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unmanned and manned missions traces from post-Sputnik missions to the present, with ...... orbiting laboratory as an alternative to bringing the sample.
JO~AL

OF GEOPHYSICAL RESEARCH, VOL. 103, NO. E12, PAGES 28,577-28,585,NOVEMBER 25, 1998

Planetary protection, sample return missions and Mars exploration: History , status, and future needs Donald NASA

L.

DeVincenzi

Ames Research

Center,

Moffeu

FieJd, CaJifomia

Margaret s. Race and Harold p, Klein SE11Institute,MountainView,California Abstract. As the prospect grows for a Mars sample return mission early in the next millennium, it will be important to ensure that appropriate planetary protection (PP) controls are incorporated into the mission design and implementation from the start. The need for these pp controls is firmly based on scientific considerations and backed by a number of national and international agreements and guidelines aimed at preventing harmful cross contamination of planets and extraterrestrial bodies. The historical precedent for the use of pp measureson both unmanned and manned missions traces from post-Sputnik missions to the present, with ~riodic modifications as new information was obtained. In consideration of the anticipated attention to pp questions by both the scientific/technical community and the public, this paper presents a comprehensive review of the major issues and problems surrounding pp for a Mars Sample Return (MSR) mission, including an analysis of arguments that have been raised for and against the imposition of pp measures. Also discussed are the history and foundations for pp policies and requirements; important research areasneeding attention prior to defining detailed pp requirements for a MSR mission; and legal and public awarenessissues that must be considered with mission planning.

I. Introduction In developing a long-term strategy for Mars exploration, attention has focused on a variety of science objectives, including the search for evidence of extant or fossil life on Mars. Recently, serious consideration has been given to a Mars Sample Return (MSR) mission which could be launched as early as the year 2004. As planning for a MSR mission gets under way, it is important to increase the pace of planning for planetary protection (PP) requirements, which are intended to avoid both forward contamination of Mars by terrestrial microbes on the outbound spacecraft, and back contan\ination of Earth's biosphere by the introduction of extant Martian organisms that could be present in a returned sample. As dictated by existing domestic and international laws and policies, PP controls are imposed with the dual intentions of protecting planets from harmful cross contamination and avoiding operations that would compromise future scientific study. Coincidentally, PP controls may also help protect the mission's scientific experiments from contamination that could compromise the data or their interpretation. Over the years, PP policy for solar system exploration missions has been develo~d for, and promulgated to, the international space science community by the Committee on Space Research (COSPAR) [DeVincenzi and Stabekis, 1984]. Until recently, the emphasis has been primarily on requirements for preventing forward contamination on outgoing spacecraft (DeVincenzi et al., 1995]. Because a sample return mission will involve both outbound and return Copyright 1998 by the American Geophysical Union. Papel'number98JEOl600. OI48-0227/98/98JE-OI600$09.00

flights, there will soon be a need to determine what specific measures will be used for both forward and back contamination controls. To date, COSP AR has not issued any formal policy guidelines on back contamination, although some guidelines have been suggested for use by mission planners and designers [DeVincenzi and Klein, 1989]. Imposing pp controls and determining the appropriate level of stringency for a Mars sample return mission are dependent on our views about whether or not Mars has an extant biota. During the next decade, about 10 additional one-way missions to Mars are anticipated. While they are likely to generate considerable information about Mars itself prior to the fIrst sample return mission, they are unlikely to resolve the debate over extant life. In the face of this continuing uncertainty, pp controls will undoubtedly be needed, and the task of setting these requirements will remain controversial. In the end, mission success may well depend on the development of appropriate, effective pp measures that satisfy technical and scientific concerns while reassuring the public that appropriate safeguards will be taken at every step. To date, the only attempts to detect the presence of an indigenous biota on Mars were carried out during the Viking mission in the late 1970s. The mission's two landers conducted a number of investigations pertinent to this question. These investigations, spanning many Martian seasons, failed to detect any measurable organic compounds in the surface matter, found no indication of any living structures, and found no unequivocal evidence for metabolic activity on the surface [Klein, 1979]. The collective investigations were interpreted to mean that the surface samples were lifeless and that, as a first approximation, this was true for the entire surface of Mars [Space Science Board, 1977; Klein ,1979].

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However, in the intervening years, debate has arisen about the validity of this sweeping conclusion [Klein, 1996]. For example, several biological niches (or "oases") have been suggested where a Martian biota might be present. Clearly, if such oases do exist, and are found to harbor living organisms, the strategy for sample return from Mars would be seriously affected. At this stage of Mars exploration, these hypothetical environmental niches have not been found, let alone investigated. Therefore if Martian samples are to be returned to Earth before extensive searches can be mounted, the prudent approach will require the application of appro{Jriate pp measures. With a MSR mission on the planning horizon~ it is important to consider pp issues comprehensively because they clearly have the potential to impact mission feasibility, complexity, and cost. It is also clear that a MSR mission has the potential to draw significant attention by special interest groups and the general public because of concerns over environmental, health and safety issues [Race. 1995]. Because questions about pp are anticipated from both the scientific/technical community and the public, the objective of this paper is to present a comprehensive review of the major issues and problems surrounding pp and MSR, including an analysis of arguments that have been raised for and against the imposition of pp measures. Also presented are discussions of the historical foundations for pp policies and requirements; legal and public awareness issues that should be considered in mission planning; and important research areas needed to establish baseline information for defining pp requirements on a MSR mission.

