Browse All : Ganymede (Jupiter Moon) and Galileo

Ganymede Topography

title	Ganymede Topography
description	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

Ganymede's Nergal Crater

title	Ganymede's Nergal Crater
date	09.06.1996
description	Two impact craters surrounded by an unusual ejecta blanket dominate this high-resolution image of the surface of Jupiter's moon Ganymede. NASA's Galileo spacecraft photographed this region as it passed Ganymede during its second orbit through the jovian system. North is to the top of the picture, and the Sun illuminates the surface from the southeast. Nergal, the larger crater, is about 8 kilometers in diameter, while the smaller (unnamed) crater to its west is 3 kilometers across. The craters are situated in a region of bright grooved terrain named Byblus Sulcus, located in the northern part of Marius Regio at 390N latitude and 2010W longitude. The distinctive ejecta blanket that surrounds them is darker nearer the craters and brighter further away. The inner region of the ejecta is characterized by a lobate appearance indicative of the flow of a liquid (or slushy) substance over the surface. The flow was probably icy surface material melted by the energy released during the impact that formed the crater. The picture covers an area about 48 by 34 kilometers across at a resolution of 86 meters per picture element. The image was taken on September 6, 1996, by the Solid-State Imaging System onboard the Galileo spacecraft. Image Credit: Brown University

Ganymede's Khensu Crater

title	Ganymede's Khensu Crater
date	09.06.1996
description	The dark-floored crater Khensu is the target of this image of Ganymede. The Solid-State Imaging System onboard the Galileo spacecraft imaged this region as it passed Ganymede during its second orbit through the jovian system. Khensu is located at 20N latitude and 1530W longitude in a region of bright terrain known as Uruk Sulcus, and is about 13 kilometers 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 righthand corner of the image. This crater is 54 kilometers 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 upper left of the picture, and the Sun illuminates the surface from nearly overhead. The image covers an area about 100 by 86 kilometers across at a resolution of 111 meters per picture element. The image was taken on September 6, 1996, by the Solid-State Imaging System onboard the Galileo spacecraft. Image Credit: Brown University

Ganymede's Northern Limb

title	Ganymede's Northern Limb
description	View of the Northern limb region on Ganymede showing the Galileo Regio region. North is to the bottom of the picture and the sun illuminates the surface from the left. The finest details that can be discerned in this picture are about 6.7 km across. The time is 8:45:09 UT on June 26, 1996. Image Credit: NASA

Europa, Ganymede, and Callisto: Surface comparison at high spatial resolution

Europa, Ganymede, and Callis …

PIA01656

Jupiter

Solid-State Imaging

Title	Europa, Ganymede, and Callisto: Surface comparison at high spatial resolution
Original Caption Released with Image	Ganymede's youngest large craters would have been created only about one billion years ago. Europa's surface in this model should be very young, with this satellite being geologically quite active even today. The images were taken by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft. They were processed by the Institute of Planetary Exploration of the German Aerospace Center (DLR) in Berlin, Germany, and scaled to a size of 150 meters per pixel (m/pixel). North is up in all images. The spatial resolution of the original data was 180 m/pixel for Europa and Ganymede and 90 m/pixel for Callisto. The Europa image was taken during Galileo's 6th orbit, the Ganymede image during the 7th, and the Callisto image during the 10th orbit. 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 [ 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 [ http://www.jpl.nasa.gov/galileo/sepo ]., These images show a comparison of the surfaces of the three icy Galilean satellites, Europa, Ganymede, and Callisto, scaled to a common resolution of 150 meters per picture element (pixel). Despite the similar distance of 0.8 billion kilometers to the sun, their surfaces show dramatic differences. Callisto (with a diameter of 4817 kilometers) is "peppered" by impact craters, but is also covered by a dark material layer of so far unknown origin, as seen here in the region of the Asgard multi-ring basin. It appears that this layer erodes or covers small craters. Ganymede's landscape is also widely formed by impacts, but different from Callisto, much tectonic deformation can be observed in the Galileo images, such as these of Nicholson Regio. Ganymede, with a diameter of 5268 kilometers (one-and-a-half times larger than the Earth's moon), is the largest moon in the solar system. Contrary to Ganymede and Callisto, Europa (diameter 3121 kilometers) has a sparsely cratered surface, indicating that geologic activity took place more recently. Globally, ridged plains and the so-called "mottled terrain" are the main landforms. In the high-resolution image presented here showing the area around the Agave and Asterius dark lineaments, older ridges dominate the surface, while a small part of the younger mottled terrain is visible to the lower left of the image center. While all three moons are believed to be nearly as old as the solar system (4.5 billion years), the age of the surfaces, i.e. the time since the last major geologic activity took place, is still subject to debate. Without having surface samples in hand, the only method to roughly determine a planet's or satellite's geologic surface age is by crater counting. However, assumptions about the impactor fluxes must be made based on theoretical models and possible observations of candidate impactors such as asteroids and comets. Asteroids should have been very common in the early days of the solar system, but this source should have been largely exhausted by about 3.8 billion years before present. For comets, the impactor flux is believed to be rather constant throughout the whole lifetime of the solar system, meaning that the probability of an impact of a large comet is similar today as it was, say, four billion years ago. Assuming the asteroids have been the dominant bodies that impacted the Galilean satellites (which is believed to be the case on the Moon, the Earth, and other inner solar system bodies as well as within the asteroid belt itself), the surfaces of Ganymede and Callisto must be old, roughly four billion years. In this case, the Europan surface would by comparison have a mean age of one-hundred to several-hundred million years. Low-level geologic activity on Europa might be possible, but Ganymede and Callisto should be geologically dead. Assuming on the other hand that comets have been the main impactors in the Jovian system, Callisto's surface would still be determined to be old, but

