Preventing the Forward Contamination of Mars
166
Preventing the Forward Contamination of Mars
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Product Details
| ISBN-13: | 9780309097246 |
|---|---|
| Publisher: | National Academies Press |
| Publication date: | 04/22/2006 |
| Pages: | 166 |
| Product dimensions: | 8.50(w) x 11.00(h) x (d) |
Read an Excerpt
PREVENTING THE FORWARD CONTAMINATION OF MARS
NATIONAL ACADEMIES PRESS
Copyright © 2006 National Academy of Sciences
All right reserved.
ISBN: 978-0-309-09724-6
Chapter One
Executive Summary
The National Aeronautics and Space Administration's (NASA's) goals for space exploration over the coming decades place a strong priority on the search for life in the universe, and the agency has set in place ambitious plans to investigate environments relevant to possible past or even present life on Mars. Over the next decade NASA plans to send spacecraft to search for evidence of habitats that may have supported extinct life or could support extant life on Mars; Europe will also send robotic explorers. These future missions, in addition to the ongoing suite, will continue to deliver scientific data about the planet and reduce uncertainties about the prospects for past or present life on Mars. To ensure that scientific investigations to detect life will not be jeopardized, scientists have pressed, as early as the dawn of the space age, for measures to protect celestial bodies from contamination by Earth organisms that could hitchhike on a spacecraft, survive the trip, and grow and multiply on the target world.
Preventing the forward contamination of Mars is the subject of this report, which addresses a body of policies, requirements, and techniques designed to protect Mars from Earth-originating organismsthat could interfere with and compromise scientific investigations. The report does not assess forward contamination with respect to potential human missions to Mars, nor does it explore issues pertaining to samples collected on Mars and returned to Earth, so-called back contamination. Those two dimensions of planetary protection, although extremely important, are beyond the scope of the charge to the Committee on Preventing the Forward Contamination of Mars. The recommendations made in this report do apply to one-way robotic missions that may serve as precursors to human missions to Mars. Included are recommendations regarding levels of cleanliness and biological burden on spacecraft destined for Mars, the methods employed to achieve those levels, and the scientific investigations needed to reduce uncertainty in preventing the forward contamination of Mars. In addition, this report urges dialogue at the earliest opportunity on broader questions about the role of planetary protection policies in safeguarding the planet Mars and an indigenous biosphere, should one exist.
In the United States, NASA has responsibility for implementing planetary protection policies that are developed in the international scientific community and, specifically, within the Committee on Space Research (COSPAR), a multidisciplinary committee of the International Council for Science (ICSU; formerly the International Council of Scientific Unions). COSPAR policies on planetary protection have evolved over time as scientists have acquired new information about Mars and other planets and about the potential for life to survive there. NASA has requested this National Research Council (NRC) study, and previous studies on the same topic from the NRC's Space Studies Board (SSB), to inform U.S. planetary protection practices; in turn, the NRC studies have provided input to the official COSPAR policies on planetary protection.
The committee evaluated current science about Mars, the ability of organisms to survive at the extremes of conditions on Earth, new technologies and techniques to detect life, methods to decontaminate and sterilize spacecraft, and the history and prior bases of planetary protection policy, as well as other relevant scientific, technical, and policy factors. It found that (1) many of the existing policies and practices for preventing the forward contamination of Mars are outdated in light of new scientific evidence about Mars and current research on the ability of microorganisms to survive in severe conditions on Earth; (2) a host of research and development efforts are needed to update planetary protection requirements so as to reduce the uncertainties in preventing the forward contamination of Mars; (3) updating planetary protection practices will require additional budgetary, management, and infrastructure support; and (4) updating planetary protection practices will require a roadmap, including a transition plan with interim requirements, and a schedule. In addition, the committee found that scientific data from ongoing Mars missions may point toward the possibility that Mars could have locales that would permit the growth of microbes brought from Earth, or that could even harbor extant life (although this remains unknown), and that these intriguing scientific results raise potentially important questions about protecting the planet Mars itself, in addition to protecting the scientific investigations that might be performed there.
