Chapter 16 - Geology of Ganymede

Robert T. Pappalardo, Geoffrey C. Collins, James W. Head III, Paul Helfenstein, Thomas B. McCord, Jeffrey M. Moore, Louise M. Procktor, Paul M. Schenk, John R. Spencer

  • Figure 18 (jpg) color version of Figure 18 (also see Plate 12)
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    Supplemental Material:

    Table of SSI observations (.pdf)
    Table of NIMS observations (.pdf) (.doc)

    Galileo SSI Footprint Map (.jpg) (SMALL .jpg)

    PIA00496.jpg
    Original Caption Released with Image:
    Scientists believe that water-ice frosts are the likely cause for the brightening seen around the circular rims of these craters located at a high northern latitude (57 degrees) on Jupiter's moon Ganymede in this image taken by NASA's Galileo spacecraft on September 6, 1996. The image, just recently radioed to Earth from the spacecraft, shows the same kind of bright, high-latitude surface areas as those first seen by the Voyager spacecraft in 1979, but at higher resolution (this image spans about 18 kilometers or 11 miles on a side). Even though the Sun is shining from the south, the north-facing walls of the ridges and craters are brighter than the walls facing the Sun. This is interpreted to mean that the very bright north-facing slopes are covered with surface water-ice frosts, and that these frosts preferentially accumulate in such high-latitude locations. Galileo scientists say that at the high resolution seen in Galileo images, the high-latitude brightness seen by Voyager is partly attributable to frosts forming on cooler, north-facing slopes.
    The right-hand side of the image is dominated by a north-south line of impact craters; the smallest ones at the top are about 2 kilometers (1.2 miles) in diameter and the large one at the bottom is about 5 kilometers (about 3 miles) in diameter. Ganymede is the largest moon in the solar system, larger than the planet Mercury and nearly the size of Mars.
    The Jet Propulsion Laboratory, Pasadena, CA, manages the mission for NASA's Office of Space Science, Washington , DC. This image and other images and data received from Galileo are posted on the Galileo mission home page on the World Wide Web at http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at http://www.jpl.nasa.gov/galileo/sepo
    Image Note: Division of Planetary Sciences Press Conference


    PIA00497.jpg
    Original Caption Released with Image:
    New terrain overlays older terrain, which overlays still older surface, in this view of part of the surface of Jupiter's moon Ganymede, taken by the camera onboard NASA's Galileo spacecraft. Galileo obtained the images that make up this mosaic when it flew past Jupiter's moon Ganymede for the second time on September 6, 1996. An area about 54 kilometers (33 miles) wide and 90 kilometers (55 miles) high is shown. Northern Marius Regio (the dark terrain at bottom), Philus Sulcus (bright terrain at center), and Nippur Sulcus (bright terrain at top) are seen illuminated by the Sun from the southeast (north is at the top).
    The key characteristics and relationships of the major terrain types on tectonically active Ganymede are seen at a resolution 16 times better than images taken by the Voyager spacecraft in 1979. At the bottom, the ancient dark terrain is seen to be very deformed by tectonic fractures and faults. An impact crater about 18 kilometers (about 11 miles) in diameter has been highly modified by faulting. More recent cross-cutting fractures and faults at center illustrate to scientists the sequence of events that have created the younger bright terrain. The lines in the middle left of the image are faults that are cross-cut by younger faults in the upper part of the image. The smooth band in the upper middle of the image may represent water-ice volcanic deposits flooding a fault valley. Clusters of small craters, representing ejecta transported from distant craters and re-impacting here, are seen in the middle of the photo. The images that make up this mosaic were taken at a range of about 11,620 kilometers (about 7,200 miles).
    The Jet Propulsion Laboratory, Pasadena, CA, manages the mission for NASA's Office of Space Science, Washington, DC. This image and other images and data received from Galileo are posted on the Galileo mission home page on the World Wide Web at http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at http://www.jpl.nasa.gov/galileo/sepo
    Image Note: Division of Planetary Sciences Press Conference

    PIA00500.jpg
    Original Caption Released with Image:
    Galileo has eyes that can see more than ours can. By looking at what we call the infrared wavelengths, the NIMS (Near Infrared Mapping Spectrometer) instrument can determine what type and size of material is on the surface of a moon. Here, 3 images of Ganymede are shown.
    Left: Voyager's camera.
    Middle: NIMS, showing water ice on the surface. Dark is less water, bright is more.
    Right: NIMS, showing the locations of minerals in red, and the size of ice grains in shades of blue.
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov.
    Image Note: Science Magazine, Volume 274, Number 5286, 18 October 1996, pp 385-388 (figure 7) Galileo Ganymede 1 Orbit

    PIA00579.jpg
    Original Caption Released with Image:
    A mosaic of four Galileo high-resolution images of the Uruk Sulcus region of Jupiter's moon Ganymede (Latitude 11 N, Longitude: 170 W) is shown within the context of an image of the region taken by Voyager 2 in 1979, which in turn is shown within the context of a full-disk image of Ganymede. North is to the top of the picture, and the sun illuminates the surface from the lower left, nearly overhead. The area shown is about 120 by 110 kilometers (75 by 68 miles) in extent and the smallest features that can be discerned are 74 meters (243 feet) in size in the Galileo images and 1.3 kilometers (0.8 miles) in the Voyager data. The higher resolution Galileo images unveil the details of parallel ridges and troughs that are principal features in the brighter regions of Ganymede. High photometric activity (large light contrast at high spatial frequencies) of this ice-rich surface was such that the Galileo camera's hardware data compressor was pushed into truncating lines. The north-south running gap between the left and right halves of the mosaic is a result of line truncation from the normal 800 samples per line to about 540. The images were taken on 27 June, 1996 Universal Time at a range of 7,448 kilometers (4,628 miles) through the clear filter of the Galileo spacecraft's imaging system.
    Launched in October 1989, Galileo entered orbit around Jupiter on December 7, 1995. The spacecraft's mission is to conduct detailed studies of the giant planet, its largest moons and the Jovian magnetic environment.
    The Jet Propulsion Laboratory manages the Galileo mission for NASA's Office of Space Science, Washington, DC.
    This image and other images and data received from Galileo are posted on the World Wide Web Galileo mission home page at http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at http://www.jpl.nasa.gov/galileo/sepo.
    Image Note: Glileo Educator's Slide Set #2

    PIA00706.jpg
    Original Caption Released with Image:
    View of Ganymede from the Galileo spacecraft during its first encounter with the Satellite. North is to the top of the picture and the sun illuminates the surface from the right. The finest details that can be discerned in this picture are about 6.7 kilometers across. The Universal Time is 8:45:09 UT on June 26, 1996. The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASAs Office of Space Science, Washington , DC. This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo
    Image Note: old mrps 76024

    PIA00707.jpg
    Original Caption Released with Image:
    Dramatic view of fine details in ice hills and valleys in an unnamed region on Jupiter's moon Ganymede. North is to the top of the picture and the sun illuminates the surface from the left. The finest details that can discerned in this picture are only 11 meters across (similar to the size of an average house) some 2000 times better than previous images of this region. The bright areas in the left hand version are the sides of hills facing the sun; the dark areas are shadows. In the right hand version the processing has been changed to bring out details in the shadowed regions that are illuminated by the bright hillsides. The brightness of some of the hillsides is so high that the picture elements 'spill over' down the columns of the picture. The image was taken on June 28, 1996 from a distance of about 1000 kilometers. The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington , DC. This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo
    Image Note: old mrps 76025

    PIA01086.jpg
    Original Caption Released with Image:
    Complex sets of ridges and grooves are visible in this image of the Nippur Sulcus region on Jupiter's largest moon Ganymede. NASA's Galileo spacecraft imaged this region as it passed Ganymede during its second orbit through the Jovian system. The Nippur Sulcus region is an example of Bright Terrain on Ganymede which is typified by multiple sets of ridges and grooves. The intersections of these sets reveal complex age relationships. North is to the top of the picture and the sun illuminates the surface from the southeast (lower right). In this image a younger sinuous northwest-southeast trending groove set cuts through and apparently destroys the older east-west trending features on the right of the image, allowing scientists to determine the sequence of events that led to the region's formation. The area contains many impact craters. The large crater in the bottom of the image is about 12 kilometers (8 miles) in diameter.
    The image, centered at 51 degrees latitude and 204 degrees longitude, covers an area approximately 79 kilometers (50 miles) by 57 kilometers (36 miles) across. The resolution is 93 meters (330 feet) per picture element. The images were taken on September 6, 1996 at a range of 9,971 kilometers (6,232 miles) by the solid state imaging (CCD) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov.

    PIA01087.jpg
    Original Caption Released with Image:
    This image shows some unusual features on the surface of Jupiter's moon, Ganymede. NASA's Galileo spacecraft imaged this region as it passed Ganymede during its second orbit through the Jovian system. The region is located at 31 degrees latitude, 186 degrees longitude in the north of Marius Regio, a region of ancient dark terrain, and is near the border of a large swathe of younger, heavily tectonised bright terrain known as Nippur Sulcus. Situated in the transitional region between these two terrain types, the area shown here contains many complex tectonic structures, and small fractures can be seen crisscrossing the image. North is to the top-left of the picture, and the sun illuminates the surface from the southeast. This image is centered on an unusual semicircular structure about 33 kilometers (20 miles) across. A 38 kilometer (24 mile) long, remarkably linear feature cuts across its northern extent, and a wide east-west fault system marks its southern boundary. The origin of these features is the subject of much debate among scientists analyzing the data. Was the arcuate structure part of a larger feature? Is the straight lineament the result of internal or external processes? Scientists continue to study this data in order to understand the surface processes occuring on this complex satellite.
    The image covers an area approximately 80 kilometers (50 miles) by 52 kilometers (32 miles) across. The resolution is 189 meters (630 feet) per picture element. The images were taken on September 6, 1996 at a range of 9,971 kilometers (6,232 miles) by the solid state imaging (CCD) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov.

