Click on the Image for Annotated Version
Using images like the one presented here, Cassini imaging scientists have
made a major finding about the mechanism powering the general circulation
of Saturn.
The image shows small-scale, sheared-out cloud features associated with
turbulent eddies in the vicinity of one of Saturn's eastward flowing jet
streams, or "jets."
The jet itself, located at 27.5 degrees south latitude, is indicated by
the large horizontal arrow. Winds in this jet have blown continuously at
speeds close to 320 kilometers per hour (200 miles per hour) for as long
as scientists have observed Saturn.
By tracking the movements of these cloud features in successive images
separated by about 10 hours (about one Saturn rotation), Cassini
scientists have confirmed that the eddies on either side of the jet give
up their energy and momentum to help keep the winds in the jet blowing.
The tilted arrows indicate the direction in which the eddies move the
energy and momentum that power the jet. The winds that accomplish this are
so strong that they combine to stretch out the eddies into bright, tilted
streaks that are visible here, parallel to the arrows.
The analysis of Cassini images covering most of Saturn's southern
hemisphere suggests that similar processes occurring all over Saturn
explain the remarkable decades-long stability of its alternating pattern
of eastward and westward jets. The same process also occurs on Jupiter,
and on Earth in the storm track along the east coast of the United States.
Prior to this discovery, it was thought that the jets on Saturn and
Jupiter were powered by an entirely different process, analogous to the
tropical circulation on Earth. But now it appears that a comparison to the
atmospheric motions in the Earth's mid-latitudes is more appropriate.
The eddies seen in this image also create circulation patterns of upward
and downward motion (in altitude) at different latitudes that help explain
the general banded structure of global cloud patterns on the Jovian
planets.
The image was taken using a spectral filter sensitive to wavelengths of
infrared light centered at 750 nanometers. The view was acquired with the
Cassini spacecraft narrow-angle camera on Feb. 5, 2005, at a distance of
approximately 3.4 million kilometers (2.1 million miles) from Saturn.
Image scale is 20 kilometers (12 miles) per pixel.
The Cassini-Huygens mission is a cooperative project of NASA, the European
Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory,
a division of the California Institute of Technology in Pasadena, manages
the mission for NASA's Science Mission Directorate, Washington, D.C. The
Cassini orbiter and its two onboard cameras were designed, developed and
assembled at JPL. The imaging operations center is based at the Space
Science Institute in Boulder, Colo.
For more information about the Cassini-Huygens mission visit
http://saturn.jpl.nasa.gov/home/index.cfm. The Cassini imaging team
homepage is at http://ciclops.org.
