NASA’S Cassini Spacecraft Images 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 2005, 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.

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