2. Background and Early History of Planetary Protection Policies After the successful launch of Sputnik on October 4, 1957, scientists were quick to recognize that if future programs capitalized on this new technology, the potential was very real for introducing terrestrial material onto other planets, and vice versa. Four months after Sputnik, the U.S. National Academy of Sciences (NAS) adopted a resolution that urged scientists to plan lunar and planetary studies with great care so as to prevent contamination of celestial objects and avoid compromising future scientific explorations and opportunities. By 1958 an international Committee on the Exploration of Extraterrestrial Space (CETEX) had been formed to consider these concerns, and reports on their deliberations soon appeared in major scientific journals [Science, 1958; Nature, 1959]. Concerns that contamination by terrestrial materials could confuse subsequent planetary experimentation were soon joined by an added dimension, namely, that bacteria and other organisms carried on spacecraft could have an irreversible impact on ecological systems indigenous to other planets [Lederberg, 1960]. At COSPAR's 1964 meeting, representatives of the international space community formulated the first quantitative objectives for planetary protection [COSPAR, 1964], thus setting the stage for the eventual approach used in planning the Viking mission to Mars. Mindful of the possibility of affecting an ecology on Mars, they adopted COSPAR Resolution 26.5, which recommended "... a sterilization level such that the probability of a single viable organism aboard any spacecraft intended for planetary landing or atmospheric penetration would be less than 1 X 10-4, and a probability limit for accidental planetary impact by unsterilized fly-by or orbiting spacecraft of 3 x 10-5 or less ...during the interval terminating at the end of the

initial period of planetary exploration by landing vehicles." (Sterilization as used throughout this paper refers to reduction of spacecraft bioload to particular defined levels, rather than elimination of all microbes per se.) In 1966 the matter of planetary protection was brought before the General Assembly of the United Nations, leading ultimately to changes in The Outer Space Treaty .With interIljltional interests at stake and the very real prospect of returning samples from the moon during the A~llo mission, Article IX was unanimously incor~rated into the treaty, instructing participating states to be guided by th~ principle of cooperation and mutual assistance in the their conduct of space activities and to pursue studies "... so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter ..."[United Nations, 1967]. In 1967, in response to COSPAR recommendations, NASA officially established a program office within the Office of Space Sciences to oversee the development of PP policies and implementation approaches. In the ensuing years, NASA issued a number of ~Iicy directives concerned with missions to the moon [NASA, 1967, 1968, 1969a] and planets [NASA ,1967, 1968, 1969b, 1972, 1976, 1988a]. For nearly two decades, NASA's basic policy for implementing planetary protection remained unchanged. Focused largely on forward contamination, the ~Iicy's main features included microbiological assays of manned and unmanned spacecraft surfaces to obtain an inventory of "outbound" organisms, and the application of statistical methods and analytical models to estimate the probability of contaminating the target celestial object [Hall, 1971a1. In early discussions about PP and Mars, it is noteworthy that the environment of Mars was thought to harbor an indigenous biota and be much more conduciv~ to biological systems than we know to be the case today. For example, at that time, it was presumed that liquid water was present on Mars' surface, its ice caps consisted of water, and its atmosphere had a pressure of 85 mbar. With this kind of "Mars," it is not surprising that COSPAR, in delineating probabilities associated with "contaminating" Mars, assigned a probability of 1.0 for the growth of terrestrial organisms on that planet. Researchers were also overly optimistic about the number of missions to Mars that would occur during the period of planetary exploration. Speculation ranged from "... 60 landers and 30 flybys and orbiters ..." [Sagan and Coleman, 1965], to "... a total of 64 interplanetary flights" between 1966 to 2000 [Light et al. , 1967], and COSPAR's estimate of "... a realistic maximum number... over a 20 year period... of about 100 landing capsules and non-landing vehicles..." [COSPAR, 1968].

3. Implementation Measures

of Planetary Protection

3.1. Manned Lunar Missions The rl!st serious application of PP requirements by the United States occurred during the Apollo program. In addition to maintaining an active program to monitor the number and variety of microorganisms on outbound Apollo vehicles [Puleo et al., 1969, 1970a, 1970b, 1973], it was clear that extraordinary measures would be needed, especially in those cases where astronauts would be involved in the deliberate or inadvertent return of lunar materials into the Earth's environment. Discussions began in the early 1960s between NASA and the U.S. Public Health Service and uJtimately led to the formation in 1967 of an Interagency Committee on Back Contamination (ICBC) to advise NASA on matters related to quarantine, sample handling, and back

DEVINCENZI Er AL.: MARS PLANETARY PRO1ECrION AND SAMPLE RETURN contamination control. Consisting of representatives of NASA, the U.S. Public Health Service, the U.S. Department of Agriculture, U.S. Department of the Interior, and the National Academy of Sciences, the ICBC subsequently develdped protocols for the quarantine, biological testing, and release of lunar samples, and for the quarantine and release of the involved astronauts [NASA, 1969c]. These activities were to be carried out in a specially built Lunar Receiving Laboratory (LRL) in Houston, where the returning astronauts were quarantined and the initial testing of lunar samples was performed behind biological barriers. Details on the quarantine aspects of the Apollo missions and suggestions for future human sample return missions can be seen elsewhere [NASA ,1969c; Phillips, 1972; Johnston et al., 1975; Bagby, 1975]. By 1971, astronauts had brought back to the LRL 382 kg of lunar rocks and soil comprising over 2000 individual specimens. Quarantine studies included tests to investigate possible adverse effects of lunar materials on 35 plant species, 11 tissue culture lines, and 15 species of animals, as well as careful biomedical monitoring of the astronauts for a minimum of 21 days. As there was no indication in any of these tests that the Moon contained harmful chemical or biological agents, quarantine testing was abandoned after the Apollo 14 mission, although chemical and physical characterization of lunar samples continued [Taylor et al., 1975]. 3.2.

Unmanned

Solar System Missions

In order to avoid cross contamination of extraterrestrial bodies, all components of unmanned, outbound U.S. spacecraft are assembled in clean rooms, and assays performed to characterize the "biological load" (bioload) of microbes in a manner similar to the Apollo spacecraft [Bond et al., 1971; Puleo et al. , 1977]. During the period of preApollo unmanned lunar missions, notably with several "Ranger" and "Surveyor" spacecraft, NASA also attempted several techniques, including the use of heat, for treatment of spacecraft components, in order to reduce their outbound microbial load. These techniques were abandoned because many of the components were found to be sensitive to these procedures. NASA policy also included mission flight designs with "capsule deflection" trajectories as an additional planetary protection safety measure. Subsequently, with the capability to orbit a planet like Mars, it also became NASA policy to design the orbits so as to prevent impacting the planet "... before the end of the period of biological interest." Originally set as December 30, 1988, the period of biological interest was later extended until December 30, 2018, in order to provide sufficient time for the detection and subsequent study of life on Mars. The change was made because the original policy did not allow sufficient time to study the planet before it became contaminated [Hall,1971b]. 3.3.

