Great Red Spot

The Great Red Spot is a vast, persistent high-pressure region in the atmosphere of Jupiter that produces the largest known anticyclonic storm in the Solar System. Distinguished by its red–orange hue, whose chemical cause remains uncertain, it lies about 22 degrees south of Jupiter’s equator and generates powerful winds that circulate in a counterclockwise direction. The storm has been an iconic feature of Jupiter since the nineteenth century and has been the subject of intensive study owing to its immense scale, dynamic behaviour and long-term stability.

Early Observations and Historical Record

The earliest definite continuous observations of the modern Great Red Spot began in September 1831, with over sixty documented sightings by 1879. Although a prominent spot was recorded between 1665 and 1713, modern research indicates that this earlier feature may have been a different storm system. The seventeenth-century observations were made largely by Giovanni Cassini, who described a long-lived, recurring spot and measured its rotation period. However, the seventy-year gap between Cassini’s last recorded sighting and the first reliable nineteenth-century observations creates uncertainty about continuity.
A minor historical puzzle concerns Donato Creti’s 1711 painting, which depicts a red spot on Jupiter. Due to optical inversion in telescopes of the time, the painting shows the feature in the northern hemisphere, although the intended depiction may still reference the seventeenth-century spot. No written account described the spot as red until the late nineteenth century, implying that the colouration familiar today may not have characterised earlier features.
A 2024 analysis concluded that the modern Great Red Spot is unlikely to be the same storm as that observed in the seventeenth century, suggesting instead that the earlier spot dissipated before a new one formed in the early nineteenth century.

Development During the Late 20th and 21st Centuries

Spacecraft observations in the latter half of the twentieth century greatly advanced understanding of the spot’s structure and evolution. On 25 February 1979 the Voyager 1 spacecraft transmitted the first high-resolution images of the storm, revealing intricate cloud patterns and atmospheric waves on scales of a few hundred kilometres. Subsequent missions, notably Galileo, Cassini–Huygens and Juno, have provided extensive visible, infrared and ultraviolet data.
Since the early twentieth century the storm has been shrinking. By 2004 its major axis had reduced to roughly half its nineteenth-century length, when it was nearly three times the diameter of Earth. If the present rate of contraction continues, the spot may become more circular by the 2040s. Observations in 2019 documented fragments peeling away from the storm’s outer edges, prompting speculation about a possible decline. However, some researchers argue that these events reflect superficial changes in cloud layers rather than a weakening of the underlying vortex and that interactions with nearby cyclones and anticyclones may explain the fragmentation.
New storm systems have also developed. Oval BA, formed in 2000 from the merger of three long-lived white ovals, turned red in 2006 and became known as the “Little Red Spot”. Astronomers tracked close approaches between Oval BA and the Great Red Spot in the early twenty-first century, though the storms did not merge.
The Juno spacecraft, in a polar orbit around Jupiter since 2016, has flown repeatedly over the Great Red Spot, including a close pass in July 2017. Juno’s data have been instrumental in studying the storm’s depth, structure and energy dynamics.

Atmospheric Dynamics and Structure

The Great Red Spot is an anticyclonic vortex rotating counterclockwise with a period of roughly 4.5 Earth days (equivalent to about eleven Jovian days). As of early 2017 the storm measured around 16,000 kilometres across—large enough to span more than a dozen Earths. Its cloud tops stand several kilometres above the surrounding atmosphere and are significantly colder, consistent with high-altitude, low-pressure conditions.
The storm’s longevity is linked to Jupiter’s lack of a solid surface. With no landmasses to create friction, atmospheric vortices can persist for centuries. Jupiter’s deep hydrogen–helium envelope allows stable circulation patterns, and the Great Red Spot is confined between a strong westward jet stream to its north and a weaker eastward jet stream to its south, creating a dynamically stable region that supports long-term rotation.
Wind speeds at the periphery of the storm reach high velocities, though flow within the interior appears far more stagnant. The storm’s rotation has slowed gradually over time, a trend associated partly with its reduction in size. Its latitude has remained exceptionally stable, shifting by only about a degree across well-documented observation periods, though its longitude drifts significantly. Because Jupiter’s rotation varies by latitude, astronomers use different longitude systems to track features; the Great Red Spot has completed multiple laps around the planet in System II coordinates since the nineteenth century.
Infrared studies reveal that the storm is colder than surrounding clouds at altitude, while the upper atmosphere above it is unusually warm. One explanation proposes that acoustic waves generated by turbulence within the storm propagate upward and break high in the atmosphere, depositing energy and heating the region. These waves may rise more than 800 kilometres above the storm’s cloud tops, creating a hot spot in the upper atmosphere.

Longevity and Future Evolution

Despite centuries of observation, the future of the Great Red Spot remains uncertain. Ongoing contraction suggests the storm may change form significantly in the coming decades, yet many researchers caution against assuming imminent disappearance. Variability in its cloud cover may create the impression of shrinkage without indicating a weakening of the vortex itself. Interactions with nearby storms may also account for observed fragmentation events.
The storm’s interactions with other atmospheric phenomena, its deep roots within Jupiter’s gaseous envelope and the stability provided by surrounding jet streams all contribute to its persistence. As spacecraft missions continue to gather data, particularly through Juno’s extended operations, understanding of the storm’s internal structure and long-term behaviour is expected to improve.