Bacterial endospores of the highly UV-resistant Bacillus subtilis strain MW01 were exposed to low Earth orbit and simulated Martian surface conditions for 559 days. It was clearly shown that solar extraterrestrial UV radiation (λ ≥110 nm) as well as the Martian UV spectrum (λ ≥200 nm) was the most deleterious factor applied; in some samples only a few spore survivors were recovered from B. subtilis MW01 spores exposed in monolayers. However, if shielded from solar irradiation, about 8% of MW01 spores survived, and 100% survived in simulated Martian conditions, compared to the laboratory controls.
Halococcus dombrowskii (ADAPT II) and a naturally UV-adapted phototrophic community (ADAPT III) were two other targets of the experiment. For ADAPT-II, no counting from the space station has been published, but preliminary ground experiments have established some tolerance levels. The results for ADAPT-III has been published. Many dyes (chlorophyll and carotenoids) used by the microbials are bleached by the UV rays, and quite a few species used in the dark control groups died. Chroococcidiopsis was the one to survive every group. Chlorella, Gloeocapsa, and Geminicoccus roseus were able to survide a lower UV level.