Fine Details of the Icy Surface of Ganymede

Fine Details of the Icy Surf …

PIA00707

Jupiter

Solid-State Imaging

Title	Fine Details of the Icy Surface of Ganymede
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 be 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

Ganymede Global

PIA00706

Jupiter

Solid-State Imaging

Title	Ganymede Global
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 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

Detail of Ganymede's Uruk Sulcus Region as Viewed by Galileo and Voyager

Detail of Ganymede's Uruk Su …

PIA00705

Jupiter

Solid-State Imaging

Title	Detail of Ganymede's Uruk Sulcus Region as Viewed by Galileo and Voyager
Original Caption Released with Image	View of the region of Ganymede's Uruk Sulcus placed on a lower resolution Voyager view taken 17 years earlier. North is to the top of the picture and the sun illuminates the surface from almost overhead in the Galileo view. The finest details that can be discerned in the Galileo picture are about 80 meters across. The four boxes outlined in white show the extent of Galileo's initial look at this area. 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

Ganymede Color Global

PIA00716

Jupiter

Solid-State Imaging

Title	Ganymede Color Global
Original Caption Released with Image	Natural color 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 dark areas are the older, more heavily cratered regions and the light areas are younger, tectonically deformed regions. The brownish-gray color is due to mixtures of rocky materials and ice. Bright spots are geologically recent impact craters and their ejecta. The finest details that can be discerned in this picture are about 13.4 kilometers across. The images which combine for this color image were taken beginning at Universal Time 8:46:04 UT on June 26, 1996. 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

Galileo Resolutions: Ganymede and the San Francisco Bay Area

Galileo Resolutions: Ganymed …

PIA00722

Jupiter

Solid-State Imaging

Title	Galileo Resolutions: Ganymede and the San Francisco Bay Area
Original Caption Released with Image	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

Pre-Dawn Temperatures on Gan …

PIA01145

Jupiter

Photopolarimeter-Radiometer

Title	Pre-Dawn Temperatures on Ganymede
Original Caption Released with Image	This infrared image of Jupiter's moon Ganymede, showing heat radiation from its surface at a wavelength of 27 microns (millionths of a meter), provides the best view yet of pre-dawn temperatures on 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 half of Ganymede's disk as seen by the approaching spacecraft. Longitudes covered range from 340 on the right of the image, through longitude zero (the direction facing Jupiter) to longitude 60 near Ganymede's limb on the left. The morning terminator, near longitude 15, curves through the middle of the image, separating areas experiencing the last hours of the long (3.5 Earth day) Ganymede night, on the left, from areas that are warming up in the morning sunshine, on the right. Ganymede's north pole is in the upper right corner of the image, and the south pole is in the lower right. Ganymede rotates from left to right. Nighttime temperatures, shown in blue and purple colors, are in the range 85 - 100 Kelvin (-306 to -279 F). The surface cools steadily during the night, so the warmest nighttime temperatures are on the left side of the disk, and temperatures drop towards the dawn terminator on the right, before warming rapidly once the sun rises (the red, yellow and white areas on the far right). Study of the rate of nighttime cooling and the rate of post-sunrise warming, will provide information about Ganymede's surface properties. The image was taken with Galileo's PPR (Photopolarimeter-Radiometer) instrument on the spacecraft's seventh orbit around Jupiter, from a range of about 190,000 kilometers (118,060 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 450 kilometers (280 miles) across, covered by each individual PPR measurement. Blue spots in the dark sky in the left-hand portion of the image are due to noise. JPL manages the Galileo mission for NASA's Office of Space Science, Washington, D.C.

Nighttime Temperatures on Ga …

PIA01146

Jupiter

Photopolarimeter-Radiometer

Title	Nighttime Temperatures on Ganymede
Original Caption Released with Image	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.

Global Map of Ganymede

PIA03781

Jupiter

Imaging Science Subsystem, I …

Title	Global Map of Ganymede
Original Caption Released with Image	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.

