Microbial ecology of the surface exploration of Mars with human-operated vehicles

Robotic and piloted spacecraft are launched from Earth with finite levels of microbial contamination that are composed of species similar to the cleanroom environments within which the vehicles are assembled. After entering the harsh environment of interplanetary space, the microorganisms on the exterior surfaces of spacecraft are subjected to biocidal factors that immediately begin to reduce the viable biomass and species diversity of the launched bioload. The harsh conditions found on the surface of Mars are only slightly more conducive to the survival of terrestrial microorganisms than are found in interplanetary space. Even the launched bioload found within a pressurized human habitat in an Earth-Mars transit vehicle will be exposed to conditions that likely will reduce the species diversity of microorganisms within the life support system. The reductions in biomass and species diversity of the launched bioloads on and within spacecraft are likely to simplify the forward contamination issues related to human expeditions on Mars by limiting the numbers of viable cells that might be dislodged from spacecraft surfaces and disperse onto the Martian terrain.