The astonishing capability of life to adapt to extreme conditions has provided a new perspective on what ‘habitable’ means. On Earth extremophiles thrive in hostile habitats, such as hot and cold deserts or Antarctic sub-glacial lakes considered as Earth analogues of Mars and icy moons of Jupiter and Saturn. Recently desert cyanobacteria were exposed to ground-based simulations of space and Martian conditions and to real space and Martian conditions simulated in low Earth orbit using facilities attached outside the International Space Station. When exposure to such conditions does not exceed repair capabilities, more data are available regarding the physico-chemical constraints that life can withstand. When the accumulated damage exceeds the survival potential, the persistence of biomarkers contributes to the search for life elsewhere. Knowledge concerning the endurance of desert cyanobacteria under space and Martian conditions contributes to the development of life support systems.

The assessment of mean lethal dose (Do) with organ weight in human organs yields a correlation coefficient of 0.94. Results indicate that as the organ weight increases, the Do decreases.