Radiobiological effects at low temperature and their relevance to astrobiology
- Paper number
IAC-05-A1.7.10
- Author
Dr. Gerda Horneck, Deutsches Zentrum fur Luft und Raumfahrt e.V. (DLR), Germany
- Year
2005
- Abstract
In search for life beyond the Earth, liquid water has been defined as one of the prerequisites for the appearance and persistence of life, because of its many life-supporting characteristics: (i) as a diffusion milieu, (ii) as a selective solvent, (iii) as a clay producer, (iv) by supporting the structures of the polymers, (v) as a driver for chemistry, and (vi) as a heat dissipater. Therefore, the requirement for liquid water being permanently available at a planet’s surface has been used for defining habitable zones around main sequence stars. Liquid water is also a reaction partner in radiobiological processes. Upon irradiation of biological systems, most energy of ionizing radiation is absorbed in the water molecules of the cells producing either ions or radicals. Especially the highly reactive free radicals may interact with essential biomolecules, such as cellular DNA, causing mutations, transformations or inactivation of the cells. The degree of this indirect radiobiological damage depends on the degree of hydration of a biological system and the diffusion rate of the radicals. This diffusion rate of the radicals is dependent on temperature. At very low temperatures the radicals are immobilized. The OH• and O2H• radicals start diffusion at 100-135 K and become fully mobile at 135 K. The H• radicals start migration at temperatures >10 K and are almost fully mobile at 77 K. Hence, at low temperatures (10-135 K) the H• radicals, by migrating to the immobile OH• and O2H• radicals are capable of recombining with them. The result is an increased radiation resistance of the biological objects upon irradiation at low temperatures. Compared to samples at room temperature, the radiation resistance of objects at low temperature can increase up to a factor of 100. This fact is especially important when assessing the radiation exposure of microorganism in Permafrost, where they have been exposed to the natural radiation for more than one million years. In this case, doses of several kGy are estimated. This high radiation resistance of microorganisms at very low temperatures has also astrobiological implications when considering that Permafrost and ice as well as high radiation doses are common features in our solar system (planets and their moons, comets, asteroids) and probably in the whole universe.
- Abstract document