Cassini Finds Recent and Unusual Geology on Enceladus
This dramatic scene from Cassini illustrates an array of processes on Saturn's moon Enceladus, a once geologically active world. Most of the larger craters appear to have softened from their original, presumably crisp appearance, and are cross-cut here by numerous faults. Image credit: NASA/JPL/Space Science Institute.
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July 26, 2005
NASA's Cassini spacecraft has obtained new, detailed images of the
south polar region of Saturn's moon Enceladus. The data reveal distinctive
geological features and the most youthful terrain seen on the moon. These
findings point to a very complex evolutionary history for Saturn's brightest,
whitest satellite.
Cassini's July 14 flyby brought it within 175 kilometers (109 miles) of the
surface of the icy moon. The close encounter revealed a landscape near the
south pole almost entirely free of impact craters. The area is also littered
with house-sized ice boulders carved by unique tectonic patterns found only
in this region of the moon.
As white as fresh snow, Enceladus has the most reflective surface in the solar
system. Previous Cassini flybys revealed Enceladus, in contrast to Saturn's
other icy moons, has lightly cratered regions, fractured plains and wrinkled terrain.
The new findings add to the story of a body that has undergone multiple
episodes of geologic activity spanning a considerable portion of its
lifetime. The moon's southernmost latitudes have likely seen the most recent activity.
These same latitudes may also bear the scars of a shift in the moon's spin rate.
If true, this speculation may help scientists understand why Enceladus has a
tortured-looking surface, with pervasive crisscrossing faults, folds and ridges.
The most remarkable images show ice blocks about 10 to 100 meters (33 to 328 feet)
across in a region that is unusual in its lack of the very fine-grained frost that
seems to cover the rest of Enceladus.
"A landscape littered with building-sized blocks was not expected," said Dr. Peter
Thomas, an imaging-team member from Cornell University, Ithaca, N.Y. "The minimal
cover of finer material and the preservation of small, crossing fracture patterns in
the surrounding areas indicate that this region is young compared to the rest of Enceladus."
False color composites of this region, created from the most recent images, show
the largest exposures of coarse-grained ice fractures seen anywhere on the moon,
which also supports the notion of a young surface at southern latitudes. Some of
the latest images may hint at the answer. The images revealed additional examples
of a distinctive "Y-shaped" tectonic feature on Enceladus. In this unusual element,
parallel ridges and valleys appear to systematically fold and deform around the
south polar terrains.
"These tectonic features define a boundary that isolates the young, south polar
terrains from older terrains on Enceladus," noted Dr. Paul Helfenstein, an associate
of the imaging team also at Cornell University. "Their placement and orientation may
tell us a very interesting story about the way the rotation of Enceladus has evolved
over time and what might have provided the energy to power the geologic activity
that has wracked this moon."
The apparent absence of sizable impact craters also suggests the south pole is
younger than other terrain on Enceladus. All these indications of youth are of great
interest to scientists, who have long suspected Enceladus as one possible source of
material for Saturn's extensive and diffuse E ring, which coincides with the moon's
orbit. Young terrain requires a means to generate the heat needed to modify the surface.
Other Cassini instrument teams are working to understand data about the temperature,
composition, particles and magnetic field. Together with image interpretation, these
data can create a more complete picture.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency
and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California
Institute of Technology in Pasadena, manages the mission for NASA's Science Mission
Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed,
developed and assembled at JPL. The imaging operations center is based at the Space
Science Institute in Boulder, Colo.
These Cassini images are available on the Web at: http://www.nasa.gov/cassini ,
http://saturn.jpl.nasa.gov and http://ciclops.org .
Carolina Martinez (818) 354-9382
Jet Propulsion Laboratory, Pasadena, Calif.
Erica Hupp/Dolores Beasley (202/358-1237/1753)
NASA Headquarters, Washington
Preston Dyches (720) 974-5859
Cassini Imaging Central Laboratory for Operations
Space Science Institute, Boulder, Colo.
2005-121
