Jupiter’s Great Red Spot has been shrinking, and no one is certain what happens when it closes

Jupiter’s Great Red Spot is the most famous storm in the Solar System, a swirling crimson oval that has raged in the planet’s atmosphere for centuries. For all its permanence in the popular imagination, the storm is not fixed: careful measurements show it has been steadily shrinking, raising a question astronomers cannot yet answer about what will happen if it keeps closing in on itself.

The spot is an anticyclone, a high-pressure vortex of clouds spinning counterclockwise faster than any hurricane on Earth. It is large enough to be seen through backyard telescopes, and its slow contraction over the past century and a half has been one of the more closely tracked changes on any planet.

A storm wider than a planet

Even in its diminished state, the Great Red Spot dwarfs the Earth. Recent measurements put its width at roughly 10,000 miles, making it about 1.3 times the diameter of the Earth. Its winds race around the oval at speeds of several hundred miles per hour, but the interior is comparatively calm, a pattern that lets the storm hold together as a coherent structure. The deep red color, whose exact chemistry is still debated, sets it apart from the paler bands of cloud that stripe the rest of the giant planet.

A century and a half of contraction

Historical records tell a story of gradual shrinkage. Observations from the late 1800s described the spot as an elongated feature stretching as much as 25,500 miles along its long axis. When NASA’s Voyager spacecraft flew past in 1979, they measured it at about 14,500 miles across, and a Hubble Space Telescope image in 1995 recorded roughly 13,020 miles. The trend has continued into the modern era, with the storm reaching some of the smallest dimensions on record and becoming rounder rather than oval as it tightens. The agency’s science program has tracked the change through repeated telescope campaigns.

What NASA’s Juno found beneath the clouds

For most of its history the Great Red Spot could only be observed from the cloud tops, leaving its depth a mystery. That changed with NASA’s Juno spacecraft, which used microwave and gravity measurements to probe beneath the visible surface. The mission found that the storm’s roots reach hundreds of miles down into the atmosphere, far deeper than the clouds yet shallow compared to the storm’s enormous width, as detailed in the Juno findings. Interestingly, even as the spot narrows, some studies suggest it may be growing taller, stretching upward as it shrinks in width.

Why it may be starving

One leading idea for the shrinkage involves the storm’s diet. The Great Red Spot is thought to grow and sustain itself partly by absorbing smaller storms and eddies that drift into it, feeding it energy and material. Researchers have suggested that a scarcity of these smaller systems in recent decades could be leaving the spot undernourished, causing it to contract. In this view the storm is not necessarily dying so much as adjusting to a changing supply of the atmospheric fuel it consumes, though the mechanism remains an area of active study rather than settled fact.

The open question of what comes next

What happens if the contraction continues is genuinely uncertain. Some scientists expect the spot to stabilize at a smaller size and persist for a long time to come, while others wonder whether it could eventually break apart or fade, ending a storm that has been watched since the age of the first telescopes. Because no one has observed the full life cycle of a vortex this large, the Great Red Spot serves as a natural experiment in planetary weather. Continued monitoring, from ground-based telescopes to spacecraft in orbit, offers the best chance of learning whether the Solar System’s grandest storm is merely resizing or slowly running out of time.

A window into the weather of gas giants

Beyond its fame, the Great Red Spot serves as a natural laboratory for understanding how storms behave on worlds with no solid surface. On Earth, hurricanes weaken and die when they move over land or cool water, but Jupiter has no ground to interrupt its storms, allowing vortices to persist for extraordinary spans of time. The Great Red Spot draws energy from the turbulent bands of wind that flow in opposite directions above and below it, and it rolls between them like a ball bearing caught between two conveyor belts. Studying how it holds together helps scientists refine models of atmospheric circulation that apply not only to Jupiter but to the other giant planets and to gas giants orbiting distant stars. Spacecraft observations have added depth to the picture, revealing that the storm extends well below the visible clouds and is warmer at its base than at its top, a structure that helps sustain its circulation. Amateur astronomers also contribute, because the spot is large enough to track from Earth, and their long records of its size and drift complement the detailed snapshots returned by orbiters. Whether the Great Red Spot eventually stabilizes, fragments, or fades, the data gathered while it shrinks will sharpen scientific understanding of how enormous, long-lived storms are born, fed, and ultimately brought to an end on planets very different from Earth.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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