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6. Planetary protection matters
5. NEWS IN BRIEF •
The 2006 COSPAR Scientific Assembly will be held in Beijing, China.
•
In the course of its Council meeting in Kiruna on 24 and 25 March 2004, ESA approved the accession of Greece and Luxembourg to the ESA convention. The two countries are expected to become full members of the Agency by 1 December 2005. [ESA Press Release, 25 March 2004]
•
ICSU announced the launch of its new web site in April - www.icsu.org.
•
The US Apollo and Soviet Luna missions of the 1960s and 1970s established a precedent of returning extraterrestrial materials to Earth that is continuing today in ongoing comet and asteroid sample-return missions. In the not too distant future, space-faring nations will begin retrieving samples of the Martian surface and subsurface and bringing them back to Earth. For these samples, planetary protection is necessary and measures are already in place to prevent the forward contamination of Mars by Earth microbes and the backward contamination of Earth by possible extraterrestrial life.
Microbes in Space
We would like to apologize for an error in the reporting of the launch of the SORCE mission (2003-004A) in CIB 158. The launch date was 25 January, not 28 January as reported. We would like to thank K. Tsuchiya for pointing this out.
Interplanetary space is a harsh environment, and Earth organisms travelling on their own are not likely to survive interplanetary travel. Nonetheless, natural and humanprovided opportunities exist for the interplanetary transport of microbial life. Earth microorganisms are tough, some being able to live in extreme environments that would quickly kill most macroorganisms. For example, microorganisms living around deep-sea hydrothermal vents (cf., Corliss et aL 1979) thrive at pressures greater than 250 atmospheres, certain lichens prefer to live inside Antarctic dry valley sandstone at temperatures well below freezing, and microbes have been found more than three kilometres below the continental surface. These extreme environments may have analogues on other solar system bodies. And it is possible that some of these tough Earth microbes may have left the Earth in the past and ended up on other solar system bodies. In space itself, Earth microbes such as the soil bacterium Bacillus subtilis have been shown (Nicholson et aL 2000) to survive for extended periods.
6. PLANETARY PROTECTION MATTERS [The following paper was written originally for readers of the IUBS newsletter Biology International, and is reproduced here with minor editorial changes to conform to the house style of the COSPAR Information Bulletin.]
Issues in Planetary Protection: History, Policy, Prospects, by John D. Rummel, NASA Headquarters, Washington, D.C. 20546 USA, IUBS Representative to COSPAR, and Chair, COSPAR Panel on Planetary Protection, Linda Billings, SETI Institute, Washington, D.C. 20024 USA Planetary protection is the term given to the policies and practices that protect other solar system bodies (e.g., planets, moons, asteroids, and comets) from terrestrial life, and that protect the Earth from life that may be brought back from other solar system bodies. In contrast to the life that we know the Earth harbours, we are beginning to learn about locations on or beneath the surface of other planets and moons where terrestrial life, at least, might thrive. Whether such bodies host indigenous life, and whether such life would be related to Earth life, is a matter of critical scientific interest.
Mars seems to possess all of the materials and some of the environments associated with life on Earth. While the surface of Mars is currently cold and dry (Soffen 1977), the planet has been characterized as nearly the Earth's twin early in solar system history. And Mars subsurface conditions are now, and may always have been, quite different than those on the surface (Mitrofanov et aL 2003, McKay et aL 1996). In a study building on earlier work (Melosh 1984, 1985, Gladman & Burns 1996, Gladman et aL 1996, and Mileikowsky et al.
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2000) examined the potential for a natural interplanetary transfer of microorganisms by the high-velocity ejection of soil and rock caused by impacts of comets and other small bodies. Addressing the potential for transfer of organisms from Mars to Earth, they concluded that "if prokaryote microbes existed or exist on Mars, viable transfer to Earth must be considered not only possible but highly probable." Conversely, they estimated that "the number of ejecta from Earth landing on Mars from 4.0 Ga to present time...was one to two orders of magnitude lower than the number of martian meteorites landing on Earth during the same period of time", but still substantial "about a billion during the last four billion years." Further studies of Mars and other worlds may be able to determine what has happened to any travelling Earth microbes and whether any extraterrestrial microbes have ever reached Earth (and, if so, what may have happened to them). A major goal of planetary protection controls on forward contamination is to preserve the planetary record of such natural processes by preventing human-caused microbial introductions. Such introductions would be most likely to cause harm on those planetary bodies that are of most interest to astrobiologists - those that show evidence of materials and environments that support life on Earth and thus might also support Earth life transported to those bodies, Mars and Europa, for example, or Saturn's moon Titan. The atmosphere of Titan, at a temperature of 94 Kelvin, is rich with nitrogen and methane. Exposed to solar ultraviolet radiation, it can generate saturated and unsaturated hydrocarbons as well as nitriles through methane photolysis (Young et al. 1984). These products can condense as aerosols and reach the surface, where some could liquify while others take solid form. The Cassini-Huygens mission to Saturn will land a probe on Titan's surface in 2005 to conduct insitu analyses that should provide further details about this environment.
