[in Japanese]

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We report results of the ground tests for Relay Satellite Transponder (RSAT) and Differential VLBI Radio Source (VRAD) for selenodesy on SELENE. Release properties of SELENE sub-satellites; Rstar/Vstar were measured by the ground tests, which have been confirmed by the on-orbit display on Micro-Lab Sat. Attitude analysis for the sub-satellites and beam pattern measurements for antennas shows that these mission instruments will provide the lunar gravity mapping with highly accurate full coverage.

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The gravitational instability in the dust layer of a protoplanetary disk with a constant Richardson number is investigated. The linear analysis of the gravitational instability is performed. The following assumptions are used: (1) One fluid model is adopted, that is, difference of velocities between dust and gas are neglected. (2) The gas is incompressible. (3) The gas flow is axisymmetric with respect to the rotation axis of the disk. Numerical results show that the critical density at the midplane is 2.85 times as large as that for the uniform dust density distribution by Sekiya (1983). Our results give a new restriction on the planetesimal formation by the gravitational instability.

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[in Japanese]

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[in Japanese]

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We have investigated obliquity variations of hypothetical terrestrial planets in habitable zones (HZs) in extrasolar planetary systems. Using analytical expressions, we have shown that the terrestrial planets in a HZ tend to be in spin-orbit resonance when the giant planet is located at where they can keep the orbits of the terrestrial planets marginally stable. We found that the systems with both small obliquity variations and stable orbits in their HZs are only 1/5 of the known extrasolar planetary systems. However, retrograde spin, or a large and/or close satellite might be able to reduce the obliquity variation.

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Geochemical characteristics of the lunar crust are vertically and horizontally demonstrated, and implication for lunar evolution is discussed.

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The LUNAR-A spacecraft will be launched at 2004, and two penetrators will be deployed on the surface of the moon. Observation of the moonquakes will be taken place by the two-axial short period, about 1 Hz, seismometer of the penetrator. The other observation on the thermal characteristics of the regolith will also be taken place. We will enlarge our understanding and knowledge about the interior of the moon throughout the mission.When the penetrator penetrates into the surface of the moon, the seismometer will be shocked more than 5000G. In other words, the seismometer is expected to hold its characteristics throughout the penetration event. In order to verify the shockproof characteristics of the lunar seismometer, we have carried out the impact shock test that is 1.25 times greater degree of shock than the expected shock level at the penetration into the surface of the moon. Before and after the impact test , we obtained the calibration data of the seismometer, including its natural frequency and decay constant. The LUNAR-A seismometer has 1.0-1.2Hz natural frequency and 0.6-0.7 decay constant for the deep moonquake observation. From the analysis of the calibration data, we found that the obtained natural frequency and decay constant of the shocked seismometer satisfied the requirements. Next, to examine the response of the shocked seismometer for ground motions of the seismometer, the seismic observation was made at Inuyama Seismic Observatory of Nagoya University. We will compare observed seismograms and calculated power spectrums obtained by the LUNAR-A seismometer, and L-4 (1Hz short period seismometer), and broadband seismometer STS-2. From the result by the observation, we will estimate the performance of the seismometer for moonquake (lateral and vertical) compared with the seismometer for earthquake.

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[in Japanese]

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X-ray fluorescence spectrometer (XRS) onboard HAYABUSA (MUSES-C) spacecraft that was launched by the fifth M-V launch vehicle on 9 May 2003. The XRS has plans to observe supernova remnants (SNR), active galactic nuclei (AGN) and cosmic X-ray backgrounds for in-flight calibration and scientific observation during the transfer and return phase. When HAYABUSA spacecraft performed tests of the ion electric propulsion system (IES) and its heater control system, the XRS observed spectra were noisy. This study shows method of reducing heat noise.

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[in Japanese]

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[in Japanese]

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A Mixture of methane (1%) and nitrogen (99%) was subjected to proton irradiation (PI), gamma irradiation (GI), UV irradiation (UV) or spark discharges (SD), and the products were analyzed to compare possible energy sources in Titan. SD mainly gave unsaturated hydrocarbons, while PI gave saturated hydrocarbons. N-containing organics were detected in PI, GI and SD, but not in UV. The formers yielded amino acids after acid-hydrolysis of solid phase products (tholin). Comparison of the present results with those by Cassini-Heygens mission will make it possible to prove major energy source in Titan.

