Survival of micro-organisms in space

Survival of coliphageT₁, tobacco mosaic virus (TMV) and spores ofPenicillium roqueforti Thom after direct exposure to space on board 6 balloons, 6 sounding rockets and 3 satellites is related to the numbers of solar UV photons incident during exposure. The survival followed exponential curves leading to complete inactivation. Solar ultraviolet radiation of wavelengths 2000 Å to 3000 Å appears to be the main cause of inactivation of broth suspended phage and, probably, TMV.T₁ phage andPenicillium spores prepared in saline were also affected by radiation shorter than 2000 Å, while TMV seems to be resistant to radiation of these wavelengths. The biological effectiveness of the solar spectrum in the area between 3000 Å to 50 000 Å was not significant. Sterilization of interplanetary spacecraft appears necessary since micro-organisms can easily be shielded against lethal radiation.