BOX 7.1 Summary of Recommendations from the 1997 Report Mars Sample Return: Issues and Recommendations

Mars Sample Return: Issues and Recommendations (NRC, 1997) concluded that the possibility of including a living organism, either active or dormant, in a sample returned from Mars cannot be ruled out altogether, although the potential for such an occurrence was judged to be low. Moreover, the report recommended that unless and until sufficient knowledge of Mars and its environment was available, due caution and care should be exercised in handling returned materials that might contain hypothetical martian microorganisms capable of inadvertently contaminating Earth and causing a risk of pathogenesis, environmental disruption, or other harmful effects.

Specifically, the report recommended that samples returned from Mars be contained and treated as though they were potentially hazardous until proven otherwise. Strict containment of all pristine sample material was urged, and special handling procedures were outlined for samples en route to and on Earth. In particular, no uncontained martian materials, including spacecraft surfaces exposed to the martian environment, should be returned to Earth unless sterilized. If sample containment cannot be verified en route to Earth, the sample, and any spacecraft components that may have been exposed to the sample, should either be sterilized or not returned to Earth. The integrity of containment should be maintained through reentry of the spacecraft and transfer of the sample to an appropriate receiving facility.

Furthermore, the distribution of unsterilized materials returned from Mars should be controlled and should occur only if rigorous analyses determine that the materials do not contain a biological hazard. Finally, the planetary protection measures adopted for the first Mars sample return missions should not be relaxed for subsequent missions without thorough scientific review and concurrence by an appropriate independent body.

particular body, then containment and special handling similar to the procedures recommended for samples returned from Mars (NRC, 1997) would be warranted.

LIKELIHOOD OF FINDING AND INCLUDING A LIVING ORGANISM IN SAMPLES FROM DIFFERENT SOLAR SYSTEM BODIES

In the absence of direct evidence of extraterrestrial life forms, consideration needs to be given to the nature of putative life forms based on analysis of terrestrial analogs and biochemical possibilities. Based on current knowledge of the geophysical and geochemical properties of various solar system bodies and contemporary views on the range of conditions under which life can originate, the conditions required for the preservation of metabolically active organisms in terrestrial environments, and the somewhat different conditions needed to preserve living organisms in a dormant form (see discussion in Chapter 1), it is possible to infer the likely metabolic groups of microorganisms that might be found on small bodies. They are most likely to be anaerobic organisms similar to those found in analogous Earth environments, including hydrothermal systems, sea ice, oligotrophic aquatic environments, deep basaltic rock, and soils.

The contemporary views of the nature of different solar system bodies are supported by a considerable body of scientific evidence that has been collected either remotely or from direct analyses of materials delivered to Earth by the natural influx of IDPs, asteroids, and meteorites. Presumably, this natural influx of extraterrestrial materials arriving over time on Earth, albeit with varying transit times in space, has exposed Earth and its biota to risks the same as or similar to those potentially posed by samples deliberately returned from these bodies. Based on the accumulated information and current thinking about the origin, persistence, and preservation of life as we know it, the possibility of including a living organism, either active or dormant, in a sample returned from bodies such as asteroids, comets, planetary satellites, or IDPs is judged by the task group to be very low overall. This judgment is further supported by the complete absence of evidence of the existence of even fossilized extraterrestrial life



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement