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The ejecta from large impacts can include large blocks of material that reimpact the surface to form secondary impact craters. The youngest lavas erupted within Oceanus Procellarum, whereas some of the oldest appear to be located on the farside. Because Apollo and Luna landing sites (all Nearside) were chosen for safety reasons or as geologically interesting but unrepresentative, their regional sampling of the Moon is biased. Although the energy resolution of the Apollo proportional counters was low, important results were obtained, such as the enhancement of Al/Si in the lunar highlands relative to the mare. Hence, for this mechanism to efficiently remove CO from the upper atmosphere, the mixing of CO throughout the atmosphere should be an efficient process. Additionally, the ejecta from oblique impacts show distinctive patterns at different impact angles: asymmetry starting around 60˚ and a wedge-shaped "zone of avoidance" free of ejecta in the direction the projectile came from starting around 45˚.[10]. The craters are formed when a solid body, such as an asteroid or comet, collides with the surface at a high velocity (mean impact velocities for the Moon are about 17 km per second). August Moon Highlands 107 Highlands Road Fareham PO15 6HZ 01329 845635. Features at 2.2, 7.5, and 9.7 keV are intrinsic to the detector. This clustering has led to the concept of a “lunar cataclysm” or a spike in the collisional history at that time. These provide a random sampling of the surface but display no impact melts older than 3.92 billion years, supporting the notion of a “cataclysm” although the storage for several hundred million years and supply of the massive impactors poses some interesting problems. The terrestrial rate is for the past 200 million years. This may result from a difference in albedo (the maria are darker than the highlands), radio emissivity and/or the microwave opacity. The problem with this scenario is that extrapolation from the rate at 3.8 billion years back to 4.5 billion years results in the accretion of a Moon several orders of magnitude larger than observed. 4b). Around 3.8 billion years ago they declined rapidly to roughly the present rate. On the Moon, surfaces are either densely covered by large craters (lunar highlands) or sparsely affected by large craters (maria) with no surfaces of intermediate crater densities. The lunar highlands/mare albedo ratio is almost a factor of 2 on the Moon, but it is only a factor of 1.4 on Mercury. This is succeeded by a rarefaction wave, which is responsible for propelling most of the ejecta out of the crater. Plagioclase feldspar is mostly found in the lunar crust, whereas pyroxene and olivine are typically seen in the lunar mantle. The Apollo 17 mission landed in an area in which the material coming from the crater Tycho might have been sampled. The surface has also experienced space weathering due to high energy particles, solar wind implantation, and micrometeorite impacts. [7] Some of the most important craters used in lunar stratigraphy formed in this recent epoch. Starting about 4.5 billion years ago,[4] the newly formed Moon was in a molten state and was orbiting much closer to Earth resulting in tidal forces. A substantial portion of the lunar surface has not been explored, and a number of geological questions remain unanswered. For example, the topography associated with the Orientale Basin (Fig. Gradually the crater and its ejecta undergo impact erosion from micrometeorites and smaller impacts. Only a few percent of the farside has been affected by mare volcanism. The July 2001 Chandra observations also provide the first remote measurements that clearly resolve discrete K-shell fluorescence lines of O, Mg, Al, and Si on the sunlit side of the Moon (see Fig. The oldest of the Mg-suite rocks have crystallization ages of about 3.85 Ga. Other than having a similar composition, the atmospheres are very different. Larger craters generally display slumping features along the inner walls that can form terraces and ledges. Lunar meteorites total ∼11.2 kg, much less than the 382 kg of Apollo and Luna material, but they provide very important lunar information. At least the smooth plains may be low iron or alkali basalts. The impact process excavates high albedo materials that initially gives the crater, ejecta, and ray system a bright appearance. An example of a sinuous rille exists at the Apollo 15 landing site, Rima Hadley, located on the rim of the Imbrium Basin. Welcome to the August Moon Highlands. The highlands are older than the visible maria, and hence are more heavily cratered. The Moon lacks a true atmosphere, which eliminates erosion due to weather; it does not have any known form of plate tectonics, it has a lower gravity, and because of its small size, it cooled more rapidly. Color ratios of lunar and Mercurian crater rays also suggest that the surface of Mercury is low in Ti4+, Fe2+, and metallic iron compared to the surface of the Moon. The amount of erosion experienced by a crater was another clue to its age, though this is more subjective. Cooling leads to stresses, crustal fracturing, and basin subsidence. The difference in color indicates the concentration of titanium that the rock has, with the green particles having the lowest concentrations (about 1%), and red particles having the highest concentrations (up to 14%, much more than the basalts with the highest concentrations). The two younger stratigraphical units can be found in crater sized spots on the Moon. In addition, three robotic Soviet Luna spacecraft returned another 326 grams (11.5 oz) from 1970 to 1976. After crystallization was about 75% complete, less dense anorthositic plagioclase feldspar crystallized