Press Release


By SpaceRef Editor
December 16, 2005
Filed under

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

“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

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

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

SpaceRef staff editor.