New Research brings Mysterious Saturn Hexagon into Focus

More than 30 years since NASA's Voyager space probes sent back the first images of Saturn, it remains the only planet in the solar system whose rotation period -- the time it takes to complete a revolution around its axis -- is not known. Years of research by the University of Basque Country Planetary Sciences Group have revealed intriguing clues about the planet's seasonal weather patterns and rotational period, according to a release from the school.

Those early Saturn images revealed a hexagonal structure in the planet's uppermost clouds surrounding its north pole. The hexagon remained virtually static, but, strangely, it contains clouds moving at more than 400 kilometers per hour in an enclosed jet stream.

Now, over six years of observation and collaboration between the Planetary Sciences Group and astronomers from around the world, researchers have been able to observe Saturn's northern pole region in detail once again and confirmed the hexagon continued in place. Measurements of the hexagon revealed the jet stream inside also remains unchanged. By determining the rotation period of the hexagonal structure, researchers hope to pin down the rotation of the planet. 

To make their observations, researchers used, among others, the astronomical cameras PlanetCam -- developed by the Planetary Sciences Group -- and Astralux at the Calar Alto Observatory in Almería, Spain, as well as high-resolution images from the Cassini spacecraft, which has been orbiting Saturn since 2004. 

As a result of the tilt of the planet, its poles experience extreme seasonal variations with nights lasting seven Earth years and 23 years of illumination of variable intensity. However, these seasons do not affect the hexagon or its jet stream, leading researchers to believe both are part of a wave deeply rooted in Saturn's atmosphere. 

"The hexagonal wavy motion of the jet stream is expected to be propagated vertically and reveal to us aspects of the planet's hidden atmosphere," said Agustín Sánchez-Lavega, head of the Planetary Sciences Group. "The movement of the hexagon could therefore be linked to the depths of Saturn, and the rotation period of this structure, which, as we have been able to ascertain, is 10 hours, 39 minutes and 23 seconds, could be that of the planet itself."

The group's study originally appeared in the journal Geophysical Research Letters.