Galerie de photos de Callisto, satellite galiléen de la planète Jupiter

<h1>PIA01510: Callisto From 8,023,000 kilometers</h1><div class="PIA01510" lang="en" style="width:300px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">This photo of Callisto, outermost of Jupiter's four Galilean satellites, was taken a few minutes after midnight (PST) Feb. 26 by Voyager 1. The distance to Callisto was 8,023,000 kilometers (4.98 million miles). The hemisphere in this picture shows a fairly uniform surface dotted with brighter spots that are up to several hundred kilometers across. Scientists believe the spots may be impact craters but higher-resolution photos will be necessary before the features can be interpreted. Callisto is about the same size as the planet Mercury -- about 5,000 kilometers (3,000 miles) in diameter. Callisto is much less massive than Mercury, however, giving density less than twice that of water. Scientists believe Callisto, therefore, is composed of a mixture of rock and ice (up to about 50 percent by weight). Its surface is darker than those of the other Galilean satellites, but is still about twice as bright as Earth's Moon. This color photo was assembled from three black and white images in the Image Processing Lab at Jet Propulsion Laboratory. JPL manages and controls the Voyager project for NASA's Office of Space Science.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01510" onclick="window.open(this.href); return false;" title="Voir l'image PIA01510: Callisto From 8,023,000 kilometers sur le site de la NASA">Voir l'image PIA01510: Callisto From 8,023,000 kilometers sur le site de la NASA.</a></div>
PIA01510: Callisto From 8,023,000 kilometers
<h1>PIA01511: Callisto From 7,000,000 kilometers</h1><div class="PIA01511" lang="en" style="width:300px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">This Voyager 1 picture of Callisto, the outermost Galilean satellite, was taken February 28 from a distance of about 5 million miles (7 million kilometers). Callisto is the darkest of the Galilean satellites but is still nearly twice as bright as the Earth's Moon. The surface shows a mottled appearance consisting of bright and dark patches. The bright spots remind scientists of rayed or bright haloed craters, similar to those seen on the Earth's Moon. The Galilean satellites all show the same face to Jupiter -- just as the Earth's Moon always shows us the same face. In this photo we see the face of Callisto that always faces Jupiter. JPL manages and controls the Voyager Project for NASA's Office of Space Science.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01511" onclick="window.open(this.href); return false;" title="Voir l'image PIA01511: Callisto From 7,000,000 kilometers sur le site de la NASA">Voir l'image PIA01511: Callisto From 7,000,000 kilometers sur le site de la NASA.</a></div>
PIA01511: Callisto From 7,000,000 kilometers
<h1>PIA01629: Textured Terrain in Callisto's Asgard Basin</h1><div class="PIA01629" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>This fascinating region of Jupiter's icy moon, Callisto, shows the transition from the inner part of an enormous impact basin, Asgard, to the outer "surrounding plains." Small, bright, fine textured, closely spaced bumps appear throughout the inner part of the basin (top of image) and create a more fine textured appearance than that seen on many of the other inter-crater plains on Callisto. At low resolution, these icy bumps make Asgard's center brighter than the surrounding terrain. What caused the bumps to form is still unknown, but they are associated clearly with the impact that formed Asgard.</p><p>The ridge that cuts diagonally across the lower left corner is one of many giant concentric rings that extend for hundreds of kilometers outside Asgard's center. Exterior to the ring (lower left corner), Callisto's surface changes significantly. Still peppered with craters, the number of icy bumps decreases while their average size increases. The fine texture is not as visible in the middle of the image. One explanation is that material from raised features (such as the ridge) may slide down slope and cover small scale features. Such images of Callisto help us understand the dynamics of giant impacts into icy surfaces, and how the large structures change with time.</p><p>North is to the top of the picture. The image, centered at 27.1 degrees north latitude and 142.3 degrees west longitude, covers an area approximately 80 kilometers (50 miles) by 90 kilometers (55 miles). The resolution is about 90 meters (295 feet) per picture element. The image was taken on September 17th, 1997 at a range of 9200 kilometers (5700 miles) by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft during its tenth orbit of Jupiter.</p><p>The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.</p><p>This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL <a href="http://solarsystem.nasa.gov/galileo/" target="_blank">http://solarsystem.nasa.gov/galileo/</a>. Background information and educational context for the images can be found at URL <a href="http://www2.jpl.nasa.gov/galileo/sepo/" target="_blank">http://www.jpl.nasa.gov/galileo/sepo</a><br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01629" onclick="window.open(this.href); return false;" title="Voir l'image PIA01629: Textured Terrain in Callisto's Asgard Basin sur le site de la NASA">Voir l'image PIA01629: Textured Terrain in Callisto's Asgard Basin sur le site de la NASA.</a></div>
