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APOLLO 16 AS 16-4471.jpgAS 16-4469 and AS 16-4471 - Crater Messier "A" (stereo pair)69 visitenessun commento
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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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APOLLO 16 AS 16-4511.jpgAS 16-4511 - Crater "Rays"55 visiteThis picture shows the striking bilateral symmetry of the rays of a small (2-Km diameter) crater in the floor of the large crater Daguerre in Mare Nectaris. Continuous areas and narrow filaments of light-gray ejecta extend from the crater across the dark mare surface through 270°, but are entirely absent in the southern 90° sector. Within the crater, dark material occurs on the southern crater wall while the remaining walls are bright. (The reader may wonder about the material whose reflectivity cannot be observed because it lies in shadow on the East wall of this crater. Until the area is observed under high Sun conditions, we are forced to make the simplifying assumption that it is bright because most of the materials visible elsewhere in the walls are bright).
This crater probably resulted from the impact of a projectile traveling from South to North along an oblique trajectory.
Its pattern of ejecta distribution is similar to that of small craters produced by the impact of missiles along oblique trajectories at the White Sands Missile Range, N. Mex. Some observers postulate that the dark material is a talus deposit of mare material that has fallen into the crater.
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APOLLO 16 AS 16-4530.jpgAS 16-4530 - Seconday impact craters, faults and rifles56 visiteLinear features of external and internal origin are contrasted in this area of Southernmost Mare Tranquillitatis.
The North-trending line of overlapping, very irregular craters along the East edge of the picture is clearly a chain of secondary impact craters. Its trend is radial to Theophilus, a large crater of early Copernican age that lies about 105 Km south of this area. The flaring shapes of some of the craters and their state of preservation also suggest that Theophilus is the primary crater. The narrow, straight rifle or graben that extends westward across the picture is clearly of internal origin. It formed when tensional forces ruptured the crust, causing the floor of the rifle to subside along faults.
Straight rifles are commonly the sites of volcanic cones or of blankets of volcanic ejecta; however, there are no signs of volcanism here that can be related to this rifle.
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APOLLO 16 AS 16-4531.jpgAS 16-4531 - Teophilus' "Peak"55 visiteA detailed view of part of the central peak complex of Theophilus. Central peaks are typical of most young, large impact craters on the Moon-and also of many manmade craters on Earth. From experimental data using controlled explosions, central peaks are known to consist of bedrock originally lying below the crater floor that, during the explosion, was uplifted, faulted, and folded by shock wave action. The irregular light-toned mountainous mass projecting above the floor of Theophilus is split into at least three enormous blocks separated by V-shaped structural valleys. Four or five circular craters without a prominent raised rim are located near or at the bases of the steep slopes. If these craters are endogenic vents rather than impact craters, their presence further suggests structural control along major fault planes. The planar walls of the northwest-trending valley contrast with other sloping surfaces of the central peak complex. They are steeper and, except for a few outcrops of protruding bedrock, are marked by linear grooves not unlike slickensides on many fault planes on Earth. Rock chutes do not seem to be a likely explanation for the grooves because there are no talus deposits or blocks at their lower ends. The debris cover is thin enough along the southern valley wall (top of picture) to show that the southern mountain block consists of layered rocks-at least five thick, light-toned layers alternate with thin, dark layers.
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APOLLO 16 AS 16-4559.jpgAS 16-4559 - Kant "P" Crater and its "inner" crater56 visiteKant "P" is a medium-sized crater located in the central highlands on the Moon's Near-Side. About 5,5 Km in diameter, its overall shape is not in the least unusual. However, the younger, small pear-shaped crater on Kant "P"'s North wall is an excellent example of the controlling effect that topographic relief plays on the shape of an impact crater. Because the small crater was formed on a steeply sloping surface, its ejecta was deposited chiefly downslope and formed a broad rim. The original rim and wall on the upslope side have been obliterated by slumping.
The slumping has left a landslide scar and has caused talus and scree to be deposited in the lower part of the crater.
