Voyager Images of Ganymede
On June 27, 1996, the Galileo spacecraft will makes its first flyby of Ganymede at a distance of only 844 km. This is over 70 times closer than the Voyager encounters.
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The bright spot near the center of the picture is five times brighter than the Moon, and may contain more than surrounding areas. The bright pattern around the spot reminds scientists of ray craters on the Moon and Mercury, and the area may in fact be an impact crater that has exposed fresh, underlying ice.
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Spacecraft: Voyager 1
Date: March 1, 1979
Distance from Ganymede: 2.6 million miles (4.2 million km)
Photo Number: P-21180
This photo shows dark features reminiscent of the dark, mare regions on the Moon. On Ganymede, however, these features have twice the brightness of lunar mare. Ganymede's north polar region appears to be covered with brighter material, and scientists say it could be water frost. Brighter spots are also scattered across this hemisphere of Ganymede.
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Spacecraft: Voyager 1
Date: March 2, 1979
Distance from Ganymede: 2.1 million miles (3.4 million km)
Photo Number: P-21186C
The surface shows light and dark markings interspersed with bright spots. The large darkish area near the center of the satellite is crossed by irregular light streaks somewhat similar to rays seen on the Moon. The bright patch in the southern hemisphere is reminiscent of some of the larger rayed craters on the Moon caused by meteorite impacts.
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Spacecraft: Voyager 1
Date: March 4, 1979
Distance from Ganymede: 1.6 million miles (2.6 million km)
Photo Number: P-21207C
The features here, the large dark regions, in the northeast quadrant, and the white spots, resemble features found on the Moon, mare and impact craters respectively. The long white filaments resemble rays associated with impacts on the lunar surface. The various colors of different regions probably represent differing surface materials.
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Spacecraft: Voyager 1
Date: March 5, 1979
Distance from Ganymede: 150,000 miles (250,000 km)
Photo Number: P-21235
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.
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Spacecraft: Voyager 1
Date: March 5, 1979
Distance from Ganymede: 150,000 miles (250,000 km)
Photo Number: P-21261C
This image shows detail on the surface with a resolution of four and a half km. It shows a variety of impact structures, including both razed and unrazed craters, and the odd, groove-like structures discovered by Voyager in the lighter regions. 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.
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Spacecraft: Voyager 1
Date: March 5, 1979
Distance from Ganymede: 150,000 miles (250,000 km)
Photo Number: P-21262C
This image shows detail on the surface with a resolution of four and a half km. It shows a variety of impact structures, including both razed and unrazed craters, and the odd, groove-like structures discovered by Voyager in the lighter regions. 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, which has rays at least 300-500 kilometers long, down to craters which have only faint remnants of bright ejects patterns. This variation suggests that, as on the Moon, there are processes which act to darken ray material, probably "gardening" by micrometeoroid impact.
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This image is near the equater of Ganymede has relatively subdued colors in the visible part of the spectrum (later, scientists will analyze Voyager pictures taken in UV). The most striking features are the bright ray craters which have a distinctly "bluer" color appearing white against the redder background.
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Spacecraft: Voyager 1
Date: March 5, 1979
Distance from Ganymede: 160,000 miles (272,000 km)
Photo Number: P-21264
The center of the picture lies at 13 latitude, 359 longitude. Many bright impact craters are shown that have radial ejecta patterns. These rays lie across and therefore are younger than the bright and dark background material. Many older impact craters are shown that have lost their rays probably by impact erosion. The bright background areas contain grooves and ridges that may be caused by faulting of the surface materials.
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Spacecraft: Voyager 1
Date: March 5, 1979
Distance from Ganymede: 152,000 miles (253,000 km)
Photo Number: P-21265
The picture is centered at 66 south latitude and 3 longitude and shows the south western limb region of Ganymede. The smallest features visible are about 2.5 kilometers (1.5 miles) across. The surface shows numerous impact craters, many of which have extensive bright ray systems. Light bands traversing the surface contain alternating bright and dark lines which probably represent deformation of the icy central material.
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Spacecraft: Voyager 1
Date: March 5, 1979
Distance from Ganymede: 158,000 miles (246,000 km)
Photo Number: P-21266
The center of the picture is at 19 south latitude and 356 longitude, and the height of the frame represents a distance of about 1000 km (600 mi) on the surface. The smallest features seen on this picture are about 2.5 km (1.5 mi) across. The surface displays numerous impact craters many of which have extensive bright ray systems. The craters lacking ray systems are probably older than those showing rays. Bright bands traverse the surface in various directions and these bright bands contain an intricate system of alternating linear bright and dark lines which may represent deformation of the crusted ice layer. These lineations are particularly evident near the top of the picture. A bright band trending in a north-south direction in the lower left-hand portion of the picture is offset along a bright line. This offset is probably due to faulting. Two light circular areas in the right upper center of the picture may be the scars of ancient impact craters which have had their topographic expansion erased by flowage of the crystal icy material.
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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.
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Spacecraft: Voyager 1
Date: March 1979
Distance from Ganymede: Not Available
Photo Number: P-21280
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Spacecraft: Voyager 2
Date: July 2, 1979
Distance from Ganymede: 4 million miles (6 million km)
Photo Number: P-21749C
This picture illustrates well the light, bluish regions near the north and sourh poles. It is known that these polar caps are composed of a light covering of water ice or frost.
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Spacecraft: Voyager 2
Date: July 7, 1979
Distance from Ganymede: 800,000 miles (1.2 million km)
Photo Number: P-21751C
The photo shows a large dark circular feature about 3200 kilometers in diameter with narrow closely-spaced light bands traversing its surface. The bright spots dotting the surface are relatively recent impact craters, while lighter circular areas may be older impact areas. The light branching bands are ridged and grooved terrain first seen on Voyager 1 and are younger than the more heavily cratered dark regions. The nature of the brightish region covering the northern part of the dark circular feature is uncertain, but it may be some type of condensate. Most of the features seen on the surface of Ganymede are probably both internal and external responses of the very thick icy layer which comprises the crust of this satellite.
