Monday, April 12, 2010

Saturn's Enigmatic Hexagon

One of our planets has a hex on it. Seriously.

Perhaps I should back up and explain. Back in 1988, scientists analyzing images of Saturn sent back by Voyager 2 noticed an odd structure in the cloud banding circling Saturn's North Pole. One of the cloud bands was shaped like a hexagon! [Godfrey, D. A., 1988: A hexagonal feature around Saturn's North Pole. Icarus (ISSN 0019-1035), vol. 76, Nov. 1988, p. 335-356., doi:10.1016/0019-1035(88)90075-9.]

The public was dazzled and puzzled by the images. Atmospheric scientists looked at them and said "Oh, a standing Rossby wave. Interesting." Some of these scientists went on to work out the hydrodynamic calculations of how this structure might have been formed as a side effect of a cyclone near the boundary of the hexagon. [Allison, M., D.A Godfrey, and R.F. Beebe, 1990: A wave dynamical interpretation of Saturn's polar hexagon. Science, 247, 1061-1063, doi:10.1126/science.247.4946.1061.]

When the Cassini probe reached Saturn in 2006, the northern polar region was shrouded in winter darkness, but the Cassini VIMS team was nevertheless able to image the region in infrared. (See image to the right.) Sure enough, the hexagonal shape was still there, although the vortex that had been swirling about one of its sides was gone, which was verified in the visible spectrum as daylight began to creep back into the polar region in early 2009.