PIA01629: Textured Terrain in Callisto's Asgard Basin
<h1>PIA01630: Callisto: Pits or Craters?</h1><div class="PIA01630" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>This image of Jupiter's second largest moon, Callisto, presents one of the mysteries discovered by NASA's Galileo spacecraft. In the upper left corner of the image, what appear to be very small craters are visible (See enlargement.) on the floors of some larger craters as well as in the area immediately adjacent to the larger craters. Some these smaller craters are not entirely circular. They are very similar to a population of unclassified "pits" seen in <a href="/catalog/PIA00745">one Callisto mosaic</a> from Galileo's ninth orbit. One possible explanation for the pits is that they represent a class of previously unseen endogenic (formed by some surface or subsurface process, rather than an impact) features. Another explanation is that they are partially eroded secondary craters. Secondary craters are formed when an initial large impact ejects large enough pieces of the surface that the pieces themselves create small craters. By studying the orientation of the pits and clusters of small craters relative to larger impacts, as well as carefully examining the physical appearance of the two groups, scientists hope to discover the origin of the pits, and the possible relationship they may have with small craters.</p><p>North is to the top of the picture, and the sun illuminates the surface from the right. The full image, centered at 20.5 degrees north latitude and 142.2 degrees west longitude, covers an area approximately 72 kilometers (45 miles) by 55 kilometers (34) miles. The resolution is about 90 meters (295 feet) per picture element. The image was taken on September 17th, 1997 at a range of 8800 kilometers (5460 miles) by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft during its tenth orbit of Jupiter.</p><p>The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.</p><p>This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL <a href="http://solarsystem.nasa.gov/galileo/" target="_blank">http://solarsystem.nasa.gov/galileo/</a>. Background information and educational context for the images can be found at URL <a href="http://www2.jpl.nasa.gov/galileo/sepo/" target="_blank">http://www.jpl.nasa.gov/galileo/sepo</a>."><a href="http://www2.jpl.nasa.gov/galileo/sepo/" target="_blank">http://www.jpl.nasa.gov/galileo/sepo</a>.</a></p><br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01630" onclick="window.open(this.href); return false;" title="Voir l'image PIA01630: Callisto: Pits or Craters? sur le site de la NASA">Voir l'image PIA01630: Callisto: Pits or Craters? sur le site de la NASA.</a></div>
PIA01630: Callisto: Pits or Craters?
<h1>PIA01631: So few Small Craters on Callisto</h1><div class="PIA01631" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>This moderately high resolution view of Jupiter's icy moon, Callisto, shows two, probably related, phenomena that were quite surprising to planetary scientists. First, a dark, mobile blanket of material covers Callisto's surface. Movement of this material occurs on slopes, as seen here on some crater walls. Second, while Callisto has a significant number of large craters, it lacks the related number of small craters which are seen in the crater size distributions of other similar bodies in our solar system. Small craters near slopes would become filled in by the downward movement of the dark material, but what erases the other small craters? One alternative is that the population of potential impactors around Jupiter has fewer small objects than previously expected.</p><p>North is to the top of the picture. The image, centered at 17.5 degrees north latitude and 142.1 degrees west longitude, covers an area approximately 74 kilometers (46 miles) by 75 kilometers (47 miles). The resolution is about 87 meters (285 feet) per picture element. The image was taken on September 17th, 1997 at a range of 8600 kilometers (5330 miles) by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft during its tenth orbit of Jupiter.</p><p>The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL <a href="http://solarsystem.nasa.gov/galileo/" target="_blank">http://solarsystem.nasa.gov/galileo/</a>. Background information and educational context for the images can be found at URL <a href="http://www2.jpl.nasa.gov/galileo/sepo/" target="_blank">http://www.jpl.nasa.gov/galileo/sepo</a>."><a href="http://www2.jpl.nasa.gov/galileo/sepo/" target="_blank">http://www.jpl.nasa.gov/galileo/sepo</a>.</a></p><br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01631" onclick="window.open(this.href); return false;" title="Voir l'image PIA01631: So few Small Craters on Callisto sur le site de la NASA">Voir l'image PIA01631: So few Small Craters on Callisto sur le site de la NASA.</a></div>
PIA01631: So few Small Craters on Callisto
