On Titan, the Polar Vortex Can Last a Shiver-Inducing 22 (Earth) Years

Saturn's moon Titan is enveloped by thick haze, making it the only moon in our solar system to have an atmosphere a little like Earth's.
Saturn's moon Titan is enveloped by thick haze, making it the only moon in our solar system to have an atmosphere a little like Earth's.
(Image: © NASA/JPL-Caltech/Space Science Institute)

And you thought unpredictable spring temperatures were annoying: On Saturn's moon Titan, chilly polar vortex periods can last to the summer solstice.

That's according to new research looking at the polar vortex on the only moon to sport a thick atmosphere like Earth's. When NASA's Cassini mission arrived at the Saturn system in 2004, scientists found a huge patch of cold air under low pressure at the moon's north pole. As the Earth-years passed and Titan's seasons gradually changed, the spacecraft even saw the birth of a vortex at the other pole. Patching those observations together, the new study attempts to understand how these structures develop, mature and dissipate.

"Why it's so interesting is that Titan is like a mini Earth with a really exotic and cold atmosphere that we can use to test climate models and things like that," Nick Teanby, a planetary scientist at the University of Bristol in the U.K. and lead author of the new research, said in a statement. "That's the big picture to why we bothered, but I guess the real motivation is just that it's really cool to try and figure this stuff out."

Related: Saturn's Moon Titan May Have 'Phantom Lakes' and Caves

Cassini wasn't able to spend a full Titan year at the moon. Instead, the spacecraft caught the latter part of the northern polar vortex. But that lasted all the way until the equivalent of the summer solstice. That would make the full phenomenon last about 22 Earth years.

Then, the spacecraft saw the beginnings of the same structure's formation at the south pole. Scientists were surprised to find that the early south polar vortex was much colder than the late-season northern polar vortex, so Teanby and his team wanted to investigate.

Titan's atmosphere isn't a perfect clone of Earth's — although both are mostly full of nitrogen, Titan's is also sprinkled with methane. It's that compound that falls out of the sky as rain on Titan, not water. And in the upper layers of Titan's atmosphere, where sunlight can reach that methane, it can trigger reactions that produce even stranger gas compounds.

What Teanby and his team found was that those exotic gases were more prevalent in the early winter and could be contributing to added chill in the early days of the polar vortex. "Earth cools in winter due to lack of sunlight over the poles, but you don't get this added effect from extra gases, whereas on Titan you've got these weird gases in there that's making the process even more extreme than it would be otherwise," Teanby said.

Although scientists still have plenty of Cassini data to analyze from the spacecraft's visit to the Saturn system, it will be many years before any mission can watch an entire Titan seasonal cycle play out. NASA is considering selecting a mission to the moon later this year, but even that spacecraft wouldn't arrive until 2034.

Email Meghan Bartels at mbartels@space.com or follow her @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.

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