Viking

Mission

to Mars

Implementation of planetary protection measures for the Viking mission in 1975-1976 (comprising two spacecraft, each with an orbiter and a lander) presented a significant challenge compared to previous unmanned missions. For one thing, the landers were planned to contact the Martian surface; for another, pre-Viking estimates of the probability of growth of tenestrial organisms was considered to be higher for Mars than for the Moon or other extraterrestrial bodies in the solar system [Space Science Board ,1970]. In addition, there were instruments aboard each lander designed to seaD::hfor metabolic activity in surface samples that might

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contain Martian microorganisms. This imposed the need to prevent any terrestrial "hitchhiker" organisms from confusing the life detection experiments. In keeping with the statistical approach to planetary protection utilized at that time, NASA issued probability parameters for use by Viking mission planners for both the orbiters and landers [Hall, 1973]. The more stringent probability parameters were assigned for the landers and included estimates for the Probability (PJ of (1) survival of organisms in space vacuum and temperature, (2) survival to space UV flux, (3) arrival of organisms at Mars, (4) surviving atmospheric entry at Mars, (5) release of organisms from the landers, and (6) growth and proliferation of terrestrial microorganisms on Mars. Finally, in arriving at the overall probability of contaminating Mars, these parameters were to be multiplied by the estimated microbial load on the spacecraft at launch [Hall. 1973]. Each Viking spacecraft was supposed to meet the criterion of 10-3 or less for the probability ( P J of contaminating Mars. Because the spacecraft were known to carry a significant bioload [Puleo et al., 1977], it was clear from the outset that the Viking landers would need to undergo active bioload reduction. After experimental tests on various techniques, dry-heat "sterilization" of the landers was eventually selected as the method for effective bioload reduction. Because the Viking landers contained sensitive metabolic assay systems, the Viking biology team imposed added heat treatment for avoiding terrestrial contamination of their instrument. Details on these methods are provided in the appendix.

3.4

Revisions

to

Planetary

Protection

Policy

In 1988, NASA made substantial revisions to its original planetary protection policies, taking into account new information acquired by U.S. and USSR. spacecraft missions to Venus and Mars in the intervening years [NASA, 1988a]. The quantitative, probabilistic methods that had been used for the Viking mission were replaced instead with planetary protection controls based on five categories of planetary missions [DeVincenzi and Stabekis, 1984]. Category I missions have targets like the Sun or Moon, which have no direct exobiological interest; categories II, III, and IV include flybys, orbiters, landers, and probes sent to planets or targets with increasing exobiological interest; and category V, with the most stringent pp controls, is reserved for sample return missions. As required by the revised policy, NASA consults theNAS Space Studies Board (SSB) and others in the scientific community for guidance in categorizing missions and establishing specific pp requirements. In 1990, NASA asked the NAS SSB to reconsider the problem of forward contamination of Mars by landers. The SSB recommended major changes in guidelines, stipulating that all spacecraft targeted to Mars, but without any life detection experiments aboard, would no longer require full sterilization [Space Studies Board, 1992]. Rather, such vehicles should still be assembled in clean rooms, but components need only be cleaned to reduce surface organics and reduce microbial loads to the levels that were obtained for the Viking spacecraft before heat sterilization. For those missions with landed payloads in which life detection experimen,s are included, "Viking-Ievel" sterilization procedures were recommended. The revised pp requirements have been applied on all recent outbound Mars missions. Mars Observer, launched in 1992, and Mars Global Surveyor, launched in November 1996, were both designated as category III orbital missions, clearly underscoring the exobiological interest in Mars and concern about potential contamination. Both involved clean

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room assembly, biasing of trajectories, and inventory of launched bioload. Mars Pathfinder, launched in December 1996 with a small rover and lander inside an aeroshell, was designated a category IV lander mission. Since no life detection experiments were on board, the Pathfinder spacecraft was subjected only to clean room assembly with treatments for bioload reduction and subsequent inventory of launched bioload (see appendix). 3.5. Implementation Measures by the USSR

or and

Planetary Protection Other Nations

In the 1960s, when the USSR mounted several unmanned missions to Venus and Mars, information about their missions was fragmentary or available mainly from newspaper reports. In some cases, it was not clear whether a particular mission was intended to be a fly by or to release a capsule to the surface of the planet. Analyzing the scant public information available, Murray et al. [1967] argued that several of these missions probably impacted Venus and Mars, some accidentally and others by design, thereby almost certainly depositing terrestrial organisms on Venus and Mars as a consequence of these impacts. Numerous statements from the Soviets during this period asserted that their missions were in compliance with COSP AR PP recommendations, although hard evidence on the methodology used to achieve these objectives is difficult to fmd. Nevertheless, it appears that a significant effort was mounted by the USSR to develop appropriate technology consistent with COSPAR guidelines. Research was conducted on the efficacy of chemical, physical, and even biological methods for this purpose. For some spacecraft components, gas mixtures like ethylene oxide and methyl bromide, were deemed desirable [Vashkov and Prishchep, 1966]. The use of gas mixtures, radiation (source unspecified), and heat for "sterilization" of different spacecraft components was also mentioned [Vashkov et al., 1972]. For the Mars 2 and Mars 3 Soviet missions in 1971, which both deposited landing capsules on the Martian surface, Vashkov claimed that a combination of measures was applied to safeguard against the deposition of terrestrial organisms on Mars. To verify spacecraft sterility, he asserted that three identical spacecraft were built for these missions, one of which was literally ground up and assayed for viable organisms! More recently, for the Mars '96 mission (which experienced an on-orbit failure and subsequent crash landing in South America), the Russians and their associates conformed to the new COSP AR guidelines for landed missions without life detection instrumentation, utilizing clean room assembly and various techniques for component sterilization and recontamination avoidance (see appendix).

4. Back Contamination Controls for Future Mars Sample Return: Recommendations and Research Needs Except in the case of the manned Apollo lunar missions, protection of Earth from "back contamination" was implied or only briefly mentioned in early NASA and COSPAR directives. Over the years, tentative PP guidelines for MSR missions have been suggested, but formal policy has not been issued [DeVincenzi and Klein , 1989]. In 1996, NASA asked the NAS SSB to undertake a study of issues related to back contamination from extraterrestrial sources, including Mars. The final report provides recommendations for consideration in the eventual formulation of back contamination controls by NASA and COSPAR. Briefly, the

AND SAMPLE RE11JRN

report recommended that returned sample materials should be verifiably contained while en route; tested and studied only under contained conditions at an appropriate receiving facility; and not removed from containment prior to completion of rigorous analyses determining that the materials do not contain a biological hazard [Space Studies Board, 1997]. As currently interpreted, the general guidelines for pp controls on a MSR mission should include (1) imposition of appropriate forward contamination measures, (2) verifiable containment of the Mars sample, (3) breaking the contact chain with the Martian surface before returning to Earth's biosphere, and (4) developing and implementing suitable protocols for quarantine testing and handling of the returned sample. Collectively, these areas are especially important because they will impact the mission design, complexity, and cost. Until specific new policies are announced by NASA, preparatory research and planning must continue for back contamination controls, particularly in the critical research areas discussed below. 4.1. Sample Contamination

Containment A voidance

and

Forward

Containment of the Mars sample will require sealing the sample in a container on the Mars surface in such a way that there is no release of contents during the return phase until the container is secured in a suitable containment facility. Although the conditions under which the sample is preserved inside the container have important scientific implications, the main objective of pp requirements is to ensure that the returned sample cannot escape to Earth's biosphere or pose any threat to it. While a majority of scientists acknowledge the low probability of finding extant Martian life in the returned samples, they still feel the need to treat the sample as if it might contain Martian organisms. Thus containment is a prudent first step in a process that will ultimately test the sample to verify whether or not it poses any type of hazard to Earth's biota. Engineering studies will be needed to develop options for containers that can be hermetically sealed, remotely on Mars, in a way that prevents material transfer outward from the container. These studies should include concepts to verify the seal and monitor its integrity during the return trip. Review of Apollo lunar container designs and consultation with agencies and organizations that handle biologically hazardous materials may be helpful in analyzing the quantitative standards and specifications for hermetic sealing necessary for anticipated Mars materials. In addition, special care must be taken to avoid forward contaI1lination. The Mars sample must be free of outbound terrestrial biological contamination which could later compromise interpretation of either quarantine testing or scientific results. Methods to avoid forward contamination may range from cleaning the entire spacecraft to cleaning only those hardware elements that will come in direct contact with the Mars samples. Research on this topic will be critical for cost effective mission designs. 4.2. Breaking Surface

the

Contact

Chain

With

the Mars

Another pp concern is that extraneous Martian materials might be attached to the outer surface or crevices of the sample return capsule (SRC) or Earth Return Vehicle (ERV) when it lifts off the Martian surface. While unlikely. it is conceivable that organisms trapped in this material could

DEVINCENZl ET AL.: MARS PLANETARY PRO1EcnON AND SAMPLE RETURN survive exposure to space vacuum and radiation and reentry into Earth's atmosphere. There is the potential therefore that Earth's biosphere could be exposed to any uncontained Martian materials. Engineering studies will be needed to define methods for preventing uncontained Martian materials from entering the biosphere. Possible solutions include but are not limited to (1) the sample container from a "dirty" Mars ascent vehicle (i.e., with Mars material adhering to the exterior) can be aseptically transferred to a "clean" ERV waiting either in Mars orbit or in deep space orbit; this rendezvous would be achieved in such a way that there would be no transfer of uncontained Mars materials to the ERV; (2) a "dirty" SRC exterior can be sterilized during transit to Earth using a variety of techniques such as burning off a magnesium outer layer, detonating a pyrotechnic outer skin layer (without affecting interior temperature in either case), and/or peeling off protective bio-bags; and (3) a "dirty" SRC can propulsively capture itself into Earth orbit, where a space shuttle can then rendezvous, retrieve, and secure it into a sealed "vault" for transport back to Earth. 4.3. Protocols for Returned Sample

Quarantine

Testing

of the

It is currently assumed that either existing or newly constructed biological containment facilities would be used to contain the samples and conduct the necessary quarantine protocol. Information on existing high level biohazard containment facilities in the United States (e.g., Center for Disease Control and Prevention (CDC) Biosafety Level 4 or equivalent) needs to be compiled and analyzed for their suitability for Mars sample return purposes. Issues for consideration include adequacy and specifications for types of biohazards and uses, compliance with forecasted worstcase or accident needs, and availability to NASA. Studies are also needed to evaluate the collective state of readiness of the United States to safely receive Mars samples and to perform definitive tests that will establish whether the samples contain biohazards needing special controls or conditions. If appropriate existing facilities are unavailable, a new containment lab will be needed. It is reasonable to assume that test methods have progressed significantly since the quarantine analyses of Apollo lunar samples in 1969-1972. These should be reviewed, summarized, and assessed for applicability to MSR. New, post-Apollo methods for biohazard testing, such as the1use of tissue culture [Bagby et a/., 1983], should be examined for conducting a quarantine protocol. The amounts of sample that would be required for such tests should be estimated and compared with the amount of sample that could feasibly be returned by current mission designs.

5. Planetary Protection Public Context

and Sample Return

in a

Even if all the technical and scientific questions about pp are answered, recommendations based purely on scientific and technical considerations may eventually playa secondary role in developing the final strategy for contamination controls on future MSR missions [DeVincenzi et al., 1991]. Numerous changes in U.S. policies, public attitudes, and oversight over the past two decades, especially in areas related to environment, health, and safety, are likely to complicate planning and implementation for a MSR mission [Race, 1995]. Using other scientific-technical con.troversies as guides, it has been possible to identify

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problematic aspects of a MSR mission from a public perspective [Race, 1994]. Two particular areas deserve special consideration, as discussed below.

5.1. Legal, Regulatory, Institutional, Decision-making Issues

and

Unlike sample return during the Apollo program, scientists and space experts deliberating about a MSR mission will be joined in the decision-making process by a vigilant public, an attentive mass media, and numerous government agencies providing oversight and review of any sample return proposal. It is almost certain that many legal, regulatory, institutional and decision-making issues will surface regardless of whether public opposition arises against the mission [Race, 1996]. In the event of public disagreement over MSR plans, there are numerous federal, state and local laws that could be used for challenging mission decisions in court. Considering the potential for administrative delays, increased costs and missed launch windows if lengthy reviews or legal challenges occur, there is need to clarify these issues early in mission planning. Probably the most important legal hurdle for a U.S. sample return mission will be imposed by the National Environmental Policy Act (NEP A), which requires all federal agencies to conduct comprehensive reviews and interdisciplinary analyses of environmental impacts prior to decision-making. NASA's guidelines require that environmental effects must be considered at the earliest stages of study and planning, along with technical and economic factors [NASA, 1988b]. NASA will be required to provide public disclosure in an environmental impact statement (EIS) of the full range of impacts, project alternatives, worst case scenarios, and uncertainties for all phases of a sample return mission. Considering the complexity of a MSR mission, it could take several years to complete the documentation, public hearings, agency consultations, and stepwise review and publication process required under NEPA (S. Dawson, Jet Propulsion Laboratory, personal communication, 1996] . In addition to NEPA requirements, a separate launch approval process may be required under Presidential Directive PD/NSC-25, which stipulates multiagency review of experiments or launches with any allegations of large-scale adverse environmental effects, however improbable the impacts may be [Brzezinski, 1977]. At this time, it appears that the EIS is likely to serve as the review document for the launch approval process, adding increased importance to preparing full administrative and research documentation as part of the NEP A/EIS process. Other legal and regulatory areas with the potential to complicate a sample return mission have also been identified [Robinson, 1992; Race, 1996] These include uncertainties about institutional control and authority; conflicting regulations and overlapping jurisdictions; questions about international treaty obligations and large-scale environmental impacts; uncertainties about the nature of Martian life; lack of federal extraterrestrial quarantine regulations, and constitutional and regulatory concerns about quarantine, public health, and safety .Additional legal complications could arise if the mission is done collaboratively with one or more international partners. Resolution of these ambiguous areas will require an integration of scientific and technical information, legal interpretation, regulatory judgments, and public perceptions. To assist in resolving these issues, it is advisable to reestablish a multiagency group similar to the ICBC, which

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was established to help direct the isolation of extraterrestrial materials and astronauts during the Apollo program. 5.2.

Public

Attitudes

and

Concerns

Experiences with other controversial NASA missions (e.g., Galileo, Cassini, Bion 11) have shown that adversarial challenges, especially in the courts, can generate intense media attention and put NASA into a position over which it has little direct control. For sample return, concerns about back contamination of Earth's biota are likely to dominate the discussions rather than operations in space per se. Mission activities most likely to come under scrutiny include those related to environment, health, safety, and management, including sample containment and monitoring; recovery and transport of samples post reentry; development and operation of quarantine facilities; protocols for handling and isolating samples during scientific study; and methods for dealing with human error or technological failures. The use of nuclear materials on the mission (e.g., radioisotope thermoelectric generators (RTG's) for power or radioisotope heating units (RHU's) for heating) would likely intensify public scrutiny and opposition. In order to understand public attitudes and concerns more fully, research has been undertaken to assess how different groups view space exploration, planetary protection, and risks of sample return. An initial survey queried Planetary Society members about various topics, like the benefits of space exploration, threats of interplanetary contamination, adaptability of life and possibility of finding life on other planets, enthusiasm for large-scale research, trust in NASA, and views about the environment [MacGregor and Slovic,1994, 1995]. Subsequent comparative information was gathered in additional surveys of the general public, students, and various life science specialists. The conclusions from over 4700 respondents indicate that people are uncertain about the possibilities of life on Mars, have serious concerns about back contamination, and have strong feelings that proper sample handling is essential [MacGregor et al., 1996]. Although most respondents felt that life on Mars is unlikely, the overwhelming majority indic~ted that a returned sample should be considered hazardous to Earth's biota until proven otherwise. While people indicated a high level of trust in NASA to carry out a successful sample return mission, they expressed mixed feelings that NASA will respect public values and opinions or honestly inform people about the risks. On a positive note, very few people agreed that possible exposure of Earth to life from Mars was reason enough to cancel a mission. These data about attitudes were collected prior to announcements about possible evidence of fossil life in Martian meteorites [McKay et al., 1996]. Should definitive findings of Martian life be made prior to a sample return mission, the public is likely to become even more focused on PP issues, quality-of-life concerns, and the adequacy of mission plans. It will be essential to communicate openly with the public throughout the decision-making process, and to respond to their legitimate concerns about planetary protection issues.

6. Planetary Protection Controls: Arguments Pro and Con In seeking reassurance about sample return handling, the public will naturally look to the scientific and technical community for information about the adequacy of pp controls. As with many controversial proposals, expert

opinion about planetary protection and sample return is mixed, with divergent views about both the necessity and stringency of pp measures. Over the years, many issues have been raised concerning pp measures that have been proposed for sample return missions. Some arguments can be readily dismissed, while others will require further study and consideration prior to the development of the official pp policy. The arguments are varied, but the more common positions are listed and analyzed briefly below.

6.1. Mars Meteorites The presence of Mars meteorites on Earth is taken by some as evidence that Earth and Mars have been cross contaminated already over geologic time. Known collectively as the SNC meteorites, these extraterrestrial materials are assumed to have come from Mars [Vichery and Melosh, 1987]. Some assert that there have been no deleterious effects on the biosphere from these meteorites, so there should be no need to implement any pp controls on a MSR mission. At present, there is no evidence either to support or disprove the claim of past deleterious effects when the meteorites landed. In addition, the meteorites spent millions of years in transit exposed to the space environment. By contrast, a MSR mission will return a "fresh," protected sample that will traverse the interplanetary distance in about 1 year, an instantaneous time in geologic terms. Furthermore, since back contamination hinges on the possible presence of living organisms, unless the Mars meteorites can be shown to have arrived on Earth with living entities, no claim can be made for biological cross contamination having occurred. Thus, at this time, Mars meteorites are not helpful for determining the need for pp controls on a MSR mission, even if fossil life forms can be verified in meteorites. 6.2.

Sterilization

It has been suggested that sterilization of Mars samples during the Earth return phase would eliminate the need for pp measures as well as address public concern regarding possible back contamination. However, it would be technically difficult to implement and verify a sterilization protocol in flight; more important, the science loss from sterilized samples would be formidable [DeVincenzi. 1976; Gooding et al., 1990]. Almost certainly, it can be expected that questions about the wisdom of acquiring and returning such samples would arise, since sterilization destroys critical information about the sample. Even if this route is adopted, and the Martian sample is sterilized, there will still be need for sample containment, breaking the contact chain, and conducting a quarantine protocol to validate that the sterilization methods were adequate.

6.3.

Quarantine

in Orbit

Some have suggested analysis of returned samples in an orbiting laboratory as an alternative to bringing the sample directly into Earth's biosphere. This would necessitate construction of a biological barrier system as well as conducting a quarantine protocol in the orbiting lab. Past studies of this option [DeVincenzi and Bagby, 1981] have shown that it would be technically feasible but costly. Another significant problem would be the difficulty of unambiguously interpreting whether any observed effects on biological experiments were caused by the Mars sample itself or by environmental effects in low Earth orbit (i.e., microgravity, radiation, artificial atmosphere).

DEVINCENZI Ef AL.: MARS PLANETARY PRO1EcnON AND SAMPLE RETURN 6.4.

Cost

and

Technical

Feasibility

Concern has been expressed that pp would impose impossible technical requirements on a MSR mission and/or will price a MSR mission out of the range of affordability: While costs and technical aspects of a MSR mission are certainly major considerations, as they were for Viking missions, they do not have priority over the requirements for pp controls imposed by domestic and international laws and policies. Put simply, pp requirements for MSR mission are not elective options; rather they are legitimate, unavoidable parts of overall mission costs and technical requirements. In any case, the costs of implementing pp requirements on a MSR mission are speculative at this time, since no detailed engineering and technical studies have been done to ascertain the costs for necessary pp measures. 6.5.

Life

Detection

It has been suggested that additional life detection experiments should be conducted on Mars prior to a MSR mission to determine whether or not living entities are present. Given the current scientific plans and tight budget constraints for future robotic missions to Mars, it is unlikely that such life detection experiments will be accomplished prior to a 2004 sample return mission. In addition, because of the difficulty of getting definitive answers robotically, it is unlikely that further life detection experiments on Mars will yield the answers needed for accurate assessmentof back contamination risks. Under these circumstances. returning samp~s under conditions of strict containment and analyzing them for hazardous components behind biological barriers are the most prudent approach to handling a sample return mission in the foreseeable future. 6.6.

Public

Threats

this matter. The first is that the question of an indigenous biota on Mars remains unresolved at present and is unlikely to be settled prior to launch of a sample return mission. One consequence of this fact is a general unease among both experts and the lay public about the prospect of releasing Martian materials into the terrestrial biosphere without adequate controls, as evidenced by surveys recently conducted with different segments of the U.S. population. Second, in addition to the scientific and technical hurdles for a sample return mission, there also remains the formidable task of complying with numerous national and international policies, laws, and guidelines, all of which focus largely on protection of Earth's environment. Given these considerations, it is imperative that engineering and operational approaches be developed early in the design process for a Mars sample return mission to protect against possible cross contamination. The full extent of these measures is beyond the scope of this paper. Nevertheless, it is already clear that detailed studies will be needed in several areas. Engineering solutions are required for breaking the contact chain with the Martian surface (i.e., preventing extraneous Martian material from being brought back to Earth inadvertently), for containment of the Mars sample: from acquisition, through interplanetary transport, to evOOtual delivery to an Earth-based containment facility. Also apparent is the need for developing the protocols and analyses to be used on the returned sample to ascertain its potential for deleterious effects on the terrestrial biosphere. What tests will be necessary to satisfy the many state, national, and international entities and agencies whose goals are protection of the environment? In what facility will the tests be done? What scientific criteria will suffice for eventual controlled distribution of Martian sample material to the scientific community? Answers to these and related questions cannot wait until the mission is launched.

A wareness

Arguments have been offered that, in general, people do not believe there is life on Mars and therefore will not be that concerned about back contamination. As pointed out earlier in this paper, a majority of both the public and experts who were queried on these questions, while skeptical about the existence of life on Mars, also feel that a returned Mars sample should be considered hazardous until proven otherwise. 6.7.

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to

the

Biosphere

It has been suggested that if life exists on Mars it would pose no threat to terrestrial life because of independent evolutionary pathways [lukes. 1994]. An oft-cited corollary is that undiscovered organisms in certain terrestrial environments would pose a greater threat to the biosphere than Martian biota. In the absence of any additional information about the presence or characteristics pf a Martian biota, these interesting speculations about effects on Earth's biota or ecosystems will remain just that.

7. Conclusions If a Mars sample return mission is to be launched early in the next millennium as currently envisaged by NASA planners. an important consideration must be the question of what measures will be needed to prevent potential contamination of Earth's biosphere by materials from ~ars. Despite various arguments against the imposition of pp control measures, two factors necessitate serious attention to

Appendix: on Various

Planetary Protection Measures Mars Exploration Missions

Used

Viking 1 and 2 Landers: Each encapsulated in a sealed, pressurized bioshield; heated at low relative humidity in a specially built oven at Kennedy Space Center. Heating temperature of approximately 110°C was applied long enough to achieve 112°C at the coldest point in the landers and held until the calculated bioload fell to acceptable levels [-30 hours and 23 hours, for Viking 1 and 2, respectively] [Martin, 1975]. Viking Biology Instrument subjected to additional special handling procedures to limit the probability of terrestrial contamination to 10-6 or less; instrument subjected to heat sterilization at 120°C for 54 hours before insertion into the lander, where it subsequently underwent the heating regime experienced by the lander as a whole [Daspit, 1991; NASA, 1975a, 1975b] Mars Observer: Category III orbiter; spacecraft assembled in class 100,000 clean rooms; aimpoint for injection of spacecraft into its orbit assured a probability of 10-5 or less of impacting the planet by the launch vehicle and 10-4 or less by the spacecraft; orbit of the vehicle was to be maintained until December 31, 2008, and thereafter with an assurance of >0.95 against impacting Mars until December 31, 2038 [Barengoltz, 1985]. Launched in 1992; failed prior to entering Mars orbit . Mars Global Surveyor: Category III orbiter; spacecraft assembled in class 100,000 or better clean rooms; trajectories were biased to miss the planet; an inventory of organic constituents aboard and other documentation was compiled [Barengoltz, 1995]. Launched in November 1996.

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DEVINCENZI ET AL.: MARS PLANETARY PRO1EcnON AND SAMPLE REnJRN

Mars Pathfinder: Category IV lander; spacecraft (with small rover and lander inside an aeroshell) assembled in class 100,000 or better clean rooms; subcomponents subjected to various treatments (heat sterilization or chemical sterilants) before assembly to reduce the number of surface and buried microorganisms; components packaged and maintained to prevent recontamination before final assembly; microbiological assays of subcomponents used to estimate total bioload in conformance with NASA Category IV guidelines [Barengoltz, 1996]. Launched in December 1996. Mars '96: (Russians and associates): Category IV with two small landed stations; without life detection instrumentation; used a variety of implementation techniques including dry heat "sterilization," beta and gamma ray radiation, ultrasonication, and various sterilants (e.g., hydrogen peroxide plasma gas, ethanol, and mixtures of ethanol, isopropanol and formaldehyde) to reduce bioload to levels at or below 300 spores/m2 (i.e., "presterilization" Viking-Ievel surface burdens); assembly of cleaned components in class 100 clean rooms; recontamination preve~ed by packaging and additional cleaning as needed [Rogovski et al..1996]. On-orbit failure after November 1996 launch. References Bagby, I.R., Ir.; Back contamination: lessons learned during the Apollo lunar quarantine program, JPL Rep. CR-560226. Jet Propul. Lab., Pasadena, Calif., 1975 Bagby, I.R., H.C. Sweet, and D.L. DeVincenzi, A quarantine protocol for analysis of returned extraerrestrial samples, Adv. Space Res. 3. 27, 1983. Barengoltz, I., Mars Observer planetary protection plan, JPL Rep. D. 2749, Jet Propul. Lab., Pasadena, California, 1985. Barengoltz, I, Mars Global Surveyor: Planetary protection plan. J P L Rep. D-12742, Jet Propui. Lab., Pasadena,Calif., 1995. Barengoltz, I., Mars Pathfinder: Planetary protection implementation document, JPL Rep. D-13645. Jet Propul.Lab., Pasadena, California, 1996. Bond, W.W., M.S. Favero, N.I. Petersen, and I.H. Marshall, Relative frequency distribution of DI25 C values for spore isolates from the Mariner-Mars 1969 spacecraft, Appl. Microbiol. 21, 832-836, 1971. Brzezinski, Z., Presidential DirectivelNSC-25 (declassified, 1985), The White House, Washington, D.C. ,1977. COSPAR, Resolution 26, Fifth Inter. Space Sci. Symp., Florence, Italy. COSPAR Ini Bull. 20,25-26, Comm. on Space Res., Paris, France, 1964. COSPAR, Sterilization Techniques for Instruments and Materials as Applied to Space Research. COSPAR Tech. Manual Series 4, 287, ed. by P.H.A. Sneath. Comm. on Space Res., Paris, France, 1968. Daspit, L., Planetary protection issues for the MESUR Mission: Probability of growth (Pg), ed. by H.P. Klein, NASA Coni. Publ.. CP-3167, 53,1991. DeVincenzi, D.L., Effect of Sterilization on the Scientific Value of a Returned Mars Soil Sample, Life Science and Space Research XV ,21,1976. DeVincenzi, D.L. and I.R. Bagby, Orbiting quarantine facility: The Antaeus Report,NASA Spec. Publ., SP-454,6, 1981. DeVincenzi, D.L., and H.P. Klein, Planetary protection issues for sample return missions, Adv. Space Res., 9(6),203-206, 1989. DeVincenzi, D.L. and P.D. Stabekis, Revised planetary protection policy for solar system exploration, Adv. Space Res. 4, 291-295, 1984. DeVincenzi, D.L., H.P. Klein, and I.R. Bagby, Planetary protection issues and future Mars Missions, NASA Coni Publ., CP-10086, 1991. DeVincenzi, D.L., P.D. Stabekis, and I. Barengoltz, Refinement of planetary protection policy for Mars Mission, Adv. Space Res. 18, 311-316,1995. Gooding, I.L., (Ed.), Scientific guidelines for the preservation of samples collected from Mars. NASA Tech. Memo.4184, 1990. Hall, L.B., Planetary Quarantine. Gordon and Breach, Newarlt, N.I., 1971a. Hall, LB., Memorandum to program managers, Mariner Mars '71 and Viking '75 (1/8nl), NASA Planet. Quarantine Off., Washington, D.C.,197Ib. gall, L.B., Memorandum on PQ policies (12/In3), NASA Planet. Quarantine Off., Washington, D.C., 1973.

