We evaluate the spatial variation of venusian surface emissivity at 1.18 um wavelength using multispectral images obtained by the Near-Infrared Mapping Spectrometer (NIMS) on board the Galileo spacecraft. To analyze the NIMS observations, synthetic spectra have been generated by means of a line-by-line radiative transfer program which includes both scattering and absorption. A modulation of emission by the cloud opacities is removed using simultaneously measured 1.74 and 2.3 um radiances.

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North-south asymmetry of steep slopes in middle latitude (30- 50) on Mars suggests differential erosion due to difference of amount of solar insolation between north and south-facing slopes. We estimate spread of formation age of asymmetric slopes by the MOLA data and restrict formation mechanism of the north-south asymmetry.

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In order to investigate scattering greenhouse effect of CO₂ ice clouds and those stability against radiative heating on a CO₂-H₂O atmosphere, we constructed a one-dimensional, radiative-convective model. The our calculations suggest that warm and wet climate is possibly induced by the stable cloud layer with visible optical depth about 1.5 when the atmospheric pressure and the radius of cloud particles are fixed 1 atm and 10 micron, respectively.

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Chemical interaction between silicates and carbon compounds within impact vapor clouds is not understood well. The thermal decomposition of silicates within impact vapor clouds may affect the carbon chemistry within impact vapor clouds. In this study, we investigate the oxidation of carbon compounds by free oxygen released from SiO2 in vapor clouds using laser-pulse heating on SiO2-polyethylene targets. The results of these experiments are also compared with those with oxygen-bearing plastic material as a target in order to estimate the amount of oxygen used in chemical reaction with carbon.

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Impact event vaporizes an impactor and target and produces a vapor cloud. The vapor cloud can accelerate the planetary atmosphere and cause the loss of atmosphere. It is called 'impact erosion'. We investigated the impact erosion in an ideal adiabatic atmosphere by computational means. The strong shock propagates vertically as predicted by Newman et al. (1999). On the other hand, horizontal flow blows the atmosphere away from the impact point. This flow pattern is not reported by any previous studies. We will discuss the parameter dependence of the amount of the atmospheric loss.

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[in Japanese]

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Chaos structure found on Europa was experimentally reproduced by the impact experiments. Two-layer model composed of water layer covered with thin ice plate was used for the target on the cratering experiments by ice projectile colliding at the velocity from 140 to 400 m/s. We have found three types of impact structures according to the impact conditions, which were simple crater, penetrated hole, and chaos failure. The shock stress propagation in ice and water could be a key process to understand the mechanism creating these different structures.

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In many icy satellites, extensional features can be seen. These surface features suggest a possibility that the surface has been fractured due to tensile stress, and various origins for the stress have been discussed. We have focused on the solidification of liquid layer and accompanying volume change. To estimate the stress in the icy shell, we performed numerical simulation for a thermal history. Besides, we calculated the stress in the viscoelastic shell due to solidification of liquid layer. Finally, we have found the distinct thermal and stress history between Europa and Ganymede.

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Impact cratering experiments at 4.2 km/sec, with nylon spheres of 7 mm in diameter on gypsum targets were performed. Fragments' velocities were measured using a target box with a slit and two high-speed cameras. All fragments created by impacts were divided into spalled fragments and shear-fractured fragments, based on their shapes, initial positions, and ejection time.

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[in Japanese]

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[in Japanese]

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We develop a new numerical code to simulate the chemical reactions within an impact vapor plume formed by cometary impact. To simulate the chemical reactions within an impact vapor plume, we couple a chemical kinetics model and a dynamics model of vapor plume. Our results show that impact velocity greatly affects chemical reaction path within vapor plume because it influences the pressure-temperature profile of impact vapor plume.

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[in Japanese]

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[in Japanese]

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It is widely accepted that terrestrial planets are formed in2 stages; the coagulation of planetesimals,which results in the formation of Mars-sized protoplanets, and the accretion of the protoplanets. The accretion process takes place in a gas disk.As the bodies grow, a gravitational gas drag makes them migrate.Past N-body simulations did not include this effect for simplification.We would like to perform the N-body simulations on formation of protoplanets including the migrating effect, and see how it effects the formation of protoplanets.

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[in Japanese]

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We tried to detect extrasolar planets by transit method using Suprime-Cam. The number of detected stars is over 30000 and their photometric accuracy is within 5%. These values strongly indicate that the Suprime-Cam is an excellent detector to search for extrasolar planets. An example of the observed light curve appears in Fig 1. This object is double star which consists of late K and early M type stars. From our detailed analysis, we have found that the flux of a late K star decreases about 3.5%. This decrease of flux can be explained by the occultation of a 1.2 Jupiter radius planet.

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[in Japanese]

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The redox reaction rates of sulfur oxides in vapor clouds are crucial for the estimation of the residence time of the sulfuric acid aerosol generated by the Chicxulub impact. Thus we have carried out laser irradiation experiment in order to estimate the redox reaction rates. The results of QMS analysis have suggested that the reaction rate is much larger than the theoretical estimation in [Ohno et al. 2004, EPSL]. In this study, we carry out spectroscopic observation in addition to QMS analysis and use the obtained results to constrain the initial thermodynamic conditions of vapor clouds.

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26Al ages of 17 chondrules from the least equilibrated CO3.0 Yamato-81020 were analyzed. The chondrule formation ages show 1.3 to 2.4 Myr for ferromagnesian chondrules and 2.9 Myr for Al-rich chondrules after CAIs formations, assuming 26Al was homogeneously distributed in the early solar nebula. The forming period of ferromagnesian chondrules in carbonaceous chondrites (CC) clearly consists with those in ordinary chondrites (OC), 1.0-2.5 Myr after CAIs. Thus, ferromagnesian chondrules in CC formed contemporaneously with ferromagnesian chondrules in OC.

