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Space Studies Board Jump to Top Search: NewsJump to Science in the Subscribe to our FREE e- Headlines newsletter! NATIONAL ACADEMY OF SCIENCES NATIONAL ACADEMY OF ENGINEERING INSTITUTE OF MEDICINE NATIONAL RESEARCH COUNCIL June 18, 2004 Current Operating Status On NASA Mars Sample-Return Mission Options Report At its October 16-18, 1996, meeting, the Space Studies Board's Committee on Planetary and Lunar Exploration (COMPLEX), chaired by Prof. Ronald Greeley (Arizona State University), conducted an assessment of the plans developed within NASA's Mars Surveyor program office to meet the long-standing scientific goal of returning martian samples to Earth for study in terrestrial laboratories. This assessment was made at the request of Dr. Jurgen Rahe, NASA's Science Program Director for Solar System Exploration, with a requested response date of early December, 1996. This assessment is based on material sent to committee members for review prior to the meeting, 1 presentations by invited experts at the October meeting, and subsequent discussions in executive sessions. The goals of Mars sample-return missions and the types of scientific investigations that could be conducted on martian specimens in terrestrial laboratories were described by Drs. Bruce Jakosky (University of Colorado), Michael Drake (University of Arizona), Alan Treiman (Lunar and Planetary Institute), and Kenneth Nealson (University of Wisconsin, Milwaukee). The various mission scenarios currently being considered by NASA were described by Dr. Jeffrey Plescia (Jet Propulsion Laboratory). According to Dr. Plescia, NASA has outlined four sample return options, characterized as baseline, paced, accelerated, and aggressive (see appendix for details). The baseline option was described to COMPLEX at its June 1996 meeting by Dr. Daniel McCleese (Jet Propulsion Laboratory) of NASA's Mars Surveyor program office. Because of the lack of details provided about the four proposed mission options (see appendix), COMPLEX must defer a specific assessment of mission plans. The committee can, however, make the following comments at this time regarding return of samples from Mars: q It seems imprudent to land a 700-kg inert payload to simulate a sample- return vehicle, as planned in the baseline option. If appropriate instruments were identified, this opportunity could provide for the collection of scientific data. http://www7.nationalacademies.org/ssb/msrrep.html (1 of 11) [6/18/2004 9:26:18 AM]
Space Studies Board q The paced and accelerated options both return what would appear to be scientifically valid samples, with earlier sample retrieval in the accelerated option. q The aggressive option's scientific potential is rich, but its scope seems unrealistically ambitious. Although COMPLEX is unable to make detailed comments on particular mission options at this time, it is able to provide observations and suggestions on implementation strategy, site selection and sampling strategy, technology requirements, and related programmatic issues. COMPLEX believes that close attention to these issues, highlighted in past National Research Council (NRC) reports, is essential for the success of Mars sample-return missions. OVERALL OBSERVATIONS In its 1996 report, Review of NASA's Planned Mars Program, 2 COMPLEX stated that "the goal of returning samples of martian soil, atmosphere, and, most importantly, rocks [should remain] a central element of NASA's planning." The scientific priorities for the study of Mars, as defined in past reports by COMPLEX, can be summarized as follows: 3, 4, 5 q Understanding the evolution of the planet's surface and interior via studies of its chemistry, lithology, and morphology on a range of scales from local to global; q Characterizing the dynamics and chemistry of the planet's atmosphere and the degree to which climatic conditions have evolved over time; q Searching the planet for extinct or extant life, including evidence of the accumulation of a reservoir of prebiotic organic compounds and the extent of any subsequent prebiotic chemical evolution; and q Determining the nature of the planet's interaction with the solar wind and the extent to which these interactions affect the state and evolution of the planet's upper atmosphere and ionosphere. Sample-return missions are relevant, if not essential, to addressing many of these goals. Therefore, the committee is pleased that NASA has taken the opportunity provided by the