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The Scientific Context for Exploration of the Moon: Interim Report 4 Priorities, Primary Scientific Findings, and Recommendations Table 1 provides a summary of scientific objectives for early lunar exploration and their principal implementation modes. These objectives and implementations provide a rich basis for the extraction of specific objectives that could be organized into a science program. The committee provides the following prioritization of these lunar science goals that flow from the 10 themes discussed in Chapter 1 and that can be accomplished by lunar measurements and analyses. The committee has used the prioritization criteria adopted by the decadal survey New Frontiers in the Solar System: An Integrated Exploration Strategy (NRC, 2003) as a guideline: scientific merit, opportunity, and technological readiness. Fundamental Solar System Science Characterize and date the impact flux (early and recent) of the inner solar system. Determine the internal structure and composition of a differentiated planetary body. Determine the compositional diversity (lateral and vertical) of the ancient crust formed by a differentiated planetary body. Characterize the volatile compounds of polar regions on an airless body and determine their importance for the history of volatiles in the solar system. Planetary Processes Determine the time scales and compositional and physical diversity of volcanic processes. Characterize the cratering process on a scale relevant to planets. Constrain processes involved in regolith evolution and decipher ancient environments from regolith samples. Understand processes involved with the atmosphere (exosphere) of airless bodies in the inner solar system. Other Opportunities (additional information is required for these) Utilize data from the Moon to characterize Earth’s early history. Determine the utility of the Moon for astrophysics observations. Determine the utility of the Moon as a platform for observations of Earth. Determine the utility of the Moon as a platform for observations of solar-terrestrial processes. Several fundamental solar system science issues are given higher priority because of their broad importance to understanding the way in which the Moon and planets have evolved as solar system bodies, especially in the first 500 million years of solar system evolution. These goals are readily addressed in the time frame specified by this report. Although still fundamental and having implications for the same processes on other planets, several other planetary processes are given somewhat lower priority because they are (1) more highly linked to later Vision activities or events and (2) focus on the Moon as a specific body. A few, such as cratering processes and ancient regolith sampling, appear to require components that extend considerably into the period when human involvement is significant. Other opportunities are listed as lower priority at this time primarily due to the lack of input to the committee for assessing these opportunities. The committee will provide a more complete prioritization of, and increased specificity for, these opportunities in its full report if relevant information becomes available.
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The Scientific Context for Exploration of the Moon: Interim Report TABLE 1 Science Themes, Goals, and Implementation Science Themes The scientific goals for each theme are discussed in detail in the text. Implementation a. Information Extraction 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. b. Orbital Measurements Orbital measurements 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. c. Sample Return The types of returned samples and of science analyses required are identified. d. Landed Experiments, Instruments, and Rovers These include science measurements for/from landed sites; category also encompasses penetrators/impactors. e. Human Fieldwork Science areas that specifically benefit from human capabilities are identified. 1. The bombardment history of the inner solar system is uniquely revealed on the Moon. Crater counts of benchmark terrain using high-resolution images. Targeted higher-resolution images of specific terrains. Sample return from the impact melt sheet of SPA, from young basalt flows, and from benchmark craters (e. g., Copernicus and Tycho). Development of in situ instrumentation for dating. Field observations provide critical geologic context; human interaction improves chances of obtaining best/ most appropriate samples. 2. The structure and composition of the lunar interior provide fundamental information on the evolution of a differentiated body. Farside gravity. High-quality topographic information. Possible information on heat flow and magnetic sounding results. Relay orbiter for farside stations (e. g., seismic). Samples from the interior are important constraints on lunar geochemistry and geophysics (e. g., remanent magnetism). Simultaneous, globally distributed seismic and heat flow network. Expanded retroreflector network. Although some landed experiments can be emplaced autonomously, it is assumed that more capable sensors are possible with human guidance/assistance. 3. The Moon’s crust is much more complicated than are the mare and highlands. Detailed global elemental and mineralogical information in a spatial context. Search for and documentation of a diversity of rock types using returned samples and lunar meteorites. Higher-spatial-resolution compositional data are desirable from priority targets. Relay orbiter for farside stations (e. g., seismic). Return samples from priority targets. Every return mission should include a bulk soil and a sieved sample with geologic documentation. Strategic site selection. Conduct in situ analyses and mineralogical and elemental characterization of the rocks and provide a thorough description of the geologic context. Determine the vertical structure using an active regional seismic network. Field observations provide critical geologic context; human interaction improves chances of obtaining best/ most appropriate samples. 4. Lunar volcanism provides a window into the thermal and compositional evolution of the Moon. Detailed global elemental and mineralogical information in a spatial context. Improved age-dating for basalts through crater counting. Stratigraphy of specific basalt flows (subsurface sounding). High- spatial-resolution compositional data desirable. Sample the youngest basalt flows. Need samples from unsampled benchmark lava flows and pyroclastic deposits. Sample a complete sequence of flows to determine the evolution of basalt composition. Strategic site selection. Conduct in situ analyses and mineralogical and elemental characterization of the rocks and provide a thorough description of the geologic context. Strategic site selection, core drilling, and active subsurface sounding to determine layering and volume.
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The Scientific Context for Exploration of the Moon: Interim Report Science Themes The scientific goals for each theme are discussed in detail in the text. Implementation a. Information Extraction 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. b. Orbital Measurements Orbital measurements 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. c. Sample Return The types of returned samples and of science analyses required are identified. d. Landed Experiments, Instruments, and Rovers These include science measurements for/from landed sites; category also encompasses penetrators/impactors. e. Human Fieldwork Science areas that specifically benefit from human capabilities are identified. 5. The Moon is an accessible laboratory for studying the impact process on planetary scales. Detailed geologic mapping of compositionally diverse craters and basins. Evaluation of upper-surface stratigraphy (sounding). Determination of the shape of craters and the distribution of ejecta. Sample returns from benchmark craters and basins. In situ compositional and structural analyses of craters and basins (via traverses). Core samples from impact melt sheets. Traverses across ejecta blankets. 6. The Moon is a natural laboratory for regolith processes and weathering on anhydrous airless bodies. Maps of regolith maturity and derivation of the temporal progression of space weathering. Identification of regions that contain ancient regolith. Evaluation of upper-surface stratigraphy (sounding). Regolith from unsampled terrain of diverse composition and age. Understand the evolution of the regolith. Sample old regolith where it is stratigraphically preserved. Obtain paleoregolith samples (exposed in selected outcrops or through deep drilling). 7. The Moon may provide important information about the early Earth and the origin of life. Cratering flux, regoliths. Better understanding of lunar cratering flux through targeted high-resolution imaging to help establish history of impacts on early Earth. Age dating of specific lunar craters and basins to improve understanding of impact history. Obtain paleoregolith samples to determine early solar activity and cosmic dust flux, and their effects on early Earth. 8. The lunar poles are special environments that may bear witness to the volatile flux over the latter part of solar system history. Primary understanding of polar environment (photometry, morphology, topography, temperature, and distribution and inventory of volatiles). High-spatial-resolution distribution of volatiles on and in the regolith poleward of 70 degrees. Cryogenically preserved sample return to determine the complexity of the polar deposits. Understand physical properties of polar regolith. Determine the localized character and lateral and vertical distribution of polar deposits. Measure chemical and isotopic composition, and physical and mineralogical characteristics. 9. Further exploration can vastly improve understanding of the fragile lunar atmosphere. Variation in mass with time and compositional inventory (“with time” refers to the lunar diurnal and Earth-orbital/ solar cycles). Variation of mass with time and identification of dominant species. Environmental monitoring near human activity. 10. The Moon may provide an excellent platform for specific types of observations. Awaiting Further Input
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The Scientific Context for Exploration of the Moon: Interim Report Many science objectives will require investigation by several techniques—orbital observations, in situ analysis, astronaut field observations, and analysis of returned samplesso a simple prioritization of individual objectives alone is not feasible. The committee has assumed that an “opportunity” criterion is specified by its statement of task, which directed it to consider LPRP robotic precursor missions and early human “sortie” missions similar to Apollo capabilities. These provide constraints of mass, power, and technology development on what can reasonably be available for implementation. “Technology readiness” is ambiguous for the more distant exploration schedule, which may allow many capabilities, currently unavailable, to be developed by the time of the missions. Nevertheless, some capabilities, such as deep drilling, are probably beyond the time horizon addressed in this report, and the committee has tried to accommodate this perspective. Although its task focused on science objectives and mission capabilities, the committee thought it necessary to consider the degree of preparation required for conducting the science that would be accomplished by the Vision. With this introduction and the above discussion of