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[in Japanese]

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The Oort Cloud,the origin of long-period comets,distributes spherically with a semi-major axis of tens of thousands of AU,but is not confirmed through observations. We attempt the detection of Oort Cloud objects approaching the planetary region. Our estimations suggest that one such object can be detected per 14 square degree. We developed a method of analysis to efficiently pick up moving objects,and have searched through the archived data taken with Suprime-Cam on the Subaru Telescope. New moving objects,distant from the ecliptic plane were detected,and their orbital elements are discussed.

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The size-range distribution of secondary craters around a lunar crater Tycho was measured. Tycho is known as a typical crater formed by an oblique impact. Both at the downrange and at the uprange of the oblique impact, the size distributions of the ejecta fragments of Tycho estimated from the size and range of the secondary craters are identical. The fragment size distributions also seem to be independent of the ejection velocity. The density profiles with range from the primary crater are different between at the downrange and the uprange.

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Dust temperature in the extrasolar planetary system is determined in the different kind of surrounding radiative environment. We have estimated dust temperature for fractal dust like BPCA (Ballistic Particle-Cluster Aggregate) using MG-Mie theory and for spherical one using Mie theory. We have found that dust temperature for fractal does not show the minimum around 10 micrometer radius, which can be seen for sphere. The other finding is that dust less than about 0.6 micrometer size shows lower temperature for fractal dust and for the larger size fractal shows higher temperature.

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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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Evolution of the atmosphere of the Earth, especially a rise of oxygen, could have related closely with global glaciations (snowball Earth events) during the Earth's history. Here we report the results of our project on geological survey of the Huronian Supergroup in Canada which may record the global glaciation and the oxygen rise in the Paleoproterozoic. We found that Mn concentrates in the sediments deposited just after the glaciation, suggesting that oxygen level was already high or may have increased just after the glaciation.

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I performed a SPH simulation of collision between porous material to investigate a relation between the strength of the material and velocity plus ejection angle of impact ejecta. I found that the velocity increases and the angle increases from the surface normal of the target as the strength increases. Using the results, we can estimate the strength of minor objects (cometary nucleus, asteroids) by hitting the surface with a projectile and monitor the ejection pattern.

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[in Japanese]

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[in Japanese]

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The SELENE (SELenological and Engineering Explorer) is a Japanese lunar polar orbiter with 14 scientific instruments. The XRS is to map major elemental composition in 20km spatial resolution, to provide the clue to understanding the lunar evolution. Energy resolution and efficient detection area of the XRS has been much improved by using arrays of Si CCD with 100cm² detection area and ultra-thin beryllium window for better transparency at low energy. We present the specification, performance and current status of the XRS and method of remote X-ray spectrometry.

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[in Japanese]

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Impact craters on gypsum targets made by oblique impacts at 4.2 km/sec are compared with those on ice, gypsum (lower impact velocity), and basalt. As shown in Burchell and Mackay (1998) which deals with impact cratering on metal targets, the crater shape-dependence on the impact angle changes with the impact conditions, such as the density ratio between target and projectile, and impact velocity.

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[in Japanese]

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[in Japanese]

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The impact of solar-wind particles on interplanetary dust grains exerts a drag force on the grains, which decreases their orbital angular momentum and limits their lifetime in a manner similar to the photon Poynting-Robertson effect. We study the solar-wind drag force for the dust aggregate taking into account the penetration of the ions through the aggregate.

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In recent years, some satellite observations turned out that suprathermal ion loss flux from polar ionosphere is of similar order as jeans escape flux.For studying the role of atmosphere loss that occurs in the region of open magnetic fields,we have attempted to construct an empirical model which estimates ion loss fluxfrom polar ionosphere. In this study, we show verification of the validity of the model and the amount of ion loss in the past, and investigate the effect on the atmospheric evolution.

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[in Japanese]

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[in Japanese]

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Among 120 extrasolar planets discovered to date, only 20 planets exist in multiple star systems.Recent theoretical study predicts that a planet can be stable in a multiplestar system which has a large semimajor axis, but current searches for planetsin multiple star systems are less extensive than those around in single stars.We have started a search for extrasolar planets in binary systems by preciseDoppler shift measurements from 2003,using HIgh Dispersion Echelle Spectrograph(HIDES) at the Okayama Astrophysical Observatory.We here report the current status of the survey.

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[in Japanese]

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We calculate the cross-section and surface area of fractal aggregate, defined as BPCA and BCCA. As a result, we confirm that both cross-section and surface area of fractal aggregate are larger than those of sphere with the equivalent mass. therefore, we can expect that the fractal aggregate is subject to the gas resistance more than the sphere. Moreover, we have found that a ratio of surface area to cross-section area of a fractal aggregate becomes the similar value to that of a sphere, i.e. about 4 regardless of its size and shape.

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We have studied the effects of dust size growth and settling on instabilities of a protoplanetary disk. As a result, we have found that although the magnetrotationally unstable region at the disk surface spreads as the total dust surface area, namely, the neutralization rate decreases due to the dust size growth and settling, the disk midplane keeps stable owing to the settling even after 10⁵ yr. Meanwhile, the whole disk becomes convectively stable after 3x10⁴ yr due to the irradiation from the central star and the decrease of the dust opacity.

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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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