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The Scientific Context for Exploration of the Moon 5 Prioritized Lunar Science Concepts, Goals, and Recommendations According to the statement of task for the Committee on the Scientific Context for Exploration of the Moon (see Appendix A): The current study is intended to meet the near-term needs for science guidance for the lunar component of the Vision for Space Exploration…. [T]he primary goals of the study are to: Identify a common set of prioritized basic science goals that could be addressed in the near-term via the LPRP1 program of orbital and landed robotic lunar missions (2008-2018) and in the early phase of human lunar exploration (nominally beginning in 2018); and To the extent possible, suggest whether individual goals are most amenable to orbital measurements, in situ analysis or instrumentation, field observation or terrestrial analysis via documented sample return. The committee based its guidelines for setting science priorities on those outlined in the National Research Council’s decadal survey New Frontiers in the Solar System: An Integrated Exploration Strategy: Scientific merit (most important). This guideline includes the degree to which an activity will test or alter an existing paradigm or prevalent hypothesis, the question of whether or not the new knowledge will have a pivotal effect on future science endeavors, and whether the new knowledge is likely to expand the factual basis of our understanding significantly. Opportunity and realism for achieving a goal. This guideline addresses whether an activity is likely to produce the desired result in the time frame specified and whether the opportunity readily exists to address the goal. Technological readiness. This guideline concerns whether the technology necessary to carry out the activity is available or anticipated in the time frame specified. New Frontiers in the Solar System discusses and prioritizes individual mission concepts for the exploration of the solar system in different cost categories. In contrast, this committee does not have comparable guidelines or bounds on how science might be implemented on and for the Moon. It has no information on what resources might 1 The Lunar Precursor and Robotic Program (LPRP) was how robotic missions were identified in the NASA letter that requested this study. The LPRP terminology is no longer in use.
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The Scientific Context for Exploration of the Moon be available or when. The near-term robotic architecture for implementation of the Vision for Space Exploration (VSE) remains blank after the planned launch in the fall of 2008 of the Lunar Reconnaissance Orbiter (LRO). In identifying prioritized basic science goals as requested in its statement of task, the committee structured its prioritization along three lines: (1) prioritization of the science concepts presented in Chapter 3, (2) prioritization of science goals identified in Chapter 3, and (3) specific integrated high-priority findings and recommendations. The prioritization is based on the consensus of the members of the committee after detailed discussion in each of these three areas. Although the rationales for the prioritization of the items in these three areas are linked throughout the discussion of this report, the implementation requirements are described in broad terms for the science concepts and in more specific terms for the eleven highest priority science goals. The committee reiterates that its priorities and recommendations relate to the near-term implementation of the Vision for Space Exploration, which includes the robotic precursors and initial human excursions on the Moon. The committee sets out a candidate lunar research strategy for the near term in Box 5.1. Planning for and implementing longer-term scientific activities on the Moon are beyond the scope of this study. BOX 5.1 Candidate Lunar Research Strategy for the Near Term The discussions and deliberations of the Committee on the Scientific Context for Exploration of the Moon can be consolidated into a near-term candidate lunar science strategy, which would fit into the time interval 2010-2022, the period after the Lunar Reconnaissance Orbiter (LRO) mission but with some overlap of the early phases of the projected Lunar South Pole Outpost described in the preliminary (2006) NASA Lunar Architecture. The committee provides here a set of preliminary concepts for activities that could be implemented by NASA. The following, which are the five highest integrated science implementation priorities that emerged from committee discussions, could be addressed: Utilize information from Apollo and post-Apollo missions or upcoming lunar science missions (U.S., as well as international) to the fullest extent. This is a low-cost/high-return element of the lunar science program. Should there be a major series of failures among the missions now projected (see Chapter 4 of this report), fill the critical information gaps with a back-up lunar orbiter mission. Conduct a robotic landed mission to explore