BIOPAN experiment LICHENS on the Foton M2 mission: Pre-flight verification tests of the Rhizocarpon geographicum-granite ecosystem

The objective of the LICHENS space experiment within the BIOPAN facility of ESA on board of the Russian Foton satellite is to test the limits of life in the hostile environment of space, and the effects of selected parameters, such as space vacuum and specific wavelength bands of extraterrestrial UV-radiation, on the viability of lichens. In preparation of this space experiment, pre-flight verification tests were performed with the lichen system Rhizocarpon geographicum on its natural granite substrate using the Planetary and Space Simulation Facilities at the DLR in Cologne, Germany. The test parameters (high temperature, UV-radiation, vacuum) were adjusted to the conditions expected to be experienced during the 15 days long space mission of LICHENS. After exposure, the maximum quantum yield of photosynthetic activity was determined as a measure of survivability of the lichen. The lichen R. geographicum was capable to fully recover from exposures to vacuum (up to 3 × 10−6 hPa for 1 week), to the full spectrum of UV-radiation (>200 nm for up to 20 h giving a final fluence of 10.89 × 106 J/m2), as well as to a combined treatment with both simulated space parameters. It was less resistant to heating: after 1 week at 40 °C the photosynthetic activity was reduced by about 20%. The results demonstrate the high resistance of the R. geographicum-granite ecosystem to simulated space conditions and justify its use in the LICHENS space experiment. It might even be capable of coping with the intense influx of extraterrestrial solar UV-radiation, which so far no biological system was able to withstand.