increased attention to Mars exploration resulting from the McKay et al. paper 6 on the ALH84001 meteorite to accelerate planning of a program of Mars sample-return missions. Yet although findings by McKay et al. have captured the public's interest, much as they have the attention of scientists, they are only suggestive. The existence of microfossils and other indicators of life in martian meteorites is far from proven and is currently the subject of intense study. Therefore, COMPLEX believes that it is inappropriate to predicate an important aspect of future martian studies on the unconfirmed results described in a single scientific paper. Rather, the appropriate scientific context within which NASA should frame its study of the possibility that life arose on Mars at some time in the past has several elements: the suggestive results from ALH84001, new findings on microbial life in extreme terrestrial environments (e.g., deep beneath Earth's crust http://www7.nationalacademies.org/ssb/msrrep.html (2 of 11) [6/18/2004 9:26:18 AM]
Space Studies Board and oceans), new perspectives on the origin of terrestrial life, current understanding of the evolution of the martian and other planetary environments, and recent findings about the existence of planets around other stars. COMPLEX agrees with many of the elements in the working paper drafted by NASA's Mars Expeditions Strategy Group, 7 as noted below. However, given the framework for martian studies outlined above, COMPLEX urges that other considerations be incorporated into the program as discussed and summarized in the following sections. Prime among COMPLEX's concerns is the inadvisability of NASA's seeking only a simple answer to the question of life on Mars, because unequivocal evidence may be hard to find. The full implications of such a question can be realized only in the context of life's origin in a planetary environment and of its subsequent evolution in conjunction with the evolution of the planet. COMPLEX, 8,9,10 the Space Studies Board's (SSB's) former Committee on Planetary Biology and Chemical Evolution, 11 and a recent NASA report 12 have each outlined a consistent strategy for the exobiologic exploration of Mars. The results from ALH84001 do not, in COMPLEX's opinion, invalidate the measured approach embodied in this strategy. On the contrary, while a suite of missions that exclusively address exobiology questions could advance the overall goals for the exploration of Mars, they could just as easily compromise future studies of Mars if the missions and their objectives are misconstrued. For example, if 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. STRATEGY ISSUES 1. The search for life on Mars is only a part of the exobiologic study of the planet and of the scientific rationale for sample-return missions. 13,14,15,16 Even if there is neither extant nor extinct life on Mars, the planet's "prebiotic" chemical evolution is an important part of the history of life in the solar system. 17,18 Study of the "prebiotic Mars" will provide a context for the possible occurrence of martian life and should be a fundamental part of the Mars sample-return program. With respect to life, Mars may provide access to a paleochemical record unavailable on Earth. 2. COMPLEX recognizes that the overall structure of the Mars sample-return and exploration program should be outlined early. However, as noted previously, 19 adaptability and flexibility of the program are of paramount importance. There should be sufficient flexibility in the program to allow later missions to take http://www7.nationalacademies.org/ssb/msrrep.html (3 of 11) [6/18/2004 9:26:18 AM]
Space Studies Board advantage of the results of earlier missions. 3. Global reconnaissance of Mars should be a high priority early in the Mars sample-return program in order to allow intelligent selection of sample collection sites and to provide a global context for analysis of sample data. 20,21 Such reconnaissance is planned from the Mars Global Surveyor (MGS); if that or subsequent orbital missions are not successful, however, pertinent measurements (such as high-resolution imaging and infrared spectroscopy from MGS) need to be obtained at the earliest opportunity. 4. The Mars sample-return program neither begins with sample collection nor ends with the return of martian samples to Earth. The Mars Surveyor program must, for example, maintain a vigorous science analysis program during and following mission activity. Sufficient resources need to be allocated within the program for timely analysis of the data returned from the spacecraft already at Mars and/or related programs such as the development of appropriate instrumentation, and for study of samples in terrestrial laboratories. 