The Saturn hexagon

Updated October 19, 2026 · 5 min read

The Saturn hexagon is a six-sided pattern of clouds around the planet's north pole, formed by a jet stream that flows along a hexagonal path at about 78° north latitude. It is about 29,000 km across, more than twice the diameter of Earth, with each side roughly 14,500 km long. First seen in Voyager images from 1980–1981, it has persisted for more than four decades and is thought to be a stable wave pattern in a fast, narrow jet.

Discovery: hiding in Voyager's pictures

Voyager 1 and 2 flew past Saturn in November 1980 and August 1981, viewing the north polar region at a low angle. A strange polygonal feature was visible in their images, but its geometry only became clear when the pictures were reprojected as if seen from above the pole. In 1988, D. A. Godfrey of the National Optical Astronomy Observatory described the "hexagonal feature" in the journal Icarus, noting that it appeared to rotate with a period close to Saturn's radio rotation period.

Telescopes on the ground and Hubble glimpsed it again in the early 1990s. When Cassini arrived in 2004, the north pole was in the darkness of winter, so the spacecraft first mapped the hexagon in thermal infrared light, which reveals heat rather than reflected sunlight. In 2006 the infrared images showed the hexagon still intact, confirming that it had survived for at least a quarter of a century. After the 2009 equinox, sunlight returned and Cassini's cameras produced the detailed views that made the hexagon famous. See Voyager.

Size and structure

Each side of the hexagon is about 14,500 km long, slightly longer than Earth's diameter, and the whole figure spans about 29,000 km. Along its edges, a jet stream races at about 100 m/s, around 360 km/h, embedded in a band of clouds and haze that marks the boundary. The jet is narrow and remarkably straight along each side, turning sharply at the corners.

Inside, at the pole itself, sits a vast cyclone. Cassini's close-up images from 2012 showed an eye roughly 2,000 km wide, many times larger than any hurricane eye on Earth, with clouds around it moving at about 150 m/s. Smaller vortices spin in the region between the cyclone and the walls of the hexagon. The structure is described in more detail alongside other polar vortices on the storms page.

The hexagon also reaches upward. A 2018 study led by Leigh Fletcher found that, as northern summer approached, a hexagonal shape appeared in the stratosphere, hundreds of kilometres above the clouds, showing that the jet's influence extends far higher than expected.

How fast does it rotate?

The hexagon as a whole rotates almost exactly with Saturn's old radio period of about 10 hours 39 minutes, the System III rotation adopted after Voyager. That was long taken as a sign that it was locked to the deep interior. Since then the planet's true rotation has been revised to about 10 hours 33 minutes, which means the hexagon actually drifts slowly relative to the bulk of the planet, as a wave pattern moving within the flow. Why its speed coincides so closely with the radio period remains an open question.

Why is it a hexagon?

No single theory is universally accepted, but several lines of work point to the same basic idea: the hexagon is a wave in a jet stream, a meander that has settled into a stable six-lobed shape.

• Laboratory experiments. In 2010, Ana Aguiar, Peter Read and colleagues at the University of Oxford spun a cylinder of water with an inner ring rotating at a different speed. When the speed difference was large enough, the boundary between the two flows broke into polygons, with the number of sides depending on the rotation rates. Hexagons appeared under conditions comparable to Saturn's.
• Shallow-jet models. In 2015, Raúl Morales-Juberías and colleagues showed in computer simulations that a narrow eastward jet near 78° N, perturbed slightly, naturally meanders into a hexagon that remains stable and drifts at a speed close to that observed.
• Deep-convection models. In 2020, Rakesh Yadav and Jeremy Bloxham produced hexagon-like jets in a model of deep convection in Saturn's interior, suggesting the pattern may be rooted thousands of kilometres down.

The debate is therefore about depth: is the hexagon a shallow weather pattern or the surface expression of deep flows? Cassini's gravity data, showing that winds extend about 9,000 km down, keeps both possibilities alive. See atmosphere.

From blue to gold

Between November 2012 and April 2016, Cassini images showed the region inside the hexagon changing color, from a deep bluish tone to golden. The cause was the season. During the long northern winter, little sunlight reached the pole and haze particles were scarce, so light scattered by clear gas looked blue. As spring progressed toward the May 2017 solstice, ultraviolet sunlight drove the production of photochemical haze inside the hexagon, which acts as a barrier that keeps haze from mixing out. The pole turned golden like the rest of the planet. See color and seasons.

Why only in the north?

Saturn's south pole has its own powerful vortex, a warm, hurricane-like storm about 8,000 km across that Cassini imaged in 2006, but no hexagon. The southern jet at similar latitudes is weaker and has a different structure, which in models does not produce a stable polygon. No other planet shows such a feature, although Juno revealed geometric clusters of cyclones around Jupiter's poles, octagonal in the north and pentagonal to hexagonal in the south, made of separate storms rather than a single jet.

Sources

• Godfrey, D. A. (1988), "A hexagonal feature around Saturn's north pole", Icarus 76
• Aguiar, A. C. B., Read, P. L. et al. (2010), "A laboratory model of Saturn's North Polar Hexagon", Icarus 206
• Fletcher, L. N. et al. (2018), "A hexagon in Saturn's northern stratosphere surrounding the emerging summertime polar vortex", Nature Communications 9
• NASA Science: Saturn