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Summary and Recommendations INTRODUCTION Task, Approach, and Scope of Report Whenever Earth-originating spacecraft intrude on the atmosphere or surface of other solar system bodies or return to Earth from one of these bodies, there is a risk of contamination by foreign substances or organisms. In the case of in situ exploration of other bodies, a major concern is disruption of scientific findings by imported material. In the case of back contamination (return to Earth of extraterrestrial material), there is concern over the possible release into the biosphere of potentially harmful organisms or substances. Since 1967, a policy of planetary protection has been in place in order to control contamination of planets by terrestrial microorganisms and organic constituents during planetary missions. In the United States, the policy is implemented by the National Aeronautics and Space Administration (NASA). It is accepted as official policy by the Committee on Space Research (COSPAR) of the International Council of Scientific Unions. The policy lays out a framework of specific planetary protection guidelines for implementing procedures for future missions. Through COSPAR, review and analysis of the policy have been ongoing and have resulted in periodic revisions in light of new information obtained from planetary exploration.1,2 In addition, the United States is a signatory to an international treaty that declares in part that "States Parties to the treaty shall pursue studies of outer space . . . so as to avoid their harmful contamination and also adverse changes in the environment of the Earth. . . ."3 1

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The Space Studies Board (SSB) of the National Research Council has served as NASA's primary advisor concerning planetary protection (or quarantine) for many years. The board, through its Committee on Planetary Biology and Chemical Evolution, has published a number of reports and letters concerning planetary protection (or quarantine) in response to NASA requests.4-12 Most recently, NASA's planetary protection officer requested that, prior to the 1992 COSPAR meeting, the board make recommendations regarding planetary protection policy for upcoming Mars missions (Appendix A). In response to this request, the board formed the ad hoc Task Group on Planetary Protection, made up of planetary scientists, biochemists, ecologists, and microbiologists who specialize in studying life in extreme environments such as the polar regions and deep oceans and lakes (Appendix B). The task group hosted a workshop in September 1991 at which extensive briefings on planned and contemplated Mars missions and the many aspects of Mars science and survival of Earth organisms were reviewed and discussed in detail (Appendix C). Scientists from Europe and the former USSR made presentations concerning their current views and approaches to planetary protection. These presentations and discussions, along with a reassessment of the SSB's 1978 report, Recommendations on Quarantine Policy for Mars, Jupiter, Saturn, Uranus, Neptune, and Titan13 (excerpted in Appendix D), form the basis for this report. Additional information considered by the task group is given in Appendix E. In keeping with NASA's request, the task group focused on making recommendations concerning the protection of Mars from forward contamination (i.e., contamination of the martian environment by terrestrial organisms) during upcoming missions by both the United States and the former Soviet Union. In so doing, it distinguished between missions whose goals include reconnaissance and measurement and those that specifically include experiments to detect life. The task group also discussed what additional knowledge will be needed in order to assure that future recommendations regarding contamination of Earth from Mars (back contamination) might be made with a higher degree of certainty than is now possible. Following a short introduction to the rationale underlying planetary exploration (Chapter 1) is a brief summary of approved and contemplated missions to Mars (Chapter 2). Chapter 3 briefly reviews the state of knowledge in several areas pertinent to the problem of planetary protection, including chemical and physical properties of Mars, and Chapter 4 discusses the limits of life on Earth and the abilities of known terrestrial organisms to withstand extreme environmental conditions, as well as new approaches to detecting life forms. Chapter 5 includes a review and comments—made in light of current knowledge—on the recommendations made in Recommendations on Quarantine Policy for Mars, Jupiter, Saturn, Uranus, Neptune, and Titan. Updates to the recommendations made in 1978 are also given in Chapter 5. Chapter 6 2

