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Grooved terrain in this area of Nippur Sulcus on Jupiter's moon Ganymede is composed of ridges and troughs spaced 1 to 2 kilometers (0.6 to 1.2 miles) apart. North is to the top. A few broad (4 to 5 kilometer (2.5 to 3.1 mile) wide) ridges such as those in the northeast and southwest corners have smaller ridges on top of them. A 12 kilometer (7 mile) diameter impact crater is superimposed on these ridges. A dark ring at the base of the crater walls may be due to a collection of dark material at the base of the steep slopes. The image is 49 by 41 kilometers (30 by 25 miles) with a resolution of 200 meters (656 feet) per picture element (pixel). This image was obtained on September 6, 1996 by the Solid State Imaging (CCD) system aboard 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. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

These images demonstrate the dramatic improvement in the resolution of pictures that NASA's Galileo spacecraft is returning compared to previous images of the Jupiter system. The frame at left was taken by the Voyager 2 spacecraft when it flew by in 1979, with a resolution of about 1.3 kilometers (0.8 mile) per pixel. The frame at right showing the same area was captured by Galileo during its first flyby of Ganymede on June 27, 1996; it has a resolution of about 74 meters (243 feet) per pixel, more than 17 times better than that of the Voyager image. In the Voyager frame, line-like bright and dark bands can be seen but their detailed structure and origin are not clear. In the Galileo image, each band is now seen to be composed of many smaller ridges. The structure and shape of the ridges permit scientists to determine their origin and their relation to other terrains, helping to unravel the complex history of the planet-sized moon. In each of these frames, north is to the top, and the sun illuminates the surface from the lower left nearly overhead (about 77 degrees above the horizon). The area shown, at latitude 10 degrees north, 167 degrees west, is about 35 by 55 kilometers (25 by 34 miles). The image was taken June 27 when Galileo was 7,448 kilometers (4.628 miles) away from Ganymede. The Jet Propulsion Laboratory manages the Galileo mission for NASA's Office of Space Science.

Voyager 2 took this picture of Ganymede on 5 March 1979. It was taken with the narrow-angle camera from a range of 270,000 kilometers. Clear examples of several of the different types of terrain common on Ganymede's surface are visible. The broad light regions running through the older dark areas are the typical grooved structures seen within most of the light regions on Ganymede. Many examples of craters of all ages can be seen in this image, including fresh, bright ray craters, large, subdued circular markings thought to be the "scars" of large ancient impacts and craters with thin, bright rims a small central crater. The Voyager Project is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science.

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. <a href="http://photojournal.jpl.nasa.gov/catalog/PIA00496">The bright patches occur mostly on the north and east facing slopes of craters and ridges</a>, 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 <a href="http://galileo.jpl.nasa.gov">http:// galileo.jpl.nasa.gov</a>. Background information and educational context for the images can be found at URL <a href="http://www.jpl.nasa.gov/galileo/sepo">http://www.jpl.nasa.gov/galileo/sepo</a>

An ancient dark terrain surface is cut by orthogonal sets of fractures on Jupiter's moon Ganymede. Subdued pits visible on unbroken blocks are the remnants of impact craters which have degraded with time. Across the top of the image, a line of these subdued pits may have been a chain of craters which are now cut apart by the northwest to southeast trending fractures. North is to the top. Younger craters appear as bright circles. The fractures in this image range from less than 100 meters (328 feet) to over a kilometer (0.62 miles) in width. They display bright walls where cleaner ice may be exposed, and deposits of dark material fill their floors. This 27 by 22 kilometer (17 by 14 mile) image of northern Marius Regio was obtained on September 6, 1996 by NASA's Galileo spacecraft at a resolution of 85 meters (278 feet) per picture element (pixel). 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. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

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 <a href="http://galileo.jpl.nasa.gov">http:// galileo.jpl.nasa.gov</a>. Background information and educational context for the images can be found at URL <a href="http://www.jpl.nasa.gov/galileo/sepo">http://www.jpl.nasa.gov/galileo/sepo</a>

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 <a href="http://galileo.jpl.nasa.gov">http:// galileo.jpl.nasa.gov</a>. Background information and educational context for the images can be found at URL <a href="http://www.jpl.nasa.gov/galileo/sepo">http://www.jpl.nasa.gov/galileo/sepo</a>

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 <a href="http://galileo.jpl.nasa.gov">http:// galileo.jpl.nasa.gov</a>. Background information and educational context for the images can be found at URL <a href="http://www.jpl.nasa.gov/galileo/sepo">http://www.jpl.nasa.gov/galileo/sepo</a>

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 <a href="http://galileo.jpl.nasa.gov">http:// galileo.jpl.nasa.gov</a>. Background information and educational context for the images can be found at URL <a href="http://www.jpl.nasa.gov/galileo/sepo">http://www.jpl.nasa.gov/galileo/sepo</a>

For Ganymede board game and it's extension Moon, by Sorry we are French. Those trays fit the original cardboard separator.

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 <a href="http://galileo.jpl.nasa.gov/galileo/sepo">http://www.jpl.nasa.gov/galileo/sepo</a>

The images used for the base of this Ganymede globe were chosen from coverage supplied by the Galileo solid-state imaging (SSI) camera and Voyager 1 and 2 spacecraft. The monochrome and color data were both processed using Integrated Software for Imagers and Spectrometers (ISIS). The individual images were radiometrically calibrated and photometrically normalized using a Lunar-Lambert function with empirically derived values. A linear correction based on the statistics of all overlapping areas was then applied to minimize image brightness variations. The image data were selected on the basis of overall image quality, reasonable original input resolution (from 20 km/pixel for gap fill to as much as 180 m/pixel), and availability of moderate emission/incidence angles for topography and albedo. The black and white monochrome base mosaic was constructed separately from the three-band color mosaic. Although consistency was achieved where possible, different filters were included for monochrome global image coverage as necessary: clear for Voyager 1 and 2; clear, near-IR (757 nm), and green (559 nm) for Galileo SSI. Individual images were projected to a Sinusoidal Equal-Area projection at an image resolution of 1 km/pixel. The global color mosaic was processed in Sinusoidal projection with an image resolution of 6 km/pixel. The color utilized the SSI filters 1-micron(991 nm) wavelength for red, SSI 559 nm for green, and SSI 413 nm for violet. Where SSI color coverage was lacking in the longitude range of 210-250, Voyager 2 wide-angle images were included to complete the global coverage. The chosen filters for the Voyager 2 data were ~530 nm for green, and ~480-500 nm for blue. The red band was synthesized in this area based on statistics calculated from the surrounding SSI 1-micron (991 nm) data and SSI and Voyager data in the blue and green bands. The final global color mosaic was then scaled up to 1 km/pixel and merged with the monochrome mosaic. The north pole and south pole regions that lack digital color coverage have been completed with the monochrome map coverage. The final global mosaic was then reprojected so that the entire surface of Ganymede is portrayed in a manner suitable for the production of a globe. A specialized program was used to create the "flower petal" appearance of the images; the area of each petal from 0 to 75 degrees latitude is in the Transverse Mercator projection, and the area from 75 to 90 degrees latitude is in the Lambert Azimuthal Equal-Area projection. The projections for adjacent petals overlap by 2 degrees of longitude, so that some features are shown twice. Names shown on the globe are approved by the International Astronomical Union. The number, size, and placement of text were chosen for a 9-inch globe. A complete list of Ganymede nomenclature can be found at the Gazetteer of Planetary Nomenclature at http://planetarynames.wr.usgs.gov. The northern hemisphere is shown on the left, and the southern hemisphere is shown on the right.

This image shows a mosaic of Buto Facula, a so-called "palimpsest" situated in Marius Regio on Jupiter's largest satellite Ganymede. Palimpsests are bright, nearly circular patches that are believed to be remnant impact features. They preferentially, but not exclusively, occur in Ganymede's more densely cratered, older, dark terrain units and may also be found on Ganymede's outer neighbor Callisto. The higher resolution digital image data in the center were obtained by the Solid State Imaging (SSI) camera system onboard the NASA spacecraft Galileo in May 1997 during Galileo's 8th orbit around Jupiter from a distance of about 18,600 km (11,560 miles). The pixel resolution is 180 m/pixel - the smallest features that are still discernible are about 360 m across. The sun illuminates the scene from the right at low angle, so morphological features are accentuated by long shadows. North is pointing towards the top of the mosaic. The lower resolution context in the background is given by Voyager images from 1979 when that spacecraft passed through the Jovian system at far greater distance from Ganymede than Galileo. The image center is about 12 degrees north of Ganymede's equator at a longitude of 24 degrees East. From the center of Buto Facula outward, several morphological zones can be distinguished. The center of the palimpsest, about 40 to 50 km (25 to 31 miles) in diameter, is dominated by a relatively smooth (at SSI resolution) area that shows isolated small hills near the limit of resolution. The outline of the smooth area is roughly elliptical and in some parts petal-shaped. Also, inward-facing scarps occur along some parts of the outer boundary of the inner zone. The next outer zone is characterized by a much rougher surface and two to three almost circular ridges that don't form closed circles but rather concentric ring arcs instead. These ridges are about 40 km apart. The outermost zone is somewhat less rough than the ridge-arc zone and shows vestiges of underlying topographic features such as dark-terrain furrows and, as seen in the northeastern part of the mosaic, covers about half of an older crater. The outward boundary of Buto Facula, about 290 km (180 miles) across, is defined by a clear albedo difference on lower-resolution Voyager images taken at higher sun illumination angle, whereas on low-sun SSI frames, chains of presumably secondary craters appear just outside of the boundary zone. This is good evidence for Buto Facula being an impact structure. A younger, fresh impact crater, about 20 km (12.5 miles) in diameter, cuts one of the ridges. Several clusters of secondaries within Buto Facula may be associated with this crater. A narrow, linear, NE-SW oriented scar about 40 km long very likely represents a crater chain whose individual craters are not well distinguishable at this resolution. Similar features may be observed elsewhere on Ganymede. Currently, there are two models that describe the origin of palimpsests. In one model, the morphology of these features was almost completely erased by viscous surface relaxation that took place over several 100 million years. According to another model, the palimpsest morphology formed almost immediately subsequent to the impact of a high-velocity projectile that punched through the crust into a liquid or plastic layer, excavating highly mobilized material that was emplaced as a slush or slurry across the surface. Densities of craters superimposed on surface features such as palimpsests are used to compare older and younger surface units. Absolute ages derived from crater densities, however, are model-dependent. In one crater chronology model, based on impacts dominated by asteroids, palimpsests may be rather old features, pointing back in time to a period of more intense bombardment than today, and may have ages on the order of 3.8 to 4 billion years. In a different model, based on impacts preferentially by comets with a more or less constant impact rate, palimpsests can be as "young" as only a few hundred million years. 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 <a href="http://galileo.jpl.nasa.gov">http://galileo.jpl.nasa.gov</a>. Background information and educational context for the images can be found at URL <a href="http://www.jpl.nasa.gov/galileo/sepo">http://www.jpl.nasa.gov/galileo/sepo</a>.

This region of grooved terrain on Jupiter's moon Ganymede has been partially covered by ejecta from an ancient impact structure known as a palimpsest. Palimpsests are circular, bright, low relief features formed long ago by impacts into Ganymede's surface when this surface behaved differently than it does today. This composite of three images was obtained by the solid state imaging (CCD) system aboard NASA's Galileo spacecraft on 6 September, 1996 (Universal Time) at a resolution of 88 meters per picture element (pixel). A lower resolution Voyager image of the same area is in the background. North is to the top. Part of this 350 kilometer (km) diameter unnamed palimpsest is visible as only a slight brightening of the surface in the upper left half of this image. The edge of the palimpsest crosses this picture from lower left to upper right. Secondary craters 5 to 7 km across produced during the palimpsest-forming impact are visible outside the palimpsest, in the lower right half of the picture. Inside the palimpsest, short northwest-southeast trending chains of similar sized craters can be discerned but with much more difficulty, as these craters inside the palimpsest are buried by ejecta. Similarly, the southwest-northeast trending grooves seen clearly outside the palimpsest can be seen with difficulty for a short distance within the palimpsest, where they have been covered by ejecta. This shows that the edge of the palimpsest is the edge of an ejecta blanket. Lower resolution images from the NASA's Voyager mission in 1979 revealed the palimpsests on Ganymede, but did not provide enough detail to allow them to be understood completely. Galileo images of this and several other palimpsests on Ganymede are used in conjunction with the Voyager images to provide a more complete understanding of just how these structures formed. 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. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

This infrared image of Jupiter's moon Ganymede, showing heat radiation from its surface at a wavelength of about 60 microns (millionths of a meter), provides the best view yet of nighttime temperatures on this hemisphere of Ganymede. Temperatures, derived from the brightness of the infrared radiation, can be determined from the colors by reference to the scale at the bottom of the image. The image, taken by NASA's Galileo spacecraft, shows most of Ganymede's nighttime hemisphere, centered on longitude 180 degrees, with north at the top. Irregular, diagonal dark stripes result from missing data, and are not real. Part of Ganymede's illuminated crescent, warmed by the late afternoon sun and appearing pink in this representation (indicating temperatures near 110 Kelvin (-260 F), is visible in the lower left, but most of the part of Ganymede that is seen here is in darkness, glowing only because it retains some heat from the previous day. Jupiter appears in the background behind Ganymede in the upper right part of the image. Although it is nighttime on this part of Jupiter, the planet remains much warmer at night than Ganymede does, with temperatures near 140 Kelvin (- 207 F), because Jupiter's atmosphere is too dense to cool down significantly during the night, and is also warmed by heat that flows up from Jupiter's interior. The coldest parts of Ganymede that are visible (appearing dark blue) are near the north and south poles, and have temperatures below 80 Kelvin (-315 F), while parts of the equator remain at temperatures up to 100 K (-279 F) through the night, and appear in bright blue and purple colors. This same side of Ganymede was seen in full sunlight on Galileo's first orbit around Jupiter, and similar measurements showed that noontime temperatures at the equator reached 150 K (-190 F), which is 90 degrees (Fahrenheit) warmer than the night-time temperatures seen here. The image was taken with Galileo's PPR (Photopolarimeter-Radiometer) instrument on the spacecraft's seventh orbit around Jupiter, from a range of about 65,000 kilometers (40,389 miles). Surface temperatures derived from the strength of infrared radiation, as was done here, are called "brightness temperatures", and may be slightly in error. The PPR instrument builds up an image by slowly scanning across the target over a period of up to one hour. The motion of Galileo relative to Ganymede during this time causes distortions in the satellite shape on the image, which therefore appears slightly non-circular. The small overlapping circles that make up the image show the size of the area, about 160 kilometers (99 miles) across, covered by each individual PPR measurement. Blue spots in the dark sky in the lower right are due to noise. JPL manages the Galileo mission for NASA's Office of Space Science, Washington, D.C.

Impact craters dominate the surface down to the smallest features visible on the dark terrain of the Nicholson Regio region of Jupiter's moon Ganymede in this image taken by NASA's Galileo spacecraft. It is the highest resolution view ever obtained of Ganymede's dark terrain. Both the regional-scale image at the bottom and high-resolution image at the top were taken by Galileo during its May 20, 2000, flyby of Ganymede. The latter are the highest resolution images ever obtained of Ganymede's dark terrain, which makes up about one third of Ganymede's surface. Impact cratering is clearly the dominant mechanism of surface modification in this relatively ancient terrain, which is analogous to the cratered highlands of Earth's Moon. Small-scale craters seem to mimic larger-scale craters, as is apparent in the similarities between the high and medium resolution scenes. The bright spots are probably fresh ice-rich ejecta excavated by the most recent impact events. North is to the top of the images and the Sun illuminates the surface from the west. The medium-resolution image, centered at ?15 degrees latitude and 337 degrees longitude, covers an area approximately 237 by 130 kilometers (147 by 81 miles) at a resolution of 125 meters (410 feet) per picture element. The high-resolution image is at 28 meters (92 feet) per picture element. This image and other images and data received from Galileo are posted on the Galileo mission home page at <a href="http://www.jpl.nasa.gov/galileo">http://www.jpl.nasa.gov/galileo</a>. Background information and educational context for the images can be found at <a href="http://www.jpl.nasa.gov/galileo/sepo">http://www.jpl.nasa.gov/galileo/sepo</a>. The Jet Propulsion Laboratory, a division of the California Institute of Technology, in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C. The images were produced by Arizona State University, Tempe, and Brown University, Providence, R.I. Their websites are at<a href="http://europa.la.asu.edu/index.html">http://europa.la.asu.edu/index.html</a> and <a href="http://www.planetary.brown.edu/">http://www.planetary.brown.edu/</a>.

This view of Ganymede was taken on the afternoon of March 5 from a range of 267,000 kilometers (167,000 miles). A bright rayed impact crater is prominent on the left side of the frame. The ejecta material extends for a thousand kilometers (600 miles). The rays are on top and therefore are younger than the brighter ridged and grooved terrain crossing the picture. These features may be breaks in the surface caused by faulting. Many older craters are visible that have lost their rays. JPL manages and controls the Voyager Project for NASA's Office of Space Science.

This perspective view, simulating a low altitude flight over the surface of Ganymede, was made possible by topographic analysis of stereo images of the Sippar Sulcus region. Such a view was made possible when Galileo passed Ganymede in May 1997, providing a virtual second "eye" to Voyager's first view in 1979. Because this view covers a large area, it reveals that younger, smoother terrains are low-lying relative to older, heavily faulted terrains. The consistently low elevations of these smooth deposits has been cited as evidence for flooding of parts of Ganymede by low-viscosity lavas, most likely liquid water or water-ice slush. This view is centered at 35 degrees south, 180 degrees west. The smallest features visible are roughly 350 to 400 meters (1,150 to 1,300 feet) across. This image was prepared by the Lunar and Planetary Institute, Houston, and included in a report by Dr. Paul Schenk et al. in the March 1, 2001, edition of the journal Nature. *Image Credit*: NASA and Lunar and Planetary Institute

This song is a classical mixture composition. Tell me what you think...

Courtesy Jet Propulsion Lab NASA

These frames demonstrate the dramatic improvement in the resolution of pictures that NASA's Galileo spacecraft is returning compared to previous images of the Jupiter system. The spacecraft's many orbits allow numerous close flyby's of Jupiter and its moons. The top left frame shows the best resolution (1.3 kilometers per picture element or pixel) data of the Uruk Sulcus region on Jupiter's moon Ganymede which was available after the 1979 flyby of the Voyager 2 spacecraft. The top right frame shows the same area as captured by Galileo during its closer flyby of Ganymede on June 27, 1996 at a range of 7,448 kilometers (4.628 miles). For comparison, the bottom frames show images of the San Francisco Bay area trimmed to the size of the Ganymede images and adjusted to similar resolutions.The Galileo image of Uruk Sulcus has a resolution of about 74 meters per pixel. The area shown is about 35 by 55 kilometers (25 by 34 miles). North is to the top, and the sun illuminates the surface from the lower left. The image taken by the Solid State Imaging (CCD) system reveals details of the structure and shape of the ridges which permit scientists to determine their origin and their relation to other terrains. These new views are helping to unravel the complex history of this planet-sized moon.The left SF Bay area image is from an image obtained by an Advanced Very High Resolution Radiometer aboard an NOAA satellite. The right SF Bay area image is from a LandSat Thematic Mapper. Golden Gate Park is clearly visible as a narrow dark rectangle towards the middle of this image. Both images were trimmed and adjusted to resolutions similar to the Ganymede images.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 Sensor: Galileo/Galileo.

Jupiter's largest satellite Ganymede is unique because it possesses an internal magnetic field strong enough to create a small magnetosphere around the satellite. The interaction between Ganymede's magentosphere and the Jovian magnetic field and magnetospheric plasma generates classic polar auroral emissions from Ganymede which have been captured in a series of stunning ultraviolet images using the Hubble Space Telescope on six different dates from 1998 to 2012. Analysis of these images (McGrath et al. 2013) has provided a nearly global mapping of the location of Ganymede's auroral ovals, which appear to be remarkably stable in the 14 years spanning the observations. The location of the auroral ovals is compared with several model predictions of the boundary between open and closed magnetic field lines (Koop and Ip 2002; Khurana et al. 2007; Jia et al. 2009), a region where strong field aligned potentials are a likely candidate to accelerate electrons that produce the auroral emissions. The location of the auroral emission is also compared with the polar cap boundary on Ganymede, thought to be produced by charged particle bombardment of the polar region, as delineated by color ratio images acquired by the Galileo mission (Khurana et al. 2007).

This picture of Ganymede, Jupiter's largest satellite, was taken by Voyager 1 on the afternoon of March 5, 1979, from a range of about 250,000 km (150,000 mi.). The center of the picture is at 60 north latitude and 318 longitude, and the distance across the bottom of the photograph is about 1000 km (600 mi.). The smallest features visible in this picture are about 5 km (3 mi.) across. This picture shows impact craters many of which display ray systems probably consisting largely of icy material thrown out by the impacts. Peculiar systems of sinuous ridges and grooves traverse the surface and are best seen near the terminator. These ridges and grooves are probably the result of deformation of the thick ice crust on Ganymede. JPL manages and controls the Voyager project for NASA's Office of Space Science.

Aeyl Shrivan - Ganymede

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.

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.

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.

This view of Arbela Sulcus, a 24-kilometer-wide (15-mile-wide) region of furrows and ridges on Jupiter's moon Ganymede, shows its relationship to the dark terrain surrounding it. NASA's Galileo spacecraft took these pictures during its May 20, 2000, flyby of Ganymede. Arbela Sulcus lies overall slightly lower than the dark terrain of Nicholson Regio, a 3,700 kilometers (3,300 mile) area in the southern hemisphere. However, along the eastern margin (bottom), a portion of the dark terrain (probably an ancient degraded impact crater) lies even lower than Arbela Sulcus. Scientists did not find bright icy material on Arbela Sulcus, indicating that this ridgy area was not created by watery volcanic activity. Instead, they found fine striations covering the surface, along with a series of broader highs and lows that resemble piano keys. This suggests that the movement of underlying tectonic plates deformed the surface. Combining images from two observations taken from different viewing perspectives provides stereo topographic information, giving valuable clues as to the geologic history of a region. North is to the right of the image. The Sun illuminates the surface from the west. The image, centered at ?15 degrees latitude and 347 degrees longitude, covers an area approximately 89 by 26 kilometers (55 by 16 miles). The image resolution is 70 meters (230 feet) per picture element. The images were taken on May 20, 2000, at a range of 3,350 kilometers (2,100 miles). The Jet Propulsion Laboratory, Pasadena, Calif., manages the Galileo mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena. This image and other images and data received from Galileo are posted on the Galileo mission home page at <a href="http://www.jpl.nasa.gov/galileo">http://www.jpl.nasa.gov/galileo</a>. The images were produced by German Aerospace Center (DLR),<a href="http://solarsystem.dlr.de/">http://solarsystem.dlr.de/</a> Background information and educational context for the images can be found at <a href="http://www.jpl.nasa.gov/galileo/sepo">http://www.jpl.nasa.gov/galileo/sepo</a>.

RIGHT: This picture shows part of the surface of Ganymede as viewed from a range-of 120,000 km by Voyager 2 on July 9th. In the foreground is typical grooved terrain as seen by Voyager 1. It consists of mutually intersecting bands of closely-spaced, parallel ridges and grooves. In the background is newly-cratered dark terrain across which can be traced several widely spaced parallel linear features. When viewed from a distance the line features appear to trace broad circular areas. The features resemble the circular ridges on Callisto that surround an almost completely annealed impact basin. The feature on Ganymede may be of similar origin but all traces of the impact itself have been destroyed. LEFT: This picture of Ganymede was taken at a range of 169,000 km by Voyager 2 on July 9th. Dark contrast terrain is separated by bright bands of grooved terrain. The band of closely spaced linear grooves in the foreground is 150 km across and appears to be offset by another narrow band at right angles, as though by faulting. A variety of ray patterns are seen around craters. One is the left of the picture, it has prominent dark rays around an inner bright halo. Other craters have dark haloes; other have diffuse bright rays. The variation is albedo patterns around the craters may be indications of layering in the surface materials. The intensity of craters suggests the dark areas are extremely old. The bright grooved terrain is less cratered and probably somewhat younger.