    PIA01090.jpg
    Original Caption Released with Image:
    The dark-floored crater, Khensu, is the target of this image of Ganymede. The solid state imaging camera on NASA's Galileo spacecraft imaged this region as it passed Ganymede during its second orbit through the Jovian system. Khensu is located at 2 degrees latitude and 153 degrees longitude in a region of bright terrain known as Uruk Sulcus, and is about 13 kilometers (8 miles) in diameter. Like some other craters on Ganymede, it possesses an unusually dark floor and a bright ejecta blanket. The dark component may be residual material from the impactor that formed the crater. Another possibility is that the impactor may have punched through the bright surface to reveal a dark layer beneath.
    Another large crater named El is partly visible in the top-right corner of the image. This crater is 54 kilometers (34 miles) in diameter and has a small 'pit' in its center. Craters with such a 'central pit' are common across Ganymede and are especially intriguing since they may reveal secrets about the structure of the satellite's shallow subsurface.
    North is to the top-left of the picture and the sun illuminates the surface from nearly overhead. The image covers an area about 100 kilometers (62 miles) by 86 kilometers (54 miles) across at a resolution of 111 meters (370 feet) per picture element. The image was taken on September 6, 1996 by the solid state imaging (CCD) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov.

    PIA01091.jpg
    Original Caption Released with Image:
    Complex tectonism is evident in these images of Ganymede's surface. The solid state imaging camera on NASA's Galileo spacecraft imaged this region as it passed Ganymede during its second orbit through the Jovian system. The 80 kilometer (50 mile) wide lens-shaped feature in the center of the image is located at 32 degrees latitude and 188 degrees longitude along the border of a region of ancient dark terrain known as Marius Regio, and is near an area of younger bright terrain named Nippur Sulcus. The tectonism that created the structures in the bright terrain nearby has strongly affected the local dark terrain to form unusual structures such as the one shown here. The lens-like appearance of this feature is probably due to shearing of the surface, where areas have slid past each other and also rotated slightly. Note that in several places in these images, especially around the border of the lens-shaped feature, bright ridges appear to turn into dark grooves. Analysis of the geologic structures in areas like this are helping scientists to understand the complex tectonic history of Ganymede.
    North is to the top-left of the image, and the sun illuminates the surface from the southeast. The image covers an area about 63 kilometers (39 miles) by 120 kilometers (75 miles) across at a resolution of 188 meters (627 feet) per picture element. The images were taken on September 6, 1996 at a range of 18,522 kilometers (11,576 miles) by the solid state imaging (CCD) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov.

    PIA01607.jpg
    Original Caption Released with Image:
    View of two impact craters that are superimposed on Memphis Facula, a large bright circular feature in the otherwise generally dark terrain in Galileo Regio on Jupiter's moon, Ganymede. These are thought to be impact craters because they share many of the features of such structures on other planets, including steep walls, flat floors, and central mountain peaks. Bright icy material is exposed on the walls, rims and peaks of these features and darker material can be seen covering the floors and streaming down the inner walls of the craters. The dark material may have been concentrated on the crater floors during the impact events. A dark line near the crater rim may be exposures of layered bedrock which has been uplifted. These craters have been degraded to the degree that their ejecta and surrounding secondary crater fields are no longer visible. The crater on the left (Chrysor) is about 6 kilometers (km) in diameter and the larger one on the right (Aleyn) is about 12 km wide. Smaller craters are seen as bright circles on the crater floors and in the surrounding areas. The density of these superposed impact features allows scientists to estimate the age of the surface and the age of the craters, thought to be many hundreds of millions of years old. Memphis Facula, a large 350 km diameter bright feature on which the craters are situated, appears to have formed from the excavation of bright water ice material during an ancient, large impact event.
    North is to the top left of the picture and the sun illuminates the surface from the bottom. The image, centered at 15 degrees latitude and 134 degrees longitude, covers an area approximately 23 by 23 kilometers. The resolution is 59 meters per picture element. The image was taken on June 27, 1996 at 6 hours, 21 minutes, 19 seconds Universal Time at a range of 2849 kilometers by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL NASA Product/Services Source List