the lunar polar environment. Determine the nature and source of volatiles within shadowed craters near one of the lunar poles, assess lunar polar atmospheric properties, and emplace a geophysical package that could include seismometer and heat flow experiments. Emplace a geophysical network to include, at a minimum, seismic and heat flow experiments, environmental sensors, and new laser ranging retroreflectors. Such a program should be coordinated with those of other countries that are likely to include lunar landed missions in their space exploration strategies. The minimum number of landed sites should be four, more or less equidistantly placed, including at least one farside site (no retroflector required). Conduct two or more robotic sample-return missions: The unique nature of the South Pole-Aitken (SPA) Basin makes this area an appropriate first target for a sample-return mission to explore central locations of the SPA Basin (a two-lander scenario was studied as a New Frontiers mission in 2006). Proper placement of these missions could assess quite old mare basalt units and melt rocks from basins that formed within the SPA Basin subsequent to the SPA Basin event. Use technology developed for the SPA Basin sample-return mission to collect samples from the youngest volcanic terrain on the Moon. Many sites that are not likely to be visited soon by astronauts could be accessed with this capability, including missions that could be carried out after humans land on the Moon. Conduct detailed exploration of the lunar crust as exposed in or near a South Polar human lunar outpost. The South Pole is on the periphery of the SPA Basin, so correlation between these two areas of sample studies would be valuable. The human mission should include appropriate field investigations, geophysics, and atmospheric investigations and could follow up on the results of an earlier robotic mission, noted above, to a shadowed crater.
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The Scientific Context for Exploration of the Moon TABLE 5.1 Implementation Options for Highest-Priority Science Goals Science Goals Implementation (a) Information Extraction (b) Orbital Measurements (c) Sample Return (d) Landed Experiments,Instruments,and Rovers (e) Human Field work An enabling new framework for lunar exploration will be provided by data from SMART-1, SELENE, Chang’e, Chandrayaan-1, and LRO. The assumptionis that all missions and key instruments will be successful. Orbital measurements are not included in the complement of missions planned for launch by 2008. The assumption is that the four missions planned will return appropriate data as planned; if not, new measurements that provide similar high-priority compositional and geophysical data need to be acquired. The types of returned samples and of science analyses required are identified. These include science measurements for/from landed sites; category also encompasses penetrators/impactors. Science areas that specifically benefit from human capabilities are identified. 1a. Test the cataclysmhypothesis by determining the spacing in time of the lunar basins. Continue geochronology of impact-melt rocks in the Apollo and meteorite collections. Use remote sensing to help determine the regional geologiccontext of returned samples. Higher-resolution images to provide targeted crater counts on selected ejecta facies. Sample return from the SPA Basin melt sheetand from floors or ejecta of basins within the SPA Basin for detailed geochemical and isotopic analyses. Develop instrumentsfor precise, in situ geochronology. Use landed geochemical instrumentation to identify best samples for return. Identify and acquire samples of impact-melt rocks in the Nectaris basin. 1b. Anchor the earlyEarth-Moon impact flux curve by determining the age of the oldest lunar basin (South Pole-Aitken Basin). Search for SPA Basin materials in existing collection. Continue study of the ancient terrestrial crater record through fieldwork and zircon evidence. Higher-resolution images to provide targeted crater counts on ejecta of basins within the SPA Basin to bound a limit on the SP A Basin age. Sample return from the SPA Basin melt sheet and from floors or ejecta of basins within the SPA Basin for detailed geochemical and isotopic analyses. Develop instrumentsfor precise, in situ geochronology. Use landed geochemical instrumentation to identify best samples for return. Human geologic fieldwork increases chances of recognizing the best samples. 1c. Establish a precise absolute chronology. Compare new remote sensing data sets with Apollo-era data sets to detect formation of new craters. Higher-resolution images to provide targeted crater counts of undisturbed ejecta surfaces from, e.g., Orientale, Imbrium, and Copernicus. Sample return from key benchmark basins, craters (e.g., Copernicus, Tycho), and lava flows for precise isotopic dating. Develop instrumentsfor precise, in situ geochronology. Use landed geochemical instrumentation to identify best samples for return. Human geologic fieldwork increases chances of recognizing the best samples.