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X-ray spectrometer onboard HAYABUSA spacecraft has a standard sample to perform comparative analysis. Comparing with the X-rays from the standard sample and asteroid surface, the dependency of induced X-ray, solar X-rays, is reduced [1].
It takes more than 2 years to reach the Asteroid, and the temporal variance of the XRS performance is investigated periodically by the observation of the X-rays from Cosmic X-ray Backgrounds, astronomical X-ray bodies, and the standard sample.
From 28 May 2003 to 30 May 2003, just after the launch of HAYABUSA, XRS observed an X-ray source: SCO-X1 [2]. The observation continued two days due to the initial checkout. Fortunately, an X.1 class solar flare happened during this term. The spectra from the standard sample were composed of Ca and Si line spectra together with Mg, Al, and Si line spectra. These data is available for the XRS in-flight calibration: energy gain and intensities. In addition, model parameter is determined by this data.
Yamamoto et al reported that the energy calibration, comparison of the energy flux between GOED 10 and XRS, and the comparison of the observation and calculation using thess data [3]. The energy calibration of the line spectra: Mg, Al, Si, Ca, and Fe, was determined within 1% accuracy comparing with ⁵⁵Fe calibration data before launch. Temporal variation of energy flux obtained by XRS showed the consistency with that obtained by GOES 10 satellite. Moreover, the model calculation was performed and compared with the observation. The comparison showed the background noise in the energy range 0.5-3keV clearly existed. This noise was serious problem to determine the intensities of Mg, Al, and Si X-ray fluorescence spectra.Therefore, we report here the method to remove this background noise, and the effect of the method.
[1] Okada, T., Fujiwara, A., Tsunemi, H., and Kitamoto, S. 2000. X-ray fluorescence spectrometer onboard MUSES-C, Adv. Space Res. 25, 345-348.
[2] Arai et al, 2003. Proc. ISAS Lunar Planet. Symp.
[3] Yamamoto et al, 2003. Proc. ISAS Lunar Planet. Symp.

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[in Japanese]

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Since the discovery of submarine hydrothermal systems (SHS) in the late 1970's, deep-sea hydrothermal systems have been proposed to be plausible environments for chemical evolution and origins of life on Earth. Bioorganics, especially amino acids are common components of all organisms and constituents a major fractions of organisms. We present the results of analysis of organic compounds including amino acids in hydrothermal water samples and chimneys directly collected from deep-sea hydrothermal systems.

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The hypothesis on exogenous origin of organic matter on the early Earth is supported by the detection of alarge variety of organic compounds in carbonaceous chondrites. We performed high velocity impactexperiments with an ISAS railgun HYPAC. In the present work, 10 mM glycine aqueous solution and amixture of ammonia, methanol and water simulating comets were used as targets. Diketopiperazine wereformed when a 10 mM glycine was used as a starting material, but none of glycine peptides were detected.When an aqueous solution containing ammonia, methanol and water was shocked by impact at the velocityof 6.4 km/s, a number of amino acids (e.g., serine and glycine) were detected after hydrolysis of the product.The present results suggest that organic material could survive and/or formed during an impact process.

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The SELENE (SELenological and Engineering Explorer) is a Japanese lunar polar orbiter and performs lunar global mapping with more than 10 scientific instruments. The XRS will map major elemental composition in 20km spatial resolution and provide the clue to understanding the lunar evolution. For that purpose, the XRS has been designed to improve energy resolution and efficient detection area. Then the X-ray detector has arrays of CCD with 100cm² detection area, and is kept below -50C by radiation cooling. Ultra-thin beryllium window are developed for better transparency at low energy. We present the specification and the current status of the XRS as prepared for the interface test, as well as the plan of pre-flight tests and observation plan.

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[in Japanese]

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[in Japanese]

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We have examined the glass inclusions in Dhofar007 cumulate eucrite and Johnstown, Tatahouine diogenites. So the glass inclusions are revealed to be high silica and incompatible elements poor from the measurement of major and trace elements abundances by using EPMA and LAM-ICP-MS. These results may imply that the original melts for the glass inclusions were formed by incongruent melting of orthopyroxenes. And we performed a shock experiment on orthopyroxene. The sample material was a high-quality single crystal enstatite from Tanzania.

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Space weathering has been invoked to explain the mismatched spectra between asteroid type and meteorite classes. It affects on the reflectance spectra as the darkening and reddening of planetary surface materials and the changes to the depths of absorption bands.
In this study we measured the bidirectional diffused reflectance spectra of L6 chondrite Yamato-75102, from 300nm to 2600nm with the particle size varied. The sample is not so suffered by weathering on terrestrial. We discuss quantitatively the dependence on particle size for the reflectance spectra characterization.

