Abstracts for fall meeting of the Japanese Society for Planetary Science
Abstracts 2006 Fall meeting of the Japanese Society for Planetary Sciences
Displaying 1-50 of 139 articles from this issue
Oral session 1: Oct. 18, 10:20-11:56
  • Hirohide Demura, Gaskell Robert, Naru Hirata, Hideaki Miyamoto, Sho Sa ...
    Session ID: 101
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Our Geomorphology group in Hayabusa Joint Scieence Team arranges information of global shape model and parameters, geology, and Itokawa nomenclature. Here we report remark-able features which have been pointed out by the team members, and nomenclature of Itokawa. (IAU approved landmarks, etc.).
    Download PDF (172K)
  • Ryosuke Nakamura, Akiko Nakamura, Naru Hirata, Shinsuke Abe, Masateru ...
    Session ID: 102
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Japanese Asteroid Explorer Hayabusa completed the surface mapping of the target S-type asteroid Itokawa during the rendez-vous phase between September and November in 2005. Furthermore, Hayabusa obtained several very high-resolution images during the descent to the surface for capturing surface sample materials. On these high resolution images , we have found several bright dots of a few centimeter size on boulders darkened by space-weathering. The bright dots are likely to be small craters produced by the hypervelocity impacts of meteoroids. We present the preliminary counting results of such small craters and discuss the implication on the meteoroids flux, timescale of space weathering and resurfacing on Itokawa.
    Download PDF (70K)
  • Shinsuke Abe, Tadashi Mukai, Ryosuke Nakamura, Naru Hirata, Olivier Ba ...
    Session ID: 103
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    The laser altimetry (LIDAR) aboard the Hayabusa spacecraft measured the surface topography of the asteroid Itokawa and the mass calculated by spacecraft position without orbiting. The mass of Itokawa was estimated as 3.5 x 1010 kg, implying a bulk density of 1.9 g/cm3 and a bulk porosity of -40% when assuming chondritic meteorite composition(density of 3.2 g/cm3) (Abe et al, Science, 2006). In order to investigate the origin of Itokawa, especially for the interior structure and surface characteristics, we will discuss about the principal axis of inertia calculated by Itokawa's shape model and also present a 50m sized biggest bouldar, named 'Yoshinodai', on the surface by using near-infrared and visible spectra.
    Download PDF (912K)
  • Tatsuaki Okada, Kei Shirai, Yukio Yamamoto, Takehiko Arai, Kazunori Og ...
    Session ID: 104
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    We present the results of remote X-ray fluorescence spectrometry of a near-Earth asteroid 25143 Itokawa with the X-ray fluorescence spectrometer (XRS) onboard Hayabusa. As has been reported, major elemental ratios of Mg/Si and Al/Si indicate that the surface of asteroid is more like an ordinary chondrite meteorite, especially LL- or L-chondrite, although some kinds of primitive achondrite are not ruled out. In this study, compositions of heavier elements such as Ca/Si and Fe/Si are quantitatively analyzed as well as the upper limit of S/Si. These results also support that the surface of Itokawa is like an ordinary chondrite, but also suggest that the surface must have experienced a little bit of thermal alteration or micro-impact processes.
    Download PDF (14K)
  • Takahiro Hiroi, Masanao Abe, Kohei Kitazato, Shinsuke Abe, Sho Sasaki, ...
    Session ID: 105
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Concerning the controversy that the visible and near-infrared (NIR) reflectance spectra of the S-type asteroids and ordinary chondrites which are the most abundant in the near-Earth region do not match with each other, especially the hypothesis of space weathering had been strongest as the explanation in the past. As the result of visible and NIR observations of an S-type asteroid 25143 Itokawa by the Hayabusa Mission, such idea has become even more assuring. Itokawa consists of bright and dark portions in general, and both of those regions in any scale show spectra indicating a mineral assemblage consistent with only those of LL chondrites among all known meteorites, wherein the only differences are the mean optical path length and the degree of space weathering. The fact that an asteroid which is made of an LL-chondrite material and space-weathered to look as an S-type asteroid suggests that many more S asteroids made of ordinary-chondrite materials (including H and L types) exist in the near-Earth region.
  • Sho Sasaki, Masateru Ishiguro, Takahiro Hiroi, Hideaki Miyamoto, Tokuh ...