The Origin of Planetary Protection Policy
protection has been a concern from the start of the Space Age. In 1958, after the launch of Sputnik, the International Council of Scientific Unions (ICSU - now the International Council for Science) introduced planetary quarantine standards for solar system exploration missions (CETEX 1958, 1959), and the US National Academy of Sciences recommended noncontaminating spaceflight practices in its 19581960 studies (cf., Derbyshire 1962). By 1967, space-faring nations had reached agreement to regulate interplanetary contamination, as articulated in Article IX of the United Nations Outer Space Treaty that entered into force on 10 October 10 of that year. The treaty states that exploration of planetary bodies will be conducted "so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter and, where necessary, shall adopt appropriate measures for this purpose...." (UN 1967). Also in 1958, ICSU formed an interdisciplinary Committee on Space Research (COSPAR), which became, and still is, the focal point of international activities relating to planetary protection. COSPAR and the International Astronautical Federation consult with the UN Committee on the Peaceful Uses of Outer Space (COPUOS) on Space Treaty matters, and COSPAR maintains an international planetary protection policy (Rummel 2002), most recently updated in October 2002. The US National Aeronautics and Space Administration (NASA) has a planetary protection policy in place as well (NASA 1999a, b), similar to that of COSPAR. Recently the Centre Nationale d'Etudes Spatiales (CNES, the French space agency) issued a planetary protection document (CNES 2002) that outlines its requirements in accord with those of COSPAR, and the European Space Agency (ESA) has implemented them on its Mars Express and Beagle-2 mission launched in 2003. The COSPAR Panel on Planetary Protection develops and makes recommendations on planetary protection policy to the COSPAR Council and Bureau. Agency and COSPAR policies describe five categories of planetary protection defined by the nature of the mission to be launched and the target body to be studied (DeVincenzi et al. 1983). No planetary protection procedures are
The fate of life on Earth and the possibility of life elsewhere have driven space exploration from its beginnings. Thus planetary
32
required for Category I missions, which include any missions to the Sun, Mercury and Pluto except for Earth-return missions. Category II missions are those for which the target body is of interest to researchers studying organic chemical evolution and the origin of life, but where biological contamination is not thought to be possible. The first steps in planetary protection for these missions are to document spacecraft trajectories, inventory onboard organic materials, and possibly provide for the archival storage of certain spacecraft materials. For Category Ill missions, flying by or orbiting planets that could be contaminated by Earth organisms, measures include those for Category II plus other restrictions. For example, spacecraft operating constraints such as a biased trajectory to avoid impact with the [targetted] planet and minimum orbital lifetime requirements may be imposed.
Academy of Sciences (which is the US member institution in COSPAR). In recent years, the SSB has provided advice on planetary protection requirements for Mars and Europa, aas well as for sample return missions to a variety of small solar system bodies such as moons, comets, and asteroids (Space Studies Board 1992, 1997, 1998, 2000, 2002a). Due to the accelerating pace of solar system exploration, including planned sample return missions, the NASA Advisory Council chartered a Planetary Protection Advisory Committee in 2002 to secure internal advice
EvolvingRequirements Planetary protection controls require updating in keeping with scientific advances. As solar system exploration advances, knowledge of environments that may contain life or that could be contaminated by Earth life grows. Characterization of biological contamination is also constantly improving, especially since the advent of molecular methods. NASA and COSPAR planetary protection measures are accordingly subject to continual reevaluation and change, in consultation with the science community. As for the US Viking missions of the 1970s, NASA cleaned its Mars landers until their total surface bioburden was no more than 3 x 10~ bacterial spores, with an average of no more than 300 bacterial spores per square metre, and their total bioburden (surface, mated, and encapsulated for launch) was 5 x 10S spores. Each lander was then packaged in a fully enclosing 'bioshield' (resembling a large casserole dish) and baked in an oven so that each portion of the spacecraft attained 111.7°C for 30 hours, in a dry-heat sterilization procedure. The Viking missions revealed that the surface of Mars was much drier and less benign than expected, though some Viking lander findings were suggestive of life (cf., Levin & Straat 1979). In 1992, the US SSB recommended easing forward contamination requirements for Mars and, subsequently, COSPAR and NASA altered their requirements for Mars lander missions, establishing the Viking presterilization surface bioburden standard as the requirement for Mars landers not attempting life detection experiments and the full Viking standard as the requirement for missions focused on life detection.
