During a flyby in July, Cassini recorded clouds drifting across the largest moon of Saturn, Titan. This may be the kickoff of summer storms on the massive moon, the first time researchers have observed cloud formation since 2010.

A Multi-Year Sunny Spell on Titan Ends With Methane Clouds

A time-lapse of clouds slipping around Titan, the largest moon of Saturn. Image credit: NASA/JPL-Caltech/Space Science Institute

Summer storms are an expected feature of Titan's weather system, previously observed and predicted by atmospheric models. They aren't quite sure why Titan has been cloud-free since a massive storm in 2010, but researchers are excited to see the clouds forming again.

A Multi-Year Sunny Spell on Titan Ends With Methane Clouds

Clouds forming near Titan's north pole. Image credit: NASA/JPL-Caltech/Space Science Institute

The methane clouds were captured moving across Ligeia Mare, a large methane sea on Titan. The timelapse captures views between July 20th and 22nd, 2014, with the clouds developing and then dissipating in the two-day period. The clouds were moving at 3 to 4.5 meters per second (7 to 10 miles per hour)

The images were captured as Cassini was departing Titan after a flyby. The temporal spacing between the images is uneven, making this a jerky timelapse. While the time-gap between the second and third frame stretches 17.5 hours, most other frames are separated by only one or two hours.

A Multi-Year Sunny Spell on Titan Ends With Methane Clouds

Is this the start of summer storm season on Titan? Image credit: NASA/JPL-Caltech/Space Science Institute

Between Saturn's long, slow orbit around the sun and Titan's lazy mosey around Saturn, a single year on Titan lasts about thirty Earth-years, with each season stretching over seven year's duration. Cassini imaging team scientist Elizabeth Turtle explains in a Jet Propulsion Laboratories press release that the onset of clouds brings its own set of questions:

"We're eager to find out if the clouds' appearance signals the beginning of summer weather patterns, or if it is an isolated occurrence. Also, how are the clouds related to the seas? Did Cassini just happen catch them over the seas, or do they form there preferentially?"

The team has just a few more years of observations, as Cassini is finally running low on fuel and will be making a dramatic exit. In its 2016 Grand Finale, the spacecraft will make more and more outrageous manoeuvres around Saturn before finally deliberately diving into the gas giant for one last glorious burst of data.