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Formation of amino acids in interstellar space was experimentally examined. A mixture of CO (or CH₃OH), NH₃ and H₂O was irradiated with high energy particles or g-rays. A wide variety of amino acids were detected in the products after acid-hydrolysis. It was suggested that complex precursors of amino acids can be formed in interstellar dusts. When the amino acid precursors were irradiated with circular polarized UV from a synchrotron, enantiomeric excess of alanine was observed in the hydrolysate of the product.

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Stability of amino acids and related compounds against radiation, impacts and heat was examined. Complex amino acid precursors formed from a mixture of CO, NH₃ and H₂O by proton irradiation showed much higher stability than free amino acids. Complex interstellar organic compounds were promising as a source of the first terrestrial biosphere for their stability in space and in hydrothermal systems of primitive Earth.

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We examine how circum-stellar disks affect the stellar wobble caused by the planet's gravity. The disk's asymmetry moves not only the position of the mass center of the star-disk-planet system but also the position of the photo-center of the light from the system. The photo-center shift induced by the disk is significant compared to the planet's effect if the planet's mass is as small as Jupiter. However, astrometry using interferometers is not sensitive to the extended disk light, and thus the effect of the disk light is greatly reduced.

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[in Japanese]

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[in Japanese]

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Recent studies (Chiang & Goldreich, 1997; Chiang et al., 2002) imply that the interior of the solar nebula is shadowed from direct exposure to sunlight, so that the H2O ice is prevented from sublimation even at the formation zone of terrestrial planets. In such circumstances, the planetesimals formed through the gravitational instability are mainly composed of ice. It is possible that the H2O in the icy planetesimals contributes the supply of water to the terrestrial planets. In this study, we examine the evolution of such icy planetesimals considering their sublimation and collisional growth.

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We investigate the migration mechanism of proto-Neptune using numerical calculation.Jupiter scatters only inner planetesimals,and forced to out of Neptune's gravity.The result of this scattering, net angular momentum that Neptune gains is positive.So Neptune migrates outward.In this reserch, we investigate the parameter dependence of migration velocity of proto-Neptune. The main parameters are distance between two planets and the mass of them. We calculate the torque between planets and planetesimals for more accurately result.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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We performed numerical simulations of dust growth and settling in turbulent protoplanetary disks and spectral energy distributions from the disks. We adopted the alpha model turbulence and assumed the turbulence is homogeneous and isotropic. Our results shows that turbulence accelerates grain growth especially in the inner part of the disk. Because of the accelerated grain growth, micron-sized grains decreases much more rapidly than the case of laminar disks.In the outer part of the disk, on the other hand, turbulence does not affect grain growth much.

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We study processes of dust growth in the Jovian subnebula, the first stage of the Galilean satellite formation. To form satellitesimals, the time of dust growth is shorter than that of dust falling to Jupiter. We perform a numerical calculation for the growth time taking into account the effect of imperfect sticking. Comparing it to the falling time, we discuss the possibility of satellitesimals formation. The result indicates that the formation is difficult without considering the effect of dust concentration or the mechanism to increase critical velocity for sticking.

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Some comets show crystalline silicate feature in the mid-infrared spectra. We have not solved the problem that such icy bodies borne in the low temperature include high temperature products such as crystalline silicate. The present status of this problem is described.

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We investigate the ablation processes of three bolides including one meteorite fall using the amplitude data. After converting the observed amplitudes of the ground displacements to the pressure amplitudes of the shockwaves (Ben-Menahem and Singh, 1981), we estimate the meteoroid diameters invoking the formula of ReVelle (1976). The results reveal the temporal changes in the meteoroid diameters along the trajectories.

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In the atmospheres of "Hot Jupiters", the absorption of the radiation from the parent star by the possible iron/silicate cloud particle, which is produced in the upward motion of the air, may drive a positive feedback loop that is somewhat similar to those operating in convective clouds in the earth or Jovian atmosphere. Here, we examine a simple linear theory on those "radiative convective instability", which shows that unstable stationary(propagating) disturbance exists if the radiative interaction of the clouds heat (cool) the atmosphere.

