July 26, 2005
Cassini Finds Recent and Unusual Geology on Enceladus
NASA -- 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.
"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.
Videos and Animations
Video 1: Zooming In On Enceladus -- As it swooped past the south pole of Saturn's moon Enceladus on July 14, 2005, Cassini acquired increasingly high-resolution views of this puzzling ice world. These views have been combined into this exciting movie sequence. The movie provides a stunning, up-close look at what is surely one of the youngest surfaces in the Saturn system.
From afar, Enceladus exhibits a bizarre mixture of softened craters and complex, fractured terrains. The movie zooms in on the southern polar terrains and closes in on one of the tectonic stripes that characterize this region which is essentially free of sizeable impact scars.
The bright oblong area seen during the zoom is an intermediate resolution image from near the time of closest approach that has been melded into the lower resolution mosaic, and artificially brightened.
The movie ends on the highest resolution image acquired by Cassini which reveals a surface dominated by ice blocks between 10 and 100 meters (33 and 330 feet) across, lying in a region that is unusual in its lack of the very fine-grained frost that seems to cover the rest of Enceladus.
The lack of frost and the absence of craters are indicators of a youthful surface.
The initial image in the movie is a large mosaic of 21 narrow-angle camera images that have been arranged to provide a full-disk view of the anti-Saturn hemisphere on Enceladus. This mosaic is a false-color view that includes images taken at wavelengths from the ultraviolet to the infrared portion of the spectrum, and is similar to another, lower resolution false-color view obtained during the flyby (see PIA06249 ). In false-color, many long fractures on Enceladus exhibit a pronounced difference in color (represented here in blue) from the surrounding terrain.
A leading explanation for the difference in color is that the walls of the fractures expose outcrops of coarse-grained ice that are free of the powdery surface materials that mantle flat-lying surfaces.
The original images in the false-color mosaic range in resolution from 350 to 67 meters (1,148 to 220 feet) per pixel and were taken from distances ranging from 61,300 to 11,100 kilometers (38,090 to 6,897 miles) from Enceladus. The mosaic is also available separately (see PIA06254).
Image scale is about 37 meters (121 feet) per pixel in the wide-angle camera image and about 4 meters (13 feet) per pixel in the narrow-angle image (see PIA06250 for these images). Both of these ultra-high resolution views were acquired from an altitude of approximately 208 kilometers (129 miles) above Enceladus as the spacecraft near the time of closest approach during the flyby.
On the Net: