Cassini Spots Icy Jet Sources on Saturn Moon

The Cassini probe has pinpointed exact locations where icy jets erupt from Saturn's icy moon Enceladus.

New carefully targeted pictures reveal details of the prominent south polar "tiger stripe" fractures from which the jets emerge. The images show the fractures are about 980 feet (300 meters) deep, with V-shaped inner walls. The outer flanks of some of the fractures show extensive deposits of fine material. Finely fractured terrain littered with blocks of ice the size of small houses surround the fractures. 

"This is the mother lode for us," said Carolyn Porco, Cassini imaging team leader at the Space Science Institute, Boulder, Colo. "A place that may ultimately reveal just exactly what kind of environment — habitable or not — we have within this tortured little moon." 

One highly anticipated result of the flyby was finding the location within the fractures from which the jets blast icy particles, water vapor and trace organics into space. Scientists are now studying the nature and intensity of this process on Enceladus, and its effects on surrounding terrain. This information, coupled with observations by Cassini's other instruments, may answer the question of whether reservoirs of liquid water exist beneath the surface.  

The high-resolution images were acquired during an Aug. 11, 2008, flyby of Enceladus, as Cassini sped past the icy moon at 40,000 miles per hour (64,000 kilometers per hour). A special technique, dubbed "skeet shooting" by the imaging team, was developed to cancel out the high speed of the moon relative to Cassini and obtain the ultra-sharp views.

"The challenge is equivalent to trying to capture a sharp, unsmeared picture of a distant roadside billboard with a telephoto lens out the window of a speeding car." said Paul Helfenstein, Cassini imaging team associate at Cornell University, Ithaca, NY., who developed and used the skeet-shoot technique to design the image sequence.

Helfenstein said that from Cassini's point of view, "Enceladus was streaking across the sky so quickly that the spacecraft had no hope of tracking any feature on its surface. Our best option was to point the spacecraft far ahead of Enceladus, spin the spacecraft and camera as fast as possible in the direction of Enceladus' predicted path, and let Enceladus overtake us at a time when we could match its motion across the sky, snapping images along the way."  

The combination of high-resolution snapshots and broader images showing the whole region is critical for understanding what may be powering the activity on Enceladus. 

The images show extensive fallout of icy particles along some of the fractures, and even in areas between two jet sources. Scientists suggest that once warm vapor rises from underground to the cold surface through narrow channels, the icy particles may condense and seal off an active vent. New jets may then appear elsewhere along the same fracture. 

"For the first time, we are beginning to understand how freshly erupted surface deposits differ from older deposits," Helfenstein said. "Over geologic time, the eruptions have clearly moved up and down the lengths of the tiger stripes."  

Cassini flew through an icy plume from Enceladus earlier this year, and detected organic molecules similar to those found in comets.

• Video: Enceladus' Cold Faithful
• Cassini's Greatest Hits: Images of Saturn
• Special Report: Cassini's Mission to Saturn