Space Exposure of Amino Acids and Their Precursors in the Tanpopo Mission Using the International Space Station

Trans. JSASS Aerospace Tech. Japan Vol. 12, No. ists29, pp. Pp_1-Pp_6, 2014 Original Paper

1, 2) 3) 4) 5) 1) By Kensei KOBAYASHI , Hajime MITA , Hikaru YABUTA , Kazumichi NAKAGAWA , Yukinori KAWAMOTO , 1) 1) 6) 7) 8) 9) Takeo KANEKO , Yumiko OBAYASHI , Kazuhiro KANDA , Satoshi YOSHIDA , Issay NARUMI , Eiichi IMAI , 10) 11) 2, 11) 10) Hirofumi HASHIMOTO , Shin-ichi YOKOBORI , Akihiko YAMAGISHI and Tanpopo WG

1)Yokohama National University, Yokohama, Japan 2)National Institutes of Natural Sciences, Tokyo, Japan 3)Fukuoka Institute of Technology, Fukuoka, Japan 4)Osaka University, Toyonaka, Japan 5)Kobe University, Kobe, Japan 6)University of Hyogo, Kamigori-cho, Japan 7)National Institute of Radiological Sciences, Chiba, Japan 8)Toyo University, Itakura-machi, Japan 9)Nagaoka University of Technology, Nagaoka, Japan 10)Institute of Space and Astronautical Science, JAXA, Sagamihara, Japan 11)Tokyo University of Pharmacy and Life Science, Hachioji, Japan

(Received June 22nd, 2013)

A wide variety of organic compounds have been found in space, and their relevance to the origin of life is discussed. Interplanetary dust particles (IDPs) are most promising carriers of extraterrestrial organic compounds, but presence of bioorganic compounds are controversial since they are so small and were collected in the terrestrial biosphere. In addition, IDPs are directly exposed to cosmic and solar radiation. Thus, it is important to evaluate the stability of organics in IDPs in space environment. We are planning a novel astrobiology mission named Tanpopo by utilizing the Exposed Facility of Japan Experimental Module (JEM/EF) of the International Space Station (ISS). Two types of experiments will be done: Capture experiments and exposure experiments. In the exposure experiments, organics and microbes will be exposed to the space environments to examine possible alteration of organic compounds and survivability of microbes. Selected targets for the exposure experiments of organic compounds are as follows: Amino acids (glycine and isovaline), their possible precursors (hydantoin and 5-ethyl-5-methyl hydantoin) and complex precursors “CAW” synthesized from a mixture of carbon monoxide, ammonia and water by proton irradiation. In addition to them, powder of the Murchison meteorite will be exposed to examine possible alteration of meteoritic organics in space. We will show the results of preparatory experiments on ground by using a UV lamp, a 60Co source, synchrotron facilities, and a heavy ion irradiation facility.

Key Words: Amino Acid Precursors, Exposure, Origins of Life, Interplanetary Dust Particles, International Space Station

1. Introduction We are planning a novel astrobiology mission named Tanpopo by utilizing the Exposed Facility of Japan It has been reported that a wide variety of organic Experimental Module (JEM-EF) on the International Space compounds are contained in carbonaceous chondrites and in Station (ISS). Two types of experiments will be done in the comets. Their relevance to the emergence of terrestrial life is Tanpopo Mission: Capture experiments and exposure widely discussed. It was suggested that more organic experiments. In order to collect cosmic dusts (including carbons were delivered to the early Earth by interplanetary IDPs) on the ISS, we are going to use extra-low density 1) dust particles (IDPs) than by meteorites or comets . IDPs aerogel, since both cosmic dusts and ISS are moving at 8 km (or micrometeorites (MMs)) have been collected in ocean s-1 or over. We have developed novel aerogel whose density sediments, Antarctic ices, and air in stratosphere. Though is 0.01 g cm-3. In the exposure experiments, organics and presence of bioorganic compounds in IDPs/MMs is expected, microbes will be exposed to the space environments to it is difficult to judge it since they are so small and were examine possible alteration of organic compounds and collected in the terrestrial biosphere. Thus it would be of survivability of microbes. Here we will report on the importance to collect IDPs out of the terrestrial biosphere. selection of organic compounds for the space exposure, and

