Appendix B
Compilation of Recommendations Concerning Mars Exploration Made by COMPLEX and Other Advisory Groups

The recommendations reprinted in this appendix are sorted by sources and ordered by date.

1. 1978

Strategy for Exploration of the Inner Planets: 1977–1987 (NRC, COMPLEX, 1978)

[1.1] A global map or image of the surface of a planet at good resolution is considered to be a major scientific contribution and is basic to any advance in the understanding of the terrestrial planets. [p. 42]

[1.2] Two important precepts have guided the Committee’s definition of primary objectives for future exploration of Mars. First is the need to carry out intensive studies of the chemical and isotopic composition and physical state of martian material to determine the major surface-forming processes and their time scales and the past and present biological potential of the martian environment. Second is the need to achieve a broad-based and balanced planetological characterization in order that meaningful comparisons can be drawn between Mars and the other members of the triad Earth-Mars-Venus. [p. 43]

[1.3] . . . [t]he primary objectives in order of scientific priority for the continued exploration of Mars are. . . the intensive study of local areas (a) to establish the chemical, mineralogical, and petrological character of different components of the surface material, representative of the known diversity of the planet; (b) to establish the nature and chronology of the major surface forming processes; (c) to determine the distribution, abundance, and sources and sinks of volatile materials, including an assessment of the biological potential of the martian environment, now and during past epochs; (d) to establish the interaction of the surface material with the atmosphere and its radiation environment. . . .

These objectives are multiply connected. For example, definition of the volatile inventory should pay proper attention to gas exchange between the planet and the solar wind.

In the following we will briefly expand on the substance of these recommended objectives and outline the recommended strategy for accomplishing them. [p. 44]

[1.4] The establishment of the chemical, mineralogical, and petrological character of the various components of the martian surface material should include (in approximate order):

  1. Gross chemical analysis (all principal chemical elements with a sensitivity of 0.1 percent by atom and an accuracy of at least 0.5 atom percent for the major constituents).



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Appendix B Compilation of Recommendations Concerning Mars Exploration Made by COMPLEX and Other Advisory Groups The recommendations reprinted in this appendix are sorted by sources and ordered by date. 1. 1978 Strategy for Exploration of the Inner Planets: 1977–1987 (NRC, COMPLEX, 1978) [1.1] A global map or image of the surface of a planet at good resolution is considered to be a major scientific contribution and is basic to any advance in the understanding of the terrestrial planets. [p. 42] [1.2] Two important precepts have guided the Committee’s definition of primary objectives for future exploration of Mars. First is the need to carry out intensive studies of the chemical and isotopic composition and physical state of martian material to determine the major surface-forming processes and their time scales and the past and present biological potential of the martian environment. Second is the need to achieve a broad-based and balanced planetological characterization in order that meaningful comparisons can be drawn between Mars and the other members of the triad Earth-Mars-Venus. [p. 43] [1.3] . . . [t]he primary objectives in order of scientific priority for the continued exploration of Mars are. . . the intensive study of local areas (a) to establish the chemical, mineralogical, and petrological character of different components of the surface material, representative of the known diversity of the planet; (b) to establish the nature and chronology of the major surface forming processes; (c) to determine the distribution, abundance, and sources and sinks of volatile materials, including an assessment of the biological potential of the martian environment, now and during past epochs; (d) to establish the interaction of the surface material with the atmosphere and its radiation environment. . . . These objectives are multiply connected. For example, definition of the volatile inventory should pay proper attention to gas exchange between the planet and the solar wind. In the following we will briefly expand on the substance of these recommended objectives and outline the recommended strategy for accomplishing them. [p. 44] [1.4] The establishment of the chemical, mineralogical, and petrological character of the various components of the martian surface material should include (in approximate order): Gross chemical analysis (all principal chemical elements with a sensitivity of 0.1 percent by atom and an accuracy of at least 0.5 atom percent for the major constituents).

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Identification of the principal mineral phases present (i.e., those making up at least 90 percent of the material in soils and rocks). Establish a classification of rocks (igneous, sedimentary, and metamorphic) and fines that define martian petrogenetic processes. State of oxidation, particularly of the fine material and rock surfaces. Content of volatiles or volatile producing species (H2O, SO3, CO2, NO2). Determination of the selected minor and trace element contents. (a) Primordial radionuclides: K with a sensitivity of at least 0.05 percent; U and Th with a sensitivity of at least 1 ppm. (b) Selected minor and trace elements (e.g., C, N, F, P, S, Cl, Ti, Ni, As, rare earth elements, Bi, Cu, Rb, Sr). Measurement of physical properties (magnetic, and, in the case of fines, density and size distribution, and rheological properties). [pp. 44-45] [1.5] The establishment of the nature and chronology of the major surface-forming processes should include determination of: Cosmic-ray exposure ages of soil and rock materials for both long and short time scales. Crystallization ages of igneous rocks, recrystallization ages of metamorphic rocks, and depositional ages of sedimentary rocks. [p. 44] [1.6] The distribution and abundance of the volatile H2O and CO2 in the martian regolith should be determined to a depth of 2 m with an accuracy of 10 percent of the concentration and a sensitivity of detection of 0.1 percent. The surface temperature and temperature gradient should be measured. [p. 45] [1.7] Evidence for the existence of life in the past or any information relative to the conditions under which it might evolve, are required to assess the biological potential of Mars. Among the measurements of the martian surface material that address this objective are the following: A complete chemical analysis including all the principal chemical elements (those present in amounts greater than 0.5 percent by atom) as well as those of special biological significance (C, N, Na, P, S, Cl) with a sensitivity of at least 100 ppm; A determination of the oxidation state of the sample and of the pH of water in equilibrium with it; The quantitative determination of the function of depth; The determination of the water-soluble constituents of the sample; The determination of the major anions and cations present if the sample is exposed to water at various pH from 5 to 9; The determination of the amounts of reduced carbon present with a sensitivity of 10 ppb; The identification of the major mineral phases present; The extensive search for possible fossil forms in martian soils and rocks. [p. 45] [1.8] It is obvious that many of these measurements have pertinence to other than the biology oriented objectives of martian exploration. Among the measurements that address the role of the environment of the martian samples and their ability to support life are Establishment of the radiation environment at the surface of Mars, including electrons above 1 MeV and photons above 10 eV and Determination of the amounts of minor constituents of the atmosphere (e.g., CH4) that may reflect the existence of conditions someplace on Mars more favorable to the development of life than were found by Viking. [p. 46] [1.9] Establishment of the interaction of the surface material with the atmosphere and its radiation environment should include the following investigations in addition to the specific analyses of surface material given above: Reactivity of fine material with the constituents of the atmosphere (e.g., solubility in water, absorptive properties for CO2, H2O, CO, or O2). Noble-gas contents and isotopic composition of atmosphere and soil to a precision of better than O.5 percent for all major isotopes. Determine the composition of the martian atmosphere at the surface over an annual cycle. Precise determination of oxygen, nitrogen, carbon, and hydrogen isotope ratios in selected components of martian surface material and atmosphere. [p. 46]

