[meteorite-list] NASA's Cassini Images Reveal Spectacular Evidence of an Active Moon (Enceladus)

[Ron Baalke]

December 6, 2005

Erica Hupp/George Deutsch 
Headquarters, Washington 
(202) 358-1237/1324

RELEASE: 05-422

NASA'S CASSINI IMAGES REVEAL SPECTACULAR EVIDENCE OF AN ACTIVE MOON

Jets of fine, icy particles streaming from Saturn's moon Enceladus 
were captured in recent images from NASA's Cassini spacecraft. The 
images provide unambiguous visual evidence the moon is geologically 
active. 

"For planetary explorers like us, there is little that can compare to 
the sighting of activity on another solar system body," said Dr. 
Carolyn Porco, Cassini imaging team leader at the Space Science 
Institute in Boulder, Colo. "This has been a heart-stopper, and 
surely one of our most thrilling results." 

The Cassini images clearly show multiple jets emanating from the 
moon's south polar region. Based on earlier data, scientists strongly 
suspected these jets arise from warm fractures in the region. The 
fractures, informally dubbed "tiger stripes," are viewed essentially 
broadside in the new images. 

The fainter, extended plume stretches at least 300 miles above the 
surface of Enceladus, which is only 300 miles wide. Cassini flew 
through the plume in July, when it passed a few hundred kilometers 
above the moon. During that flyby, Cassini's instruments measured the 
plume's constituent water vapor and icy particles. 

Imaging team members analyzed images of Enceladus taken earlier this 
year at similar viewing angles. It was a rigorous effort to 
demonstrate earlier apparitions of the plumes, seen as far back as 
January, were in fact real and not due to imperfections in the 
camera. 

The recent images were part of a sequence planned to confirm the 
presence of the plumes and examine them in finer detail. Imaging team 
member Dr. Andrew Ingersoll from the California Institute of 
Technology in Pasadena, said, "I think what we're seeing are ice 
particles in jets of water vapor that emanate from pressurized vents. 
To form the particles and carry them aloft, the vapor must have a 
certain density, and that implies surprisingly warm temperatures for 
a cold body like Enceladus." 

Imaging scientists are comparing the new images to earlier Cassini 
data in hopes of arriving at a more detailed, three-dimensional 
picture of the plumes and understanding how activity has come about 
on such a small moon. They are not sure about the precise cause of 
the moon's unexpected geologic vitality. 

"In some ways, Enceladus resembles a huge comet," said Dr. Torrence 
Johnson, imaging team member from NASA's Jet Propulsion Laboratory 
(JPL) in Pasadena. "Only, in the case of Enceladus, the energy source 
for the geyser-like activity is believed to be due to internal 
heating by perhaps radioactivity and tides rather than the sunlight 
which causes cometary jets." The new data also give yet another 
indication of how Enceladus keeps supplying material to Saturn's 
gossamer E ring. 

Additional points of contact: Carolina Martinez, JPL, (818) 354-9382; 
Preston Dyches, Space Science Institute, (720) 974-5859. 

The Cassini-Huygens mission is a cooperative project of NASA, the 
European and Italian Space Agencies. JPL, a division of the Caltech, 
manages the mission for NASA's Science Mission Directorate. 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. 

For the latest Cassini images on the Web, including a time sequence 
showing the plumes, visit: 

http://saturn.jpl.nasa.gov 

http://www.nasa.gov/cassini 

http://ciclops.org  

	
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