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The Scientific Context for Exploration of the Moon 4a. Determine the compositional state (elemental, isotopic, mineralogic) and compositional distribution (lateral and depth) of the volatile componentin lunar polar regions. Analyze existing and new data and integrate information (photometry, morphology, topography, temperature, hydrogen and surface frost distribution) from the polar regions to improve knowledge of volatile spatial distribution. High-spatial resolution distribution of volatiles on and in the regolith poleward of 70 degrees. Cryogenically preserved samples to determine the detailed elemental and isotopic composition of soils from permanently shaded regions. Measure elemental and isotopic composition of gas evolved from regolith in permanent shade heated up to 700 K, obtained from depths greater than 10 cm and up to a meter. Determine the presence of refractory volatile-bearing species including water-bearing minerals, complex organics, and clathrates. Determine elemental composition, especially hydrogen, for immediate surroundings of sampling site. Determine any local stratigraphy using geophysical methods. Support technology development for operation at low temperatures for long duration. Search for evidence of complex volatile historyof polar soils, including examination and sampling of shallow and deep trenches. Support technology development forfield studies in regions of permanent shade, including aspects of site disturbance by high-temperature equipment. 3a. Determine theextent and composition of the primary feldspathic crust, KREEP layer, and other products of planetary differentiation. High-resolution global maps of mineralogy and geochemistry to characterize important geological and geochemical units. Geophysical measurements of representative regions. Higher-resolution geophysical (e.g., seismic, gravitational) measurements for modeling crustal structure and understanding extent of crustal units. Sample return from major lunar terranes (e.g., feldspathic highlands, SPA Basin, PKT) for detailed geochemical and isotopic analysis. Establish/participate in an international network of ground-based geophysical instruments. Determine mineralogy and petrology across multi-kilometer traverses at selected craters. Acquire wider variety of samples (for in situ study and return) through sifting, drilling, and identification of unusual samples. 2a. Determine the thickness of the lunar crust (upper and lower) and characterize its lateral variability onregional and global scales. Lateral variability addressed by careful analysis of high-quality topography (LRO) with existing gravity models. High-resolution gravity measurements toallow separation of flexure, density, and thickness effects. Samples from previously unsampled regions to provide constraints on lateral variability of crustal composition and density. Establish a geophysical network to determine crustal thickness from analyses of natural and artificial seismic events. Human installation of seismic instrumentation provides for better sensitivity to extremely small lunar seismic signals.
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The Scientific Context for Exploration of the Moon Science Goals Implementation (a) Information Extraction (b) Orbital Measurements (c) Sample Return (d) Landed Experiments, Instruments, and Rovers (e) Human Fieldwork An enabling new framework for lunar exploration will be provided by data from SMART-1, SELENE, Chang’e, Chandrayaan-1, and LRO. The assumption is that all missions and key instruments will be successful. Orbital measurements are not included in the complement of missions planned for launch by 2008. The assumption is that the four missions planned will return appropriate data as planned; if not, new measurements that provide similar high-priority compositional and geophysical data need to be acquired. The types of returned samples and of science analyses required are identified. These include science measurements for/from landed sites; category also encompasses penetrators/impactors. Science areas that specifically benefit from human capabilities are identified. 2b. Characterize the chemical/physical stratification in the mantle, particularly the nature of the putative 500-km discontinuity and the composition of the lower mantle. Return of samples representative of the upper mantle (e.g., SPA Basin) provides a geochemical framework for the interpretation of seismic and magnetic sounding data. Establish a global (including farside) geophysical network to determine the seismic and resistivity structure of the mantle from analyses of moonquake signals and low-frequency electromagnetic sounding. Human installation of seismic instrumentation provides for better sensitivity to extremely small lunar seismic signals. 8a. Determine theglobal density, composition, and time variability of the fragile lunar atmosphere before it is perturbed by further human activity. Ultraviolet spectral measurements from LRO will provide upper limits or measurements of species such as Ar using resonantly scattered sunlight. Mass spectrometers flown in low lunar orbit (<50 km) could provide in situ measurements of lunar atmospheric species. A network of surface mass spectrometers could monitor poleward migration of volatiles. Backpack mass spectrometers could provide sensitive monitoring of atmospheric pollution.