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[1.10] The circulation of the atmosphere of Mars provides the closest analogy to that of the Earth in the solar system, and it therefore serves as an ideal test site for dynamical and climatic theories developed for the Earth. Mechanical and thermal effects of topography on circulation, baroclinic instability, forcing and propagation of tides, generation of dust storms, and long-term climatic variations represent specific topics relevant to both the Earth and Mars. Neither the Viking landers nor Mariner orbiters have provided adequate information to define the global circulation pattern. Atmospheric temperature measurements with a resolution of roughly 5 degrees in latitude, 30 degrees in longitude, and 5 km in altitude between the surface and at least 30 km are needed. This goal could be achieved using a downward viewing infrared sounder in a low-altitude, circular, polar orbit. Much more detailed knowledge of atmospheric waves, including tides and Rossby waves, of the hydrological cycle, of regional meteorology, of the role of dust in the general circulation, and of winds above the boundary layer, is also needed. These problems could be addressed using about four ground-based stations with lifetimes exceeding one martian year and spaced between high latitudes and tropical regions. These stations should be sited to provide at least one triangular network with roughly 1000 km sides, and each station should measure pressure, temperature, relative humidity, atmospheric opacity, and wind velocity. The benefits to be derived from simultaneous measurements from the orbiter and the ground station network should be determined and assessed. [pp. 46–47] [1.11] Determination of the internal structure of Mars, including the thickness of a crust and the existence and size of a core, and measurement of the location, size, and temporal dependence of martian seismic events is an objective of the highest importance. The level of martian seismicity, however, has not been established by the Viking seismology experiment. The possibility cannot be excluded on the basis of currently available data that the seismicity level may be substantially below the upper bound set by the Viking 2 seismometer results and/or that the absorption characteristics of the martian interior may be comparable with or enhanced over those of the earth’s mantle. In such an eventuality, the number of seismic signals recordable on the martian surface from distances of greater than 1000 km may be very few. In spite of this uncertainty, which has been recognized in assessing the relative priority of the determination of internal structure and dynamics as a major scientific objective for Mars exploration, we regard the likelihood of detectable natural seismic events as sufficiently high to recommend that a passive seismic network be established on the martian surface. Such a network should consist of at least three stations with broadband sensors, each with a sensitivity at least 100 times improved over the Viking seismometers, spaced approximately 1000 km apart and operating simultaneously for a period of at least one year. [p. 47] [1.12] Accurate determination of the moment of inertia of Mars, a valuable constraint on internal structure, requires measurement of the martian precessional constant. This measurement can be made from the long-term tracking of one or more landed transmitters, an experiment that may also yield information on the existence of a martian Chandler wobble and on other polar motions. Combined mapping of gravity and topography will allow global extrapolation of locally derived seismic structure and will address the question of martian isostasy as a function of space and time. [p. 47] [1.13] Determination of the character of the martian magnetic field and elucidation of the nature of the planet’s interaction with the solar wind and the structure and dynamics of the upper atmosphere are essential objectives of continuing Mars study. . . . Measurements sufficient to separate an internal, global-scale magnetic field from the solar-wind-induced field and to establish the presence of an internal field having a surface intensity approaching 10–5 G should be carried out. Confident separation of internal global and regional fields from the induced external components would be facilitated by simultaneous measurements of both the plasma and the magnetic field as well as measurements in the free-streaming solar wind. [p. 48] [1.14] The interaction between the solar wind and Mars’ upper atmosphere presents a host of problems that are fundamental to our understanding of both Mars and of planetary atmospheres in general. Among the major issues are the physical processes that produce mass exchange between the atmosphere and the solar-wind flow and the atmospheric mass-loss (or gain) rates that result; these escape processes are essential to our understanding of the evolution of Mars’ atmosphere. Characterization of the Mars solar-wind interaction will require establishing the distribution of neutral atmospheric constituents, as well as the ionized plasma and charged-particle distributions from both the solar wind and the atmosphere separately. These should be carried out both in the dayside interaction region, near an altitude of 300

