Icy world of Enceladus
Thu Mar 17, 2005 at 08:58 UTC
Image Credit: NASA/JPL/Space Science Institute
Full resolution image
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.
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.
Image Credit: NASA/JPL/Space Science Institute
Full resolution image
Some geological regions on Enceladus are old and retain large numbers of impact craters; younger areas exhibit many generations of tectonic troughs and ridges. Subtle differences in color may indicate different ice properties, such as grain sizes, that will help unravel the sequence of geologic events leading to the current strange landscape.
This false-color view is a composite of individual frames obtained using filters sensitive to green (centered at 568 nanometers) and infrared light (two infrared filters, centered at 752 and 930 nanometers respectively). The view has been processed to accentuate subtle color differences. The atmosphere of Saturn forms the background of this scene (its color has been rendered grey to allow the moon to stand out).
The Sun illuminates Enceladus from the left, leaving part of it in shadow and blocking out part of the view of Saturn. This view shows the anti-Saturn hemisphere, centered nearly on the equator.
The images comprising this view were taken with the Cassini spacecraft narrow-angle camera at a distance of approximately 94,000 kilometers (58,000 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 48 degrees. Resolution in the image is about 560 meters (1,800 feet) per pixel.
Image Credit: NASA/JPL/Space Science Institute
Full resolution image
Extending through the center of this image is a system of rifts 3 kilometers wide (2 mile) and lanes of grooved terrain 20 kilometers wide (12 mile), which separate two distinct geological provinces. To the right of the boundary is older, cratered terrain - a region peppered with craters ranging from 10 kilometers (6 miles) in diameter, down craters near the limit of resolution. The region is believed to be old because it has accumulated a relatively high density of impact craters over time and the topography is soft and muted, suggesting that it is covered by a layer of particulate materials. The cratered terrain is cut crosswise by numerous faults and fractures ranging in width from hundreds of meters to a few kilometers.
On the left side of the scene are grooved, icy plains. This broad, relatively flat region is scored by an extensive band of parallel grooves that appear to subdivide the surface into narrow lanes approximately 1 kilometer or half a mile wide. The low abundance of impact craters and crisp relief on topographic features here imply that this region is geologically much younger than the cratered terrain at the right.
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 pinkish cast 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 greenish tones in this false-color image) than the typical surface materials in this region. The fractures seem to penetrate down to a material that is texturally or compositionally different than most surface materials. 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 mantle flat-lying surfaces. It is also possible that the color identifies some compositional difference between buried ice and ice at the surface.
The scene is located on the side of Enceladus that faces away from Saturn. The images were obtained with the Cassini spacecraft narrow-angle camera when the spacecraft was at a distance of approximately 25,700 kilometers (15,969 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 46 degrees. Resolution in the image is about 150 meters (490 feet) per pixel.
Image Credit: NASA/JPL/Space Science Institute
Full resolution image
The surface of Enceladus is almost uniformly white and even though the natural color of this scene has been exaggerated in intensity, no obvious departure from the uniform hue is apparent. The image was also processed to enhance contrast while avoid saturation of the brightest parts of the scene. Hence, the surface does not have the brightness of fresh snow, as it would appear to the human eye.
The Sun is illuminating the surface from the left of the image and at a low enough angle that the rugged ridge crests near upper left (which range in height from 50 to 100 meters or 164 to 328 feet) cast dramatic shadows, as at the top center of the image. The origin of the very small dark spots in the ridged terrain is uncertain. They could be shadows cast by small, building-sized outcrops (approximately 60-meter or 200-feett high) just at the limits of resolution.
Intriguingly, the craters in this scene are quite subdued, indicating that they have been degraded by some process. The craters clearly predate most of the fractures.
Additionally, multiple sets of fractures running in different directions can be seen. One set above the lower right has a gentle appearance similar to that of the craters. In contrast, the fractures running along the left are fresher. By studying differences in the morphology and patterns of the fractures, scientists will be able to learn about Enceladus' crust and how it, and geologic processes acting within it, have changed over time.
Images obtained using red, green and blue spectral filters were combined to create this view. The image was taken with the Cassini spacecraft narrow-angle camera at a distance of approximately 5,200 kilometers (3,200 miles) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 39 degrees. The scene is centered on a region at -3 degrees latitude and 218 degrees longitude.
Image Credit: NASA/JPL/Space Science Institute
Full resolution image
Enceladus shows substantial differences in composition or, more likely, particle size on its surface. Redder areas correspond to larger grain sizes, and appear to be correlated with craters and ridged regions. The surface of Enceladus is nearly pure water ice; no other components have been identified yet.
The middle of the image is located at the equator near a longitude of 210 degrees. The image is about 100 kilometers (63 miles) square. The image shows the ratio of reflected light at 1.34 and 1.52 microns, wavelengths that are not visible to the human eye.
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.
