The Scientific Context for Exploration of the Moon (2007) / Chapter Skim
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3 Science Concepts and Goals
3 Science Concepts and Goals
Pages 20-46
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From page 20... ...
The heavily cratered surface of the Moon testifies to the importance of impact events in the evolution of terrestrial planets and satellites and the exceptional ability of the lunar surface to record them all. Lunar bombardment history is intimately and uniquely intertwined with that of Earth, where the role of early intense impacts and the possible periodicity of large impact events in the recent past on the atmosphere, environment, and early life underpin our understanding of habitability.
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From page 21... ...
X X X 1e. Study the role of secondary impact craters on X crater counts.
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From page 22... ...
8d. Learn how water vapor and other volatiles are X released from the lunar surface and migrate to the poles where they are adsorbed in polar cold traps.
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From page 23... ...
and major impact basins within the SPA Basin will probably resolve this issue. The precision required to date these events accurately requires isotopic analysis of well-chosen samples in terrestrial laboratories.
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From page 24... ...
Traditionally the lunar chronostratigraphic systems are based on ejecta blankets of large impact craters and basins that serve as marker horizons similar to terrestrial fossil or ash layers. These impact basins and young craters are stratigraphic benchmarks that allow the global determination of the relative age of lunar surfaces that have not been or cannot be directly accessed.
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From page 25... ...
However, other groups argued that Zunil might only be a special case, not representative for lunar impact craters in general, and that secondary craters can easily be detected and omitted from crater counts. Detailed studies of young lunar impact craters and the distribution and number of their secondary impact craters will help to better understand the process of secondary impact cratering and its possible effects on crater statistics.
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From page 26... ...
One possibility is that this boundary could represent the maximum depth of the lunar magma ocean, and an Al- and Mg-rich primitive mantle exists below 500 km. In this case all the Al in the primordial lunar crust must have been extracted from the upper mantle, and much of the mare basaltic magmatism must have involved melting above 500 km.
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From page 27... ...
, and understanding the processes responsible for lunar magnetism hold similar promise. Studies of lunar crustal magnetism could provide a powerful tool for probing the thermal evolution of the lunar crust, mantle, and core, as well as the physics of magnetization and demagnetization processes in large basin-forming impacts.
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From page 28... ...
Remelting of the mantle cumulate package drove fire-fountaining, lava flows, and plutonic emplacement, while large impact craters excavated and distributed the KREEP layer over the lunar surface. In this very simplified model, the composition of the crust has been thought of as generally homogeneous at any point on the Moon, modified only by thin, surface basalt flows or later impacts that scrambled the upper crust (regolith)
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From page 29... ...
and may represent the primary lunar crust, more tightly bounding researchers' calculations of the magma ocean process and lunar bulk composition. Scence Goal 3b -- Inventory the variety, age, distribution, and origin of lunar rock types.
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From page 30... ...
The concept of the lunar magma ocean depends to a large extent on understanding the composition and structure of the lunar crust and the bulk composition of the Moon. Key to this understanding is knowing the distribution and volume of plagioclase, mafic rocks, and incompatible-element rich rocks (KREEP)
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From page 31... ...
Significant admixture with lunar soil, or the presence of alternating layers of soil and ice, would not necessarily be detected 1The lunar surface temperature in nonpermanently shaded regions varies night to day from about 100 K to 400 K
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From page 32... ...
. Scientific understanding of the lunar atmosphere and the behavior of molecules on the lunar surface will be important in understanding the potential for lunar contamination from the re source extraction processes.
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From page 33... ...
Based in part on studies of polar temperatures and the expected surface distribution of the polar volatiles, it has been suggested that the hydrogen is mostly composed of water ice. If the polar deposits are dominantly composed of cometary or asteroidal material, one may additionally expect that other volatile elements or compounds would be present in the lunar cold traps.
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From page 34... ...
Solar wind directly illuminates the cold traps, and solar wind gas can be trapped, as it is trapped in lunar equatorial soil that experiences temperatures as high as 400 K Comets, wet asteroids, and interplanetary dust particles can contribute their water and other volatiles through transport and trapping to the poles, or by direct impacts into the permanent shade.
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From page 35... ...
The host of physical changes that occur as the lunar surface is exposed to space weathering can be studied using polar soil that weathers at extremely low temperatures. For example, the extremely low temperatures may inhibit the formation of glass that is ubiquitous elsewhere on the Moon.
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From page 36... ...
Concept 5: Lunar volcanism provides a window into the thermal and compositional evolution of the Moon. As discussed in Concept 3, understanding of lunar crustal evolution has been tied for many years to somewhat simplified models of the lunar magma ocean, which explained global trends in crustal composition but left many questions unanswered at regional and local scales.
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From page 37... ...
Within the existing sample collection, the range of volcanic glass compositions is large, and it is likely that this range will expand even further as new deposits are sampled and their composition and age are assessed. Because of the role of pyroclastic deposits in approximating primary magmas, more examples of these deposits will provide information on the depth of the magma ocean, the character of the lunar mantle, and of course the nature of the mare basalt source regions.
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From page 38... ...
. The large number of lunar impact craters over a wide range in diameters provides the basis of statistically sound investigations, such as, for example, depth/diameter ratios, which in turn have implications for the possible layering and strength of the lunar crust but can also be extrapolated to other planetary bodies.
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From page 39... ...
Lunar impact craters provide direct information about the excavation, transport, and deposition of materials by a major impact event. SOURCE: NASA Apollo 17 AS17-M-2444.
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From page 40... ...
Together with field observations and drilling data, such studies revealed that central peaks of complex craters are the product of uplift of deeper target lithologies. For terrestrial craters with diameters between 4 km and 250 km, the amount of uplift can be expressed by a simple power law.
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From page 41... ...
Deposition of ejecta is an important factor in the mixing of lunar surface materials. Because this process is very complex on the scale of individual samples, there is only limited consensus on the nature and absolute extent of such mixing.
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From page 42... ...
The probability of finding meteorites from the ancient Earth will be greater in regoliths of older age. Sampling of these ancient regolith layers can be carried out by drilling through interspersed volcanic rock and regolith or by collecting rocks in the walls of impact craters or along rilles.
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From page 43... ...
Science Goal 7d -- Separate and study rare materials in the lunar regolith. The regolith collects fragments of rocks that come to the Moon as meteorites as well as impact ejecta from across the lunar surface.
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From page 44... ...
Several landers would be advantageous, since not every point on the lunar surface experiences the same conditions -- for example, locations near the poles will be quite different from those nearer the equator. Astronauts could be used to distribute a network of sensors on the lunar surface.
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From page 45... ...
Science Goal 8d -- Learn how water vapor and other volatiles are released from the lunar surface and migrate to the poles where they are adsorbed in polar cold traps. Evidence for volatile species, including H2O, CO, CO2, and CH4, was found sporadically by Apollo sensors, but these detections remain unconfirmed.
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From page 46... ...
Later, as rocket traffic and human activities perturb the lunar atmosphere from its native state, studies of the environmental effects of human and robotic activity would be highly illuminating, as an "active experiment" in planetary-scale atmospheric modification. Before extensive human and robotic activity alters the tenuous lunar atmosphere, it is important to understand its composition, transport mechanisms, and escape processes.
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