Ice-frosted crater tops on G …

PIA00496

Jupiter

Solid-State Imaging

Title	Ice-frosted crater tops on Ganymede
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

Stereo View of Ganymede's Galileo Region

Stereo View of Ganymede's Ga …

PIA00521

Jupiter

Solid-State Imaging

Title	Stereo View of Ganymede's Galileo Region
Original Caption Released with Image	Topographic detail is seen in this stereoscopic view of the Galileo Regio region of Jupiter's moon Ganymede. The picture is a computer reconstruction from two images taken by NASA's Galileo spacecraft this summer. One image of the Galileo Regio region was taken June 27, 1996, at a range of 9,515 kilometers (about 5,685 miles) with a resolution of 76 meters. The other was taken September 6, 1996 at a range of 10,220 kilometers (about 6,350 miles) with a resolution of 86 meters. The topographic nature of the deep furrows and impact craters that cover this portion of Ganymede is apparent. The blue-sky horizon is artificial. The Galileo mission is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, D.C. 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 URL http://www.jpl.nasa.gov/galileo/sepo

Stereo View of Ganymede's Ga …

PIA00498

Jupiter

Solid-State Imaging

Title	Stereo View of Ganymede's Galileo Regio
Original Caption Released with Image	New topographic detail is seen in a stereoscopic view of this part of Jupiter's moon Ganymede. The newly processed picture is a computer reconstruction from two images taken by NASA's Galileo spacecraft this summer. One image of the Galileo Regio region was taken June 27, 1996, at a range of 9,515 kilometers (about 5,685 miles) and the other was taken at a range of 10,220 kilometers (about 6,350 miles) on September 6, 1996. The topographic nature of the deep furrows and impact craters that cover this portion of Ganymede is apparent. The blue-sky horizon is artificial. 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

Ganymede G1 & G2 Encounters - Interior of Ganymede

Ganymede G1 & G2 Encounters …

PIA00519

Jupiter

Title	Ganymede G1 & G2 Encounters - Interior of Ganymede
Original Caption Released with Image	Voyager images are used to create a global view of Ganymede. The cut-out reveals the interior structure of this icy moon. This structure consists of four layers based on measurements of Ganymede's gravity field and theoretical analyses using Ganymede's known mass, size and density. Ganymede's surface is rich in water ice and Voyager and Galileo images show features which are evidence of geological and tectonic disruption of the surface in the past. As with the Earth, these geological features reflect forces and processes deep within Ganymede's interior. Based on geochemical and geophysical models, scientists expected Ganymede's interior to either consist of: a) an undifferentiated mixture of rock and ice or b) a differentiated structure with a large lunar sized "core" of rock and possibly iron overlain by a deep layer of warm soft ice capped by a thin cold rigid ice crust. Galileo's measurement of Ganymede's gravity field during its first and second encounters with the huge moon have basically confirmed the differentiated model and allowed scientists to estimate the size of these layers more accurately. In addition the data strongly suggest that a dense metallic core exists at the center of the rock core. This metallic core suggests a greater degree of heating at sometime in Ganymede's past than had been proposed before and may be the source of Ganymede's magnetic field discovered by Galileo's space physics experiments. Galileo's primary 24 month mission includes eleven orbits around Jupiter and will provide observations of Jupiter, its moons and its magnetosphere. The Galileo mission is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, D.C. 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.

NIMS Ganymede Surface Map

PIA00500

Jupiter

Near Infrared Mapping Spectr …

Title	NIMS Ganymede Surface Map
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.

Calderas" on Ganymede?

PIA01614

Jupiter

Solid-State Imaging

Title	Calderas" on Ganymede?
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 [ 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 [ http://www.jpl.nasa.gov/galileo/sepo ]

Ganymede's Nippur Sulcus

PIA00497

Jupiter

Solid-State Imaging

Title	Ganymede's Nippur Sulcus
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

Fresh Impact Craters on Gany …

PIA01609

Jupiter

Solid-State Imaging

Title	Fresh Impact Craters on Ganymede
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 [ 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 [ http://www.jpl.nasa.gov/galileo/sepo ]

Dome crater Neith on Jupiter's satellite Ganymede

Dome crater Neith on Jupiter …

PIA01658

Jupiter

Solid-State Imaging

Title	Dome crater Neith on Jupiter's satellite Ganymede
Original Caption Released with Image	This image shows crater Neith, an unusual impact structure about 160 km (100 miles) in diameter, situated on Jupiter's largest satellite, Ganymede. Impact features like Neith have been called "penepalimpsests" by some investigators or "dome craters" by others and are considered to be transitional between craters and palimpsests. Palimpsests are bright, nearly circular patches that are believed to be remnant impact features. They occur also on Callisto, Ganymede's neighbor farther distant from Jupiter. Four images of Neith were obtained under low sun elevation in April 1997 during Galileo's 7th orbit around Jupiter with the Solid State Imaging (SSI) system from a distance of about 15,500 km (9,600 miles) to produce this mosaic. The pixel resolution is about 150 m/pixel - the smallest features that are still discernible are about 300 m across. The sun illuminates the scene from the right. North is approximately pointing towards the top of the mosaic. Neith is situated at about 29 degrees northern latitude and 9 degrees western longitude on Ganymede. The most striking feature in Neith is a large, circular dome about 45 km in diameter. The dome is surrounded by a wreath of rugged terrain. The wreath does not represent the original crater rim but the rim of a large central pit instead. The rim itself is barely visible and is located along the outer boundary of a relatively smooth, circular area, assumed to be the crater floor, which in turn surrounds the wreath of rugged terrain. In some parts along the rim, inward-facing scarps may be seen. The rim is not circular but appears to be petal-shaped. Outside the rim, a continuous ejecta blanket may be discerned. The morphology of impact features such as Neith results either from the response of a relatively weak target material to a high-energy impact or from long-term viscous relaxation of the surface subsequent to impact. Absolute ages derived from crater frequency measurements are model-dependent. In one crater chronology model, based on impacts dominated by asteroids, Neith may be old and very likely was formed during a period of more intense bombardment than today, about 3.9 billion years ago. In a different model, based on impacts preferentially by comets with a more or less constant impact rate, Neith may be only about 1 billion years old. 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 [ 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 [ http://www.jpl.nasa.gov/galileo/sepo ].

A Tumultuous Past for Ganymede's Dark Terrain

A Tumultuous Past for Ganyme …

PIA01612

Jupiter

Solid-State Imaging

Title	A Tumultuous Past for Ganymede's Dark Terrain
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 [ 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 [ http://www.jpl.nasa.gov/galileo/sepo ]

Marius Regio, Ganymede

PIA01617

Jupiter

Solid-State Imaging

Title	Marius Regio, Ganymede
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 [ 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 [ http://www.jpl.nasa.gov/galileo/sepo ]

Regional View of Ganymede

PIA01618

Jupiter

Solid-State Imaging

Title	Regional View of Ganymede
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 [ http://photojournal.jpl.nasa.gov/catalog/PIA01088 ], was imaged during the spacecraft's second orbit, as were Philus Sulcus and Nippur Sulcus [ http://photojournal.jpl.nasa.gov/catalog/PIA00497 ], 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 [ 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 [ http://www.jpl.nasa.gov/galileo/sepo ]

Pedestal craters Gula and Achelous on Ganymede

Pedestal craters Gula and Ac …

PIA01660

Jupiter

Solid-State Imaging

Title	Pedestal craters Gula and Achelous on Ganymede
Original Caption Released with Image	This image shows a Galileo high-resolution mosaic of craters Gula (top), about 40 km (25 miles) in diameter, and Achelous (bottom), about 35 km (21.8 miles) in diameter, projected on a lower-resolution background of image data that were obtained in the late 70s by the NASA Voyager spacecraft. The two Galileo frames used for the mosaic of Gula and Achelous were taken under low sun elevation in April 1997 during Galileo's 7th orbit around Jupiter with the Solid State Imaging (SSI) camera system onboard this NASA spacecraft that has been orbiting Jupiter since December 1995. The images were taken from a distance of about 17,500 km from Ganymede. The pixel resolution is about 180 m/pixel - the smallest features that are still discernible are about 360 m across. The sun illuminates the scene from the right. North is pointing towards the top of the Galileo mosaic. Both craters are situated between 60 and 65 degrees northern latitude at about 12.5 degrees western longitude. A characteristic feature of both craters, almost identical in size, is the "pedestal" - an outward-facing, relatively gently sloped scarp that terminates the continuous ejecta blanket. Similar features may be seen in ejecta blankets of Martian craters, suggesting impacts into a volatile (ice)-rich target material. Furthermore, both craters appear crisp and feature terraces. Gula has a prominent central peak, Achelous instead may show the remnant of a collapsed central peak or a central pit that is not fully formed. On lower-resolution images taken under higher sun illumination angle, both craters are shown to have extended bright rays, especially Achelous, which demonstrates that these two craters are younger than the respective surrounding landscape. 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 [ 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 [ http://www.jpl.nasa.gov/galileo/sepo ].

Buto Facula - A palimpsest o …

PIA01659

Jupiter

Solid-State Imaging

Title	Buto Facula - A palimpsest on Ganymede
Original Caption Released with Image	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 http://galileo.jpl.nasa.gov [ 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 [ http://www.jpl.nasa.gov/galileo/sepo ].

