For decades, spacecraft images of Jupiter and Saturn have puzzled planetary scientists. Despite being similar in size and composition, the two gas giants display dramatically different weather systems at their poles. Jupiter hosts a striking formation: a central polar vortex encircled by eight massive storms, resembling a rotating crown. Saturn, by contrast, is capped by a single enormous cyclone, shaped like a near-perfect hexagon.
Now, researchers at the Massachusetts Institute of Technology believe they have identified a key reason behind this cosmic contrast — and the answer may lie deep beneath the planets’ cloud tops.
In a new study published in the Proceedings of the National Academy of Sciences, the MIT team suggests that the structure of a planet’s interior — specifically, how “soft” or “hard” the base of a vortex is — determines whether polar storms merge into one giant system or remain as multiple smaller vortices.
“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,” says study author Wanying Kang, assistant professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS) in a media release issued by the institute. “I don’t think anyone’s made this connection between the surface fluid pattern and the interior properties of these planets. One possible scenario could be that Saturn has a harder bottom than Jupiter.”
A long-standing planetary mystery
The contrast has been visible for years thanks to two landmark NASA missions. The Juno spacecraft, which has been orbiting Jupiter since 2016, revealed a dramatic polar arrangement of swirling storms, each roughly 3,000 miles wide — nearly half the diameter of Earth. Cassini, which orbited Saturn for 13 years before its mission ended in 2017, documented the planet’s iconic hexagonal polar vortex, stretching nearly 18,000 miles across.
“People have spent a lot of time deciphering the differences between Jupiter and Saturn,” says Jiaru Shi, the study’s first author and an MIT graduate student. “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.”
Simulating storms on gas giants
To tackle the question, the researchers turned to computer simulations. They created a two-dimensional model of atmospheric flow designed to mimic how storms might evolve on a rapidly rotating gas giant.
While real planetary vortices are three-dimensional, the team argued that Jupiter’s and Saturn’s fast spin simplifies the physics. “In a fast-rotating system, fluid motion tends to be uniform along the rotating axis,” Kang explains. “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.”
The model allowed the scientists to test thousands of possible planetary conditions, varying factors such as rotation rate, internal heating, planet size and — crucially — the density of material beneath the vortices. Each simulation began with random chaotic motion and tracked how storms evolved over time.
The outcomes consistently fell into two categories: either the system developed one dominant polar vortex, like Saturn, or several coexisting vortices, like Jupiter.
The decisive factor turned out to be how much a vortex could grow before being constrained by the properties of the layers beneath it.
When the lower layers were made of softer, lighter material, individual vortices could not expand indefinitely. Instead, they stabilized at smaller sizes, allowing multiple storms to coexist at the pole. This matches what scientists observe on Jupiter.
But when the simulated vortex base was denser and more rigid, vortices were able to grow larger and eventually merge. The end result was a single, planet-scale storm — remarkably similar to Saturn’s massive polar cyclone.
“This equation has been used in many contexts, including to model midlatitude cyclones on Earth,” Kang says. “We adapted the equation to the polar regions of Jupiter and Saturn.”
The findings suggest that Saturn’s interior may contain heavier elements or more condensed material than Jupiter’s, giving its atmospheric vortices a firmer foundation to build upon.
“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 says. “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.”
Reading the interiors from the skies
Planetary scientists have long struggled to infer the internal structures of gas giants, where pressures and temperatures are far beyond what can be reproduced in laboratories. This new work offers a rare bridge between visible atmospheric patterns and hidden planetary composition.
Beyond explaining two of the Solar System’s most visually striking storms, the research could shape how scientists interpret observations of distant exoplanets as well — worlds where atmospheric patterns might be the only clues to what lies within.
For now, Jupiter’s swirling crown of storms and Saturn’s solitary hexagon may be doing more than decorating the poles of two distant giants. They may be quietly revealing the deep, unseen architecture of the planets themselves.