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The Scientific Context for Exploration of the Moon 2c. Determine the size, composition, and state (solid/liquid) of the core of the Moon. Establish a global (including farside) geophysical network to determine the seismic and resistivity structure of the deep interior from analyses of moonquake signals and low-frequency electromagnetic sounding, and to improve the measurement of the dynamical parameters of the Moon through Earth-based laser tracking. Human installation of seismic instrumentation provides for better sensitivity to extremely small lunar seismic signals. 3b. Inventory the variety, age, distribution, and origin of lunar rock types. Continue to search for exotic components in existing samples and remote sensing data. Use remote sensing to help determine the regional geologic context of returned samples. Higher-resolution global and regional mineralogic and geochemical maps to identify unusual lithologies and provide context for returned samples and meteorites. Higher-resolution images to provide targeted crater counts. Sample returns from representative and previously unsampled locations (selected from global compositional maps). Develop instruments for precise, in situ geochronology. Use landed geochemical instrumentation to identify best samples for return. Acquire wider variety of samples (for in situ study and return) through sifting, drilling, identification of unusual samples. 8b. Determine the size, charge, and spatial distribution of electrostatically transported dust grains and assess their likely effects on lunar exploration and lunar-based astronomy. LRO cameras maydetect horizon glow during limb-scanning operations. Dedicated limb-scanning measurements of scattered sunlight from dust clouds could provide maps of lunar dust transport. Deposition of lunar dust on optical surfaces could be monitored by surface-based instruments. Determine effects of human activity on dustenvironment. NOTE: Acronyms are defined in Appendix B.
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The Scientific Context for Exploration of the Moon PRIORITIZATION OF SCIENCE CONCEPTS The eight science concepts discussed in Chapter 3 address broad areas of scientific research. Each has multiple components and is linked (see Table 3.1) to different aspects of the overarching themes—early Earth-Moon system, terrestrial planet differentiation and evolution, solar system impact record, and lunar environment—presented in Chapter 1. In addition, there are multiple avenues for implementation (information extraction; orbital measurements, sample return; landed experiments, instruments, and rovers; and human fieldwork; see Table 4.1). In order to provide a sense of the overall importance of each of the eight broad science concepts, the committee evaluated only the scientific merit of each concept to rank order these concepts. They are listed in order throughout this report and in Tables 3.1 and 4.1. It should be noted that all concepts discussed are viewed to be scientifically important and their ordering in this report is simply a relative ranking: The bombardment history of the inner solar system is uniquely revealed on the Moon. The structure and composition of the lunar interior provides fundamental information on the evolution of a differentiated planetary body. Key planetary processes are manifested in the diversity of lunar crustal rocks. The lunar poles are special environments that may bear witness to the volatile flux over the latter part of solar system history. Lunar volcanism provides a window into the thermal and compositional evolution of the Moon. The Moon is an accessible laboratory for studying the impact process on planetary scales. The Moon is a natural laboratory for regolith processes and weathering on anhydrous airless bodies. Processes involved with the atmosphere and dust environment of the Moon are accessible for scientific study while the environment remains in a pristine state. PRIORITIZATION OF SCIENCE GOALS Within the science concepts, the committee identified 35 specific science goals that can be addressed at least in part during the early phases of the VSE. For these science goals, the committee evaluated their science merit as well as the degree to which they are possible to achieve within the limits of current or near-term technical readiness and practical accessibility. Within their respective science concepts, these goals are listed in order of their overall priority ranking (a-e) in Table 3.1. The committee also evaluated and rank ordered all 35 specific science goals together, apart from the science concepts with which they are grouped. The 11 highest-ranking lunar science goals are listed below and in Table 5.1 in priority order. To achieve this group of goals, the committee identified possible means of implementation (see Table 5.1). The committee’s highest-priority science goals are the following: 1a. Test the cataclysm hypothesis by determining the spacing in time of the creation of the lunar basins. The history of impacts in the early Earth-Moon system, in particular around 3.9 Ga, the time that life was emerging on Earth, is a critical chapter in terrestrial planet evolution. Understanding this period is important for several reasons: as tests of our models of the impact rate, planetary accretion, impact frustration of life, magma ocean formation and evolution, and extension and verification of the chronology. In order to answer the question of whether there was a cataclysm at 3.9 Ga, sample returns from the oldest impact basins combined with high-resolution imaging from orbit are required. 