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APOLLO 16 AS 16-4653.jpgAS 16-4653 - Secondary Craters' Clusters54 visiteThese 3 clusters of secondary craters (see arrows) are on the East flank of the larger crater Ptolemaeus near the center of the Moon's Near-Side. Each cluster has a ridged and hummocky appearance. The primary crater has not been identified in this case, but the configuration of the clusters tells us that it must be to the South of Ptolemaeus. Note that the South-facing side of each cluster is more sharply defined than the North-facing side.
This is a consequence of the oblique trajectory of impacting fragments that causes the ejecta of the secondary craters to be propelled away (down range) from the primary crater. Observations of manmade impact craters have shown that the individual fragments within a cluster of secondary debris strike the surface nearly simultaneously.
In the process, ejecta from one secondary collides and interferes with ejecta from adjacent craters, producing a ridged and hummocky surface.
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APOLLO 16 AS 16-5006 (1).jpgAS 16-5006 - Details of King Crater (1)55 visiteHere is an enlarged vertical view of more flow lobes inside King Crater. Fine lineations radial to King are prominent in the ejecta blanket behind (South-East of) the lobate fronts. The term "deceleration lobe" has been applied because the lobes occur only where the ejecta slowed down and came to rest on slopes that face toward King. They resemble terrestrial rock avalanche deposits that came to rest after climbing a small slope. Some lobes overlap each other outward like shingles.
The sketch (2) shows what would probably be seen in a cutaway view. The arrow shows the direction of movement of the ejecta over the old landscape.
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APOLLO 16 AS 16-5006 (2).jpgAS 16-5006 - Sketch of the details of King Crater (2)53 visitenessun commento
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APOLLO 16 AS 16-5410.jpgAS 16-5410 - Number "8"54 visiteThis 18-km-long ''figure 8" pair of noncircular craters near the crater Guericke probably was not formed by hypervelocity impacts of bodies from space. It could be a secondary impact feature formed by projectiles from the Imbrium Basin, 700 Km to the North. The terrace at the base of the crater walls could be debris from the walls or a "bathtub ring" left by a formerly higher stand of the mare fill. Alternatively, the crater pair and the terrace could have been formed by volcanic eruptions.
The superposed bright crater is younger than and unrelated to either the "figure 8" pair or the mare.
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APOLLO 16-0692.jpgAS 16-0692 - Teophilus Crater54 visiteTheophilus is a relatively young crater similar in size but slightly older than Copernicus. It lies on the eastern edge of the Kant Plateau, an elevated area in the Central Highlands along the northwestern margin of Mare Nectaris. Part of Nectaris is visible as the smooth, dark area near the horizon at the left edge. Like Copernicus and Aristarchus, Theophilus has ruggedly terraced walls and a complex central peak protruding through a level floor. Smooth-surfaced material is present in "pools" at various levels on the terraces, on parts of the crater floor, and on the ejecta that blanket the near (North) side of the crater.
As one alternative, the pools may have been emplaced as fluid lava.
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APOLLO 16-4136-A.jpgAS 16-4136 - Cratered Region near Mandel'shtam (1)56 visiteThis view looks southward near Mandel'shtam on the Lunar Far-Side. Most young lunar craters wider than about 40 Km have flows on their rims that resemble lava flows or mud flows on Earth. The unnamed crater near the top is about 14 Km wide and was recognized by H. J. Moore (1972) as being the smallest crater known to have such flows. Flows in the middle of the picture surged downhill off the high rim of the crater making lobes and tongues and leaving behind drained channels with levees.
In the area to the right of the crater, enlarged in the next frame, are some thin lobate flows that apparently rode over small hills, as if these flows were propelled outward from the crater with sufficient velocity to climb the hills. Ejecta deposits farther than about 1 Km from the rim are radially lineated and are smoother than the ground immediately surrounding the crater. The crisp, blocky zone around the crater is typical of many fresh craters.
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