    Session ID: 106
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    In 2005, HAYABUSA observed an S-type asteroid Itokawa (with size of 550m) by onboard camera AMICA (Saito et al., 2006). Almost 80% of the surface is rough and boulder-rich but it has weathered spectrum on average. Optically, the surface of Itokawa is divided into brighter (and bluer) areas and darker (and redder) areas. In rough zones, dark boulder-rich surfaces usually superpose on bright materials. We can interpret impact-induced seismic shaking or shaking at planetary encounters should remove dark weathered boulder-rich surface to expose underlying relatively fresh bright area. High resolution images indicate that these bouldered surface are optically weathered. To check the possibility that the rock surface could be weathered, we irradiate pulse laser on meteorite fragments with cut flat surface under vacuum. For comparison, we also irradiate pellet samples where particle size is smaller than 125 microns. Fresh meteorites NWA1794 and Bensour were chosen because spectral observation of Itokawa suggested its similarity with LL5 and LL6 chondrites. As expected, significant darkening and reddening are observed at irradiating pellet samples.
    Download PDF (107K)
  • Makoto Yoshikawa, Jun'ichiro Kawaguchi, Akira Fujiwara, Masanao Abe, T ...
    Session ID: 107
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    The observation of Asteroid Itokawa by Hayabusa spacecraft has brought us a lot of new knowledge for very small (about 500m in length) S-type asteroid. We already have started to consider next space mission to small bodies in the solar system. For the next asteroid mission, we would like to explore C-type asteroid, which is also major type in the asteroid belt. This type of asteroid is supposed to have organic matter or water more than S-type asteroid, and it is important to study the material related to life. In this paper, we present the current plan for the next exploration to asteroids. We also want to encourage many researchers to join our asteroid mission.
    Download PDF (88K)
  • Takehiko Arai, Tatsuaki Okada, Manabu Kato
    Session ID: 108
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    X-ray fluorescence spectrometry is a powerful tool in order to determine elemental composition of solid planet.The XRS will use a standard sample method, called SSP method, which is qualitative analysis method in order to measure major elemental composition. In this study, we developed newly analysis techniques of SSP. It has advantage of degree of accuracy. In this presentation, we introduce the SSP method and analysis procedure of HAYABUA/XRS with this method.
    Download PDF (74K)
Oral session 2: Oct. 18, 13:30-14:30
  • Noriyuki Namiki, Takahiro Iwata, Makiko Ohtake, Tomoko Arai, Takamitsu ...
    Session ID: 109
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Japanese lunar mission, SELENE, is to be launched in summer, 2007. Developments of scientific instruments are close to completion. Now we move to focus on analyses of observational data and scientific outcomes of SELENE. In order to make as much contribution to lunar science as possible from new observations, we propose a strategic plan for integrated science of SELENE. Our basic idea is to analyze observational data in four stages. First stage is to draw 2D geologic maps of both lunar maria and high land. Second stage is to reveal subsurface structure of maria, and highland if possible. Third stage is to investigate special topics such as crustal dichotomy and differentiation of basaltic magma on the basis of 2D and 3D maps. And in the last stage, we aim to study the origin and evolution of the moon. After several meetings held for the integrated science, we set four fundamental issues to be answered by SELENE observations; (1) tectonic history of maria, (2) crustal formation from magma ocean, (3) exploration of polar region, and (4) structure of multi ring basin. We have organized four sub-WG, and these groups are making research plan for respective issues at present.
    Download PDF (22K)
  • Akira Yukishita, Jun Nitta, Kayoko Azuma, Manabu Kanzawa, Syouta Kikuc ...
    Session ID: 110
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    SELENE is a Japanese exploration mission to the moon that will launch in 2007. This mission will bring lunar mapping data. The purpose of this research is development of lunar GIS database, which archive and analyze SELENE data. We develop a prototype of lunar GIS database based on ESRI ArcGIS. The original system is modified to handle the lunar geographic coordinate system. Our new system will be able to deliver many kind of thematic maps of the moon to endusers through the internet.
    Download PDF (69K)
  • Jun'ichi Haruyama, Tomokatsu Morota, Chikatoshi Honda, Yasuhiro Yokota ...
    Session ID: 111
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    The Terrain Camera(TC) is a mission instrument on SELENE, that takes stereo-images of the surface of the Moon with 10m resolution. The data of TC will be depacketed, decompressed, radiometrically calibrated, geometrically corrected, and so on, in the SELENE Operation and Analysis Center(SOAC) in the Institute and Astronautical Science (ISAS)/Japan Space and Aeronautical Exploration Agency (JAXA). From the TC stereo pairs, digital terrain model (DTM) scene/maps will also be produced in SOAC. The products will be delivered via SELENE Level 2 data base. The systems that proceed the TC data have been programmed and installed into SOAC, already. We have checked the format of each product from the systems, procedure times, and so on, through various tests including interface tests to confirm the possibility of fast generation of products by the systems. In our nominal ground system operation plan, the systems for radiometrically calibration and geometrically correction and DTM production will be started their operation after a data volume (such as of a half of month) of the depacketed and decompressed (L2A) data are piled up. The detailed procedure parameters are will be investigated for both view points of time and accuracy.
