increases in sensitivity and in the diagnostic value of techniques to detect organic molecules in extraterrestrial samples, particularly in situ, will be an important part of the overall effort to assess the existence of past or present life in the solar system. The committee concludes that it is crucial to continue the development of techniques to detect and analyze in situ organic chemical systems of either biotic or abiotic origin, with the goal of increasing the techniques' sensitivity and diagnostic capability.
In situ life detection will require commitment to a small subset of available techniques because spacecraft resources will always be constrained, at least for the foreseeable future. Hence, a specific set of hypotheses regarding the samples to be analyzed must be made prior to launch; this intrinsically decreases the likelihood of successfully detecting life, because such hypotheses are invariably based on Earth-centric assumptions. On the other hand, in situ analysis is not subject to the concern of back contamination of Earth; hence sample handling is, in that respect, greatly simplified. Whether and to what extent attempts to detect life in situ will be made prior to return of a sample to Earth is an unresolved issue in NASA's Mars Exploration Program. Potential confusion of the results by terrestrial contaminants is a particular concern for in situ studies, because of the limited number and types of tests that can be done. Accurate knowledge of the prelaunch level of terrestrial contamination and a method of tagging terrestrial organisms would maximize the chances of an interpretable result.
Because of the continuing rapid improvements in technology, it is not appropriate at this time to recommend a specific set of techniques for in situ life detection, but in situ life detection will require commitment to a small set of potential techniques with significant lead time to ensure that they can be space qualified. The committee encourages continued efforts to develop innovative and miniaturizable techniques for in situ life detection. It must be stressed that selecting the combination of techniques for in situ life detection is dependent as well on the physical and chemical characteristics of the sampling site on a particular planetary body.
Appropriate site selection is crucial to maximizing the chances of finding evidence for extant or extinct life in samples either analyzed in situ or collected for return to Earth. While this point seems obvious, the committee notes that over the history of Mars exploration the engineering constraints associated with safe operations usually have conflicted with reaching the most scientifically interesting sites. For Mars, this means that landing site selection cannot be based primarily on issues of spacecraft safety. Furthermore, proper site selection will require a series of missions including orbital reconnaissance followed by exploration of selected sites by landed vehicles. An informed and continuing dialogue between scientists engaged in life detection and mission planners is essential if astrobiologically interesting samples from Mars are to be obtained.