Saturn’s north pole hexagon and aurora

This nighttime view of Saturn’s north pole by the visual and infrared mapping spectrometer VIMS) on NASA’s Cassini orbiter reveals a dynamic, active planet at least 75 kilometres below the normal cloud tops seen in visible light. Clearly revealed is the bizarre six-sided hexagon feature present at the north pole. This image was acquired by the Cassini visual and infrared mapping spectrometer on 29 October 2006, from an average distance of 905 000 kilometres above the clouds.

This image is one of the first clear images of the north polar region ever acquired from a unique polar perspective. In this image, the blue color shows high-altitude emissions from atmospheric molecules excited by charged particles smashing into the atmosphere along Saturn’s powerful magnetic field lines, producing the aurora at very high altitudes in Saturn’s atmosphere. The red color indicates the amount of 5-micron wavelength radiation, or heat, generated in the depths of the warm interior of Saturn that escapes the planet. Clouds blocking this light are revealed as silhouettes against the background thermal glow of the planet.

This image is among the first to capture the entire hexagonal feature and north polar region in one shot. It is also one of the first polar views using Saturn’s thermal glow at 5 microns (seven times the wavelength visible to the human eye) as the light source. This allows polar cloud features to be revealed during the persistent nighttime conditions under way during north polar winter.

The strong brightness of the hexagon feature indicates that it is primarily a clearing in the clouds, which extends deep into the atmosphere, at least down to the 3-bar (3-Earth atmospheres pressure) level, about 75 kilometres below the clouds and hazes seen in visible wavelengths. Thick clouds border both sides of the narrow feature, as indicated by the adjacent dark lanes paralleling the bright hexagon. This image and other 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.