Taken together, the committee's recommendations constitute a roadmap for 21st-century planetary protection that emphasizes research and development; interim requirements; management and infrastructure for the transition to a new approach; and a systematic plan, process, and time line.
This executive summary presents a subset of the committee's recommendations. All of the committee's recommendations are included and discussed in Chapter 8.
RESEARCH AND DEVELOPMENT FOR 21st-CENTURY PLANETARY PROTECTION
For the most part, the bulk of NASA research and development on techniques to prevent the forward contamination of Mars was conducted during the Viking era, when the agency was preparing to send two landers to Mars that would include life-detection experiments. Since the Viking program, continuing though comparatively little research has been done on planetary protection techniques, owing to the 20-year hiatus in Mars lander missions (Viking in 1976, Mars Pathfinder in 1996), the post-Viking perspective that Mars was a dry and barren place, and the expense and effort required to research, develop, and implement new requirements to prevent the forward contamination of Mars.
The techniques currently available to detect contamination of spacecraft by microbes to some extent reflect the technologies that might be used to detect life on solar system bodies such as Mars. Life-detection techniques have advanced considerably, in part because of burgeoning biotechnology sciences and industries, allowing researchers the opportunity to employ molecular methods to identify the kinds and numbers of organisms that might be found in a spacecraft assembly area or on a spacecraft destined for Mars.
Knowledge about the diversity of organisms in clean rooms where spacecraft are assembled or on the spacecraft themselves has several important implications for planetary protection. At present, however, the standard assay method used for detecting microbes on spacecraft-a method that relies on detecting the presence of heat-resistant, spore-forming bacteria, which serve as a proxy for bioburden on the spacecraft-does not provide information about other organisms that might be present on spacecraft. Such organisms include the extremophiles-terrestrial organisms that survive and grow under severe conditions on Earth such as extremes of temperatures (hot and cold) and salinity, low availability of water, high levels of radiation, and other conditions previously considered hostile to life. Based on current understanding of Mars, it is thought that such organisms, especially the cold-loving ones (psychrophiles and psychrotrophs), are among those that might have the best chance of surviving and replicating in martian near-surface environments, as discussed in Chapter 5. Knowing specifically about the organisms present in assembly, test, and launch operations environments that might have the potential to survive a trip to, and possibly grow on, Mars would allow engineers to tailor methods to decontaminate a spacecraft and its instruments more effectively prior to launch than is now done. Other organisms with known intolerances for conditions much less severe than the harshness of interplanetary travel would be of less concern for preventing forward contamination, although efforts to clean spacecraft would still be important for many missions.
A more tailored approach to bioburden reduction could also reduce the costs of implementing planetary protection as compared with the costs of existing approaches such as heat sterilization, which subjects a spacecraft, or specific parts of a spacecraft, to high temperatures over several hours in order to reduce the bioburden to the levels required by NASA for life-detection missions. Furthermore, heat sterilization, which was researched for and applied on the Viking mission in 1976, has not been tested for its effectiveness in eliminating extremophiles or other organisms now known to tolerate high heat. The committee therefore concluded that, ultimately, preventing the forward contamination of Mars requires an understanding of the kinds of organisms that could be present on spacecraft and sterilization or decontamination measures tailored to eliminate those organisms of concern.
To that end, the committee recommends a suite of research and development measures to enable updating of planetary protection practices to reflect the latest science and technology.