Johnston, R.S., I.A. Mason, B.C. Wooley, G.W. McCollum, and B.I.Mieszkuc, Biomedical results of Apollo, edited by R.S. Iolmston et al., NASA Spec. Publ., SP-368, 407-424,1975. Iukes, T.: 1994, Lessons from evolution: Ruling out danger, Planet. Rep., 14,13-15, 1994. Klein, H.P., The Viking mission and the search for life on Mars, Rev. Geophys.,17, 1655-1662,1979. Klein, H.P., On the search for extant life on Mars, lcarus 120, 431436, 1996. LedeIberg, I., Exobiology: Approaches to life beyond Earth, Science 132.393-400,1960. Light, 1.0., C.W. Craven, W. Vishniac, and LB. Hall, A discussion of the planetary quarantine constraints, Life Sci. Space Res. V, 7-23, 1967. MacGregor, D.G. and P. Slovic., The planetary exploration survey. Planet. Rep.. xiv(4), 20a-21a, 1994. MacGregor, D.G. and P. Slovic, The planetary exploration survey: What society members think about planetary protection, Planet. Rep.. X\I(2) ,4-6, 1995. MacGregor, D.G., P.Slovic and M.S. Race, Lay and expert Peffeptions of planetary protection, Rep. 96-9, Decision Res. Inc., Eugene, Oreg., 1996. Martin, I.S., Viking '75 program lander capsule sterilization plan, Rep. M75-147-O, NASA Langley Res.Cen., Hampton, Virginia, 1975. McKay, D.S., E.K. Gibson Ir., K.L Thomas-Keptra, H. Vall, C.S.Romanek, S.I. Oemett, X.D.F. 01 iller, C.R. Maechling, and R.N. Zare, Search for past life on Mars: Possible relic biogenic activity in Martian meteorite ALH84001, Science 273, 924-930, 1996. Murray, B.C., M.E. Davies and P.K. Eckman, Planetary contamination II: Soviet and U.S. practices and policies, Science, 155, 15051511,1967. NASA, Outbound s{'acecraft: basic policy relating to lunar and planetary contamInation control, NASA Rep. NPD-8020.7, Washington, D.C., 1967. NASA, NASA standard procedures for the microbiological examination of space hardware, NASA Rep. NHB-5340.1A, Washington, D.C. , 1968. NASA, Back contamination and quarantine containment requirements for manned lunar missions, NASA Rep. NPD-8020.13, Washington, D.C., 1969a. NASA, Planetary quarantine provisions for unmanned planetary missions, NASA Rep. NHB-8020.12, Washington, D.C., 1969b. NASA, Summary of lunar quarantine biotest protocols, rev.B, Rep.MSC-00013, NASA Manned Spaceflight Cen., Houston, Tex., 1969c. NASA, Outbound planetary biological and organic contamination control policy and responsibility, NASA Rep. NPD-8020.10A, Washington, D.C., 1972. NASA, Post launch analysis of compliance with COSPAR recommendations, Spacecraft A Doc. M75-155-05, NASA Viking Project Office, Washington D.C., 1975a. NASA, Post Launch Analysis of Compliance with COSPAR Recommendations, Spacecraft A Doc. M75-155-06, NASA Viking Proj.Off., Washington D.C., 1975b. NASA, Quarantine provisions for unmanned extraterrestrial missions, NASA RepNHB-8020.12A, Washington ,D.C., 1976. NASA, Biological contamination control for outbound and inbound planetary spacecraft, NASA NMI-8020.7A, Washington, D.C., 1988a. NASA, Implementing the provisions of the National Environmental Policy Act, NASA Handbook NHB 8800.11, Washington, D.C., 1988b. Nature, Contamination by extra-terrestrial exploration, Nature 183, 925-928,1959. Phillips, C., The planetary quarantine program: Origins and achievements, NASA Rep. SP4902, Washington, D.C., 1972. Puleo, I.R., G.S. Oxboro and R.C. Graves, Microbial contamination detected on the Apollo 9 spacecraft, Proc. Annu. Tech. Meet.. Am. Assoc. Contam. ConI.. 8, 80-83, 1969. Puleo, I.R., N.D. Fields, B. Moore, and R.C. Graves, Microbial contamination associated with the Apollo 6 spacecraft during final assembly and testing, Space Life Sci. 2, 48-56, 1970a. Puleo, I.R., G.S. Oxborrow, N.D. Fields, and H.E. Hall, Quantitative and qualitative microbial profiles of the Apollo 10 and II spacecraft, Appl. Microbiol.. 20, 384-389, 1970b.. Puleo, I.R., G.S. Oxborrow, N.D. Fields, C.M. Herring, LS. and Smith, Microbiological profIles of the Viking spacecraft, Appl. Microbiol. 26,838-845,1973. Puleo, I.R., N.D. Fields, S.L Bergstrom, G.B. Oxborrow, P.D. Stabekis, and R.C. Koukol, Microbiological profiles of the Viking spacecraft, Appl. Environ. Microbiol. 33,379-384,1977. Race, M.S., Anticipating the reaction: Public concem about sample return missions, Planet. Rep. , xiv(4), 20-22, Iuly/Aug. 1994. Race, M.S., Societal issues as Mars mission impediments: Planetary

DEVINCENZI ET AL.: MARS PLANETARY PRO1ECI10N AND SAMPLE RETURN protection and contamination concerns, Adv. Space Res. 15(3), 285-292, 1995. Race, M.S., Planetary protection, legal ambiguity and the decision making process for Mars sample return, Adv. Space Res., 18(1!2), 345-350, 1996. Robinson, G.S., Exobiological contamination: The evolving law, Ann. AirSpace Law, XVII-I, 325-367,1992. Rogovski, G., V. Bogomolov, M. Ivanov, J. Runavot, A. Debus, A. Victorov, and J.C. Darbord, Planetary protection program for Mars 94/96 mission, Adv. Space Res. 18(1!2), 323-332, 1996. Sagan, C. and S. Coleman, Spacecraft sterilization standards and contamination of Mars, J. Astronaut. Aeronaut. 3.22-27, 1965. Science, Development of international efforts to avoid contamination of extraterrestrial bodies, Science, 128, 887-889, 1958. Space Science Board, Review of Sterilization Parameter Probability of Gr.;wth (Pg!, Natl. Acad.Press, Washington D.C., 1970. Space Science Board, Post-Viking Biological Investigations of Mars. Natl. Acad. Press, Washington, D.C., 1977. Space Studies Board, Biological Contamination of Mars: Issues and Recommendations, Natl. Acad.Press, Washington D.C., 1992. Space Studies Board, Mars Sample Return: Issues and Recommendations. Natl. Acad.Press, Washington D.C., 1997. Taylor, G.R., B.J. Mieszkuc, R.C. Sirnmonds, and C.H. Walkinshaw, Bi(XDedical results of Apollo,NASA Spec. Publ.. SP-368,1975.

28,585

United Nations, 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.. Doc. AlRESI222(XXI); T/AS No.6347. New YoJi(, U.S. A., 1967. V ashkov , V .1. and A.G. Prishchep, The effectiveness of sterilization by means of the mixture of ethylene oxide and methyl bromide, presented at COSPAR Meeting, Comm. on Space Res., Vienna, 1966. Vashkov, V.I., Ramkova, N.V., Scheglova, G.V., Skala, L.Z., and Nekhorosheva, A.G., Verification of the efficacy of spacecraft sterilization, Life Sci, /4. 199-202, 1972. Vichery A.M. and H.J. Melosh, The large crater origin of SNC meteorites, Science 237: 738-743. 1987

D.L. DeVincenzi, NASA Arnes Research Center, MS Moffett Field CA 94035. (ernai1: [email protected])

245-1,

H.P. Klein and M.S. Race, SETI Institute, 2035 Landings Drive, Mountain View, CA 94043. (ernail: [email protected]; rnracern001@aol. corn) (Received March 27, 1998; revised May 4, 1998; accepted May 4, 1998.)