We present evidence that Jupiter-family comets (JFCs) supply substantial materials into the interplanetary space. Nine JFCs were observed by ground-based telescopes with optical CCD cameras. The obtained images were compared with the semi-analytical dynamical model of the dust particles emitted with none-zero velocities. It is found that all of these comets emitted big particles (>1mm) within 2 AU, and injected their mass at the rate of 23 kg/s on average. We suggest that JFCs constitute a significant fraction of the total mass of interplanetary dust particles. Another finding is that the maximum size of the particles from nuclei is likely to depend on the perihelion distance. Around the Earth orbit, several centimeter-sized particles could be released from JFCs, which might be observable as fireball on earth.
The meteor shower activity is thought to be proportional to the activities of the parent comet. So-called dust trail theory provides us a new approach to its quantitative comparison. We here present the result of our application to the comet P/Giacobini-Zinner and its related meteor shower, the Giacobinids
The nucleus of the Comet 73P/Schwassmann-Wachmann had been split into many fragments at least past two returns. Since the related dense dust trail has been detected in the space infrared observation, the strong activity of the meteor shower is highly expected in the future. We applied the so-called dust-trail theory to this interesting object, and obtained several results on the future encounter with the dust trail. In this presentation, we introduce our results on the forecasts.
The Orionid outburst observed in 2006 resulted in strong activity, continuing for about four days. We have found that this activity was caused by the dust trails formed by meteoroids ejected from 1P/Halley in -1265, -1197 and -910. The orbital period of these meteoroids had six times the Jovian orbital period. Therefore, the mean motion resonance with Jupiter is thought to have forced these meteoroids move close to intersect the Earth's orbit.
The oxygen atoms in meta-stable state are considered to be generated by the photo-dissociation of parent molecules such as H2O, CO2, etc. H2O molecule is usually thought as the most dominant source of these oxygen atoms in meta-stable state when a comet is at around 1 AU from the Sun. However, The ratio of green to red doublet lines, which indicates the ratio of O(1S) to O(1D), would give us a clue to dis-tinguish the source of meta-stable oxygen atoms from different parent molecules.
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 evaporation of silicate dust particles in the post-shock region and the thermal evolution of the dust vapor by carrying out the 1-dimensional hydrodynamical simulation of passage of a shock front. We obtained the density and temperature evolutions of the dust vapor. Based on these results, we will discuss the results of our numerical simulation.
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. Compound chondrules are composed of two or more chondrules fused together. In this study, we propose a new scenario for compound chondrule formation in framework of the shock-wave heating model. We model the disruption of molten cm-sized parent dust particle exposed to high-velocity gas flow in order to estimate the efficiency of mutual collisions between small fragments. The predicted collision frequency was ~0.1 - 1 or more, which is about one order of magnitude larger than the observational compound fraction. We find that the predictions of our model are consistent with other observational data. We conclude that this new model can account for compound chondrule formation.
A model to describe nucleation and growth of dust was developed by taking heterogeneous condensation into consideration. The condensation sequence, assemblage, and size distribution was investigated as a function of cooling time and pressure of gas. The results were compared with recent infrared observations and dust formation condisionts were estimated.
We calculated numerically the motion and the temperature of the dust entering into the atmosphere to evaluate the magnitude of the ram pressure acting on the dust particle when it solidifies. Then we take into account the decrement of the size by evaporation. Furthermore we obtained an analytic solution for the shape of the molten particle and quantified the magnitude of the dust particle's deformation. As a result, it seems highly likely that some dust particles that have proper entry parameters form prolate cosmic spherules. We compared the magnitude of the deformation of the dust particles calculated in this study with that of the collected cosmic spherules. Then we could explain the magnitude of the deformation of collected cosmic spherule.
