Saturn: the "Ringed Beauty" and His Moons
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Rhea-PIA07575.jpgTirawa Impact Basin on Rhea54 visiteThe giant Tirawa impact basin straddles the day and night boundary on Saturn's moon Rhea in this view from the Cassini spacecraft. The ancient basin is 5 Km deep in places, as measured in NASA Voyager images. The whole basin is about 360 Km across.
The prominent bright splotch to the southeast of Tirawa is ejecta from a fairly fresh crater. This view of Rhea (1.528 Km, such as about 949 miles across) reveals terrain slightly to the East of a similar Cassini view, released earlier (see Diversity of Impacts). The sunlit surface in this view is principally on the leading hemisphere of Rhea. North is up and rotated 13° to the left.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 13, 2005, at a distance of approx. 2 MKM (about 1,2 MMs) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 50°. Resolution in the original image was 12 kilometers (7 miles) per pixel. The image has been contrast-enhanced and magnified by a factor of two to aid visibility.
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Rhea-PIA07583.jpgRhea, from about 255.000 Km90 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.
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Rhea-PIA07606.jpgHalf-Rhea, in the darkness...55 visiteOriginal caption:"This half-lit view beautifully captures the ponderously old and cratered surface of Saturn's icy moon Rhea. The sunlit terrain shown here is on the moon's Leading Hemisphere, on the side of Rhea that always faces toward Saturn. North is up and rotated 20° to the left.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 21, 2005, at a distance of approximately 922.000 Km (about 573.000 miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 88°. The image scale is 6 Km (about 4 miles) per pixel".
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Rhea-PIA07614.jpgMimas, Rhea and the Rings54 visiteOriginal caption:"The Saturn moon Mimas is much smaller than Rhea, but the geometry of this scene exaggerates the actual differences in size. Here, Mimas is on the opposite side of the rings from Rhea and Cassini. Saturn's shadow slices across the Ring-plane here.
The view looks toward the Saturn-facing hemisphere on Mimas and the anti-Saturn hemisphere on Rhea.
The image was taken in visible light with the narrow-angle camera on Sept. 9, 2005, from a distance of approx. 1,5 MKM (about 900.000 miles) from Rhea. Mimas was located on the far side of the Rings, such as about 670.000 Km (approx. 420.000 miles) farther from Cassini. The image scale is roughly 9 Km (about 6 miles) per pixel on Rhea and 13 Km (about 8 miles) per pixel on Mimas".
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Rhea-PIA07686.jpgRhea (enhanced but real colors) from about 341.000 Km55 visiteOriginal caption:"This close view of Rhea prominently shows two large impact basins on the ancient and battered moon. The great age of these basins is suggested by the large number of smaller craters that are overprinted within them.
Terrain visible in this view is on the side of Rhea that faces away from Saturn. North on Rhea is up and tilted 30° to the left. This enhanced color view was created by combining images taken using filters sensitive to ultraviolet, visible green and infrared light.
The images were taken with the Cassini spacecraft narrow-angle camera on Dec. 23, 2005, at a distance of approximately 341.000 Km (approx. 212.000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 42°. The image scale is approx. 2 Km (a little more than 1 mile) per pixel".
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Rhea-PIA07689.jpgRhea54 visiteOriginal caption:"Scarred and battered Rhea fills the Cassini spacecraft's view. Notable here is the sharp relief of steep crater walls near the terminator.
Icy Rhea (1.528 Km --> 949 miles across) is Saturn's second-largest moon. This view shows terrain on Rhea's Trailing Hemisphere. North is up and rotated 22° to the left.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 24, 2005 at a distance of approximately 267.000 Km (such as 166.000 miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 59°. Image scale is 2 Km per pixel".
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Rhea-PIA07764.jpgRhea's "Ray Crater" (alias the "Great White Splat") and scarps from 511 Km54 visite(...) Cassini spacecraft snapped this image of the Eastern rim of Saturn's moon Rhea's bright, Ray Crater. The impact event appears to have made a prominent bright splotch on the Leading Hemisphere of Rhea. Because Cassini was traveling so fast relative to Rhea as the flyby occurred, the crater would have been out of the camera's field of view in any earlier or later exposure. The crater's total diameter is about 50 Km, but this rim view shows details of terrains both interior to the crater and outside its rim. The prominent bright scarp, left of the center, is the crater wall, and the crater interior is to the left of the scarp. The exterior of the crater (right of the scarp) is characterized by softly undulating topography and gentle swirl-like patterns that formed during the emplacement of the large crater's continuous blanket of ejecta material.
