[BAO01-P05] たんぽぽ計画におけるアミノ酸およびその前駆体の宇宙曝露：第１報
キーワード：The Tanpopo Mission, Amino acids, Amino acid precursors, Exposed Facility of the International Space Station, Solar ultraviolet light, Origins of life
Since a wide variety of organic compounds including amino acids have been detected in carbonaceous chondrites [1], it is plausible that organic compounds delivered by extraterrestrial bodies played important roles in the generation of terrestrial life. Cosmic dusts (IDPs) are another candidate of carriers of extraterrestrial organics [2]: Chyba and Sagan [3] suggested that cosmic dusts delivered much more organics to the primitive Earth than meteorites and comets. It is difficult, however, to detect bioorganics in cosmic dusts if they are collected in the terrestrial biosphere.
We initiated the first Japanese astrobiology mission on the International Space Station (ISS) named the Tanpopo Mission in 2015. In the mission, we intended to collect dusts flying in low Earth orbit by using ultra-low density silica gel (aerogel), and to expose organic compounds and microorganisms to space environments [4]. One of the major objectives is to examine possible delivery of organic compounds including amino acids by cosmic dusts. Thus amino acids in captured dusts are analyzed, and stability of selected organic compounds (free amino acids and their precursors) is evaluated in the mission. The first sample returned to the Earth in August 2016 after about 1 year’s space exposure. Here we report the first analytical results of the organic exposure experiment in the Tanpopo Mission.
Two free amino acids (glycine, and isovaline) and their possible precursors (hydantoin and 5-ethyl-5-methylhydantoin), together with products by proton irradiation of a gas mixture of 13CO, NH3 and H2O (hereafter abbreviated as CAW) were selected in the organic exposure experiment: CAW is a mixture of complex organic compounds including amino acid precursors [5]. All the organic materials used were labeled with 13C. Aqueous solution of each of these materials was added to one of dimples on an aluminum plate, and dried. Then the surface of the materials was covered with hexatriacontane to avoid scattering. Each plate for space exposure was covered with a SiO2 or MgF2 window. The same kind of plates were prepared for (i) dark controls (exposed in space but no light allowed), (ii) cabin controls (stored in the JEM cabin), and (iii) ground controls.
Alanine thin film was used as a VUV dosimeter based on a dissociation experiment with a 172 nm eximer lamp [6]. Optically stimulated luminescence dosimeter (OSLD) and silver activated phosphate glass dosimeter (RPLD) were used as radiation dosimeters. The dosimeters and the exposure plates were combined together to be an exposure panel, which was attached to an ExHAM module and exposed on the Exposed Facility (EF) of Japanese Experimental Module (JEM) of ISS.
The material in each dimple was collected by using small amount of methanol and water. Amino acids were determined by HPLC (Amino acid precursors and CAW were determined after acid-hydrolysis). The materials were also analyzed by GC/MS and LC/MS.
Preliminary results and discussion will be shown in the poster. We are expecting return of another set of samples in 2017 after 2 years’ exposure.
The authors thank to JAXA, National Institute of Natural Sciences (NINS) Astrobiology Center, and Ministry of Education, Culture, Sports, Science and Technology (MEXT) for their financial supports. We also express our thanks to the members of the Tanpopo Research Team.
[1] K. Kvenvolden et al., Nature, 228, 923-926 (1970). [2] G. J. Flynn, Earth Planets Space, 65, 1159–1166 (2013). [3] C. Chyba and C. Sagan C., Nature, 355, 125-132 (1992). [4] A. Yamgishi et al., Trans. JSASS Space Tech., 7, Tk49-55 (2009). [5] Y. Takano et al., Appl. Phys. Lett., 84, 1410-1412 (2004). [6] Y. Izumi et al., Orig. Life Evol. Biosph., 41, 385-395 (2011).
We initiated the first Japanese astrobiology mission on the International Space Station (ISS) named the Tanpopo Mission in 2015. In the mission, we intended to collect dusts flying in low Earth orbit by using ultra-low density silica gel (aerogel), and to expose organic compounds and microorganisms to space environments [4]. One of the major objectives is to examine possible delivery of organic compounds including amino acids by cosmic dusts. Thus amino acids in captured dusts are analyzed, and stability of selected organic compounds (free amino acids and their precursors) is evaluated in the mission. The first sample returned to the Earth in August 2016 after about 1 year’s space exposure. Here we report the first analytical results of the organic exposure experiment in the Tanpopo Mission.
Two free amino acids (glycine, and isovaline) and their possible precursors (hydantoin and 5-ethyl-5-methylhydantoin), together with products by proton irradiation of a gas mixture of 13CO, NH3 and H2O (hereafter abbreviated as CAW) were selected in the organic exposure experiment: CAW is a mixture of complex organic compounds including amino acid precursors [5]. All the organic materials used were labeled with 13C. Aqueous solution of each of these materials was added to one of dimples on an aluminum plate, and dried. Then the surface of the materials was covered with hexatriacontane to avoid scattering. Each plate for space exposure was covered with a SiO2 or MgF2 window. The same kind of plates were prepared for (i) dark controls (exposed in space but no light allowed), (ii) cabin controls (stored in the JEM cabin), and (iii) ground controls.
Alanine thin film was used as a VUV dosimeter based on a dissociation experiment with a 172 nm eximer lamp [6]. Optically stimulated luminescence dosimeter (OSLD) and silver activated phosphate glass dosimeter (RPLD) were used as radiation dosimeters. The dosimeters and the exposure plates were combined together to be an exposure panel, which was attached to an ExHAM module and exposed on the Exposed Facility (EF) of Japanese Experimental Module (JEM) of ISS.
The material in each dimple was collected by using small amount of methanol and water. Amino acids were determined by HPLC (Amino acid precursors and CAW were determined after acid-hydrolysis). The materials were also analyzed by GC/MS and LC/MS.
Preliminary results and discussion will be shown in the poster. We are expecting return of another set of samples in 2017 after 2 years’ exposure.
The authors thank to JAXA, National Institute of Natural Sciences (NINS) Astrobiology Center, and Ministry of Education, Culture, Sports, Science and Technology (MEXT) for their financial supports. We also express our thanks to the members of the Tanpopo Research Team.
[1] K. Kvenvolden et al., Nature, 228, 923-926 (1970). [2] G. J. Flynn, Earth Planets Space, 65, 1159–1166 (2013). [3] C. Chyba and C. Sagan C., Nature, 355, 125-132 (1992). [4] A. Yamgishi et al., Trans. JSASS Space Tech., 7, Tk49-55 (2009). [5] Y. Takano et al., Appl. Phys. Lett., 84, 1410-1412 (2004). [6] Y. Izumi et al., Orig. Life Evol. Biosph., 41, 385-395 (2011).