Pp_1 Trans. JSASS Aerospace Tech. Japan Vol. 12, No. ists29 (2014) the results of preparatory experiments on ground. solar radiation (UV, X-rays) before the delivery to the Earth. A number of amino acids were detected in water extract of We examined possible alteration of amino acids, their carbonaceous chondrites. It is controversial whether precursors and nucleic acid bases in interplanetary space by meteorites contain free amino acids or amino acid precursors. irradiation with high-energy photons and heavy ions.

When dusts are formed from meteorites or comets in A mixture of CO, NH3 and H2O was irradiated with interplanetary space, they are exposed to high-energy particles high-energy protons from a van de Graaff accelerator (TIT, and photons. In order to evaluate stability and possible Japan). The resulting products (hereafter referred to as alteration of amino acid-related compounds, we chose amino CAW) are complex precursors of amino acids. CAW, amino acids (glycine and isovaline) and hydantoins (precursors of acids (DL-isovaline, glycine), hydantoins (amino acid amino acids), and products of proton irradiation of a mixture precursors) and nucleic acid bases were irradiated with of CO, NH3 and H2O (CAW; containing high molecular continuous emission (soft X-rays to IR; hereafter referred to as weight precursors of amino acids2)). soft X-rays irradiation) from BL-6 of NewSUBARU We performed ground simulation experiments by using synchrotron radiation facility (Univ. Hyogo). They were also accelerators (HIMAC, NIRS, Japan and NewSUBARU, irradiated with heavy ions (eg., 290 MeV/u C6+) from HIMAC University of Hyogo, Japan), which showed that amino acid accelerator (NIRS, Japan). precursors were much more stable than free amino acids After soft X-rays irradiation, water insoluble materials were against radiation. The ground simulation also showed that formed. Recovery ratios of amino acid precursors (CAW and solar UV is more lethal than cosmic rays for organic hydantoins) were higher than free amino acids after irradiation compounds in interplanetary space. with either soft X-rays or heavy ions. Nucleic acid bases The Tanpopo Mission is the first Japanese astrobiology showed higher stability than free amino acids and their space experiment, which is now scheduled to start in 20143). precursors. Samples will be retrieved 1-3 years after launch. We can Complex amino acid precursors with high molecular expect to have the first IDPs sampled in space to see what weights could be formed in simulated dense cloud kind of organics can be delivered by IDPs. In addition to this environments. They would have been altered in the early capture experiments, we are going to expose selected organic solar system by irradiation with soft X-rays from the young compounds and meteorite powders to space environments to Sun, which caused increase of hydrophobicity of the organics examine stability and alteration of possible extraterrestrial of interstellar origin. They were taken up by parent bodies of organic compounds in space. This exposure experiment is meteorites or comets, and could have been delivered to the similar experiments of PROCESS that was performed within Earth by meteorites, comets and cosmic dusts. Cosmic dusts the EXPOSE-E mission on board of the ISS4). A special were so small that they were directly exposed to the solar feature of our experiment is that amino acid precursors, radiation, which might be critical for the survivability of especially high molecular weight complex organics will be organics in them. The stability of IDPs’ organic compounds in exposed in addition of free amino acids as EXPOSE-E. In this space environments will be tested in the exposure experiments paper, we described objectives of the organics-exposure in the Tanpopo Mission. experiments in the Tanpopo Mission, and showed preliminary results of ground simulation experiments for the preparation 3. Ground Simulation of Alteration of Amino of the mission, together with experimental setups in space. Acid-Related Compounds in Earth Orbit

