This false-color Cassini mosaic of Saturn's moon Enceladus captures in a
single view, much of the frigid moon's diverse geology.
Cratered terrain dominates most of the scene. The relatively dense
accumulation of impact craters implies that this terrain is among the
oldest on the moon's surface. Near the bottom of the picture is a crater
20 kilometers wide (12-mile) with a prominent dome-shaped structure in its
center. The entire area is transected by a complex web of fractures and
faults; some are as narrow as a few hundred meters, others as wide as 5
kilometers (3 miles).
The rims and interiors of many craters seem to be sliced by a pervasive
system of narrow, parallel grooves into slabs or lanes that typically are
a kilometer (about a half-mile) in width. The widely varied appearances
of fractures in this region attest to the fact that the surface of
Enceladus has been shaped by a long history of intense tectonic activity.
The oldest fractures are characterized by a soft, muted appearance and are
overprinted by numerous, superimposed impact craters. More recent
fractures exhibit topographic relief that is relatively "crisp" in
appearance, and they appear to slice through pre-existing impact craters
and older fractures.
On the right side of the image is a conspicuous and twisted network of
ridges and troughs forming a distinct tectonic region on Enceladus. The
paucity of craters and the sharp appearance of the topography in this
area indicate that this is a relatively young terrain on Enceladus.
This view is a composite of images taken using filters sensitive to
ultraviolet (centered at 338 nanometers), green (centered at 568
nanometers), and near-infrared (centered at 930 nanometers) light, and
has been processed to accentuate subtle color differences. The uppermost
surface of these terrains has a relatively uniform grayish color in this
picture, suggesting that it is covered with materials of homogeneous
composition and grain size. However, many of the fractures reveal a
distinctly different color (represented by pale-bluish tones in this
false-color image) than the typical surface materials. These "colored"
fractures seem to penetrate down to a material that is texturally or
compositionally different than most of the material at the surface.
One possibility is that the walls of the fractures expose outcrops of
solid ice, or ice with different grain-sizes compared to powdery surface
materials that blanket flat-lying surfaces. It is also possible that the
color identifies some compositional difference between buried ice and ice
at the surface. The distinct coloration of "youthful" fracture walls are
nearly absent in the oldest fractures. This is consistent with the
possibility that the older fractures are covered with a drape of
particulate material which mantles nearly all the oldest features on the
satellite.
In the early 1980's, NASA's Voyager mission to the outer planets revealed
a strikingly similar arrangement of terrains on Miranda, an icy moon of
Uranus (see PIA00141). Miranda is 470-kilometers-wide (290 miles),
nearly as large as Enceladus (504 kilometers, or 313 miles wide). The
similarities in size and tectonic history on these objects may suggest
that remarkably similar physical processes have controlled the separate
geological evolutions of these bodies.
The images that comprise this mosaic were obtained during Cassini's
closest approach to Enceladus on March 9, 2005. The images was taken in
visible green light with the Cassini spacecraft narrow-angle camera at a
distance of approximately 29,000 kilometers (18,000 miles) from Enceladus
and at a Sun-Enceladus-spacecraft, or phase, angle of 46 degrees.
Resolution in the original images is about 170 meters (560 feet) per
pixel.
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, D.C. The
Cassini orbiter and its two onboard cameras were designed, developed and
assembled at JPL. The imaging team is based at the Space Science
Institute, Boulder, Colo.
For more information about the Cassini-Huygens mission, visit
http://saturn.jpl.nasa.gov and the Cassini imaging team home page,
http://ciclops.org.