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Astronomie - Saturn-Monde im Focus von Cassini

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The Odd Trio
The Cassini spacecraft captures a rare family photo of three of Saturn's moons that couldn't be more different from each other! As the largest of the three, Tethys (image center) is round and has a variety of terrains across its surface. Meanwhile, Hyperion (to the upper-left of Tethys) is the "wild one" with a chaotic spin and Prometheus (lower-left) is a tiny moon that busies itself sculpting the F ring.
To learn more about the surface of Tethys (660 miles, or 1,062 kilometers across), see PIA17164. More on the chaotic spin of Hyperion (168 miles, or 270 kilometers across) can be found at PIA07683. And discover more about the role of Prometheus (53 miles, or 86 kilometers across) in shaping the F ring in PIA12786.
This view looks toward the sunlit side of the rings from about 1 degree above the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 14, 2014.
The view was acquired at a distance of approximately 1.2 million miles (1.9 million kilometers) from Tethys and at a Sun-Tethys-spacecraft, or phase, angle of 22 degrees. Image scale is 7 miles (11 kilometers) 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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Tethys' Terrains
Tethys' trailing side shows two terrains that tell a story of a rough past. To the north (up, in the image) is older, rougher terrain, while to the south is new material dubbed "smooth plains" by scientists.
The smooth plains are roughly antipodal to the large impact crater Odysseus. Odysseus, which is on the far side of Tethys (660 miles, or 1,060 kilometers across) from this perspective, is out of view. (See PIA12588 for a view of Odysseus.) It's thought that the impact that created Odysseus also created the smooth plains, although exactly how this happened is not yet clear.
This view looks toward the trailing hemisphere of Tethys. North on Tethys is up and rotated 2 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Nov. 27, 2013.
The view was obtained at a distance of approximately 1.1 million miles (1.8 million kilometers) from Tethys. Image scale is 7 miles (11 kilometers) per pixel.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. 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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The tumbling and irregularly shaped moon Hyperion rotates away from the Cassini spacecraft in this movie taken during a distant encounter in Dec. 2005. A shadow closes over the large crater at bottom as the movie progresses.
Hyperion (280 kilometers, or 174 miles across) is covered with closely packed and deeply etched pits. The warming action of the Sun on water ice lying beneath a darkened layer of surface material apparently has deepened and exaggerated the depressions already created by impacts.
Cassini scientists now think that Hyperion’s unusual appearance can be attributed to the fact that it has an unusually low density for such a large object, giving it weak surface gravity and high porosity. These characteristics help preserve the original shapes of Hyperion’s craters by limiting the amount of impact ejecta coating the moon’s surface. Impactors tend to make craters by compressing the surface material, rather than blasting it out. Further, Hyperion’s weak gravity, and correspondingly low escape velocity, means that what little ejecta is produced has a good chance of escaping the moon altogether.
Quelle: NASA
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