2. Origins of Organic Compounds in IDPs 3.1. Selection of target molecules It has been shown that amino acid precursors can be formed 5-8) It was suggested that organics in extraterrestrial bodies such in interstellar environments , and that amino acids or their 9,10) as meteorites, comets and IDPs were originally formed in ice precursors are present in carbonaceous chondrites . It was also reported that glycine was found in cometary dusts mantles of interstellar dusts in dense cloud, since isotopic 11) studies of organic compounds in meteorites and comets returned by the Stardust Mission . Thus it is possible that 4) IDPs that has been ejected from asteroids or comets have suggested that they were formed in quite cold environments . amino acids or their precursors. Among a great number of Irradiation of frozen mixture of possible interstellar molecules amino acids found in carbonaceous chondrites, we selected including CO (and/or CH3OH), NH3 and H2O with 5,6) 7,8) glycine and isovaline to study the stability of amino acids in high-energy particles or ultraviolet light gave amino acid space. The former is one of the simplest and the most precursors (molecules that give amino acids after hydrolysis) abundant protein amino acids. The latter is non-protein with high molecular weights. Such complex organic amino acids and enantiomeric excesses were reported in molecules were taken in planetesimals or comets in the early isovaline extracted from carbonaceous chondrites12). Their solar system. Prior to the generation of the terrestrial life, possible precursors, hydantoin and 5-ethyl-e-methyl hydantoin extraterrestrial organics were delivered to the primitive Earth were also added to the target list, together with complex by such small bodies as meteorites, comets and space dusts. amino acid precursors, CAW. These organics would have been altered by cosmic rays and

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Table 1. Estimated recoveries after 1 year irradiation in Earth Orbit. UV irradiation Cosmic rays Heat Total 㻌 172 nm 60Co J-ray Carbon ion 100 oC 㻌 Glycine 2 × 10-5 1.0 1.0 1.0 2 × 10-5 Isovaline 3 × 10-5 > 0.99 > 0.99 1.0 3 × 10-5 Hydantoin 0.29 1.0 1.0 1.0 0.29 Ethylmethylhydanotin 0.72 > 0.99 > 0.99 >0.99 0.72 Complex organics (CAW) 0.36 1.0 1.0 1.0 0.36

3.2. Irradiation of target molecules with UV, J-rays and international space station (EF/ISS). Here the flux of VUV -2 -1 heavy ions on ISS orbit was estimated to be 0.12 J m s for 120 nm to In the space environments, UV-light and cosmic rays 200 nm radiation13). Thus, the maximum yearly dose of 3 -2 (high-energy ions and J-ray) will cause the alteration of VUV172 nm in LEO was estimated to 3.8 × 10 kJ m . However organic compounds. Therefore, experiments to examine JEM-EF will not always be oriented towards the sun, and possible photolysis and radiolysis of organic compounds in there will be shadowing by other parts of the ISS, e.g. solar space environments were performed. panels. The actual UV dose could be calculated with the In order to examine the stability of the target molecules record of ISS orbit. In addition, we will monitor the total against VUV, Xe-excimer lamp (at 172 nm; Ushio standard VUV dose with an alanine dosimeter, which will be explained type excimer light emission unit) was used. Solution of later. exposure samples were added into the small hole (1 mmI) on It can be seen that the most fatal factor for organic a SUS plate and dried under reduced pressure. Then the plate compounds in low Earth orbit (LEO) is UV, and effects of the was placed in the vacuum chamber and were irradiated for 6.2 other factors (cosmic rays and heat) would be negligible. We h at 4 × 1014 photons s-1 cm-2 and the irradiation was can expect that appreciable percentage of amino acid equivalent for 4 days irradiation around the ISS orbital. After precursors would survive after 1 year’s exposure in LEO, irradiation, samples were extracted with water and analyzed while very limited part of the original free amino acids would by HPLC. be recovered. We also irradiated the target molecules with synchrotron radiation soft X-rays at NewSUBARU BL06 (University of 4. Exposure of Meteorite Grains for Understanding of Hyogo, Japan), with J-rays from a 60Co source (TARRI, JAEA, Space Weathering Effect on Asteroidal Regolith Japan) and with carbon ion beam (290 MeV/u) at the HIMAC biology beam line (NIRS, Japan). In each irradiation Space weathering on the surface regolith of asteroids could experiment, amino acids or their precursors were irradiated in have been one of the important processes for chemical a solid state. Thermal stability at 100°C of the compounds evolution in the early Solar System. However, meteorite were also tested. samples are lack of asteroid surface information. For the first 3.3. Stability of amino acids and their precursors against time, the preliminary examination of Itokawa asteroid high-energy photons and particles particles returned by Hayabusa mission has revealed the 14) J-Rays and heavy ion beam irradiation with dose of ISS evidence of space weathering on the mineral particles and environment for one year induced little decomposition of the irradiation history of the asteroid regolith15). The space organic compounds. However, UV irradiation was critical for weathering effect on organic compounds has been unknown organic compounds. Although almost all glycine and isovaline since organic compounds have not been detected from were decomposed, recovery of hydantoin, 5-ehtyl-5-methyl Itokawa particles16), but more information about these hydantoin and CAW were approximately 29 %, 72%, and 36% processes is expected from future asteroid sample return respectively, with UV dose of ISS environment for one year. missions, such as Hayabusa-2, OSIRIS-REx, and Marco Amino acids precursors (hydantoins and CAW) were more Polo-R, which will sample the surface regolith of stable than free amino acids in space environments. carbonaceous asteroids. Soft X-rays irradiation experiments showed the same After irradiation of olivine pellets covered by polystyrene tendency: Free amino acids (glycine and isovaline) with energetic ions, Kanuchova et al.17) have shown changes decomposed more rapidly than their precursors (hydantoins in their UV-Vis-NIR reflectance spectra. However, the and CAW). composition of polystyrene is quite different compared to that Table 1 shows estimated recovery ratios after 1 year’s of organic materials in asteroids (meteorites), and thus it will exposure to space environments in the exposed facility of the be necessary to examine more realistic samples. In the

