At the poles of Jupiter, enormous cyclones swirl in neat geometric patterns that stay stable for years at a time, a phenomenon that remains unexplained and that scientists have said hints at the need for new physics.
The hurricane-force storms were first discovered by NASA’s Juno mission, which has captured unprecedented observations of Jupiter since it arrived in orbit around the planet in 2016. In the planet’s northernmost region, a central cyclone is located near the pole, while eight others dance around it at lower circumpolar latitudes in an octagonal pattern. In the south, a similar cluster of five cyclones form the shape of a pentagon.
Now, scientists led by Andrew Ingersoll, who serves as Earle C. Anthony Professor of Planetary Sciences at the California Institute of Technology, have shed new light on the strange storms that encircle Jupiter’s north pole, each of which is about as large as the continental United States.
Their results suggest that an “anticyclonic ring” of winds that blow in the opposite direction of the cyclones “is needed for the stability of the polygonal pattern,” though the team noted that other questions about the storms remain, according to a study published on Thursday in Nature Astronomy.
“Since 2017 the Juno spacecraft has observed a cyclone at the north pole of Jupiter surrounded by eight smaller cyclones arranged in a polygonal pattern,” the researchers said in the study. “It is not clear why this configuration is so stable or how it is maintained.”
“The polygons and the individual vortices that comprise them have been stable for the four years since Juno discovered them,” the team added. “The polygonal patterns rotate slowly, or not at all….In contrast, Saturn has only one vortex, a cyclone, at each pole.”
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To get a firmer read on how the polygons form and then remain so steady, Ingersoll and his colleagues measured the winds and dynamics of the extraterrestrial tempests with Juno’s Jovian InfraRed Auroral Mapper (JIRAM) instrument. JIRAM is able to spot details of the poles down to scales of 180 kilometers (110 miles), a resolution that exposes a torrent of winds that acts as a kind of brace for the cyclones, which is the key to their stability.
However, what the team weren’t able to see in the observations is as consequential as what they did spot. The researchers noted that they did not find “the expected signature of convection,” the process by which heat is transferred through churning fluids, in contrast to previous research, according to the study.
Ingersoll and his colleagues said that future work is needed to reconcile these conflicting datasets, noting in their new work that “a parallel study of Jupiter’s south polar vortices, focusing on vorticity and stability, represents a step in the right direction.”
These beautiful geometric storms are just one of many mysterious processes on Jupiter that scientists are hoping to probe with missions such as Juno, or the newly launched James Webb Space Telescope. As the solar system’s biggest planet, Jupiter has no lack of bizarre and unique phenomena, but it can also serve as a model to understand similar observations on other planets, including Earth.
"These cyclones are new weather phenomena that have not been seen or predicted before," said Cheng Li, a Juno scientist at the University of Michigan, Ann Arbor, and a co-author of the new study, in a 2019 NASA statement about previous research.
"Nature is revealing new physics regarding fluid motions and how giant planet atmospheres work,” he said. “We are beginning to grasp it through observations and computer simulations. Future Juno flybys will help us further refine our understanding by revealing how the cyclones evolve over time."