<h1>PIA01632: Callisto's Varied Crater Landscape</h1><div class="PIA01632" lang="en" style="width:720px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>This portion of the surface of Callisto, Jupiter's second largest moon, contains an immensely varied crater landscape. A large, degraded crater dominates the southern (bottom) portion of the image. There are fresh to highly degraded craters at all sizes, but a relatively low number of small, fresh craters. A diagonal "trench" cuts across a crater rim in the north (top) of the image. Several clusters of small craters appear throughout the image. Images revealing the appearance and numbers of craters, help establish which erosional processes take place on a planet's surface, and help determine a relative age for the surface.</p><p>North is to the top of the picture. The image, centered at 13.4 degrees north latitude and 141.8 degrees west longitude, covers an area approximately 61 kilometers (38 miles) by 60 kilometers (37 miles). The resolution is about 85 meters (280 feet) per picture element. The horizontal black lines indicate gaps in the data received for this image. The image was taken on September 17th, 1997 at a range of 8400 kilometers (5200 miles) by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft during its tenth orbit of Jupiter.</p><p>The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.</p><p>This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL <a href="http://solarsystem.nasa.gov/galileo/" target="_blank">http://solarsystem.nasa.gov/galileo/</a>. Background information and educational context for the images can be found at URL <a href="http://www2.jpl.nasa.gov/galileo/sepo/" target="_blank">http://www.jpl.nasa.gov/galileo/sepo</a>."><a href="http://www2.jpl.nasa.gov/galileo/sepo/" target="_blank">http://www.jpl.nasa.gov/galileo/sepo</a>.</a></p><br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01632" onclick="window.open(this.href); return false;" title="Voir l'image PIA01632: Callisto's Varied Crater Landscape sur le site de la NASA">Voir l'image PIA01632: Callisto's Varied Crater Landscape sur le site de la NASA.</a></div>
PIA01632: Callisto's Varied Crater Landscape
<h1>PIA01634: Asgard Multi-Ring Structure on Callisto</h1><div class="PIA01634" lang="en" style="width:594px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>This mosaic shows the Asgard multi-ring structure on Callisto, Jupiter's second largest icy moon. The <a href="/catalog/PIA00517">Asgard structure</a>, centered near 30 degrees north latitude, 142 degrees west longitude, is approximately 1700 km across (1,056 miles) and consists of a bright central zone surrounded by discontinuous rings. The rings are fractures that formed when Callisto's surface was struck by a large comet or asteroid. Previous analysis of Asgard identified three major zones: 1) interior bright plains in the center, 2) a zone of inward facing cliffs and, 3) a zone of discontinuous concentric troughs. The mosaic combines high resolution data of 88 meters per picture element (pixel) taken on the tenth orbit of the Galileo spacecraft around Jupiter in September 1997, with low resolution data of 1.1 kilometers (km) per pixel obtained on the third orbit in November 1996. The improved resolution of images obtained by the Solid State Imaging (SSI) system on board NASA's Galileo spacecraft allows for new insights into the Asgard multi-ring system.</p><p>Galileo images show that the bright central plains includes a young dome crater, named Doh, located on its southwestern margin (at the top of the high resolution strip). Doh is about 50 km (30 miles) in diameter. Dome craters contain a central mound instead of a bowl shaped depression or the central mountain typically seen in craters. The inner rings of Asgard appear to be degraded ridges in the high resolution data, rather than inward-facing cliffs or scarps as previously interpreted from lower resolution images. In the outermost rings, dark non-ice material that slid down the walls of the troughs has made their floors darker than the surrounding cratered plains.</p><p>North is to the top of the picture. The high resolution images were obtained with the clear filter of the Solid State Imaging (SSI) system when NASA's Galileo spacecraft was less than 9,500 kilometers from Callisto. There appears to be a diffuse darker stripe, beginning near the middle and continuing down the strip of higher resolution frames. This darkening is due to the processing used to place the higher resolution frames into the background context.</p><p>The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission or NASA's Office of Space Science, Washington, DC.</p><p>This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL <a href="http://galileo.jpl.nasa.gov"> http://galileo.jpl.nasa.gov</a>. Background information and educational context for the images can be found at <a href="http://www2.jpl.nasa.gov/galileo/sepo/" target="_blank">http://www.jpl.nasa.gov/galileo/sepo</a>.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01634" onclick="window.open(this.href); return false;" title="Voir l'image PIA01634: Asgard Multi-Ring Structure on Callisto sur le site de la NASA">Voir l'image PIA01634: Asgard Multi-Ring Structure on Callisto sur le site de la NASA.</a></div>
