The microbial case for Mars and its implication for human expeditions to Mars

Mars is considered as key target for the search of life beyond the Earth. As well as carbon based chemistry and an adequate energy source, water in liquid phase has been considered a prerequisite for habitability. By analogy with terrestrial extremophilic microbial communities, e.g., those thriving in arid, cold, salty environments and/or those exposed to intense UV radiation, potential oases on Mars are suggested. They are connected with areas where liquid water still exists under the current conditions, but also sulfur rich subsurface areas for chemoautotrophic communities, rocks for endolithic communities, permafrost regions, hydrothermal vents, soil or evaporite crusts are of interest. The presence of humans on the surface of Mars will substantially increase the research potential; however, prior to any human exploratory mission the critical issues concerning human health and wellbeing as well as planetary protection issues need to be investigated.