    PIA01608.jpg
    Original Caption Released with Image:
    During Galileo's second orbit, a series of images were obtained within the northern polar cap of Jupiter's moon, Ganymede, across a north-south trending boundary between the grooved terrain of Philae Sulcus and the dark terrain of Galileo Regio. The blurry appearing background of this scene is the best Voyager image of the area, at a resolution of about 1.4 kilometers per picture element. The Voyager data shows that the grooved terrain of Philae Sulcus to the west (left) is bright, and the older terrain of Galileo Regio to the east (right) is dark; however, this brightness difference is not at all apparent in the high resolution Galileo images. Instead, bright and dark patches occur in both Philae Sulcus and in Galileo Regio. The bright patches occur mostly on the north and east facing slopes of craters and ridges , which are expected to be colder, and therefore to collect frost in this high latitude region. The principal way that Ganymede's terrain types can be distinguished in the high resolution Galileo images is by their texture: the "bright" grooved terrain shows north-south trending ridges and grooves, and the ancient "dark" terrain shows a rolling appearance and is more heavily cratered.
    North is to the top of the picture and the sun illuminates the surface from the lower right. The image, centered at 63 degrees latitude and 168 degrees longitude, covers an area approximately 94 by 64 kilometers. The finest details that can discerned in this picture are about 92 meters across. The images were taken on September 6, 1996 beginning at 18 hours, 52 minutes, 46 seconds Universal Time at a range of 2266 kilometers by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http:// galileo.jpl.nasa.gov . Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

    PIA01609.jpg
    Original Caption Released with Image:
    Oblique view of two fresh impact craters in bright grooved terrain near the north pole of Jupiter's moon, Ganymede. The craters postdate the grooved terrain since each is surrounded by swarms of smaller craters formed by material which was ejected out of the crater as it formed, and which subsequently reimpacted onto the surrounding surface. The crater to the north, Gula, which is 38 kilometers (km) in diameter, has a distinctive central peak, while the crater to the south, Achelous, (32 km in diameter) has an outer lobate ejecta deposit extending about a crater radius from the rim. Such images show the range of structural details of impact craters, and help in understanding the processes that form them.
    North is to the top of the picture and the sun illuminates the surface from the right. The image, centered at 62 degrees latitude and 12 degrees longitude, covers an area approximately 142 by 132 kilometers. The resolution is 175 meters per picture element. The images were taken on April 5, 1997 at 6 hours, 33 minutes, 37 seconds Universal Time at a range of 17,531 kilometers by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http:// galileo.jpl.nasa.gov . Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

    PIA01610.jpg
    Original Caption Released with Image:
    View of a chain of craters named Enki Catena on Jupiter's moon, Ganymede. This chain of 13 craters probably formed by a comet which was pulled into pieces by Jupiter'’s gravity as it passed too close to the planet. Soon after this breakup, the 13 fragments crashed onto Ganymede in rapid succession. The Enki craters formed across the sharp boundary between areas of bright terrain and dark terrain, delimited by a thin trough running diagonally across the center of this image. The ejecta deposit surrounding the craters appears very bright on the bright terrain. Even though all the craters formed nearly simultaneously, it is difficult to discern any ejecta deposit on the dark terrain. This may be because the impacts excavated and mixed dark material into the ejecta and the resulting mix is not apparent against the dark background.
    North is to the bottom of the picture and the sun illuminates the surface from the left. The image, centered at 39 degrees latitude and 13 degrees longitude, covers an area approximately 214 by 217 kilometers. The resolution is 545 meters per picture element. The image was taken on April 5, 1997 at 6 hours, 12 minutes, 22 seconds Universal Time at a range of 27282 kilometers by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http:// galileo.jpl.nasa.gov . Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

    PIA01612.jpg
    Original Caption Released with Image:
    Dark terrain of Nicholson Regio on Jupiter's moon, Ganymede. On the left is a crater that has been torn apart by tectonic forces. A lane of ridges and grooves (probably extensional fault blocks) cuts through the crater and distorts its originally circular shape. Though such deformation is more typical of Ganymede's bright grooved terrain, this image demonstrates that extreme tectonic disruption has occurred in the satellite's dark terrain also. The pair of oblong craters on the right was formed by the impact of a gravitationally bound pair of asteroids or a split comet. The oblong shapes of the craters suggest that the impactors struck the surface at a shallow angle. Toward the top left, an old crater has been partially buried by dark ejecta tossed from another impact about 50 kilometers to the north of this image.
    North is to the top of the picture and the sun illuminates the surface from the right. The image, centered at 14 degrees south latitude and 352 degrees longitude, covers an area approximately 111 by 93 kilometers. The resolution is 180 meters per picture element. The image was taken on April 5, 1997 at 6 hours, 31 minutes, 44 seconds Universal Time at a range of 17,840 kilometers by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov . Background information and educational context for the images can be found at URL http://www.jpl .nasa.gov/galileo/sepo

