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| Ultimi arrivi - Saturn: the "Ringed Beauty" and His Moons |
The_Rings-PIA10079.jpgSaturnian "Propellers" (context frame)60 visiteThe Cassini spacecraft captures 8 new propeller-like features within Saturn's A-Ring in what may be the propeller "hot zone" of Saturn's Rings.
Propeller features form around small moonlets that are not massive enough to clear out ring material, but are still able to pull smaller ring particles into a shape reminiscent of an airplane propeller. Scientists believe that propellers represent moonlet wakes, which are denser than the surrounding ring material and appear bright in the images.
Propellers were first discovered in Cassini images taken during Saturn orbit insertion in 2004. This new image is from a more extensive study of the full A-Ring and provides evidence that these features are not distributed evenly as previously thought, but are instead grouped in a 3000 Km-wide (about 1860 mile) Propeller Belt.
The largest propeller seen here is noted in the white dashed box, and it indicates the presence of a 150-meter (490-foot) moonlet. The size is inferred from the radial separation of the propeller wings. The propeller is seen in another image and is shown in the upper left box.
The reappearance of the propellers clearly demonstrates their orbital motion.MareKromiumOtt 27, 2007
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The_Rings-PIA10080.jpgSaturnian "Propellers" (extra-detail mgnf)61 visiteThis set of Cassini spacecraft images shows a close-up view of 2 propeller structures in Saturn's A-Ring. These images are part of a large view that captures eight new propeller-like features in what may be the propeller "hot zone" of Saturn's Rings. Propellers were first discovered in Cassini images taken during Saturn orbit insertion in 2004.
Propellers form around small moonlets that are not massive enough to clear out ring material, but are still able to push the ring particles into a shape reminiscent of an airplane propeller.
These pictures show 2 new propellers close up (one centered on each image). These images were put together from images in the Planetary Data System, a web site which archives and distributes scientific data from NASA planetary missions.
The image on the top shows a propeller induced by a 150-meter (490-foot) moonlet.
Smaller bright spots in the image are artifacts. The image on the bottom shows another propeller located just outside of the Encke Gap. Fine horizontal stripes seen in the image are wakes induced by the moon Pan.
In the top clear-filter image, taken during a stellar occultation on Aug. 20, 2005, the Cassini spacecraft narrow-angle camera observed the unlit side of the Rings, with a phase angle of 126°. The images were taken at 1 minute intervals with 0,05" exposure time. Image resolution is 1 Km (0,6 miles) per pixel.
The bottom clear-filter image was taken few hours later with 2" exposure time. Image resolution is roughly 1,5 Km (a little less than 1 mile) per pixel. MareKromiumOtt 27, 2007
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Japetus-PIA08403.jpgMiddle Northern Latitudes of Japetus57 visiteCassini soars above the many pits and basins in the rolling landscape of Saturn's moon Japetus. This mosaic view looks out onto an area close to the Northern bright/dark boundary, but still within the Dark Region, Cassini Regio.
Near upper left is a large crater with terraced walls, a mostly flat floor and a prominent group of peaks in its center. The sharp features make this likely one of the youngest craters in this area of Japetus. Cassini imaged another similarly flat-floored and relatively fresh crater during its Dec. 2004 Japetus flyby.
The mosaic consists of 3 image footprints across the surface of Japetus. The view is centered on terrain near 43,3° North Latitude, 138° West Longitude. Image scale is approx. 75 meters (246 feet) per pixel.
The clear spectral filter images in this mosaic were obtained with the Cassini spacecraft narrow-angle camera on Sept. 10, 2007, at a distance of approx. 13.500 Km (about 8.400 miles) from Japetus and at a Sun-Japetus-Spacecraft, or phase, angle of 139°.MareKromiumOtt 17, 2007
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The_Rings-PIA08389_fig1.jpgThe Rings55 visiteA scan across Saturn's incredible halo of ice rings yields a study in precision and order. This natural color mosaic was acquired by the Cassini spacecraft as it soared 39 degrees above the unilluminated side of the Rings.
Major named gaps are labeled at the top. The main rings themselves, along with the F-Ring, are labeled at the bottom, along with their inner and outer boundaries.
The view combines 45 images -- 15 separate sets of red, green and blue images -- taken over the course of about 2,5 hours, as Cassini scanned across the Rings.
The images in this view were obtained on May 9, 2007, at a distance of approx. 1,1 MKM (about 700,000 miles) from Saturn. Image scale in the radial (horizontal) direction is about 6 Km (approx. 4 miles) per pixel.MareKromiumOtt 17, 2007
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Tethys-PIA08401.jpgThe Edge of Tethys56 visiteThe cold, cratered landscape of Saturn's moon Tethys shines in stark relief in this crescent view. Aside from its obvious aesthetic beauty, this particular Cassini mosaic was obtained mainly to understand important details about how the surface of Tethys reflects light at high phase angles (the Sun-Tethys-Spacecraft viewing angle). The beautiful interplay of light with surface topographic features is an important factor in this regard. The surface is heavily cratered, and at this oblique angle the craters give the surface a highly scalloped appearance.