High Latitude "Bright" and "Dark" Terrains on Ganymede

High Latitude "Bright" and " …

PIA01608

Jupiter

Solid-State Imaging

Title	High Latitude "Bright" and "Dark" Terrains on Ganymede
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 [ http://photojournal.jpl.nasa.gov/catalog/PIA00496 ], 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 [ 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 [ http://www.jpl.nasa.gov/galileo/sepo ]

Ganymede Uruk Sulcus High Resolution Mosaic Shown in Context

Ganymede Uruk Sulcus High Re …

PIA00579

Jupiter

Solid-State Imaging

Title	Ganymede Uruk Sulcus High Resolution Mosaic Shown in Context
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.

Completing a Global Map of G …

PIA01606

Jupiter

Solid-State Imaging

Title	Completing a Global Map of Ganymede
Original Caption Released with Image	When NASA's two Voyager spacecraft passed through the Jupiter system in 1979, they captured many high resolution images of the Galilean satellites, but these encounters left some regions of these four largest Jovian moons poorly seen. One of the primary objectives of NASA's Galileo mission was to acquire images of areas that Voyager could not see. This is one such image, showing part of the leading hemisphere of Ganymede. Many fragmented regions of dark terrain split by lanes of bright grooved terrain cover the surface. Several bright young craters can be seen, including a linear chain of craters near the center of the image which may have resulted from the impact of a fragmented comet, similar to comet Shoemaker-Levy/9 which hit Jupiter in 1994. North is to the top of the picture and the sun illuminates the surface from the left. The mosaic, centered at 0 degrees latitude and 285 degrees longitude, covers an area approximately 2800 by 5100 kilometers. The resolution is 3.6 kilometers per picture element. The images were taken on February 21, 1997 at 20 hours, 25 minutes, 29 seconds Universal Time at a range of 34,386 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 [ 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 [ http://www.jpl.nasa.gov/galileo/sepo ]

Dark-floored Impact Craters …

PIA01607

Jupiter

Solid-State Imaging

Title	Dark-floored Impact Craters on Ganymede
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 http://www.jpl.nasa.gov/galileo/sepo [ http://galileo.jpl.nasa.gov/galileo/sepo ]

Ganymede Galileo Regio High Resolution Mosaic Shown in Context

Ganymede Galileo Regio High …

PIA00580

Jupiter

Solid-State Imaging

Title	Ganymede Galileo Regio High Resolution Mosaic Shown in Context
Original Caption Released with Image	Ancient impact craters shown in this image of Jupiter's moon Ganymede taken by NASA's Galileo spacecraft testify to the great age of the terrain, dating back several billion years. At the margin at the left, half of a 19-kilometer-diameter (12-mile) crater is visible. The dark and bright lines running from lower right to upper left and from top to bottom are deep furrows in the ancient crust of dirty water ice. The origin of the dark material is unknown, but it may be accumulated dark fragments from many meteorites that hit Ganymede. In this view, north is to the top, and the sun illuminates the surface from the lower left about 58 degrees above the horizon. The area shown is part of Ganymede's Galileo Regio region at latitude 18 degrees north, longitude 147 degrees west, it is about 46 by 64 kilometers (29 by 38 miles) in extent. Resolution is about 80 meters (262 feet) per pixel. The image was taken June 27 at a range of 7.563 kilometers (4,700 miles). 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.

Ganymede's Trailing Hemisphe …

PIA01666

Jupiter

Solid-State Imaging

Title	Ganymede's Trailing Hemisphere
Original Caption Released with Image	In this global view of Ganymede's trailing side, the colors are enhanced to emphasize color differences. The enhancement reveals frosty polar caps in addition to the two predominant terrains on Ganymede, bright, grooved terrain and older, dark furrowed areas. Many craters with diameters up to several dozen kilometers are visible. The violet hues at the poles may be the result of small particles of frost which would scatter more light at 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 the polar 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 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 URLhttp://galileo.jpl.nasa.gov [ http://galileo.jpl.nasa.gov ]. Background information and educational context for the images can be found at URLhttp://www.jpl.nasa.gov/galileo/sepo [ http://www.jpl.nasa.gov/galileo/sepo ]

Swaths of Grooved Terrain on …

PIA01615

Jupiter

Solid-State Imaging

Title	Swaths of Grooved Terrain on Ganymede
Original Caption Released with Image	A swath of grooved terrain named Erech Sulcus cuts north-south across the ancient dark terrain of Marius Regio. The multiple scales of ubiquitous grooves in Erech Sulcus probably formed when tectonic forces pulled apart the icy surface of Jupiter's moon, Ganymede. Similar sets of faults occur in rift zones on Earth, as in eastern Africa. The southern edge of Erech Sulcus is truncated by the smoother bright terrain of Sippar Sulcus, trending roughly east-west. The relatively smooth appearance of Sippar Sulcus hints that icy volcanism once paved over the area. North is to the top of the picture and the sun illuminates the surface from the right. The mosaic, centered at 16 degrees south latitude and 177 degrees longitude, covers an area approximately 950 by 560 kilometers. The resolution is 143 meters per picture element. The images were taken on May 7, 1997 at 15 hours, 24 minutes, 39 seconds Universal Time at a range of 14,263 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 [ 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 [ http://www.jpl.nasa.gov/galileo/sepo ]

