No. 63: May-Jun 1989
"By piecing together pictures of Saturn taken by the Voyager-2 spacecraft, David A. Godfrey (National Optical Astronomy Observatories) has discovered an unusual feature in the planet's atmosphere. His mosaics reveal a hexagon centered on the north pole. Since neither probe flew directly over the pole, the complete scene has to be created by 'stretching' a series of photographs taken from the side as Saturn rotated, then fitting them into a polar projection."
The straight sides of the hexagon are each about 13,800 kilometers long. The entire structure rotates with a period of 10h 39m 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).
(Anonymous; "A Hex on Saturn," Sky and Telescope, 77:246, 1989.)
Comment. Note the similarities between the hexagon and the radial spoke structure sometimes seen in the atmosphere of Venus, as described in AVO6 in our catalog: The Moon and the Planets. Ordering details for this book are here.