5. Planetary protection requirements should be defined as early in the program as is feasible. These requirements will ultimately determine the time scale regarding the availability of samples for analysis in terrestrial laboratories. The SSB's Task Group on Issues in Sample Return is currently investigating these topics and related issues, such as the role of regulatory agencies and public perception of the risk associated with sample-return missions. 22 ISSUES REGARDING SELECTION OF SAMPLE-RETURN SITES 1. Selection of samples to be returned to Earth must be optimized in order to provide the best opportunities for learning as much as possible about Mars. For example, the sampling mechanism could have the ability to discard a previously selected specimen should a more interesting one be found. Randomly selected rocks or sediments, even from interesting sites, are unlikely to be adequate samples for exobiologic analysis. 23,24,25 Similarly, landing sites for sample- return missions should be selected on the basis of scientific potential rather than engineering constraints alone. The future flexibility of the program should be provided for by identifying a diversity of sites early. 2. The report of NASA's Mars Expeditions Strategy Group 26 identifies three broad environments as potential sample-return sites. These are sites associated with ancient ground water, ancient surface water, and modern ground water. Recognizing that current knowledge of martian geology and geochemistry derives primarily from Viking data, new information from near-term missions, such as Mars Global Surveyor, should have a significant impact on final site selection if adequate resources are provided for data analysis. The set of sites selected should represent different geologic environments relevant to the several objectives of a balanced program of Mars exploration. 27 In this regard, the ancient ground water site and the ancient aqueous environment appear to be well chosen. http://www7.nationalacademies.org/ssb/msrrep.html (4 of 11) [6/18/2004 9:26:19 AM]
Space Studies Board 3. Sites should be selected where the relevant geologic record is best preserved and most easily studied. The physical and chemical conditions necessary for the origin and early development of life are unknown, even on Earth. As noted in past NRC documents, 28,29,30 locating relevant sites is dependent on data collected from prior missions, and a broad-based study of Mars is essential to this process. Sites defined to provide maximum information on the physical and chemical conditions early in martian history are especially important, because early conditions are most likely to be relevant to the origin and early evolution of life. Of the two ancient sites, the ground water (highland) site is probably the better choice for the first sample-return mission because older, possibly more diverse, materials should be present. TECHNOLOGY DEVELOPMENT 1. The capability should be developed for significant mobility (tens of kilometers) to allow sampling of a diverse suite of rocks from a landing site. 31,32,33 The probability of making significant advances in exobiologic investigations depends critically on the quality of the material returned, and increased mobility provides the capability to examine numerous samples before a final selection is made. This capability would greatly enhance the collection of an optimal suite of returned samples, as well as permit a detailed characterization of the environmental context of a site. 2. A broad suite of capable, miniature instruments for in situ determination of the geomorphology, mineralogy, petrology, and chemistry of a site should be developed. 34,35 These instruments will aid in sample selection and determination of the environmental context of samples. The suite of instruments developed should cover the range of currently feasible, as well as anticipated, measurement techniques to permit flexibility in instrument selection and to respond to new discoveries. 3. Methods should be developed for landing close to surface target sites. The size of the major axis of the landing-error ellipse should be smaller than the range of the rovers. This capability will allow complex geologic sites to be targeted safely and within reach of rovers. Examples of potentially interesting sites include volcanic systems, sedimentary basins, or channel floors, walls, and ejecta deposits. 