The puzzling behaviour of Titan's atmosphere has been revealed by researchers at the University of Bristol for the first time.
By analysing data from the Cassini-Huygens mission, a joint venture between NASA, the European Space Agency (ESA), and the Italian Space Agency, the team have shown that the thick, hazy atmosphere of Saturn's largest moon doesn't spin in line with its surface, but instead wobbles like a gyroscope, shifting with the seasons.
Titan is the only moon in the Solar System with a significant atmosphere, and one that has long captivated planetary scientists. Now, after 13 years of thermal infrared observations from Cassini, researchers have tracked how Titan's atmosphere tilts and shifts over time.
"The behaviour of Titan's atmospheric tilt is very strange!" said Lucy Wright, lead author and postdoctoral researcher at Bristol's School of Earth Sciences. "Titan's atmosphere appears to be acting like a gyroscope, stabilising itself in space.
"We think some event in the past may have knocked the atmosphere off its spin axis, causing it to wobble.
"Even more intriguingly, we've found that the size of this tilt changes with Titan's seasons."
The team studied the symmetry of Titan's atmospheric temperature field and found that it isn't centred exactly on the pole, as expected. Instead, it shifts over time, in step with Titan's long seasonal cycle -- each year on Titan lasts nearly 30 years on Earth.
Professor Nick Teanby, co-author and planetary scientist at Bristol said: "What's puzzling is how the tilt direction remains fixed in space, rather than being influenced by the Sun or Saturn.
"That would've given us clues to the cause. Instead, we've got a new mystery on our hands."
This discovery will impact NASA's upcoming Dragonfly mission, a drone-like rotorcraft scheduled to arrive at Titan in the 2030s. As Dragonfly descends through the atmosphere, it will be carried by Titan's fast-moving winds -- winds that are about 20 times faster than the rotation of the surface.
Understanding how the atmosphere wobbles with the seasons is crucial for calculating the landing trajectory of Dragonfly. The tilt affects how the payload will be carried through the air, so this research can help engineers better predict where it will touch down.
Dr Conor Nixon, planetary scientist at NASA Goddard and co-author of the study, added: "Our work shows that there are still remarkable discoveries to be made in Cassini's archive.
"This instrument, partly built in the UK, journeyed across the Solar System and continues to give us valuable scientific returns.
"The fact that Titan's atmosphere behaves like a spinning top disconnected from its surface raises fascinating questions -- not just for Titan, but for understanding atmospheric physics more broadly, including on Earth."
The team's findings contribute to a growing body of research suggesting Titan is not just Earth-like in appearance but an alien world with climate systems all its own, and many secrets still hidden beneath its golden haze.