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km, and in the nightside, downstream magnetosphere, or wake region ranging to several Mars radii. In addition, the fluxes of energetic particles that may be accelerated by the Mars solar-wind interaction should be established. [p. 48] [1.15] Potassium, thorium, and uranium should be determined to a sensitivity comparable with the levels in Apollo 11 basalts, and the following elements with an accuracy of 10 percent at the indicated concentrations: Fe, 1 percent; Ti, 0.5 percent; Si, 5.0 percent; O, 5.0 percent; Mg, 4.0 percent; H, 1.0 percent. The measurement of Al, Ca, Na, Mn, and Ni would be highly desirable. [p. 49] [1.16] The diversity of the martian surface, as well as the wide range of environmental conditions and our ignorance of some of the key processes active on the martian surface, compel us to the view that the scientific objectives will best be met by exploring broad areas that exhibit the effects of distinctive processes that have influenced martian involution and by the intensive study of an intelligently selected suite of martian samples returned to Earth. The selection of returned materials should be based on our understanding of the global and local diversity of martian terrains and environments. [p. 49] [1.17] To understand the current and past processes operating both at and near the surface of Mars, it is essential to explore the diversity of martian terrains that are apparent on both global and local scales. We therefore recommend that detailed exploration, on both global and local scales, of the diverse environments of Mars for purposes of understanding surface, near-surface, and atmospheric processes is a worthy goal in its own right and should be accomplished within the next decade. To this end, intensive local investigations in selected areas of 10 to 100 km in extent should be carried out, and, in addition, measurements at single points of extreme planetary environments should if possible be exploited. These local investigations should explore terrain and sample diversity with a wide range of chemical, mineralogical, and physical techniques. Both the analytical techniques and the manipulative skills of the experimental devices should be much advanced from those used on Viking, but without attempting to duplicate an Earth laboratory. Several science objectives requiring global-scale investigations can be accomplished with orbiters. Geochemical and geophysical mapping and atmospheric temperature soundings should if possible be carried out over the entire planet with spatial resolution compatible with science objectives. We emphasize that geochemical and geophysical mapping experiments must provide results that are clearly interpretable in terms of fundamental planetary characteristics and processes. [p. 49] [1.18] Geochemical and geophysical mapping and atmospheric temperature soundings should be carried out over the entire planet with spatial resolution compatible with science objectives. We emphasize that geochemical and geophysical mapping experiments must provide results that are clearly interpretable in terms of fundamental planetary characteristics and processes. In addition, temperature sounding should cover the full diurnal and seasonal cycles. Investigation of Mars’ magnetic field and atmospheric interaction with the solar wind requires both dayside and nightside measurements. [p. 50] [1.19] The Space Science Board (see Opportunities and Choices in Space Science, 1974, National Academy of Sciences, Washington, D.C., 1975, p. 19) has previously recommended for Mars that the “long-term objectives of exobiology and surface chemistry investigation are best served by the return of an unsterilized surface sample to Earth” and further recommended that Mars sample return be adopted as a long-term goal. The Committee has thoroughly reconsidered this matter and concluded that understanding of the basic physical-chemical mechanisms that govern the surface of Mars can only be obtained by sophisticated and interactive analytical investigations. The return of martian surface and subsurface samples to Earth laboratories will allow the full range of the most sophisticated analytical techniques to be applied for the study of chronology, elemental and isotopic chemistry, mineralogy, and petrology and for the search for current and fossil life. In addition, such samples will be available to future scientists for study with improved techniques or with wholly new concepts compared with those available at the time the sample return mission was designed. We therefore reaffirm our view that the return of unsterilized surface and subsurface samples to Earth is a major technique for the exploration of Mars. Samples of distinctive materials, including rocks and fines, should be selected from an area of at least 2 m2, based on visual inspection and major elemental analyses at the landing site. Materials should be selected that reflect the diversity of the local environment and the processes of broader planetary evolution. Samples should be returned to Earth in a manner that preserves their integrity and that is free from terrestrial contamination. [p. 50] [1.20] With regard to the role of life-seeking experiments in the future exploration of Mars, COMPLEX is in accord with the general views expressed by CPBCE [Committee on Planetary Biology and Chemical Evolution, a former Committee of the Space Studies Board]. Based on the goal of understanding how the appearance of life in the

