NRC studies (NRC, 2002b). The committee also urges NASA to set an operational value for the life detection threshold limit through a separate advisory process drawing on a broad range of relevant expertise.

Recommendation: The committee recommends that NASA establish zones of minimal biologic risk (ZMBRs) with respect to the possible presence of Martian life during human missions to Mars. In order to do so, NASA should conduct a precursor in situ experiment at a location as reasonably close to the human mission landing sites as possible to determine if organic carbon is present. The measurement should be on materials from the surface and down to a depth to which astronauts may be exposed. If no organic carbon is detected at or above the life detection threshold, the landing site may be considered a ZMBR. If no measurement technique can be used to determine if organic carbon is present above the life detection threshold, or if organic carbon is detected above that threshold, a sample should be returned to Earth for characterization prior to sending humans to Mars.

There has been some concern that if a sample return is required, the planning for the first human mission to Mars may be delayed until a sample can be obtained. The committee believes that, even should a sample be required because organic carbon has been found, a baseline mission plan for a mission to Mars and even hardware development may still proceed under the assumption that a sample return will not find anything significant enough with regard to Martian biology to invalidate the baseline mission plan.

Return Vehicle Contamination

To prevent contamination of Earth by Martian material, great care must be exercised to ensure the containment of all material returned from Mars to Earth. There must be a sterile, intermediate transfer conducted in space that ensures Earth's environment will not be exposed to any Martian material, including dust or soil deposits on the outside surface of the return vehicle. The protocols for such a sterile transfer will be complex and, if the transfer is unsuccessful, may require that the return vehicle be discarded in space and never returned to Earth. Ultimately, however, only contained materials should be transported back to Earth, unless sterilized first (NRC, 1997).

REFERENCES

Clark, B.C., A.K. Baird, R.J. Weldon, D.M. Tsuasaki, L. Schnabel, and M.P. Candelaria. 1982. “Chemical Composition of Martian Fines.” Journal of Geophysical Research 87:10,059-10,067.

Greeley, R., ed. 2001. Scientific Goals, Objectives, Investigations, and Priorities, Mars Exploration Program/Payload Analysis Group (MEPAG), March 2. Also known as Jet Propulsion Laboratory (JPL) Publication 01-7 (2001). JPL, Pasadena, Calif.

National Research Council (NRC). 1997. Mars Sample Return: Issues and Recommendations. National Academy Press, Washington, D.C.

NRC. 2002a. Assessment of Mars Science and Mission Priorities. National Academy Press, Washington, D.C.

NRC. 2002b. The Quarantine and Certification of Martian Samples. National Academy Press, Washington, D.C.

Wanke H., J. Bruckner, G. Dreibus, R. Rieder, and I. Ryabchikov. 2001. “Chemical Composition of Rocks and Soils at the Pathfinder Site.” Space Studies Review 96: 317-330.



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