In its 1997 report on sample return from Mars, the Space Studies Board of the National Research Council (NRC) noted that the only risk of significant, adverse effects would be from returning a replicating organism. Furthermore, the report noted: "While the probability of returning a replicating biological entity in a sample from Mars" 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" when dealing with returned samples.

More recently, a 1998 NRC report on small solar system bodies (asteroids, comets, planetary satellites, and interplanetary dust) recommended a similarly cautious approach for samples returned from anywhere else within the solar system that could have environmental conditions conducive for harboring life. We have not detected life elsewhere in the solar system - at least not yet. Nonetheless, the rationale behind the conservative approach to sample handling is similar to the environmental, health and safety measures taken on Earth when transporting or handling infectious agents or importing non-native organisms to a new area. Better safe than sorry.

Planetary Protection: What It Is and Why It's Needed

In order to retrieve samples from another place in the solar system that might harbor life, careful planning is required to ensure that mission designs incorporate measures to safeguard both the Earth and other solar system bodies from cross contamination. These measures, collectively known as planetary protection (PP) measures, are actually tied to international law. The Outer Space Treaty of 1967 specifically requires that all space exploration must be done in a way that avoids harmful contamination to celestial bodies or adverse changes in the environment of the Earth from the introduction of extraterrestrial materials.

Over the years, planetary protection policies for solar system exploration missions have been developed by the members of the international Committee on Space Research (COSPAR). PP policies specifically address the prevention of two types of cross-contamination: 1) forward contamination, the transport of terrestrial microbes on outbound spacecraft; and 2) back contamination, the introduction to Earth of organisms that could be present in materials or samples returned from extraterrestrial locations.

The task of planning effective PP measures requires blending information about what we know about biological systems and extraterrestrial environments, with educated speculation about what conditions might exist in the extreme habitats where samples will be collected. Because of our ignorance about life beyond the Earth, PP measures are deliberately designed to deal with organisms at least as capable of surviving extreme conditions as the toughest organisms found on this planet. Admittedly, decisions about handling returned samples in the near term will be made in the face of scientific uncertainty and a lack of definitive information, but that doesn't make it the stuff of science fiction.

For centuries, the possibility of discovering extraterrestrial life has both tantalized the public and given rise to occasional doses of anxiety. Serious scientists may be comfortable with quantitative estimates of low risks and non-zero probabilities, but the public wants to know what it would really mean to have alien life on Earth. This can have humorous consequences, but points to an overall need to keep the public informed. For example: after the NRC sample return report was published in the summer of 1998, it's findings were playfully lampooned by Gene Weingarten in the Washington Post Style Section. Weingarten translated the official communication about "putative life forms" and non-zero risks into a "Plain English" version as follows: "First you start coughing, and then a slime-flecked, fanged weasel from Hell bursts out of your chest cavity."

Isn't science fiction helpful! Because of public interest and concern about extraterrestrial life, there will undoubtedly be plenty of questions about the safety of returning samples that may contain alien life to Earth. Whether the concerns are caused by overactive imaginations, repeated exposure to Hollywood-style aliens, distrust of government bureaucrats, or basic scientific questions, it will be important to address them responsibly.

Although the public's sophistication may differ from scientists' in its views about the potential hazards of alien life, surprisingly their conclusions on what to do about it are the same as those recommended by experts. In recent research comparing the general public and scientists in their perceptions about risks of returning samples from Mars, the overwhelming conclusion was that returned samples should be considered hazardous to Earth's biota until proven otherwise. That is exactly what the NRC recommended, and it's precisely what NASA plans to do.

Planetary Protection Needs

Mission planners are mindful of the NRC recommendations that samples from Mars and other places with biological potential should be strictly contained, and that this containment be verified during the entire return trip. Moreover, if containment cannot be verified en route to Earth, the sample, and any spacecraft components that may have been exposed to the sample or extraterrestrial environment, will either be sterilized in space or not returned to Earth. Integrity of containment will be maintained through re-entry of the spacecraft and transfer of the sample to an appropriate receiving facility under quarantine conditions.

Finally, pristine sample materials will not be removed from containment prior to completion of rigorous analyses that demonstrate the materials are nonhazardous. If any portion of the sample is removed from containment prior to completion of these analyses, it will first be sterilized.

Translating these recommendations into effective, implementable measures is not an easy task. The work requires a careful implementation of PP requirements to balance biosafety considerations, the needs of planetary scientists, the constraints of spacecraft engineers, and the budgetary limits of administrators. Clearly, back contamination concerns are the primary driver in the current deliberations about preparing for the many and different samples expected to arrive in the coming decade. Protection of the Earth is, of course, the bottom line.

Planetary Science Needs

But whether or not extraterrestrial samples are of biological interest, strict containment of a different sort is also required to rigorously protect extraterrestrial materials from Earthly contamination while they are studied. The containment concerns of the space science community are strongly driven by the need to protect the scientific integrity of returned materials and preserve samples in a pristine and unaltered state, down to the isotopic composition level. In contrast to the biosafety community, the space science community has historically done containment by means of physical barriers, such as containers and cabinets that minimize exchange of gaseous molecules, prevent exposure to terrestrial contaminants, and preserve samples in a pristine state.

Viewed quite simply, the need for containment in the space community is actually driven by two distinctly different emphases: on one hand, traditional biosafety and planetary protection concerns, and on the other, sample protection and science considerations. The former emphasizes keeping materials in, while the latter emphasizes keeping contaminants out. On top of the conflicting containment needs, the problem of planetary protection is made even more difficult by spacecraft engineering demands.

Spaceflight Engineering Needs

In addition to meeting biosafety and planetary science needs, additional design constraints are imposed by spaceflight engineering challenges. All materials and mechanisms used during extraterrestrial sample return missions must work in the space environment of extremely low pressure, low and high temperatures, and prolonged, intense radiation. Robotic containment mechanisms must be reliable and their allowance for mass and power consumption will be extremely strict because of the size and weight restrictions imposed by spaceflight. In addition, there must be a careful integration of all mobile and stationary containment mechanisms and systems used in flight and on Earth.

Borrowing From Past Experiences and Other Fields

Although containment and handling of returned extraterrestrial materials will undoubtedly be complicated, it is not unprecedented. The conceptual and operational approaches used during the Apollo program are still applicable, albeit with considerable updating in technology, science and legal requirements. In retrospect, while there were admittedly some problems experienced in handling early samples from the moon, the quarantine facilities and testing protocols that were used ultimately accomplished their objective of safely containing and screening incoming materials to determine whether they could be eventually released.

Only about 500 grams of Martian materials will be returned during the first sample return mission. As such, the sample receiving facilities for Martian materials (and presumably for materials from other solar system bodies as well) can be far less elaborate than the first Lunar Receiving Laboratory, which provided quarantine and containment for all returning astronauts, spacecraft, and lunar materials during its operation from 1969-72.

Additional information of relevance to the handling of potentially biohazardous extraterrestrial materials has been learned by analyzing containment and quarantine approaches used in the biomedical and genetic engineering sectors. Recent NASA workshops on biocontainment and biohazard analyses have invited specialists from diverse organizations with expertise in handling and testing biohazardous materials (e.g., CDC, EPA, USDA, US Army, university researchers, and biomedical and aerospace corporations). The expert consensus is that nothing about the anticipated nature of extraterrestrial materials will require truly unique methods or technologies. Existing biosafety guidelines and available equipment and technologies will be appropriate or adaptable for quarantining and handling incoming extraterrestrial samples.

Finally, important design input for future extraterrestrial sample processing has also been learned from the handling of meteorites, lunar materials and interplanetary dust samples at Johnson Space Center (JSC) over the past several decades. The on-going lessons learned from routine containment and analysis of diverse non-biological samples of extraterrestrial origin will be helpful in many ways, especially in areas related to sample characterization, preservation, cleanliness, and sterilization techniques.

While we can be inventive in devising new ways to contain and analyze returned extraterrestrial samples, it would not be wise to attempt using methods with which we have no experience, just because they are new. For example, it has been suggested (and studied by NASA) that it might be advantageous to conduct the analysis of returned samples on a space station orbiting the Earth. Some have suggested that an orbiting station might provide a greater deal of isolation from the sample and its potential risks, and hence more safety to the Earth.

Nonetheless, a careful examination of the space station option also shows that, in the foreseeable future, we will not have either the array of analytical techniques or the experience with basic biological sciences on-orbit that would allow such rigorous testing to be done in space. And while we don't really know how to do even basic microbiological experimentation effectively in space, we do know that any space station left in orbit around the Earth will eventually crash to the surface, thereby ending the advantage of space station separation in a very permanent and uncontrolled fashion. An orbital solution, in fact, brings in more problems than it solves.

Overall, a far more reasonable approach is to bring a returned sample safely to Earth, and then treat it with the same basic capabilities with which we routinely handle dangerous biological and chemical substances on Earth.

Conclusion

Extraterrestrial sample return missions will no doubt generate considerable public interest because of the excitement about potential extraterrestrial life as well as questions about possible adverse effects on Earth, however unlikely they may be. Undoubtedly, decisions about planetary protection will be scrutinized by the public. It should also be anticipated that information will be disseminated widely by the mass media and the Internet.

Through the environmental impact statement process, the public will have ample opportunity to examine information about mission plans, risk assessments, biocontainment decisions, laboratory operations, testing procedures, worst case scenarios, and contingency plans. Ultimately the overall success of sample return missions may depend, in part, on how confident the public is that biosafety and planetary protection concerns have been addressed.

No one expects either an Andromeda Strain or a War of the Worlds from returned extraterrestrial samples. Even so, NASA's approach to sample return planning will continue to be conservative and based on sound science and engineering principles. Using a conservative approach does more than satisfy PP requirements and international treaty obligations. It also contributes to mission success by lowering the prospects of Earthly contamination that could confound the interpretation of results.

Returning Martian samples to Earth will be a momentous scientific and technological advance that must be accomplished carefully and responsibly. Solving the challenges of containment and biosafety will be critical to mission success -- for protecting researchers and the biosphere; for maintaining the integrity of the samples for a wide variety of studies; and for fostering public confidence and support for this exciting human achievement.