橋本 博文

「たんぽぽ」計画の中で予定されている、大気圏突入前に宇宙塵を捕獲し地球に運び込まれる有機物分析と、生体関連有機物の宇宙環境での安定性を調べる曝露実験という２つのサブテーマに関わる地上模擬実験で得られた結果について報告する。二段式軽ガス銃を用いた宇宙塵捕獲実験では、不溶性有機物として存在するアミノ酸は、遊離のアミノ酸と比べ安定性が高いことが裏付けられたとともに、超低密度シリカエアロゲルを用いることにより宇宙塵を変成が抑制された条件で捕獲できることを確認した。また、原子状酸素による有機物の変成を調べるために、アミノ酸やタンパク質を曝露用アルミ板に詰め、曝露模擬実験を行った。AO照射量 8.2 × 1019 atoms cm-2の時、標準試料であるカプトン膜では約10%の重量減少が、芳香族炭化水素などには着色が観測された。

Manned Mars exploration, especially for extended periods of time, will require recycle of materials to support human life. Here, a conceptual design is developed for a Martian agricultural system driven by biologically regenerative functions. One of the core biotechnologies function is the use of hyper-thermophilic aerobic composting bacterial ecology. These thermophilic bacteria can play an important role in increasing the effectiveness of the processing of human metabolic waste and inedible biomass and of converting them to fertilizer for the cultivation of plants. This microbial technology has been already well established for the purpose of processing sewage and waste materials for small local communities in Japan. One of the characteristics of the technology is that the metabolic heat release that occurs during bacterial fermentation raises the processing temperature sufficiently high at 80-100 degrees C to support hyper-thermophilic bacteria. Such a hyper-thermophilic system is found to have great capability of decomposing wastes including even their normally recalcitrant components, in a reasonably short period of time and of providing a better quality of fertilizer as an end-product. High quality compost has been shown to be a key element in creating a healthy regenerative food production system. In ground-based studies, the soil microbial ecology after the addition of high quality compost was shown to improve plant growth and promote a healthy symbiosis of arbuscular mycorrhizal fungi. Another advantage of such high processing temperature is the ability to sterilize the pathogenic organisms through the fermentation process and thus to secure the hygienic safety of the system. Plant cultivation is one of the other major systems. It should fully utilize solar energy received on the Martian surface for supplying energy for photosynthesis. Subsurface water and atmospheric carbon dioxide mined on Mars should be also used in the plant cultivation system. Oxygen and food production for human thus rely on local Martian resources. A tree growing subsystem will also give an interesting feature to Martian agriculture. In addition to producing excess oxygen, trees' rigid body will provide structural material, which can be used for habitat construction. The combination of hyper-thermophilic aerobic composting, plant cultivation, and tree growing with utilizing in-situ natural local resources available on Mars can provide important elements which can enable space agriculture on Mars. (c) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

Engineering a life-support system for living on Mars requires the modeling of heat and mass transfer. This report describes the analysis of heat and mass transfer phenomena in a greenhouse dome, which is being designed as a pressurized life-support system for agricultural production on Mars. In this Martian greenhouse, solar energy will be converted into chemical energy in plant biomass. Agricultural products will be harvested for food and plant cultivation, and waste materials will be processed in a composting microbial ecosystem. Transpired water from plants will be condensed and recycled. In our thermal design and analysis for the Martian greenhouse, we addressed the question of whether temperature and pressure would be maintained in the appropriate range for humans as well as plants. Energy flow and material circulation should be controlled to provide an artificial ecological system on Mars. In our analysis, we assumed that the greenhouse would be maintained at a subatmospheric pressure under 1/3-G gravitational force with 1/2 solar light intensity on Earth. Convection of atmospheric gases will be induced inside the greenhouse, primarily by heating from sunlight. Microclimate (thermal and gas species structure) could be generated locally around plant bodies, which would affect gas transport. Potential effects of those environmental factors are discussed on the phenomena including plant growth and plant physiology and focusing on transport processes. Fire safety is a crucial issue and we evaluate its impact on the total gas pressure in the greenhouse dome.

The major purpose of manned exploration on Mars is to find extraterrestrial life in either extant or extinct forms. Space agriculture is necessary to carry out such manned exploration on Mars in the long term, as it is very reasonable method to provide human beings with foods and to recycle materials. A conceptual design of space agriculture for habitation on Mars is developed by Space Agriculture Saloon. We design confined greenhouse dome to create living environment on Mars based on the constraints from planetary protection together with humanistic requirements and wellness. Hyper-thermophilic aerobic composting microbial ecology is proposed to process metabolic wastes and inedible biomass for recycling materials. A great number of bacteria were brought by human beings from the Earth to Mars. It is eventually a keen issue whether terrestrial life forms brought into Mars could prevent the forward contamination on exploration sites or not. When we plan unmanned and manned exploration of Mars, whole scenario should be carefully planned based on the requirements of astrobiology. We should avoid contamination of Mars before we could find life forms exist and well characterized, or confirm that life have never evolved on Mars. We propose an extension of the planetary protection policy, which has been discussed and issued by COSPAR and IAU at scoping the horizon of manned missions. Any planning of space agriculture or manned exploration should meet such international regulation defined and revised for the new scope.

In order to investigate influence of low pressure on a germination of a plant, the germination rates of white radish, buckwheat and qing-geng-cai were measured under low pressure in pure oxygen. The results of germination experiments show that the germination rate of buckwheat is the highest in three species of plant at 4kPa. The tolerance of buckwheat to the low pressure environment is the highest in this stage. Germination rates of buckwheat were also investigated at different temperature. As a result, the germination rate at 20℃ was higher than that at 25℃.

Artificial greenhouse gases could be used to warm Mars in order to make it habitable. Here we present new laboratory measurements of the thermal infrared absorption spectra of seven artificial greenhouse gases (CF4, C2F6, C3F8, SF6, CF3Cl, CF3Br, CF2Cl2) at concentrations from 10-7 up to unity. We used a radiative-convective multilayer model to compute the warming caused by a mixture of the four fluorine-based greenhouse gases. The results show that for current Mars, C3F8 produces the largest warming: 0.56 K and 33.5 K for partial pressures of 10-3 Pa and 1 Pa, respectively. Averaged over partial pressures from 0.01 to 1 Pa, the range of most interest for planetary ecosynthesis, CF4, C2F6, and SF6 were 17%, 49%, and 48% as effective as C3F8, respectively. The optimal mixture of the four fluorine-based greenhouse gases, taking into account the overlapping of their absorption bands, was 16% more effective than pure C3F8, averaged over the range 0.01 Pa to 1 Pa. Energy balance calculations suggest that the addition of ∼0.2 Pa of the best greenhouse gases mixture or ∼0.4 Pa of C3F8 would shift the equilibrium to the extent that CO2 would no longer be stable at the Martian poles and a runaway greenhouse effect would result. Copyright 2005 by the American Geophysical Union.

Artificial greenhouse gases could be used to warm Mars in order to make it habitable. Here we present new laboratory measurements of the thermal infrared absorption spectra of seven artificial greenhouse gases (CF4, C2F6, C3F8, SF6, CF3Cl, CF3Br, CF2Cl2) at concentrations from 10(-7) up to unity. We used a radiative-convective multilayer model to compute the warming caused by a mixture of the four fluorine-based greenhouse gases. The results show that for current Mars, C3F8 produces the largest warming: 0.56 K and 33.5 K for partial pressures of 10(-3) Pa and 1 Pa, respectively. Averaged over partial pressures from 0.01 to 1 Pa, the range of most interest for planetary ecosynthesis, CF4, C2F6, and SF6 were 17%, 49%, and 48% as effective as C3F8, respectively. The optimal mixture of the four fluorine-based greenhouse gases, taking into account the overlapping of their absorption bands, was 16% more effective than pure C3F8, averaged over the range 0.01 Pa to 1 Pa. Energy balance calculations suggest that the addition of similar to 0.2 Pa of the best greenhouse gases mixture or similar to 0.4 Pa of C3F8 would shift the equilibrium to the extent that CO2 would no longer be stable at the Martian poles and a runaway greenhouse effect would result.

