| Risultati della ricerca nelle immagini - ""D"" |
APOLLO 16 AS 16-4502.jpgAS 16-4502 - The beautiful Isidorus "D"56 visiteThis oblique view of the crater Isidorus "D" was taken with the PanCam on Apollo 16. Isidorus "D" is about 15 Km in diameter and is located in the highlands between Mare Tranquillitatis and Mare Nectaris.
Evidence of avalanching (Howard, 1973) and of other types of downslope movement of material are clearly visible on the inner walls of the crater. The streaks resembling shooting stars on the left wall appear to be avalanche scars. The avalanches probably were spearheaded by large blocks followed by fine-grained material. On the near wall (arrow) a larger landslide terminates in a straight line against the relatively flat crater floor. In the shadowed part of the crater wall many short irregular benches or narrow terraces mark the tops of masses of slumped material. The brightness of the avalanche scars is an indication of their freshness; in general, freshly exposed lunar materials are brighter than undisturbed materials nearby.
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The_Rings-PIA11664.jpgSpiral Corrugation across the C and D-Rings56 visiteCaption NASA:"Alternating light and dark bands, extending a great distance across Saturn’s D and C-Rings, are shown here in these Cassini images taken one month before the Planet’s August 2009 Equinox.
The C-Ring stretches across the upper left and middle of the image. The D-Ring is barely visible amid the noise in the lower right of the image.
The periodic brightness variations in the Rings have a subtler, narrow appearance in this mosaic of three Cassini images than other larger features of the Rings, such as the Columbo Gap which appears as a black arc on the left of the center frame of the mosaic. These brightness variations are almost certainly caused by the changing slopes in the rippled Ring-Plane, much like the corrugations of a tin roof.
Although previous Cassini observations (see PIA08325) had revealed corrugations in the D-Ring extending over 500 miles (about 800 Km), this image shows these features extending for 6200 miles (about 10.000 Km) into the C-Ring.
Later Equinox images revealed the true dimension of this Corrugation, extending completely across the C ring, right up to the inner B-Ring edge for a total breath of about 17.000 Km (approx. 11.000 miles) -- see PIA11670 and PIA11671.
This and other new imagery supports earlier evidence that something dramatic happened in the early 1980s to initiate this feature.
In 2006, imaging scientists speculated that a collision with a comet or asteroid may have disturbed the D-Ring. That explanation seems less likely now that this and other new images show the effect spread over a much broader radial range, extending right up to the inner B-Ring. Scientists continue to investigate the cause of this disturbance.
Whatever caused the corrugation apparently tilted a vast region of the inner rings relative to Saturn’s gravitational field in a relatively short period of time during the early 1980s. In the intervening years, the natural tendency for inclined orbits to systematically and slowly wobble at different rates, depending on their distance from Saturn, has created a tightly wound spiral corrugation in the Ring-Plane.
This view looks toward the unilluminated side of the Rings from about 24° above the Ring-Plane.
The D-Ring has been brightened relative to C-Ring to enhance visibility.
The images were taken in Visible Light with the Cassini Spacecraft narrow-angle camera on July 11, 2009. The view was acquired at a distance of approx. 470.000 Km (about 292.000 miles) from Saturn and at a Phase Angle of 25°.
Image scale is roughly 2 Km (about 1,25 miles) per pixel".MareKromium
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