PIA01634: Asgard Multi-Ring Structure on Callisto
<h1>PIA01648: Impact Craters on Icy Callisto: Doh crater and Asgard</h1><div class="PIA01648" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>This composite of Jupiter's icy moon Callisto combines data from two orbits showing several types of impact craters. North is to the top of the picture; the sun illuminates the surface from the east. The global image on the right shows one of the largest impact structures on Callisto, the Asgard multi-ring structure located near 30 degrees north latitude, 142 degrees west longitude. The Asgard structure is approximately 1700 kilometers (1,054 miles) across and consists of a bright central zone surrounded by discontinuous rings. The rings include degraded ridges near the central zone and troughs at the outer margin, which resulted from deformation of the icy crust following impact.</p><p>Smaller impacts have smashed into Callisto after the formation of Asgard. The young, bright-rayed crater Burr located on the northern part of Asgardis about 75 kilometers (46 miles) across. Galileo images show a third type of impact crater in this image, a dome crater named Doh, located in the bright central plains of Asgard. Doh (left image) is about 55 kilometers (34 miles) in diameter, while the dome is about 25 kilometers (15 miles) across. Dome craters contain a central mound instead of a bowl shaped depression or central mountain (peak) typically seen in larger impact craters. This type of crater could represent penetration into a slushy zone beneath the surface of the Asgard impact.</p><p>The global image on the right was taken on November 4, 1996, at a distance of 111,900 kilometers (69,400 miles) by the solid state imaging (SSI) camera onboard NASA's Galileo spacecraft during its third orbit around Jupiter. The image on the left was obtained at a resolution of 90 meters (295 feet) per picture element on September 16, 1997 during Galileo's tenth orbit when the spacecraft was less than 9,500 kilometers (6,000 miles) from Callisto.</p><p>The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.</p><p>This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL<a href="http://solarsystem.nasa.gov/galileo/" target="_blank">http://solarsystem.nasa.gov/galileo/</a>. Background information and educational context for the images can be found at <a href="http://www2.jpl.nasa.gov/galileo/sepo/" target="_blank">http://www.jpl.nasa.gov/galileo/sepo</a>.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01648" onclick="window.open(this.href); return false;" title="Voir l'image PIA01648: Impact Craters on Icy Callisto: Doh crater and Asgard sur le site de la NASA">Voir l'image PIA01648: Impact Craters on Icy Callisto: Doh crater and Asgard sur le site de la NASA.</a></div>
PIA01648: Impact Craters on Icy Callisto: Doh crater and Asgard
<h1>PIA01649: The Valhalla Multi-ring Structure on Callisto</h1><div class="PIA01649" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>These images of Callisto, the outermost of the Galilean satellites of Jupiter, reveal a surface characterized by impact craters. The global view (lower left) is dominated by a large bulls-eye feature, the Valhalla multi-ring structure, consisting of a bright inner region about 600 kilometers (370 miles) across. Valhalla's 4,000 kilometer(2,500 mile) diameter make it one of the largest impact features in the solar system. Callisto is 4,800 kilometers (3,000 miles) in diameter. In this global view, the sun illuminates the surface from near the center, in the same way a full moon is seen from Earth when illuminated by the sun.</p><p>The image on the right shows part of Valhalla at moderate resolution. At this resolution, the surface is appears to be somewhat smooth, with a lack of numerous small impact craters. Valhalla's outer rings are clearly seen to consist of troughs which could be fractures in the crust which resulted from the impact. The bright central plains possibly were created by the excavation and ejection of "cleaner" ice or liquid water from beneath the surface, with a fluid-like massfilling the crater bowl after impact.</p><p>North is to the top of the picture. For the moderate resolution view on the right, the sun illuminates the surface from the left and the resolution is approximately 400 meters per picture element. The images were obtained on June 25, 1997 by the solid state imaging (SSI)system on NASA's Galileo spacecraft at a range of about 40,000 kilometers(25,000 miles) from Callisto during Galileo's ninth orbit of Jupiter. The global image on the left is centered at 0.5 degrees south latitude and 56 degrees longitude. The resolution is 14 kilometers per picture element. The images were obtained on November 5, 1997 at a range of 68,400 kilometers(42,400 miles) during Galileo's eleventh orbit of Jupiter.</p><p>The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.</p><p>This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL<a href="http://solarsystem.nasa.gov/galileo/" target="_blank">http://solarsystem.nasa.gov/galileo/</a>. Background information and educational context for the images can be found at URL<a href="http://www2.jpl.nasa.gov/galileo/sepo/" target="_blank">http://www.jpl.nasa.gov/galileo/sepo</a>."><a href="http://www2.jpl.nasa.gov/galileo/sepo/" target="_blank">http://www.jpl.nasa.gov/galileo/sepo</a>.</a></p><br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01649" onclick="window.open(this.href); return false;" title="Voir l'image PIA01649: The Valhalla Multi-ring Structure on Callisto sur le site de la NASA">Voir l'image PIA01649: The Valhalla Multi-ring Structure on Callisto sur le site de la NASA.</a></div>
