Saturn's atmosphere is constantly swimming with turbulent jet streams — but where do they get their energy to form in the first place? This has been one of the biggest mysteries about Saturn for decades.
Now, using data acquired from the Agency's Cassini spacecraft, NASA scientists think they have the answer: the energy for the jet streams comes from within the planet itself.
"We know the atmospheres of planets such as Saturn and Jupiter can get their energy from only two places: the sun or the internal heating," explains NASA Goddard's Tony Del Genio, lead author on the paper describing the team's findings, published in the latest issue of the journal Icarus. "The challenge has been coming up with ways to use the data, so that we can tell the difference."
Del Genio's team met this challenge, by analyzing seven years' worth of photos of the ringed planet with automated cloud tracking software. This allowed the researchers to determine close to 120,000 wind vectors from 560 images, giving them the biggest, most detailed picture yet of the planet's atmospheric dynamics. By capturing these photos with filters that allowed Cassini to see near-infrared light, the researchers were able to get their first detailed look at atmospheric disturbances — called eddies — that give rise to jet streams, accelerating them "like rotating gears driving a conveyor belt." According to NASA:
By seeing for the first time how these eddies accelerate the jet streams at two different altitudes, scientists found the eddies were weak at the higher altitudes where previous researchers had found that most of the sun's heating occurs. The eddies were stronger deeper in the atmosphere. Thus, the authors could discount heating from the sun and infer instead that the internal heat of the planet is ultimately driving the acceleration of the jet streams, not the sun.
The mechanism that best matched the observations would involve internal heat from the planet stirring up water vapor from Saturn's interior. That water vapor condenses in some places as air rises and releases heat as it makes clouds and rain. This heat provides the energy to create the eddies that drive the jet streams.
"Understanding what drives the meteorology on Saturn, and in general on gaseous planets, has been one of our cardinal goals since the inception of the Cassini mission," said Carolyn Porco,head of Cassini's imaging team, in a statement. "It is very gratifying to see that we're finally coming to understand those atmospheric processes that make Earth similar to, and also different from, other planets." [NASA]