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| Ultimi arrivi - Saturn: the "Ringed Beauty" and His Moons |
Saturn-PIA07731-2.jpgSpokes (2)58 visiteAt the bottom left corner of the 1 st and 2nd image, the bright inner edge of the A-Ring is visible. Continuing radially inward (or toward Saturn) are several bands that lie within the Cassini Division, bounded by the bright outer edge of the B-Ring. The rounded shadow of Saturn cuts across the Rings in the image at right.
Cassini's first sighting of Spokes occurs on the unilluminated side of the Rings, in the same region in which they were seen during the Voyager flybys. Although the most familiar Voyager images of spokes showed them on the sunlit side of the Rings, spokes also were seen on the unilluminated side.
In Voyager images, when Spokes were seen at low phase angles, they appeared dark; when seen at high phase angles, they appeared bright. The Spokes seen here are viewed by Cassini at a very high phase angle, which is about 145° at the center of each image.Set 18, 2005
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Saturn-PIA07731-1.jpgSpokes (1)60 visiteAfter much anticipation, Cassini has finally spotted the elusive "spokes" in Saturn's Rings.
"Spokes" are the ghostly Radial Markings discovered in the Rings by NASA's Voyager spacecraft 25 years ago. Since that time, Spokes had been seen in images taken by NASA's Hubble Space Telescope but had not, until now, been seen by Cassini.
These three images, taken over a span of 27', show a few faint, narrow Spokes in the outer B-Ring. The Spokes are about 3500 Km (2200 miles) long and about 100 Km wide (60 miles). The motion of the Spokes here is from left to right.
They are seen just prior to disappearing into the Planet's shadow on the Rings.
Set 18, 2005
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Rhea~1.jpgRhea56 visiteThe icy, cratered surface of Saturn's moon Rhea is seen in this HR image taken by Voyager 1 on November 11, 1980, from a distance of about 85.000 Km (such as approx. 52.800 miles) as the spacecraft passed over the Satellite's North Pole. The heavily cratered surface attests to the Satellite's ancient age. The largest craters, 50 to 100 Km across and several Km deep, are freshly preserved in Rhea's icy crust. The craters and landscape resemble those on the Moon and Mercury and are unlike the flattened crater forms that have collapsed in the soft icy crusts of the Jovian moons Callisto, Ganymede and Europa.
Scientists believe that Rhea (which is just 1600 Km - about 995 miles - in diameter, compared to the 5.500 Km of diameter of Ganymede) froze and became rigid, behaving like a rocky surface, very early in its history.Set 18, 2005
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Pan-PIA07587.jpgPan running in his "lane"58 visiteSaturn's moon Pan occupies the Encke Gap at the center of this image, which also displays some of the A-Ring's intricate wave structure. Pan is 26 Km (about 16 miles) across.
The two most prominent bright banded features seen on the left side of the image are Spiral Density Waves, which propagate outward through Saturn's Rings. The bright crests represent areas with higher ring particle densities.
The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on Aug. 1, 2005, at a distance of approx. 794.000 Km (about 493.000 miles) from Pan. The image scale is 5 Km (such as 3 miles) per pixel.Set 16, 2005
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Telesto-PIA07586.jpgTelesto70 visiteCaption originale:"The blob of light seen here is Saturn's moon Telesto, which shares its orbital path with much larger Tethys. Telesto is 24 Km across.
Although this view may hint at a flattened, potato-like shape for Telesto (a common shape for Saturn's smaller moons), no features on the moon's surface can be resolved here.
The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on Aug. 1, 2005, at a distance of approximately 768.000 Km from Telesto and at a Sun-Telesto-spacecraft angle of 37°. Resolution in the original image was 5 Km per pixel. The image has been contrast-enhanced and magnified by a factor of 4 to aid visibility".Set 15, 2005
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KeelerMoon-PIA07584.jpgS/2005 S1: the "Keeler-Gap" Moon58 visiteCassini's cameras were retargeted to capture the tiny Keeler Gap Moon S/2005 S1, visible at the center and first discovered by Cassini a few months ago. Waves raised in the gap edges by the Keeler moonlet's gravity are clearly visible here. Scientists can use the height of the waves to determine the little moon's mass.
The Keeler moon is 7 Km (about 4,3 miles) across and orbits within its 42-km (about 26-mile) wide gap. The much larger Encke Gap (325 Km, or 200 miles wide) is seen here at the upper right (...). This image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 1, 2005, at a distance of approx. 853.000 Km (or about 530.000 miles) from Saturn. The image scale is 5 Km (3 miles) per pixel. The image has been contrast-enhanced and magnified by a factor of 3 to aid visibility.Set 12, 2005
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Phoebe-PIA06075.jpgPhoebe's SkyLine58 visiteImages like this one, showing bright wispy streaks thought to be ice revealed by subsidence of crater walls, are leading to the view that Phoebe is an ice-rich body overlain with a thin layer of dark material. Obvious down slope motion of material occurring along the walls of the major craters in this image is the cause for the bright streaks, which are over-exposed here. Significant slumping has occurred along the crater wall at top left.
The slumping of material might have occurred by a small projectile punching into the steep slope of the wall of a pre-existing larger crater. Another possibility is that the material collapsed when triggered by another impact elsewhere on Phoebe. Note that the bright, exposed areas of ice are not very uniform along the wall. Small craters are exposing bright material on the hummocky floor of the larger crater.
