Galerie de photos d'Encelade, satellite de la planète Saturne

PIA11121: Enceladus Oct. 9, 2008 Flyby - Posted Image #3	PIA11122: Enceladus Oct. 9, 2008 Flyby - Posted Image #4
PIA11123: Enceladus Oct. 9, 2008 Flyby - Posted Image #5	PIA11124: Enceladus Rev 91 Flyby - Skeet Shoot #1
PIA11125: Enceladus Rev 91 Flyby - Skeet Shoot #8	PIA11127: Enceladus Rev 91 Flyby - Skeet Shoot #9
$<h1>PIA11133: A Tectonic Feast</h1><div class="PIA11133" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>On Oct. 5, 2008, just after coming within 25 kilometers (15.6 miles) of the surface of Enceladus, NASA's Cassini captured this stunning mosaic as the spacecraft sped away from this geologically active moon of Saturn. </p><p>Craters and cratered terrains are rare in this view of the southern region of the moon's Saturn-facing hemisphere. Instead, the surface is replete with fractures, folds, and ridges—all hallmarks of remarkable tectonic activity for a relatively small world. In this enhanced-color view, regions that appear blue-green are thought to be coated with larger grains than those that appear white or gray. </p><p>Portions of the tiger stripe fractures, or sulci, are visible along the terminator at lower right, surrounded by a circumpolar belt of mountains. The icy moon's famed jets emanate from at least eight distinct source regions, which lie on or near the tiger stripes. However, in this view, the most prominent feature is Labtayt Sulci, the approximately one-kilometer (0.6 miles) deep northward-trending chasm located just above the center of the mosaic.</p><p>Near the top, the conspicuous ridges are Ebony and Cufa Dorsae. This false-color mosaic was created from 28 images obtained at seven footprints, or pointing positions, by Cassini's narrow-angle camera. At each footprint, four images using filters sensitive to ultraviolet, visible and infrared light (spanning wavelengths from 338 to 930 nanometers) were combined to create the individual frames. The mosaic is an orthographic projection centered at 64.49 degrees south latitude, 283.87 west longitude, and it has an image scale of 196 kilometers (122.5 miles) per pixel. The original images ranged in resolution from 180 meters (594 feet) to 288 meters (950 feet) per pixel and were acquired at distances ranging from 30,000 to 48,000 kilometers (18,750 to 30,000 miles) as the spacecraft receded from Enceladus. The view was acquired at a Sun-Enceladus-spacecraft, or phase, angle of 73 degrees. </p><p>The Cassini-Huygens mission 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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.</p><p>The Cassini-Huygens mission 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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.</p><p>For more information about the Cassini-Huygens mission visit <a href="http://saturn.jpl.nasa.gov" class="external free" target="wpext">http://saturn.jpl.nasa.gov/</a>. The Cassini imaging team homepage is at <a href="http://ciclops.org" class="external free" target="wpext">http://ciclops.org</a>.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA11133" onclick="window.open(this.href); return false;" title="Voir l'image PIA11133: A Tectonic Feast sur le site de la NASA">Voir l'image PIA11133: A Tectonic Feast sur le site de la NASA.</a></div>$ PIA11133: A Tectonic Feast	PIA11134: Enceladus Rev 91 Flyby - Skeet Shoot 1-4 Mosaic
$<h1>PIA11135: Tiger Stripes...Magnified!</h1><div class="PIA11135" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p><a href="/figures/PIA11135_fig1.jpg" class="external free" target="wpext"><br />Annotated Version</a><br />Click on the image</p><p>During two close flybys of Saturn's moon Enceladus in 2008, the cameras on NASA's Cassini acquired several very high-resolution images of specific regions of the south polar terrain. These images have been used to construct this detailed mosaic of the moon's famous tiger stripe fractures. </p><p>A special spacecraft maneuver dubbed "the skeet shoot" was employed to make smear-free imaging at close range possible. The ground track of the camera's pointing was selected to cut swaths across three tiger stripes, or sulci, the prominent rifts through which jets of water vapor and ice particles are actively jetting. The swaths during the two flybys were chosen to pass over specific locales on the surface. In total, six of the eight regions on or near the tiger stripes known to be warm sites of previously observed jet sources were imaged. </p><p>This clear filter mosaic includes all of the skeet-shoot images overlain on images acquired at lower resolution of regions near Damascus, Baghdad and Cairo Sulci. The annotated version identifies the locations of the six targeted jet source sites (solid yellow circles) as well as the footprints, or outlines, of Cassini's narrow-angle camera views of the surface during the skeet-shoot maneuvers on August 10 (green squares) and October 31 (orange squares). Although visible in other lower-resolution images, jet source site VIII (dashed yellow circle) was not targeted in the skeet shoot. Within the colored squares, image scales range from 9 meters (30 feet) to 39 meters (129 feet) per pixel.