Microbial Diversity and Its Relationship to Planetary Protection

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Abstract
As summarized by Rummel (56) and Rummel and Meyer (57), while exploring our solar system and the universe at large, spacefaring nations must be committed to avoiding biological contamination of other planetary systems while also protecting the Earth from potential harm caused by materials returned from space. Most scientists accept this, and there are interna- tional treaties and regulations addressing these issues (6, 62). Thus, planetary protection is now a part of planning for all extraterrestrial missions (64), and the rules regarding these activities are prepared by an international group known as the Committee on Space Research (COSPAR) (Paris, France). Spacefaring nations generally adhere to the scientific and tech- nical standards developed by COSPAR. COSPAR describes five categories for interplanetary mis- sions, and there are suggested ranges of planetary protection requirements for each category. The following descriptions are set forth in the COSPAR regulations (6). Category I includes any mission to a target body that is not of direct interest for understanding the process of chemical evolution or the origin of life; no protection of such bodies is warranted, and no planetary protection requirements are imposed by COSPAR policy. Category II missions are missions whose target bodies are of significant interest relative to the process of chemical evolution and the origin of life but in which there is only a remote chance that contamination carried by a spacecraft could jeopardize future exploration. COSPAR requires only simple documentation that includes preparation of a short planetary protection plan in the form of an outline of intended or potential impact targets, brief pre- and postlaunch analyses detailing impact strategies, and a postencounter and end-of- mission report providing the location of impact, if such an event occurs. Category III missions (mostly flyby and orbiter missions) are missions to a target body of chemical evolution and/or origin-of-life interest or for which scientific opinion indicates that there is a significant chance of contamination that could jeopardize a future biological experiment. COSPAR requires documentation of planetary protection issues and some implementation of protection procedures that include at a minimum trajectory biasing, the use of cleanrooms during spacecraft assembly and testing, and possibly spacecraft bioburden reduction. An inventory of bulk constituent organ- ics is required if the probability of impact is significant. Cate- gory IV missions (mostly probe and lander missions) target a body of chemical evolution and/or origin-of life-interest or for which scientific opinion indicates that there is a significant chance of contamination that could jeopardize future biologi- cal experiments. COSPAR requires detailed documentation of planetary protection issues, including a bioassay to enumerate spacecraft bioburden, an analysis of the probability of contam- ination that may include trajectory biasing, use of cleanrooms during spacecraft assembly, bioload reduction, partial steriliza- tion of any direct contact hardware, and a bioshield for that hardware. The requirements and compliance are similar to those imposed for the Viking missions, with the exception of complete lander or probe sterilization. Category V comprises all return-to-Earth missions, where the concern is the protec- tion of the terrestrial system comprising the Earth and the Moon. The Moon must be protected from back-contamination to retain freedom from planetary protection requirements for