NIMS Observes Melkart Crater on Ganymede

NIMS Observes Melkart Crater …

PIA00878

Jupiter

Near Infrared Mapping Spectr …

Title	NIMS Observes Melkart Crater on Ganymede
Original Caption Released with Image	The top figure is an image of the crater Melkart on Ganymede, at a wavelength of 0.85 microns, taken by the Near Infrared Mapping Spectrometer (NIMS) on the Galileo spacecraft, The crater is illuminated by the Sun from the left. The finest detail that can be seen is approximately 30 km in size. What is most obvious, and of great interest, are the two concentric ring structures and the central dome. The walls of these rings are in shadow on the left, and are in sunlight on the right. To understand how these rings and central dome are thought to form, consider a pebble dropped into a pond. Ripples spread out from the center, oscillating up and down. The rings and dome forming Melkart are a snapshot of these ripples in the ice of Ganymede, possibly caused by the impact of a comet or asteroid. Similar features on the Moon are only associated with much larger craters as the stronger Moon rock behaves this way only with large impacts. NIMS can obtain images at many different wavelengths from 0.7 to 5.2 microns. The spectrum shows the amount of reflected light as a function of wavelength from the crater floor of Melkart. Several distinct absorption features, caused by water ice, are evident at 1.5 and 2.0 microns. Beyond 3.0 microns the intensity increases again as the longer wavelengths are more sensitive to Ganymede's thermal radiation. The shape of the absorption features suggest that the ice is mixed with hydrated minerals. These relatively dark minerals probably cause the variations in ice brightness seen at visible wavelengths. 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://www.jpl.nasa.gov/ galileo.

Ganymede and Jupiter

PIA02862

Sol (our sun)

Imaging Science Subsystem

Title	Ganymede and Jupiter
Original Caption Released with Image	The solar system's largest moon, Ganymede, is captured here alongside the planet Jupiter in a color picture taken by NASA's Cassini spacecraft on Dec. 3, 2000. Ganymede is larger than the planets Mercury and Pluto and Saturn's largest moon, Titan. Both Ganymede and Titan have greater surface area than the entire Eurasian continent on our planet. Cassini was 26.5 million kilometers (16.5 million miles) from Ganymede when this image was taken. The smallest visible features are about 160 kilometers (about 100 miles) across. The bright area near the south (bottom) of Ganymede is Osiris, a large, relatively new crater surrounded by bright icy material ejected by the impact, which created it. Elsewhere, Ganymede displays dark terrains that NASA's Voyager and Galileo spacecraft have shown to be old and heavily cratered. The brighter terrains are younger and laced by grooves. Various kinds of grooved terrains have been seen on many icy moons in the solar system. These are believed to be the surface expressions of warm, pristine, water-rich materials that moved to the surface and froze. Ganymede has proven to be a fascinating world, the only moon known to have a magnetosphere, or magnetic environment, produced by a convecting metal core. The interaction of Ganymede's and Jupiter's magnetospheres may produce dazzling variations in the auroral glows in Ganymede's tenuous atmosphere of oxygen. Cassini is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini mission for NASA's Office of Space Science, Washington, D.C.

Hotspots on Io During the Ganymede 2 Encounter

Hotspots on Io During the Ga …

PIA00836

Jupiter

Near Infrared Mapping Spectr …

Title	Hotspots on Io During the Ganymede 2 Encounter
Original Caption Released with Image	The Near Infrared Mapping Spectrometer (NIMS) on the Galileo spacecraft imaged Io at high spectral resolution at a range of 439,000 km (275,000 miles) during the G2 encounter on 6 September 1996. This image shows, on the right, Io as seen by NIMS, centered on 150 W longitude. The image on the left shows the same view point from Voyager data (from the encounters in 1979 and 1980). The NIMS image can be compared to the NIMS hotspot image from the G1 orbit (June 1996) to monitor changes on Io. The most dramatic feature of the G2 image is the hotspot at Malik Patera. Preliminary analysis of the data yields a temperature of at least 1000 K (727 C) for this hotspot, an increase of more than 300 K from the G1 encounter. In the overlap area of the G1 and G2 images all the hotspots seen during the G1 encounter are also seen in the G2 image. Other hotspots were seen, including one at the Pele plume origin site. This image is at the 4 micron band to best view the Malik hotspot. Most of the other hotspots are best seen at longer wavelengths. NIMS is continuing to observe Io to monitor volcanic activity throughout the Galileo mission. 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.