</p><p>The Cassini-Huygens mission 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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.</p><p>For more information about the Cassini-Huygens mission visit <a href="http://saturn.jpl.nasa.gov" class="external free" target="wpext">http://saturn.jpl.nasa.gov/</a>. The Cassini imaging team homepage is at <a href="http://ciclops.org" class="external free" target="wpext">http://ciclops.org</a>.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA11135" onclick="window.open(this.href); return false;" title="Voir l'image PIA11135: Tiger Stripes...Magnified! sur le site de la NASA">Voir l'image PIA11135: Tiger Stripes...Magnified! sur le site de la NASA.</a></div>$ PIA11135: Tiger Stripes...Magnified!	$<h1>PIA11136: Enceladus' Jets</h1><div class="PIA11136" lang="en" style="width:768px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p><a href="/archive/PIA11136.mov" class="external free" target="wpext"><br />Movie Clip</a><br />Click on the image</p><p>The most prominent jets of vapor and icy particles emerging from the south polar terrain of Saturn's moon Enceladus are shown here in graphical form in a movie clip of a "rotating" Enceladus. </p><p>A mosaic constructed of images of Enceladus' southern hemisphere (see <a href="/catalog/PIA11126">PIA11126</a>) from NASA's Cassini spacecraft imaging science sub-system was projected onto a computer model of the moon to which vectors indicating the direction of the jets were added. </p><p><b>About the Video</b><br />Reconstructing the Past on Enceladus<br />The video demonstrates two examples of the interpretation of tectonic spreading along the tiger stripe fractures in the south polar terrain of Saturns moon Enceladus. The first part of the video shows a simple example in which an old relict tiger stripe is believed to have lost its tip after it was sheared off by tectonic forces and pushed away from its parent by spreading. In the meantime, the parent tiger stripe has managed to regenerate a replacement tip, probably by the creation of new icy crust from upwelling soft ice. The orphaned "clone" now sits by itself, connected to the parent only by two parallel fault lines. The movie shows that, if the orphaned tiger stripe tip can be slid along the parallel faults back into place on the parent rift, the fit is remarkably good. Striated material between the clone and the replacement tip represents new icy crust material that must have been created during the spreading process.</p><p>The second part of the video demonstrates how this video-reconstruction technique can be used to infer a possible spreading history of the region between two tiger stripes: Alexandria Sulcus and Cairo Sulcus. The process begins by snipping-out and closing the gap that corresponds to Alexandria Sulcus and its upraised flanks. The gap is closed by matching the remaining right and left edges like a jigsaw puzzle. The closure is accomplished by sliding along a prominent fault nearly perpendicular to one end of Alexandria. This segment of the video is repeated four times with arrows that mark previously offset features that come into alignment after Alexandria is closed.</p><p>Next, Cairo Sulcus is closed along a lower fault that is parallel to the one along which Alexandria was closed. After the Cairo is removed, the closure is continued along the same fault until all of the intervening terrain has been removed. During this process, a mysterious 14-kilometer-sized elliptical feature appears by matching a semi-circular feature that previously existed on the right side of Cairo with the left side of an oval-shaped feature that exists between Alexandria and Cairo. In this way, the gap between Cairo and Alexandria can be closed completely, but there remains a length of the fault that suggests even more spreading may have occurred. Closing the gap all the way along this fault results in the reappearance of a feature that resembles the elliptical structure seen earlier. This feature is perhaps a relict impact crater or the surface expression of a rising warm diapir or icy convection cell. </p><p>The video was created based on images of the south pole of Enceladus taken from this map, see <a href="/catalog/PIA11126">PIA11126</a>. </p><p>The Cassini-Huygens mission 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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.</p><p>For more information about the Cassini-Huygens mission visit <a href="http://saturn.jpl.nasa.gov" class="external free" target="wpext">http://saturn.jpl.nasa.gov/</a>. The Cassini imaging team homepage is at <a href="http://ciclops.org" class="external free" target="wpext">http://ciclops.org</a>.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA11136" onclick="window.open(this.href); return false;" title="Voir l'image PIA11136: Enceladus' Jets sur le site de la NASA">Voir l'image PIA11136: Enceladus' Jets sur le site de la NASA.</a></div>$ PIA11136: Enceladus' Jets