Numerous small craters conspicuously pepper the larger crater's floor and much of the area immediately outside of it. However, in some places, such as terrain in the top portion of the image and the bright crater wall, the terrain appears remarkably free of the small impacts. The localized "shot pattern" and non-uniform distribution of these small craters indicate that they are most likely secondary impacts -- craters formed from fallback material excavated from a nearby primary impact site. Because they exist both inside and outside the large crater in this image, the source impact of the secondary impacts must have happened more recently than the impact event that formed the large crater in this scene.
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Rhea-PIA07765.jpgCraters, Slopes and Scarps on Rhea (HR)54 visiteCraters within craters cover the scarred face of Saturn's moon Rhea in this oblique, HR view of terrain on the moon's Western Hemisphere.
A large, degraded crater lies at the center, filled with rolling mounds and many smaller craters. A couple of linear depressions are visible in the terrain (especially at lower right), possibly marking tectonic faults. The crater is about 90 Km-wide (about 56-miles) and is located at 8,5° South Latitude and 154,9 West Longitude. The moon's icy regolith, or loose surface material, has likely been pummeled into a fine powder over the eons.
This is one of the highest-resolution images of Rhea's surface obtained during Cassini's close flyby on Nov. 26, 2005, during which the spacecraft swooped to within 500 Km of the large moon.
The clear filter image was acquired with the wide-angle camera at an altitude of approx. 620 Km above Rhea.
Image scale is about 85 mt (approx. 280 feet) per pixel.
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Rhea-PIA07769.jpgRhea and Dione (false colors)54 visiteOriginal caption:"Saturn's cratered, icy moons, Rhea and Dione, come alive with vibrant color that reveals new information about their surface properties. To create these false-color views, ultraviolet, green and infrared images were combined into a single black and white picture that isolates and maps regional color differences. This "color map" was then superimposed over a clear-filter image of each moon. The combination of color map and brightness image shows how the colors vary across the moon's surface in relation to geologic features. The origin of the color differences is not yet understood, but may be caused by subtle differences in the surface composition or the sizes of grains making up the icy soil. (...) The images have not been scaled to show the moons' proper relative sizes".
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Rhea-PIA08120.jpgRhea, from 245.000 Km and in "extreme" false colors...54 visiteBright, wispy markings stretch across a region of darker terrain on Rhea. In this extreme false-color view, the roughly North-South fractures occur within strips of material (which appear greenish here) that are a different color from the surrounding cratered landscape. To create the false-color view, ultraviolet, green and infrared images were combined into a single black and white picture that isolates and maps regional color differences. Most of the large-scale variations in brightness across the surface are removed by this process. This color map was then superimposed over a clear-filter image. The origin of the color differences is not yet understood, but it may be caused by subtle differences in the surface composition or grain sizes making up the icy soil. Wispy markings were seen on the trailing Hemispheres of both Rhea and Dione, in images taken by Voyager spacecrafts, and were hypothesized by some researchers to be the result of material extruded onto the surface by ice volcanism.
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Rhea-PIA08121.jpgThe incoherent surface of Rhea54 visiteThis intense false-color view highlights and enhances color variations across the cratered and cracked surface of Saturn's moon Rhea.
To create the false-color view, ultraviolet, green and infrared images were combined into a single black and white picture that isolates and maps regional color differences. This "color map" was then superposed over a clear-filter image. The origin of the color differences is not yet understood, but it may be caused by subtle differences in the surface composition or grain sizes making up the icy soil.
This view shows terrain on the trailing hemisphere of Rhea. North is up.
The images were taken using the Cassini spacecraft narrow-angle camera on Jan. 18, 2006, at a distance of approx. 268.000 Km (about 166.000 miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of 115°. Image scale is about 2 Km (roughly 1,2 miles) per pixel.
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Rhea-PIA08146.jpgRhea and the Rings55 visiteCrater-scarred Rhea floats in the distance, peeking out from behind Saturn's partly shadowed Rings. This view looks upward from just beneath the Ring-Plane. The far side of the Rings is masked by Saturn's shadow.
The North Pole of Rhea is obscured by part of the A-ring and the sharply defined F-Ring.
A few bright wispy markings curl around the eastern limb of Rhea.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 22, 2006, at a distance of approx. 2,2 MKM (about 1,4 MMs) from Rhea. The image scale is about 13 Km (roughly 8 miles) per pixel on Rhea.
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