    Download PDF (104K)
  • Tomokatsu Morota, Jun'ichi Haruyama, Yasuhiro Yokota, Chikatoshi Honda ...
    Session ID: 112
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    We evaluate an accuracy of the lunar Digital Terrain Model (DTM) that will be obtained by SELENE/TC.
    Download PDF (741K)
  • Chikatoshi Honda, Tomokatsu Moroda, Yasuhiro Yokota, Makiko Ohtake, Ju ...
    Session ID: 113
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    The effect of sun elevation condition of imaging to the crater size-frequency distribution will have to be considered. As consequently, the accuracy of age determination using the crater size-frequency distribution must be improved.
    Download PDF (107K)
Oral session 3: Oct. 18, 14:40-15:28
  • Makiko Ohtake, Hiroshi Takeda, Aya Yamamoto, Tomoko Arai
    Session ID: 114
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    We study visible and near infrared reflectance spectra of a newly identified magnesian anorthosite Dho489.
    Download PDF (115K)
  • Tomoko Arai
    Session ID: 115
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    This paper discusses two types of differentiation trend in the lunar basaltic magma, found in the Pre-Imbrium and Post-Imbrium basalt samples on the lunar nearside. The oldest basalt (4.23 Ga) in 14305 shows the calc-alkaline trend in the terrestrial basaltic magma. In contrast, the young (2.87 Ga) mare basalt NWA 773 shows the tholeiitic trend. This infers the physical and chemical condition of the pre- and post-Imbrium basaltic magmatism is distinct especially in the volatile-element abundance.
    Download PDF (163K)
  • Yu Sasaki, Kentaro Trada, Yuuji Sano
    Session ID: 116
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    The lunar meteorites have been valuable sources for understanding the evolution of the Moon's crust, because each meteorite could potentially provide a new insight into the thermal history of unexplored regions on the Moon. In spite of their scientific interests, chronological studies of lunar basaltic meteorites have not been well understood, since the most of basaltic meteorites are brecciated and consist of mixtures of materials with different origins. We report here the in-situ U-Pb dating of phosphates in four Very-Low-Ti and three Low-Ti lunar meteorites by Sensitive High Resolution Ion Microprobe (SHRIMP).
    Download PDF (72K)
  • Aya Yamamoto, Tomoko Arai, Hiroshi Takeda, Masamichi Miyamoto
    Session ID: 117
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    To understand a correlation between reflectance spectra of Apollo samples that can be the ground truth data of the Moon and petrology and mineralogy of those samples is very important for analyzing remote sensing data such as SELENE. In this study, we measured UV/VIS/NIR reflectance spectra of five anorthosite samples from Apollo 16 landing sites, and examine the spectral result with their petrology and mineralogical compositions. Those samples show clear absorption feature of low-Ca pyroxene in their spectra except for 60025. These results indicate that anorthositic highland crust on the nearside of the moon shows various spectroscopic characteristics with brecciation and shock metamorphism.
    Download PDF (378K)
Oral session 4: Oct. 18, 15:45-17:15
  • Shoko Oshigami, Noriyuki Namiki
    Session ID: 118
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    About 200 Venusian channels have been classified into 6 types. Sinuous rilles and canali are both composed of a single main conduit with meandering. Sinuous rilles are typically from several 10s to a hundred and several 10s of km long and show narrowing with downstream distance. Canali are from several 100s to several 1000s of km long and have characteristics similar to terrestrial rivers such as cut-off meanders and point-bars. First, we reconstructed cross-sectional topography of 10 sinuous rilles and Baltis Vallis, a 6800-km long canali-type channel, from the brightness of Magellan SAR images. The groove-like morphology as well as the paucity of levee structures indicates that both sinuous rilles and Baltis Vallis are erosional in origin. Second, we examined depth distributions along the channels on the basis of the cross-sectional profiles. The depth of sinuous rilles decreases with increasing distance. The decreasing trend of depth consistent with numerical results of thermal erosional models indicates thermal erosion. In contrast, the undulations in depth distribution along the Baltis Vallis can be explained by mechanical erosion. Difference in formational process between Baltis Vallis and sinuous rilles is considered to reflect the diversity of igneous activity on Venus.
    Download PDF (192K)
  • Takayuki Honda, Akiko Nakamura, Tadashi Mukai
    Session ID: 119
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Recently, it was shown the opposition surge, which appears in small phase angles in scattered light from surfaces of small bodies such as asteroids, appears in the light scattered by rocky surfaces.
    In this study, we performed measurements of the light scattered by rock chips and particle layers at low phase angles. Measurements were performed using a multi phase angle near infrared spectrometer at Kobe University with the incident angle fixed at 2 degree and the phase angle varied within 0-25 degrees. Focus was put on how the opposition surge depends on different factors of the surface, i.e., reflectance, roughness and porosity of the surface.
    We will show the results of several types of bulk chips, particle layers and sintered powders, and will discuss on the effect of the three factors above.
    Download PDF (39K)
  • Toru Suyama, Koji Wada, Hidekazu Tanaka
    Session ID: 120
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    In protoplanetary disks, dust particles grow through mutual collisions. Dust particles are compressed by collisions and they can not keep the fluffy structure in the course of dust growth. The structure-evolution is important problem for the cross section, strength and the optical property. In this study, we perform N-body simulations of dust collisions and examine the compression process. At low velocity collisions, dust particles are not compressed and keep the fluffy structure. If collisional velocity is high, dust particles are compressed. We clarified the relation between the density and the collisional velocity from our simulation.
    Download PDF (146K)
  • Yasuyuki Saito, Jun Takita, Ki-ichi Horai, Satoshi Tanaka
    Session ID: 121
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Lunar surface Heat-flow value was measured by Apollo 15 and 17 missions, which are started on July 31, 1971 and December 12, 1972, respectively. Langseth et al. (1976) concluded that the heat flow values were reduced substantially to 21 mW/m2 and 14 mW/m2 for these two Apollo sites respectively using the data until 1974. These values have been widely accepted as the appropriate measured ones at present day. However no one has analyzed Heat-Flow Experiment (HFE) data since the first of the 1975. We could archive the HFE data between March 1, 1976 and September 30, 1977. As a result of the analysis of all of the data, the lunar surface heat-flow values was corrected to be about 3.7 mW/m2. It indicates that the bulk U abundance is 9.5 ppb assuming that 3.7 mW/m2 equals the global mean value of the lunar surface heat-flow. This value is about half as much as that of the Earth (about 20 ppb; Mason, 1979).
    Download PDF (260K)
  • Daisuke Fujiwara, Sei-ichiro Watanabe
    Session ID: 122
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    We showed a process of dust circulation in protoplanetary disks using the disk model with the puffed-up inner rim, which has the shadowed region behind (Dullemond et al. 2001). Then, we found that the abundance of dust particles is enhanced in the inner shadowed region of the disk due to dust circulation. Recently, Krauss and Wurm (2005), Wurm and Krauss (2006) suggested that the dust can move outward in the radial direction due to photophoresis. The photophoresis is based on the interaction between the particle with a radiation-induced non-uniform temperature distribution over its surface and the surrounding gas.Depending on the gas pressure, photophoresis can be stronger than the radiation pressure and gas drag at the optically thin region of the disk. Therefore, photophoresis may be effectively influence the motion of dust particles at the inner rim of the disks, where the gas pressure is high and the disk is optically thin. In this presentation, we will show the results of numerical simulations of dust circulation, taking the effect of photophoresis into account.
    Download PDF (80K)
  • Kouhei Kitazato, Masanao Abe, Beth Clark, Shinsuke Abe, Masateru Ishig ...
    Session ID: 123
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    The near-infrared spectrometer (NIRS) on the Hayabusa spacecraft obtained spatially resolved reflectance spectra of 25143 Itokawa between September 12 and November 24, 2005. In this study, we had modeled a photometric function of the asteroid surface based on the observed spectral data and have investigated the surface heterogeneity of asteroid Itokawa.
    Download PDF (68K)
Oral session 5: Oct. 19, 10:15-11:51
  • Kana Murazawa, Masahiko Arakawa
    Session ID: 201
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Collisional heating is an important mechanism of the thermal metamorphism induced in the meteorite parent body and the impact energy is efficiently converted into thermal energy when the parent body has a large porosity. Therefore, we tried to measure the residual temperature caused by impact in order to clarify the thermal evolution of a highly porous body . At low-speed impact experiments (vi<100m/s), a porous silica with the porosity of 40% was collided on a granite block. At High-speed experiments (60-430m/s), an ice projectile impacted on a porous silica disk with the porosity of 60%. The impacted silica projectile and disk were observed by an infrared video camera to measure the residual temperature in it. As a result, the low velocity experiments reveled dT=0.13Vi0.84. The high velocity impacts reveled dT=0.65x10-2Vi0.96.
    Download PDF (20K)
  • Satoru Yamamoto, S. Olivier Barnouin-Jha, Takashi Toriumi, Seiji Sugit ...
    Session ID: 202
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    In this study, using a laser sheet, we observed the formation and collapse processes of transient crater for different targets. Polycarbonate projectiles were impacted vertically into soda-lime glass sphere targets with different material properties. We found that the increase rate in diameter of crater cavity during excavation processes does not follow a simple power-law relation; the increase rate at late stages of excavation processes decreases with increasing time, and depends on target material properties. We also showed that the transient crater collapses owing to gravity, resulting in increase in diameter and decrease in depth. The degree of collapse was also shown to depend on target material properties. In addition, the crater shape (depth-diameter ratio) for final craters showed target material property dependence, while that for transient craters did not. Based on these results, we discuss the effects of target material properties on the scaling relation.
