Great Red Spot

Jupiter’s Great Red Spot is a large oval of clouds rotating counterclockwise in the planet’s southern hemisphere. It is an anticyclone: a high-pressure atmospheric circulation, unlike the low-pressure cyclones familiar on Earth. Winds circulate around the oval at speeds far greater than those of terrestrial storms. The Spot has been observed since at least 1830, but whether it is the same storm as descriptions in older records is uncertain; its precise age is not known.

The Great Red Spot is not a fixed feature. Its dimensions and shape change, and long-running observations indicate that it has contracted from the much larger oval recorded in earlier telescopic and spacecraft observations. Researchers have documented variations in its size and appearance, but the physical processes behind those changes are still being investigated. The name refers to its characteristic reddish colour, which can vary in intensity; the chemistry responsible for the colour is not fully settled.

NASA’s Juno mission has examined the Spot with instruments that can probe beneath Jupiter’s cloud cover. Microwave observations found that its roots extend hundreds of kilometres below the visible clouds. Separate measurements of Jupiter’s gravity during Juno flybys constrained the vortex to the upper 500 kilometres of the atmosphere. These results show that the storm has substantial vertical structure, while also placing limits on how deeply it reaches into the planet.

The Spot offers scientists a long-lived example of atmospheric circulation on a gas giant. Comparing its changing outline, winds and interior structure helps researchers test how giant planetary storms form and persist. Jupiter’s atmosphere is not a solid surface, so the visible oval marks cloud patterns within a deep, moving atmosphere. Although the Spot is often described as a single enduring storm, its observable properties evolve, and its ultimate longevity cannot be predicted from its historical record alone.