http://saturn.jpl.nasa.gov/news/feat...e20050905a.cfm

Contact:
Carolina Martinez (818) 354-9382
Jet Propulsion Laboratory, Pasadena, Calif.

Cassini Discovers Saturn's Dynamic Clouds Run Deep
September 5, 2005

Cassini scientists have discovered an unexpected menagerie of clouds
lurking in the depths of Saturn's complicated atmosphere.

"Unlike the hazy, broad, global bands of clouds regularly seen in
Saturn's upper atmosphere, many of the deeper clouds appear to be
isolated, localized features," said Dr. Kevin H. Baines, a member of
the
visual and infrared mapping spectrometer team from NASA's Jet
Propulsion
Laboratory, Pasadena, Calif. "They come in a large variety of sizes and
shapes, including circular and oval shapes, donut shapes, and swirls."

These clouds are deep in the atmosphere, about 30 kilometers (19 miles)
underneath the upper clouds usually seen on Saturn. They also behave
differently from those in the upper atmosphere and are made of
different
materials. They are made of either ammonium hydrosulfide or water, but
not ammonia -- generally thought to comprise the upper clouds.

Scientists are using the motions of these clouds to understand the
dynamic weather of Saturn's deep atmosphere and get a three-dimensional
global circulation picture of Saturn. They have mapped low-altitude
winds over nearly the entire planet. Comparing these winds to the winds
at higher altitudes has led them to conclude that substantial wind
shears exist at Saturn's equator. These shears are similar to wind
shear
observed by Galileo at Jupiter, indicating that similar processes occur
on both planets. The new wind speeds measured by the mapping
spectrometer shows that winds blow about 275 kilometers per hour (170
miles per hour) faster deeper down than in the upper atmosphere.

Besides the donut-shaped and other localized cloud systems, dozens of
planet girdling lanes of clouds also appear in the new images. Such
lanes -- known as "zones"-- are commonly seen in the upper clouds of
Saturn and the other large planets. However, these deeper-level lanes
are surprisingly narrow and more plentiful than seen elsewhere,
including the upper clouds of Saturn. They also have a much more
thread-like structure than normally seen in Jupiter or Saturn's upper
atmosphere, with many of the thread-like structures and swirls
connected
to discrete cloud "cells," which look like convective cells on Earth.

The visual and infrared mapping spectrometer took high-resolution,
near-infrared images of the deep clouds during four close passes of
Saturn between February and July of this year. The images were at a
wavelength seven times greater than visible to the human eye and five
times greater than available to the Cassini visual camera.

The scientists used a new technique that allowed them to image the deep
clouds silhouetted against the background radiation of heat generated
by
the planet's interior. Until now, imaging clouds in the depths of
Saturn
has not been practical since upper-level hazes and clouds obscure the
view.

"Instead of using sunlight as the source of radiation for imaging the
deep clouds residing underneath the obscuring layer of upper-level
clouds, we developed a new technique that uses Saturn's own thermal
heat
as a source of light," said Baines. "It's like looking down at a
well-lit city from an aircraft at night, and seeing the black areas
against the city lights, which tells you there is a cloud there
blocking
the light. Saturn emits its own radiant glow, which looks much like the
glow of city lights at night."

Tracking these thermally-backlit clouds for several days enabled the
determination of wind speeds at the deepest levels ever measured on
Saturn.

"Understanding cloud development in the depths of Saturn will sharpen
our understanding of global circulation throughout Saturn and of the
major planets," said Baines.

These findings were presented in a news briefing at the 37th Annual
Meeting of the Division for Planetary Sciences meeting held this week
in
Cambridge, England.

More information on the Cassini-Huygens mission is available at
http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini .

The Cassini-Huygens mission is a cooperative project of NASA, the
European Space Agency and the Italian Space Agency. JPL, a division of
the California Institute of Technology in Pasadena, manages the
Cassini-Huygens mission for NASA's Science Mission Directorate,
Washington, D.C. The Cassini orbiter was designed, developed and
assembled at JPL. The visual and infrared mapping spectrometer team is
based at the University of Arizona.