FOR RELEASE:  April 23, 1998

PHOTO NO.:  STScI-PRC98-18


AN INFRARED VIEW OF SATURN

In honor of NASA Hubble Space Telescope's eighth anniversary, we have
gift wrapped Saturn in vivid colors. Actually, this image is courtesy of
the new Near Infrared Camera and Multi-Object Spectrometer (NICMOS),
which has taken its first peek at Saturn. The false-color image - taken
Jan. 4, 1998 - shows the planet's reflected infrared light. This view
provides detailed information on the clouds and hazes in Saturn's
atmosphere.

The blue colors indicate a clear atmosphere down to a main cloud layer.
Different shadings of blue indicate variations in the cloud particles,
in size or chemical composition.  The cloud particles are believed to be 
ammonia ice crystals. Most of the northern hemisphere that is visible 
above the rings is relatively clear.  The dark region around the south 
pole at the bottom indicates a big hole in the main cloud layer.

The green and yellow colors indicate a haze above the main cloud layer.
The haze is thin where the colors are green but thick where they are
yellow.  Most of the southern hemisphere (the lower part of Saturn)
is quite hazy. These layers are aligned with latitude lines, due to
Saturn's east-west winds.

The red and orange colors indicate clouds reaching up high into the
atmosphere. Red clouds are even higher than orange clouds. The
densest regions of two storms near Saturn's equator appear white.
On Earth, the storms with the highest clouds are also found in tropical
latitudes. The smaller storm on the left is about as large as the
Earth, and larger storms have been recorded on Saturn in 1990 and 1994.

The rings, made up of chunks of ice, are as white as images of ice taken
in visible light. However, in the infrared, water absorption causes various
colorations. The most obvious is the brown color of the innermost ring.
The rings cast their shadow onto Saturn. The bright line seen within
this shadow is sunlight shining through the Cassini Division, the
separation between the two bright rings. It is best observed on the left
side, just above the rings. This view is possible due to a rare geometry
during the observation. The next time this is observable from Earth
will be in 2006. An accurate investigation of the ring's shadow also
shows sunlight shining through the Encke Gap, a thin division very 
close to the outer edge of the ring system.

Two of Saturn's satellites were recorded, Dione on the lower left and
Tethys on the upper right. Tethys is just ending its transit across the
disk of Saturn. They appear in different colors, yellow and green, 
indicating different conditions on their icy surfaces.

Wavelengths: A color image consists of three exposures (or three
film layers). For visible true-color images, the wavelengths of these
three exposures are 0.4, 0.5, and 0.6 micrometers for blue, green, and
red light, respectively. This Saturn image was taken at longer infrared
wavelengths of 1.0, 1.8, and 2.1 micrometers, displayed as blue, green,
and red. Reflected sunlight is seen at all these wavelengths, since
Saturn's own heat glows only at wavelengths above 4 micrometers.

Image credit:  Erich Karkoschka (University of Arizona), and NASA.