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Jupiter’s Great Red Spot—the largest wind storm in the Solar System—is shrinking, and a new study may help explain why.

Located in Jupiter’s southern hemisphere, the Great Red Spot is a rotating red-orange high-pressure oval more than 10,000 miles across. It consistently blows more than 200 miles per hour in a counterclockwise direction, making it technically an anticyclone.

And it has been shrinking for the better part of a century, especially in the last 50 years. Although its latitude remains relatively constant, its longitude shrank from 40 degrees in the late 19th century to 14 degrees in 2016, when NASA’s Juno spacecraft arrived at the planet for a series of orbits.

“Many people have looked at the Great Red Spot over the past 200 years and been as fascinated by it as I have been,” said Caleb Keaveny, Ph.D. student at Yale’s Graduate School of Arts and Sciences and lead author of a new study in the journal Icarus.

“A lot of these people weren’t professional astronomers – they were just passionate and curious. That, plus the curiosity I see in people when I talk about my work, makes me feel like I’m part of something bigger than myself.”

Part of the curiosity surrounding the Great Red Spot has to do with the many mysteries that surround it, despite the fact that it has been extensively studied. Astronomers don’t know exactly when the spot formed, why it formed, or even why it’s red.

For the study, Keaveney, who is part of Yale’s Department of Earth and Planetary Sciences, and his co-authors, Gary Luckman of North Carolina State University and Timothy Dowling of the University of Louisville, focused on the influence of smaller, transient storms on the large red spot.

The researchers ran a series of 3D simulations of the spot using the Explicit Planetary Isentropic-Coordinate (EPIC) model, an atmospheric model for planetary applications developed by Dowling in the 1990s. Some of these simulated interactions between the Great Red Spot and smaller storms of varying frequency and intensity, while another set of control simulations omitted the small storms.

A comparison of the simulations suggests that the presence of other storms has strengthened the Great Red Spot, causing the spot to grow larger.

“We found through numerical simulations that by feeding the Great Red Spot a diet of smaller storms, as are known to occur on Jupiter, we could modulate its size,” Chiavoni said.

In part, the researchers based their modeling on long-lived high-pressure systems observed closer to home in Earth’s atmosphere. These systems – known as “heat domes” or “blocks” – occur regularly in the westerly jet streams that circulate in Earth’s mid-latitudes and play a major role in extreme weather events such as heat waves and droughts.

The longevity of these “blocks” is linked to interactions with smaller, transient weather mechanisms, including high-pressure eddies and anticyclones.

“Our research has compelling implications for meteorological phenomena on Earth,” Keaveny said. “Interactions with nearby weather systems have been shown to sustain and amplify heat domes, motivating our hypothesis that similar interactions at Jupiter may sustain the Great Red Spot.” In confirming this hypothesis, we provide further support to this understanding of Earth’s heat domes. “

Keaveney said additional modeling will allow researchers to refine the new findings and perhaps shed light on the original formation of the Great Red Spot.