and floated, forming an anorthositic crust about 50 km in thickness. They are richer in iron than terrestrial basalts, and also have lower viscosities. This is the Eratosthenian unit. These differences in albedo suggest that there are systematic differences in the surface composition between the two bodies. FIGURE 4. Relative concentration of various elements on the lunar surface (in weight %), Relative concentration (in weight %) of various elements on lunar highlands, lunar lowlands, and Earth, Yu. Very early on, cratering rates were high. Since the iron content of lavas is thought to be representative of their mantle source regions, it is estimated that Mercury's mantle has about the same FeO content (<6 weight percent) as the crust, indicating Mercury is highly reduced with most of the iron in the core. The average bulk density of the lunar highlands crust is 2,550 kilograms per meter cubed, which is 12 percent lower than generally assumed. The power of the reflected and fluoresced X-rays observed by ROSAT in the 0.1- to 2-keV range coming from the sunlit surface was determined to be only 73 kW. The mafic impact melt breccias, which are typified by the low-K Fra Mauro composition, have a higher proportion of iron and magnesium than typical upper crust anorthositic rocks, as well as higher abundances of KREEP. Computer simulations indicate that the cumulative thickness of materials ejected from major craters in the lunar highlands is 2–10 km. The atoms that compose the solar wind – mostly helium, neon, carbon and nitrogen – hit the lunar surface and insert themselves into the mineral grains. [15] These lunar pits are found in several locations across the Moon, including Marius Hills, Mare Ingenii and Mare Tranquillitatis. On both planets, CO2 gas is photodissociated (molecules are broken up) by sunlight at high altitudes into carbon monoxide (CO) and oxygen (O). A microwave image of the full Moon reveals that the maria are ∼5 K warmer than the highlands. All solid bodies in the solar system are subject to impact by asteroidal and cometary debris. Basin-sized impacts will have also affected any existing atmosphere, hydrosphere, and potential biosphere. The regolith contains rocks, fragments of minerals from the original bedrock, and glassy particles formed during the impacts. However, a low angle impact can produce a central peak that is offset from the midpoint of the crater. Although the initial Apollo-era analyses suggested a crustal thickness of about 60 km at this site, recent reanalyses of this data suggest that it is thinner, somewhere between about 30 and 45 km. However, this was before the GX5-1 data were acquired, which clearly show lunar night side X-rays from the early morning (trailing) hemisphere as well. The identification of these mineral fragments led to the bold hypothesis that a large portion of the Moon was once molten, and that the crust formed by fractional crystallization of this magma ocean. This suggests a low ilmenite (FeTiO3) content, the mineral that is largely responsible for the dark appearance of the lunar maria. Another significant component of the crust are the igneous Mg-suite rocks, such as the troctolites, norites, and KREEP-basalts. The most distinctive aspect of the Moon is the contrast between its bright and dark zones. This is likely caused by surface topography, which causes permanent shadowing at high latitudes and transient effects in the equatorial regions, where crater floors and hillsides are alternately in shadow and sunlight as the day progresses. The reaction CO + OH → CO2 + H frees up H, which eventually may lead to the formation of hydrogen peroxide (H2O2), a strong oxidizer. The upper curve is for the day side hemisphere (when Venus is near superior conjunction), the lower curve is for the night side hemisphere (when Venus is near inferior conjunction). However, it is unlikely that a causal relationship exists between the impact event and mare volcanism because the impact basins are much older (by about 500 million years) than the mare fill. When you look at the moon through binoculars or a small telescope, the first thing you notice is that the lunar … Alternatively, it is possible that on airless bodies such as the Moon, transient magnetic fields could be generated during impact processes. Furthermore, Oceanus Procellarum, which is the largest expanse of mare volcanism on the Moon, does not correspond to any known impact basin. By following these meandering rilles back to their source, they often lead to an old volcanic vent. 5). Dust storms prevail in Mars’ lower atmosphere, and the formation of OH in such storms occurs close to the surface where the water abundance is highest. As we just saw, the most densely cratered surfaces formed prior to 3.8 billion years ago, and the cratering rate has been roughly constant since that time. The major products of volcanic processes on the Moon are evident to Earth-bound observers in the form of the lunar maria. At the bottom of the lunar stratigraphical sequence the pre-Nectarian unit of old crater plains can be found. Many of the lunar basalts contain small holes called vesicles, which were formed by gas bubbles exsolving from the magma at the vacuum conditions encountered at the surface. The Apollo program brought back 380.05 kilograms (837.87 lb) of lunar surface material,[16] most of which is stored at the Lunar Receiving Laboratory in Houston, Texas, and the uncrewed Soviet Luna programme returned 326 grams (11.5 oz) of lunar material. This recombination proceeds faster in the presence of chemistry involving hydroxyl radicals (OH), derived from water vapor. At short wavelengths, one probes approximately down to Venus’ cloud layers.

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