1b. Anchor the early Earth-Moon impact flux curve by determining the age of the oldest lunar basin (South Pole-Aitken Basin). Although the enormous South Pole-Aitken Basin is stratigraphically the oldest basin on the Moon, its absolute age is completely unconstrained. All models of the first few hundred million years of solar system history depend on whether the large basins are part of a decreasing flux of material swept up by growing planet embryos or a later separate pulse of planetesimal-sized bodies. Details of the lunar stratigraphy can be better defined by integrated high-resolution imagery and topography, but it is essential to provide an absolute date for
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The Scientific Context for Exploration of the Moon the oldest basin, the South Pole-Aitken Basin, with the type of precision that can only be obtained in Earth-based laboratories with returned samples. 1c. Establish a precise absolute chronology. A well-calibrated lunar chronology not only can be used to date unsampled lunar regions, but it can also be applied to date planetary surfaces of other planets in the inner solar system through modeling. An absolute lunar chronology is derived from combining lunar crater counts with radiometric sample ages and is thus the most precise—and in some cases the only—technique to date planetary surfaces for which samples have not been or cannot be obtained. In order to determine the precise shape of the lunar chronology curve, samples should be returned from several key benchmark craters, young lava flows, and old impact basins, which also need to be imaged at high spatial resolution. 4a. Determine the compositional state (elemental, isotopic, mineralogic) and compositional distribution (lateral and depth) of the volatile component in lunar polar regions. The extremely low temperature surfaces in permanent shade at the lunar poles have been accumulating ices and other volatile-bearing materials for at least 2 billion years. This potential scientific bonanza contains information on the history of volatile flux in the recent solar system and is a natural laboratory for studying how volatiles develop in the space environment. However, there is a near-total lack of understanding of the nature and extent of these polar materials. Landed missions to the poles will produce entirely new knowledge of this unknown territory. 3a. Determine the extent and composition of the primary feldspathic crust, KREEP layer, and other products of planetary differentiation. The lunar magma ocean has been the cornerstone of lunar petrology since the return of the Apollo samples and has gone on to form the basis for our understanding of differentiation processes in all the terrestrial planets, including Earth and Mars. Many details of the differentiation process can be told through the geochemistry and distribution of key lunar rock types that we think are primary products. Regional orbital remote sensing will be needed to identify areas that contain these rocks and how they fit into the global picture. Geophysical data, particularly seismic profiling of the lunar crust, help identify the depth and extent of important layers in the lunar crust. Both human and robotic landed missions can provide targeted sample return so that we can study these products in the same detail as for the Apollo samples. 2a. Determine the thickness of the lunar crust (upper and lower) and characterize its lateral variability on regional and global scales. The lunar crust provides basic constraints on the characteristics of the lunar magma ocean from which it formed. Its volume fixes the extent of differentiation of the original lunar material, and differences between the upper and lower crust, along with global-scale variations in thickness, provide essential clues to the processes that formed the outermost portions of the Moon. A seismic network of at least regional extent is essential for providing this information. 2b. Characterize the chemical/physical stratification in the mantle, particularly the nature of the putative 500-km discontinuity and the composition of the lower mantle. The structure of the mantle has been affected by the initial differentiation of the Moon by magma ocean fractionation and core formation as well as any subsequent evolution, such as mantle overturn and sub-solidus convection. All of these processes will have left their marks in terms of compositional and mineralogical stratification, and detailed knowledge of this structure may allow us to decipher the Moon’s earliest history. The seismic discontinuity tentatively identified by the Apollo seismic experiment has particular significance in differentiation models, as it may represent the base of the original magma ocean. The only effective methods for probing the lunar mantle are global-scale seismology and electromagnetic sounding. 8a. Determine the global density, composition, and time variability of the fragile lunar atmosphere before it is perturbed by further human activity. Although the density of the lunar atmosphere was fairly well characterized on the nightside by Apollo, 90 percent of the atmospheric constituents were not identified. The measurements need to be extended to the dayside, and the composition of the atmosphere should be determined as completely as possible. It is crucial that these measurements be made before the atmosphere is perturbed by future human landings; therefore, this topic was ranked higher in implementation priority than in scientific priority. Both orbital and surface deployments of mass spectrometers are needed to make the required measurements. 2c. Determine the size, composition, and state (solid/liquid) of the core of the Moon. At this point the very existence of a metallic lunar core, while likely, has not been fully established. Yet its size and composition play a fundamental role in determining the initial bulk composition of the Moon and the subsequent differentiation of the
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The Scientific Context for Exploration of the Moon mantle, as well as the Moon’s thermal and magnetic history. Measurements from a globally distributed network of seismometers, augmented by electromagnetic sounding and precision laser tracking of variations in lunar rotation, will be necessary to characterize the lunar core. 3b. Inventory the variety, age, distribution, and origin of lunar rock types. After the formation of the primary products of the lunar magma ocean, the Moon continued to produce a rich diversity of rocks by numerous geologic processes. Erupted basalts, emplaced plutons, and remelted impact-melt sheets all contain clues to continued geologic activity on the Moon and the processes that enabled this activity. Understanding when and how the diversity of lunar rocks formed and how they are at present distributed allows the prediction of where else on the Moon they may be located, even if they are not expressed at the surface. Laboratory analysis of returned samples from diverse locations on the Moon enables complete, high-precision geochemical, mineralogical, and isotopic characterization of diverse lunar rocks. Higher-resolution geochemical and mineralogical remote sensing databases are also crucial in providing geologic context for unusual lithologies. 8b. Determine the size, charge, and spatial distribution of electrostatically transported dust grains and assess their likely effects on lunar exploration and lunar-based astronomy. Lunar dust is an important constituent of the lunar environment. Because of illumination by sunlight and the impact of the solar wind, the dust is electrostatically charged and is levitated and transported by electric fields produced by the solar wind. The transport of the dust and its deposition on surfaces will place important limitations on human activities and on astronomical observations that may be planned for the Moon. Surface measurements of dust, which can be made robotically and later with astronaut assistance, are needed to characterize the dust environment and its effects on deployed systems and instrumentation. INTEGRATED HIGH-PRIORITY FINDINGS AND RECOMMENDATIONS In arriving at the priority science concepts presented in Chapter 3 and the specific goals presented in Chapter 3 and above, the committee found that there were a number of larger integrated issues and concerns that were not fully captured either in the discussion of the science concepts or in the science goal priorities and their implementation. The committee therefore developed a group of integrating findings and recommendations that envelop, complement, and supplement the scientific priorities discussed in the report: Finding 1: Enabling activities are critical in the near term. A deluge of spectacular new data about the Moon will come from four sophisticated orbital missions to be launched between 2007 and 2008: SELENE (Japan), Chang’e (China), Chandrayaan-1 (India), and the Lunar Reconnaissance Orbiter (United States). Scientific results from these missions, integrated with new analyses of existing data and samples, will provide the enabling framework for implementing the VSE’s lunar activities. However, NASA and the scientific community are currently underequipped to harvest these data and produce meaningful information. For example, the lunar science community assembled at the height of the Apollo program of the late 1960s and early 1970s has since been depleted in terms of its numbers and expertise base. Recommendation 1a: NASA should make a strategic commitment to stimulate lunar research and engage the broad scientific community2 by establishing two enabling programs, one for fundamental lunar research and one for lunar data analysis. Information from these two recommended efforts—a Lunar Fundamental Research Program and a Lunar Data Analysis Program—would speed and revolutionize understanding of the Moon as the Vision for Space Exploration proceeds. Recommendation 1b: The suite of experiments being carried by orbital missions in development will provide essential data for science and for human exploration. NASA should be prepared to recover data lost due to 2 See also National Research Council, Building a Better NASA Workforce: Meeting the Workforce Needs for the National Vision for Space Exploration, The National Academies Press, Washington, D.C., 2007.