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solar system is related to the chemical history of the solar system, COMPLEX has formulated a strategy for future Mars exploration on the following premises: Characterization of the chemical composition and physical state of materials on the surface and below the surface and the interaction of these materials with the atmosphere and sunlight are of basic importance to understanding the biologic potential of the planet. The abundance and distribution of carbon compounds and water (including liquid water) in different materials is of significance. The direct search for the study of chemical effects that relate to metabolic activity in martian materials and the intensive search for possible martian fossils should be carried out on unsterilized material returned to Earth without contaminating them with terrestrial materials. Substantial attention and sensitivity toward the biologic potential of the martian environment should be associated with the in situ chemical and physical characterization of Mars without directing specific efforts towards active life-seeking experiments. [pp. 53–54] [1.21] The CPBCE report distinguished between biologically relevant experiments that should be conducted remotely on the surface of Mars in an ensuing mission or missions and those that should be conducted on samples returned to Earth. For the former, it recommended analyses on samples of those characteristics that would constitute items of paramount importance to present or past biology and to organic chemical evolution, namely, the presence of reduced carbon, and the isotopic state of carbon, the amount and state of water, the presence of water-soluble electrolytes, and the existence of nonequilibrium gas compositions. It recommended that specific “life-seeking” metabolic-type experiments not be conducted remotely on the martian surface, but that they only be conducted on unsterilized samples returned to Earth. [p. 53] 2. 1990 The Search for Life’s Origins: Progress and Future Directions in Planetary Biology and Chemical Evolution (NRC, CPBCE, 1990) [The Committee on Planetary Biology and Chemical Evolution] recommends studies to: [2.1] Conduct chemical, isotopic, mineralogical, sedimentological, and paleontological studies of martian surface materials at sites where there is evidence of hydrologic activity in any early clement epoch, through in situ determinations and through analysis of returned samples; of primary interest are sites in the channel networks and outflow plains; highest priority is assigned to sites where there is evidence suggestive of water-lain sediments on the floors of canyons as in the Valles Marineris system, particularly Hebes and Candor chasmata. [p. 124] [2.2] Reconstruct the history of liquid water and its interactions with surface materials on Mars through photogeologic studies, space-based spectral reflectivity measurements, in situ measurements, and analysis of returned samples. [p. 124] 3. 1990 1990 Update to Strategy for Exploration of the Inner Planets (NRC, COMPLEX, 1990) [3.1] The importance of the scientific objectives of study of the martian atmosphere, interior, magnetic field, and global properties should be given equal priority with the objective of intensive study of local areas. [p. 5] [3.2] The geochemical, isotopic, and paleontological study of martian surface material for evidence of previous living material should be a prime objective of future in situ and sample return missions. [p. 5] [3.3] Consistent with the SSB [Space Studies Board] report The Search for Life’s Origins: Progress and Future Directions in Planetary Biology and Chemical Evolution (National Academy Press, Washington, D.C., 1990), the committee endorses the continued search for evidence of past life and biochemical evolution on Mars, as well as the continuing study of the history of water on Mars. [p. 21] 4. 1994 An Integrated Strategy for the Planetary Sciences: 1995-2010 (NRC, COMPLEX, 1994) [4.1] Two kinds of precise positional measurements provide information on internal structure and dynamics. The first is a very accurate determination of the spin angular-momentum vector of a planet (both amplitude and

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direction) to monitor length-of-day changes, nutation, and precession. In some circumstances, such measurements can allow determination of the planet’s first-order interior structure and whether the planet has a liquid core, as well as the nature of core-mantle coupling; this has been done for the Moon and could be done for Mars and Mercury. The second type of measurement, which is regional and is similar to that made possible by the Global Positioning System on Earth, can lead to the detection of small relative crustal movements (of the order of 1 cm/yr or, possibly, 1 mm/yr in the future). Such measurements could provide interesting new information for a planet with suspected active tectonism, such as Venus and possibly Mars. [p. 88] [4.2] Sample return may remain the only viable way of determining chronologies, but it should be emphasized that determination of even relatively imprecise ages can be very valuable in some cases. The flexibility, affordability, and feasibility of achieving many of these goals would be greatly enhanced by development of even crude dating techniques that could be placed aboard landed science packages. [pp. 98–99] [4.3] A better understanding of the present climate of Mars inevitably depends also on understanding its present general circulation—the means by which heat, carbon dioxide, water vapor, and dust are transported. General circulation model simulations have shown that the dramatic martian seasonal surface-pressure variation, measured by the Viking landers, has two comparable components—one due to seasonal exchange with the polar caps and the other due to redistribution of atmospheric mass by the large-scale circulation. The modeling shows that a quantitative understanding of the seasonal CO2 cycle and of the intimately linked cycles of dust and water requires knowledge of the large-scale seasonally varying pattern of atmospheric pressure and the closely related surface wind pattern responsible for raising and redistributing dust. Orbiters can determine the atmospheric temperature field and the dust and water loading but cannot measure the surface pressure with sufficient accuracy, and the pressure is a crucial dynamic boundary condition. Conversely, information on the surface pressure without data on the thermal field through the interior of the atmosphere is incomplete information. Ideally, the orbiter and lander measurements should be conducted simultaneously, because together they permit the construction of the full three-dimensional circulation. It has long been recognized that an orbiter, together with at least 15 or 20 surface stations, is required to achieve a good characterization of the system. [pp. 128–129] [4.4] To resolve the issue of whether or not Mars had an early warm climate, the processes that created the observed channels and valley networks need to be elucidated, and the climatic implications of the processes need to be determined. More specific knowledge of the water budget in the crust of Mars and more accurate determinations of isotopic abundances, for example, the D/H abundance ratios, in the atmospheres of Venus and Mars will help to resolve this issue. [p. 131] [4.5] The martian atmosphere is a high-priority region for study. It presents questions of climate variability, atmospheric origin, chemical stability, and atmospheric dynamics. Many of these questions are of particular interest among a broad community because Mars is similar enough to Earth to allow scientifically useful comparisons. Particular emphasis should be placed on long-term monitoring of dynamical behavior with good spatial resolution, such as can be performed by an orbiter. Surface meteorological stations, preferably accompanied by use of an orbiter, are the next step. Eventually, subsurface volatile reservoirs will need to be investigated to reach an understanding of atmospheric and climate history. [p. 135] [4.6] At Mars, it is important to gain a first-order understanding of how the solar wind interacts with this planet and to begin the study of martian aeronomy. [p. 172] [4.7] Mars is a marvelous place to study the processes that control atmospheric dynamics on terrestrial planets. Significant progress can be made through the deployment of a long-lived global network of surface meteorological stations. These outposts should provide essential data on the daily weather and, when combined with simultaneous sounding from orbit, will lead to much-improved general circulation models. These stations should also be used to determine the seasonal cycles of carbon dioxide, water, and dust and thereby learn something about how the layered martian polar sediments are deposited . . . . One of the outstanding unknowns in geophysics concerns the internal structures of planets. This subject has profound ramifications for studies of origins and surface geology, since differentiation provides heat to mix the original materials and to shape later events. The easiest way to probe beneath Mars’s surface is with a set of widely spaced seismometers that could be placed aboard the meteorological stations described above. These same stations should carry sophisticated geochemical laboratories to assay local materials. [p. 192]

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5. 1995 An Exobiological Strategy for Mars Exploration (NASA, 1995) [5.1] High-resolution imaging of selected sites by means of mid-IR mapping spectrometry is needed to identify surface expressions of aqueous mineralization, such as hydrothermal systems or spring deposits. [p. 54] [5.2] We recommend establishment of a sequence of landed missions, beginning with development of a geochemically oriented payload capable of regional chemical and mineralogical analyses, oxidant identification, and volatile-element detection. This payload should be dispatched to a geologically diverse range of sites, which would be identified by means of high-resolution orbital data. This series of landed missions would lead in turn to identification of a limited number of sites of well-defined exobiological interest to which would then be dispatched a more exobiologically focused payload incorporating molecular and isotopic analysis of crustal volatiles. This phase of exploration would also involve high resolution local imagery aimed at assessing local lithologies for their potential to preserve fossils or to harbor extant life. [p. 54] [5.3] Positive results for either preserved organic matter, potentially fossiliferous rocks, or habitats suggestive of extant life would then require deployment of highly focused experiments designed to test for modes of prebiotic chemistry, the presence of fossils, or evidence for metabolic activity, respectively. [p. 54] [5.4] Landed missions should possess the mobility necessary to generate regional rather than purely local data. Such mobility will allow access to sites that may be virtually unreachable by fixed landers for landing safety considerations. [p. 54] [5.5] Many of the techniques in geochemistry and paleontology that are used in exobiology-related studies on Earth do not lend themselves to field applications. Of particular relevance here is the difficulty that may be anticipated in conclusively identifying fossils of past life on Mars without returning a sample. Furthermore any positive signal from a robotic life-detection experiment would obviously demand confirmation in a terrestrial laboratory. For these reasons we recommend sample return as a key part of the long-range exobiology mission strategy. Clearly a sample return would follow after a series of surface lander and rover missions had analyzed samples from sites that had been identified as of particular interest. [p. 54] 6. 1996 “Scientific Assessment of NASA’s Mars Sample-Return Mission Options” (NRC, COMPLEX, 1996) [6.1] . . . [I]f the single objective of sample-return missions is to resolve the question of life on Mars, then highly successful missions could be characterized as failures if they do not return microfossils or living organisms. Therefore, justification of missions in terms of their bearing on the question of martian life alone would be a disservice to the scientific community and to the public, and would have a detrimental impact on the potential scientific results for exobiology and the other planetary science disciplines. Consequently, NASA should focus its Mars program, and sample-return missions in particular, on the more comprehensive goal of understanding Mars as a possible abode of life, a goal that is fully compatible with previous recommendations. [p. 2] [6.2] [COMPLEX] is guardedly optimistic that NASA’s current planning for Mars sample return missions will be consistent with the priorities outlined in past NRC [National Research Council] reports, provided that NASA takes into account the issues discussed above, as summarized here: Formulate a program of Mars sample-return missions in the context of recent developments in the planetary, life, and astronomical sciences and directed toward the comprehensive goal of understanding Mars as a possible abode of life. Incorporate previously developed strategies for determining “prebiotic” chemical evolution into the Mars sample-return program. Maintain adaptability and flexibility in the Mars sample-return program to take into account possible new discoveries from ongoing Mars missions. Ensure that the global reconnaissance of Mars is implemented as early as possible. Ensure that sites and samples are selected that are consistent with established strategies for exobiology and martian exploration. To understand the results from each mission and to provide input for the planning of ongoing missions during the entire Mars exploration program, there must be an adequate, ongoing data-analysis program.

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Ensure that sample handling strategies, including planetary protection issues, are judiciously formulated and implemented. Develop the capability for achieving long-range (tens of kilometers) mobility and high-precision landing. Develop a broad suite of capable, miniature instruments for in situ measurements of surface properties relevant to exobiology and general martian exploration. Develop the criteria to enable the unambiguous identification of biotic signatures. Increase the rate of collection of antarctic meteorites relevant to Mars by, for example, increasing the efficiency of field collection procedures. [p. 5] 7. 1996 “The Search for Evidence of Life on Mars” (McCleese Report) (NASA, Mars Expeditions Strategy Group, 1996) [7.1] The members of the Mars strategy group recommend that the search for life on Mars should be directed at locating and investigating, in detail, those environments on the planet which were potentially most favorable to the emergence (and persistence) of life: ancient ground water environments; ancient surface water environments; and modern ground water environments. [7.2] We urge strongly that the investigation strategy emphasize sampling at diverse sites. It is specifically recommended that the implementation of the program of exploration of Mars be aimed at the study of a range of ancient and modern aqueous environments. These environments may be accessed by exploring the ejecta of young impact craters, by investigating material accumulated in outflow channels, and by coring. [7.3] In-situ studies conducted on the surface of Mars are essential to our learning more about Martian environments and for selecting the best samples for collection. However, for the next 10 years or more, the essential analyses of selected samples must be done in laboratories on Earth . . . “high precision” (i.e., sophisticated, state-of-the-art) analytical techniques must be used, such as those found in only the most advanced laboratories here on Earth. [7.4] We also believe that to achieve widely accepted confirmation of Martian life, all three of the following must be clearly identified and shown to be spatially and temporally correlated within rock samples: 1) organic chemical signatures that are indicative of life, 2) morphological fossils (or living organisms), 3) supporting geochemical and/or mineralogical evidence (e.g., clearly biogenic isotopic fractionation patterns, or the presence of unequivocal biominerals). These characteristics can not be properly evaluated without the return of a variety of Martian samples to Earth for interdisciplinary study in appropriate laboratories. [7.5] Precursor orbital information must be obtained, as well, to select the best sites for surface studies. We can already say with reasonable certainty, however, that the ancient highlands represent a region of great potential, and that at least the initial focused studies should be performed there. Maps of surface mineralogy will be needed to enhance investigations within the highlands and enable searches elsewhere. This work begins with the launch of the Mars Global Surveyor (MGS) later this year. Additional measurements from orbit at higher spatial resolution are essential to identify productive sites (e.g., regions containing carbonates) at scales accessible by surface rovers. In addition, instruments capable of identifying near-surface water, water bound in rocks, and subsurface ice, would greatly accelerate and make more efficient our search for environments suitable for life. [7.6] For ancient ground water environments, a sample return mission can occur relatively soon, since the necessary precursor information for site selection is already available from existing orbital photogeologic data, including Mariner 9 and Viking imagery, or will be provided by Mars Surveyor orbiters in ’96, ’98 and ’01. [7.7] For ancient surface water environments, orbital and surface exploration/characterization should precede sample return because identification of extensive areas of carbonates and evaporites is highly desirable. This implies the use of advanced orbital and in-situ instruments for mineral characterization. [7.8] Sample return missions will retrieve the most productive samples if they are supported by extensive searches, analyses and collections performed by sophisticated rovers. These should be capable of ranges of 10’s of kilometers in order to explore geologically diverse sites. The specific samples to be returned to Earth would be selected using criteria that increase the probability of finding direct evidence of life as well as the geological context, age and climatic environment in which the materials were formed.

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8. 1996 “Scientific Assessment of NASA’s Solar System Exporation Roadmap” (NRC, COMPLEX, 1996) [8.1] COMPLEX has attached very high priority to a better understanding of martian atmospheric circulation as the key component of the climate system and for comparative studies of atmospheric dynamics. Yet, this Roadmap campaign does not effectively address this key objective for Mars. [p. 4] 9. 1998 “Assessment of NASA’s Mars Exploration Architecture” (NRC, COMPLEX, 1998) [9.1] . . . [A]n appropriate focus for NASA’s Mars program is the comprehensive goal of understanding Mars as a possible abode of past or present life. [p. 10] [9.2] To the extent possible, information must be obtained on the global martian environment in order to understand the events in the history of the martian samples and of the planet in general. [p. 2] 10. 2000 NASA Strategic Plan 2000 (NASA, 2000) Only items relevant to Mars exploration are listed. [10.1] Objectives Learn how galaxies, stars, and planets form, interact, and evolve Look for signs of life in other planetary systems Understand the formation and evolution of the solar system and the Earth within it Probe the evolution of life on Earth, and determine if life exists elsewhere in the solar system Understand our changing Sun and its effects throughout the solar system Investigate the composition, evolution, and resources of Mars, the Moon, and small bodies [p. 18] [10.2] Near-term Plans (2000–2005) Investigate Saturn, its rings, and moon Titan. Analyze the structure and composition of comets, understand the history of Mars, and return dust and solar wind samples Conduct laboratory and field research on the origin of life on Earth (Astrobiology Initiative), and search for water on Mars Obtain images of the Earth’s magnetosphere during geomagnetic storms, search for evidence of water on Mars, and characterize the number and orbits of Near Earth Objects Explore the surface and atmosphere of Mars, survey the structure and composition of asteroids, and investigate the composition and structure of comets [p. 18] [10.3] Mid-term Plans (2006–2011) Learn about formation of the rocky planets, investigate the nature of the early solar system by returning a sample from a comet, and continue exploration of Mars Continue research on life on Earth and potential biological history of Mars, and search for liquid water ocean on Jupiter’s moon, Europa Investigate selected sites on Mars in detail Continue exploration of Mars, ascertain the presence of a liquid water ocean on Europa, and return a sample from a comet nucleus [p. 19] [10.4] Long-term Plans (2012–2025) Complete reconnaissance of the Solar System by flying by Pluto, studying Neptune and its satellite Triton, and conducting advanced studies of Mars Search for evidence of biological activity on Europa, study the prebiotic chemistry of Saturn’s moon Titan, and explore promising solar system targets to search for evidence of past or present life. Integrate solar system findings with the search for life in other planetary systems Continue exploration of the inner solar system in support of possible human exploration [p. 19]

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11. 2000 “Mars Exploration Program: Scientific Goals, Objectives, Investigations, and Priorities” (NASA, MEPAG, 2001) Extracted from the December 2000 edition of the MEPAG report, “Mars Exploration Program: Scientific Goals, Objectives, Investigations, and Priorities,” edited by R. Greeley. An exhaustive discussion of Mars science priorities, the MEPAG report is at once valuable and frustrating. It is valuable because it is one of the few committee studies that makes any attempt to prioritize science objectives. It is frustrating because it is so ambitious and inclusive as to be unrealistic. Detailed discussions have been removed in the extracted material that follows to make the list short enough to be included in this appendix. The report is organized into broad Goals, and each goal into narrower Objectives. Quoting from the report: Within each objective, the investigations are listed [in priority order] as determined within each discipline. There was no attempt to synthesize the overall set of investigations, but it was recognized that synergy among the various goals and objectives could alter the priorities in an overall strategy. Completion of all the investigations will require decades of effort. It is recognized that many investigations will never be truly complete (even if they have a high priority) and that evaluations of missions should be based on how well the investigations are addressed. While priorities should influence the sequence in which the investigations are conducted, it is not intended that they be done serially, as many other factors come into play in the overall Mars Program . . . . [pp. 1–2] This section groups all the top-priority (No. 1) investigations listed, across objectives, under a Category 1. The same is done with Categories 2, 3, . . . 10. MEPAG would protest, with some justice, that this is a pointless and misleading exercise. Constructing a top-priority category with contributions from all the objectives makes the assumption that all “objectives” are equally important. This, of course, is not the case, but MEPAG, like every other study group, refused to consider the relative importance of the objectives and the disciplines they reside in. This method of grouping also penalizes those objectives whose representatives recognized many needed investigations, which relegates most of the investigations to high-numbered (implied low-priority) categories. Nonetheless, the categories, at least the low-numbered ones, do crudely express MEPAG’s priorities, which gives the categories some value. For more detail and fairness, the reader is directed to the original MEPAG report. 11.1, Category 1 [11.1.1] Map the 3-dimensional distribution of water in all its forms. . . . Requires global mapping by remote sensing and, if possible, seasonal changes in near-surface water budgets. [p. 2] [11.1.2] Determine the locations of sedimentary deposits formed by ancient and recent surface and subsurface hydrological processes. . . . Requires global geomorphic and mineral mapping, followed by the in situ “ground truth” for orbital data and to identify sites for sample return. [p. 4] [11.1.3] Search for complex organic molecules in rocks and soils. . . . Requires studies of modern aqueous environments and aqueous paleoenvironments preserved in ancient sedimentary rocks. Targets for in situ studies must be first identified from orbit, then mobile platforms (rovers), and returned samples. [p. 6] [11.1.4] Determine the processes controlling the present distributions of water, carbon dioxide and dust. . . . Requires global mapping and then landed observations on daily and seasonal time scales. [p. 7] [11.1.5] Find physical and chemical records of past climates. . . . Requires remote sensing of stratigraphy and aqueous weathering products, landed exploration, and returned samples. [p. 10] [11.1.6] Determine the present state, distribution and cycling of water on Mars. . . . Requires global observations using geophysical sounding and neutron spectroscopy, coupled with measurements from landers, rovers, and the subsurface. [p. 12] [11.1.7] Characterize the configuration of Mars’ interior. . . . Requires orbital and lander data. [p. 17] [11.1.8] Determine the radiation environment at the Martian surface and the shielding properties of the Martian atmosphere [HEDS]. . . . Requires simultaneous monitoring of the radiation in Mars’ orbit and at the surface, including the ability to determine the directionality of the neutrons at the surface. [p. 18]

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11.2, Category 2 [11.2.1] Carry out in situ exploration of possible liquid water in the subsurface. . . . Requires drilling to km depths and instruments to detect water in all forms, CO2 clathrate, and to analyze rocks, soils and ices for organic compounds or to detect life. [p. 2] [11.2.2] Search for Martian fossils. . . . Requires orbital mapping, in situ analysis, and sample returns. [p. 5] [11.2.3] Determine the changes in crustal and atmospheric inventories of organic carbon through time. . . . [T]his objective is posed in a historical way that requires a stratigraphic framework (established through geological mapping) and returned samples. [p. 7] [11.2.4] Determine the present-day stable isotopic and noble gas composition of the present-day bulk atmosphere. [p. 9] [11.2.5] Characterize history of stratigraphic records of climate change at the polar layered deposits, the residual ice caps. . . . Requires orbital, in situ observations and returned samples. [p. 11] [11.2.6] Evaluate sedimentary processes and their evolution through time, up to and including the present. . . . Requires knowledge of the age, sequence, lithology and composition of sedimentary rocks (including chemical deposits), as well as the rates, durations, environmental conditions, and mechanics of weathering, cementation, and transport processes. [p. 12] [11.2.7] Determine the history of the magnetic field. . . . Requires orbiter in eccentric orbit or low-altitude platform. [p. 17] [11.2.7] Characterize the chemical and biological properties of the soil and dust [HEDS]. . . . The requirements can and may have to be met through sample studies on Earth. Earth sample return provides significant benefits to HEDS technology development programs. [p. 19] 11.3, Category 3 [11.3.1] Explore high priority candidate sites (i.e., those that provide access to near-surface liquid water) for evidence of extant (active or dormant) life. . . . Requires in situ life experiments on subsurface materials and laboratory analysis of returned samples. [p. 3] [11.3.2] Determine the timing and duration of hydrologic activity. . . . Requires the development of stratigraphic (age) framework, in situ measurements, and sample returns from key sites for radiometric dating. [p. 6] [11.3.3] Determine long-term trends in the present climate. [p. 9] [11.3.4] Calibrate the cratering record and absolute ages for Mars. . . . Requires absolute ages on returned rock (not soil) samples of known crater ages. [p. 13] [11.3.5] Determine the chemical and thermal evolution of the planet. . . . Requires measurements from orbiter and lander. [p. 18] [11.3.6] Understand the distribution of accessible water in soils, regolith, and Martian groundwater systems [HEDS]. . . . Requires geophysical investigations and subsurface drilling and in situ sample analysis. [p. 20] 11.4, Category 4 [11.4.1] Determine the array of potential energy sources to sustain biological processes. . . . Requires orbital mapping and in situ investigations. [p. 3] [11.4.2] Determine the rates of escape of key species from the Martian atmosphere, and their correlation with solar variability and lower atmosphere phenomenon (e.g. dust storms). . . . Requires: Global orbiter observations of species (particularly H, O, CO, CO2 and key isotopes) in the upper atmosphere, and monitoring their variability over multiple Martian years. [p. 9] [11.4.3] Evaluate igneous processes and their evolution through time, including the present. . . . Requires global imaging, geologic mapping, techniques for distinguishing igneous and sedimentary rocks, evaluation of current activity from seismic monitoring, and returned samples. [p. 13]