A number of Mars missions have been operated, and it is suggested that plenty of water was present on the surface of Mars. Now the aim of missions is moved from "follow the water" to "follow the carbon". Many methods to detect extant and/or extinct life have been proposed, but there is no comprehensive one since we do not know the nature of Martian life if any. We proposed the methods based on the detection of enzymatic activity: Fluorescence microscopy methods with esterase substrates, and butch methods with phosphatase substrates. When CFDA-AM (substrate which gives fluorescence after hydrolyzed) was used, most of terrestrial microorganisms could be detected, while only 1 % of them could be detected by using the cultivation method. By using p-nitrophenyl phosphate or 4-methylumbelliferyl phosphate, we could detect microbial activities in such terrestrial extreme environments as core samples of submarine hydrothermal sub-vents, chimneys of submarine hydrothermal vents, and surface soils in Antarctica. It is promising to detect extraterrestrial extant life by using these enzymatic detection methods, combined with other chemical methods such as analysis of D/L ratios of amino acids.
Asteroid Multiband Imaging Camera (AMICA) has acquired more than 1400 multispectral and high-resolution images of its target asteroid Itokawa since late August 2005. In this presentation we summarize the design and the performance of AMICA. In addition we describe the details of the methods, assumptions and model in the calibration, based on both preflight and inflight measurements.
We are investigating next missions of Hayabusa, which is the sample return mission from Asteroid Itokawa. Itokawa is an S-type asteroid, so next targets are C or D-type asteroids or dormant comets. Such objects are important from the scientific point of view. Also we should plan new mission so that we can get much more products. In this paper, we summarize what we have discussed about our new mission to primitive bodies in the solar system.
Hayabusa 2 is an asteroid sample return mission following Hayabusa mission. This mission is now under study and mission target is c-type asteroid 1999JU3. From summer 2007 to April 2008 the observation from the earth is favorable conditions. This chance of observation is the first in 8 years from discovery. About 1999JU3 we had known only spectral type until now so we had observed lightcurve of it in July 2007. As a result we have found that its rotational period is about under 6 hours. This time, we will report about information of 1999JU3 we had get until now for example the result of lightcurve from July to September and about the result of AKARI in May and so on.
The Planetary Sample Curation Facility of Japan will be completed at the end of fiscal 2007. The facility will treat the sample of "Hayabusa". The sample will be protected from the environments of Earth's conditions, and analized and described in cooperation with other institutes of Japan. The basic research of contamination protection is the other aim of the facility for the future planetary sample returen mission. We represent the status and spacifications of the facility, decided by the study board of geochemists, planetary scientists, and others.
In protoplanetary disks, planetesimals are formed through the gravitational instability or simple coalescence. If the gravitational instability occurs, it needs that dust aggregates becomes large aggregates (a few m) that gas drag force is not efficient. Small dust aggregates have the fluffy structure. However, dust aggregates are compressed before it becomes large. Thus, large dust aggregates can not have such fluffy structure. Such compression change the cross section. The gas drag force which govern the dust motion is proportional to cross section. Thus, when and how to occur compression is important on dust growth. In this study, we perform the N-body simulation of aggregate collisions. We repeat collisions between two aggregates. The initial aggregate is the aggregate obtained in the preceding collision. In our simulation, collisions between dust which have a variety of the impact velocity occur. We examined the density change at such collisions. We introduce the pressure and construct the model which is consistent with our numerical simulations.
We carried out three-dimensional hydrodynamic simulations to examine disruption of the molten dust particle exposed to fast gas flow and estimated the ejection velocity, average size, and number of ejectors in the framework of shock-wave heating model. We found that collision frequency predicted from our numerical results is much higher than observational frequency of compound chondrules for various parameters (radius of parent particle, ram pressure of gas flow, viscosity of molten part). We also found that two individual ejectors collide actually in our simulation because of the effect that one ejector blocks out the gas flow toward another one (shadow effect).
Water-containing minerals, phyllosilicates, have been found often in extraterrestrial objects such as carbonaceous chondrite or interplanetary dust particles. Their formation mechanisms in the early solar system have been discussed vigorously. Hydrothermal alteration by low-temperature water in the interior of the planetesimals is proposed as the most plausible origin of phyllosilicates. Experiments were demonstrated by using single-stage propellant gun. Recovered samples were observed with TEM and SEM. We found clear evidences of experimental serpentinization of olivine by impact with water based on the investigation of the shock-recovered samples with TEM. Formation of micro-cleaves in olivine crystals by the impact event and subsequent alteration by impact-generated supercritical water promoted rapid serpentinization of olivine. The present results suggest a new model that abundant serpentine might have easily been formed by collisions between icy and silicate objects even in low temperature region of the early solar system. The water in phyllosilicates is widely thought to be a major source of water for some planets. It is highly likely that serpentine formed by shock events in the early solar system might have a dominant carrier of the water on the Earths.
In the case of airless bodies, space weathering effects are so strong that their surface reflectance spectra show reddened continua, lowered albedos, and attenuated absorption features. Thus, important features for detecting component minerals and their chemical compositions are suppressed. A simple model was proposed which accounts for the optical effects of nanophase reduced iron particles in a semi-transparent matrix (Hapke 2001). An improved version of this Hapke's model is introduced. And in the surface reflectance spectra of planets, we often find a composite absorption band in wavelength due to the component silicates. As a method of deconvolving this complex absorption band into those of its component minerals, MGM is used as a standard way. Each mineral species usually has multiple bands which overlap with one another and those of other minerals, making it difficult to assign the deconvolved bands into individual mineral components. Because the relationship between the chemical composition and absorption band characteristics of some minerals are known to some extent, it is expected that the above problem can be solved by utilizing such knowledge.
Cratering on brittle materials in the strength regime is controlled by each target strength, initial peak pressure, shock attenuation rate in the target, and density ratio between target and projectile materials. We showed that the crater depth and di-ameter depends on the uniaxial compressive and tensile strength, respectively (Hiraoka et al., submitted). In the solar system, porous structure has been found to be common among small bodies (e.g. Britt et al., 2002). Thus, we investigate the effect of target porosity on the cratering in the strength regime. We made sintered glass bead-silicate mixtures as the target. We performed impact cratering experiments on mixture targets at high velocity (2.5km/s to 3.5km/s) and low velocity (about 200m/s) and measured uniaxial compressive and tensile strength. In order to investigate the effect of density ratio between target and projectile materials we used glass and stainless sphere as the projectile. We will compare the results with previous studies and report the effect of density ratio and target porosity on the cratering.
Some planetesimals scattered by dynamical excitation are pumped up their inclinations. They spend most time in high ecliptic latitude region where the frequency of encounter with planets or resonances and collision between planetesimals are less. High-inclined main-belt asteroids are considered to retain the population and size distribution of such planetesimals. To investigate them, we performed a survey for small asteroids with high inclination in high ecliptic latitude field. We analyzed the archive data of Subaru Telescope using our new-developed detection method. More than 80 small asteroids were detected in the field of the ecliptic latitude 20o-50o. We will discuss their number density and size distribution.
Poleward-facing slopes are preferentially flattened more than equatorward-facing slopes in the middle latitudes of Mars. In this study, we confirm whether the process of the preferential flattening were active during the Amazonian, based on statistical investigation of impact craters on the relatively new surface of the Alba Patera region. In most cases, the angle of the poleward-facing wall is lower than that of the equatorward-facing wall of each crater at latitudes from 35 N to over 50 N. Shallow craters have both poleward-facing walls, the surface of which seems to be covered with ice-rich material, and floors which tend slightly to incline toward poleward. This may suggest that repeated formation and downward deformation of ice-rich mantling on poleward-facing walls, which is interpreted to have been formed at high obliquity, result in the formation of thick ice-rich infilling. Poleward-facing slopes may be preferentially flattened by the ice-rich deposits rather than erosional modification.
