In response to a request from the National Aeronautics and Space Administration (NASA), the National Research Council's Space Studies Board convened the Task Group on Issues in Sample Return to examine issues surrounding the return to Earth of samples collected from other solar system bodies. The primary impetus for the study is the planned Mars sample-return mission tentatively scheduled for launch in 2005, but the conclusions and recommendations presented in this report apply to samples returned from any solar system body with a comparable potential for harboring life. This report builds on the findings and recommendations contained in a 1992 report from the Space Studies Board, Biological Contamination of Mars: Issues and Recommendations (SSB, 1992), which addresses the forward contamination problem—the unintentional conveyance of terrestrial biota to Mars aboard landers sent from Earth—and contains substantial information regarding the geological and climatological history of Mars, which is not repeated here. The present report focuses on issues of potential back contamination—how to protect Earth from possible contamination by putative martian biota conveyed in a sample collected from the martian surface and returned to Earth.
The task group was asked to assess the potential for a viable exogenous biological entity being included in a sample returned to Earth from Mars, and the potential for large-scale effects if such an entity were inadvertently introduced into the biosphere of Earth. As explained in Chapters 2 and 4, the potential for either of these occurrences is judged to be low but not zero. It is worth noting that the only potential widespread threat posed by sample material returned from Mars is the possibility of introducing a replicating biological entity of nonterrestrial
origin into Earth's biosphere. The amount of material to be returned is too small to pose any concern about possible toxicity, and any potential danger to researchers analyzing the samples would be obviated by standard laboratory control procedures.
Another question posed to the task group was what scientific investigations could be undertaken to reduce uncertainty regarding the possibility of extant life on Mars. This topic is addressed in Chapter 5. The task group was also asked to assess the status of technical measures for preventing the return of uncontained and unsterilized material of martian origin and, finally, to recommend criteria for controlled distribution of sample material. Technical measures that might be deployed to reduce the risk of loss of containment of sample material are discussed in Chapter 9. No attempt has been made to be comprehensive in this regard as it is recognized that NASA is a preeminent engineering organization, and its technical expertise far outstrips that of the task group.
With regard to criteria for controlled distribution of sample material, the need is clear. In order to maximize the scientific return of a sample return mission, the sample material must be distributed to research centers with particular analytic capabilities. The task group has made several recommendations (see Chapters 4 and 6) with respect to sample containment, handling, and controlled distribution. Detailed protocols for controlled distribution ultimately will be the responsibility of an oversight panel that includes representation from other federal agencies (see Chapter 8) together with the science team associated with the sample-receiving facility (see Chapter 7).