    Download PDF (130K)
  • Yasuhiko Takagi, Sunao Hasegawa, Hajime Yano, Satoru Yamamoto, Seiji S ...
    Session ID: 203
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Impact cratering experiments in microgravity environment were performed using a drop tower. The results showed no gravity effect. Details of experimental procedures and results will be presented at the session.
    Download PDF (371K)
  • Kensuke Hiraoka, Akiko M. Nakamura
    Session ID: 204
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    A strength dominated cratering continues until when the target strength becomes higher than the stress caused by impact, which propagates from impact site with attenuation. Since the cratering on brittle materials depends on both compressive and tensile stress, we must measure the compressive and tensile strength of target.
    We made sintered glass bead-silicate mixtures as the target. Both compressive and tensile strength of glass bead-silicate mixtures were measured with changing silicate content at low strain rate by uniaxial compression and Brazilian test, respectively. We performed impact cratering experiments on mixture targets at high velocity (2.5km/s to 3.5km/s) and low velocity (about 200m/s). We will compare the results with the case of ice-silicate mixtures and report the differences between them.
    Download PDF (19K)
  • Chisato Okamoto, Masahiko Arakawa
    Session ID: 205
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Planetesimals were supposed to be porous bodies with homogenous internal structure. In their growth process, planetesimals collided each other to grow in their sizes and the thermal evolution of their interiors could cause pressure sintering, melting and gravity differentiation of the constituent materials. As a result, there could be a lot of growing bodies with heterogeneous internal structure such as silicate core-porous silicate mantle and rock mantle-metal core. So, we should consider a collisional phenomenon not only for homogenous bodies but also for layered bodies to study the planetary accretion process. A lot of experimental data (e.g. fragment velocity and largest fragment mass) on impact disruption have been presented by previous studies of homogeneous materials such as basalt and ice. But we do not have any experimental data on the collisional disruption of layered bodies. So, we investigate the collisional strength and fragment velocities of layered targets in order to clarify the difference of reaccumulation condition between homogenous targets and layered targets. In this study, we picked up a porous mantle-silicate core body as a layered body.
    Download PDF (13K)
  • Toshihiko Kadono, Masahiko Arakawa, Takashi Ito
    Session ID: 206
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    The distribution of angular velocity of fragments caused by impact disruption has been based on the data of "observable" fragments mainly from target surfaces. Recently, we carry out the experiments with glass plate targets, in which the angular velocities of most fragments can be measured. We extrapolate the relation between the size and angular velocity of fragments obtained by the experiments to asteroid sizes. The extrapolated values agree well with the observational results of the Karin family and some fast rotators.
    Download PDF (82K)
  • Takaaki Takeda, Keiji Ohtsuki
    Session ID: 207
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Recent observations suggest that many of small asteroids (100m $<$ R $<$ 100km) may be gravitational aggregates.Since collisions change the spin of these asteroids, their spin distribution would provide useful information about their origin and collisional evolution.However, little has been studied on the efficiency of angular momentum transfer during collision between rubble pile objects.Using N-body method to simulate impact event between rubble pile objects, we have examined transfer of angular momentum to a target (or the largest remnant if the impact is disruptive) from the orbital angular momentum of an impactor. Our simulations show low angular momentum transfer efficiency at disruptive collisions, and we found a clear relationship between the angular momentum transfer efficiency and the degree of disruption.Also, we exmined the spin-down effect of the assymetrical ejection of fragments due to the initial spin of the target, and confirmed that the rubble pile objects spin down by collisions.The rotating object spins down proportionally to the amount of mass ejection.In the case that about half the mass of the target is lost by a head-on collision, the target spins down 30-50%.
    Download PDF (176K)
  • Koji Wada, Hidekazu Tanaka, Toru Suyama, Hiroshi Kimura, Tetsuo Yamamo ...
    Session ID: 208
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Coagulation and fragmentation processes of dust aggregates by their mutual collisions in a protoplanetary disk are important to understand planetesimal formation. Recently we carried out numerical simulations of dust aggregate collisions and obtained results on the processes of aggregate compression and disruption almost consistent with those by Dominik and Tielens (1997). These simulations, however, were restricted to the head-on collision. Since offset collisions are thought to be common in dust aggregate collisions, we have to evaluate the effect of offset collisions on the aggregate structure. In this study, we carry out 3-D numerical simulations of BCCA aggregate collisions with various values of impact parameter. Through the results on the gyration radius of aggregate and the number of contacts per particle in an aggregate, we discuss the effect of offset collision on the dust aggregate structure.
