This detailed Cassini view of the monstrous vortex at Saturn's south pole
provides valuable insight about the mechanisms that power the planet's
atmosphere.
This view is 10 times more detailed than any previous image of the polar
vortex. See PIA11103 for a more oblique, wide-angle view that provides
context for this close-up.
Previous images revealed an outer ring of high clouds surrounding a region
previously thought to be mostly clear air interspersed with a few puffy
clouds that circulate around the center. This new image shows that what
looked like puffy clouds at lower resolution are actually vigorous
convective storms that form yet another distinct, inner ring. In other
words, they are deep convective structures seen through the atmospheric
haze. One of the deeper structures (at the 10 o'clock position) has
punched through to a higher altitude and created its own little vortex.
The ring is similar to the eyewall of a terrestrial hurricane, but much
larger. The clear air there is warm, like the eye of a terrestrial
hurricane, but on Saturn it is locked to the pole, whereas a terrestrial
hurricane drifts around.
Convective structures are small regions of intense upwelling air, but the
clear air of the vortex eye indicates that this is generally an area of
downwelling. Convection is an important part of the planet's energy budget
because the warm upwelling air carries heat from the interior. In a
terrestrial hurricane, the convection occurs in the eyewall. Here it seems
to occur in the eye as well. The camera filter used for this image
captures light at wavelengths where atmospheric gases like methane are
fairly transparent, allowing for detailed views of deep cloud features.
Other filters (see PIA09859) use light that is
strongly absorbed by methane gas; the light bounces off the high clouds,
making them visible, but gets absorbed before it reaches the low clouds.
Such "methane-band" images of the south polar vortex reveal that the
convective clouds do not reach up to the base of the stratosphere, as
convective clouds on Earth do. This view was acquired from 56 degrees
below the ringplane. The image has been digitally reprojected to show the
scene as it would appear to an observer positioned directly above the pole.
The image was taken with the Cassini spacecraft narrow-angle camera on
July 14, 2008, using a combination of two spectral filters sensitive to
wavelengths of polarized visible light centered at 617 and infrared light
centered at 750 nanometers. The view was obtained at a distance of
approximately 392,000 kilometers (243,000 miles) from Saturn and at a
sun-Saturn-spacecraft, or phase, angle of 60 degrees. Image scale is 2
kilometers (1 mile) 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/. The Cassini imaging team
homepage is at http://ciclops.org.