For landers, in Category IV, all Category II and III requirements may apply (except for orbital lifetime), and restrictions on biological contamination are generally more severe, possibly including comprehensive decontamination and sterilization of the spacecraft, depending on its destination. Category V missions may be deemed "unrestricted Earth return" missions, with no additional planetary protection requirements on the return portion of the mission, or "restricted Earth return" missions. These missions may include all Category II, Ill, and IV restrictions plus severe restrictions on the handling of returned samples until their biological status is determined. The implementation of planetary protection policy is agency-specific and, depending on the nature of the solar-system exploration, may be quite complex. NASA, for example, maintains an office to oversee the application of procedures and guidelines to ensure compliance with its planetary protection policy. The agency's Associate Administrator for Space Science is responsible for planetary protection at NASA, and the agency's Planetary Protection Officer oversees the policy, assigns requirements to solar system exploration missions and, occasionally, requests recommendations on its application [of the procedures] from the Space Studies Board (SSB) of the US National Research Council (NRC), the operating arm of the US National
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Today, spacecraft going to any solar system body with the potential to support present-day Earth life must undergo stringent cleaning and sterilization. Planetary protection techniques applied to spacecraft bound for Mars include clean manufacturing processes for spacecraft components and the use of cleanroom techniques during spacecraft assembly, test and launch operations. Bioloads are reduced by methods such as alcohol wiping, dry heat treatment and hydrogen peroxide sterilization (Debus et aL 1998). Radiation treatment is an option for some assemblies, and molecular detection methods such as Limulus amoebocyte lysate, polymerase chain reaction, and adenosine triphosphate (ATP) measurement may also be employed to characterize bioload.
requirements are expected to cover any return concerns about sample condition and landing site targeting. For "restricted Earth return" missions, especially those which will return complex samples from a planetary surface or subsurface, the primary challenge is to devise a return sample containment system that provides a reliability perhaps as high as 0.999999 while meeting mass and cost constraints. It is also important to ensure that the sample container or other portions of the spacecraft do not inadvertently bring back other, uncontained, materials from the target body. The cost of meeting stringent Category V requirements on a Mars surface sample return mission is estimated at about 5-10% of the entire mission budget. How these requirements will affect overall mission success is also a consideration.
Cultivation-based microbial assays (cf., NASA 1999c) still constitute the standard forward contamination prevention method, in part because of the lack of comparability with molecular methods and also because of the additional personnel, training and requirements associated with molecular methods. These new methods are attractive, however, because a bioload measurement that could take three days with a cultivation assay may be made in less than one hour using a molecular method. In an operational first, NASA supplemented its standard cultivation-based assays with a Limulus amoebocyte lysate assay in preparing its two Mars Exploration rovers for launch in 2003. Because the Martian atmosphere is a significant factor in the potential for spreading Earth microbes on the planet, the greatest planetary protection challenge for Mars spacecraft is surface cleanliness. Europa, while it has no atmosphere to speak of, features a brutal radiation environment that could kill any exposed Earth organisms, but not necessarily those buried deep within the radiation shielding of the spacecraft. Thus spacecraft bound for Europa will have to be cleaned from the inside out. Species-specific assays may help to eliminate some of the more radiation-tolerant organisms. Mission designers will have to ensure that a spacecraft's interior is protected from recontamination after clean assembly.
Future considerations
With Mars mission planning tentatively calling for sample return missions starting in the second decade of this century, NASA and CNES have collaborated to develop criteria for Mars sample handling before release from postflight containment, along with a protocol for addressing those criteria (Rummel et al. 2002). The 'Draft Test Protocol for Detecting Possible Biohazards in Martian Samples Returned to Earth' specifies tests and procedures needed to safeguard samples against contamination. Among the assumptions underlying this protocol are that samples will not be sterilized before return to Earth, sample containers will be opened only in designated receiving facilities, and only small amounts of sample material (500-1000 grams) will be returned. Of that material, the amount of sample material used to determine whether any biohazard is present will be the minimum necessary. Issues to be addressed in establishing planetary protection requirements for a Mars sample return mission include physical/ chemical analyses needed to complement biochemical or biological screening of sample material, identification of those analyses that must be done in containment and those that can be accomplished using sterilized material outside of containment, and facility capabilities necessary to comply with the protocol. Sample return processing criteria in the draft protocol call for screening samples before release from
For Category V "unrestricted Earth return" missions, science and mission safety
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containment for radioactivity and potential chemical hazards. Further testing will be required for samples providing any indication of life-related molecules such as proteins and nucleic acids. Biohazard testing will involve assays for replication in media with various organic and inorganic carbon sources, effect/growth on various cell cultures and whole organisms, and effect on the ecosystem level. The protocol will not be finalized until the first sample is on its way back to Earth, so that procedures and requirements will be up to date in relation to scientific and technological advances. While a primary focus of planetary protection activities is the search for evidence of life on Mars, NASA's current approach to planetary protection is "all of the planets, all of the time." Reflective of the COSPAR policy, NASA's planetary protection policy goals are to ensure that all of its solar system exploration missions establish appropriate precautions against forward and backward contamination, that the Agency's planetary protection procedures and requirements are in line with the latest relevant scientific findings, that advanced technologies continue to be developed and applied to meet evolving planetary protection requirements, and that the Agency continues to coordinate with other national and international agencies on planetary protection issues and implementation.
References
CETEX 1958 Development of international effforts to avoid contamination by extraterrestrial exploration. Science, 128, 887-889. CETEX 1959 Contamination by extraterrestrial exploration. Nature, Lond., 183, 925-928. CNES 2002 Planetary Protection Requirements. Referentiel Normatif du CNES (RNCCNES-R-14). Corliss, J.B. & Ballard, R.D. 1977 Oases of life in the cold abyss. National Geographic, 152, 441-453. Debus, A., J. et aL 1998 Mars 96 small station biological decontamination. Advances in Space Research, 22, 401-409. Derbyshire. G.A. 1962 Resum6 of some earlier extraterrestrial contamination activities. In: A Review of Space Research, Chapter 10, p. 11. Washington, D.C.: National Academy of Sciences. DeVincenzi, D.L., Stabekis, P.D. & Barengoltz J.B. 1983 A proposed new policy for planetary protection. Advances in Space Research, 3 (8), 13-21.
Gladman, B. & Burns, J.A. 1996 Martian meteorite transfer: simulation. Science, 272, Questions of life and needs for 161-162. planetary protection will continue to bound the acceptable range of future missions into the Gladman, B.J. et al. 1996 The exchange of solar system. As knowledge of the solar system impact ejecta between terrestrial planets. grows, implementation of planetary protection Science~ 271, 1387-1392. provisions will grow more precise, guided by our knowledge of the potential for Earth Levin, G.V. & Straat, P.A. 1979 Journal of contamination, our ability to measure and Molecular Evolution, 14, 167. control it, and our quest to discover extraterrestrial life. It is expected that COSPAR McKay, D.S. et al. 1996 Search for past life on will continue to act as a forum and repository for Mars: possible relic biogenic activity in martian global planetary protection knowledge, policy meteorite ALH84001. Science, 273, 924-930. and plans to prevent the harmful contamination of space and will provide an international forum Melosh, H.J. 1984 Impact ejection, spallation for exchanging such information. For its part, and the origin of meteorites. Icarus, 59, 234NASA will contribute toward maintaining this 260. long and fruitful tradition of global cooperation in planetary protection by working closely with Melosh, H.J. 1985 Ejection of rock fragments COSPAR and other national space agencies as from planetary bodies. Geology, 13, 144-148. the exploration of our solar system moves forward.
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Mitrofanov, I.G. et al. 2003. CO2 snow depth and subsurface water-ice abundance in the northern hemisphere of Mars. Science, 300 (5628), 2081-2084. NASA 1999a Biological contamination control for outbound and inbound planetary spacecraft. NASA Policy Directive (NPD) 8020.7E. Washington, D.C.: NASA Headquarters. NASA 1999b Planetary protection provisions for orbotic extraterrestrial missions. NASA Procedures and Guidelines (NPG) 8020.12B. Washington, D.C.: NASA Headquarters. NASA 1999c NASA standard procedures for the microbial examination of space hardware. NASA Procedures and Guidelines (NPG) 5340.1C. Washington, D.C.:NASA Headquarters. NASA 2002 A Draft Test Protocol for Detecting Possible Biohazards in Martian Samples Returned to Earth (NASA/CP-2002-211842). Hanover, MD: NASA Center for AeroSpace Information. http://a257.g.akamaitech.net/7/257/2422/14mar 20010800/e-docket.access.gpo..gov/2003/0319287.htm Nicholson, W.L. et al. 2000 Resistance of Bacillus endospores to extreme terrestrial and extraterrestrial environments. Microb. MoL Biol. Rev., 64, 548-572.
Space Studies Board, National Research Council 1998 Evaluating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies. Task Group on Sample Return from Small Solar System Bodies. Washington, D.C.: National Academy of Sciences. http://www.nap.edu/books/0309061369/html/ind ex.html Space Studies Board, National Research Council 2000 Preventing the Forward Contamination of Europa. Task Group on the Forward Contamination of Europa. Washington, D . C . : National Academy of Sciences. http://www.nap.edu/books/N 1000231/html Space Studies Board, National Research Council 2002a The Quarantine and Certification of Martian Samples. Committee on Planetary and Lunar Exploration. Washington, D.C.: National Academy of Sciences. http://www.nap.ed u/books/0309075718/html/ind ex.html Space Studies Board, National Research Council 2002b New Frontiers in the Solar System: An Integrated Exploration Strategy. Solar System Exploration Survey Committee. Washington, D.C.: National Academy of Sciences.
7. P R O G R E S S OF S P A C E R E S E A R C H Space Studies Board, National Research O C T O B E R 2002 Council 1992 Biological Contamination of Mars: Issues and Recommendations. Task Group on As advised in the COSPAR Information Planetary Protection. Washington, D.C.: Bulletins 158 and 159, a report on the progress National Academy of Sciences. of space research is compiled on behalf of the UN Office for Outer Space Affairs from reports Space Studies Board, National Research submitted by the COSPAR Scientific Council 1997 Mars Sample Return: Issues and Commission Chairs every two years Recommendations. Task Group on Issues in coinciding with the years of COSPAR Scientific Sample Return. Washington, D.C.: National Assemblies. While the resulting survey is Academy of Sciences. published by the UN in the document Highlights http ://www.nap.edu/books/O309057 33 7/html/ind in Space Research, we now finish reproducing ex.html the 2002 report, the first two parts having been reproduced in the Bulletin issues referred to above. We are pleased to acknowledge the permission of the UN Office for Outer Space Affairs and the coordinators of the inputs, respectively, for reproducing the sections of the document, for biennium 2001-2002, included in this issue of the Bulletin.
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The 2006 COSPAR Scientific Assembly will be held in Beijing, China.
•
In the course of its Council meeting in Kiruna on 24 and 25 March 2004, ESA approved the accession of Greece and Luxembourg to the ESA convention. The two countries are expected to become full members of the Agency by 1 December 2005. [ESA Press Release, 25 March 2004]
•
ICSU announced the launch of its new web site in April - www.icsu.org.
•
The US Apollo and Soviet Luna missions of the 1960s and 1970s established a precedent of returning extraterrestrial materials to Earth that is continuing today in ongoing comet and asteroid sample-return missions. In the not too distant future, space-faring nations will begin retrieving samples of the Martian surface and subsurface and bringing them back to Earth. For these samples, planetary protection is necessary and measures are already in place to prevent the forward contamination of Mars by Earth microbes and the backward contamination of Earth by possible extraterrestrial life.
Microbes in Space
We would like to apologize for an error in the reporting of the launch of the SORCE mission (2003-004A) in CIB 158. The launch date was 25 January, not 28 January as reported. We would like to thank K. Tsuchiya for pointing this out.
Interplanetary space is a harsh environment, and Earth organisms travelling on their own are not likely to survive interplanetary travel. Nonetheless, natural and humanprovided opportunities exist for the interplanetary transport of microbial life. Earth microorganisms are tough, some being able to live in extreme environments that would quickly kill most macroorganisms. For example, microorganisms living around deep-sea hydrothermal vents (cf., Corliss et aL 1979) thrive at pressures greater than 250 atmospheres, certain lichens prefer to live inside Antarctic dry valley sandstone at temperatures well below freezing, and microbes have been found more than three kilometres below the continental surface. These extreme environments may have analogues on other solar system bodies. And it is possible that some of these tough Earth microbes may have left the Earth in the past and ended up on other solar system bodies. In space itself, Earth microbes such as the soil bacterium Bacillus subtilis have been shown (Nicholson et aL 2000) to survive for extended periods.
6. PLANETARY PROTECTION MATTERS [The following paper was written originally for readers of the IUBS newsletter Biology International, and is reproduced here with minor editorial changes to conform to the house style of the COSPAR Information Bulletin.]
Issues in Planetary Protection: History, Policy, Prospects, by John D. Rummel, NASA Headquarters, Washington, D.C. 20546 USA, IUBS Representative to COSPAR, and Chair, COSPAR Panel on Planetary Protection, Linda Billings, SETI Institute, Washington, D.C. 20024 USA Planetary protection is the term given to the policies and practices that protect other solar system bodies (e.g., planets, moons, asteroids, and comets) from terrestrial life, and that protect the Earth from life that may be brought back from other solar system bodies. In contrast to the life that we know the Earth harbours, we are beginning to learn about locations on or beneath the surface of other planets and moons where terrestrial life, at least, might thrive. Whether such bodies host indigenous life, and whether such life would be related to Earth life, is a matter of critical scientific interest.
Mars seems to possess all of the materials and some of the environments associated with life on Earth. While the surface of Mars is currently cold and dry (Soffen 1977), the planet has been characterized as nearly the Earth's twin early in solar system history. And Mars subsurface conditions are now, and may always have been, quite different than those on the surface (Mitrofanov et aL 2003, McKay et aL 1996). In a study building on earlier work (Melosh 1984, 1985, Gladman & Burns 1996, Gladman et aL 1996, and Mileikowsky et al.
3]
2000) examined the potential for a natural interplanetary transfer of microorganisms by the high-velocity ejection of soil and rock caused by impacts of comets and other small bodies. Addressing the potential for transfer of organisms from Mars to Earth, they concluded that "if prokaryote microbes existed or exist on Mars, viable transfer to Earth must be considered not only possible but highly probable." Conversely, they estimated that "the number of ejecta from Earth landing on Mars from 4.0 Ga to present time...was one to two orders of magnitude lower than the number of martian meteorites landing on Earth during the same period of time", but still substantial "about a billion during the last four billion years." Further studies of Mars and other worlds may be able to determine what has happened to any travelling Earth microbes and whether any extraterrestrial microbes have ever reached Earth (and, if so, what may have happened to them). A major goal of planetary protection controls on forward contamination is to preserve the planetary record of such natural processes by preventing human-caused microbial introductions. Such introductions would be most likely to cause harm on those planetary bodies that are of most interest to astrobiologists - those that show evidence of materials and environments that support life on Earth and thus might also support Earth life transported to those bodies, Mars and Europa, for example, or Saturn's moon Titan. The atmosphere of Titan, at a temperature of 94 Kelvin, is rich with nitrogen and methane. Exposed to solar ultraviolet radiation, it can generate saturated and unsaturated hydrocarbons as well as nitriles through methane photolysis (Young et al. 1984). These products can condense as aerosols and reach the surface, where some could liquify while others take solid form. The Cassini-Huygens mission to Saturn will land a probe on Titan's surface in 2005 to conduct insitu analyses that should provide further details about this environment.
The Origin of Planetary Protection Policy
protection has been a concern from the start of the Space Age. In 1958, after the launch of Sputnik, the International Council of Scientific Unions (ICSU - now the International Council for Science) introduced planetary quarantine standards for solar system exploration missions (CETEX 1958, 1959), and the US National Academy of Sciences recommended noncontaminating spaceflight practices in its 19581960 studies (cf., Derbyshire 1962). By 1967, space-faring nations had reached agreement to regulate interplanetary contamination, as articulated in Article IX of the United Nations Outer Space Treaty that entered into force on 10 October 10 of that year. The treaty states that exploration of planetary bodies will be conducted "so as to avoid their harmful contamination and also adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter and, where necessary, shall adopt appropriate measures for this purpose...." (UN 1967). Also in 1958, ICSU formed an interdisciplinary Committee on Space Research (COSPAR), which became, and still is, the focal point of international activities relating to planetary protection. COSPAR and the International Astronautical Federation consult with the UN Committee on the Peaceful Uses of Outer Space (COPUOS) on Space Treaty matters, and COSPAR maintains an international planetary protection policy (Rummel 2002), most recently updated in October 2002. The US National Aeronautics and Space Administration (NASA) has a planetary protection policy in place as well (NASA 1999a, b), similar to that of COSPAR. Recently the Centre Nationale d'Etudes Spatiales (CNES, the French space agency) issued a planetary protection document (CNES 2002) that outlines its requirements in accord with those of COSPAR, and the European Space Agency (ESA) has implemented them on its Mars Express and Beagle-2 mission launched in 2003. The COSPAR Panel on Planetary Protection develops and makes recommendations on planetary protection policy to the COSPAR Council and Bureau. Agency and COSPAR policies describe five categories of planetary protection defined by the nature of the mission to be launched and the target body to be studied (DeVincenzi et al. 1983). No planetary protection procedures are
The fate of life on Earth and the possibility of life elsewhere have driven space exploration from its beginnings. Thus planetary
32
required for Category I missions, which include any missions to the Sun, Mercury and Pluto except for Earth-return missions. Category II missions are those for which the target body is of interest to researchers studying organic chemical evolution and the origin of life, but where biological contamination is not thought to be possible. The first steps in planetary protection for these missions are to document spacecraft trajectories, inventory onboard organic materials, and possibly provide for the archival storage of certain spacecraft materials. For Category Ill missions, flying by or orbiting planets that could be contaminated by Earth organisms, measures include those for Category II plus other restrictions. For example, spacecraft operating constraints such as a biased trajectory to avoid impact with the [targetted] planet and minimum orbital lifetime requirements may be imposed.
Academy of Sciences (which is the US member institution in COSPAR). In recent years, the SSB has provided advice on planetary protection requirements for Mars and Europa, aas well as for sample return missions to a variety of small solar system bodies such as moons, comets, and asteroids (Space Studies Board 1992, 1997, 1998, 2000, 2002a). Due to the accelerating pace of solar system exploration, including planned sample return missions, the NASA Advisory Council chartered a Planetary Protection Advisory Committee in 2002 to secure internal advice
EvolvingRequirements Planetary protection controls require updating in keeping with scientific advances. As solar system exploration advances, knowledge of environments that may contain life or that could be contaminated by Earth life grows. Characterization of biological contamination is also constantly improving, especially since the advent of molecular methods. NASA and COSPAR planetary protection measures are accordingly subject to continual reevaluation and change, in consultation with the science community. As for the US Viking missions of the 1970s, NASA cleaned its Mars landers until their total surface bioburden was no more than 3 x 10~ bacterial spores, with an average of no more than 300 bacterial spores per square metre, and their total bioburden (surface, mated, and encapsulated for launch) was 5 x 10S spores. Each lander was then packaged in a fully enclosing 'bioshield' (resembling a large casserole dish) and baked in an oven so that each portion of the spacecraft attained 111.7°C for 30 hours, in a dry-heat sterilization procedure. The Viking missions revealed that the surface of Mars was much drier and less benign than expected, though some Viking lander findings were suggestive of life (cf., Levin & Straat 1979). In 1992, the US SSB recommended easing forward contamination requirements for Mars and, subsequently, COSPAR and NASA altered their requirements for Mars lander missions, establishing the Viking presterilization surface bioburden standard as the requirement for Mars landers not attempting life detection experiments and the full Viking standard as the requirement for missions focused on life detection.
For landers, in Category IV, all Category II and III requirements may apply (except for orbital lifetime), and restrictions on biological contamination are generally more severe, possibly including comprehensive decontamination and sterilization of the spacecraft, depending on its destination. Category V missions may be deemed "unrestricted Earth return" missions, with no additional planetary protection requirements on the return portion of the mission, or "restricted Earth return" missions. These missions may include all Category II, Ill, and IV restrictions plus severe restrictions on the handling of returned samples until their biological status is determined. The implementation of planetary protection policy is agency-specific and, depending on the nature of the solar-system exploration, may be quite complex. NASA, for example, maintains an office to oversee the application of procedures and guidelines to ensure compliance with its planetary protection policy. The agency's Associate Administrator for Space Science is responsible for planetary protection at NASA, and the agency's Planetary Protection Officer oversees the policy, assigns requirements to solar system exploration missions and, occasionally, requests recommendations on its application [of the procedures] from the Space Studies Board (SSB) of the US National Research Council (NRC), the operating arm of the US National
33
Today, spacecraft going to any solar system body with the potential to support present-day Earth life must undergo stringent cleaning and sterilization. Planetary protection techniques applied to spacecraft bound for Mars include clean manufacturing processes for spacecraft components and the use of cleanroom techniques during spacecraft assembly, test and launch operations. Bioloads are reduced by methods such as alcohol wiping, dry heat treatment and hydrogen peroxide sterilization (Debus et aL 1998). Radiation treatment is an option for some assemblies, and molecular detection methods such as Limulus amoebocyte lysate, polymerase chain reaction, and adenosine triphosphate (ATP) measurement may also be employed to characterize bioload.
