High Strangeness at Jupiter’s Poles: Geometric Arrays of Storms

The study, authored by scientists from an international group of institutions including the University of Chicago, is published in March 8’s Nature as part of a set of four papers dedicated to new observations from the Juno spacecraft.

Juno launched in 2011 with the ambitious mission of finally seeing beneath the dense clouds covering Jupiter. On July 4, 2016, it finally reached the planet’s orbit. Since then it’s been orbiting the planet, taking pictures and measuring the planet’s profile in infrared, microwave, ultraviolet, gravity and magnetism—and answering questions scientists have had about Jupiter for decades.

For hundreds of years, this gaseous giant planet appeared shrouded in colorful bands of clouds extending from dusk to dawn, referred to as zones and belts. The bands were thought to be an expression of Jovian weather, related to winds blowing eastward and westward at different speeds. This animation illustrates a recent discovery by Juno that demonstrates these east-west flows, also known as jet-streams penetrate deep into the planet’s atmosphere, to a depth of about 1,900 miles (3,000 kilometers). Due to Jupiter’s rapid rotation (Jupiter’s day is about 10 hours), these flows extend into the interior parallel to Jupiter’s axis of rotation, in the form of nested cylinders. Below this layer the flows decay, possibly slowed by Jupiter’s strong magnetic field. The depth of these flows surprised scientists who estimate the total mass involved in these jet streams to be about 1% of Jupiter’s mass (Jupiter’s mass is over 300 times that of Earth). This discovery was revealed by the unprecedented accuracy of Juno’s measurements of the gravity field.

Credits: NASA/JPL-Caltech/SwRI/ASI

One of these was the question of what lay at its elusive poles. When scientists got the first images, they were stunned. At the north pole, eight storms surrounded one storm at the center. At the south pole, it was the same arrangement, only with five storms. But the numbers stayed oddly constant; the storms weren’t drifting and merging, as our current understanding of the science suggested they should.

“They are extraordinarily stable arrangements of such chaotic elements,” said Morgan O’Neill, a University of Chicago postdoctoral scholar and a co-author on the paper. “We’d never seen anything like it.”

The geometry rang a faint bell in O’Neill’s mind, though. She found it in the library of strange physical phenomena only observed under special conditions in the laboratory. In the 1990s, scientists observed a similar behavior as they used electrons to simulate a frictionless, turbulent 2-D fluid as it cools. Instead of merging, which tends to happen in such 2-D flows, small vortices would clump together and form equally spaced arrays, or “vortex crystals,” around a center.

This computer-generated image is based on an infrared image of Jupiter’s north polar region that was acquired on February 2, 2017, by the Jovian Infrared Auroral Mapper (JIRAM) instrument aboard Juno during the spacecraft’s fourth pass over Jupiter.

Credits: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM

It’s not yet clear whether the same physics underlies both these behaviors, O’Neill said, but it is tantalizing. “The next step is: Can you create a model that builds a virtual planet and predicts these flows?” she said. With further studies, they can understand the forces at play in the swirling storms.

A greater understanding of the physics behind the flows and dynamics of storms is helpful on every planet; though O’Neill did her PhD on the dynamics of cyclones on gas giants (including a prediction that Jupiter’s poles would not look like Saturn’s: “I got it…partially right,” she said), she now uses similar storm modeling to study hurricanes on Earth.

This composite image, derived from data collected by the Jovian Infrared Auroral Mapper (JIRAM) instrument aboard NASA’s Juno mission to Jupiter, shows the central cyclone at the planet’s north pole and the eight cyclones that encircle it.

Credits: NASA/JPL-Caltech/SwRI/ASI/INAF/JIRAM

The study was led by Alberto Adriani with Rome’s Institute for Space Astrophysics and Planetology. Other authors on the study were from the Jet Propulsion Laboratory, Caltech, the British Astronomical Association, the Southwest Research Institute, NASA Goddard Space Flight Center, the University of Michigan, Cornell University, the University of Atacama in Chile and the Planetary Science Institute, as well as the Institute for Space Astrophysics and Planetology, the University of Bologna, the Italian Space Agency and the Institute of Atmospheric Sciences and Climate, all in Italy.

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