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, <a href="http://photojournal.jpl.nasa.gov/catalog/PIA01088">Byblus Sulcus</a>, was imaged during the spacecraft's second orbit, as were Philus Sulcus and <a href="http://photojournal.jpl.nasa.gov/catalog/PIA00497">Nippur Sulcus</a>, 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 <a href="http://galileo.jpl.nasa.gov">http://galileo.jpl.nasa.gov</a> . Background information and educational context for the images can be found at URL <a href="http://www.jpl.nasa.gov/galileo/sepo">http://www.jpl.nasa.gov/galileo/sepo</a>

This is New Horizons' best image of Ganymede, Jupiter's largest moon, taken with the spacecraft's Long Range Reconnaissance Imager (LORRI) camera at 10:01 Universal Time on February 27 from a range of 3.5 million kilometers (2.2 million miles). The longitude of the disk center is 38 degrees West and the image scale is 17 kilometers (11 miles) per pixel. Dark patches of ancient terrain are broken up by swaths of brighter, younger material, and the entire icy surface is peppered by more recent impact craters that have splashed fresh, bright ice across the surface. With a diameter of 5,268 kilometers (3.273 miles), Ganymede is the largest satellite in the solar system. This is one of a handful of Jupiter system images already returned by New Horizons during its close approach to Jupiter. Most of the data being gathered by the spacecraft are stored onboard and will be downlinked to Earth during March and April 2007.

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NASA's Galileo spacecraft, now in orbit around Jupiter, returned this optical navigation image June 3, 1996, showing that the spacecraft is accurately targeted for its first flyby of the giant moon Ganymede on June 27. The missing data in the frame is the result of a special editing feature recently added to the spacecraft's computer to transmit navigation images more quickly. This is first in a series of optical navigation frames, highly edited onboard the spacecraft, that will be used to fine-tune the spacecraft's trajectory as Galileo approaches Ganymede. The image, used for navigation purposes only, is the product of new computer processing capabilities on the spacecraft that allow Galileo to send back only the information required to show the spacecraft is properly targeted and that Ganymede is where navigators calculate it to be. "This navigation image is totally different from the pictures we'll be taking for scientific study of Ganymede when we get close to it later this month," said Galileo Project Scientist Dr. Torrence Johnson. On June 27, Galileo will fly just 844 kilometers (524 miles) above Ganymede and return the most detailed, full-frame, high-resolution images and other measurements of the satellite ever obtained. Icy Ganymede is the largest moon in the solar system and three-quarters the size of Mars. It is one of the four large Jovian moons that are special targets of study for the Galileo mission. Of the more than 5 million bits contained in a single image, Galileo performed on-board editing to send back a mere 24,000 bits containing the essential information needed to assure proper targeting. Only the light-to-dark transitions of the crescent Ganymede and reference star locations were transmitted to Earth. The navigation image was taken from a distance of 9.8 million kilometers (6.1 million miles). On June 27th, the spacecraft will be 10,000 times closer to Ganymede.

his color picture of Ganymede in the region 30 S 180 W shows features as small as 6 kilometers (3.7 miles) across. Shown is a bright halo impact crater that shows the fresh material thrown out of the crater. In the background is bright grooved terrain that may be the result of shearing of the surface materials along fault planes. The dark background material is the ancient heavily cratered terrain -- the oldest material preserved on the Ganymede surface.

his color picture of Ganymede in the region 30 S 180 W shows features as small as 6 kilometers (3.7 miles) across. Shown is a bright halo impact crater that shows the fresh material thrown out of the crater. In the background is bright grooved terrain that may be the result of shearing of the surface materials along fault planes. The dark background material is the ancient heavily cratered terrain -- the oldest material preserved on the Ganymede surface.

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. <A HREF="http://www.sciencemag.org/science/scripts/display/full/274/5286/377.html">Science Magazine Article</A>

These two frames, derived from images of Jupiter's moon Ganymede by NASA's Galileo and Voyager spacecraft, show bright terrain types and topography within an area called Sippar Sulcus in Ganymede's southern hemisphere. All three dominant structural styles of the bright regions -- grooved terrain, smooth terrain and reticulate terrain -- are represented. The left frame (a) is a mosaic of images taken by Galileo with a resolution of 180 meters (590 feet) per pixel superimposed on lower-resolution Voyager images. A swath of smooth terrain crosses the scene diagonally from upper right to center left. Irregularly shaped enclosures are interpreted as calderas, which, on Earth, are depressions typically caused by collapse of subsurface lava reservoirs. The numerous bright patches are due to secondary impacts from creation of a large crater, Osiris, which is out of the frame to the right. The right frame (b) shows a digital elevation model of the three-dimensional shape of the same scene. Relative elevation values have been color-coded and merged with the Galileo image mosaic. The inset shows a geological map highlighting areas of grooved terrain (g, black), reticulate terrain (r, gray), smooth terrain (s, white), calderas (hatched), and locations for higher-resolution views PIA-XXC [fig3a] (upper box) and PIA-XXD [fig3b] (lower box). These images were prepared by the Lunar and Planetary Institute, Houston, and included in a report by Dr. Paul Schenk et al. in the March 1, 2001, edition of the journal Nature. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Galileo and Voyager missions for NASA's Office of Space Science, Washington, D.C. Images and data received from Galileo are posted on the Galileo mission home page at http://www.jpl.nasa.gov/galileo. Background information and educational context for the images can be found at http://www.jpl.nasa.gov/galileo/sepo.

Sound Art by Peter David Smith AKA Speculativism

The New Horizons Long Range Reconnaissance Imager (LORRI) took this 4-millisecond exposure of Jupiter and two of its moons at 01:41:04 UTC on January 17, 2007. The spacecraft was 68.5 million kilometers (42.5 million miles) from Jupiter, closing in on the giant planet at 41,500 miles (66,790 kilometers) per hour. The volcanic moon Io is the closest planet to the right of Jupiter; the icy moon Ganymede is to Io's right. The shadows of each satellite are visible atop Jupiter's clouds; Ganymede's shadow is draped over Jupiter's northwestern limb. Ganymede's average orbit distance from Jupiter is about 1.07 million kilometers (620,000 miles); Io's is 422,000 kilometers (262,000 miles). Both Io and Ganymede are larger than Earth's moon; Ganymede is larger than the planet Mercury.

This montage compares New Horizons' best views of Ganymede, Jupiter's largest moon, gathered with the spacecraft's Long Range Reconnaissance Imager (LORRI) and its infrared spectrometer, the Linear Etalon Imaging Spectral Array (LEISA). LEISA observes its targets in more than 200 separate wavelengths of infrared light, allowing detailed analysis of their surface composition. The LEISA image shown here combines just three of these wavelengths -- 1.3, 1.8 and 2.0 micrometers -- to highlight differences in composition across Ganymede's surface. Blue colors represent relatively clean water ice, while brown colors show regions contaminated by dark material. The right panel combines the high-resolution grayscale LORRI image with the color-coded compositional information from the LEISA image, producing a picture that combines the best of both data sets. The LEISA and LORRI images were taken at 9:48 and 10:01 Universal Time, respectively, on February 27, 2007, from a range of 3.5 million kilometers (2.2 million miles). The longitude of the disk center is 38 degrees west. With a diameter of 5,268 kilometers (3,273 miles), Ganymede is the largest satellite in the solar system.

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Carbonaceous chondrites contain abundant veins of water soluble salts, including carbonates and hydrated sulfates of Mg, Ca, Na, Ni, and Fe. These constitute over 1/4 of the mass of the meteorite Orgueil. Magnesium sulfate is the most abundant salt, constituting nearly half the mass of all salt components combined (anhydrous), and 73 pct. of the highly water soluble salts. The assumption that icy satellites and asteroids contain rock compositionally similar to carbonaceous chondrites suggests that salts may be important in the cryoigneous evolution of icy satellites and asteroids. Ordinary chondrites, an alternative rock component of icy satellites, lack abundant salts, although their anhydrous silicate assemblages are unstable with respect to water and would react to produce salts upon initial melting of ice. Some basic physiochemical properties are reviewed of likely cryovolcanic brines and how the existence of soluble salts in Ganymede might affect its structure and evolution is considered. Observations indicate late stage (post heavy bombardment and post tectonic) volcanism on Ganymede. The highly fluid character of Ganymedian volcanism is consistent with extrusions of either water or salt water brines.

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Terrain units and topography of the area where a bright swath called Erech Sulcus intersects northern Sippar Sulcus on Jupiter's moon Ganymede are shown in these two frames derived from images of Jupiter's moon Ganymede by NASA's Galileo and Voyager spacecraft. The left frame (a) is a mosaic of images taken by Galileo with a resolution of 140 meters (460 feet) per pixel. Erech Sulcus is the band of grooved terrain extending north-south between two blocks of older, dark terrain. It is about 75 meters (about 250 feet) wide. A portion of Sippar Sulcus, nearly perpendicular to Erech Sulcus, lies to the south. A caldera to the right is truncated by a narrow lane of Sippar's smooth terrain. The right frame (b) shows a digital elevation model of the three-dimensional shape of the same scene. Relative elevation values, estimated from comparison of Galileo and lower-resolution Voyager images, have been color-coded and merged with the image mosaic. The bright terrain of Sippar Sulcus lies at a lower elevation than the dark terrain bordering it. These images were prepared by the Lunar and Planetary Institute, Houston, and included in a report by Dr. Paul Schenk et al. in the March 1, 2001, edition of the journal Nature. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Galileo and Voyager missions for NASA's Office of Space Science, Washington, D.C. Images and data received from Galileo are posted on the Galileo mission home page at http://www.jpl.nasa.gov/galileo. Background information and educational context for the images can be found at http://www.jpl.nasa.gov/galileo/sepo .

This mosaic of Voyager 2 images taken July 9, 1979, shows a prominent rayed crater on Jupiter's icy moon, Ganymede. The view on the left is a monochrome image, and that on the right is the same scene shown in false color designed to accentuate the icy ejecta rays splashed out by the impact. This crater is about 150 km (93 miles) across. Like several other large craters in this scene, the rayed one has a central pit, whose origins remain speculative but may involve impact melting or solid-state fluidization of the icy crust. Bright crater rays on Ganymede, like those on our own Moon, are useful to geologists because they constitute a set of features that were laid across the moon's surface at a discrete point in time--thus they serve as time markers that can be used to establish the sequence of events that shaped Ganymede's surface. For instance, the crater rays appear to be painted over, hence are younger than, areas of grooved terrain (lower left quadrant), whereas a somewhat smaller crater at the center of the scene has icy ejecta that appears to bury (hence, post-dates) the large crater ray system. One can conclude that the grooved terrain formed first, then the large crater and its rays, and then the smaller crater and its fresh icy ejecta deposits.

This color picture as acquired by Voyager 1 during its approach to Ganymede on Monday afternoon (the 5th of March). At ranges between about 230 to 250 thousand km. The image shows detail on the surface with a resolution of four and a half km. This picture is just south of PIA001515 (P21161) and shows more craters. It also shows the two distinctive types of terrain found by Voyager, the darker ungrooved regions and the lighter areas which show the grooves or fractures in abundance. The most striking features are the bright ray craters which havE a distinctly "bluer" color appearing white against the redder background. Ganymede's surface is known to contain large amounts of surface ice and it appears that these relatively young craters have spread bright fresh ice materials over the surface. Likewise, the lighter color and reflectivity of the grooved areas suggests that here too, there is cleaner ice. We see ray craters with all sizes of ray patterns, ranging from extensive systems of the crater in the northern part of this picture, which has rays at least 300-500 kilometers long, down to craters which have only faint remnants of bright ejecta patterns. This variation suggests that, as on the Moon, there are processes which act to darken ray material, probably "gardening" by micrometeoroid impact. JPL manages and controls the Voyager project for NASA's Office of Space Science.

The shallow, scalloped depression in the center of this picture from NASA's Galileo spacecraft is a caldera-like feature 5 to 20 kilometers(3 to 12 miles) wide on Jupiter's largest moon, Ganymede. Calderas are surface depressions formed by collapse above a subsurface concentration of molten material. Some shallow depressions in bright, smooth areas of Ganymede have some overall similarities to calderas on Earth and on Jupiter's moon Io. On Ganymede, caldera-like depressions may serve as sources of bright, volcanic flows of liquid water and slush, an idea supported by a Ganymede photo obtained by Galileo during its seventh orbit and available at <a href="http://photojournal.jpl.nasa.gov/catalog/PIA01614">PIA01614</a>. In the more recent image here, from Galileo's 28th orbit, a tall scarp marks the western boundary of a caldera-like feature. The western scarp is aligned similarly to older tectonic grooves visible in the image, suggesting the feature has collapsed along older lines of weakness. The interior is mottled in appearance, yet smooth compared to most of Ganymede's bright terrain seen at high resolution. The eastern boundary of the caldera-like feature is cut by younger, grooved terrain. Small impact craters pepper the scene, but the lack of a raised rim argues against an impact origin for the caldera-like feature itself. Instead, water-rich icy lava may have once flowed out of it toward the east. If so, later tectonism could have erased any telltale evidence of volcanic flow fronts. Direct evidence for icy volcanism on Ganymede continues to be elusive. North is to the top of the picture and the Sun illuminates the surface from the left. The image, centered at -24 degrees latitude and 318degrees longitude, covers an area approximately 162 by 119 kilometers(101 by 74 miles). The resolution is 43 meters (141 feet) per picture element. This image and other images and data received from Galileo are posted on the Galileo mission home page at <a href="http://www.jpl.nasa.gov/galileo">http://www.jpl.nasa.gov/galileo</a>. Background information and educational context for the images can be found at <a href="http://www.jpl.nasa.gov/galileo/sepo">http://www.jpl.nasa.gov/galileo/sepo</a>. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C. This image was produced by Brown University, Providence, R.I.,<a href="http://www.planetary.brown.edu/">http://www.planetary.brown.edu/</a>.

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.

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 <a href="http://galileo.jpl.nasa.gov">http://galileo.jpl.nasa.gov</a> . Background information and educational context for the images can be found at URL <a href="http://www.jpl.nasa.gov/galileo/sepo">http://www.jpl.nasa.gov/galileo/sepo</a>

This circular 36 kilometer (22 mile) diameter impact crater near the north pole of Jupiter's moon Ganymede has a floor that is partially brightened. On September 6, 1996, NASA's Galileo spacecraft obtained images of an 18 kilometer (11 miles) wide swath through this area. The Galileo data, acquired at a resolution of 46 meters (151 feet) pixel (picture element), is shown overlain on data obtained by NASA's Voyager spacecraft in 1979. In Voyager data the crater was thought to be flooded by icy volcanism, but in Galileo data it is seen to be brightened by frost deposition. The Voyager data, taken at a resolution of 1.3 kilometers (0.8 miles) per pixel, shows a circular feature with a bright deposit on the northern half of its floor. North is toward the top of the picture. Illumination in the image is from the southeast, and frost appears to be collecting on north facing slopes of ridges and crater rims. Fractures cross the floor of the large crater, and the northeastern rim displays two large blocks of ice which have collapsed off the side of the steep crater wall. The Galileo images were taken by the Solid State Imaging (CCD) system at a range of about 2243 kilometers (1391 miles) from the surface of Ganymede. 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. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo