cassini imaging team at the Johns Hopkins University Applied Physics Lab in Laurel, Md.
It's been a long time since such floating clumps of methane gas have been spotted in the icy moon's nitrogen-rich atmosphere. Ever since a major storm blew through Titan's midsection near the end of 2010, the skies on this Saturnian satellite have remained largely clear, Turtle said. But this sunny weather caught some scientists off guard: According to their models, more clouds should have started to crop up as Titan approached its summer season.
Such seasonal changes are more challenging to track far out in the solar system, given that a year on Titan lasts some 30 years on Earth (and each season is about seven years long). It takes a while to establish "annual" patterns on such long time scales, and so it becomes particularly disconcerting when the atmosphere's behavior doesn't fit the predicted models.
The clouds then are a welcome sign that perhaps the planetary scientists' long-held theories are not too far off base. Here's an animation showing their movement across the moon's surface.
"It's just a tantalizing hint that the summer storms are starting," Turtle said, "but we'll have to keep observing to see."
Cassini is scheduled for another flyby in late August that could reveal whether clouds are building for some summer tempests, as they predict.
It's also one of the few spots in our solar system very rich in complex organic molecules, giving it some potential for life-friendly environments. (The chances of any form of life ever having existed are still very low, however – as low as the surface temperature, which sits at about 290 degrees below zero.)