NASA should require the routine collection of phylogenetic data to a statistically appropriate level to ensure that the diversity of microbes in assembly, test, and launch operations (ATLO) environments, and in and on all NASA spacecraft to be sent to Mars, is reliably assessed. NASA should also require the systematic archiving of environmental samples taken from ATLO environments and from all spacecraft to be sent to Mars. (Recommendation 5, Chapter 8)
NASA should sponsor research on those classes of microorganisms most likely to grow in potential martian environments. Given current knowledge of the Mars environment, it is most urgent to conduct research on psychrophiles and psychrotrophs, including their nutritional and growth characteristics, their susceptibility to freeze-thaw cycles, and their ability to replicate as a function of temperature, salt concentration, and other environmental factors relevant to potential spaceflight and to martian conditions. (Recommendation 6, Chapter 8)
NASA should ensure that research is conducted and appropriate models developed to determine the embedded bioburden (the bioburden buried inside nonmetallic spacecraft material) in contemporary and future spacecraft materials. Requirements for assigned values of embedded bioburden should be updated as the results of such research become available. (Recommendation 7, Chapter 8)
NASA should sponsor studies of bioburden reduction techniques that are alternatives to dry-heat sterilization. These studies should assess the compatibility of these methods with modern spacecraft materials and the potential that such techniques could leave organic residue on the spacecraft. Studies of bioburden reduction methods should also use naturally occurring microorganisms associated with spacecraft and spacecraft assembly areas in tests of the methods. (Recommendation 8, Chapter 8)
NASA should sponsor research on nonliving contaminants of spacecraft, including the possible role of propellants for future Mars missions (and the potential for contamination by propellant that could result from a spacecraft crash), and their potential to confound scientific investigations or the interpretation of scientific measurements, especially those that involve the search for life. These research efforts should also consider how propulsion systems for future missions could be designed to minimize such contamination. (Recommendation 9, Chapter 8)
NASA should take the following steps to transition toward a new approach to assessing the bioburden on spacecraft:
-Transition from the use of spore counts to the use of molecular assay methods that provide rapid estimates of total bioburden (e.g., via limulus amebocyte lysate (LAL) analysis) and estimates of viable bioburden (e.g., via adenosine triphosphate (ATP) analysis). These determinations should be combined with the use of phylogenetic techniques to obtain estimates of the number of microbes present with physiologies that might permit them to grow in martian environments.
-Develop a standard certification process to transition the new bioassay and bioburden assessment and reduction techniques to standard methods.
-Complete the transition and fully employ molecular assay methods for missions to be launched in 2016 and beyond. (Recommendation 11, Chapter 8)
INTERIM REQUIREMENTS FOR USE UNTIL R&D EFFORTS ARE COMPLETE
Until the above-recommended R&D activities have been completed, the committee believes that the existing framework for planetary protection methods should be updated to reflect recent science regarding environments on Mars and knowledge about extremophiles. There is too much new information about the planet and new science about microorganisms not to update the existing framework of planetary protection requirements while research efforts are being conducted.
The most critical issue regarding Mars science and the potential forward contamination of Mars concerns socalled special regions. A "special region" is defined by COSPAR planetary protection policy as being "a region within which terrestrial organisms are likely to propagate, or a region which is interpreted to have a high potential for the existence of extant martian life forms" (COSPAR, 2003, p. 71). Under existing COSPAR policy, missions to Mars are categorized as IVa (those without life-detection instruments), IVb (those with life-detection instruments), or IVc (those going to special regions, regardless of instrumentation), and COSPAR policy sets levels of bioburden reduction differently for missions categorized as IVa, IVb, or IVc. Missions categorized as IVa are allowed higher levels of bioburden than missions that will carry life-detection instruments (IVb) or missions going to special regions (IVc).
The committee found, as discussed in Chapter 4, that there is at this time insufficient data to distinguish confidently between "special regions" and regions that are not special. Scientific results from the Mars Exploration Rovers and Orbiter missions have provided evidence for the existence of past water on Mars and suggest that it is substantially more likely that transient liquid water may exist near the surface at many locations on Mars. It is very difficult on the basis of current knowledge to declare with confidence that any particular regions are free of this possibility. Additional information is needed to identify the presence of liquid water, and collection of such data should continue to be a high priority.
NASA's Mars Exploration Office should assign high priority to defining and obtaining measurements needed to distinguish among special and nonspecial regions on Mars. (Recommendation 10, Chapter 8)
The committee developed a new set of categorizations for Mars missions, IVs (missions to special regions) and IVn (missions not going to special regions). In the absence of sufficient data to distinguish IVs from IVn, the committee recommends that all landed missions to Mars be treated as IVs until additional data indicate or allow otherwise.
For the interim period until updated planetary protection methods and techniques can be fully implemented,
-NASA should replace Categories IVa through IVc for Mars exploration with two categories, IVn and IVs. Category IVs applies to missions that are landing or crashing in, or traversing, excavating, or drilling into, special regions; Category IVn applies to all other Category IV missions.
-Each mission project should (in addition to meeting the requirements imposed by Categories IVn and IVs) ensure that its cleanliness with respect to bioburden and nonliving contaminants of concern is sufficient to avoid compromising its experiments, in consultation with NASA's planetary protection officer. (Recommendation 12, Chapter 8)
Until measurements are made that permit distinguishing confidently between regions that are special on Mars and those that are not, NASA should treat all direct-contact missions (i.e., all Category IV missions) as Category IVs missions. (Recommendation 13, Chapter 8)
(Continues...)
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Table of Contents
Contents EXECUTIVE SUMMARY....................1
1 INTRODUCTION....................11
Policy Basis for Planetary Protection....................12
The Outer Space Treaty....................13
Protecting Science and Protecting Mars....................14
Past Delivery of Microorganisms to Mars....................16
Issues in and Organization of This Report....................20
References....................21
2 POLICIES AND PRACTICES IN PLANETARY PROTECTION....................22
Planetary Protection Policy....................22
Implementation Requirements....................28
Maintaining Cleanliness During Launch....................33
Current Limitations of Standard Methods and Implementing Requirements....................33
References....................34
3 FUTURE MARS EXPLORATION: THE ROLLING WAVE....................36
Increasing Complexity, Capability, and Creativity....................38
The Rolling Wave....................39
References....................40
4 ENVIRONMENTS ON MARS RELATIVE TO LIFE....................41
Biogenic Materials....................42
Utilizable Energy....................42
Liquid Water....................43
A Catalog of Potentially Special Regions....................54
Techniques for Assessing the Distribution and State of Subsurface Water on Mars....................57
Measurements Needed to Identify Special Regions....................61
Spacecraft Access and Special Regions....................63
Summary....................63
References....................64
5 EXPANDING OUR KNOWLEDGE OF THE LIMITS OF LIFE ON EARTH....................69
Modern Views of MicrobialDiversity....................69
Modern Technology and Microbial Ecology....................70
Organisms at the Limits of Life....................72
Life in Extreme Environments....................73
Probability of Growth on Mars....................84
Summary....................85
References....................86
6 ADVANCES IN TECHNOLOGIES FOR LIFE DETECTION AND BIOBURDEN REDUCTION....................91
Examples of Methods for Assessing Total Viable Cell Count....................91
Examples of Methods for Estimating Biodiversity....................94
Methods for Reducing Bioburden....................99
Summary....................102
References....................103
7 ASSESSING NONLIVING CONTAMINANTS OF CONCERN....................105
Types of Contaminants....................106
Determination of Acceptable Levels of Contamination....................108
Summary....................109
References....................109
8 A PATH FORWARD FOR PLANETARY PROTECTION IN THE 21st CENTURY....................111
Expanding the Purpose of Planetary Protection: Safeguarding of Indigenous Life as Well as Protection of Mission Science?....................112
Programmatic Support....................112
Needed Research and Reconnaissance....................115
Transition to a New Approach....................117
Interim Requirements....................118
References....................123
9 TRANSITION PROCESS AND TIME LINE....................124
Approach....................124
Implementation Time Line....................126
APPENDIXES A Biographical Sketches of Committee Members and Staff....................131
B Recommendations from Two Previous NRC Reports on Forward Contamination....................135
C Summary of Procedures Currently Used to Assess Bioburden in Spacecraft Assembly Clean Rooms and on Spacecraft....................138
D History of Recommended Values for Probability of Growth....................140
E Approaches to Bioburden Reduction for Lander Missions to Mars....................141
F Ambiguities in Geomorphic Interpretation: Martian Gullies....................144
G Spacecraft Propellant and By-Products as Potential Contaminants....................148
H Acronyms and Abbreviations....................152