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[in Japanese]

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²⁶Al in a meteorite is measured in order to clarify terrestrial age of an antarctic meteorite, secular change of fall frequency, the problem of pairing, etc. As a measuring method, it is carrying out by two methods, ultra low background gamma-ray counting system and AMS. Here, while explaining both measuring methods, the adjustment of the measured value between both methods is also reported.

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Information of the lunar remote-sensing (Clementine and Lunar Prospector) and sample return (e.g., Apollo) missions are integrated and discussed to understand lunar early evolution and crustal formation processes.

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[in Japanese]

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[in Japanese]

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Surface roughness and backscattering enhancement of impact fragments are experimentally investigated. Reflected light from the surface of small solar system body shows an enhancement in backward direction, that is attributed to so-called shadow-hiding mechanism and coherent backscattering mechanism of particulate or rough surfaces. The laboratory results are discussed in comparison with the previous results of powdery surfaces and the observational data of backscattering properties of asteroids.

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[in Japanese]

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The degradation states of lunar impact craters are significant information to identify the eruption age of lunar maria. The terrain camera (TC) installed on SELENE will provide high-resolution (10m/pixel from the SELENE 100km altitude) stereo images of the lunar surface that are required on the detailed study of lunar crater morphology. We discuss the possibility of study of lunar crater degradation status by TC data on the basis of the recent results of TC flight model tests.

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[in Japanese]

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The first global remote X-ray and gamma-ray spectrometry have been proposed for the Bepi Colombo mission, to map abundances of major and radioactive elements on the surface of Mercury. The Mercury Planetary Orbiter (MPO) that orbits around the relatively low altitude (400 x 1500 km) appropriate for surface global mapping. We present the outlines of X-ray and Gamma-ray spectrometers that have been designed with new technologies such as the X-ray detector using GaAs array on ASIC as well as the low-power stirling cryostat for pure germanium Gamma-ray detector.

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We present multi-color photometric and spectroscopic observations of C/2002 CE10. The derived diameter and the geometric albedo are 11.4 (+0.9/-0.8)km and 0.02 (+0.006/-0.003), respectively. From the photometric analysis in BVRI, its surface color are in the taxonomy of D-type. From the time-resolved differential photometry, rotational period is determined to be 8.187 hrs.Consequently, this object is very dark, red and a very inactive cometary nucleus. Information on such minor body allow us to investigate evolutional link between comets and asteroids.

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There are two important things about the hydrodynamic escape of an atmosphere due to irradiation of the Solar UV. One is the relation between intensity of the Solar UV and stellar age. The other is the efficiency of the conversion of the incoming Solar UV energy to the potential energy of escaping gas. I compile the data of the Extreme Ultraviolet Explorer and investigated the relation between intensities of the solar UV and stellar ages. I develop a numerical code to solve the time-dependent hydrodynamic equations, and compare the numerical results with analytical solutions.

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Infrared spectra of plagioclase feldspar were measured using FT-IR spectrometer.The systematic spectral variation depending on the chemical composition of samples was observed. The dust formation process in the circumstellar region of oxygen-rich stars will be discussed.

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Titan, the largest satellite of Saturn, has a dense atmosphere containing nitrogen and methane, where hydrocarbons and nitriles are present as minor constituents. We irradiated a mixture of methane and nitrogen with high energy protons to simulate reactions in lower Titan atmosphere . Complex organic compounds (tholin) was formed, and hydrolysates of tholin gave amino acids in high yields. The present results suggest that bioorganic compounds can be formed from tholin and water ice delivered by comets.

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Europan visco-elastic deformation due to its non-synchronous rotation is calculated. The solutions for the period of the rotation and the viscosity of the shell are investigated on the basis of this calculation. These solutions satisfy the pre-existing constraints and explain the tidal stress field consistent with the orientations of the lineaments. The solutions range between 1 and 100 My in the period and between 10²¹ and 10²³ Pa.s in the surface viscosity.

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Under the environment of a high vacuum like the moon or an asteroid, it can be considered that the thermal properties can be assumed by two states, temperature and porosity. In the case of high porosity, as a process of heat conduction, contribution by radiation becomes large. If The major goal of this study is to calculate such models for atmosphereless bodies and to compare these calculation and radio observational data.