science themes and priorities, the committee provides the following list of findings and recommendations, divided into two categories. The first category directly addresses the scientific objectives. In Chapter 5, related findings and recommendations are derived from the committee’s consideration of the challenges facing NASA in the implementation of a lunar science program of the type envisioned by the science objectives and implementation approach recommended here. PRINCIPAL FINDING: Lunar activities apply to broad scientific and exploration concerns. Lunar science as described in this report has much broader implications than simply studying the Moon. For example, a better determination of the lunar impact flux during early solar system history would have profound implications for the evolution of the solar system, the early Earth, and the origin of life. A better understanding of the lunar interior would bear on models of planetary formation in general and the origin of the Earth-Moon system in particular. And exploring the possibly ice-rich lunar poles could reveal important information about the history and distribution of solar system volatiles. Furthermore, although some of the committee’s objectives are focused on lunar-specific questions, one of the basic principles of comparative planetology is that each world studied enables researchers to better understand other worlds, including our own. Improving our understanding of such processes as cratering and volcanism on the Moon will provide valuable points of comparison for these processes on the other terrestrial planets. Table 2 shows linkages between the science goals for the recommended lunar exploration program and broader scientific and applied concerns. 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 Vision’s lunar activities. However, NASA and the scientific community are currently underequipped to harvest this 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 1: The committee urges NASA to make a strategic commitment to stimulate lunar research and engage the broad scientific community1 by establishing two enabling programs, one for fundamental lunar research and one for lunar data analysis. Information from these two efforts, the Lunar Fundamental Research Program and the Lunar Data Analysis Program, will speed and revolutionize understanding of the Moon as the Vision for Space Exploration proceeds. 1 See also National Research Council, Issues Affecting the Future of the U.S. Space Science and Engineering Workforce: Interim Report, The National Academies Press, Washington, D.C., 2006.
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The Scientific Context for Exploration of the Moon: Interim Report TABLE 2 Relationship of Lunar Science Goals to Broad Scientific Areas Science Goals Astrobiologya PlanetaryScienceb Early Solar System >4.0 Billion YearsAgoc Cosmo-chemistryd In Situ Resource Utilizatione Human Habitation Issuesf Solar system impact flux X X X X Planetary interiors X X X X Planetary crusts X X X X X Planetary volcanism X X X Cratering process X X Regolith evolution X X X X Early Earth X X X Polar areas X X X X X Atmosphere X X X Astrophysics Awaiting further input. Earth science Awaiting further input. Solar-terrestrial processes Awaiting further input. a Astrobiology: Lunar investigations focused on early conditions in the inner solar system will have applications to astrobiology, because of its consideration of the conditions during the emergence of life on Earth. b Planetary Science: Many of the processes that are available for study on the Moon, such as volcanism, impact, and regolith formation, are also of fundamental importance on other planets and small bodies of the solar system. c Early Solar System: The Moon provides a unique window on early solar system processes, in particular the early impact history of the inner solar system. d Cosmochemistry: Determining the bulk composition of the Moon will provide important information about the origin of the Earth-Moon system. e In Situ Resource Utilization: Accomplishing the objectives of the science program will provide necessary information for assessing the distribution of lunar resources and establishing the most appropriate methods to extract them. f Human Habitation Issues: Many of the objectives, such as more accurately determining the seismic activity of the Moon, will inform design considerations for lunar habitation, and all will play into the decision eventually of where to establish a permanent lunar outpost. FINDING 2: Explore the South Pole-Aitken basin. 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, 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 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.)
