Abstract
A strong species of lichens was sorted out to expose the extreme conditions which will be encountered by interplanetary space, followed our previous work of fungal and moss spores. Caloplaca flavovirescens was the most resistant lichen among 10 kinds (9 species) of the lichens examined against temperature fluctuations in vacuum, UV irradiation and cosmic ion irradiation (examined 3 species). The survival rate decreased about 24% by the thermal cycle treatment under vacuum (<1Pa) for 6 weeks under the condition of temperature fluctuations between −80°C and 80°C once every 90 min. The rate after one year is extrapolated to be 4.7% (cultivation method) and 7.1% (fluorescent method) under the supposition of the exponential decrease of survival rate continue for a long period of time. The growth rates did not decrease after the temperature fluctuations between −60°C and 60°C with the same periodicity. The survival rate of the lichen was decreased by 5% at 1,413mJ/cm2 of UV-C (254nm) irradiation. The survival rate of the lichen was decreased by about 20% after 335Gy irradiation of helium beam, and the 10% survival rate (D10) was calculated for 1,640 Gy from the extrapolation of regression equation. This amount will be equivalent to 130 - 1,300 year irradiation at the outer environment of ISS. The reduction rate of carbon beam seems somewhat larger than that of helium beam. As far as these factors concerned, C. flavovirescens inside the container which prevent UV, will survive for several years at the ISS outer environment.