Various organic compounds including complex organic compounds have been detected in comets. Cometary organics are supposed to be formed in interstellar dust (ISD) environments. We examined possible formation of bioorganic compounds in ISDs through simulation experiments and compared with that in primitive Earth atmosphere. It was shown that a wide variety of amino acids were formed in simulated ISD environments in the form of precursors. Pyrimidine bases (uracil, cytosine and thymine) were also formed from the possible interstellar media. These results suggest that comets can bring no less types of bioorganics to planets than those formed in primitive Earth atmosphere. Not only Earth, but also other planetary bodies like Mars and Europa received cometary organics during the late heavy bombardment era. They can be included in possible habitable areas whatever primitive planetary atmosphere they had. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

An ice mantle mixture of carbon monoxide, ammonia (or dinitrogen), and water was irradiated in a highly vacuumed cryostat with ultraviolet light at 10 K. The primary products were identified as amino acid precursors when ammonia was used as a nitrogen source, which strongly suggested abiotic formation of bioorganic compounds in ice mantle of interstellar dusts in molecular clouds. The present results have significant implication for organic formation in interstellar dust ice mantles and the energetics of nitrogen fixation.

The formation of prebiotic organics in outer space has been simulated on ground. In order to verify abiotic formation of such compounds in earth orbit, the concept of cosmobiology experiment was developed. Simulated interstellar ice over dust grains is exposed to vacuum ultraviolet light and other space environment to induce organic formation. A system configuration and its engineering specification were,determined to meet the scientific requirements, which were defined by the ground based study. The system consists of cryogenics to keep volatile species solidified, optics to filter and amplify the ultraviolet portion of the solar light for the accelerated irradiation of sample, and analysis subsystem to evaluate formation of organics in-situ together with post flight analysis of involatile products in trace. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

The survival conditions of microorganisms under extremely severe environment are of interest in various areas of biology, sterilization, and space engineering, especially where resistance to microorganisms is concerned. Despite the interest, the resistance to microorganisms under extremely severe environment such as space environment or other planetary environment is not known well. In order to investigate survival conditions of microorganisms under extremely severe environment, surviving fractions for spores and vegetative cells of Bacillus subtilis were surveyed in various chemical species of atmosphere at various pressures and various temperatures, and the dependence on time for surviving fractions was examined. The results show: (i) Surviving fractions depend on chemical species of atmosphere. (ii) At high pressure and high temperature, surviving fractions are low and the resistance of spores is stronger than that of vegetative cells. (iii) Surviving fractions decrease as first-order reaction along with time elapsed.

A hermetically materially-closed aquatic microcosm containing bacteria, algae, and invertebrates was developed as a tool for determining the changes of ecological systems in space. The species composition was maintained for more than 365 days. The microcosm could be readily replicated. The results obtained from the simulation models indicated that there is a self-regulation homeostasis in coupling of production and consumption, which make the microcosm remarkably stable, and that the transfer of metabolites by diffusion is one of the important factors determining the behavior of the system. The microcosms were continuously irradiated using a Co-60 source. After 80 days, no elimination of organisms was found at any of the three irradiation levels (0.015, 0.55 and 3.0 mGy/day). The number of radio-resistance bacteria mutants was not increased in the microcosm at three irradiation levels. We proposed to research whether this microcosm is self-sustainable in space. When an aquatic ecosystem comes under stress due to the micro-gravity and enhanced radiation environment in space, whether the ecosystem is self-sustainable is not known. An aquatic ecosystem shows what happens as a result of the self-organizational processes of selection and adaptation. A microcosm is a useful tool for understanding such processes (Beyers and Odum, 1993). We have proposed researching whether a microcosm is self-sustainable in space. The benefits of this project will be: (1) To acquire data for design of a Controlled Ecological Life Support System, (2) Possibility of microbial mutation in a space station. We report that a hermetically materially-closed microcosm, which could be a useful tool for determining changes of ecological processes in space, was developed, and that the effects of microgravity and enhanced radiation on the hermetically materially-closed microcosm were estimated through measurements on the Earth and simulation models. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

Organic compounds in comets are of interest since they could be the sources of the terrestrial biosphere. They are supposed to be formed in an interstellar dust (ISD) environment. We performed laboratory simulation of the formation of bioorganic compounds in ISD environments: Amino acid precursors were detected in the products after ice mixture of CO (or CH4, CH3OH), NH3 and H2O. The present results should be confirmed in actual space conditions, such as in an exposed facility of JEM. We are designing an apparatus of such exobiology experiments in earth orbit (EEEO). Basic designs proposed for EEEO. remaining problems, and expected outcome will be discussed. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

The Japanese portion of International Space Station offers opportunities to conduct exobiology experiments and observations at its exposed facility. Preparatory studies have been conducted to define proposals for its possible utilization. Research subjects have been proposed from quite diverse fields of exobiology. It ranges from a basic scientific mission, such as a survey on formation and fate of organic materials under space environment, to a part of an engineering project related to quarantine technology for planetary probes dedicated to exobiology exploration. Besides technical feasibility of implementation of those payloads on the space system, scientific assessment is strongly required to elucidate key issues of exobiology conducted in near Earth orbit. Even research facilities in low Earth orbit, although literally in space, give quite a different environment from that of interstellar space in many aspects. Scientific significance of conducting exobiology there should be based on uniqueness of employing microgravity and its synergetic effects with other factors for exobiology. Because of the quite limited chance of executing space experiments, as well as high cost of its execution, proposed subjects should be proved to possess great competitiveness against studies on the ground where space environment could also be well simulated with less cost. An international forum for exobiology might play an important role to formulate prioritized plan and strategy of the discipline. Such a body could orchestrate exobiology in Earth orbit under complementary relationships among scientific endeavors carried on by scientists who participate in collaborative efforts. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

Simulation experiments on ground have shown that "amino acid precursors", which give amino acids after acid-hydrolysis, can be formed when an ice mixture simulating ice mantles of interstellar dust particles (ISDs) is irradiated with high energy particles or UV light. It is strongly suggested that such bioorganic compounds were delivered by comets for the first biosphere on the Earth. It is of great interest to confirme this hypothesis in actual space conditions, such as in an exposed facility of JEM. Fundamental designs for such exobiology experiments in earth orbit (EEEO) will be discussed.

Ecological cultivation capsules (ECC), that is a materially sealed microcosm, composed of primary producers, consumers and bacteria as a decomposer were developed in order to cultivate bacteria without any artificial operation for long duration more than 10 years in space. It is planned to be left on the space station to study the process that bacteria in MIR space station had acquired their resistance to cosmic ray radiation as well as ultra-violet light. As contrasted with the space experiment, bacteria are cultivating in the ECC on the ground to trace the changes of bacteria under the simulated radiation dose in Earth orbit.

A conceptual design was developed for a cosmo-biology experiment. It is intended to expose simulated interstellar ice materials deposited on dust grains to the space environment. The experimental system consists of a cryogenic system to keep solidified gas sample, and an optical device to select and amplify the ultraviolet part of the solar light for irradiation. By this approach, the long lasting chemical evolution of icy species could be examined in a much shorter time of exposure by amplification of light intensity. The removal of light at longer wavelength, which is ineffective to induce photochemical reactions, reduces the heat load to the cryogenic system that holds solidified reactants including CO as a constituent species of interstellar materials. Other major hardware components were also defined in order to achieve the scientific objectives of this experiment. Those are a cold trap maintained at liquid nitrogen temperature to prevent the contamination of the sample during the exposure, a mechanism to exchange multiple samples, and a system to perform bake-out of the sample exposure chamber. This experiment system is proposed as a candidate payload implemented on the exposed facility of Japanese Experiment Module on International Space Station.

The vibrational energy of molecules in phase-changing processes was studied by measuring the infrared absorption spectra using a Fourier transform infrared (FTIR) spectrometer. IR spectra of (NO)(2)(nu(1), nu(4)), CO2(nu(2), nu(3)), N2O(nu(1), nu(2), nu(3)), and C2H2(nu(3),nu(5)) in the gas, cluster, and solid phases were compared. Absorption bands of solid-phase molecules are blue or red shifted from those of gas-phase molecules: but those for the cluster phase are always blue shifted from those for the solid phase. This leads to two kinds of vibrational energy change when the phase changes from gas to solid : blue and red shifts, and red and red shifts of the absorption bands. These results can he explained in terms of the vibrational mechanisms of the epsilon, sigma, and m effects, which characterize the effective potential and mass of molecules.

The infrared absorption spectra of N_2O and CO_2 molecular clusters formed in a supersonic free jet expansion were measured at various source gas pressures and solvent densities. The infrared absorption spectra of N_2O and CO_2 were measured at different positions in the vicinity of the condensate and compared with the monomer and cluster spectra. These spectra are compared with the vibrational spectra of clustering molecules calculated using the molecular dynamics method. The results show that the measured spectra have a distinct difference between the large-size (L) and the small-size (S) clusters. In the case of N_2O, L clusters were observed in a wide range of spatial position, but S clusters were formed in a limited region from the condensate. In the case of CO_2, L clusters were replaced by S clusters at higher pressures. The distance from the condensate at which the S clusters were observed depended on the pressure, and the clustering region of the L clusters was proportional to approximately the cubic power of the mean free path.