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The Scientific Context for Exploration of the Moon failure of missions or instruments by reflying those missions or instruments where those data are deemed essential for scientific progress. Finding 2: Strong ties with international programs are essential. The current level of planned and proposed activity indicates that almost every space-faring nation is interested in establishing a foothold on the Moon. Although these international thrusts are tightly coupled to technology development and exploration interests, science will be a primary immediate beneficiary. NASA has the opportunity to provide leadership in this activity, an endeavor that will remain highly international in scope. Recommendation 2: NASA should explicitly plan and carry out activities with the international community for scientific exploration of the Moon in a coordinated and cooperative manner. The committee endorses the concept of international activities as exemplified by the recent “Lunar Beijing Declaration” of the 8th ILEWG (International Lunar Exploration Working Group) International Conference on Exploration and Utilization of the Moon (see Appendix D). Finding 3: Exploration of the South Pole-Aitken Basin remains a priority. The answer to several high-priority science questions identified can be found within the South Pole-Aitken Basin, the oldest and deepest observed impact structure on the Moon and the largest in the solar system. Within it lie samples of the lower crust and possibly the lunar mantle, along with answers to questions on crater and basin formation, lateral and vertical compositional diversity, lunar chronology, and the timing of major impacts in the early solar system. Missions to South Pole-Aitken Basin, beginning with robotic sample returns and continuing with robotic and human exploration, have the potential to be a cornerstone for lunar and solar system research. (A South Pole-Aitken Basin sample-return mission was listed as a high priority in the 2003 NRC decadal survey report New Frontiers in the Solar System: An Integrated Exploration Strategy.3) Recommendation 3: NASA should develop plans and options to accomplish the scientific goals set out in the high-priority recommendation in the National Research Council’s New Frontiers in the Solar System: An Integrated Exploration Strategy’s (2003) through single or multiple missions that increase understanding of the South Pole-Aitken Basin and by extension all of the terrestrial planets in our solar system (including the timing and character of the late heavy bombardment). Finding 4: Diversity of lunar samples is required for major advances. Laboratory analyses of returned samples provide a unique perspective based on scale, precision, and flexibility of analysis and have permanence and ready accessibility. The lunar samples returned during the Apollo and Luna missions dramatically changed understanding of the character and evolution of the solar system. Scientists now understand, however, that these samples are not representative of the larger Moon and do not provide sufficient detail and breadth to address the fundamental science concepts outlined in Table 3.1 in this report. Recommendation 4: Landing sites should be selected that can fill in the gaps in diversity of lunar samples. Mission plans for each human landing should include the collection and return of at least 100 kg of rocks from diverse locations within the landing region. For all missions, robotic and human, to improve the probability of finding new, ejecta-derived diversity among smaller rock fragments, every landed mission that will return to Earth should retrieve at least 1 kg of rock fragments 2 to 6 mm in diameter separated from bulk soil. Each mission should also return 100 to 200 grams of unfractionated regolith. 3 National Research Council, New Frontiers in the Solar System: An Integrated Exploration Strategy, The National Academies Press, Washington, D.C., 2003.
Representative terms from entire chapter: