ger to the researchers analyzing the samples would be obviated by standard laboratory control procedures.

The only risk posed by a sample returned from Mars is the potential for including a replicating organism that could possibly grow and multiply on Earth. The possibility of such an occurrence is remote (see Chapters 2 and 4), but it is not zero. Therefore, adequate precautions must be taken. In Chapter 4 the task group recommends that martian sample material be contained and treated as though potentially hazardous until proven otherwise.

Evaluation of the sample for potential hazards should focus exclusively, then, on searching for evidence of living organisms, their resting states (e.g., spores or cysts), or their remains in the sample. Attempts to cultivate putative organisms, or to challenge plant and animal species or tissues, are not likely to be productive. Moreover, if viable exogenous biological entities are discovered in the sample material, prudence would indicate that they remain segregated from Earth's biosphere (i.e., they should remain in containment or be made nonviable through sterilization).

In keeping with the task group's recommendation in Chapter 4, if viable biological entities are discovered in sample material returned from Mars, and those entities cannot be accounted for by terrestrial organisms conveyed on the outbound spacecraft, then the sample material should be deemed hazardous and no portion should be removed from containment without first being sterilized.