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[11.4.4] Measure atmospheric parameters and variations that affect atmospheric flight [HEDS]. . . . Requires instrumented aeroentry shells or aerostats. [p. 20] 11.5, Category 5 [11.5.1] Determine the nature and inventory of organic carbon in representative soils and ices of the Martian crust. . . . Requires in situ exploration and sample return. [p. 4] [11.5.2] Search for micro-climates. . . . Requires global search for sites based on topography or changes in volatile distributions and surface properties (e.g., temperature or albedo). [p. 10] [11.5.3] Characterize surface-atmosphere interactions on Mars, including polar, eolian, chemical, weathering, and mass-wasting processes. Interest here is in processes that have operated for the last million years as recorded in the upper 1 m to 1 km of geological materials. . . . Requires orbital remote sensing of surface and subsurface, and in situ measurements of sediments and atmospheric boundary layer processes. [p. 14] [11.5.4] Determine electrical effects in the atmosphere [HEDS]. . . . Requires experiments on a lander. [p. 21] 11.6, Category 6 [11.6.1] Determine the distribution of oxidants and their correlation with organics. . . . Requires instruments to determine elemental chemistry and mineralogy. [p. 4] [11.6.2] Determine the production and reaction rates of key photochemical species (O3, H2O2, CO, OH, etc.) and their interaction with surface materials. [p. 10] [11.6.3] Determine the large-scale vertical structure and chemical and mineralogical composition of the crust and its regional variations. This includes, for example, the structure and origin of hemispheric dichotomy. . . . Requires remote sensing and geophysical sounding from orbiters and surface systems, geologic mapping, in-situ analysis of mineralogy and composition of surface material, returned samples, and seismic monitoring. [p. 15] [11.6.4] Measure the engineering properties of the Martian surface [HEDS]. . . . Requires in-situ measurements at selected sites. [p. 21] 11.7, Category 7 [11.7.1] Document the tectonic history of the Martian crust, including present activity. . . . Requires geologic mapping using global topographic data combined with high-resolution images, magnetic and gravity data, and seismic monitoring. [pp. 15–16] [11.7.2] Determine the radiation shielding properties of Martian regolith [HEDS]. . . . Requires an understanding of the regolith composition, a lander with the ability to bury sensors at various depths up to a few meters. Some of the in situ measured properties may be verified with a returned sample. [p. 22] 11.8, Category 8 [11.8.1] Evaluate the distribution and intensity of impact and volcanic hydrothermal processes through time, up to and including the present. . . . Requires knowledge of the age and duration of the hydrothermal system, the heat source, and the isotopic and trace element chemistry and mineralogy of the materials deposited. [p. 16] [11.8.2] Measure the ability of Martian soil to support plant life [HEDS]. . . . Requires in-situ measurements and process verification. [p. 22] 11.9, Category 9 [11.9.1] Characterize the topography, engineering properties, and other environmental characteristics of candi-date outpost sites. Site certification for human outposts requires a set of data about the specific site that can best be performed by surface investigations [HEDS]. [p. 22] 11.10, Category 10 [11.10.1] Determine the fate of typical effluents from human activities (gases, biological materials) in the Martian surface environment [HEDS]. [p. 22]

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REFERENCES Mars Expeditions Strategy Group, National Aeronautics and Space Administration (NASA), “The Search for Evidence of Life on Mars,” 1996, available online at <http://geology.asu.edu/~jfarmer/mccleese.htm>. Also available in National Aeronautics and Space Administra-tion, Science Planning for Exploring Mars, JPL Publication 01-7, Jet Propulsion Laboratory, Pasadena, Calif., 2001. NASA, An Exobiological Strategy for Mars Exploration, NASA, Washington, D.C., 1995. NASA, Strategic Plan 2000, NASA, Washington, D.C., 2000. NASA, Mars Exploration Payload Assessment Group (MEPAG), “Mars Exploration Program: Scientific Goals, Objectives, Investigations, and Priorities,” December 2000, in Science Planning for Exploring Mars, JPL Publication 01-7, Jet Propulsion Laboratory, Pasadena, Calif., 2001. NRC (National Research Council), COMPLEX (Committee on Planetary and Lunar Exploration), Strategy for Exploration of the InnerPlanets: 1977–1987, National Academy Press, Washington, D.C., 1978. NRC, Committee on Planetary Biology and Chemical Evolution (CPBCE), The Search for Life’s Origins: Progress and Future Directions inPlanetary Biology and Chemical Evolution, National Academy Press, Washington, D.C., 1990. NRC, COMPLEX, 1990 Update to Strategy for Exploration of the Inner Planets, National Academy Press, Washington, D.C., 1990. NRC, COMPLEX, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press, Washington, D.C., 1994. NRC, COMPLEX, “Scientific Assessment of NASA’s Mars Sample-Return Mission Options,” letter report, Space Studies Board, NRC, Washington, D.C., 1996. NRC, COMPLEX, “Scientific Assessment of NASA’s Solar System Exploration Roadmap,” letter report, Space Studies Board, NRC, Washington, D.C., 1996. NRC, COMPLEX, “Assessment of NASA’s Mars Exploration Architecture,” letter report, Washington, D.C., 1998.