PIA01649: The Valhalla Multi-ring Structure on Callisto
<h1>PIA01656: Europa, Ganymede, and Callisto: Surface comparison at high spatial resolution</h1><div class="PIA01656" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>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.</p><p>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.</p><p>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 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.</p><p>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.</p><p>The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.</p><p>This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL <a href="http://solarsystem.nasa.gov/galileo/" target="_blank">http://solarsystem.nasa.gov/galileo/</a>. Background information and educational context for the images can be found at URL <a href="http://www2.jpl.nasa.gov/galileo/sepo/" target="_blank">http://www.jpl.nasa.gov/galileo/sepo</a><br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01656" onclick="window.open(this.href); return false;" title="Voir l'image PIA01656: Europa, Ganymede, and Callisto: Surface comparison at high spatial resolution sur le site de la NASA">Voir l'image PIA01656: Europa, Ganymede, and Callisto: Surface comparison at high spatial resolution sur le site de la NASA.</a></div>
PIA01656: Europa, Ganymede, and Callisto: Surface comparison at high spatial resolution
<h1>PIA01657: Crater Tindr on Callisto - an oblique impact?</h1><div class="PIA01657" lang="en" style="width:449px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>This single-frame image shows crater Tindr on Jupiter's satellite Callisto, the moon with the oldest surface of the four so-called "Galilean" satellites (of which Callisto is also most distant from Jupiter). The diameter of this impact feature is about 70 km (43.5 miles). Tindris situated close to Callisto's equator at a longitude of about 5 degrees East. The image was obtained in September 1997 with the Solid State Imaging (SSI) system onboard NASA's Galileo spacecraft, which has been orbiting the Solar System's largest planet since December 1995.</p><p>Shadows are long and accentuate morphology on the surface, because the image was taken under low sun illumination. The image was captured from a distance of about 40,000 km (25,000 miles) during Galileo's 10th orbit around Jupiter. The resolution is about 390 m/pixel, the smallest features that are still discernible are about 780 m across. The sun illuminates the scene from the left. North is pointing towards the top of the image. The image covers an area approximately 150 x 150 km.</p><p>Tindr is slightly irregular in shape. This could be the consequence of an oblique impact. Along its eastern and southeastern part, the rim appears degraded; only isolated hills or hill chains are still visible. The floor shows numerous irregular pits, features that are found in some other Callistoan craters and also in Callisto's dark cratered plains. These features are believed to be caused by sublimation of subsurface volatiles. Subradial streaks outside the crater rim are due to impact debris creating secondary craters some distance away from Tindr. Continuous ejecta covers several older craters, especially in the northeastern part of the scene. The Tindr ejecta merge into surrounding cratered plains without a distinct morphologic or albedo boundary. Apparently the dark material blanketing Callisto's surface globally was emplaced after Tindr had formed.</p><p>Absolute ages derived from measured crater densities are model-dependent. In one crater chronology model, based on impacts dominated by asteroids, Tindr may be an old feature, about 3.9 billion years old, pointing back in time into a period of more intense bombardment than today. In another model, based on impacts preferentially by comets with a more or less constant impact rate, Tindr can be much younger, about 1 billion years old.</p><p>The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.</p><p>This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL <a href="http://solarsystem.nasa.gov/galileo/" target="_blank">http://solarsystem.nasa.gov/galileo/</a>. Background information and educational context for the images can be found at <a href="http://www2.jpl.nasa.gov/galileo/sepo/" target="_blank">http://www.jpl.nasa.gov/galileo/sepo</a>.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01657" onclick="window.open(this.href); return false;" title="Voir l'image PIA01657: Crater Tindr on Callisto - an oblique impact? sur le site de la NASA">Voir l'image PIA01657: Crater Tindr on Callisto - an oblique impact? sur le site de la NASA.</a></div>
PIA01657: Crater Tindr on Callisto - an oblique impact?
