Saturn’s active north pole

This image was acquired by Cassini's VIMS instrument on 29 October 2006, from an average distance of 902 000 kilometres above the cloud tops of Saturn, and shows a 'hexagon-like' atmospheric vortex.

This bizarre six-sided feature encircle the north pole of Saturn near 78 degrees north latitude. This image is one of the first clear images ever taken of the north polar region as seen from a unique polar perspective.

Originally discovered and last observed by a spacecraft during NASA’s Voyager flybys of the early 1980’s, the new views of this polar hexagon taken in late 2006 prove that this is an unusually long-lived feature on Saturn.

This image is the first to capture the entire feature and north polar region in one shot, and is also the first polar view using Saturn’s thermal glow at 5 microns (seven times the wavelength visible to the human eye) as the light source. This allows the pole to be revealed during the night-time conditions presently underway during north polar winter. Previous images from Voyager and from ground-based telescopes suffered from poor viewing perspectives, which placed the feature and the north pole at the extreme northern limb (edge) of the planet.

To see the deep atmosphere at night, the infrared instrument images the thermal glow radiating from Saturn’s depths. Clouds at depths about 75 kilometres lower than the clouds seen at visible wavelengths block this light, appearing dark in silhouette.

To show clouds as features that are bright or white rather than dark, the original image has been contrast reversed to produce the image shown here. The nested set of alternating white and dark hexagons indicates that the hexagonal complex extends deep into the atmosphere, at least down to the 3-Earth-atmosphere pressure level, some 75 kilometres underneath the clouds seen by Voyager.

Multiple images acquired over a 12-day period between 30 October and 11 November 2006, show that the feature is nearly stationary, and likely is an unusually strong pole-encircling planetary wave that extends deep into the atmosphere.