Cassini Finds Saturn's Winds Change With Altitude And Small Storms Emerging Out Of Large Ones
MEDIA RELATIONS OFFICE CASSINI IMAGING CENTRAL LABORATORY FOR OPERATIONS (CICLOPS) SPACE SCIENCE INSTITUTE, BOULDER, COLORADO http://ciclops.org
Preston Dyches (720) 974-5823 CICLOPS/Space Science Institute, Boulder, Colo.
For Immediate Release: February 24, 2005
CASSINI FINDS SATURN'S WINDS CHANGE WITH ALTITUDE AND SMALL STORMS EMERGING OUT OF LARGE ONES
The changing faces of Saturn's windy equatorial region and its turbulent southern mid-latitudes are revealed in the first Cassini Imaging Team report on Saturn's atmosphere, to appear in the Feb. 25 issue of the journal Science.
During NASA Voyager flybys of 1980-1981, winds in Saturn's equatorial region were clocked at 470 meters per second (1,060 miles per hour), ten times the speed of Earth's jet stream, making Saturn's equator the windiest place in the solar system.
During the 1990s, though, observations from NASA's Hubble Space Telescope suggested that the equatorial jet had slowed down to about 275 meters per second (about 615 miles per hour). The Cassini imaging experiment's suite of filters sense different altitudes in the atmosphere and have made it possible to interpret this apparent slowing of the wind.
By tracking the motions of cloud features seen through a spectral filter that senses deep in Saturn's atmosphere, imaging scientists have measured equatorial wind speeds of about 325 to 400 meters per second (725 to 895 miles per hour), between the Voyager and Hubble values. On the other hand, measurements taken in a spectral region where methane strongly absorbs, and therefore senses higher altitudes in the atmosphere, suggest wind speeds consistent with the Hubble values. These observations imply that wind speeds decrease with height in Saturn's equatorial region, and that the apparent slowing of the wind from the Voyager epoch to the Hubble epoch may instead have been a result of storms that raised cloud tops to higher levels where winds are slower.
Outside the equatorial region, winds have been remarkably stable from the Voyager to Hubble to Cassini eras. A major question for Cassini atmospheric scientists has been: What maintains the remarkably energetic winds on Saturn?
Cassini images have captured for the first time possible evidence of processes that may act to maintain the jets. Early in the mission, the region near 35 degrees South latitude as observed to be especially active, with at least one long-lived thunderstorm erupting from time to time, and a variety of more compact ovals appearing and merging. One sequence captured dark spots arising from the upper level outflow of a convective storm. These spots are of the same type that are seen to merge with the jets and give up their energy to them. These observations are a possible first glimpse into the process by which energy is transferred by convection from Saturn's interior to help sustain its strong cloud-level winds.
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 Cassini-Huygens 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 team is based at the Space Science Institute, Boulder, Colo.