requirements are expected to cover any return concerns about sample condition and landing site targeting. For "restricted Earth return" missions, especially those which will return complex samples from a planetary surface or subsurface, the primary challenge is to devise a return sample containment system that provides a reliability perhaps as high as 0.999999 while meeting mass and cost constraints. It is also important to ensure that the sample container or other portions of the spacecraft do not inadvertently bring back other, uncontained, materials from the target body. The cost of meeting stringent Category V requirements on a Mars surface sample return mission is estimated at about 5-10% of the entire mission budget. How these requirements will affect overall mission success is also a consideration.
Cultivation-based microbial assays (cf., NASA 1999c) still constitute the standard forward contamination prevention method, in part because of the lack of comparability with molecular methods and also because of the additional personnel, training and requirements associated with molecular methods. These new methods are attractive, however, because a bioload measurement that could take three days with a cultivation assay may be made in less than one hour using a molecular method. In an operational first, NASA supplemented its standard cultivation-based assays with a Limulus amoebocyte lysate assay in preparing its two Mars Exploration rovers for launch in 2003. Because the Martian atmosphere is a significant factor in the potential for spreading Earth microbes on the planet, the greatest planetary protection challenge for Mars spacecraft is surface cleanliness. Europa, while it has no atmosphere to speak of, features a brutal radiation environment that could kill any exposed Earth organisms, but not necessarily those buried deep within the radiation shielding of the spacecraft. Thus spacecraft bound for Europa will have to be cleaned from the inside out. Species-specific assays may help to eliminate some of the more radiation-tolerant organisms. Mission designers will have to ensure that a spacecraft's interior is protected from recontamination after clean assembly.
Future considerations
With Mars mission planning tentatively calling for sample return missions starting in the second decade of this century, NASA and CNES have collaborated to develop criteria for Mars sample handling before release from postflight containment, along with a protocol for addressing those criteria (Rummel et al. 2002). The 'Draft Test Protocol for Detecting Possible Biohazards in Martian Samples Returned to Earth' specifies tests and procedures needed to safeguard samples against contamination. Among the assumptions underlying this protocol are that samples will not be sterilized before return to Earth, sample containers will be opened only in designated receiving facilities, and only small amounts of sample material (500-1000 grams) will be returned. Of that material, the amount of sample material used to determine whether any biohazard is present will be the minimum necessary. Issues to be addressed in establishing planetary protection requirements for a Mars sample return mission include physical/ chemical analyses needed to complement biochemical or biological screening of sample material, identification of those analyses that must be done in containment and those that can be accomplished using sterilized material outside of containment, and facility capabilities necessary to comply with the protocol. Sample return processing criteria in the draft protocol call for screening samples before release from
For Category V "unrestricted Earth return" missions, science and mission safety
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containment for radioactivity and potential chemical hazards. Further testing will be required for samples providing any indication of life-related molecules such as proteins and nucleic acids. Biohazard testing will involve assays for replication in media with various organic and inorganic carbon sources, effect/growth on various cell cultures and whole organisms, and effect on the ecosystem level. The protocol will not be finalized until the first sample is on its way back to Earth, so that procedures and requirements will be up to date in relation to scientific and technological advances. While a primary focus of planetary protection activities is the search for evidence of life on Mars, NASA's current approach to planetary protection is "all of the planets, all of the time." Reflective of the COSPAR policy, NASA's planetary protection policy goals are to ensure that all of its solar system exploration missions establish appropriate precautions against forward and backward contamination, that the Agency's planetary protection procedures and requirements are in line with the latest relevant scientific findings, that advanced technologies continue to be developed and applied to meet evolving planetary protection requirements, and that the Agency continues to coordinate with other national and international agencies on planetary protection issues and implementation.
References
CETEX 1958 Development of international effforts to avoid contamination by extraterrestrial exploration. Science, 128, 887-889. CETEX 1959 Contamination by extraterrestrial exploration. Nature, Lond., 183, 925-928. CNES 2002 Planetary Protection Requirements. Referentiel Normatif du CNES (RNCCNES-R-14). Corliss, J.B. & Ballard, R.D. 1977 Oases of life in the cold abyss. National Geographic, 152, 441-453. Debus, A., J. et aL 1998 Mars 96 small station biological decontamination. Advances in Space Research, 22, 401-409. Derbyshire. G.A. 1962 Resum6 of some earlier extraterrestrial contamination activities. In: A Review of Space Research, Chapter 10, p. 11. Washington, D.C.: National Academy of Sciences. DeVincenzi, D.L., Stabekis, P.D. & Barengoltz J.B. 1983 A proposed new policy for planetary protection. Advances in Space Research, 3 (8), 13-21.