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Asteroid 4 Vesta is a peculiar asteroid due to its basaltic composition. Many multi-band observations for Vesta were carried out and at last the image of Vesta were obtained by Hubble Space Telescope in 1994, and a geologic map was made.2003.
We made the visual observation using a transportable 10 cm refracting telescope with a MUTOH CV-16 CCD in ECAS filter system. Infrared observations were carried out using 105cm Schmidt telescope with Mitsubishi 1040 x 1040 PtSi CSD (KONIC) in H band at Kiso Observatory. And we made spectroscopic observation (500nm to 900nm) using a 65 cm reflecting telescope and GCS (Gunma Compact Spectrograph) at Gunma Astronomical Observatory.
We report consideration of the effect of space weathering as well as the inhomogeneous distribution of minerals on the surface of Vesta.

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The P-type asteroids, together with the D-type asteroids, used to be believe to be more primitive than any known carbonaceous chondrites and would not come to the Earth as a meteorite. Because the P asteroids fall in between the C/G/B/F asteroids and the D/T asteroids in reflectance spectral property and radial distribution around the Sun, now that the Tagish Lake meteorite fell and turned out to be possibly from a D or T type asteroid, it is natural to believe that the P asteroids are made of materials intermediate of the thermally metamorphosed CI/CM chondrites and the Tagish Lake meteorite.

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Planets are formed by accretion of planetesimals.The thermal history of planets are partly depending onthe thermal evolution of planetesimals especially whenthe size of proto-planet is still small, sincethe planetesimal's internal thermal energy is addedto the proto-planet's interior if the accretingplanetesimal is not fully disrupted by the impact.Thus, we construct a new model for thermal evolutionof planetesimals and evaluate the effect onto the thermalevolution of proto-planet.

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We have succeeded in detecting a dust trail along the orbit of the short-period comet 81P/Wild2 , the target of the Stardust mission, which will fly by 81P/Wild2 in 2004 January. Based on our observation, it is likely that the trail is composed of dust particles with a diameter of about 1mm. During the flyby phase of the Stardust spacecraft, the spacecraft will come across the impacts of such large dust particles along the comet's orbit. In this study , we examine the impact fluence and impact velocity of the dust particles onto the Stardust spacecraft.

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Technology-demonstrating spacecraft"HAYABUSA" launched in May 9,2003 is now under the routine operation after the initial test phase. The ion engine is continuously operating and onboard calibration test of the remote sensing instrumentswas made. Future plan of HAYABUSA and preparation for the sample analysis are also reported.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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We present the results of initial operation, the current status, and the future observation plan of the X-ray fluorescence spectrometer (XRS) onboard Hayabusa, which was launched with the fifth M-V launch vehicle on May 9th, 2003. The XRS observes X-rays characteristic of elements excited by solar irradiation, to determine major elemental composition of asteroid Itokawa (1998SF36). Then we classify the S-class asteroid and prospect the degree of evolution processes. During the two-year long cruising phase, the XRS are checked out its function and the detectors against radiation damage, and observes X-ray bodies such as super nova remnants or active galactic cores as well as cosmic backgrounds of X-rays for in-flight calibration. The XRS also monitors solar X-rays using the standard sample. Flight demonstration of the newly developed onboard computer proves usability for more than 20 days.

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Building up the New Minor Body Exploration Missions in the Post-Hayabusa Era

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It is controversial whether the planetesimals are formed through continuous dust sticking due to non-gravitational forces, or they are formed by the gravitational instability of the dust layer in a protoplanetary disk. We examined the former process taking account of the gas flow around a dust aggregate. The results are as follows: (a) A small dust aggregate collides once with a large aggregate. The collision velocity is about 50m/s. (b) The small dust aggregate breaks into monomers by the collision. (c) The monomers never collide with the large dust aggregate due to the gas drag of the flow around the large aggregate. Thus, the planetesimal formation through dust sticking seems difficult to occur.

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The dust density distribution in the dust layer would reach the constant Richardson number distribution (Sekiya, 1998) due to the mixing of the turbulence caused by the shear instability. We performed the analysis of the shear instability of dust layer in a protoplanetary disk with the constant Richardson number density distribution, and revealed that this distribution is stable. The planetesimal formation due to the gravitational fragmentation of the dust layer is possible.

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The infrared excess in the SEDs (Spectral Energy Distributions) of protoplanetary disks is observed only around stars younger than 10⁷ yr. This is thought to be because the life time of protoplanetary disks is less than 10⁷ yr. In this study, we perform simulations of dust growth and settling in passive disks and investigate evolution of optical properties of protoplanetary disks due to dust growth. As a result of growth, dust particles has a power-law size distribution with the index of -3. The dust growth decreases the disk optical thickness. We also found that the dust growth can reproduce the decay in luminosity of infrared radiation in 10^6-7 yr. Our result suggests that the life time of gaseous disks can be longer than 10⁷ yr.

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[in Japanese]

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T Tauri stars are thought to be progenitors of planetary systems like the solar system. Structure of them may determine the final state of the planetary system. It has been deduced by calculating model spectral energy distributions (SEDs) and images and by comparing them with observations. However, anisotropic scattering by dust particles has not been incorporated adequately in previous work. Here, we examined to what extent the anisotropic scattering (Mie scattering) may affect SEDs and images. We found that this effect is not negligible. Also, it is suggested that our radiative equilibrium calculations can be used to estimate the inclination of and the dust sizes in the disk.

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[in Japanese]

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We investigate gravitational interaction between a planet and an optically thin protoplanetary disk, taking account of radiative transfer. A planet excites two density waves on both sides of the planet orbit due to Lindblad resonances. The outer density wave exerts a negative torque on the planet while the inner density wave exerts a positive torque. The sum of the two torque gives the net torque on the planet. As a first step, we examine one of the torques (one-side torque) in the present study. In most previous studies of density waves, the isothermal equation of state has been assumed.In this study, solving the energy equation in the linear calculation, we examine the effect of energy transfer on the wave excitation. In protoplanetary disks, the energy is transfered is by radiation and the radiative transfer is governed by dust opacity. At the stage of planet formation, the dust opacity is expected to be sufficiently low because of dust growth and planetesimal formation. Thus we assume an optically thin gaseous disk. The efficiency of radiative transfer increases with the amountof dust in optically thin disks. We consider the amount of dust as a parameter and calculate the one-side torque on a planet. Due to radiative transfer, the values of the one-side torque is deviated only by about 10\% from the isothermal case. However, it is also found that the gas in the Hill sphere of the planet has a large contribution on the one-side torque.This large contribution in the Hill sphere may change the net torque sufficiently.

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In the Jovian planet region, after the formation of protoplanets, they begin to capture the surrounding nebular gas gravitationally and become gaseous giant planets such as Jupiter and Saturn (Mizuno 1980, Bodenheimer and Pollack 1986, Ikoma et al. 2000). The formation time of these gaseous planets depends strongly on a solid core mass (i.e., a protoplanet's mass). Especially, Ikoma et al. (2000) pointed out that, in order to form massive gaseous envelopes of the present Jovian planets around protoplanets within the nebular life time, a protoplanet's mass must exceed a critical mass. However, we find that a typical mass of a protoplanet formed in the Jovian planet region in the minimum mass solar nebula model is smaller than the above-mentioned critical mass. This means that a protoplanet formed in the minimum mass solar nebula cannot become the present gaseous giant planets alone.
One of the possible ways to resolve this difficulty in the formation of Jovian planets is to consider the collision and accretion between protoplanets. If we think about this possibility, we are confronted with a difficult problem. In the presence of the nebular disk, a protoplanet system is expected to be prevented from undergoing an orbital instability (and, as a matter of course, collisions between protoplanets), since the nebular gas has an effect of suppressing eccentricities of protoplanets through gravitational and hydrodynamical interaction (Adachi et al. 1976, Ward 1988, Artymowicz 1993). Thus, we need to investigate the orbital stability of a protoplanet system in the nebular disk in detail.
In the present study, we investigated the orbital stability of a protoplanet system in the nebular gas through orbital calculations, for the cases where the masses of protoplanets are equally 3 times as massive as that of the earth. The tidal (gravitational) interaction between a protoplanet and the nebular gas is taken into account as a drag force proportional to the random velocity of a protoplanet. In numerical simulations, five equal-mass protoplanets are distributed with an equal separation distance and their initial eccentricities and inclinations are set to be zero.
Through long term orbital calculations, we obtained the following results:(1) The logarithm of the orbital instability time of a system without a gas disk increasesin proportion to the separation distance between protoplanets.(2) In the presence of the nebular gas, the instability time of a system becomes extremely large compared with the orbital instability time in the absence of the gaseous disk by the effect of the drag force due to the nebular gas and the system substantially doesn't experience an orbital instability, when the separation distance is larger than a critical separation distance. (3) The value of a critical separation distance becomes large with a decrease in the surface density of the nebular gas.
Furthermore, we obtained a semi-analytical expression for a critical separation distance, partly using our simulation results. Finally, applying our results to the orbital stability of a protoplanet system in the Jovian planet region, we found that in the presence of the minimum mass solar nebula, the orbital instability of a protoplanet system never occurs in the Jovian planet region. Considering that, in order to form the gaseous giant planets, the remaining gaseous disk around protoplanets must be as massive as the minimum mass solar nebula, we concluded that the protoplanets did not experience orbital instabilities in the formation process of Jovian planets.