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Fig. 1. An apparatus for space exposure experiments of microbes and organic compounds in Tanpopo mission. This is a rectangular Fig. 3. Absorption spectra of alanine film. An arrowshows the solid of 100 mm × 100 mm × 20 mm. It can divide into 20 cut-off wavelength of SiO2. independent small chamber and we can independently use each chamber (Fig. 2). compositions will be compared with those of pre-exposed meteorite samples. De Gregorio et al.18) has demonstrated the increase of the isotopic ratio of deuterium to hydrogen (D/H) of polymer resins after electron irradiation. Dworkin et al.19) has synthesized organic vesicular structures by UV photolysis of interstellar ice analogs with a repetitive warming-freezing process. According to these experiments, the alteration of chemical and/or morphologic compositions of meteoritic organics will be expected after the experimental space weathering. Finally, it will be expected to learn the role of minerals for the alteation of organics in meteorite matrix, which is a complementary study with SEVO experiment in O/OREOS mission which investigates the photocatalytic role 20) Fig. 2. The cross section of a unit cell. An MgF2 (or quartz) window of mineral surface . with 16mm in diameter is attached at the top of the unit, and 0.3 Pm filter is at the bottom to contain the microbe while the sample is 5. Exposure Facility for the Tanpopo Mission exposed to the space vacuum. An apparatus for exposure experiments is shown in Fig. 1. This is a rectangular solid of 100 mm × 100 mm × 20 mm. It Tanpopo project, we propose to conduct an exposure can divide into 20 independent small chamber and we can experiment of meteorite grains on ISS in order to understand independently use each chamber. The cross section of a the space weathering alteration of molecular, isotopic, and small chamber is shown in Fig. 2. A MgF2 window of 16mm morphological compositions of organic materials. The Low in diameter is attached at the top of the small chamber, and a Earth Orbit environment provides similar conditions as those filter of 0.3 mm is at the bottom. We can expose some acting on the surface regolith, e.g., multiple irradiation samples, including organic compounds and microorganisms, energies (e.g., UV, radiation) and temperature cycle in sunrise without contamination of surroundings. and sunset, which are difficult to reproduce in a laboratory experiment. For a sample preparation, suspended Murchison 6. Vacuum Ultraviolet Dosimetry and Photochemistry of meteorite particles in water will be dropped and fixed onto a Alanine Film silicon nitride membrane window TEM grid and the grid will be placed on the exposure plate. After 1-3 years of exposure at In order to develop the vacuum ultraviolet dosimeter, it is ISS, the returned samples will be analyzed by micro-X-ray necessary to find material with a main absorption in the absorption near edge structure (XANES), transmission vacuum ultraviolet (VUV) region. Here we will try an electron microscope (TEM), and nano-secondary ion mass alanine film deposited on a quartz or MgF2 windows. Because spectrometry (SIMS). The obtained molecular and isotopic absorption cross-section is negligibly small at the wavelength region longer than 200 nm as shown in Fig. 3, this alanine

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Fig. 4. 172 nm photolysis curve of alanine film. Lamp intensity 15 -1 I0 was 5.2 x 10 photons s . dosimeter is sensitive at the region of 160 < O < 190 nm when we chose high quality SiO windows such as suprasil quartz of which transmission is 30 % at 160 nm. Fig. 5. Schematic presentation of alanine VUV dosimeter. a: According to the photolysis experiment with 172 nm Mesh, b and e: Quartz windows, c: alanine film and d: Coating 21) excimer lamp by Izumi et al. , alanine film was decomposed material. as shown in Fig. 4 with the rate constant of k =1.8 × 10-18 compare the stability between free amino acids and amino photon-1; dn/dt = -knI , where n the number of survived 0 acid precursors in space. In addition, we are going to study alanine molecules and I the number of absorbed photons per 0 the alteration processes of extraterrestrial complex organic unit time. Using these data, we will develop a VUV dosimeter as shown in Fig. 5. In the figure, the mesh was used to compounds in space. guard and the coating material is used to prevent the We selected 2 free amino acids (glycine and isovaline) and 3 amino acid precursors (hydantoin, 5-ethyl-5-methyl sublimation loss of alanine molecule from the film. hydantoin, and complex amino acid precursors “CAW” Survival rate of the alanine film after irradiation at the synthesized from CO, NH and H O by proton irradiation. location of the international space station was roughly 3 2 They will be exposed to solar VUV and cosmic radiation on estimated from the solar irradiance spectrum observed by 13) JEM-EF for 1-3 years. Powder of the Murchison meteorite satellite and from an appropriate attenuation factor 0.015 by will also be exposed. Dose will be monitored with the the mesh and a neutral density filter, to be 70, 49 and 34 % alanine VUV dosimeter. after one, two and three years, respectively. After the laboratory simulation experiments, we estimate Photochemical reaction will be studied through the analysis that at least amino acid precursors will survive after a few of returned samples. One of important target molecule is years’ exposure in space. Detailed analysis of the exposed alanylalanine. According to Izumi et al. 21), quantum yield of samples after return to Earth will contribute to the alanylalanine production was roughly estimated to be 1.3 × understanding of the roles of extraterrestrial organics in 10-3 photon-1 at the beginning stage of irradiation. Detection of chemical evolution and generation of life on the Earth or alanylalanine is the direct evidence of chemical evolution elsewhere. resulted from solar irradiation at the space. Acknowledgments 7. Conclusions The authors thank to Dr. Katsunori Kawasaki, Dr. Yoshiyuki Oguri, Dr. Hitoshi Fukuda (Tokyo Institute of The Tanpopo Mission is the first astrobiological mission by Technology), for their kind help in proton irradiation utilizing ISS/JEM. Among a number of subthemes of the experiments. They also express their thanks to Dr. Hajime Tanpopo Mission, “exposure of organic compounds in space” Yano, JAXA/ISAS for his helpful discussion. aims to test the hypothesis that extraterrestrial organics played The present work was partly supported by JSPS KAKENHI importantd deliver organic compounds more safely than large (Grant No. 24654181 for KK and Grant No. 22340166 for comets and meteorites, but they had been exposed to strong MH) and by JAXA Space Utilization WG program. A part of solar and cosmic radiation in interplanetary space. Amino the present work was performed in the research project with acids in free forms are not so stable against radiation and heat, Heavy Ions at NIRS-HIMAC. but their precursors are much more stable than free amino acids. In the present subtheme of the mission, we will

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