A bizarre six-sided feature encircling the north pole of Saturn near 78
degrees north latitude has been spied by the visual and infrared mapping
spectrometer on NASA's Cassini spacecraft. 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
nighttime 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
kilometers (47 miles) 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 kilometers (47 miles) underneath the clouds seen
by Voyager. Multiple images acquired over a 12-day period between Oct. 30
and Nov. 11, 2006, show that the feature is nearly stationary, and likely
is an unusually strong pole-encircling planetary wave that extends deep
into the atmosphere.
This image was acquired on Oct. 29, 2006, from an average distance of
902,000 kilometers (560,400 miles) above the cloud tops of Saturn.
For more information about the Cassini-Huygens mission visit
http://saturn.jpl.nasa.gov/home/index.cfm. The visual and infrared mapping
spectrometer team homepage is at http://wwwvims.lpl.arizona.edu.