    Download PDF (165K)
Oral session 6: Oct. 19, 13:20-14:32
  • Yuri Aikawa
    Session ID: 209
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Sublimation temperature of CO is about 20K. CO is considered to be frozon onto dust grains in low-temperature (T < 20K) regions of protoplanetary disks. Dartois et al. (2003), however, estimated the CO temperature to be 13K by observing two rotational transitions of CO in the disk. In this presentation, I will show that the turbulent mixing in the vertical direction can produce observable amount of low-temperature CO.
  • Minoru Sekiya, Shigeru Wakita
    Session ID: 210
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Numerical simulation of the gravitational instability of the dust layer in a protoplanetary disk is performed assuming that the turbulence is sufficiently weak. Cartesian coordinates which rotate with the local Keplerian velocity are used. The static equilibrium is assumed for the direction of the rotational axis of the disk. One fluid model of dust and gas is assumed. The shearing box boundary condition is used. The results for various parameters are presented.
    Download PDF (117K)
  • Takayuki Tanigawa, Masahiro Ikoma
    Session ID: 211
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Long term evolution of gas giant planets in the gascapturing stage is investigated by an analytic way and determine thefinal mass as a function of disk surface density, temperature,viscosity, and semi-major axis of the planet. By this results, we caninversely infer the initial condition of the disk from the present massand semi-major axis of gas giant planets like extra-solar planets.
    Download PDF (32K)
  • Keisuke Takahashi, Hiroshi Kobayashi, Sei-ichiro Watanabe
    Session ID: 212
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Solar system has experienced planetary migration in its formation stage. Especially, Neptune has an evidence of outward migration in the 3:2 mean motion resonance in the Kuiper belt objects. In the point of view of planetary formation theory, outer ice giant planet needs planetarymigration to shortening its growth time. Several simulations about planetary migration has done, and some results indicate that planet can migrate outward when disk has enough mass, but there are few works to understand the basic mechanism. In our work, we would like to focusattention on the mass flux that step over the planet to formulate the planetary migration. That kind of mass flux works as a fuel of migration.
    Download PDF (178K)
  • Ryuji Morishima, Ben Moore, Joachim Stadel
    Session ID: 213
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Remnant planetesimals might have played an important role to reduce enhanced orbital eccentricities of the terrestrial planets formed by giant impacts. However, it is not clarified how much small planetesimals exist in the giant impact phase, because simulations in the runaway growth and giant impact phases have been conducted rather independently. We conduct direct N-body simulations through the accretion of planets beginning from a planetesimal disk. The runway phase is simulated with the parallel tree-code PKDGRAV (Richardson et al. 2000), up to 100,000 yrs with adopting artificially enhanced radii. The giant impact phase is simulated with the hybrid symplectic code Mercury (Chambers 1999) up to 100Myr. Fixing the total mass and angular momentum to the values for the current terrestrial planets, we vary the width of the initial planetesimal disk (0.01-0.5AU) and the number of planetesimals (1000-5000). We find that in most of the cases a planetesimal disk results in three planets with similar size, although we sometimes obtain two planets for an initially narrow disk. There is a weak correlation between the initial width of a planetesimal disk and the final separation of planets. Also, orbital eccentricities of final planets are small enough for the initial width of 0.5AU.
    Download PDF (79K)
  • Masahiro Ogihara, Shigeru Ida, Alessandro Morbidelli
    Session ID: 214
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    We have investigated the final accretion stage of terrestrial planets from Mars-massprotoplanets that formed through oligarchic growth in a disk comparable to the minimummass solar nebula (MMSN), through N-body simulation including random torques exertedby disk turbulence due to Magneto-Rotational-Instability. For the torques, we used thesemi-analytical formula developed by Laughlin et al. (2004). The damping of orbitaleccentricities (in all runs) and type-I migration (in some runs) due to the tidal interactionswith disk gas are also included.
    We have carried out aseries of N-body simulations including the random torques with different gas surface density and strengthof turbulence. We found that the orbital eccentricities pumped up by the turbulent torquesand associated random walks in semimajor axes tend to delay isolation of planets, resultingin more coagulation of planets. The eccentricities are still damped after planets becomeisolated. As a result, the number of final planets decreases with increase in strength ofthe turbulence, while Earth-mass planets with small eccentricities are still formed.
    Download PDF (227K)
Oral session 7: Oct. 19, 14:50-16:02
  • Eiichiro Kokubo, Shigeru Ida
    Session ID: 215
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    The final stage of terrestrial planet formation is known as the giant impact stage where protoplanets collide one another to form planets. We statistically investigate this stage by using N-body simulations. As initial conditions, we adopt the oligarchic growth model of protoplanets. We systematically change the radial size of the initial protoplanet system. We show the dependence of the mass and orbital properties of the assembled planets on the initial protoplanet system size.The number of planets in the terrestrial planet region barely depends on the initial system size, while the mass of the individual planet increases with the initial system size.
    Download PDF (122K)
  • Makiko Nagasawa, Eiichiro Kokubo
    Session ID: 216
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    We studied dynamical evolution of the Hot Jupiters orbiting around young host stars with other planets. In the stage of planet formation, the host stars are in pre-main stage and are surrounded by the protoplanetary disks. As the host stars evolve to the main sequence, the stellar radii and the speed of rotation change and the gas disks are depleted. They cause evolution of the orbits of Hot Jupiters. When the Hot Jupiters have large eccentricities, the tidal dissipation of energy during the circularization would induce their interior heating, inflation, Roche lobe overflow, and mass losses. We studied the necessary conditions for the survival of hot Jupiters. We found that the Hot Jupiters in the multiple planetary system orbiting around young stellar objects whose spin periods are longer than a few days may be highly vulnerable to the dissipation of the disk and evolution of the stars.
    In the multiple planetary system, orbital instability of planets followed by the tidal circularization is a candidate for the formation mechanism of the Hot Jupiters. We also studied the efficiency of this process. We found the Hot Jupiters can be formed due to the Kozai mechanism.
    Download PDF (110K)
  • Akiko Sakamoto, Yutaka Abe
    Session ID: 217
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    It is considered that our solar system was formed from the proto-solar nebula. When protoplanets becomes as massive as the present Mars, they attract the surrounding solar nebula gas and gain solar-type atmospheres (Hayashi et al., 1979; Nakazawa et al., 1985). Mizuno et al. (1980; 1982) calculated the amounts of rare gases captured by the growing proto-Earth. They showed that the proto-Earth captured too much more He and Ne than those exist in the present Earth's atmosphere.
    On the other hand, Kominami & Ida (2002) showed that the nebula gas with 10-3~10-4 times of the minimum mass solar nebula (MMSN) model is necessary to damp eccentricities of planets to the present level (order of 0.01). Although this density of the solar nebula gas is much smaller than that of the MMSN model, it is still large enough for the proto-Earth to capture very large amounts of He and Ne.
    In order to resolve this problem, we examine the possibility that the gas temperature in a thin solar nebula was much higher than that of previous estimates. Increase in the gas temperature results in increase in the thermal energy of nebula gas compared to the gravitational potential. Thus, it results in order of magnitude decrease of the amount of nebula gas (i.e., He and Ne) captured by the proto-Earth.
    Download PDF (97K)
  • Hiroshi Kobayashi, Sei-ichiro Watanabe, Tetsuo Yamamoto, Hiroshi Kimur ...
    Session ID: 218
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    We investigate the sublimation effect on dust-deblis disks. We assume a constant dust production. When we consider migration of dust grains only due to Poynting-Robertson effect, the surface number density is constant for radial distance. The sublimation effect slow down the migration due to Poynting-Robertson drag and dust grains accumulate in the sublimation region. As a result, the surface number density in the region is about 10 times higher than that in outer region.
    Download PDF (130K)
  • Taku Takeuchi, Oliver Krauss
    Session ID: 219
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Photophoresis in optically thin disks is studied. Dust particles accumulate at the locations where Knudsen number (the ratio of the mean free path of gas molecules to the dust particle size) Kn>1. Photophoresis works to make a dust ring whose inner radius is determined by the condition Kn=1. The ring inner radius does not depend on particles' physical properties, and locates at 0.03-0.3 AU. The condition Kn=1 for inner ring radius provides us a method for the observational test to check if photophoresis actually occurs or not.
    Download PDF (125K)
  • Ryuji Morishima, Heikki Salo, Keiji Ohtsuki
    Session ID: 220
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    The thermal infrared brightness of Saturn's rings isinvestigate based on the classical radiative transfer.In our model, the vertical heterogeneity of spin frequencies of ring particles and the heat transport due to vertical motion of particles are taken into account. We adopt a bimodal size distribution, in which rapidly spinning small particles with large orbital inclinations have surface temperatures closer to isothermal,relative to those for non-spinning large particles with small orbital inclinations. We find that our model reproduces surprisingly well the ring temperatures obtained by both Earth-based observations and by Cassini CIRS. For Earth-based observations, the large temperature increase with solar elevation angle observed in the A andB rings (called the tilt effect) can be reproduced contributed by all the effects mentioned above.Observations by Cassini CIRS show reduced temperatures at high solar phase angles, suggesting that at least some fraction of slowly spinning particles is necessary. Our model suggests that the contribution of slowly spinningparticles to the cross section is about 0.5, 0.8, and 0.5 for the A, B, and C rings, respectively.
    Download PDF (45K)
Oral session 8: Oct. 20, 10:15-11:51
  • Minoru Ozima
    Session ID: 301
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    On the mean oxygen isotope composition of the solar system.
    Download PDF (103K)
  • Junya Miki, Aki Takigawa, Shogo Tachibana, Gary Huss
    Session ID: 302
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    We applied nucleosynthesis yields in type II supernovae with mixing-fall back to the initial abundances of short-lived radionuclides, once existed in the early solar system. The initial abundances of 26Al, 41Ca, 53Mn, 60Fe and the lower limit of 36Cl can be explained by injection of the ejecta from a type II supernova of a massive star (>25Msolar) to the solar system with dilution of 10^-4-10^-5 and a time interval of 0.8-1 Myr. This indicates that the solar system was born neaby a massive star.
    Download PDF (120K)
  • Ryosuke Machida, Yutaka Abe
    Session ID: 303
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Recent studies (Chiang & Goldreich, 1997; Chiang et al., 2002) imply that the interior of the protoplanetary disk is shadowed from direct exposure to sunlight, so that the H2O ice is prevented from sublimation even at the formation region of terrestrial planets. If planetesimals are formed in such opaque protoplanetary disks, they should be mainly composed of H2O ice. We call such planetesimals icy planetesimals hereafter.
    We have investigated the evolution of icy planetesimals at the formation region of terrestrial planets. The collisional growth and the sublimation of icy planetesimals are especially important to estimate the abundance of H2O that survives until the formation of protoplanets. In addition, the internal structure and the thermal history of icy planetesimals have strong effects on the water supply to the planets.
    In this study, we investigate the thermal history of icy planetesimals heated by short-lived radioactive elements such as 26Al.
    Download PDF (89K)
  • Takashi Fukui, Kiyoshi Kuramoto
    Session ID: 304
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Oxygen isotopic composition of chondritic constituents(CAIs and chondrules) implies the existence of 16O-rich/17O- and 18O-rich oxygen reservoirs and the mechanicalmixing of them with various mixing ratio in the solarnebula. Recent studies suggest that CO self-shieldingeffect in parent molecular clouds produces the 16O-rich CO gas and 17O- and 18O-rich H2O ice.In this study, the mixing process of these reservoirsand its effect on the oxygen isotopic composition ofprotoplanetary accretion disks are proposed. Due to thepreferential dust transport in an accretion disk,17O- and 18O-rich H2O vapor enriches inside thesnow line. The degree of enrichment increases with decayof T Tauri accretion, following that the oxygen isotopiccomposition of the inner disk gradually evolves from16O-rich to 17O- and 18O-rich. We numerically simulateabove processes for the main oxygen reservoirs includingH2O and silicate, and follow the oxygen isotopicevolution quantitatively. Results are compared with theisotopic and chronological analysis of CAIs and chondrulesto clarify the oxygen isotopic evolution in the solar nebula.
    Download PDF (178K)
  • Erika Kurahashi, Noriko Kita, Hiroko Nagahara, Yuichi Morishita
    Session ID: 305
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    26Al ages of FeMg chondrules in a primitive CO chondrite are similar to those in the least equilibrated ordinary chondrites (1.0-2.5Ma after CAI formation). Bulk chemical compositions of the CO chondrules have higher FeO contents relative to those of ordinary chondrite chondrules. CO chondrules formed contemporaneously with ordinary chondrite chondrules in a different redox condition in early solar system. Using behaviors of silicates, organics and H2O ices with distance from the Sun in a protoplanetary disk and its time evolution, we propose an qualitative chondrule forming model.
    Download PDF (129K)
  • Masayuki Uesugi, Takeshi Akaki
    Session ID: 306
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Compound chondrules are composed of two or more chondrules fused together. We focus our attention on the compound chondrules, in order to investigate the chondrule formation process. We observed textures of the constituent chondrules, and measured the three-dimensional structures of them.
    Download PDF (45K)
  • Hitoshi Miura, Taishi Nakamoto, Masao Doi
    Session ID: 307
    Published: 2006
    Released on J-STAGE: June 01, 2007
    CONFERENCE PROCEEDINGS FREE ACCESS
    Millimeter-sized, spherical silicate grains abundant in chondritic meteorites, which are called as chondrules, are considered to be a strong evidence of the melting event of the dust particles in the protoplanetary disk. One of the most plausible scenarios is that the chondrule precursor dust particles are heated and melt in the high-velocity rarefied gas flow (shock-wave heating model). We considered the deformation of rotating molten dust particles exposed to the gas flow by using the three-dimensional hydrodynamic simulation. We found that the molten droplet just before solidification deforms to prolate shape and its shape is very similar to the prolate chondrules measured by Tsuchiyama et al. (2003). Our results strongly suggest that once-melted precursor particles of such prolate chondrules have solidified in the high-velocity gas flow with a proper rotation rate.
    Download PDF (110K)
feedback
Top