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Jupiter's Great Red Spot stands out as the most iconic feature of the planet, easily outgrowing the Earth in size. This enduring storm—first reliably recorded in 1878—continues to captivate scientists as advances in telescopic and spacecraft technology reveal more about its dynamics and enduring mystery.

Its wind speeds are changing

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As the largest permanent storm in the solar system, the Great Red Spot is an anti‑cyclonic vortex that spins opposite to Earth’s hurricanes, driven by high‑pressure zones that push air outward. Observations from the Hubble Space Telescope have measured wind speeds of roughly 400 mph—far exceeding even the most powerful Earth hurricanes. Recent analyses show that the outer edge is accelerating, while the inner region is slowing, hinting at a calmer “eye” similar to terrestrial storms. These subtle shifts required a decade of high‑resolution imaging to detect.

It appears red because sunlight hits its upper gases

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The spot’s distinctive hue results from sunlight scattering through the upper layers of ammonia and acetylene clouds. Laboratory experiments from 2014 demonstrated that this interaction produces a reddish glow, while the deeper clouds underneath are likely white or gray. This explanation supersedes earlier theories that invoked the breakdown of ammonium hydrosulfide, which laboratory work showed would produce a green tint instead.

It was once three times Earth’s width, but it’s shrinking

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Initially estimated at 25,500 mi across in the 19th century, the Great Red Spot has narrowed to just 10,250 mi today—a reduction of about 580 mi per year based on Voyager, Hubble, and ground‑based observations. The contraction may be due to energy exchange with neighboring storms, though the exact mechanism remains unclear. With Earth’s diameter at 7,926 mi, the spot now measures only about 1.3 times larger than our planet.

It wobbles

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High‑resolution Hubble images from late 2023 and early 2024 reveal that the storm’s center oscillates, a motion described by scientists as “jiggling like a bowl of gelatin.” This instability appears linked to changing wind patterns and the jet streams surrounding the vortex, though further study is needed to unravel the underlying causes.

It may have been spotted in the 17th century

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Records of the Great Red Spot date back to 1885, yet observations by Robert Hooke and Giovanni Cassini in 1664 hint at an earlier appearance. While Hooke’s notes could refer to a moon’s shadow, Cassini’s descriptions align more closely with the modern spot, albeit without the distinct red coloration—possibly due to the observational limitations of the era.

It can change its shape and color

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Voyager and Hubble data show that as the spot’s diameter decreases, its depth increases—cloud tops rise higher. Correspondingly, the hue has shifted from a deep red to a more orange tone, consistent with the sunlight‑scattering theory involving ammonia and acetylene. These long‑term observations help scientists model the storm’s evolution and anticipate future changes.

There is a Red Spot Jr., too, though it used to be white

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In the early 2000s, Hubble captured a second, smaller storm—Red Spot Jr.—located roughly 2,000 mi from the main vortex. Initially called White Oval BA, its clouds rose into the upper atmosphere, producing a red tint similar to the Great Red Spot. The presence of this secondary storm suggests that Jupiter’s atmosphere may be undergoing broader climatic shifts.