Lumps Within Ganymede

PIA05077

Jupiter

Solid-State Imaging

Title	Lumps Within Ganymede
Original Caption Released with Image	Scientists have discovered irregular lumps beneath the icy surface of Jupiter?s largest moon, Ganymede. These irregular masses may be rock formations, supported by Ganymede?s icy shell for billions of years. This mosaic of Jupiter?s moon Ganymede consists of more than 100 images acquired with NASA?s Voyager and Galileo spacecrafts. The gravity anomalies or lumps inferred from the Galileo radio Doppler data are shown in red. The mosaic shows the surface of Ganymede with its geographic coordinate system and the Galileo gravity results superimposed. The trajectory path of Galileo?s second Ganymede flyby on September 6, 1996, is shown in green. There are no obvious geologic features associated with the anomalies. For images and information about the Galileo mission, visit http://www.jpl.nasa.gov [ http://www.jpl.nasa.gov ].

Ganymede Mosaic

PIA00081

Jupiter

Imaging Science Subsystem - …

Title	Ganymede Mosaic
Original Caption Released with Image	The hemisphere of Ganymede that faces away from the Sun displays a great variety of terrain. In this Voyager 2 mosaic, photographed at a range of 300,000 kilometers, the ancient dark area of Regio Galileo lies at the upper left. Below it, the ray system is probably caused by water-ice, splashed out in a relatively recent impact.

Ganymede - Galileo Mosaic Overlayed on Voyager Data in Uruk Sulcus Region

Ganymede - Galileo Mosaic Ov …

PIA00281

Jupiter

Solid-State Imaging

Title	Ganymede - Galileo Mosaic Overlayed on Voyager Data in Uruk Sulcus Region
Original Caption Released with Image	A mosaic of four Galileo high-resolution images of the Uruk Sulcus region of Jupiter's moon Ganymede is shown within the context of an image of the region taken by Voyager 2 in 1979. The image shows details of parallel ridges and troughs that are the principal features in the brighter regions of Ganymede. The Galileo frames unveil the fine-scale topography of Ganymede's ice-rich surface, permitting scientists to develop a detailed understanding of the processes that have shaped Ganymede. Resolution of the Galileo images is 74 meters (243 feet) per pixel, while resolution of the Voyager image is 1.3 kilometers (0.8 mile) per pixel. In this view, north is to the top, and the sun illuminates the surface from the lower left nearly overhead. The area shown, at latitude 10 degrees north, longitude 168 degrees west, is about 120 by 110 kilometers (75 by 68 miles) in extent. The image was taken June 27 at a range of 7,448 kilometers (4,628 miles). The Jet Propulsion Laboratory manages the Galileo mission for NASA's Office of Space Science.

Ganymede - Comparison of Voyager and Galileo Resolution

Ganymede - Comparison of Voy …

PIA00277

Jupiter

Solid-State Imaging

Title	Ganymede - Comparison of Voyager and Galileo Resolution
Original Caption Released with Image	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.

Ganymede - Ridges, Grooves, Craters and Smooth Areas of Uruk Sulcus Region

Ganymede - Ridges, Grooves, …

PIA00276

Jupiter

Solid-State Imaging

Title	Ganymede - Ridges, Grooves, Craters and Smooth Areas of Uruk Sulcus Region
Original Caption Released with Image	Ridges, grooves, craters and relatively smooth areas in the Uruk Sulcus region of Jupiter's moon Ganymede are shown in this high-resolution image captured by NASA's Galileo spacecraft during its first flyby of Ganymede on June 27, 1996. This image was taken when Galileo was 7,448 kilometers (4.628 miles) away from Ganymede, north is to the top of the picture, and sunlight illuminates the surface from the lower left nearly overhead (77 degrees above the horizon). The area shown, at latitude 10 degrees north, longitude 168 degrees west, is about 55 by 35 kilometers (34 by 25 miles), the smallest features that can be discerned are 74 meters (243 feet). The line-like features are sunlit ridges, often arranged in parallel sets. The patterns of ridges and grooves indicate that extension (pulling apart) and shear (horizontal sliding) have both shaped the icy landscape. The Jet Propulsion Laboratory manages the Galileo mission for NASA's Office of Space Science.

Optical Navigation Image of …

PIA00273

Jupiter

Solid-State Imaging

Title	Optical Navigation Image of Ganymede
Original Caption Released with Image	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.

Ganymede - Dark Terrain in Galileo Regio

Ganymede - Dark Terrain in G …

PIA00278

Jupiter

Solid-State Imaging

Title	Ganymede - Dark Terrain in Galileo Regio
Original Caption Released with Image	This view of a part of the Galileo Regio region on Jupiter's moon Ganymede shows fine details of the dark terrain that makes up about half of the surface of the planet-sized moon. One of many ancient impact craters in the region is visible at the middle left. The crater is cut by numerous fractures, showing that the ancient crust was highly deformed early in Ganymede's history. Dark areas may have originated from dark material thrown off by dark meteorites hitting the surface in thousands of impact events. In this view, north is to the top and the sun illuminates the surface from the lower left about 58 degrees above the horizon. The area shown, at latitude 19 degrees north, longitude 149 degrees west, is about 19 by 26 kilometers (12 by 16 miles), resolution is about 80 meters (262 feet) per pixel. The image was taken June 27 at a range of 7.652 kilometers (4,755 miles). The Jet Propulsion Laboratory manages the Galileo mission for NASA's Office of Space Science.

Ganymede - Mixture of Terrains and Large Impact Crater in Uruk Sulcus Region

Ganymede - Mixture of Terrai …

PIA00280

Jupiter

Solid-State Imaging

Title	Ganymede - Mixture of Terrains and Large Impact Crater in Uruk Sulcus Region
Original Caption Released with Image	A mixture of terrains studded with a large impact crater is shown in this view of the Uruk Sulcus region of Jupiter's moon Ganymede taken by NASA's Galileo spacecraft during its first flyby of the planet-sized moon on June 27, 1996. The image shows fine details of bright areas that make up about half of the surface of Ganymede. Pock-marked, ancient, heavily cratered terrain is seen at the top, it is cut by younger, line-like structures in the lower left of the image. The bright, circular feature in the lower middle is an impact crater with some dark ejecta superimposed on the linear ridges. These types of relationships revealed by Galileo allow scientists to work out the complex geologic history of Ganymede. In this view, north is to the top and the sun illuminates the surface from the lower left nearly overhead. The area shown, at latitude 10 degrees north, longitude 168 degrees west, is about 59 by 40 kilometers (36 by 25 miles), and the resolution is 74 meters (80 yards) per picture element. The image was taken on June 27 at a range of 7,448 kilometers (4.628 miles). The Jet Propulsion Laboratory manages the Galileo mission for NASA's Office of Space Science.

Ganymede - Ancient Impact Craters in Galileo Regio

Ganymede - Ancient Impact Cr …

PIA00279

Jupiter

Solid-State Imaging

Title	Ganymede - Ancient Impact Craters in Galileo Regio
Original Caption Released with Image	Ancient impact craters shown in this image of Jupiter's moon Ganymede taken by NASA's Galileo spacecraft testify to the great age of the terrain, dating back several billion years. At the margin at the left, half of a 19-kilometer-diameter (12-mile) crater is visible. The dark and bright lines running from lower right to upper left and from top to bottom are deep furrows in the ancient crust of dirty water ice. The origin of the dark material is unknown, but it may be accumulated dark fragments from many meteorites that hit Ganymede. In this view, north is to the top, and the sun illuminates the surface from the lower left about 58 degrees above the horizon. The area shown is part of Ganymede's Galileo Regio region at latitude 18 degrees north, longitude 147 degrees west, it is about 46 by 64 kilometers (29 by 38 miles) in extent. Resolution is about 80 meters (262 feet) per pixel. The image was taken June 27 at a range of 7.563 kilometers (4,700 miles). The Jet Propulsion Laboratory manages the Galileo mission for NASA's Office of Space Science.

Secondary Craters on Ganymed …

PIA01061

Jupiter

Solid-State Imaging

Title	Secondary Craters on Ganymede
Original Caption Released with Image	Two large, ancient impact craters, known as palimpsests, have modified this area of dark terrain on Jupiter's moon Ganymede. In lower resolution images from the Voyager mission in 1979, it was observed that the diffuse edge of a large, circular bright feature cut through this area. This image was obtained by the Solid State Imaging (CCD) system aboard NASA's Galileo spacecraft, on September 6, 1996, at a higher resolution of 190 meters (623 feet) per picture element (pixel). North is to the top. The diffuse margin of this palimpsest is noticeable only as a gradual increase in the area covered by bright hummocks toward the western edge of the image. A more recent palimpsest-forming impact to the south has peppered this area with chains and clusters of secondary craters ranging from 5.7 to 1.2 kilometers (3.5 to 0.7 miles) in diameter. The image covers an area of 73 by 65 kilometers (45 by 40 miles). 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

Grooves and Craters on Ganym …

PIA01059

Jupiter

Solid-State Imaging

Title	Grooves and Craters on Ganymede
Original Caption Released with Image	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

Palimpsest secondary craters on Ganymede

Palimpsest secondary craters …

PIA01060

Jupiter

Solid-State Imaging

Title	Palimpsest secondary craters on Ganymede
Original Caption Released with Image	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

Ganymede Groove Lanes

PIA01056

Jupiter

Solid-State Imaging

Title	Ganymede Groove Lanes
Original Caption Released with Image	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

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