    PIA01613.jpg
    Original Caption Released with Image:
    View of Nicholson Regio on Jupiter's moon, Ganymede, showing heavily fractured dark terrain and a lane of smooth bright terrain. North is to the top of the picure. A smooth, linear plank-like strip of bright terrain cuts across the southeast (lower right) corner of the image. Just west (left) of this is a very heavily fractured lane of dark terrain, curving towards the south. This fractured lane looks bright in lower resolution Voyager images and may be transitional between the older, heavily fractured dark terrain, and younger, less densely cratered bright terrain. The many other fractures visible within the dark terrain probably result from extension in the area. Some of these fractures were focused around weaknesses created by older craters (such as the one just east of the image center).
    The sun illuminates the surface from the right. The image, centered at 14 degrees south latitude and 352 degrees longitude, covers an area approximately 144 by 144 kilometers. The resolution is 180 meters per picture element. The image was taken on April 5, 1997 at 6 hours, 31 minutes, 35 seconds Universal Time at a range of 17,842 kilometers by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL NASA Product/Services Source List

    PIA01614.jpg
    Original Caption Released with Image:
    NASA's Galileo imaging camera targeted an area in Sippar Sulcus on Jupiter's moon, Ganymede. Images obtained in 1979 by NASA's Voyager spacecraft showed that the area contained curvilinear and arcuate scarps or cliffs. These features appeared to be depressions which were candidate sources for some of the water ice volcanism thought to form the bright grooved terrain on Ganymede. The high resolution Galileo images seen here reveal that one of these structures contains a lobate, flow-like feature that is the best candidate yet seen for an icy volcanic lava flow on Ganymede. The prominent depression with scalloped walls and internal terraces is about 55 kilometers (km) in length and 17 to 20 km wide. On the floor of the inner depression is a lobate flow-like deposit 7 to 10 km wide with ridges that are curved outward (and apparently downslope) toward a cross-cutting lane of grooved terrain. The morphology of this structure suggests the possibility of volcanic eruptions creating a channel and flow, and cutting down into the surface.
    North is to the bottom of the picture and the sun illuminates the surface from the left. The mosaic, centered at 31 degrees south latitude and 189 degrees longitude, covers an area approximately 91 by 62 kilometers. The resolution is 172 meters per picture element. The images were taken on May 7, 1997 at 15 hours, 18 minutes, 35 seconds Universal Time at a range of 17,489 kilometers by the Solid State Imaging(SSI) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov . Background information and educational context for the images can be found at URL http://www.jpl .nasa.gov/galileo/sepo

    PIA01616.jpg
    Original Caption Released with Image:
    View of a boundary between bright and dark terrain at the southern border of Galileo Regio on Jupiter's moon, Ganymede. A narrow, 15 kilometer wide, band of fractured bright terrain runs from the upper left to lower right of this image. The dark terrain on either side of this band of bright terrain has been highly fractured in multiple directions by tectonic activity. The large bright circular feature in the upper right is probably an impact crater that has been topographically relaxed, perhaps indicating that the subsurface was warm in this region at some point in its history before the formation of the bright terrain. Such images help determine how the ancient dark terrain on Ganymede was converted into younger bright terrain.
    North is to the top of the picture and the sun illuminates the surface from nearly overhead. The image, centered at 7 degrees latitude and 157 degrees longitude, covers an area approximately 81 by 58 kilometers. The resolution is 160 meters per picture element. The image was taken on May 7, 1997 at 15 hours, 21 minutes, 16 seconds Universal Time at a range of 16218 kilometers by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL ihttp://galileo.jpl.nasa.gov . Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

    PIA01617.jpg
    Original Caption Released with Image:
    This image shows a highly fractured lane of grooved terrain, Lagash Sulcus, which runs through an area of heavily cratered dark terrain within Marius Regio on Jupiter's moon Ganymede. The boundary between these two units is marked by a deep trough. Outside the groove lane, little fracturing is evident, suggesting that deformation is largely concentrated within the bright grooved area. The bright, heart-shaped feature just below the image center may be a patch of bright terrain, or the feature may be related to ancient impact event.
    North is to the top of the picture and the sun illuminates the surface from the upper right. The image, centered at 17 degrees south latitude and 156 degrees longitude, covers an area approximately 230 by 230 kilometers. The resolution is 288 meters per picture element. The images were taken on June 6, 1997 at 14 hours, 56 minutes, 11 seconds Universal Time at a range of 28655 kilometers by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http:// galileo.jpl.nasa.gov . Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