Gladman, B. & Burns, J.A. 1996 Martian meteorite transfer: simulation. Science, 272, Questions of life and needs for 161-162. planetary protection will continue to bound the acceptable range of future missions into the Gladman, B.J. et al. 1996 The exchange of solar system. As knowledge of the solar system impact ejecta between terrestrial planets. grows, implementation of planetary protection Science~ 271, 1387-1392. provisions will grow more precise, guided by our knowledge of the potential for Earth Levin, G.V. & Straat, P.A. 1979 Journal of contamination, our ability to measure and Molecular Evolution, 14, 167. control it, and our quest to discover extraterrestrial life. It is expected that COSPAR McKay, D.S. et al. 1996 Search for past life on will continue to act as a forum and repository for Mars: possible relic biogenic activity in martian global planetary protection knowledge, policy meteorite ALH84001. Science, 273, 924-930. and plans to prevent the harmful contamination of space and will provide an international forum Melosh, H.J. 1984 Impact ejection, spallation for exchanging such information. For its part, and the origin of meteorites. Icarus, 59, 234NASA will contribute toward maintaining this 260. long and fruitful tradition of global cooperation in planetary protection by working closely with Melosh, H.J. 1985 Ejection of rock fragments COSPAR and other national space agencies as from planetary bodies. Geology, 13, 144-148. the exploration of our solar system moves forward.
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Mitrofanov, I.G. et al. 2003. CO2 snow depth and subsurface water-ice abundance in the northern hemisphere of Mars. Science, 300 (5628), 2081-2084. NASA 1999a Biological contamination control for outbound and inbound planetary spacecraft. NASA Policy Directive (NPD) 8020.7E. Washington, D.C.: NASA Headquarters. NASA 1999b Planetary protection provisions for orbotic extraterrestrial missions. NASA Procedures and Guidelines (NPG) 8020.12B. Washington, D.C.: NASA Headquarters. NASA 1999c NASA standard procedures for the microbial examination of space hardware. NASA Procedures and Guidelines (NPG) 5340.1C. Washington, D.C.:NASA Headquarters. NASA 2002 A Draft Test Protocol for Detecting Possible Biohazards in Martian Samples Returned to Earth (NASA/CP-2002-211842). Hanover, MD: NASA Center for AeroSpace Information. http://a257.g.akamaitech.net/7/257/2422/14mar 20010800/e-docket.access.gpo..gov/2003/0319287.htm Nicholson, W.L. et al. 2000 Resistance of Bacillus endospores to extreme terrestrial and extraterrestrial environments. Microb. MoL Biol. Rev., 64, 548-572.
Space Studies Board, National Research Council 1998 Evaluating the Biological Potential in Samples Returned from Planetary Satellites and Small Solar System Bodies. Task Group on Sample Return from Small Solar System Bodies. Washington, D.C.: National Academy of Sciences. http://www.nap.edu/books/0309061369/html/ind ex.html Space Studies Board, National Research Council 2000 Preventing the Forward Contamination of Europa. Task Group on the Forward Contamination of Europa. Washington, D . C . : National Academy of Sciences. http://www.nap.edu/books/N 1000231/html Space Studies Board, National Research Council 2002a The Quarantine and Certification of Martian Samples. Committee on Planetary and Lunar Exploration. Washington, D.C.: National Academy of Sciences. http://www.nap.ed u/books/0309075718/html/ind ex.html Space Studies Board, National Research Council 2002b New Frontiers in the Solar System: An Integrated Exploration Strategy. Solar System Exploration Survey Committee. Washington, D.C.: National Academy of Sciences.
7. P R O G R E S S OF S P A C E R E S E A R C H Space Studies Board, National Research O C T O B E R 2002 Council 1992 Biological Contamination of Mars: Issues and Recommendations. Task Group on As advised in the COSPAR Information Planetary Protection. Washington, D.C.: Bulletins 158 and 159, a report on the progress National Academy of Sciences. of space research is compiled on behalf of the UN Office for Outer Space Affairs from reports Space Studies Board, National Research submitted by the COSPAR Scientific Council 1997 Mars Sample Return: Issues and Commission Chairs every two years Recommendations. Task Group on Issues in coinciding with the years of COSPAR Scientific Sample Return. Washington, D.C.: National Assemblies. While the resulting survey is Academy of Sciences. published by the UN in the document Highlights http ://www.nap.edu/books/O309057 33 7/html/ind in Space Research, we now finish reproducing ex.html the 2002 report, the first two parts having been reproduced in the Bulletin issues referred to above. We are pleased to acknowledge the permission of the UN Office for Outer Space Affairs and the coordinators of the inputs, respectively, for reproducing the sections of the document, for biennium 2001-2002, included in this issue of the Bulletin.
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