approach involves aseptic transfer of the sample canister through a biobarrier to a receiving spacecraft that returns the sample to Earth. A possible variant of this approach, which avoids hand-off to a second craft, is to pass the sample canister through a biobarrier that fully encloses the Earth reentry vehicle on Mars. Once in space, the biobarrier would be opened like a cocoon to release the Earth reentry vehicle. Technical challenges include the selection of biobarrier materials, designing practical pass-through and sealing mechanisms, and validating the method.

In an alternative approach, all spacecraft surfaces that could be exposed to the martian surface would be coated with a pyrotechnic material that would be ignited in space during the return trip to Earth in order to heat the surfaces and sterilize any attached martian material. As with any method, extensive validation and testing would be required. Such testing would include analysis of the efficacy of heating across a steep gradient and avoidance of ablation or partial detachment of surface material that could defeat sterilization.

It must be assumed that putative martian organisms will be resistant to ultraviolet radiation and able to tolerate high vacuum. Possible mechanisms of biotic transfer within and on the return spacecraft must be considered. Such mechanisms include vibrations and shocks and micrometeorite erosion of surfaces, including a possibly dusty near-Mars environment owing to the proximity of two moons, Phobos and Deimos.



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