Microbe space exposure experiment at International Space Station (ISS) proposed in "Tanpopo" mission

Yokobori, Shinichi*; Yang, Y.*; Sugino, Tomohiro*; Kawaguchi, Yuko*; Fushimi, Hidehiko*; Narumi, Issei; Hashimoto, Hirofumi*; Hayashi, Nobuhiro*; Kawai, Hideyuki*; Kobayashi, Kensei*; Marumo, Katsumi*; Mita, Hajime*; Nakagawa, Kazumichi*; Okudaira, Kyoko*; Tabata, Makoto*; Takahashi, Yuichi*; Yamashita, Masamichi*; Yano, Hajime*; Yoshimura, Yoshitaka*; Yamagishi, Akihiko*

To explain how organisms on the Earth were originated at the quite early stage of the history of Earth, Panspermia hypothesis was proposed. Recent findings of the Martian meteorite suggested possible existence of extraterrestrial life, and interplanetary migration of life as well. On the other hand, microbes have been collected from high altitude using balloons, aircraft and meteorological rockets since 1936, though it is not clear how could those microbes be ejected up to such high altitude. Spore forming fungi and Bacilli, and Deinococci have been isolated in these experiments. If microbes could be found present even at the higher altitude of low earth orbit (400 km), the fact would endorse the possible interplanetary migration of terrestrial life. We proposed the "Tanpopo" mission to examine possible interplanetary migration of microbes on Japan Experimental Module (JEM) of the International Space Station (ISS). In our proposal, microorganisms will be exposed to the space environment with/without model-clay materials that might protect microorganisms from vacuum UV and cosmic rays. Spore of sp., and vegetative cells of and our novel deinococcal species isolated from high altitude are candidates for the exposure experiment. In preliminary experiments, clay-materials tend to increase survivability of microorganisms under irradiation of heavy ion beam and other radiation. In this paper, we discuss current status of exposure experiment of microorganisms defined for the Tanpopo mission.