36,37 4. Development of high-spatial-resolution (centimeter to meter) instruments and platforms to extend the global characterization of rock and soil materials to scales appropriate for lander and rover operations should be pursued. 38 These data should be available in time for site selection and return of samples. 5. It can be argued that sampling techniques should be developed to optimize the mass of the returned samples, to reach less-weathered material in the interior of rocks, and to sample at depth. 39 Natural processes, such as impacts, may have exposed rocks and material from depth, but innovative technologies may still be http://www7.nationalacademies.org/ssb/msrrep.html (5 of 11) [6/18/2004 9:26:19 AM]
Space Studies Board needed to obtain samples suitable for meeting the scientific objectives of any given mission. The ubiquitous, superoxidizing material covering the martian surface material may, however, obviate such requirements for unweathered samples. Even so, technologies to allow sample manipulation for selection and subsampling of large fragments will be important because of the constraints on sample-return mass. 6. Sample handling and return technologies necessary to satisfy planetary protection requirements and to preserve samples in a pristine state should be developed in a timely manner, according to previous reports. 40,41 These topics are currently under consideration by the SSB's Task Group on Issues in Sample Return (TGISR). COMPLEX defers additional consideration of these topics until after the publication of TGISR's report. 42 RELATED WORK 1. Criteria need to be developed for the unambiguous identification of biotic signatures. The ALH84001 meteorite illustrates the need to distinguish between biotic and abiotic mechanisms at the nanometer scale. 43 Terrestrial laboratory studies and field work are required to understand the chemical signatures in soils and rocks affected by living organisms as well as those caused by purely chemical means. In the former case, there is a need to understand better the diversity of organisms and environments, and their interaction at the microbiological scale. In the latter case, there is a need to know more about the redox chemistry, isotope fractionation, mineralogy, and physiochemical processes that mimic or preceded life. The goal is to be able to distinguish in a definitive manner between biotic and abiotic processes in ancient environments, in particular by analysis of meteorite samples found on Earth as well as samples returned directly from Mars. Previous studies 44,45 have discussed in detail some of these experimental procedures. However, ALH84001 provides an important example of current procedures and limitations to address exobiologic questions. In order to arrive at definitive results regarding life and its origins using small samples, specialized equipment and laboratories will be required. 2. Research on related antarctic meteorites should be improved. The collection of additional martian meteorites will be useful for putting the ALH84001 results into a broader context and for additional studies of evidence of past life or prebiotic materials from Mars. The rate of collection could, according several past participants in the Antarctic Search for Meteorites (ANSMET) program, be increased if, for example, field-collection procedures in Antarctica are made more efficient by eliminating excessive requirements for documenting sample locations. Tests have demonstrated that equipping ANSMET teams with Global Positioning System receivers would allow precise determination of locations, without taking much time away from sample collection. SUMMARY RECOMMENDATIONS http://www7.nationalacademies.org/ssb/msrrep.html (6 of 11) [6/18/2004 9:26:19 AM]
