Saturn's hexagon
David Godfrey pieced together the first view of Saturn's hexagon in 1987. He analyzed fly-by data from the Voyager mission that had flown past the planet six years earlier. The spacecraft captured images during its 1981 journey, but no one saw the shape until Godfrey combined them. Cassini-Huygens returned to the site in 2006 to confirm the pattern persisted for decades. Cassini could only capture thermal infrared images until January 2009 when sunlight finally reached the north pole. Amateur astronomers later used modest telescopes on Earth to photograph the feature after it emerged into light. The hexagon rotates at the same speed as Saturn's internal radio emissions.
The sides of the hexagon stretch about 13,800 kilometers long. This distance exceeds the diameter of Earth by a significant margin. The structure spans roughly 29,000 kilometers across its widest point. Atmospheric gases within this jet stream move at speeds reaching 540 kilometers per hour. The entire formation completes one rotation every 10 hours and 39 minutes. Unlike other clouds visible in the atmosphere, this feature does not shift longitude over time. A vortex exists inside the northern hexagon while another sits at the south pole without forming a polygon. The radius of such an hexagon may be slightly greater than its side length due to Saturn's oblate spheroid shape.
Between 2012 and 2016 the hexagon shifted from blue to golden hues. Cassini spacecraft recorded these changes as the pole received direct sunlight during seasonal shifts. One hypothesis suggests sunlight creates haze particles that alter the color. The north pole remained dark for years before entering sunlight in January 2009. These observations proved the phenomenon was dynamic rather than static. The southern pole lacks a similar hexagonal pattern despite hosting its own vortex. Hubble observations confirmed the absence of a hexagon at Saturn's south pole.
Researchers developed theories linking the hexagon to Rossby waves in early studies. Allison Godfrey and Beebe published their wave dynamical interpretation in Science on the 2nd of March 1990. Oxford University scientists proposed steep latitudinal gradients in wind speed create the shape. Laboratory experiments rotated circular tanks of liquid at different speeds to simulate conditions. Six-sided shapes emerged most frequently though three to eight sides also appeared. Turbulent flow between rotating fluid bodies with dissimilar speeds generates these polygons. Stable vortices form on the slower side of the boundary and interact to space themselves evenly around the perimeter. Polygons do not appear unless speed differential and viscosity parameters stay within specific margins.
A 2020 study from California Institute of Technology examined geometric arrangements of polygons. Storms surrounded by rings of winds turning opposite directions create anticyclonic shielding. This shielding produces mutual rejection between cyclones through vorticity gradients. The polar cyclone on Saturn cannot maintain polygonal patterns like Jupiter due to larger size and slower wind speed. Deep barotropic instability remains a viable explanation for the sustained hexagon. Cassini's wind speed measurements rule out shallower barotropic instability during the encounter period. Moist convection influences the North Polar vortex system but does not alter core conclusions about stability. Baroclinic instabilities may also contribute to maintaining the structure over time.
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Common questions
Who discovered Saturn's hexagon and when was it first identified?
David Godfrey pieced together the first view of Saturn's hexagon in 1987. He analyzed fly-by data from the Voyager mission that had flown past the planet six years earlier.
How large is Saturn's hexagon compared to Earth?
The sides of the hexagon stretch about 13,800 kilometers long. This distance exceeds the diameter of Earth by a significant margin while the structure spans roughly 29,000 kilometers across its widest point.
When did Cassini spacecraft confirm Saturn's hexagon persisted for decades?
Cassini-Huygens returned to the site in 2006 to confirm the pattern persisted for decades. The spacecraft captured thermal infrared images until January 2009 when sunlight finally reached the north pole.
Why does Saturn's hexagon change color between blue and golden hues?
Between 2012 and 2016 the hexagon shifted from blue to golden hues as the pole received direct sunlight during seasonal shifts. One hypothesis suggests sunlight creates haze particles that alter the color.
What scientific theory explains the formation of Saturn's hexagon shape?
Allison Godfrey and Beebe published their wave dynamical interpretation in Science on the 2nd of March 1990. Oxford University scientists proposed steep latitudinal gradients in wind speed create the shape through turbulent flow between rotating fluid bodies with dissimilar speeds.