$<h1>PIA11137: Reconstructing the Past on Enceladus</h1><div class="PIA11137" lang="en" style="width:640px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p><a href="/archive/PIA11137.mov" class="external free" target="wpext"><br />Movie Clip</a><br />Click on the image for the movie</p><p><p>This video demonstrates two examples of the interpretation of tectonic spreading along the "tiger stripe" fractures in the south polar terrain of Saturn's moon Enceladus. </p><p>The first part of the video shows a simple example in which an old relict tiger stripe is believed to have lost its tip after it was sheared off by tectonic forces and pushed away from its parent by spreading. In the meantime, the parent tiger stripe has managed to regenerate a replacement tip, probably by the creation of new icy crust from upwelling soft ice. The orphaned "clone" now sits by itself, connected to the parent only by two parallel fault lines. </p><p>The movie shows that, if the orphaned tiger stripe tip can be slid along the parallel faults back into place on the parent rift, the fit is remarkably good. Striated material between the clone and the replacement tip represents new icy crust material that must have been created during the spreading process. </p><p>The second part of the video demonstrates how this video-reconstruction technique can be used to infer a possible spreading history of the region between two tiger stripes: Alexandria Sulcus and Cairo Sulcus. The process begins by snipping-out and closing the gap that corresponds to Alexandria Sulcus and its upraised flanks. The gap is closed by matching the remaining right and left edges like a jigsaw puzzle. The closure is accomplished by sliding along a prominent fault nearly perpendicular to one end of Alexandria. This segment of the video is repeated four times with arrows that mark previously offset features that come into alignment after Alexandria is closed. </p><p>Next, Cairo Sulcus is closed along a lower fault that is parallel to the one along which Alexandria was closed. After the Cairo is removed, the closure is continued along the same fault until all of the intervening terrain has been removed. During this process, a mysterious 14-kilometer-sized elliptical feature appears by matching a semi-circular feature that previously existed on the right side of Cairo with the left side of an oval-shaped feature that exists between Alexandria and Cairo. In this way, the gap between Cairo and Alexandria can be closed completely, but there remains a length of the fault that suggests even more spreading may have occurred. Closing the gap all the way along this fault results in the reappearance of a feature that resembles the elliptical structure seen earlier. This feature is perhaps a relict impact crater or the surface expression of a rising warm diapir or icy convection cell. </p><p>This video was created based on images of the south pole of Enceladus taken from this map, see <a href="/catalog/PIA11126">PIA11126</a>.</p><p>The Cassini-Huygens mission 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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.</p><p>For more information about the Cassini-Huygens mission visit <a href="http://saturn.jpl.nasa.gov" class="external free" target="wpext">http://saturn.jpl.nasa.gov/</a>. The Cassini imaging team homepage is at <a href="http://ciclops.org" class="external free" target="wpext">http://ciclops.org</a>.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA11137" onclick="window.open(this.href); return false;" title="Voir l'image PIA11137: Reconstructing the Past on Enceladus sur le site de la NASA">Voir l'image PIA11137: Reconstructing the Past on Enceladus sur le site de la NASA.</a></div>$ PIA11137: Reconstructing the Past on Enceladus	$<h1>PIA11138: Spreading Ridge Transforms On Enceladus</h1><div class="PIA11138" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>These two side-by-side images compare a characteristic sea-floor spreading feature on Earth, known as a spreading ridge transform, to a very similar looking arrangement of "tiger stripe" rift segments in the south polar terrain region of Saturn's moon Enceladus. </p><p>The left image shows a shaded relief map of bathymetry (or sonar-like topography) data covering a fast-spreading ridge along the Earth's East Pacific Rise at 9.5 degrees north latitude, 104 degrees west longitude. Spreading ridges are laterally offset in a characteristic "zig-zag" pattern that closely matches the offset pattern seen on the Enceladus tiger stripe rifts. Striations parallel to the seafloor ridges are produced symmetrically when upwelling magma in the rifts solidify and become welded on each side of the central trench. </p><p>In contrast, the transform-like structure on Enceladus (in the image on the right) is flanked by a very complicated arrangement of old fractures. If the Enceladus feature is indeed a type of transform, it indicates spreading in a way that significantly differs from sea-floor spreading: Either the Enceladus feature is not spreading symmetrically from the center of the tiger stripe rifts as usually occurs in terrestrial sea-floor spreading centers, or else the original indicators of symmetrical spreading have been erased by a complicated superposed fracture history. </p><p>The Enceladus data were acquired by NASA's Cassini spacecraft's imaging science sub-system during four close-targeted flybys of Enceladus in March, August and October 2008. </p><p>The Cassini-Huygens mission 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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.</p><p>For more information about the Cassini-Huygens mission visit <a href="http://saturn.jpl.nasa.gov" class="external free" target="wpext">http://saturn.jpl.nasa.gov/</a>. The Cassini imaging team homepage is at <a href="http://ciclops.org" class="external free" target="wpext">http://ciclops.org</a>.</p><p>Sea-floor bathymetry data ©2008 MGDS; www.marine-geo.org from Carbotte, S.M., R. Arko, D.N. Chayes, W. Haxby, K. Lehnert, S. O'Hara, W.B.F. Ryan, R.A. Weissel, T. Shipley, L. Gahagan, K. Johnson, T. Shank (2004), New Integrated Data Management System for Ridge2000 and MARGINS Research, Eos Trans. AGU, 85(51), 553, DOI: 10.1029/2004EO510002.]<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA11138" onclick="window.open(this.href); return false;" title="Voir l'image PIA11138: Spreading Ridge Transforms On Enceladus sur le site de la NASA">Voir l'image PIA11138: Spreading Ridge Transforms On Enceladus sur le site de la NASA.</a></div>$ PIA11138: Spreading Ridge Transforms On Enceladus
PIA11139: Enceladus Offset Spreading Center	$<h1>PIA11140: Ancient Terrain on Enceladus</h1><div class="PIA11140" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>This figure shows a possible history of the south polar terrain on Saturn's moon Enceladus. </p><p>The top figure is a digital map that shows the four major "tiger stripe" fractures and the ropey terrain between them near the south pole of Enceladus. The data were acquired by NASA's Cassini spacecraft, imaging science sub-system during four close-targeted flybys of Enceladus in March, August and October 2008. </p><p>Cassini scientists have recently inferred that tectonic spreading, somewhat like tectonic sea-floor spreading on Earth, occurs between and along the tiger stripes. However, unlike sea-floor spreading on Earth, where upwelling hot magma fills the central rift of a spreading ridge as the ridge spreads symmetrically to either side of the rift, on Enceladus the spreading is asymmetric. Like a conveyor belt, newly created icy crust on Enceladus spreads out asymmetrically (i.e., in one direction) relative to the tiger stripes. </p><p>It appears that a broad zone of spreading pushes from the western hemisphere side of the south polar terrain region (left side of the top panel) to the eastern side of the region (right side of the top panel). The map in the top panel is about 110 kilometers (68 miles) wide. If the tiger stripes and much of the surrounding terrain are snipped out of the map along the right tectonic contacts, the remaining sections can be pieced back together like a jigsaw puzzle. The reassembled puzzle shows what the tiger stripe region might have looked like long ago before much spreading took place. </p><p>The bottom panel shows the reconstruction of a possible paleo-terrain that may have existed early in the geological history of the south polar region. This reconstruction indicates that at least 73 kilometers (45 miles) of spreading may have occurred over time. After the reconstruction, a curious elliptical ring-shaped feature appears along the left edge at about the location where the spreading seems to have originated. A wavy pattern of ropey terrain deflects around the elliptical feature. Imaging scientists have speculated that perhaps this is a relict impact feature or the surface expression of a warm, rising diapir (convective cell) that may drive the spreading through convection, much the same way that convection drives plate tectonics on Earth.</p><p>The Cassini-Huygens mission 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 mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.</p><p>For more information about the Cassini-Huygens mission visit <a href="http://saturn.jpl.nasa.gov" class="external free" target="wpext">http://saturn.jpl.nasa.gov/</a>. The Cassini imaging team homepage is at <a href="http://ciclops.org" class="external free" target="wpext">http://ciclops.org</a>.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA11140" onclick="window.open(this.href); return false;" title="Voir l'image PIA11140: Ancient Terrain on Enceladus sur le site de la NASA">Voir l'image PIA11140: Ancient Terrain on Enceladus sur le site de la NASA.</a></div>$ PIA11140: Ancient Terrain on Enceladus
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