POLICYFORUM

PLANETARY SCIENCE

International policies for protection of Mars and Biologically Reversible Exploration other planets from biological contamination need to be maintained and strengthened. Christopher P. McKay

he international Committee on Space that was the target for the arm on the Phoenix will have to deal with any contamination left Research (COSPAR) has established lander is a special region, and the arm was on Mars by previous explorers, so that it does Ta “planetary protection” policy that therefore heat-sterilized and placed within a not flourish instead. involves not contaminating other worlds in a biobarrier bag before launch to Mars in 2007. Sterilization of robotic spacecraft, while no way that would jeopardize the conduct of Pieces of the rest of the Phoenix lander, which longer policy, is at least possible. With human future scientific investigations. As a signatory were undoubtedly contaminated, are visible exploration, sterilization is not an option. Nor is to the 1967 Outer Space Treaty, the United on the surface of Mars. it realistic to imagine that a human base could States is required by article IX to avoid “harm- Any hitchhiking organisms exposed to be so carefully engineered that it would release ful contamination” of the other worlds of the the martian environment are killed in min- no microorganisms into the environment. Solar System. However, further revisions to utes by the ultraviolet radiation from the Sun The spacecraft that have landed on Mars the policy are needed. (3). Bacteria shielded inside the spacecraft have all been surface missions. Contaminants The two Viking landers that arrived on would not be killed but would remain dor- will remain local and static and can be re- Mars in 1976 were heat-sterilized to comply mant because of the dry conditions. Over moved without requiring an effort vastly with planetary protection. After Viking, hundreds of thousands of years, they would larger than the missions that carried the con- be killed by galactic cos- tamination. Even at the crash sites, debris mic radiation (4). from Earth extends no more than a few meters In 2006, when the U.S. into the surface. Reversing the contamination National Research Council involves recovering the spacecraft parts and emphasized the importance exposing any contaminated dirt to the steriliz- of special regions on Mars ing ultraviolet (UV) sunlight. However, if, for (5), it also recommended example, robotic or human explorers drill to that National Aeronautics investigate a subsurface aquifer, biologically and Space Administration reversible exploration would require rigorous (NASA) work with COSPAR sterilization of any components that go down and other organizations to the drill hole. Similarly, if human explorers convene an international establish bases inside caves (12), the naturally workshop that would focus sterilizing effect of the surface UV would be on “ethical implications lost, and contamination would be persistent. and the responsibility to We should not do anything now that would The heat shield from the Mars Exploration Rover Opportunity photographed explore Mars in a manner close off options for the future. I propose that in February 2005. Debris on Mars could shield microorganisms from UV light. that minimizes the harmful COSPAR, in its upcoming discussions, set a impacts of those activities policy that all Mars exploration be biologically COSPAR determined that given the inhos- on potential indigenous biospheres.” This reversible and that this policy extend to human pitable conditions on Mars, sterilization was would include discussion of whether revisions exploration as well. no longer required unless the spacecraft to current planetary protection policies are specifically intended to search for life as one needed and how to involve the public in dis- References of its scientific goals. Thus, the Pathfinder cussions about related ethical issues. This was 1. J. Barengoltz, in 2005 IEEE Aerospace Conference Proceedings, Big Sky, MT, 6 to 12 March 2005 (IEEE, spacecraft and the two Mars Exploration the first official suggestion that consideration Piscataway, NJ, 2005), pp. 253–261. Rovers (Spirit and Opportunity) arrived at should be given to any indigenous life on 2. COSPAR, “Report on the 34th COSPAR Assembly,” Mars with an estimated bioburden exceeding Mars even if it is microbial (6). This workshop COSPAR Inform. Bull. no. 156, 24 (April 2003). 3. A. C. Schuerger, Icarus, 165, 253 (2003). many hundreds of thousands of bacteria (1) is planned for 2009. 4. G. Kminek, J. L. Bada, K. Pogliano, J. F. Ward, Radiat. (see photo). What do we do if we find life on Mars? It is Res. 159, 722 (2003). In 2003, COSPAR revised its planetary possible that martian life is on the same tree of 5. National Research Council, Preventing the Forward Contamination of Mars (National Academies Press, protection policy for Mars from a probabilis- life as Earth life because of the exchange of Washington, DC, 2006), pp. 362–372. tic approach to one that was based on the mis- meteorites between the two planets (7, 8). 6. C. P. McKay, Planet. Rep. 21, 4 (July/August 2001). sion objectives and target (2). It includes the Alternatively, it may be that life on Mars rep- 7. B. P. Weiss et al., Science 290, 791 (2000). notion of “special regions,” regions in which resents a second genesis—an independent ori- 8. N. H. Sleep, K. Zahnle, J. Geophys. Res. 103, 28529 (1998). biocontamination from Earth might grow and gin of life (9). Contamination by even one 9. C. P. McKay, PLoS Biol 2, e302 (2004). thus require special protection. Any spacecraft Earth bacterium may be a serious issue of 10. C. P. McKay, O. B. Toon, J. F. Kasting, Nature 352, 489 components that enter such a special region environmental ethics. Furthermore, if we find (1991). 11. M. M. Marinova, C. P. McKay, H. Hashimoto, J. Geophys. have to be heat-sterilized. The subsurface ice evidence of a second genesis, then this may Res. 110, E03002 (2005). open discussions of warming Mars to help 12. P. J. Boston et al., Gravit. Space Biol. Bull. 16, 121 (2003). NASA/JPL/CORNELL Space Sciences, NASA-Ames Research Center, Moffett that alien life to flourish (10, 11). Scientists Field, CA 94035, USA; [email protected] 10.1126/science.1167987

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