Spores of Bacillus subtilis were exposed to space in theBIOPAN facility of the European Space Agency onboard of the Russian Earth-orbiting FOTON satellite. The spores were exposed either in dry layers without any protecting agent, or mixed withclay, red sandstone, Martian analogue soil or meteorite powder,in dry layers as well as in so-called `artificial meteorites', i.e. cubes filled with clay and spores in naturally occurring concentrations. After about 2 weeks in space, their survival was tested from the number of colony formers. Unprotected spores in layers open to space or behind a quartz window were completely or nearly completely inactivated (survival rates in most cases≤10^-6). The same low survival was obtained behind a thin layer of clay acting as an optical filter. The survival rate was increased by 5 orders of magnitude and more, if the spores in the dry layer were directly mixed with powder of clay,rock or meteorites, and up to 100% survival was reached in soilmixtures with spores comparable to the natural soil to spore ratio. These data confirm the deleterious effects of extraterrestrial solar UV radiation. Thin layers of clay, rock or meteorite are only successful in UV-shielding, if they are indirect contact with the spores. The data suggest that in a scenario of interplanetary transfer of life, small rock ejecta ofa few cm in diameter could be sufficiently large to protectbacterial spores against the intense insolation; however, micron-sized grains, as originally requested by Panspermia, may notprovide sufficient protection for spores to survive. The data arealso pertinent to search for life on Mars and planetaryprotection considerations for future missions to Mars.