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[in Japanese]

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[in Japanese]

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Habitable conditions are important environmental indicators of extrasolar planet. One important habitability con-dition is stability of liquid water for geological timescale. Tajika and Matsui (1990)(1) show stabilization of the sur-face temperature by carbon cycle against the increase of solar radiation with Sun's evolution. Kasting et al.(1993)(2) obtain the range of orbital radii for the continuously habitable planets con-sidering both the carbon cycle and the runaway greenhouse effect.
The atmospheric temperature depends on the incident energy flux and the greenhouse effect in the atmosphere. The amount of carbon dioxide, which is an important greenhouse gas, in the atmos-phere depends on the balance between fluxes of degassing and fixation as car-bonates. Hence, the large degassing flux results in strong greenhouse effect, and warm environment. The degassing rate depends on thermal history, which is dependent on the planetary size. Thus, planetary radius affects the evolution of the atmospheric temperature. However, the size dependence of the habitability condition is not well discussed yet.
Here, we investigate the planetary size dependence of the stability of liq-uid water over geological time scale by examining the length of the period while the surface temperature is kept above freezing. Since the solar flux in-creases with the Sun's evolution, the degassing rate of CO₂ required for keep-ing the surface temperature decreases with time. On the other hand, owing to planetary cooling, the degassing rate decreases with time. Thus, on a rapidly cooling planet, namely a small planet, the degassing rate decreases below the critical value that is required for keeping the surface temperature. In the fol-lowing, we define the "lifetime" of a habitable planet as the period while the surface temperature is kept above a certain reference temperature. For sim-plicity, we assume that the atmospheric and the surface temperatures are the same. We consider 3 reference surface temperatures: 15C which is annually and globally averaged temperature on the present Earth, 5C, and the standard tem-perature 25C . Using simple expressions of the thermal evolution and degassing rate, the greenhouse warming, and the carbonate formation rate, we investigate the dependence of the lifetime of plan-ets on the planetary size and orbital radius.
As the result, lifetime has a linearly relation to planetary radius. And the dependence of lifetime on incident en-ergy flux is stronger than the linear relation. We investigate requirements for stability of liquid water during 4.5 billion years. Planetary radius is larger than the Mars-size for the re-quirements and orbital radius is smaller than 1.12AU when planetary radius is Mars-size. The model in this time has a large uncertainty. And we estimate the requirements without considering temper-ature distribution from north to south and the other greenhouse effect like de-pendance of CO₂ column abundance in the atmosphere. The next step is to clarify the effect of these factors on the life-time of the planet.
(1)Tajika, E. and Matsui, T.(1990):The evolution of the terrestrial environ-ments. In "Origin of the Earth"(Newsoms, M. E. and Jones. H. eds.), Oxford Univ. Press, pp.347-370
(2)Kasting, J. F., Whitmire, D. P., Reynolds, R. T.(1993):Habitable Zones a-round Main Sequence Stars, Icarus, 101, 108-128, 1993

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The observation of recent gullies related to a possibility of the existence of liquid water on present Mars has been concerned in recent years. Some models assume formation of gullies by liquid water but they cannot explain the absence of the features in the equator regions. Other models assume CO2 as a volatile associated with the formation of gullies. We show that a latitude of the boundary between regions with CO2 consolidation on poleward-facing slops and those without CO2 condensation is about a latitude of 30. The result suggests a possibility of some correlation between the existence of CO2 and the formation of gullies.

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[in Japanese]

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Recent estimates of the solar isotopic compositions of C and N, deciphered from the solar wind component implanted into lunar grains, suggest that bulk of meteoritic C and N are largely enriched in 13C and 15N compared to their proto-solar compositions. Since C and N in primitive meteorites are predominantly in form of organics, such information permits us to explore the possible place and processes of organic birth in the interstellar or circumstellar gas medium. Systematic enrichment of 13C in bulk of meteoritic organics, by ~10 % compared to the proto-solar composition, implies that the bulk of meteoritic organics could have formed in a warm and dense space medium, such as in the proto-planetary disk illuminated by ultra-violet light from the proto-Sun.

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