National Aeronautics and Space Administration Planetary Protection Office

Mars Sample Return: Issues and Recommendations
Task Group on Issues in Sample Return. National Academies Press, Washington, DC (1997).

Available online:

As stated in NASA Management Instruction 8020.7, the Space Studies Board (SSB) of the National Research Council (NRC) serves as the primary adviser to NASA on planetary protection policy, the purpose of which is to preserve conditions for future biological and organic exploration of planets and other solar system objects and to protect Earth and its biosphere from potential extraterrestrial sources of contamination. In October 1995 NASA requested that the SSB provide advice on planetary protection issues related to possible sample-return missions from Mars and other near-Earth solar system bodies. In response, the SSB established the Task Group on Issues in Sample Return to address:

  1. The potential for a living entity to be included in a sample to be returned from another solar system body, in particular Mars;
  2. The scientific investigations that should be conducted to reduce uncertainty in the above assessment;
  3. The potential for large-scale effects on the environment resulting from the release of any returned entity;
  4. The status of technological measures that could be taken on a mission to prevent the unintended release of a returned sample into Earth’s biosphere; and
  5. Criteria for controlled distribution of sample material, taking note of the anticipated regulatory framework.

Although focused on sample-return missions from Mars, the recommendations can be generalized to any mission that could return a sample from an extraterrestrial object with a similar potential for harboring life.


Although current evidence suggests that the surface of Mars is inimical to life as we know it, there remain plausible scenarios for extant microbial life on Mars – for instance in possible hydrothermal oases or in subsurface regions. The surface environment of Mars, from which early samples are most likely to be returned, is highly oxidizing, is exposed to a high flux of ultraviolet radiation, is devoid of organic matter, and is largely devoid of liquid water. It is unlikely that life of any kind, as we currently understand it, either active or dormant, could survive in such an inhospitable environment. If active volcanism, or near-surface liquid water, is discovered on Mars, or if the subsurface environment is found to be considerably less oxidizing and wetter than the surface, the occurrence of extant life on the planet becomes more plausible.

Contamination of Earth by putative martian microorganisms is unlikely to pose a risk of significant ecological impact or other significant harmful effects. The risk is not zero, however.In the event that living martian organisms were somehow introduced into Earth’s environment, the likelihood that they could survive and grow and produce harmful effects is judged to be low. Any extant martian microorganisms introduced into Earth’s biosphere would likely be subject to the same physical and chemical constraints on their metabolic processes as are terrestrial organisms. Thus, extraterrestrial organisms would be unlikely to mediate any geochemical reactions that are not already catalyzed by Earth organisms. They would be unlikely to be able to compete successfully with Earth organisms, which are well adapted to their habitats. Because pathogenesis requires specific adaptations to overcome the extensive defenses possessed by all Earth organisms, virulent extraterrestrial pathogens are unlikely. Subcellular disease agents, such as viruses and prions, are biologically part of their host organisms, and so an extraterrestrial source is extremely unlikely. Conceivably, putative extraterrestrial organisms could be capable of opportunistic infections or toxicity, as are some terrestrial bacteria, but such a risk can be eliminated by standard laboratory control procedures.

The potential for large-scale effects, either through pathogenesis or ecological disruption, is extremely small. Thus, the risks associated with inadvertent introduction of exogenous microbes into the terrestrial environment are judged to be low. However, any assessment of the potential for harmful effects involves many uncertainties, and the risk is not zero.

Uncertainties with regard to the possibility of extant martian life can be reduced through a program of research and exploration that might include data acquisition from orbital platforms, robotic exploration of the surface of Mars, the study of martian meteorites, the study of Mars-like or other extreme environments on Earth, and the study of returned samples. However, each returned sample should be assumed to contain viable exogenous biological entities until proven otherwise. The SSB task group strongly endorses NASA’s Exobiological Strategy for Mars Exploration (NASA, 1995). Such an exploration program, while likely to greatly enhance our understanding of Mars and its potential for harboring life, nonetheless is not likely to significantly reduce uncertainty as to whether any particular returned sample might include a viable exogenous biological entity-at least not to the extent that planetary protection measures could be relaxed.

Recommendations – Sample Return and Control

  1. Samples returned from Mars by spacecraft should be contained1 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. While the probability of returning a replicating biological entity in a sample from Mars, especially from sample-return missions that do not specifically target sites identified as possible oases,2 is judged to be low and the risk of pathogenic or ecological effects is lower still, the risk is not zero. Therefore, it is reasonable that NASA adopt a prudent approach, erring on the side of caution and safety.
  2. If sample containment cannot be verified en route to Earth, the sample, and any spacecraft components that may have been exposed to the sample should either be sterilized in space or not returned to Earth. The engineering and design of any sample-return mission should incorporate some means of verifying sample containment during transit and prior to return to Earth. Means should also be available to sterilize the sample, and any spacecraft components that may have been exposed to it, in flight or to prevent their return to Earth in the event that containment cannot be verified.
  3. Integrity of containment should be maintained through reentry of the spacecraft and transfer of the sample to an appropriate receiving facility. The points in a mission where loss of containment is most likely to occur include operations on the martian surface; inter-vehicle transfer of sample material; vehicle reentry, descent, and landing; and subsequent transfer of the sample container to a receiving facility. Techniques and protocols that can ensure containment at these vulnerable points should be designed into the mission.
  4. 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 should first be sterilized. Returned samples should be considered potentially hazardous until they have been reasonably demonstrated to be non-hazardous. Distribution of unsterilized sample material should occur only after rigorous physical, chemical, and biological analyses confirm that there is no indication of the presence of any exogenous biological entity. If any portion of the sample is removed from containment prior to this determination, it should first be sterilized. The development of effective sterilization techniques that preserve the value of treated material for other (non-biological) types of scientific analysis should be the subject of research by NASA and by the science team associated with the sample-receiving facility.
  5. The planetary protection measures adopted for the first Mars sample-return missions should not be relaxed for subsequent missions without thorough scientific review and concurrence by an appropriate independent body. Samples returned from the martian surface, unless returned from sites specifically targeted as possible oases, are unlikely to harbor life as we know it, and there may be some pressure to reduce planetary protection requirements on subsequent sample-return missions if prior samples are found to be sterile. Presumably, however, subsequent missions will be directed toward locations on Mars where extant life is more plausible, based on data acquired from an integrated exploration program, including prior sample-return missions. Thus, planetary protection measures may become more rather than less critical as the exploration program evolves. At some point it may be reasonable to relax the requirements, but this should only be done after careful scientific review by an independent body.

Recommendation – Sample Evaluation

A research facility for receiving, containing, and processing returned samples should be established as soon as possible once serious planning for a Mars sample-return mission has begun. At a minimum, the facility should be operational at least two years prior to launch. 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. An advisory panel of scientists should be constituted with oversight responsibilities for the facility.

It was evident from the Apollo experience that the science team, and therefore the lunar receiving facility as a whole, would have been more effective if the team members had had prior experience working together as a group on common problems before receiving lunar samples. During the preliminary study of those samples, loss of containment and compromise of quarantine occurred on several occasions. Some of these occurrences might have been avoided had the science team and the receiving facility been operational well before return of the samples.

To avoid similar problems during the initial investigation of returned martian samples and to provide sufficient time to develop and validate the requisite life detection, containment, and sterilization technologies, the receiving facility and its associated science team should be established well in advance of the launch of any sample-return mission. The facility should include appropriately stringent biological containment capability and be staffed by a broadly multidisciplinary team of scientists. When fully constituted, the science team should strive to include diverse expertise in such areas as effective biological containment, geological and biological sample processing and curation, microbial paleontology and evolution, field ecology and laboratory culture, cell and molecular biology, organic and light stable isotope geochemistry, petrology, mineralogy, and martian geology.

Recommendations – Program Oversight

  1. 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 one year prior to the establishment of the sample-receiving facility (at least three years prior to launch).
    To coordinate regulatory and other oversight responsibilities, NASA should establish a panel analogous to the Interagency Committee on Back Contamination that coordinated regulatory and oversight activities during the lunar sample-return missions. To be effective, planetary protection measures should be integrated into the engineering and design of any sample-return mission, and, for an oversight panel to be in a position to coordinate the implementation of planetary protection requirements, it should be established as soon as serious planning for a Mars sample-return mission has begun. For the panel to be able to review and approve any plans for a Mars sample-receiving facility, the panel should be in place at least one year before the sample-receiving facility is established.
  2. An administrative structure should be established within NASA to verify and certify adherence to planetary protection requirements at each critical stage of a sample-return mission, including launch, reentry, and sample distribution. An internal administrative structure, with clearly defined lines of authority, is required to verify and certify adherence to planetary protection requirements at each critical stage of a sample-return mission, including launch, reentry, and sample distribution. The certification should be sequential. That is, the mission should not be allowed to proceed to the next stage until planetary protection requirements for that stage and each preceding stage have been met. For example, reentry should not be authorized unless containment has been verified or the material to be returned has been sterilized. The required internal structure is already partly in place at NASA, but the lines of authority should be more clearly specified and a certification process should be implemented for each mission stage.
  3. Throughout any sample-return program, the public should be openly informed of plans, activities, results, and associated issues. In light of the public’s past response to other controversies involving science and technology, it is possible that environmental and quality-of-life issues will be raised in the context of a Mars sample-return mission. If so, it is likely that the adequacy of NASA’s planetary protection measures will be questioned in depth. The most effective strategy for allaying fear and distrust is to inform early and often as the program unfolds. Acknowledging the public’s legitimate interest in planetary protection issues, and thereby keeping the public fully informed throughout the decision-making process related to sample return and handling, will go a long way toward addressing the public’s concerns.