| Piú viste - Saturn: the "Ringed Beauty" and His Moons |
Enceladus-N00030059.jpgEnceladus, from approx. 27.000 Km57 visitenessun commento
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Enceladus-N00030084.jpgEnceladus, from approx. 17.000 Km57 visiteAncora il grande cratere che avevamo visto nel frame precedente, più vicino di oltre 4000 Km. Stupenda, semplicemente, la visione del terminatore di Encelado ed i conseguenti grandi contrasti luce-ombra, determinati dalle differenti altezze dei rilievi fotografati.
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Enceladus-N00030097.jpgEnceladus, from approx. 12.000 Km57 visiteAncora un grande e tortuoso crack della superficie di questa luna che, non più nè meno di Giapeto o Mimas, ci mostra, a mano a mano che ci avviciniamo, un volto capace di suscitare dei grandi interessi e che fa nascere infinite curiosità.
Perchè Encelado è così luminosa?
Che cosa è successo alla superficie di Encelado, e quando?
Proveremo un landing anche su Encelado, in futuro?!?...
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Enceladus-N00030103.jpgEnceladus, from approx. 6.000 Km57 visitenessun commento
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Enceladus-N00030265.jpgEnceladus, from approx. 925.000 Km57 visitenessun commento
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Epimetheus-PIA06605.jpgEpimetheus, from approx. 2,5 MKM57 visiteCaption NASA originale:"One of Saturn's strange co-orbital moons, Epimetheus, was captured by Cassini in this view. Irregularly shaped Epimetheus occasionally swaps orbits with nearby Janus and both moons play a role in maintaining the outer edge of Saturn's bright A-Ring. Epimetheus is 116 Km (approx. 72 miles) across.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 22, 2005, at a distance of approximately 2,5 MKM (approx. 1,6 MMs) from Epimetheus and at a phase angle of 90°.
Resolution in the image is 15 Km (approx. 9 miles) per pixel.
The image has been contrast-enhanced to aid visibility".
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Enceladus-PIA06206_modest.jpgEnceladus (close-up)57 visiteCaption NASA originale:"Fractures are nearly ubiquitous in this terrain, cutting across each other and across impact craters. Scientists can use the relationships between different features to determine the order in which they formed, thereby unraveling the moon's past. For example, almost all the craters in this mosaic have fractures running through their rims and floors, indicating that the craters formed first. This means that Enceladus has been geologically active relatively recently, especially compared to some of its neighbors in the Saturn system. There is an impressive variety of fractures visible here--from the wide east-west rifts near the upper left of the mosaic to the very fine north-south fractures in the center (which are approximately 100 to 400 meters). Due to the complexity of this terrain, the task of unraveling Enceladus' history promises to be a worthy challenge for planetary scientists".
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Enceladus-PIA06208.jpgEnceladus (full-disk) - false colors57 visiteCaption NASA originale:"During its very close flyby on March 9, 2005, the Cassini spacecraft captured this false-color view of Saturn's moon Enceladus, which shows the wide variety of this icy moon's geology. Some geological regions on Enceladus are old and retain large numbers of impact craters; younger areas exhibit many generations of tectonic troughs and ridges. Subtle differences in color may indicate different ice properties, such as grain sizes, that will help unravel the sequence of geologic events leading to the current strange landscape. In the early 1980's, NASA's Voyager mission to the outer planets revealed a strikingly similar arrangement of terrains on Miranda, an icy moon of Uranus (see PIA 00141). Miranda is 470-Km-wide (290 miles), nearly as large as Enceladus (504 Km). The similarities in size and tectonic history on these objects may suggest that remarkably similar physical processes have controlled the separate geological evolutions of these bodies. The Sun illuminates Enceladus from the left, leaving part of it in shadow and blocking out part of the view of Saturn. This view shows the anti-Saturn hemisphere, centered nearly on the equator".
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Enceladus-PIA06209.jpgEnceladus' "crispy & fractured" surface (false colors)57 visiteExtending through the center of this image is a system of rifts 3 Km wide and lanes of grooved terrain 20 Km wide, which separate 2 distinct geological provinces. To the right of the boundary is older, cratered terrain - a region peppered with craters ranging from 10 Km in diameter, down to craters near the limit of resolution. The region is believed to be old because it has accumulated a relatively high density of impact craters over time and the topography is soft and muted, suggesting that it is covered by a layer of particulate materials. The cratered terrain is cut crosswise by numerous faults and fractures ranging in width from hundreds of meters to a few Km. On the left side of the scene are grooved, icy plains. This broad, relatively flat region is scored by an extensive band of parallel grooves that appear to subdivide the surface into narrow lanes approx. 1 Km wide. The low abundance of impact craters and crisp relief on topographic features here imply that this region is geologically much younger than the cratered terrain at the right.
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Enceladus-PIA06210.jpgEnceladus' "crispy & fractured" surface (false colors)57 visiteTo human eyes, Enceladus appears almost completely white, but false color reveals intriguing details. This view is a composite of images taken using filters sensitive to ultraviolet (centered at 338 nnmts), green (centered at 568 nnmts), and near-infrared (centered at 930 nnmts) light and has been processed to accentuate subtle color differences. The uppermost surface of these terrains appears uniformly grey in this picture, suggesting that they are covered with materials of homogeneous composition and grain size. However, the walls of many of the fractures appear to be somewhat bluer than typical surface materials. It is possible that the difference in color identifies outcrops of solid ice on the walls of fractures, or ice with different grain-sizes, compared to powdery surface materials. It is also possible that the color identifies some compositional difference between buried ice and ice at the surface. The surface is peppered with craters of all sizes, from the 21-Km diameter crater at the top of the image, down to tiny craters near the limit of resolution. The prominent crater at the top contains a central, domelike structure more than 11 kilometers (7 miles) in diameter. The dome, the crater -- and indeed the entire scene -- is sliced by a complex network of fractures ranging in width from hundreds of meters in some places, to over three kilometers (2 miles) in others.
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Tethys in natural colors-V2.jpgTethys in natural colors57 visiteCaption NASA originale:"Voyager 2 obtained this image of Tethys on Aug. 25, when the spacecraft was 594.000 Km from this moon of Saturn. This photograph was compiled from images taken through the violet, clear and green filters of Voyager's narrow-angle camera. Tethys shows two distinct types of terrain - bright, densely cratered regions and relatively dark, lightly cratered planes that extend in a broad belt across the satellite. The densely cratered terrain is believed to be part of the ancient crust of the satellite; the lightly cratered planes are thought to have been formed later by internal processes. Also clearly seen is a trough that runs parallel to the terminator (the day-night boundary, seen at right). This trough is an extension of the huge canyon system that also Voyager 1 saw and photographed . This system extends nearly 2/3rds the distance around Tethys".
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Saturn-tilted.jpgTilted Saturn57 visiteCaption NASA originale:"Saturn's whirling vortices and feathery cloud bands are the signs of a restless world. Cassini captured this arresting view of the giant planet scored by bold shadows cast by the rings. The rings are seen edge-on in this dramatic, artfully tilted scene.
The image was taken with the Cassini spacecraft wide-angle camera on March 6, 2005, at a distance of approx. 1,7 MKM (1 MMs) from Saturn through a filter sensitive to wavelengths of infrared light centered at 750 nnmts. The image scale is 10 Km per pixel".
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