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The Scientific Context for Exploration of the Moon: Interim Report RECOMMENDATION 2: NASA should develop plans and options to accomplish the scientific goals set out in the New Frontiers in the Solar System: An Integrated Exploration Strategy’s (NRC, 2003) high-priority recommendation, 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 early heavy bombardment). FINDING 3: Determine the composition and structure of the lunar interior. Determining the structure and composition of the interior of the Moon, from the outer layers of the crust to the deep core, will provide enormous insight into many of the highest-priority scientific questions. Long-duration geophysical stations (with broad-band seismometers, heat flow measurements, and precision tracking capability) implemented at multiple (six or more) sites are required to provide comprehensive subsurface information. RECOMMENDATION 3: Because a globally distributed network of many geophysical stations is critical for these investigations, an international effort should be pursued to coordinate the development of a standard, small set of key instruments (e.g., seismometer, thermal profiler, retro-reflector, etc.) and to cooperate in providing for its wide deployment across the Moon. FINDING 4: Maximize the diversity of lunar samples. 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. We 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 themes outlined in Table 1. Laboratory analyses of returned samples provide a unique perspective based on scale, precision, flexibility, and permanence/accessibility. RECOMMENDATION 4: Landing sites should be selected that can fill in the gaps in diversity of lunar samples. To improve the probability of finding new, ejecta-derived diversity, every landed mission that will return to Earth should retrieve at a minimum two special samples: (a) a bulk undisturbed soil sample (200 g minimum) and (b) at least 1 kg of rock fragments 2 to 6 mm in diameter sieved from bulk soil. These samples would be in addition to those collected at specific high-priority sampling targets within the landing site. FINDING 5: Proceed with lunar surface mission development and the site selection process. Plans to return to the Moon will involve the selection of surface exploration sites. The selection process will involve, among many factors, scientific potential, ease of access, potential to conduct traverses, options for future build-up to an outpost or base, resource utilization potential, and explorer safety. Many of the science goals listed in Table 1 depend critically on site selection, although a given site might satisfy several requirements of several different goals. In the period under consideration for this report, both robotic and human sample return capabilities can be considered. RECOMMENDATION 5: Development of a comprehensive process for lunar landing site selection that addresses the science goals of Table 1 should be started by a science definition team. The choice of specific sites should be permitted to evolve as understanding of lunar science progresses through the refinement of science goals and the analysis of existing and newly acquired data. Final selection should be done with full input of the science community in order to optimize science return while meeting engineering and safety constraints.
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The Scientific Context for Exploration of the Moon: Interim Report FINDING 6: Understand the lunar polar deposits and environment. Almost nothing is known about the sources of volatiles at the lunar poles and the processes operating on these volatiles. Additionally, there is almost no information about the physical properties of the lunar soils in permanently shaded regions. Finally, there is no knowledge of how robotic and human activities on the Moon will affect and change the unique and possibly fragile lunar polar environment. RECOMMENDATION 6: NASA should carry out activities to understand the inventory, lateral distribution, composition (chemical, isotopic, mineralogic), physical state, and stratigraphy of the lunar polar deposits. This understanding will be gained through analyses of orbital data and in situ data from landed missions in the permanently shaded regions. In situ studies should occur early enough in the lunar program to prevent substantial change in the polar environment due to robotic and human activities. FINDING 7: Understand and characterize the lunar atmosphere. The lunar atmosphere is the only surface boundary exosphere (SBE) in the solar system that is sufficiently accessible to study in detail. Despite many Apollo and Earth-based measurements, numerous aspects of the lunar atmosphere (e.g., composition, interaction processes) remain unknown. Furthermore, the lunar atmosphere is so extremely fragile that robotic and human activities can completely transform the nature—possibly permanently—of this pristine environment. RECOMMENDATION 7: To document the lunar atmosphere in its pristine state, early observational studies of the lunar atmosphere should be made, along with studies of the sources of the atmosphere and the processes responsible for its loss. These include a full compositional survey of all major and trace components of the lunar atmosphere down to a 1 percent mixing ratio, determination of the volatile transport to the poles, documentation of sunrise/sunset dynamics, determination of the variability of indigenous and exogenous sources, and determination of atmospheric loss rates by various processes. FINDING 8: Evaluate the Moon’s potential as an observation platform. Observation from the Moon may be useful to astrophysics, studies of the Sun-Earth connection, Earth science, and some parts of astrobiology. There are uncertainties in the environmental benefits, disadvantages, potential mitigations, and costs of the Moon as an observation platform relative to alternate space sites, requiring a thorough study. RECOMMENDATION 8: The committee recommends that a thorough study be done by NASA to evaluate the suitability of the Moon as an observational site for studies of Earth, Sun-Earth connections, astronomy, and astrophysics. FINDING 9: Establish strong ties with international programs. 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 9: NASA is encouraged to 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 “Beijing Declaration” of the 8th International Conference on Exploration and Utilization of the Moon.
Representative terms from entire chapter: