Astronomers using infrared imaging have shown that Saturn has a warm polar vortex, and is the only such planet known in the solar system.
A persisting hexagonal wave pattern around the north polar vortex in the atmosphere at about 78?N was first noted in the Voyager images. Unlike the north pole, HST imaging of the south polar region indicates the presence of a jet stream, but no strong polar vortex nor any hexagonal standing wave. However, NASA reported in November 2006 that the Cassini spacecraft observed a 'hurricane-like' storm locked to the south pole that had a clearly defined eyewall. This observation is particularly notable because eyewall clouds have not been seen on any planet other than Earth (including a failure to observe an eyewall in the Great Red Spot of Jupiter by the Galileo spacecraft).
The straight sides of the northern polar hexagon are each about 13,800 kilometers long. The entire structure rotates with a period of 10h 39 m 24s, the same period as that of the planet's radio emissions, which is assumed to be equal to the period of rotation of Saturn's interior. The hexagonal feature does not shift in longitude like the other clouds in the visible atmosphere.
The pattern's origin is a matter of much speculation. Most astronomers seem to favor some sort of standing-wave pattern in the atmosphere; but the hexagon might be a novel sort of aurora. More extreme speculation has Saturn's radio emissions emanating from the hexagon (something we can see and which has the right rotation period) rather than from the planet's interior (something we cannot see). Polygon shapes have been replicated in spinning buckets of fluid in a laboratory.
