Tigers may not change their streaks, but Jupiter sure does. The surprisingly smooth bands of alternating dark and light clouds periodically change their appearance, but the reason for these cyclical fluctuations remains a mystery. Now, after examining data on Jupiter’s magnetic field collected by the Juno probe, a team of scientists from Japan, Spain and the United Kingdom believe they have cracked it. The observed changes in Jupiter’s bands coincide with magnetic fluctuations in the gaseous world.

“You can get wave-like motions called torsional oscillations in the planet’s magnetic field,” explains mathematician Chris Jones of the University of Leeds in England.

“The fascinating thing is that when we calculate the periods of these torsion oscillations, they match the periods you see in the infrared emission from Jupiter.”

From afar, Jupiter looks serene like a sunrise, with pale creams and burnt caramels. These darker bands are known as belts, while the paler ones are known as zones.

Despite their calm appearance, the belts and regions are part of Jupiter’s wild weather system. They rotate around the giant planet in opposite directions – the belts move against Jupiter’s rotation, the zones move with it – and at different heights. Belts are elevation zones, so cloud tops in belts are higher than cloud tops in uplift areas.

In the infrared range, the color scheme changes in reverse. The light bands darken and the dark bands shine brightly, indicating that the belts have much thinner cloud cover than the regions. Earth has similar (albeit smaller and weaker) belts of atmospheric circulation, suggesting some similarities in how each world creates these atmospheric features.

However, the weather on Jupiter is so different from the weather on Earth that it is impossible to predict what one planet is doing to another. What’s more, Jupiter’s clouds have cyclical changes associated with changes in infrared data seen 50 kilometers (30 miles) below the surface, baffling scientists.

“Everything changes every four or five years,” says Jones. “The colors of the arches can change, and sometimes you see global shocks where all the air goes crazy for a while, and it’s a mystery why.”

Juno has been studying Jupiter since 2016 and has been collecting a lot of data about Jupiter’s various structures and properties. One of them is the planet’s magnetic field, a vast magnetic structure created by Jupiter’s dynamo, a convective and conductive fluid swirling inside the planet that converts kinetic energy into magnetic energy.

The world also has a dynamo. Earth’s dynamo creates magnetic torsion oscillations, a kind of magnetic “wave” that oscillates in and out symmetrically around the planetary axis under the influence of rapid rotation. By examining years of magnetic field data collected by Juno, Hori and his colleagues were able to detect signs of similar fluctuations on Jupiter. And very excitingly, it seemed related to the band shifts and infrared variations of the planet.

“We hypothesize that torsional oscillations cause shear, which disrupts slow convective flows at deep depths that carry heat flow into the visible troposphere,” they write in their paper.

This can cause significant weather distortions and change the rise and fall patterns of Jupiter’s clouds. The team also monitored a region of high magnetic field concentration near the equator, called the Great Blue Spot. They saw it slowing down, suggesting the start of a new swing.

Continuing to observe the planet to see how the clouds will change in the near future could help the team test or refine their theory and figure out how.

“Uncertainties and questions remain, particularly how torsional oscillations cause the observed infrared variation, possibly reflecting complex cloud/aerosol dynamics and responses. These questions require further investigation,” says Hori.

“Still, I hope our paper can open a window to explore the hidden depths of Jupiter, just as seismology does for the Earth and helioseismology for the Sun.”