    PIA01618.jpg
    Original Caption Released with Image:
    View of the Marius Regio and Nippur Sulcus area of Jupiter's moon, Ganymede showing the dark and bright grooved terrain which is typical of this satellite. This regional scale view was imaged near the terminator (the line between day and night) and provides geologic context for small areas that were imaged at much higher resolution earlier in the tour of NASA's Galileo spacecraft through the Jovian system. The older, more heavily cratered dark terrain of Marius Regio is rutted with furrows, shallow troughs perhaps formed as a result of ancient giant impacts. Bright grooved terrain is younger and is formed through tectonism probably combined with icy volcanism. The lane of grooved terrain in the lower left, Byblus Sulcus , was imaged during the spacecraft's second orbit, as were Philus Sulcus and Nippur Sulcus , seen here in the upper left. Placing the small higher resolution targets of Galileo's second orbit into the context of more distant, lower resolution views of the areas surrounding and connecting them, and imaging them along Ganymede's terminator, allows for an integrated understanding of Ganymede' s geology.
    North is to the top left of the picture and the sun illuminates the surface from the lower right. The image, centered at 43 degrees latitude and 194 degrees longitude, covers an area approximately 664 by 518 kilometers. The resolution is 940 meters per picture element. The image was taken on May 7, 1997 at 12 hours, 50 minutes, 11 seconds Universal Time at a range of 92,402 kilometers by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov . Background information and educational context for the images can be found at URL http://www.jpl .nasa.gov/galileo/sepo

    PIA01619.jpg
    Original Caption Released with Image:
    View of the Tiamat Sulcus region on Jupiter's moon, Ganymede, imaged just after local sunrise. The illumination from such a low sun angle highlights the grooved topography of Tiamat. Furrows and fractures are apparent in the surrounding dark terrain also. North-south trending Tiamat Sulcus is divided in two by Kishar Sulcus, which trends east-west. The southern portion of Tiamat is wider than its northern portion, indicating that there has been a greater degree of extension south of Kishar Sulcus than north of it. The portion of Kishar Sulcus to the right of Tiamat Sulcus appears to have slid horizontally (with respect to the left portion of Kishar Sulcus) along a northwest-southeast trending strike-slip fault.
    North is to the top of the picture and the sun illuminates the surface from the right. The image, centered at 1 degree south latitude and 204 degrees longitude, covers an area approximately 386 by 387 kilometers. The resolution is 494 meters per picture element. The image was taken on May 7, 1997 at 14 hours, 15 minutes, 7 seconds Universal Time at a range of 48,859 kilometers by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.
    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov . Background information and educational context for the images can be found at URL http://www.jpl .nasa.gov/galileo/sepo

    PIA01666.jpg
    Original Caption Released with Image:
    In this global view of Ganymede's trailing side, the colors are enhancedto emphasize color differences. The enhancement reveals frosty polar capsin addition to the two predominant terrains on Ganymede, bright, grooved terrain and older, dark furrowed areas. Many craters with diametersup to several dozen kilometers are visible. The violet hues at the polesmay be the result of small particles of frost which would scatter more lightat shorter wavelengths (the violet end of the spectrum). Ganymede's magnetic field, which was detected by the magnetometer on NASA's Galileo spacecraft in 1996, may be partly responsible for the appearance of thepolar terrain. Compared to Earth's polar caps, Ganymede's polar terrain is relatively vast. The frost on Ganymede reaches latitudes as low as 40 degrees on average and 25 degrees at some locations. For comparison with Earth, Miami, Florida lies at 26 degrees north latitude, and Berlin, Germany is located at 52 degrees north.
    North is to the top of the picture. The composite, which combines images taken with green, violet, and 1 micrometer filters, is centered at 306 degrees west longitude. The resolution is 9 kilometers (6 miles) per picture element. The images were taken on 29 March 1998 at a range of 918000 kilometers (570,000 miles) by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft.
    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo missionfor NASA's Office of Space Science, Washington, DC.
    This image and other images and data received from Galileo are postedon the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov . Background information andeducational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

