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. Cassini Images Reveal Spectacular Evidence Of An Active Moon

Recent Cassini images of Saturn's moon Enceladus backlit by the sun show the fountain-like sources of the fine spray of material that towers over the south polar region. Image credit: NASA/JPL/Space Science Institute.
Pasadena CA (JPL) Dec 07, 2005
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 that 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 186 kilometers (300 miles) above the surface of Enceladus, which is only 186 kilometers 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 that 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, 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 views 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.


False-color views of Saturn's cratered, icy moons, Rhea and Dione. Image credit: NASA/JPL/Space Science Institute.
"In some ways, Enceladus resembles a huge comet," said Dr. Torrence Johnson, imaging team member from NASA's Jet Propulsion Laboratory.

"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.

Cassini's Photo Album From A Season Of Icy Moons
Pasadena CA (JPL) Dec 07 - Wrapping-up a phenomenally successful year of observing Saturn's icy moons, the Cassini mission is releasing a flood of new views of the moons Enceladus, Dione, Rhea, Hyperion, and Iapetus.

The moons and their intricacies are being highlighted today at a news briefing held today at the American Geophysical Union meeting in San Francisco, Calif.

Several new images of Rhea, a moon measuring 1,528 kilometers (949 miles) across, were taken during Cassini's most recent close flyby on November 26. During the encounter, Cassini dipped to within 500 kilometers (310 miles) of Rhea's surface.

Additional new images include two "zoomable" mosaics of Rhea and Hyperion at high resolution; false-color views revealing compositional variation on the surfaces of Hyperion, Dione and Rhea; two movies reproducing Cassini's exciting encounters with Iapetus and Hyperion; and dazzling new images of the plumes of Enceladus, including a time-lapse movie.

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Bright Highlands And Dark Plains
Pasadena CA (SPX) Dec 02, 2005
This is a perspective view of the surface of Saturn's moon Titan near the Huygens probe landing site that includes the bright-dark boundary between the bright highlands and lower dark plains.
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