NASA’s Cassini spacecraft has seen something never before seen on another planet-a hurricane-like storm at Saturn’s south pole with a well-developed eye, ringed by towering clouds. The “hurricane” spans a dark area inside a thick, brighter ring of clouds. It is approximately 5,000 miles across, or two-thirds the diameter of Earth.
A movie taken by Cassini’s camera over a three-hour period reveals winds around Saturn’s south pole blowing clockwise at 350 miles per hour. The camera also saw the shadow cast by a ring of towering clouds surrounding the pole, and two spiral arms of clouds extending from the central ring. These ring clouds, 20 to 45 miles above those in the center of the storm, are two to five times taller than the clouds of thunderstorms and hurricanes on Earth.
“It looks like a hurricane, but it doesn’t behave like a hurricane,” says Dr. Andrew Ingersoll, a member of Cassini’s imaging team at the California Institute of Technology, Pasadena. “Whatever it is, we’re going to focus on the eye of this storm and find out why it’s there.”
In the Cassini imagery, the eye looks dark at infrared wavelengths where methane gas absorbs the light and only the highest clouds are visible.
Infrared images taken by the Keck I telescope in Mauna Kea, Hawaii, had previously shown Saturn’s south pole to be warm. Cassini’s composite infrared spectrometer has confirmed this with higher-resolution temperature maps of the area. The spectrometer observed a temperature increase of about 2 Kelvin (4 degrees Fahrenheit) at the pole. The instrument measured high temperatures in the upper troposphere and stratosphere, regions higher in the atmosphere than the clouds seen by the Cassini imaging instruments.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency, and the Italian Space Agency. The Jet Propulsion Laboratory, at the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter was designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo. The visual and infrared mapping spectrometer team is based at the University of Arizona. The composite infrared spectrometer team is based at Goddard.
See saturn.jpl.nasa.gov, www.nasa.gov/cassini, and ciclops.org.