    PIA02571.jpg
    Original Caption Released with Image:
    Impact craters dominate the surface down to the smallest featuresvisible on the dark terrain of the Nicholson Regio region of Jupiter'smoon Ganymede in this image taken by NASA's Galileo spacecraft. It isthe highest resolution view ever obtained of Ganymede's dark terrain.
    Both the regional-scale image at the bottom and high-resolution imageat the top were taken by Galileo during its May 20, 2000, flyby ofGanymede. The latter are the highest resolution images ever obtained ofGanymede's dark terrain, which makes up about one third of Ganymede'ssurface.
    Impact cratering is clearly the dominant mechanism of surfacemodification in this relatively ancient terrain, which is analogous tothe cratered highlands of Earth's Moon. Small-scale craters seem tomimic larger-scale craters, as is apparent in the similarities betweenthe high and medium resolution scenes. The bright spots are probablyfresh ice-rich ejecta excavated by the most recent impact events.
    North is to the top of the images and the Sun illuminates the surfacefrom the west. The medium-resolution image, centered at ?15 degreeslatitude and 337 degrees longitude, covers an area approximately 237 by130 kilometers (147 by 81 miles) at a resolution of 125 meters (410feet) per picture element. The high-resolution image is at 28 meters (92feet) per picture element.
    This image and other images and data received from Galileo are postedon the Galileo mission home page at http://www.jpl.nasa.gov/galileo .Background information and educational context for the images can befound at http://www.jpl.nasa.gov/galileo/sepo .
    The Jet Propulsion Laboratory, a division of the California Instituteof Technology, in Pasadena, manages the Galileo mission for NASA'sOffice of Space Science, Washington, D.C.
    The images were produced by Arizona State University, Tempe, and BrownUniversity, Providence, R.I.. Their websites are at http://europa.la.asu.edu/index.html and http://www.planetary.brown.edu/ .

    PIA02573.jpg
    Original Caption Released with Image:
    This view of the Nicholson Regio/Arbela Sulcus region on Jupiter's moonGanymede, taken by NASA's Galileo spacecraft, shows the stark contrastbetween the smooth bright terrain and the surrounding highly fractureddark terrain.
    This observation was designed in part to distinguish between differentmodels for how Arbela Sulcus and other groove lanes on Ganymede wereformed. The volcanic model suggests that a relatively clean, water-richlava filled a tectonic depression, then cooled to create a smoothsurface. Tectonic models suggest that focused faulting and deformationof older dark terrain destroyed the pre-existing texture, which wasbrightened by exposure of underlying, clean ice. Analysis of thesephotos suggests a third and unexpected possibility: Arbela Sulcus may besimilar to some bands on another of Jupiter's moons, Europa, formed bytectonic crustal spreading and renewal.
    North is to the upper left of the picture and the Sun illuminates thesurface from the west. The image, centered at ?14 degrees latitude and347 degrees longitude, covers an area approximately 258 by 116kilometers (160 by 72 miles). The resolution is 133 meters (436 feet)per picture element. The images were taken on May 20, 2000, at a rangeof 13,100 kilometers (8,140 miles).
    This image and other images and data received from Galileo are posted onthe Galileo mission home page at http://www.jpl.nasa.gov/galileo .Background information and educational context for the images can befound at http://www.jpl.nasa.gov/galileo/sepo .
    The Jet Propulsion Laboratory, a division of the California Instituteof Technology in Pasadena, manages the Galileo mission for NASA's Officeof Space Science, Washington, D.C.
    This image was produced by DLR (German Aerospace Center), Berlin, andBrown University, Providence, R.I., http://solarsystem.dlr.de/ and http://www.planetary.brown.edu/ .

    PIA02577.jpg
    Original Caption Released with Image:
    The ancient, dark terrain of Nicholson Regio (left) shows many largeimpact craters, and zones of fractures oriented generally parallel tothe boundary between the dark and bright regions of Jupiter?s moonGanymede. In contrast, the bright terrain of Harpagia Sulcus (right) isless cratered and relatively smooth.
    The nature of the boundary between ancient, dark terrain and younger,bright terrain, the two principal terrain types on Ganymede, wasexplored by NASA?s Galileo spacecraft on May 20, 2000. Subtle parallelridges and grooves show that Harpagia Sulcus?s land has been smoothedout over the years by tectonic processes.
    North is to the top of the picture. The Sun illuminates the surface fromthe left. The image, centered at ?14 degrees latitude and 319 degreeslongitude, covers an area approximately 213 by 97 kilometers (132 by 60miles.) The resolution is 121 meters (about 250 feet) per pictureelement. The images were taken on May 20, 2000, at a range of 11,800kilometers (about 7,300 miles).
    The Jet Propulsion Laboratory, Pasadena, Calif., manages the Galileomission for NASA's Office of Space Science, Washington, D.C. JPL is adivision of the California Institute of Technology in Pasadena.
    This image and other images and data received from Galileo are posted onthe Galileo mission home page at http://www.jpl.nasa.gov/galileo .Background information and educational context for the images can befound at http://www.jpl.nasa.gov/galileo/sepo .
    This image was produced by DLR (German Aerospace Center), Berlin, http://solarsystem.dlr.de/ . PIA02578.jpg
    Original Caption Released with Image:
    The boundary between the bright terrain of Harpagia Sulcus (right) anddark terrain of Nicholson Regio (left) areas of Jupiter?s moon Ganymedesprings out when viewed through red/blue 3-D glasses, in this imagetaken by NASA?s Galileo spacecraft as it flew by Ganymede on May 20,2000.
    Details of the rough, ancient, heavily cratered dark terrain ofNicholson Regio are in stark contrast to the very smooth, bright, youngterrain of Harpagia Sulcus. In the center lies the transition to theboundary between these two regions, providing evidence that extensionalfaulting marks the boundary. A series of steep slopes deform the darkterrain close to the boundary. In the bright terrain, a deep trough andflanking ridge delimit the boundary.
    North is to the top of the picture. The Sun illuminates the surface fromthe left. The imaged region, centered at ?14 degrees latitude and 319degrees longitude, covers an area approximately 25 by 10 kilometers(15.5 by 6 miles.) The resolutions of the two data sets are 20 meters(66 feet) per picture element and 121 meters (397 feet) per pictureelement. The higher resolution images were taken at a range of 2,000kilometers (about 1,200 miles).
    The Jet Propulsion Laboratory, Pasadena, Calif., manages the Galileomission for NASA's Office of Space Science, Washington, D.C. JPL is adivision of the California Institute of Technology in Pasadena.
    This image and other images and data received from Galileo are posted onthe Galileo mission home page at http://www.jpl.nasa.gov/galileo . Theimage was produced by the German Aerospace Center (DLR), http://solarsystem.dlr.de and Brown University, http://www.planetary.brown.edu/ . Background information and educationalcontext for the images can be found at http://www.jpl.nasa.gov/galileo/sepo .