<h1>PIA02253: Callisto</h1><div class="PIA02253" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">This black and white image of Callisto was taken by Voyager 2 about 3:20 A.M PDT Saturday, July 7, from a range of about 1.1 million kilometers (675,000 miles). The picture has been enhanced to reveal detail in the scene. Voyager l's high resolution coverage was of the hemisphere just over the right-hand (eastern) horizon, and the large ring structure discovered by Voyager 1 is just over the eastern limb. This image shows yet another ring structure in the upper part of the picture. Callisto exhibits some of the most ancient terrain seen on any of the satellites. Scientists think Callisto's surface is a mixture of ice and rock dating back to the final stages of planetary accretion (over 4 billion years ago) when the surface was pockmarked by a torrential bombardment of meteorites. Younger craters show as bright spots, probably because they expose fresh ice and frost.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA02253" onclick="window.open(this.href); return false;" title="Voir l'image PIA02253: Callisto sur le site de la NASA">Voir l'image PIA02253: Callisto sur le site de la NASA.</a></div>
PIA02253: Callisto
<h1>PIA02277: Callisto basin</h1><div class="PIA02277" lang="en" style="width:797px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>This picture of a multi-ring basin on Callisto was taken the morning of March 6, 1979, from a distance of about 200,000 km. The complicated circular structure seen at left center is similar to the large circular impact basins that dominate the surface of the Earth's moon and also the planet Mercury. The inner parts of these basins are generally surrounded by radially lineated ejecta and several concentric mountainous ring structures that are thought to form during the impact event. This multi-ring basin on Callisto consists of light floored central basin some 300 km in diameter surrounded by at least eight to ten discontinuous rhythmically spaced ridges. No radially lineated ejecta can be seen. The ring structures on Moon and Mercury have been likened to ripples produced on a pond by a rock striking the water. The great number of rings observed around this basin on Callisto is consistent with its low planetary density and probable low internal strength. JPL manages and controls the Voyager project for NASA's Office of Space Science.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA02277" onclick="window.open(this.href); return false;" title="Voir l'image PIA02277: Callisto basin sur le site de la NASA">Voir l'image PIA02277: Callisto basin sur le site de la NASA.</a></div>
PIA02277: Callisto basin
<h1>PIA02593: Opposite Side of Callisto from Valhalla Impact</h1><div class="PIA02593" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>The heavily cratered portion of the surface of Jupiter's moon Callisto, seen in this image recorded by NASA's Galileo spacecraft, resembles most of Callisto that's been seen in high resolution. This adds evidence to a theory that Callisto may hold an underground ocean.<p>The area in the image is the opposite point, or antipode, of Callisto's Valhalla impact basin. The antipode of any point on a sphere is the opposite point on a line through the center of the sphere. Antipodes of major impact sites on some other worlds similar in size to Callisto, such as Mercury and Earth's moon, show a grooved and hilly terrain attributed to seismic shocks focusing on those points from the distant impacts. The antipode of <a href="/catalog/PIA02445">Mercury's Caloris impact site</a> is one example. When Galileo flew near Callisto on May 25, 2001, scientists sought an image to check the Valhalla antipode for similar signs of disruption.<p>Computer modeling has suggested that if Callisto had a water layer in its interior, that layer would have dispersed the seismic shock waves from the ancient Valhalla impact. The absence of grooved and hilly terrain at the Valhalla antipode is consistent with that possibility. Magnetic-field measurements have previously suggested that Callisto has a layer of liquid water deep below its surface.<p>This image, taken from a distance of 32,000 kilometers (about 20,000 miles) shows details at the Valhalla antipode down to a size of about 330 meters (about 1,250 feet) across. Callisto is the outermost of Jupiter's four large moons. Its surface of ice and rock is the most heavily cratered of any moon in the solar system.<p>For a view of this image in context click <a href="/figures/PIA02593_cntxt.jpg">here</a>.<p>The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C. Additional information about the spacecraft and its discoveries is available on the Galileo home page at <a href="http://solarsystem.nasa.gov/galileo/" target="_blank">http://solarsystem.nasa.gov/galileo/</a>.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA02593" onclick="window.open(this.href); return false;" title="Voir l'image PIA02593: Opposite Side of Callisto from Valhalla Impact sur le site de la NASA">Voir l'image PIA02593: Opposite Side of Callisto from Valhalla Impact sur le site de la NASA.</a></div>
PIA02593: Opposite Side of Callisto from Valhalla Impact
<h1>PIA02861: Europa and Callisto under the watchful gaze of Jupiter</h1><div class="PIA02861" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>One moment in an ancient, orbital dance is caught in this color picture taken by NASA's Cassini spacecraft on Dec. 7, 2000, just as two of Jupiter's four major moons, Europa and Callisto, were nearly perfectly aligned with each other and the center of the planet.<p>The distances are deceiving. Europa, seen against Jupiter, is 600,000 kilometers (370,000 miles) above the planet's cloud tops. Callisto, at lower left, is nearly three times that distance from the cloud tops. Europa is a bit smaller than Earth's Moon and has one of the brightest surfaces in the solar system. Callisto is 50 percent bigger -- roughly the size of Saturn's largest satellite, Titan -- and three times darker than Europa. Its brightness had to be enhanced in this picture, relative Europa's and Jupiter's, in order for Callisto to be seen in this image.<p>Europa and Callisto have had very different geologic histories but share some surprising similarities, such as surfaces rich in ice. Callisto has apparently not undergone major internal compositional stratification, but Europa's interior has differentiated into a rocky core and an outer layer of nearly pure ice. Callisto's ancient surface is completely covered by large impact craters: The brightest features seen on Callisto in this image were discovered by the Voyager spacecraft in 1979 to be bright craters, like those on our Moon. In contrast, Europa's young surface is covered by a wild tapestry of ridges, chaotic terrain and only a handful of large craters.<p>Recent data from the magnetometer carried by the Galileo spacecraft, which has been in orbit around Jupiter since 1995, indicate the presence of conducting fluid, most likely salty water, inside both worlds.<p>Scientists are eager to discover whether the surface of Saturn's Titan resembles that of Callisto or Europa, or whether it is entirely different when Cassini finally reaches its destination in 2004. <p>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.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA02861" onclick="window.open(this.href); return false;" title="Voir l'image PIA02861: Europa and Callisto under the watchful gaze of Jupiter sur le site de la NASA">Voir l'image PIA02861: Europa and Callisto under the watchful gaze of Jupiter sur le site de la NASA.</a></div>
PIA02861: Europa and Callisto under the watchful gaze of Jupiter
<h1>PIA03455: Callisto Close-up with Jagged Hills</h1><div class="PIA03455" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>The highest-resolution views ever obtained of any of Jupiter's moons, taken by NASA's Galileo spacecraft in May 2001, reveal numerous bright, sharp knobs covering a portion of Jupiter's moon Callisto.</p><p>The knobby terrain seen throughout the top inset is unlike any seen before on Jupiter's moons. The spires are very icy but also contain some darker dust. As the ice erodes, the dark material apparently slides down and collects in low-lying areas. Over time, as the surface continues to erode, the icy knobs will likely disappear, producing a scene similar to the bottom inset. The number of impact craters in the bottom image indicates that erosion has essentially ceased in the dark plains shown in that image, allowing impact craters to persist and accumulate.</p><p>The knobs are about 80 to 100 meters (260 to 330 feet) tall, and they may consist of material thrown outward from a major impact billions of years ago. The areas captured in the images lie south of Callisto's large Asgard impact basin.</p><p>The smallest features discernable in the images are about 3 meters (10 feet) across.</p>The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C. Additional information about the spacecraft and its discoveries is available on the Galileo home page at <a href="http://solarsystem.nasa.gov/galileo/" target="_blank">http://solarsystem.nasa.gov/galileo/</a>.</p><br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA03455" onclick="window.open(this.href); return false;" title="Voir l'image PIA03455: Callisto Close-up with Jagged Hills sur le site de la NASA">Voir l'image PIA03455: Callisto Close-up with Jagged Hills sur le site de la NASA.</a></div>
