|Budget Amount *help
¥1,600,000 (Direct Cost : ¥1,600,000)
Fiscal Year 1991 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 1990 : ¥1,200,000 (Direct Cost : ¥1,200,000)
The subject is not restricted to an academic curiosity, but concerns a dangerous problem for the contamination of space environment with terrestrial microorganisms carried by space probes. If terrestrial microorganisms can not survive in space environment even for a short period, we can reduce expenditure for the sterilization of space probes. On the other hand, if organisms can survive for a significant period under such environments, the planets in our solar system might be contaminated by terrestrial microorganisms and microfloras. Several species of terrestrial microorganisms, i. e., virus, bacteria, yeast and fungi have been tested in this study. The space environment was simulated with a wide range of temperature (100K-500K), high vacuum (1x10^<-8>torr) by using cryostat, and proton irradiation from a Van de Graaff accelerator in Tokyo Institute of Technology. After the exposure to the simulated space environments, survival rates of the microorganisms were examined.
Tobacco Mosaic virus, some kinds coccus, Bacillus subtilis spores, Aspergilus niger spores, Clostridium mangenoti spores and epiphytic algae of Syowa station in Antarcia showed considerably high survival rates (about 10%-80%) even after the proton irradiation equivalent to a space flight for about 250 years. The results are particularly surprising in view of the fact that some terrestrial organisms might be able to survive for a significant period under space environment. But, these findings should be confirmed by space experiments onboard space crafts or space stations in future.