| Piú viste - MOON |
APOLLO 17 AS 17-149-22838.jpgAS 17-49-22838 - Crater Chain (Far-Side)53 visiteThis oblique view taken with the Hasselblad camera shows a crater chain on the Far-Side, about 500 Km North of Tsiolkovsky. For an idea of the scale, the large crater near the upper left corner is about 26 Km wide. The origin of this chain is controversial. To some geologists, the irregular shape of many of the craters suggests that the chain was formed by the impact of a stream of ejecta from a large primary crater. The presence of herringbone ridges would have strengthened this interpretation, but none are visible; perhaps the high Sun angle and the oblique viewing angle of this scene have obscured them. To others the simple geometry of the chain suggests a volcanic origin. However, there is an apparent lack of faulting to control the alinement of the craters and an apparent absence of a blanket of volcanic ejecta.
The origin of this chain may not be decipherable until, and unless, additional photography becomes available.
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APOLLO 17 AS 17-3107.jpgAS 17-3107/3105/3103 - Euler Crater (HR)53 visiteParts of 3 frames from the Apollo 17 PanCam were mosaicked to form this HR view of the crater Euler, in South-Western Mare Imbrium (an exceptionally fine example of a young mediumsized crater). 27-Km in diameter, Euler has most of the features that typify young craters in this size range. Its sharp rim shows little evidence of rounding. A solid blanket of ejecta is visible for approximately 1/2 crater diameter outside the rim and the radial pattern of secondary craters, crater clusters, ridges and grooves is visible outward to a full crater diameter.
Terraces formed by slumping of the steep crater walls, probably contemporaneously with the formation of the crater, are clearly evident. The steepness of the walls and the fact that the crater floor is below the level of the surrounding mare surface indicate that relatively little erosion and infilling have occurred. Other features typical of medium-sized craters are the central peak and the level floor surrounding the central peak. The pattern of ejecta around Euler is notably asymmetric because the area was later flooded by mare lavas that inundated parts of the ejecta blanket and other ejecta features.
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APOLLO 16 AS 16-1973.jpgAS 16-1973 - The "Davy Crater Chain"53 visiteThe Davy Crater Chain (arrow) is one of the most spectacular chains of craters on the Moon. It extends for about 50 Km across the floor of the large, very old crater Davy "Y" and onto its eastern rim. The chain may be related in origin to the pair of irregular craters Davy "G" and Davy "GA", 75 Km from the furthest end of the chain.
Two origins have been proposed: some lunar geologists believe it is a chain of secondary impact craters and others believe it is a line of volcanic craters. The simple geometry of the Davy Chain, the symmetry and uniform spacing of its individual craters and its alinement with Davy "G", strongly support, in my opinion, a volcanic origin. Also arguing against a secondary impact origin is the fact that the Davy Chain is a lone feature. There are no other similar chains with this trend in the area. Secondary crater chains tend to occur in large numbers within the belt of secondary craters surrounding a large primary crater.
On Earth some rocks from deep within the crust have been brought to the surface through volcanic orifices, thus providing a means of studying material that would otherwise be inaccessible. For this reason the Davy area was once seriously considered as a landing site. However, when the originally planned number of Apollo missions was reduced, the Davy area was one of those eliminated.
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APOLLO 17 AS 17-3072.jpgAS 17-3062 - Timocharis Crater53 visiteThis oblique view of the crater Timocharis in Southe-Eastern Mare Imbrium illustrates how the original diameter of a crater is enlarged by slumping of its walls. Its present diameter is about 35 Km. The sparsity of small superposed craters on the walls of Timocharis - in contrast to their density on its floor and rim - is caused by the erosive effect of downslope movement of material on the steep walls. Timocharis, like many other young impact craters of similar size, possesses a well-defined central peak complex. Such structures are believed to result from elastic rebound of the bedrock immediately after the impacting event. However, the central peak of Timocharis apparently has been substantially modified by a large superimposed crater.
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APOLLO 15 AS 15-9866.jpgAS 15-9866 - Jansen "B" Crater53 visiteHigh Sun views such as this often show fascinating dark and bright patterns that would be overwhelmed by highlights or shadows if the Sun were lower in the sky. This view of the 17-Km-wide crater Jansen "B" shows numerous bright avalanche deposits on the steep crater walls, apparently originating at outcrop ledges near the top of the wall. Most avalanches stop in a moat at the base of the wall, but a few in the foreground extend out onto the irregular, inward- sloping floor.
The floor is a jumble of slump blocks.
Avalanching appears to be a major means of erosion on steep lunar slopes.
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APOLLO 15 AS 15-9874.jpgAS 15-9874 - Dawes Crater53 visiteThis is a near vertical view of the crater Dawes, 18 Km in diameter. Morphologically it is typical of many lunar craters in the 15- to 20-Km size range. It lacks terraced walls and distinct central peaks but has an extremely rough floor. Small terracelike structures on the crater floor (upper left, lower right) occur where the wall is bowed outward and probably represent slump deposits where portions of the crater wall have collapsed into the crater. Local stratigraphy is revealed in the walls of the crater, and material of different albedo is seen streaming down into the crater from various levels. The dark layer clearly visible in the upper part of the crater wall represents the thin mare deposits in this part of Northern Mare Tranquillitatis. The lighter gray material below it is a combination of underlying submare material and talus from units higher on the crater wall. The highest unit (white and gray) probably represents the ejecta blanket and may consist primarily of lighter lunar crustal material excavated from beneath the mare.
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APOLLO 17 AS 17-3081.jpgAS 17-3081 - Pytheas Crater (HR)53 visiteThe Apollo 17 Panoramic Camera provided this high-resolution, enlarged view of the South Wall of Pytheas. Pytheas is about the same size as Bessel, but is located in South-Central Mare Imbrium, almost 1100 km West of Bessel.
The outcrops in the walls of the two craters are remarkably similar.
These and the many other craters in mare areas that contain outcrops of dark horizontally layered rock demonstrate the moonwide uniformity of conditions in the upper part of the mare basins.
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APOLLO 17 AS 17-2265.jpgAS 17-2265 - Proclus Crater53 visiteThis oblique view looks South over the 26-Km-diameter crater Proclus in the highlands at the Western edge of Mare Crisium. Proclus is a young rayed crater that is distinctive because of the marked asymmetry of its ray system-a characteristic visible even in Earth-based telescopic views. The excluded zone is along the South-West edge (top of photograph) but is visible in this moderate Sun photo only as a slight albedo change. Laboratory experiments suggest that a low trajectory angle might account for the asymmetry. A number of large blocks can be seen at the edge of the crater rim. The exceptionally large block (arrow) is about 200 mt wide and, judging from the length of the shadow it casts, nearly as high. As in several other craters shown in this chapter, a darker layer is present in the upper part of the crater wall.
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97-SMART_1_impact_sites_mineralcolours.jpgThe "Impact Site" of SMART-1 (mineralogy)53 visitenessun commento
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APOLLO 15 AS 15-9299.jpgAS 15-9299 - Le Monnier Crater53 visiteOn January 16, 1973, the Soviet unmanned roving vehicle Lunokhod 2 was landed by Luna 21 in or near this area in the South-Eastern part of the crater Le Monnier. This crater is a large (61 Km) pre-Imbrian crater cut into terra at the Eastern edge of Mare Serenitatis before Serenitatis was flooded by mare laves. Part of Le Monnier's Southern wall fills the lower part of the picture. A conspicuous chain of elongate depressions has formed in the lava-filled floor of the crater. The chain trends 22 Km northward and its pattern is quite surely controlled by an underlying fracture system. Regionally, the inferred fracture system is concentric to the grossly circular Serenitatis Basin and in this area trends Northward. No comparably young structural features having the same trend cut the terrae surrounding Le Monnier. However, older structures having this trend occur in the southern and northern walls and rims of Le Monnier. The aligned depressions on the mare are mostly 300 to 400 mt wide and 30 to 60 mt deep. The three deepest stretches are 1 to 2 km long and about 50 to 65 m deep. These depressions probably were the locus of fissure eruptions of mare basalt. Withdrawal of the last lava back into the fissure may have created subsurface voids into which collapse took place, causing the depressions and accounting for the absence of raised rims on the depressions.
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APOLLO 17 AS 17-3125.jpgAS 17-3125 - Rimless crater53 visiteThe very young rimless crater near the center of this picture is located near the area where Oceanus Procellarum and Mare Imbrium join. The crater apparently formed in regolith-covered mare basalt. It differs from lunar impact craters of comparable size and age by its lack of a raised rim, surrounding ejecta deposit, or associated secondary impact craters. In addition, its interior walls do not show the steep slopes with craggy outcrops of rock in their upper parts, nor the streams of debris-avalanche deposits and talus that are usually seen in the walls of impact craters of comparable age and size.
Judging from the clear and sharply formed pattern of concentrically curved grooves and scarps that surround the hole, the material near this depression has apparently subsided into a subsurface void. Because of the extreme rarity and inferred short lifetime of steep slopes on the Moon, the latest subsidence must have taken place very recently, after most of the 50- to 300- m diameter craters that densely pepper the nearby mare surface were formed. Movement of the regolithic debris layer during subsidence apparently smoothed out most, if not all, of the craters that must have existed near the depression. Now the depression is surrounded by low, curved fault scarps and narrow, curved grooves that may be fault troughs (grabens) or may represent drainage of regolithic debris into cracks that opened in the underlying sagging basalt rock. The few craters that have formed on the subsided surface compare in density to the craters formed on the cluster (arrow) of Aristarchus secondary impact craters and associated herring- bone ridges; comparable ages for the Aristarchus secondary features and the depression are thus indicated. The subsidence was triggered either by the ground shock or seismic wavetrain generated when Aristarchus was formed 300 km to the west, or by the impacts of the secondary features.
The subdued depression in the upper left may be a similar older feature that was flooded by a later lava flow that now covers the area. The density of craters within the depression and the density on the surrounding lava are comparable. Alternatively, the subsidence there may have been incomplete; however, there is no sign that this subsidence is as young as that in the deeper crater
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APOLLO 16 AS 16-5410.jpgAS 16-5410 - Number "8"53 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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