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Craters, craters everywhere on Saturn's moon Rhea CASSINI PHOTO RELEASE Posted: December 7, 2005
This view consists of 21 clear-filter images and is centered at 0.4 degrees south latitude, 171 degrees west longitude. The giant Tirawa impact basin is seen above and to the right of center. Tirawa, and another basin to its southwest, are both covered in impact craters, indicating they are quite ancient. The bright, approximately 40-kilometer-wide (25-mile) ray crater seen in many Cassini views of Rhea is located on the right side of this mosaic (at 12 degrees south latitude, 111 degrees west longitude). There are few signs of tectonic activity in this view. However, the wispy streaks on Rhea that were seen at lower resolution by NASA's Voyager and Cassini spacecraft, were beyond the western (left) limb from this perspective. In high-resolution Cassini flyby images of Dione, similar features were identified as fractures caused by extensive tectonism. Rhea is Saturn's second-largest moon, at 1,528 kilometers (949 miles) across. The images in this mosaic were taken with the Cassini spacecraft narrow-angle camera during a close flyby on Nov. 26, 2005. The images were acquired as Cassini approached the moon at distances ranging from 79,190 to 58,686 kilometers (49,206 to 36,466 miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of about 19 degrees. Image scale in the mosaic is 354 meters (1,161 feet) per pixel.
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 kilometers-wide (56-miles) and is located at 8.5 degrees south latitude, 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 kilometers (310 miles) of the large moon. Rhea is 1,528 kilometers (949 miles) across and is Saturn's second largest moon, after planet-sized Titan. The clear filter image was acquired with the wide-angle camera at an altitude of 620 kilometers (385 miles) above Rhea. Image scale is about 85 meters (280 feet) per pixel.
The crater's total diameter is about 50 kilometers (30 miles), 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. This is one of the highest-resolution images of Rhea's surface obtained during Cassini's very close flyby on Nov. 26, 2005, during which the spacecraft swooped to within 500 kilometers (310 miles) of the large moon. Rhea is 1,528 kilometers (949 miles) across and is Saturn's second largest moon, after planet-sized Titan. The clear filter image was acquired with the wide-angle camera at an altitude of 511 kilometers (317 miles) above Rhea. Image scale is about 34 meters (112 feet) per pixel. 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. |
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