Unlocking Jupiter & Saturn's Secrets: Polar Cyclones Show Deep Interior Differences

New research by MIT planetary scientists shows how striking differences in the polar vortex patterns of Jupiter and Saturn may be driven by deep interior properties, offering fresh clues about the structure of gas giants. “Our study shows that, depending on the interior properties and the softness of the bottom of the vortex, this will influence the kind of fluid pattern you observe at the surface,” said MIT’s Dr. Wanying Kang. The study was inspired by images of Jupiter and Saturn that have been taken by NASA’s Juno and Cassini missions. Juno has been orbiting around Jupiter since 2016, and has captured stunning images of the planet’s north pole and its multiple swirling vortices. From these images, scientists have estimated that each of Jupiter’s vortices is immense, spanning about 5,000 km (3,000 miles) across. Cassini, prior to intentionally burning up in Saturn’s atmosphere in 2017, orbited the ringed planet for 13 years. Its observations of Saturn’s north pole recorded a single, hexagonal-shaped polar vortex, about 29,000 (18,000 miles) wide. “People have spent a lot of time deciphering the differences between Jupiter and Saturn,” said MIT graduate student Jiaru Shi. “The planets are about the same size and are both made mostly of hydrogen and helium. It’s unclear why their polar vortices are so different.” The authors set out to identify a physical mechanism that would explain why one planet might evolve a single vortex, while the other hosts multiple vortices. To do so, they worked with a two-dimensional model of surface fluid dynamics. While a polar vortex is three-dimensional in nature, they reasoned that they could accurately represent vortex evolution in two dimensions, as the fast rotation of Jupiter and Saturn enforces uniform motion along the rotating axis. “In a fast-rotating system, fluid motion tends to be uniform along the rotating axis,” Dr. Kang said. “So, we were motivated by this idea that we can reduce a 3D dynamical problem to a 2D problem because the fluid pattern does not change in 3D.” “This makes the problem hundreds of times faster and cheaper to simulate and study.” Following this reasoning, the researchers developed a two-dimensional model of vortex evolution on a gas giant, based on an existing equation that describes how swirling fluid evolves over time. “This equation has been used in many contexts, including to model midlatitude cyclones on Earth,” Dr. Kang said. “We adapted the equation to the polar regions of Jupiter and Saturn.” The scientists applied their two-dimensional model to simulate how fluid would evolve over time on a gas giant under different scenarios. In each scenario, they varied the planet’s size, its rate of rotation, its internal heating, and the softness or hardness of the rotating fluid, among other parameters. They then set a random ‘noise’ condition, in which fluid initially flowed in random patterns across the planet’s surface. Finally, they observed how the fluid evolved over time given the scenario’s specific conditions. Over multiple different simulations, they observed that some scenarios evolved to form a single large polar vortex, like Saturn, whereas others formed multiple smaller vortices, like Jupiter. After analyzing the combinations of parameters and variables in each scenario and how they related to the final outcome, they landed on a single mechanism to explain whether a single or multiple vortices evolve. As random fluid motions start to coalesce into individual vortices, the size to which a vortex can grow is limited by how soft the bottom of the vortex is. The softer, or lighter the gas is that is rotating at the bottom of a vortex, the smaller the vortex is in the end, allowing for multiple smaller-scale vortices to coexist at a planet’s pole, similar to those on Jupiter. Conversely, the harder or denser a vortex bottom is, the larger the system can grow, to a size where eventually it can follow the planet’s curvature as a single, planetary-scale vortex, like the one on Saturn. If this mechanism is indeed what is at play on both gas giants, it would suggest that Jupiter could be made of softer, lighter material, while Saturn may harbor heavier stuff in its interior. “What we see from the surface, the fluid pattern on Jupiter and Saturn, may tell us something about the interior, like how soft the bottom is,” Shi said. “And that is important because maybe beneath Saturn’s surface, the interior is more metal-enriched and has more condensable material which allows it to provide stronger stratification than Jupiter.” “This would add to our understanding of these gas giants.” The team’s findings will appear in the Proceedings of the National Academy of Sciences. _____ Jiaru Shi & Wanying Kang. 2026. Polar vortex dynamics on gas giants: Insights from 2D energy cascades. PNAS, in press;