interplanetary dust particles for which samples are available at present). The final two sessions dealt with techniques for detecting viable (including spore-forming) organisms and the signs of past life, respectively. Appendix B of this report gives the workshop agenda. Appendix C lists (and the enclosed CD-ROM contains) the set of papers written by the invited speakers at the workshop. The report itself presents introductory and concluding material written by COEL to relate the papers to the questions to be addressed. To facilitate discussion of the papers and workshop sessions, the introductory material is organized in parallel with the workshop sessions rather than the four questions listed above. The conclusions and recommendations (Chapter 5), however, are grouped in parallel with the questions themselves. The committee emphasizes that this is a workshop report, rather than a detailed strategy study, and so drawing very specific conclusions and recommendations is not appropriate.

CONCLUSIONS AND RECOMMENDATIONS

Detecting Organisms on a Spacecraft Prior to Launch: Preventing Forward Contamination

The most strikingly definitive result coming from the workshop concerns the dramatic improvement in laboratory techniques designed to detect terrestrial organisms, with principal application to spacecraft sterilization and hence forward planetary protection. As new techniques become available, they have to be incorporated into planetary protection protocols because current NASA protocols (based on culturing techniques) could miss up to 99 percent of microorganisms. Also, some techniques may not be suited to distinguishing between viable and nonviable organisms, a key issue in considering forward and back contamination.

Recommendations regarding specific sterilization techniques and levels of sterilization in order to avoid contamination of other planetary bodies were beyond the original purview of the workshop and this report. The main issue regarding sterilization from the point of view of the workshop is the ability to sample, poststerilization, the remaining level of terrestrial microorganisms to ensure that it is below the value required for a particular mission. Because all terrestrial organisms rely on the same basic biochemistry—specifically and most importantly, the RNA and DNA nucleic acid bases—amplification techniques to detect very small remnant levels of contamination are well understood.

The committee recommends that studies of future missions to astrobiologically interesting targets include explicit consideration of the types of sterilization for spacecraft systems, subsystems, and components and that sterilization costs be included in a realistic fashion. The committee recommends that special near-term emphasis be given to the issues of sample selection, spacecraft sample handling, and sample characterization. The committee also encourages further work to refine sterilization approaches to minimize impacts on mission costs and success.

Detection of Living Organisms in a Returned Sample

The committee is strongly encouraged by the multidisciplinary efforts to define the possible range of processes indicative of living organisms. Given the extreme difficulty (or impossibility) of inductively describing all possible living processes based on terrestrial biochemistry, no single approach, or even combination of approaches, will guarantee success with a given sample. Multiple approaches, both chemical (including isotopic and molecular) and microscopic, are key to the successful detection of life in a sample. Because of the rapid improvements in the technology for a variety of techniques, coupled with the realization that return of a sample from Mars (the highest-priority target in life detection) remains a decade away, it would be premature to recommend a particular technique or set of techniques at present.

The committee concludes that a number of very sensitive and specific techniques are available for detecting living or once-living organisms in a returned sample; however, these techniques depend on the organisms ' being composed of essentially terrestrial biopolymers. While other techniques exist for detecting a potentially broader suite of nonterrestrial-like (but carbon-based) organisms, their results will not be as definitive. Hence, multiple approaches will be required to establish the presence of life in a definitive fashion, unless such life happens to be essentially terrestrial in nature. There is a pressing need to develop



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