Unlike some HR crescent views of Saturn's moons, this image truly gives Tethys the appearance of being composed of ice and frost. There appear to be numerous sun glints sparkling across the surface. Some of these might be specular (or mirror-like) reflections off of exposed walls of solid ice inside craters, or they might be uniformly large, frosty or icy-particle covered facets of topography that are so oriented as to give exceptionally bright but diffuse reflections.
The shadows cast by most craters in the scene are not dark, but rather, they are illuminated by light bouncing off of their sunlit walls and those of other craters. This light, which has been scattered multiple times, makes visible some details along the shadowed walls and floors of craters that would not otherwise be visible in this viewing geometry.
This mosaic was assembled from four clear filter, narrow-angle camera images, with low resolution, wide-angle camera data filling a small gap in coverage. The view is an orthographic projection and has a resolution of 211 meters (692 feet) per pixel. An orthographic view is most like the view seen by a distant observer looking through a telescope. North is up.
The view was obtained by the Cassini spacecraft on June 29, 2007, from a distance of approximately 38.000 Km (about 24.000 miles) and at a Sun-Tethys-Spacecraft, or phase, angle of 152°.
MareKromiumOtt 17, 2007
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Rhea-PIA08402.jpgRayed Crater on Rhea (3D)90 visiteRhea's surface gains some depth in this stereo image, or anaglyph, which features the bright and geologically young-looking rayed crater on the moon's Leading Hemisphere. The view was created from images taken during Cassini's close encounter with Rhea on Aug. 30, 2007.
The crater is about 48 Km (approx. 30 miles) wide, and its rays extend several hundred kilometers outward. The rim of this crater is quite sharply defined, and there are few small craters overprinted onto it. These characteristics, along with the brightness of the crater and its rays are indicative of a feature formed relatively recently in geologic history.
The hummocky floor of the crater possesses a central peak and clusters of small craters. The little craters may be secondary impact sites, formed by ejecta from the primary impact that landed in the crater, or they could have been formed by material that had broken off of the body that struck Rhea.
This stereo image is a mosaic consisting of seven Cassini spacecraft narrow-angle camera images. The view is an orthographic projection centered on 12° South Latitude, 112° West Longitude and has a resolution of 45 meters (148 feet) per pixel. An orthographic view is most like the view seen by a distant observer looking through a telescope. North is up.
The clear filter images for this stereo image were taken from distances ranging from about 17.000 Km (approx. 10.600 miles, for the red-colored image) to 7.500 Km (such as about 4.700 miles, for the blue/green-colored image) from Rhea.MareKromiumOtt 17, 2007
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Tethys-PIA08400.jpgOdysseus is looking up!58 visiteThe vast expanse of the crater Odysseus spreads out below Cassini in this mosaic view of Saturn's moon Tethys.
The crater (about 450 Km or approx. 280 miles across) is a remarkably well-preserved example of an ancient multi-ringed impact basin: the outer ring is defined by steep, cliff-like walls that descend to generally broad internal terraces. The inner ring is formed by a prominent, crown-shaped, 140-Km (88-mile) diameter circular band of icy mountains. Multi-ring basins are seen on rocky bodies as well as icy ones.
The complex internal structure and multi-ringed nature of these very large basins are believed to arise from the rebound of intense shock waves that penetrated the body at the time of impact.
This mosaic was assembled from four clear filter, narrow-angle camera images. The view is an orthographic projection centered on 3° South Latitude, 119° West Longitude and has a resolution of 572 meters (0,35 mile) per pixel. An orthographic view is most like the view seen by a distant observer looking through a telescope. North is up.
The view was obtained by the Cassini spacecraft on Aug. 30, 2007, from a distance of approximately 97.000 Km (about 60.000 miles) and at a Sun-Tethys-Spacecraft, or phase, angle of 51°.MareKromiumOtt 17, 2007
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Saturn-PIA08387.jpgA View from Japetus58 visiteWhile on final approach for its Sept. 2007 close encounter with Saturn's moon Japetus, Cassini spun around to take in a sweeping view of the Saturn System.
Japetus is the only major moon of Saturn with a significant inclination to its orbit. From the other major satellites, the Rings would appear nearly edge-on, but from Japetus, the Rings usually appear at a tilt, as seen here.
This natural color mosaic consists of 15 red, green and blue spectral filter images acquired in five wide-angle camera footprints that swept across the scene.