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gives additional recommendations concerning collection of essential data, spacecraft sterilization and bioburden assessment, and future research, as well as legal and societal issues and NASA's overall planetary protection program. Background Understanding the origin and evolution of life has been an important goal of NASA; studies in this area generate some of the more interesting scientific questions for all mankind. One promising approach to understanding life's origins is that of searching for life elsewhere, primarily on other planets, where physical, hydrological, and geochemical properties might favor (or might have favored in the past) the existence of replicating biotic systems like those found on Earth. Historically, Mars has been the planet of choice for understanding life's origins. With the technological advances that accompanied the advent of spacecraft exploration, our ability to conduct detailed studies of planets in the solar system improved dramatically. As our knowledge of present conditions on the surface of Mars has increased, there has been a concomitant decrease in any expectation that life as we know it could exist on the surface of the planet. At the same time, it is important to remember that (1) Viking lander sites have not been representative of the entire planet and (2) the early state of Mars seems to have differed quite markedly from its present state and may have been characterized by the presence of abundant liquid water and a more substantial atmosphere. Future life-detection missions to Mars must include investigation of other more biologically relevant, desirable sites where evidence of the survival of either molecular or morphologically preserved cells or cell components may exist. As in the past, it is necessary to continue to take precautions to ensure planetary protection, both from forward and back contamination. With respect to forward contamination, NASA's historic concern has been to preserve pristine conditions on the planets for future experiments with biological and organic constituents that might lead to insights concerning the origin and evolution of life in the cosmos. Knowledge has increased substantially since the Viking mission. Recommendations for planetary protection that guided the Viking mission may not be relevant to missions being flown today or to those planned for the future. As more information is acquired about a given extraterrestrial body, assessment of the amount of planetary protection needed to protect that body from contamination should change accordingly. The process must be iterative and must allow for altering the techniques used to ensure protection as we learn more about planetary conditions and the probability of contamination. 3

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FUTURE MISSIONS At this time, there are two approved missions to Mars: the U.S. Mars Observer mission to be launched in October 1992 and the Soviet Mars 94/96 mission. Both NASA and the European Space Agency (ESA) are studying a network mission that involves placing numerous small stations on the surface of the planet. In addition, both the United States and the former Soviet Union have been studying various rover and sample return missions for some time. These missions, which will gradually improve our knowledge of the environmental parameters of Mars and enhance our ability to select and protect appropriate landing sites, are discussed in detail in Chapter 2. SURFACE ENVIRONMENT OF MARS Despite an incomplete understanding of the surface environment of Mars, it is generally agreed that conditions are extremely inhospitable to terrestrial life. Various aspects of the surface environment have relevance to the issue of forward contamination, including both growth on Mars of organisms from Earth and the lifetime of bioorganic matter deposited on the martian surface. Chapter 3 of this report reviews the state of knowledge regarding the martian surface, including its chemistry, solar radiation flux, temperature, water, volcanism, and past climate conditions. LIMITS OF LIFE ON EARTH: EXPANSION OF THE MICROBIAL WORLD AND DETECTION OF LIFE Life in Extreme Environments The Task Group on Planetary Protection assessed past reports and current views on the range of environmental conditions believed to exist on Mars and unanimously agreed that it is extremely unlikely that a terrestrial organism could grow on the surface of Mars. It is clear that the most extreme environments on Earth where organisms can replicate are considerably less extreme than the environments that are known to occur over most of the martian surface. Particularly important in this regard are the high levels of ultraviolet radiation, the thin atmosphere, the extremely low maximum temperatures, and the absence of liquid water on the surface. Based on current knowledge of conditions on Earth that limit cell growth and on the best estimates of surface conditions on Mars, the task group concluded that no known terrestrial organisms could grow on the martian surface. However, this does not imply that life does not exist anywhere on the planet. There is far too little information to assess the possibility that life may exist in subsurface environments associated with hydrothermal activity or in selected microenvironments free from the 4

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harsh conditions previously mentioned, or to conclude that organisms resembling terrestrial life forms did not evolve on Mars. The task group concentrated on the problem of forward contamination by intact cells or components of cells that could be detected by sophisticated molecular methods in future expeditions designed to look for evidence of extant or past life on Mars. Planning for present and future missions to Mars must include awareness of new results obtained from studies of extreme environments as well as the inevitable extension of the limits of environments where growth and survival can take place. Advances in understanding the microbiology of extreme environments have been accompanied by advances in the development of new methods and considerably more accurate and sensitive instruments for detecting the presence of life and life-related molecules and for identifying their evolutionary relatedness. Nevertheless, it is not a straightforward matter to define the ranges of physical and chemical conditions on Earth in which organisms can grow, replicate, or survive for extended periods. During the 13 years since the SSB's last report on planetary protection, Recommendations on Quarantine Policy for Mars, Jupiter, Saturn, Uranus, Neptune, and Titan, bacteria have been detected or isolated from many of Earth's hostile environments—the dry, extremely cold subsurfaces and interiors of rocks in the dry valleys of the Antarctic, hot environments associated with submarine and terrestrial volcanoes and geothermal systems, and deep subsurface sediments and aquifers. Chapter 4 includes a review of these organisms. Life Detection and Bioburden Determination for Planetary Protection Techniques for assessing the existence of microorganisms have advanced dramatically since pre-Viking days. These advances will have a strong impact both on bioburden assessment procedures and on future life- detection experiments. New methods have been developed with increasingly greater sensitivity and specificity. The task group strongly recommends that efforts be made to explore current analytical methods for use in bioburden assessment and inventory procedures before spacecraft assembly and launch. In addition to epifluorescent microscopic techniques for directly counting viable cells, many other new methods have been developed, such as the polymerase chain reaction, allowing greatly increased sensitivity of detection by enzymatically amplifying specific biomarkers of even a single cell to detectable levels. The appeal of these techniques is their extreme sensitivity. In many cases, single cells can be detected and identified with confidence. 5

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ASSESSMENT OF THE 1978 REPORT Review Recommendations on Quarantine Policy for Mars, Jupiter, Saturn, Uranus, Neptune, and Titan, the 1978 report by the then Space Science Board's Committee on Planetary Biology and Chemical Evolution, established a quarantine policy for exploratory, one-way missions to Mars, Jupiter, Saturn, Uranus, Neptune, and Titan planned for 1974 to 1994. The task group's assessment of this report is limited to an evaluation of information and past recommendations concerning Mars. After the 1978 report was issued, NASA began to look for ways to simplify planetary protection procedures as they applied to particular upcoming planetary missions, and to minimize the use of mathematical models. Prior to the 1978 report, the criteria used for determining categories of planetary contamination were those established by international agreement through COSPAR. They stipulated that the probability of contamination (Pc) should be less than 1 x 10-3 for each planet. Considerable uncertainty was engendered by this probabilistic approach to planetary protection. Concern related to this point has been expressed over the years by virtually every group that has analyzed the problem, and indeed by NASA. Although the probability of depositing a microbe or some organic material indicative of life is very high (microbes and organic contaminants have almost certainly been deposited by past missions), our expectations regarding the likelihood of permanent contamination as a result of microbial growth (expressed as the probability of growth, Pg) have been steadily reduced as we have learned more about Mars. The NASA studies that followed the 1978 report culminated in a 1984 report to COSPAR that greatly deemphasized the probabilistic approach and introduced the concept of target planet and mission-type categories.14 This approach, which is reviewed in Chapter 5, directly reflects the degree of concern for a given planet, in the context of a particular type of mission. Recommendations of the Task Group The task group views the problem of forward contamination as separable into two principal issues: (1) the potential for growth of terrestrial organisms on Mars and (2) the importation of terrestrial organic contaminants, living or dead, in amounts sufficient to compromise the search for evidence of past or present life on Mars itself. The guidelines concerning probabilities of growth (Pg) issued by the Space Science Board in its 1978 report were recently reassessed in a 1991 NASA report.15 Comments and estimates made by the participants illustrate a consensus that the Pg values for terrestrial organisms on Mars 6

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are probably lower than the 1978 estimates. However, this observation does not alter the case as far as contamination of a possible past or extant martian biosphere is concerned. Prudence dictates that bioload reduction on all lander missions to Mars must continue to be seriously addressed. The issue of spacecraft cleanliness is particularly crucial when life- detection experiments are included in the scientific payload. The deliberations of the task group were greatly aided by the MESUR mission workshop that resulted in the above-mentioned 1991 report. That report, together with the comprehensive briefings given by experts on relevant matters, led the task group to concur unanimously with the following conclusion from the MESUR workshop: Forward contamination, solely defined as contamination of the martian environment by growth of terrestrial organisms that have potential for growth on Mars, is not a significant hazard. However, forward contamination more broadly defined to include contamination by terrestrial organic matter associated with intact cells or cell components is a significant threat to interpretation of results of in situ experiments specifically designed to search for evidence of extant or fossil martian microorganisms. Based on the MESUR group's consensus and the task group's agreement with it, the task group makes the following recommendations for control of forward contamination, each tied to specific mission objectives. Landers carrying instrumentation for in situ investigation of extant martian life should be subject to at least Viking-level sterilization procedures. Specific methods for sterilization are to be determined. Viking technology may be adequate, but requirements will undoubtedly be driven by the nature and sensitivity of the particular experiments. The objective of this requirement is the reduction, to the greatest feasible extent, of contamination by terrestrial organic matter and/or microorganisms deposited at the landing site. Spacecraft (including orbiters) without biological experiments should be subject to at least Viking-level presterilization procedures—such as clean-room assembly and cleaning of all components—for bioload reduction, but such spacecraft need not be sterilized. Table 1.1 in Chapter 1 summarizes Viking-level procedures, and Appendix E includes a detailed description of the procedures. The task group sees little utility in further attempts to estimate actual probability-of-contamination values in various martian environmental regimes. In the absence of crucial data relating to the survivability and growth potential of terrestrial organisms on Mars, such exercises are purely subjective. The task group emphasizes that the philosophical intent underlying the 1978 report—to protect Mars from terrestrial contamination so as not to jeopardize future experiments aimed at detecting martian life—is still profoundly important. 7

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ADDITIONAL RECOMMENDATIONS Recommendations for Research The task group strongly recommends that a sequence of unpiloted missions to Mars be undertaken well in advance of a piloted mission. Any future changes in recommendations to ensure planetary protection, especially for piloted or sample return missions, will depend on the acquisition of new data. With regard to these missions, the task group recommends that a broad spectrum of martian sites be examined, with emphasis on measurements that provide data most likely to contribute to models that provide for a better understanding of the probability of life on Mars and where best to go to find it. Until such data are available, it will be impossible to make informed decisions concerning landings for in-depth biological study. Such data will also greatly affect the ability to make future decisions concerning the rigor required for spacecraft cleanliness and possible sterilization. Location of martian lander sites should take into account our rudimentary but growing understanding of Mars and our extensive knowledge of the basic requirements of life. It is also important to consider the subsurface of Mars. Within a site, it may prove important to plan for data collection that probes below the readily accessible surface, in order to obtain information on subsurface environments. Microenvironments—whether on the surface or in isolated vents, cracks, or layers of the subsurface—may exist now or may once have existed at some time in the past. Properly designed experiments may be able to address the issue of spatial and (perhaps) temporal heterogeneity and its possible relationship to our ability to evaluate the biotic and abiotic status of a given site. Collection of appropriate data should allow the scientific community to amend planetary protection policy recommendations for back contamination, perhaps resulting in recommendations similar to the alterations in procedures for assessing forward contamination suggested by this task group. The determination of current or inferred past geophysical conditions on Mars may help identify locations where life- detection missions should be sent. Recommendations Regarding Assessment of Spacecraft Bioload The task group's recommendation to reduce bioload on all spacecraft and to sterilize those spacecraft used in life-detection missions assumes the use of Viking procedures. However, the task group recommends that the Viking protocols for assessment of spacecraft bioloads be upgraded to include state-of-the-art methods for the determination of bioload. It is critical that methods for assessing bioload 8

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be compatible with methods used to detect life, with methods for both assessment and detection reflecting the same limits and sensitivity. Data on bioloads of Viking components and spacecraft are not relevant to current life-detection procedures. Modern methods of bioburden assessment should be developed for and applied to spacecraft destined for future Mars missions, especially those carrying in situ extant life-detection experiments. Although immediate use of these techniques is not a feasible goal, the development of the methodology in anticipation of future life- detection missions is absolutely essential. Recommendations Concerning Other Issues Piloted Versus Unpiloted Missions Missions carrying humans to Mars will contaminate the planet. It is therefore critical that every attempt be made to obtain evidence of past and/or present life on Mars well before these missions occur. The issues of forward and back contamination have societal, legal, and international implications. These implications are serious, and they deserve discussion and attention. Societal Issues A substantial number of active national and international organizations are on the alert for environmental abuse. There is every reason to take seriously the concern (already expressed in some cases) about contamination of Mars and almost certainly about the issue of back contamination of Earth by martian samples. Although public concern over such issues is often sincere and productive, it at times becomes distorted and exaggerated in the media, leading to public misunderstanding and opposition. The task group recommends that NASA inform the public about current planetary protection plans and provide continuing updates concerning Mars exploration and sample return. Legal Issues There are also legal issues that must be addressed, involving international restrictions as well as federal, state, and local statutes that may come into play. There are currently no binding international agreements concerning forward or back contamination. The task group recommends as essential that efforts be made (1) to assess the legal limits (and implied liabilities) in existing legislation that relates to martian exploration and (2) to pursue the establishment of international standards that will safeguard the scientific integrity of research on Mars. Furthermore, the task group recommends that 9

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NASA make a strong effort to obtain international agreement for a planetary protection policy. NASA Planetary Protection Program Although a planetary protection officer currently exists at NASA, there is no budgeted program (as there was during the Viking Program) to implement needed planetary protection research, a public education program, examination of legal and international issues, and the like. The task group recommends that NASA redefine the responsibilities and authority of its planetary protection officer and provide sufficient resources to carry out the recommendations made in this report. SUMMARY OF RECOMMENDATIONS All of the recommendations put forward by the task group in this report are summarized below. Each is discussed further in the full report in the chapter(s) indicated. 1. Efforts should be made to adopt current molecular analytical methods for use in bioburden assessment and inventory procedures for spacecraft assembly and launch for future missions, and also to develop new methods for the same purposes (Chapters 4 and 5). 2. Landers carrying instrumentation for in situ investigation of extant martian life should be subject to at least Viking-level sterilization procedures. Specific methods for sterilization are to be determined; Viking technology may be adequate, but requirements will undoubtedly be driven by the nature and sensitivity of the particular experiments. The rationale for this requirement is the reduction, to the greatest feasible extent, of contamination by terrestrial organic matter that is deposited at the site by microorganisms or organic residues carried on the spacecraft (Chapter 5). 3. Spacecraft (including orbiters) without biological experiments should be subject to at least Viking-level presterilization procedures— such as clean-room assembly and cleaning of all components—for bioload reduction, but such spacecraft need not be sterilized (Chapter 5). 4. A sequence of unpiloted missions to Mars should be undertaken well in advance of a piloted mission (Chapter 6). 5. A broad spectrum of martian sites should be examined with emphasis on measurements that provide data most likely to contribute to a better understanding of the probability of life on Mars and where best to go to be able to detect it (Chapter 6). 6. The Viking protocols for assessment of spacecraft bioloads should be upgraded to include state-of-the-art methods for the determination of bioload (Chapter 6). 7. NASA should inform the public about current planetary protection plans and provide continuing updates concerning Mars exploration and sample return (Chapter 6). 10

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8. It is essential to assess the legal limits (and implied liabilities) in existing legislation that relates to martian exploration and to pursue the establishment of international standards that will safeguard the scientific integrity of research on Mars (Chapter 6). 9. NASA should make a strong effort to obtain international agreement for a planetary protection policy (Chapter 6). 10. NASA should redefine the responsibilities and authority of its planetary protection officer and provide sufficient resources to carry out the above recommendations (Chapter 6). REFERENCES 1. DeVincenzi, D.L., and P.D. Stabekis. 1984. "Revised Planetary Protection Policy for Solar System Exploration." Adv. Space Res. 4:291-295 2. DeVincenzi, D.L. 1990. "Planetary Protection Issues and the Future Exploration of Mars." Adv. Space Res. December preprint. 3. United Nations. 1967. Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies. U.N. Document No. 6347, January. 4. Space Science Board, 1967, "Study on the Biological Quarantine of Venus," report of an ad hoc panel, January 9, National Academy of Sciences, Washington, D.C. 5. Space Science Board, 1970, "Review of Sterilization Parameter Probability of Growth (Pg)," report of an ad hoc review group, July 16-17, National Academy of Sciences, Washington, D.C. 6. Space Science Board, 1976, "On Contamination of the Outer Planets by Earth Organisms," report of the Ad Hoc Committee on Biological Contamination of Outer Planets and Satellites, Panel on Exobiology, March 20, National Academy of Sciences, Washington, D.C. 7. Space Science Board, 1976, "Recommendations on Quarantine Policy for Uranus, neptune, and Titan," report of the Panel on Exobiology, May 24, National Academy of Sciences, Washington, D.C. 8. Space Science Board, National Research Council, 1977, Post-Viking Biological Investigations of Mars, Committee on Planetary Biology and Chemical Evolution, National Academy of Sciences, Washington, D.C. 9. Space Science Board, National Research Council, 1978, Recommendations on Quarantine Policy for Mars, Jupiter, Saturn, Uranus, Neptune, and Titan, Committee on Planetary Biology and Chemical Evolution, National Academy of Sciences, Washington, D.C. 11

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10. Letter report from SSB Chairman Thomas Donahue to NASA Office of Space Science and Applications Associate Administrator Burton I. Edelson regarding planetary protection policy, November 22, 1985 (unpublished). 11. Letter report from Committee on Planetary Biology and Chemical Evolution to Arnauld E. Nicogossian, director, Life Sciences Division, NASA, regarding the planetary protection categorization of the Comet Rendezvous-Asteroid Flyby mission, May 16, 1986 (unpublished). 12. Letter report from Committee on Planetary Biology and Chemical Evolution to John D. Rummel, chief, Planetary Quarantine Program, Office of Space Science and Applications, NASA, regarding a formal recommendation on planetary protection categorization of the Comet Rendezvous-Asteroid Flyby mission and the Titan-Cassini mission, July 6, 1988 (unpublished). 13. See Space Science Board, National Research Council, 1978. 14. See DeVincenzi and Stabekis, 1984. 15. Klein, H.P. 1991. Planetary Protection Issues for the MESUR Mission: Probability of Growth (Pg), NASA conference publication, NASA Ames Research Center, Moffett Field, Calif. 12