Space Studies Board In summary, COMPLEX believes that whether or not the results of McKay et al. are confirmed, the measured approach to the exploration of Mars advocated by COMPLEX and other groups is the optimum strategy for advancing our understanding of Mars on all fronts. Moreover, the committee is guardedly optimistic that NASA's current planning for Mars sample-return missions will be consistent with the priorities outlined in past NRC reports, provided that NASA takes into account the issues discussed above, as summarized here: 1. 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. 2. Incorporate previously developed strategies for determining "prebiotic" chemical evolution into the Mars sample-return program. 3. Maintain adaptability and flexibility in the Mars sample-return program to take into account possible new discoveries from ongoing Mars missions. 4. Ensure that the global reconnaissance of Mars is implemented as early as possible. 5. Ensure that sites and samples are selected that are consistent with established strategies for exobiology and martian exploration. 6. 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. 7. Ensure that sample handling, including planetary protection issues, are judiciously formulated and implemented. 8. Develop the capability for achieving long-range (tens of kilometers) mobility and high-precision landing. 9. Develop a broad suite of capable, miniature instruments for in situ measurements of surface properties relevant to exobiology and general martian exploration. 10. Develop the criteria to enable the unambiguous identification of biotic signatures. 11. Increase the rate of collection of antarctic meteorites relevant to Mars by, for example, increasing the efficiency of field collection procedures. REFERENCES 1. Mars Expeditions Strategy Group, "The Search for Evidence of Life on Mars," http://www7.nationalacademies.org/ssb/msrrep.html (7 of 11) [6/18/2004 9:26:19 AM]
Space Studies Board Jet Propulsion Laboratory, Pasadena, California, September 26, 1996. 2. Space Studies Board, National Research Council, Review of NASA's Planned Mars Program, National Academy Press, Washington, D.C., 1996, p. 26. 3. Space Studies Board, National Research Council, 1990 Update to Strategy for Exploration of the Inner Planets, National Academy Press, Washington, D.C., 1990, pp. 21-24. 4. Space Studies Board, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press, Washington, D.C., 1994, pp. 61, 90, 93, 94, 96, 100, 117, 126, 129, and 132. 5. Space Studies Board, National Research Council, Review of NASA's Planned Mars Program, National Academy Press, Washington, D.C., 1996, pp. 10-11. 6. D. McKay et al., "Search for Past Life on Mars: Possible Relict Biogenic Activity in Martian Meteorite ALH84001," Science, August 16, 1996, p. 924. 7. Mars Expeditions Strategy Group, "The Search for Evidence of Life on Mars," Jet Propulsion Laboratory, Pasadena, California, September 26, 1996. 8. Space Studies Board, National Research Council, Review of NASA's Planned Mars Program, National Academy Press, Washington, D.C., 1996, p. 10. 9. Space Science Board, National Research Council, Space Science in the Twenty- First Century, National Academy Press, Washington, D.C., 1988, pp. 90-91. 10. Space Studies Board, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press, Washington, D.C., 1994, p. 61. 11. Space Studies Board, National Research Council, The Search for Life's Origins: Progress and Future Directions in Planetary Biology and Chemical Evolution, National Academy Press, Washington, D.C., 1990, p. 76. 12. Exobiology Program Office, Exobiological Strategy for Mars Exploration, NASA, Washington, D.C., 1995. 13. Space Studies Board, National Research Council, Review of NASA's Planned Mars Program, National Academy Press, Washington, D.C., 1996, p. 10. 14. Space Studies Board, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press, Washington, D.C., 1994, p. 104. 15. Space Studies Board, National Research Council, 1990 Update to Strategy for http://www7.nationalacademies.org/ssb/msrrep.html (8 of 11) [6/18/2004 9:26:19 AM]
Space Studies Board Exploration of the Inner Planets, National Academy Press, Washington, D.C., 1990, p. 5. 16. Space Science Board, National Research Council, Space Science in the Twenty-First Century, National Academy Press, Washington, D.C., 1988, p. 91. 17. Space Studies Board, National Research Council, Review of NASA's Planned Mars Program, National Academy Press, Washington, D.C., 1996, pp. 10-11. 18. Space Studies Board, National Research Council, The Search for Life's Origins: Progress and Future Directions in Planetary Biology and Chemical Evolution, National Academy Press, Washington, D.C., 1990, p. 77. 19. Mars Expeditions Strategy Group, "The Search for Evidence of Life on Mars," Jet Propulsion Laboratory, Pasadena, California, September 26, 1996, p. 5. 20. Space Studies Board, National Research Council, Review of NASA's Planned Mars Program, National Academy Press, Washington, D.C., 1996, p. 22. 21. Space Studies Board, National Research Council, 1990 Update to Strategy for Exploration of the Inner Planets, National Academy Press, Washington, D.C., 1990, p. 24. 