Elsewhere on this image, there are local areas of outcropping along the larger crater wall where denser, more resistant material is located. Whether these outcrops are large blocks being exhumed by landslides or actual 'bedrock' is not currently understood.
The crater on the left, with most of the bright streamers, is about 45 kilometers (28 miles) in diameter, front to back as viewed. The larger depression in which the crater sits is on the order of 100 kilometers (62 miles) across. The slopes from the rim down to the hummocky floor are approximately 20 kilometers (12 miles) long; many of the bright streamers on the crater wall are on the order of 10 kilometers (6 miles) long. A future project for Cassini image scientists will be to work out the chronology of slumping events in this scene.
This image was obtained at a phase, or Sun-Phoebe-spacecraft, angle of 78 degrees, and from a distance of 11,918 kilometers (7,407 miles). The image scale is approximately 70 meters (230 feet) per pixel. No enhancement was performed on this image.
Set 10, 2005
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Rhea-PIA07583.jpgRhea, from about 255.000 Km93 visiteSaturn's moon Rhea is an alien ice world, but in this frame-filling view it is vaguely familiar. Here, Rhea's cratered surface looks in some ways similar to our own Moon, or the planet Mercury. But make no mistake - Rhea's icy exterior would quickly melt if this moon were brought as close to the Sun as Mercury.
Instead, Rhea preserves a record of impacts at its post in the Outer Solar System.
For exemple, the large impact crater at center left (near the terminator), called Izanagi, is just one of the numerous large impact basins on Rhea.
This view shows principally Rhea's Southern Polar Region, centered on 58° South and 265° West.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 1, 2005, at a distance of approx. 255.000 Km (such as about 158.000 miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 62°.
The image scale is 2 Km (about 1,2 miles) per pixel.Set 10, 2005
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Prometheus-PIA07582.jpgCrossing the Rings...58 visiteOriginal caption:"Prometheus has just passed - and gravitationally disturbed - some of the fine particulate material in the F-Ring, creating the sheared gap visible in the inner strands of the Ring. This view looks down from about 10° above the ringplane. Prometheus and the Rings are sunlit from below. At lower right lies the outermost part of the A-Ring, which grows suddenly brighter outside of the 42-Km-wide (such as about 26-miles) Keeler Gap.
The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on Aug. 2, 2005, at a distance of approximately 632.000 Km (approx. 392.000 miles) from Prometheus and at a Sun-Prometheus-spacecraft, or phase, angle of 122°. Image scale is 4 Km (about 2 miles) per pixel".Set 09, 2005
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Dione-PIA07581.jpgThe "Old Face" of Dione58 visiteOriginal NASA caption"Dione's Southern Polar Region (as shown here) contains fractures whose softened appearance suggests that they have different ages than the bright braided fractures seen in the image to the North. This Region is also notably brighter than the near equatorial terrain at the top of the image. At center, several of the bright, radial streaks mark a feature named Cassandra, which may be a rayed crater or a tectonic feature.
This view of Dione (1118 Km across) captures high southern latitudes on the Moon's trailing hemisphere.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 1, 2005, at a distance of approx. 269.000 Km(about 167.000 miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 41°. Image scale is 2 Km (about 1,2 miles) per pixel".Set 08, 2005
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Pandora-N00039277.jpgPandora, from about 52.000 Km57 visiteOriginal NASA caption:"N00039277.jpg was taken on September 05, 2005 and received on Earth September 06, 2005. The camera was pointing toward PANDORA at approximately 51.749 Km away".Set 07, 2005
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Saturn-PIA03559.jpgSaturn's clouds in 3D59 visiteSaturn's clouds and hazes at three different levels in the atmosphere are depicted in the image on the right, as observed by the visual infrared mapping spectrometer on the Cassini spacecraft.
In the image, red represents the deepest clouds yet found on Saturn. They are at an altitude where pressure is nearly double Earth's sea-level air pressure. The spectrometer saw these clouds using a 5.1 micron wavelength. Brightness levels in the original image were inverted to show cloud as bright features. Green is an image taken simultaneously at 1.6 micron wavelength, showing upper-level clouds near and above the altitude where atmospheric pressure equals Earth's sea-level air pressure, a pressure expressed as 1 bar. Blue is an image taken at 2.05 micron, a wavelength which is limited to showing only higher cloud level due to absorption of light by the hydrogen gas comprising the bulk of Saturn's atmosphere. Blue indicated clouds of an altitude where atmospheric pressure is only about 70 percent of Earth's sea-level air pressure. Thus, the aqua-colored feature over the equator is high-altitude haze residing 10 kilometers (6 miles) altitude above the typical zonal features seen in reflected sunlight over the planet (green).
The image on the left shows only the upperatmosphere above the 1-bar level, and is the view seen in reflected sunlight as observed by cameras not capable of seeing the thermal radiation of Saturn. Red in this image was taken at 2.79 micron, a wavelength that absorbs ammonia. The greenish appearance of the south pole indicates that ammonia gas is enhanced there.
As opposed to the uniform bands of hazes and clouds seen over the planet at pressures near and less than 1 bar, clouds at the 2-bar level (red, in right-hand image) are distinct, and come in a variety of shapes and sizes.
Set 07, 2005
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