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From our results of experimental study of cratering formation on ice-rock mixture targets, crater volume decreases with increasing silicate content by 50wt%. Because secondary craters made by low velocity impacts of the ejecta from craters are small in scale, the laboratory results can be applied to them. We study whether the distribution of epithermal neutron flux measured by Mars Odyssey correlates with the size frequency distribution of secondary craters on Mars and discuss whether the size frequency distribution of Martian secondary crater is an indicator of the distribution of water ice.

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One strategy in the search for life is the study of atmospheric spectral features for signs of severe disequilibrium chemistry that could be indicative of biological activity.In order to investigate the feasibility of observation, we have calculated the synthesized infrared spectra for several terrestrial-type atmospheres with clouds, which represent inhabited planets, our Earth, and other terrestrial planets including early Earth-type planets.

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To apply for possible asteroid interior exploration in the future, this study aims to better understand basic physical property of granular materials such as space exposed regolith regarding elastic waves. We have discovered speed of sound in regolith simulants made of glass bead is independent on porosity but dependent on grain size in the 40 - 220 micrometers range. Although actual cases are more complexed, these results suggest the possibility of using velocity measurement of elastic wave of to investigate regolith size on asteroidal surfaces.

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[in Japanese]

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Dust shape is assumed as a sphere. In this study, we analyze how the irregular particle contributes to the silicate feature. We used a fractal aggregate (BPCA) as an irregular particle. We apply Mie theory for the sphere, and DDA code for the fractal aggregate to compute the absorption efficiencies. As the result, no significant feature exists, the temperature grain is derived and the silicate features are revealed near a wavelength 10micronmeters for both sphere and fractal aggregate. We found when the radius is larger the feature appears in fractal aggregate while in the sphere.

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We have modeled the density and temperature profiles as well as the spectral energy distributions of protoplanetary disks, taking into account the fractal structure of dust grains. As a result of comparing the models for the dust particles of fractal aggregates and compact spheres, we have found that if the disk consists of 3 micron-sized dust particles, the temperature at the disk surface is higher in the model of the fractal aggregates, which results in stronger dust continuum emission.

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In order to reproduce Si isotopic ratios in presolar grains from supernovae, we investigate Si isotopic ratios in the mixtures of supernova ejecta. We calculate detailed nucleosynthesis of the supernova explosions using He star models. When we consider the mixing of Ni, Si/S, He/C, and He/N-layers, Si isotopic ratios of the mixtures of 3.3 M supernova model and 8 M hypernova model well reproduce those of presolar grains from supernovae.

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[in Japanese]

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[in Japanese]

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White lithic clasts in the Begaa LL3 chondrite are about 3mm in apparent diameter. The major constituents are magnesian olivine, magnesian low-Ca pyroxene, anorthitic plagioclase. The mineralogy of the clast is similar to those of plagioclase-rich inclusions but different in the absence of metal and sulfides. The oxygen compositions of the clasts are essentially identical to the Earth value and homogeneous within the clast. The O-compositions suggest that the clasts have originated from the precursor or in the ambient gas isotopically similar to the Earth.

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[in Japanese]

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We investigated that the possibility of the depletion by the ejection of iron inclusions during the melting of chondrules, through performing the calculation of the stability of an melted iron inclusion on the surface of a melted chondrule.

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Shock-wave heating model is one of the plausible models for chondrule formation, though the generation of shock waves has not been understood clearly. In this study, we examine whether the shock waves in the solar nebula are generated by X-ray flares. We have conducted MHD simulations of X-ray flares, and found that shock waves of several tens km/s of velocity could be generated at the upper layer of the solar nebula. Such shock conditions at the upper layer of the nebula seem to be appropriate for chondrule formation.

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We examined behavior of a partially molten dust particle with shock-wave heating model. We analytically solved hydrodynamical equations for the core-mantle structure particles with linear approximation, and obtained the deformation, internal flow, and pressure distribution. Also we obtained conditions in which liquid mantle may be stripped off from the solid core. When a dust particle has a dense structure and the dust radius is larger than about 5mm, the stripping is expected to occur before the entire dust particle melts. When a dust is porous, the critical size becomes about 2mm.

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[in Japanese]

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