22. Space Studies Board, National Research Council, Mars Sample Return: Issues and Recommendations, National Academy Press, Washington, D.C., 1996, in preparation. 23. Space Studies Board, National Research Council, Review of NASA's Planned Mars Program, National Academy Press, Washington, D.C., 1996, p. 23. 24. Space Studies Board, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press, Washington, D.C., 1994, p. 104. 25. Space Science Board, National Research Council, Post-Viking Biological Investigations of Mars, National Academy of Sciences, Washington, D.C., 1977, pp. 14 and 23. 26. Mars Expeditions Strategy Group, "The Search for Evidence of Life on Mars," Jet Propulsion Laboratory, Pasadena, California, September 26, 1996, p. 2. 27. Space Studies Board, National Research Council, Review of NASA's Planned Mars Program, National Academy Press, Washington, D.C., 1996, p. 10. 28. Space Studies Board, National Research Council, Review of NASA's Planned Mars Program, National Academy Press, Washington, D.C., 1996, pp. 10-11. http://www7.nationalacademies.org/ssb/msrrep.html (9 of 11) [6/18/2004 9:26:19 AM]
Space Studies Board 29. Space Studies Board, National Research Council, An Integrated Strategy for the Planetary Sciences: 1995-2010, National Academy Press, Washington, D.C., 1994, p. 103. 30. Space Science Board, National Research Council, Space Science in the Twenty-First Century, National Academy Press, Washington, D.C., 1988, pp. 88- 89. 31. Space Science Board, National Research Council, Strategy for Exploration of the Inner Planets: 1977-1987, National Academy of Sciences, Washington, D.C., 1978, p. 44. 32. Space Science Board, National Research Council, Space Science in the Twenty-First Century, National Academy Press, Washington, D.C., 1988, p. 93. 33. Space Studies Board, National Research Council, Review of NASA's Planned Mars Program, National Academy Press, Washington, D.C., 1996, p. 23. 34. Space Science Board, National Research Council, Space Science in the Twenty-First Century, National Academy Press, Washington, D.C., 1988, p. 93. 35. Space Studies Board, National Research Council, Review of NASA's Planned Mars Program, National Academy Press, Washington, D.C., 1996, p. 25. 36. Space Studies Board, National Research Council, Biological Contamination of Mars: Issues and Recommendations, National Academy Press, Washington, D.C., 1992, pp. 51 and 53. 37. Space Science Board, National Research Council, Space Science in the Twenty-First Century, National Academy Press, Washington, D.C., 1988, p. 104. 38. Space Studies Board, National Research Council, Review of NASA's Planned Mars Program, National Academy Press, Washington, D.C., 1996, p. 22. 39. Space Studies Board, National Research Council, Review of NASA's Planned Mars Program, National Academy Press, Washington, D.C., 1996, p. 23. 40. Space Studies Board, National Research Council, Biological Contamination of Mars: Issues and Recommendations, National Academy Press, Washington, D.C., 1992. 41. Space Science Board, National Research Council, Strategy for Exploration of the Inner Planets: 1977-1987, National Academy of Sciences, Washington, D.C., 1978, p. 50. 42. Space Studies Board, National Research Council, Mars Sample Return: Issues and Recommendations, National Academy Press, Washington, D.C., 1996, in http://www7.nationalacademies.org/ssb/msrrep.html (10 of 11) [6/18/2004 9:26:19 AM]
Space Studies Board preparation. 43. D. McKay et al., "Search for Past Life on Mars: Possible Relict Biogenic Activity in Martian Meteorite ALH84001," Science, August 16, 1996, p. 924. 44. Space Studies Board, National Research Council, The Search for Life's Origins: Progress and Future Directions in Planetary Biology and Chemical Evolution, National Academy Press, Washington, D.C., 1990, p. 77. 45. Space Science Board, National Research Council, Strategy for Exploration of the Inner Planets: 1977-1987, National Academy of Sciences, Washington, D.C., 1978, pp. 44-56. Last update 2/10/00 at 4:27 pm Site managed by the SSB Web Group. To comment on this Web page or report an error, please send feedback to the Space Studies Board. Subscribe to e-newsletters | Feedback | Back to Top Copyright © 2004. National Academy of Sciences. All rights reserved. 500 Fifth St. N.W., Washington, D.C. 20001. Terms of Use and Privacy Statement http://www7.nationalacademies.org/ssb/msrrep.html (11 of 11) [6/18/2004 9:26:19 AM]