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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.
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Spacecraft: Voyager 2
Date: July 8, 1979
Distance from Ganymede:
Photo Number: P-21755
These images show different views of the largest block of dark, heavily cratered terrain seen on the giant moon. The bottom image shows objects three to four miles across; has a resolution of about 1.5 miles. The light, linear stripes recurring across the dark region resemble the outer rings of the large ring structure on Callisto. If these features are in fact related to an ancient ring structure formed by a large impact, their small curvature suggests that the original structure was even larger than one seen on Callisto. There is no apparent trace now of the center of this suggested structure, which must have been destroyed by the resurfacing evident over most of Ganymede in the grooved terrain. Another interpretation is that these features are not impact-related rings but are internally produced fractures crossing the dark terrain, similar to the grooved bands.
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Spacecraft: Voyager 2
Date: July 1979
Distance from Ganymede: 194,000 miles (313,000 km)
Photo Number: P-21761C
This scene is approximately 1,300 kilometers (806 miles) across. It shows part of dark, densely cratered block which is bound on the south by lighter, and less cratered, grooved terrain. The dark blocks are believed to be the oldest parts of Ganymede's surface. Numerous craters are visible, many with central peaks. The large bright circular features have little relief and are probably the remnants of old, large craters that have been annealed by flow of the icy near-surface material. The closely-spaced arcuate, linear features are probably analogous to similar features on Ganymede which surround a large impact basin. The linear features here may indicate the former presence of a large impact basin to the southwest.
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Spacecraft: Voyager 2
Date: July 1979
Distance from Ganymede: Not Available
Photo Number: P-21762
This 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.
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This 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.
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Spacecraft: Voyager 2
Date: July 1979
Distance from Ganymede: 195,000 miles (312,000 km)
Photo Number: P-21769
This image shows features down to about 5 to 6 kilometers across. Clear examples of several of the different types of terrasin common on Ganymede's surface are visible (right). The boundary of the largest region of dark ancient terrain on Ganymede can be seen to the east (right), revealing some of the light linear features which may be all that remains of a large ancient impact structure similar to the large ring structure on Callisto. The broad light regions running through the image are the typical grooved structures seen within most of the light regions on Ganymede. To the lower left is another example of what might be evidence of large scale lateral motion in Ganymede's crust. The band of grooved terrain (about 100 kilometers wide) in this region appears to be offset by 50 kilometers or more on the left hand edge by a linear feature perpendicular to it. A feature similar to this one was previously discovered by Voyager 1. These are the first clear examples of strike-slip style faulting on any planet other than Earth. Many examples of craters of all ages can be seen in this image, ranging from fresh, bright ray craters to large, subdued circular markings thought to be the "scars" of large ancient impacts that have been flattened by glacier-like flows.
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Spacecraft: Voyager 2
Date: July 9, 1979
Distance from Ganymede: 62,000 miles (100,000 km)
Photo Number: P-21770
This image shows numerous impact craters, many with bright ray systems. The rough mountainous terrain at lower right is the outer portion of a large fresh impact basin which post-dates most of the other terrain. At bottom, portions of grooved terrain transect other portions indicating they are younger. This may be the result of the intrusion of new icy material which comprises the crust of Ganymede. The dark patches of heavily cratered terrain (right center) are probably ancient icy material formed prior to the grooved terrain. The large rayed crater at upper center is about 150 kilometers (93 miles) in diameter.
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Spacecraft: Voyager 2
Date: July 8, 1979
Distance from Ganymede: 53,000 miles (85,000 km)
Photo Number: P-21771
Ancient cratered terrain on Jupiter's giant satellite Ganymede is portrayed. A large variety of impact craters of different ages are shown. The brightest craters are the youngest. The ejecta blankets fade with age. Shown in the center is a bright patch that represents the rebounding of the floor of the crater. The dirty ice has lost all topography except for faint circular patterns. Also shown are the "Callisto type" curved troughs and ridges that mark an ancient enormous impact basin. The basin itself has been destroyed by later geologic processes. Only the ring features are preserved on the ancient surface. Near the bottom of the picture, these curved features are truncated by the younger grooved terrain.
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This image clearly shows the large dark area Regio Galileo, was well as much of the lighter grooved terrain discovered by Voyager 1. The bright spots are impact craters. This image also shows what appears to be polar caps, extending down to about latitude 45 degrees in both the norther and southern hemispheres.
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Spacecraft: Voyager 2
Date: July 1979
Distance from Ganymede: Not Available
Photo Number: 260-671
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Spacecraft: Voyager
Date: July 1979
Distance from Ganymede: Not Available
Photo Number: 260-750B
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Spacecraft: Voyager
Date: July 1979
Distance from Ganymede: Not Available
Photo Number: 260-678A
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This image clearly shows the large dark area Regio Galileo, was well as much of the lighter grooved terrain discovered by Voyager 1. The bright spots are impact craters. This image also shows what appears to be polar caps, extending down to about latitude 45 degrees in both the norther and southern hemispheres.
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Spacecraft: Voyager 2
Date: July 9, 1979
Distance from Ganymede: Not Available
Photo Number: 260-637
Surface features as small as 1 km are visible in this mosaic of Voyager 2 images. The grooves seen in the images are basically long, parallel mountain ridges, 10 to 15 km from crest to crest - about the same scale as the Appalachian mountains in the Eastern United States. The numerous impact craters superposed on the mountain ridges indicates that they are old - probably formed several billion years ago.
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