Moons visible in this image: Dione at center left, Enceladus near the left side ansa (or ring edge), Mimas is a speck against the ring shadows on Saturn's Western Limb, Rhea can be seen against the bluish backdrop of the Northern Hemisphere, Tethys is near the right ansa, and Titan near lower right.
The images were obtained on Sept. 10, 2007, at a distance of approx. 3,3 MKM (such as about 2,1 MMs) from Saturn at a Sun-Saturn-Spacecraft, or phase, angle of 33°. Image scale is about 195 Km (approx. 121 miles) per pixel on the Planet. MareKromiumOtt 17, 2007
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Saturn-PIA08388.jpgLooking at the Giant60 visiteSaturn sits nested in its rings of ice as Cassini once again plunges toward the graceful giant. This natural color mosaic was acquired by the Cassini spacecraft as it soared 39° above the unilluminated side of the Rings.
Little light makes its way through the Rings to be scattered in Cassini's direction in this viewing geometry, making the Rings appear somewhat dark compared to the reflective Planet. The view can be contrasted with earlier mosaics designed to showcase the Rings rather than the Planet, which were therefore given longer exposure times.
Bright clouds play in the blue-gray skies of the North. The Ring shadows continue to caress the Planet as they slide farther South toward their momentary disappearance during Equinox in 2009.
The Rings' reflected light illuminates the Southern Hemisphere on Saturn's night side.
The scene is reminiscent of the parting glance of NASA's Voyager 1 as it said goodbye to Saturn in 1981 (see PIA00335). Cassini, however, will continue to orbit Saturn for many years to come.
Three of Saturn's moons are visible in this image: Mimas (about 397 Km across) at the 2 o'clock position, Janus (about 181 Km across) at the 4 o'clock position and Pandora (about 84 Km across) at the 8 o'clock position. Pandora is a faint speck just outside the narrow F-Ring.
This mosaic was constructed from wide-angle camera images taken just before the narrow-angle camera mosaic PIA08389.
The view combines 45 images -- 15 separate sets of red, green and blue images -- taken over the course of about two hours, as Cassini scanned across the entire Main Ring System.
The images in this view were obtained on May 9, 2007, at a distance of approx. 1,1 MKM (about 700.000 miles) from Saturn.
Image scale is about 62 Km (approx. 39 miles) per pixel. MareKromiumOtt 17, 2007
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Saturn-PIA08390.jpgMirrors of Darkness...58 visiteOur robotic explorer Cassini regards the shadow-draped face of Saturn.
This view looks toward the unilluminated side of the Rings from about 14° above the Ring-Plane. In this viewing geometry all of the Main Rings, except for the B-Ring, appear transparent. The Rings cast their mirror image onto the Planet beyond.
Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were acquired with the Cassini spacecraft wide-angle camera on June 9, 2007, at a distance of approx. 1,6 MKM (about 972.000 miles) from Saturn.
Image scale is roughly 90 Km (about 56 miles) per pixel. MareKromiumOtt 17, 2007
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Saturn-PIA08392.jpgShadows on the Giant58 visiteLike a silvery pearl, an icy moon crosses the face of Saturn, while 2 of its siblings cast shadows onto the Planet.
Rhea hangs in the foreground. Near upper left on Saturn is the small shadow of Mimas. Near lower right is the penumbral shadow of Japetus - the part of the moon's shadow where Japetus does not completely block the Sun.
This view looks toward the unilluminated side of the Rings from less than 1° above the Ring-Plane. The Rings' shadows drape across the Northern Hemisphere. Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were obtained with the Cassini spacecraft wide-angle camera on June 15, 2007, at a distance of approx. 1,2 MKM (such as about 744.000 miles) from Rhea and 1,7 MKM (1,1 MMs) from Saturn.
Image scale is roughly 71 Km (about 44 miles) per pixel on Rhea and 103 Km (about 64 miles) on Saturn.MareKromiumOtt 17, 2007
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Saturn-PIA08393.jpgThe "Opposition Effect" (again)59 visiteThe Opposition Effect, a brightness surge that is visible on Saturn's Rings when the Sun is directly behind the Spacecraft, is captured here as a colorful halo of light moving across Saturn's Sunlit Rings. The rainbow of color seen here is actually an artifact and a by-product of the spot's movement and the way the color image was produced. Cassini acquires color images by taking sequential exposures using red, green and blue spectral filters, which are then composited together to form a color view. The bright patch traveled across the Rings between exposures taken for this view, creating a series of 3 colorful spots showing its position at 3 separate moments.
This view looks toward the Sunlit side of the Rings from about 9° below the Ring-Plane.
The images in this view were acquired with the Cassini spacecraft wide-angle camera on June 12, 2007, at a distance of approx. 523.000 Km (such as about 325.000 miles) from Saturn.
Image scale is roughly 31 Km (about 19 miles) per pixel.
MareKromiumOtt 17, 2007
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