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Assessment of Planetary Protection Requirements for MARS: Sample Return Missions Summary NASA maintains a planetary protection policy to avoid the forward biological contamination of other worlds by terrestrial organisms, and back biological contamination of Earth from the return of extraterrestrial materials by spaceflight missions. Forward-contamination issues related to Mars missions were addressed in a 2006 report of the National Research Council’s (NRC’s) Space Studies Board (SSB), Preventing the Forward Contamination of Mars.1 However, it has been more than 10 years since back-contamination issues were last examined. Driven by a renewed interest in Mars sample return missions, this report reviews, updates, and replaces the planetary protection conclusions and recommendations contained in the NRC’s 1997 report Mars Sample Return: Issues and Recommendations.2 It is the understanding of the Committee on the Review of Planetary Protection Requirements for Mars Sample Return Missions that its conclusions and recommendations will be developed at the tactical level by subsequent groups specifically charged with the development of implementable protocols for the collection, handling, transfer, quarantine, and release of martian samples. This is the approach that was taken by NASA after its receipt of the 1997 Mars report. Indeed, the development of broad strategic guidelines by SSB committees and the subsequent development of tactical plans for their implementation by NASA committees is a general approach that has served the space-science community well for most of the past 50 years. The specific issues addressed in this report include the following: The potential for living entities to be included in samples returned from Mars; Scientific investigations that should be conducted to reduce uncertainty in the above assessment; The potential for large-scale effects on Earth’s environment by any returned entity released to the environment; Criteria for intentional sample release, taking note of current and anticipated regulatory frameworks; and The status of technological measures that could be taken on a mission to prevent the inadvertent release of a returned sample into Earth’s biosphere. IMPORTANCE OF MARS SAMPLE RETURN A sample-return mission is acknowledged to be a major next step in the exploration of Mars because it can address so many high-priority science goals. The NRC’s 2003 solar system exploration decadal survey, for example, highlighted three areas where unambiguous answers to key science issues are unlikely without a sample return mission:3
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Assessment of Planetary Protection Requirements for MARS: Sample Return Missions The search for life; Geochemical studies and age dating; and Understanding of climate and coupled atmosphere-surface-interior processes. Returning samples to Earth is desirable for a number of reasons, including the following: Complex sample-preparation issues relating to some high-priority activities are more readily tackled in terrestrial laboratories than they are by robotic means on Mars; Instrumentation that is not amenable to spacecraft application because of its bulk, mass, or power requirements can be used on Earth to analyze samples; and A greater diversity of instruments can be used on Earth to study samples than can be packaged to fit within the confines of any one robotic spacecraft or series of spacecraft, including instruments that were not available when the sample-return mission was launched. REPORT ORGANIZATION Since the purpose of this document is to revise, update, and replace the NRC’s 1997 report Mars Sample Return: Issues and Recommendations, it is most logical to organize it around the basic question, What has changed since the release of the 1997 report? Changes is scientific understanding can be summarized in the following manner: New insights on the roles played by surface and subsurface water throughout martian history and the potential for habitable environments on Mars—Chapter 2; Advances in microbial ecology that illuminate the limits of adaptability of life on Earth—Chapter 3; New understanding of the physical and chemical mechanisms by which evidence of life might be preserved on Mars and how that life might be detected in martian samples—Chapter 4; and New understanding of pathogenesis and the nature of biological epidemics, as well as additional insights as to the possibility that viable martian organisms might be transported to Earth by meteorites—Chapter 5. The changes in the technical and/or policy environment can be organized as follows: A significant expansion of the size of the Mars exploration community and broadening of the scope of mission activities by both traditional and new space powers—Chapter 2; Greater societal awareness of the potential for technical activities to cause harmful changes in the global environment—Chapter 5; The de facto internationalization of a Mars sample return mission and subsequent sample-handling, sample-processing, sample-analysis, and sample-archiving policies—Chapter 6; The drafting and publication by NASA, with the assistance of international partners, of initial Mars sample-handling and biohazard-testing protocols based on the recommendations in the NRC’s 1997 Mars report—Chapter 6; The development of nondestructive methods of analysis that can be used to map the microscale spatial distribution of minerals and biological elements in samples—Chapter 6; and The proliferation of biocontainment facilities driven by biosecurity concerns and associated changes in public policy and with public acceptance of such facilities—Chapter 7; and Lessons learned about the practical and logistical aspects of Mars sample return from experience with the Genesis and Stardust missions as well as experience gained from the planning for and commissioning of new biocontainment facilities—Chapter 7.
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Assessment of Planetary Protection Requirements for MARS: Sample Return Missions CONCLUSIONS AND RECOMMENDATIONS The committee’s conclusions and recommendations are organized according to the task outlined in the charge it was given by NASA. The Potential for Living Entities in Samples Returned from Mars The assessment of martian habitability made by the authors of the NRC’s 1997 Mars report led them to recommend that: “Samples returned from Mars by spacecraft should be contained and treated as though potentially hazardous until proven otherwise. No uncontained martian materials, including spacecraft surfaces that have been exposed to the martian environment, should be returned to Earth unless sterilized” (p. 3). The present committee finds that the knowledge gained from both orbital and landed missions conducted over the last decade, combined with findings from studies of martian meteorites, has enhanced the possibility that habitable environments were once widespread over the surface of Mars. In addition, the potential for modern habitable environments, both as transient surface environments and as stable habitats in the deep subsurface, is much better understood. Understanding the range of environmental conditions to which terrestrial life has adapted has directly shaped current views of martian habitability and the potential for samples returned from Mars to contain evidence of life. A substantial and growing body of evidence shows that life not only is present but also frequently thrives under extreme environmental conditions. Consideration of advances in microbial ecology over the past decade led the committee to reach the following conclusions: Biological studies have continued to expand the known environmental limits for life and have led to the discovery of novel organisms and ecosystems on Earth; Some living species on Earth have been shown to survive under conditions of extreme radiation, subfreezing temperatures, high salinity, extremely high and low pH, and cycles of hydration to dehydration present on Mars today; The discovery, in deep subsurface environments on Earth, of microbial ecosystems that are able to survive on inorganic sources of energy has greatly enhanced the potential for chemoautotrophic life in subsurface environments on Mars; and Studies have confirmed the potential for the long-term viability of terrestrial microorganisms sequestered in deposits of some extreme terrestrial environments (e.g., ices and evaporates) that have high relevance for Mars exploration. Advances in the knowledge of environmental conditions on Mars today and in the past, combined with advances in understanding of the environmental limits of life, reinforce the possibility that living entities could be present in samples returned from Mars. Therefore, the committee concurs with and expands on the 1997 recommendation that no uncontained martian materials should be returned to Earth unless sterilized. Recommendation: Based on current knowledge of past and present habitability of Mars, NASA should continue to maintain a strong and conservative program of planetary protection for Mars sample return. That is, samples returned from Mars by spacecraft should be contained and treated as though potentially hazardous until proven otherwise. No uncontained martian materials, including spacecraft surfaces that have been exposed to the martian environment, should be returned to Earth unless sterilized. The Potential for Large-Scale Effects on Earth’s Environment A key issue of concern is the possibility that a putative martian organism inadvertently released from containment could produce large-scale negative pathogenic effects in humans, or could have a destructive impact on Earth’s ecological systems or environments.
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Assessment of Planetary Protection Requirements for MARS: Sample Return Missions The committee concurs with the basic conclusion of the NRC’s 1997 Mars study that the potential risks of large-scale effects arising from the intentional return of martian materials to Earth are primarily those associated with replicating biological entities, rather than toxic effects attributed to microbes, their cellular structures, or extracellular products. Therefore, the focus of attention should be placed on the potential for pathogenic-infectious diseases, or negative ecological effects on Earth’s environments. Like the 1997 committee, the present committee finds that the potential for large-scale negative effects on Earth’s inhabitants or environments by a returned martian life form appears to be low, but is not demonstrably zero. A related issue concerns the natural introduction of martian materials to Earth’s environment in the form of martian meteorites. Although exchanges of essentially unaltered crustal materials have occurred routinely throughout the history of Earth and Mars, it is not known whether a putative martian microorganism could survive ejection, transit, and impact delivery to Earth or would be sterilized by shock pressure heating during ejection or by radiation damage accumulated during transit. Likewise, it is not possible to assess past or future negative impacts caused by the delivery of putative extraterrestrial life, based on present evidence. Thus, the conclusion reached from assessment of large-scale effects resulting from intentional and natural sample return is that a conservative approach to both containment and test protocols remains the most appropriate response. Scientific Investigations to Reduce Uncertainties Uncertainties in the current assessment of martian habitability and the potential for the inclusion of living entities in samples returned from Mars might be reduced by continuing activities in the following general areas: spacecraft missions to Mars, combined with related laboratory, theoretical, and modeling activities; investigations of the ecological diversity and environmental extremes of terrestrial life; geobiological studies of both modern and ancient Mars-relevant environments on Earth, with particular emphasis on biosignature preservation; and studies relating to the interplanetary transport of viable organisms. The committee finds that the following activities are particularly relevant to reducing uncertainties: Remote-sensing and in situ exploration of Mars with the goal of answering questions relating to martian habitability, including those concerned with the presence of water in surface and subsurface environments through time, the distribution of biogenic elements, and the availability of redox-based energy sources (e.g., those based on the oxidation of ferrous iron and reduced sulfur compounds); Studies of martian meteorites to help refine understanding of the history of interactions of Mars’s rock-water-atmosphere system throughout the planet’s history; Studies of the metabolic diversity and environmental limits of microbial life on Earth; Studies of the nature and potential for biosignature preservation in a wide range of Mars-analog materials on Earth; Investigations of the prolonged viability of microorganisms in geological materials; Evaluation of the impacts of post-depositional (diagenetic) processes (deep burial, impact shock, subfreezing temperatures) on the long-term retention of biosignatures in ancient geological materials; Determination of reliable criteria for the definitive identification of biosignatures in ancient materials; Assessment of the potential for impact-mediated interchanges of viable organisms between Earth and Mars; Development of laboratory-based and in situ analytical approaches for biosignature analysis. Criteria for Intentional Sample Release There is a broad consensus in the scientific community that samples collected on Mars and returned to Earth must be contained and treated as potentially biologically hazardous until they are declared safe for release from containment by applying recommended protocols, including rigorous physical and chemical characterization, life detection analyses, and biohazard testing. It is important to emphasize that the high level of containment recom-
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Assessment of Planetary Protection Requirements for MARS: Sample Return Missions mended for the handling and testing of martian samples is based on a deliberate decision to adopt a conservative approach to planetary protection and is not because of the anticipated nature of pristine martian materials or organisms. If anything, however, the discoveries over the past decade about environmental conditions on Mars today and in the past and about terrestrial extremophiles have supported an enhanced potential for the presence of liquid water habitats and, perhaps, microbial life on Mars. Thus it is appropriate to continue this conservative approach. A factor that could potentially complicate the policies and protocols relating to sample containment and biohazard evaluation is the de facto internationalization of a Mars sample return mission. All serious planning for Mars sample return is founded on the premise that the scope, complexity, and cost of such a mission are beyond the likely resources of any one space agency. Although no major issues have arisen to date, the international interest in of Mars sample return raises the possibility that differences in national policies and legal frameworks of concerned parties might complicate issues relating to sample quarantine and biohazard certification. Changes to the requirements for sample containment or criteria for sample release were issues of concern in the NRC’s 1997 report Mars Sample Return, which recommended that: “The planetary protection measures adopted for the first Mars sample-return mission should not be relaxed for subsequent missions without thorough scientific review and concurrence by an appropriate independent oversight body” (p. 4). The present committee concurs with the spirit of that recommendation, with three provisos: first, that the protocols for sample containment, handling, testing, and release be articulated in advance of Mars sample return; second, that the protocols be reviewed regularly to update them to reflect the newest standards; and third, that international partners be involved in the articulation and review of the protocols. Recommendation: Detailed protocols for sample containment, handling, and testing, including criteria for release from a sample-receiving facility (SRF), should be clearly articulated in advance of Mars sample return. The protocols should be reviewed periodically as part of the ongoing SRF oversight process that will incorporate new laboratory findings and advances in analytical methods and containment technologies. International partners involved with the implementation of a Mars sample return mission should be a party to all necessary consultations, deliberations, and reviews. The NRC’s 1997 Mars report recommended that: “Controlled distribution of unsterilized materials returned from Mars should occur only if rigorous analyses determine that the materials do not contain a biological hazard. If any portion of the sample is removed from containment prior to completion of these analyses, it must … be sterilized” (p. 4). Subsequent NRC and NASA reports have made related, but in some cases conflicting, statements. Irrespective of these conflicts, there are critical issues concerning the selection of the aliquots for biohazard testing and the nature of the tests to be employed. The discussion of advances in geobiology and biosignature detection in Chapter 4 raises the possibility that viable organisms might be preserved over a prolonged span of time within certain geological deposits. The discussion in Chapter 6 led the committee to conclude that the distribution of extant and fossil organisms and biomolecules in rocks, soils, and ices is heterogeneous at microscopic scales of observation, and this heterogeneity requires careful consideration because it complicates the selection of representative aliquots for biohazards testing. Recommendation: Future protocol guidelines should carefully consider the problems of sample heterogeneity in developing strategies for life detection analyses and biohazards testing in order to avoid sampling errors and false negatives. The limited amount of material likely to be returned from Mars demands that nondestructive means of analysis be employed to the maximum extent possible in sample characterization and biohazards testing. Recommendation: The best nondestructive methods must be identified for mapping the microscale spatial distributions of minerals, microstructures, and biologically important elements within returned martian samples.
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Assessment of Planetary Protection Requirements for MARS: Sample Return Missions It is highly likely that many of the appropriate nondestructive methods will require the use of techniques that cannot feasibly be implemented within the confines of an SRF. Thus, a critical issue concerns the design of secondary containers for transporting samples to outside laboratory facilities where they can be analyzed (under containment) using advanced analytic techniques. Recommendation: Sample characterization in laboratories outside the primary sample-receiving facility will require the design of secondary containers for safely transporting samples and interfacing with a potentially wider variety of instruments. Technological Measures to Prevent the Inadvertent Release of Returned Samples Planetary protection considerations require that martian materials be securely contained within a sample canister for their journey from Mars, through their collection and retrieval on Earth, and in subsequent transport and confinement in an SRF. With respect to the journey from Mars to an SRF, the NRC’s 1997 Mars report concluded that the integrity of the seal of the sample canister should be verified and monitored during all phases of a Mars sample return mission. The present committee found this requirement to be overly prescriptive. Establishing the technical means to verify containment has proven to be a stumbling block in past mission studies. Elaborate steps must be taken to guarantee that the sample canister is sealed at every stage of its journey from Mars to an SRF. Resources might be better spent in simply improving containment (e.g., by using multiple seals) rather than designing elaborate means of monitoring. The first priority should be to ensure that the samples remain reliably contained until opened in an SRF. The means by which this result is achieved will best be determined by those designing the implementation of a Mars sample return mission. Recommendation: The canister(s) containing material returned from Mars should remain sealed during all mission phases (launch, cruise, re-entry, and landing) through transport to a sample-receiving facility where it (they) can be opened under strict containment. No facility currently exists that combines all of the characteristics required for an SRF. However, the committee found that there is a long, well-documented history of both the successful biocontainment of pathogenic and infectious organisms and a capability for maintaining the scientific integrity of extraterrestrial and planetary materials. Thus, the committee concluded that the requirement for handling and testing returned martian materials in a single facility combining both biocontainment and integrity-maintaining functions is both appropriate and technically feasible, albeit challenging. The NRC’s 1997 Mars report contained a four-part recommendation relating to various aspects of the establishment and operation of an SRF. The first part concerned the need for such a facility: “A research facility for receiving, containing, and processing returned samples should be established as soon as possible after serious planning for a Mars sample-return mission has begun” (p. 5). Although the present committee supports the intent of this recommendation, it emphasizes that the initiation of planning for an SRF must also include the initiation of planning for, and development of, the activities that will take place there. Recommendation: Because of the lengthy time needed for the complex development of a sample-receiving facility (SRF) and its associated biohazard-test protocol, instrumentation, and operations, planning for an SRF should be included in the earliest phases of the Mars sample return mission. The second part of the 1997 recommendation discussed the timescale for the establishment of an SRF: “At a minimum the facility should be operational at least 2 years prior to launch [of a Mars sample return mission]” (p. 5). The phrase “2 years prior to launch” is ambiguous because it could imply launch from Earth or launch from Mars. More specificity is needed as to the duration of the SRF’s running-in period and the activities to be undertaken during that period. Recent experience with the design, construction, and/or commissioning of new BSL-4 facilities in the United States and overseas suggests that a 2-year running-in period is too optimistic. Facilities
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Assessment of Planetary Protection Requirements for MARS: Sample Return Missions may become “operational” at BSL-2 or BSL-3 levels 2 years after completion but do not become fully operational as BSL-4 facilities for several additional years. Thus, it is essential to specify that an SRF be fully operational at least 2 years prior to the return of samples to Earth. Recommendation: Construction and commissioning of a sample-receiving facility should be completed and fully operational at least 2 years prior to the return of samples to Earth, in order to allow ample time for integrated testing of the facility, the overall test protocol, and instrumentation well in advance of receiving returned martian materials. The third part of the 1997 recommendation concerned the roles and responsibilities of an SRF’s staff: “The facility should be staffed by a multidisciplinary team of scientists responsible for the development and validation of procedures for detection, preliminary characterization, and containment of organisms (living, dead, or fossil) in returned samples and for sample sterilization” (p. 5). The present committee concurs with this recommendation. Recommendation: A sample-receiving facility should employ multidisciplinary teams of scientists to develop, validate, and perform a rigorous battery of tests that will be used to determine whether and when unsterilized materials returned from Mars may be approved for controlled distribution, or full release from containment. The final part of the NRC’s 1997 recommendation concerning an SRF dealt with scientific oversight: “An advisory panel of scientists should be constituted with oversight responsibilities for the facility” (p. 5). The committee concurs with this recommendation, but in addition recommends including technical issues relating to an SRF within the oversight committee’s terms of reference. The oversight committee’s independence should also be specified. Recommendation: An independent science and technical advisory committee should be constituted with oversight responsibilities for materials returned by a Mars sample return mission. Related Issues Two additional important issues not specifically related to an SRF concern independent oversight of planetary protection policies and public engagement in activities related to Mars sample return. The NRC’s 1997 Mars report saw a need for high-level oversight of all planetary protection requirements associated with Mars sample return: “A panel of experts, including representatives of relevant governmental and scientific bodies, should be established as soon as possible once serious planning for a Mars sample-return mission has begun, to coordinate regulatory responsibilities and to advise NASA on the implementation of planetary protection measures for sample-return missions. The panel should be in place at least 1 year prior to the establishment of the sample-receiving facility (i.e., at least 3 years prior to launch)” (pp. 5-6). The committee does not believe that this recommendation is appropriate given the potential conflicts between planetary protection concerns and scientific or operational issues inherent in NASA’s current advisory structure—i.e., with the Planetary Protection Subcommittee (PPS) reporting to the NASA Advisory Council (NAC) via the NAC’s Science Committee. There is a critical need for the PPS, or its equivalent, and the NASA planetary protection officer to be formally situated within NASA in a way that will allow for the verification and certification of adherence to all planetary protection requirements at each stage of a Mars sample return mission, including launch, re-entry and landing, transport to an SRF, sample testing, and sample distribution. Clear lines of accountability and authority at the appropriate levels within NASA should be established for both the PPS (or an equivalent group) and the planetary protection officer, in order to maintain accountability and avoid any conflict of interest with science and mission efforts. Recommendation: To ensure independent oversight throughout the lengthy and complex process of planning and implementing a Mars sample return mission, planetary protection policy and regulatory oversight for all aspects
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Assessment of Planetary Protection Requirements for MARS: Sample Return Missions of sample return should be provided by both the Planetary Protection Subcommittee (or an equivalent group) and the NASA planetary protection officer, each having suitable authority and accountability at an appropriate administrative level within NASA. Finally, the NRC’s 1997 Mars report recommended that: “Throughout any sample-return program, the public should be openly informed of plans, activities, results, and associated issues” (p. 6). The present committee concurs with this recommendation and believes that it is also important to explicitly extend the policy of openness to encompass both the sample-return mission and the construction, testing, and operation of an SRF. Recommendation: The public should be informed about all aspects of Mars sample return, beginning with the earliest stages of mission planning and continuing throughout construction, testing, and operation of a sample-receiving facility. NOTES 1. National Research Council, Preventing the Forward Contamination of Mars, The National Academies Press, Washington, D.C., 2006. 2. National Research Council, Mars Sample Return: Issues and Recommendations, National Academy Press, Washington, D.C., 1997. 3. National Research Council, New Frontiers in the Solar System: An Integrated Exploration Strategy, The National Academies Press, Washington, D.C., 2003, pp. 198-199.