PIA03455: Callisto Close-up with Jagged Hills
<h1>PIA03456: Global Callisto in Color</h1><div class="PIA03456" lang="en" style="width:740px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>Bright scars on a darker surface testify to a long history of impacts on Jupiter's moon Callisto in this image of Callisto from NASA's Galileo spacecraft.<p>The picture, taken in May 2001, is the only complete global color image of Callisto obtained by Galileo, which has been orbiting Jupiter since December 1995. Of Jupiter's four largest moons, Callisto orbits farthest from the giant planet.<p>Callisto's surface is uniformly cratered but is not uniform in color or brightness. Scientists believe the brighter areas are mainly ice and the darker areas are highly eroded, ice-poor material.<p>The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C. Additional information about the spacecraft and its discoveries is available on the Galileo home page at <a href="http://solarsystem.nasa.gov/galileo/" target="_blank">http://solarsystem.nasa.gov/galileo/</a>.</p><br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA03456" onclick="window.open(this.href); return false;" title="Voir l'image PIA03456: Global Callisto in Color sur le site de la NASA">Voir l'image PIA03456: Global Callisto in Color sur le site de la NASA.</a></div>
PIA03456: Global Callisto in Color
<h1>PIA09258: Capturing Callisto</h1><div class="PIA09258" lang="en" style="width:500px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>The New Horizons Long Range Reconnaissance Imager (LORRI) captured these two images of Jupiter's outermost large moon, Callisto, as the spacecraft flew past Jupiter in late February. New Horizons' closest approach distance to Jupiter was 2.3 million kilometers (1.4 million miles), not far outside Callisto's orbit, which has a radius of 1.9 million kilometers (1.2 million miles). However, Callisto happened to be on the opposite side of Jupiter during the spacecraft's pass through the Jupiter system, so these images, taken from 4.7 million kilometers (3.0 million miles) and 4.2 million kilometers (2.6 million miles) away, are the closest of Callisto that New Horizons obtained.<p><p>Callisto's ancient, crater-scarred surface makes it very different from its three more active sibling satellites, Io, Europa and Ganymede. Callisto, 4,800 kilometers (3000 miles) in diameter, displays no large-scale geological features other than impact craters, and every bright spot in these images is a crater. The largest impact feature on Callisto, the huge basin Valhalla, is visible as a bright patch at the 10 o'clock position. The craters are bright because they have excavated material relatively rich in water ice from beneath the dark, dusty material that coats most of the surface.<p><p>The two images show essentially the same side of Callisto -- the side that faces Jupiter -- under different illumination conditions. The images accompanied scans of Callisto's infrared spectrum with New Horizons' Linear Etalon Imaging Spectral Array (LEISA). The New Horizons science team designed these scans to study how the infrared spectrum of Callisto's water ice changes as lighting and viewing conditions change, and as the ice cools through Callisto's late afternoon. The infrared spectrum of water ice depends slightly on its temperature, and a goal of New Horizons when it reaches the Pluto system (in 2015) is to use the water ice features in the spectrum of Pluto's moon Charon, and perhaps on Pluto itself, to measure surface temperature. Callisto provided an ideal opportunity to test this technique on a much better-known body.<p><p>The left image, taken at 05:03 Universal Time on February 27, 2007, is centered at 5 degrees south, 5 degrees west, and has a solar phase angle of 46 degrees. The right image was taken at 03:25 Universal Time on February 28, 2007. It is centered at 4 degrees south, 356 degrees west, and has a solar phase angle of 76 degrees.</p><br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA09258" onclick="window.open(this.href); return false;" title="Voir l'image PIA09258: Capturing Callisto sur le site de la NASA">Voir l'image PIA09258: Capturing Callisto sur le site de la NASA.</a></div>
PIA09258: Capturing Callisto