    PIA02579.jpg
    Original Caption Released with Image:
    These images, taken by NASA's Galileo spacecraft on its May 20, 2000,flyby of Jupiter?s moon Ganymede, illustrate the boundary and differentelevations between the dark, ancient terrain of Nicholson Regio (left)and bright, younger terrain of Harpagia Sulcus (right.) The bottom imageis a wide view of the boundary, and the top image is an enlargement ofthe colorized strip.
    An important goal of Galileo?s Ganymede encounter was to understand thenature of the boundary between ancient, dark terrain and younger, brightterrain. The camera was aimed at the boundary to obtain both veryhigh-resolution images (top) and medium-resolution context images(bottom). Color-coded elevations are indicated relative to the averageelevation of the sampled area, with high elevation marked in red, andlow in blue. Combining the two image mosaics allows scientists to derivea detailed description of the region from the overlap. The data showsthat there are approximately 200 meters (about 650 feet) of topographicrelief within the bright terrain here, and a deep depression marks theboundary between bright and dark terrains.
    North is to the top of the pictures. The Sun illuminates the surfacefrom the left. The larger image, centered at ?14 degrees latitude and319 degrees longitude, covers an area approximately 213 by 97 kilometers(132 by 60 miles.) The resolution of the high-resolution image is 20meters (about 65 feet) per picture element, and the context image is at121 meters (397 feet) per picture element. The higher resolution imagewas taken at a range of 2000 kilometers (over 1,200 miles).
    The Jet Propulsion Laboratory, Pasadena, Calif., manages the Galileomission for NASA's Office of Space Science, Washington, D.C. JPL is adivision of the California Institute of Technology in Pasadena.
    This image and other images and data received from Galileo are posted onthe Galileo mission home page at http://www.jpl.nasa.gov/galileo . Theimages were produced by the German Aerospace Center (DLR) http://solarsystem.dlr.de/ , and Brown University, http://www.planetary.brown.edu/ . Background information and educationalcontext for the images can be found at http://www.jpl.nasa.gov/galileo/sepo .

    PIA02582.jpg
    Original Caption Released with Image:
    NASA's Galileo spacecraft took this image of dark terrain withinNicholson Regio, near the border with Harpagia Sulcus on Jupiter's moonGanymede. The ancient, heavily cratered dark terrain is faulted by aseries of scarps.
    The faulted blocks form a series of 'stair-steps' like a tilted stack ofbooks. On Earth, similar types of features form when tectonic faultingbreaks the crust and the intervening blocks are pulled apart and rotate.This image supports the notion that the boundary between bright and darkterrain is created by that type of extensional faulting.
    North is to the right of the picture and the Sun illuminates the surfacefrom the west (top). The image is centered at -14 degrees latitude and320 degrees longitude, and covers an area approximately 16 by 15kilometers (10 by 9 miles). The resolution is 20 meters (66 feet) perpicture element. The image was taken on May 20, 2000, at a range of2,090 kilometers (1,299 miles).
    This image and other images and data received from Galileo are postedon the Galileo mission home page at http://www.jpl.nasa.gov/galileo .Background information and educational context for the images can befound at http://www.jpl.nasa.gov/galileo/sepo .
    The Jet Propulsion Laboratory, a division of the California Instituteof Technology in Pasadena, manages the Galileo mission for NASA's Officeof Space Science, Washington, D.C.
    This image was produced by Brown University, Providence, R.I., http://www.planetary.brown.edu/ .