Planetesimals had repeated collisional disruption and/or accretion. As planetesimals collided each other to grow in their sizes, pressure sintering, melting and gravity differentiation of the constituent materials could cause the changes of their interiors. As a result, there could be a lot of growing bodies with heterogeneous internal structures; silicate core-porous silicate mantle body and metal core-rock mantle body. Therefore, we should consider a collisional phenomenon not only for homogenous bodies but also for core-mantle bodies to strictly 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, gypsum and ice. But we do not have any experimental data on the collisional disruption of core-mantle bodies. Therefore, we performed impact experiments on core-mantle targets in order to study the differences of fragment mass distributions, fragment velocity distributions and impact strengths between homogenous targets and core-mantle targets. We used a glass core-gypsum mantle target as a core-mantle target.
The Lunar suface gravimeter(the LSG) on Apollo 17 was aimed to detect gravitational wave.However,it was found out that the LSG was working as a seismometer. On this study, we analized the LSG data and evaluated its quality.Also, we estimated the mean thickness of the lunar crust from the data.
Oxygen isotopic heterogeneity among chondritic constituents (16O-rich CAIs and 16O-poor chondrules) reflects evolution in oxygen isotopic composition of the inner solar nebula gas. Yurimoto and Kuramoto (2004) have suggested that the oxygen isotopic evolution at the inner nebula was induced by subsequent enhancement of 16O-depleted H2O which produced by photochemical process in the parent molecular cloud. In their model, the excess H2O was supplied from outer part of the nebula with inward migration of ice-covered dust particles and evaporation of the icy mantle. However, they did not consider migration of silicate dust particles which apparently result in depletion of chondrule precursors. In this study, we perform a numerical simulation of radial transport of H2O and silicate in a turbulent protoplanetary disk considering difference in adhesive properties between H2O ice and silicate. As a result, sticky ice-covered dust particles grow up to ~cm and efficiently migrate inward supplying excess water vapor to the inner nebula, while small (~sub-mm) silicate particles are well coupled to the nebula gas and retained in the inner nebula over ~Myr.
In the dust layer of a protoplanetary disk, a dust aggregate move toward a central star due to the gas friction. On the other hand, the gas moves outward by gaining the angular momentum. Thus, dust and gas move in the different directions, respectively. In this case, it is known that the streaming instability occurs. We performed numerical simulations of shear and streaming instabilities in the dust layer. Our simulations show that stronger instability occurs if the gradient of the dust profile exists.
Protoplanetary disks are mainly heated by radiation from the central star. Since the incident stellar flux at any radius is sensitive to the disk structure near that location, an unstable feedback may be present. We calculate the quasi-static thermal evolution of irradiated disks by directly integrating the optical depths to determine the optical surface and the total emitting area-filling factor of surface dust. We show that, in disks with modest mass accretion rates, thermal waves are spontaneously and continually excited in the outer disk, propagate inward through the planet-forming domains, and dissipated at small radii where viscous dissipation is dominant. This state is quasi-periodic over several thermal timescales and its pattern does not depend on the details of the opacity law. The viscous dissipation resulting from higher mass accretion stabilizes the instability and an approximately steady state is realized throughout the disk. In passive protostellar disks, these waves induce a significant change in SEDs because the midplane temperatures can vary by a factor of two between the exposed and shadowed regions.
The meter-sized particles rapidly fall into the central star due to the gas drag force, before planetesimal formation. Thus, some outflow mechanisms are required for planetesimal formation. We consider the stellar radiation pressure induced the dust outflow for a weak turbulent disk with the puffed-up inner rim, where magnetorotational instability is induced because of thermal ionization of alkali metal. Our main objective is to investigate a possibility for the realization of dust circulation in the protoplanetary disk. We will report results by new numerical simulation code.
We performed numerical simulations of the gravitational instability of the dust layer in a protoplanetary disk. We compared results begin with Q=5 and 2. We also compared results for perturbations given once initially, and continually at each Keplerian shear.
We study dust aggregate collisions to construct a model of their structure evolution in protoplanetary disks. We carry out three-dimensional simulations of aggregate collisions and examine the compression and disruption processes. We take clusters of ballistic cluster-cluster aggregation (BCCA) as initial structures and study their head-on collisions. For aggregate compression due to collision, we succeed in obtaining a scaling law on the gyration radius of the resultant aggregate as a function of the impact energy using the fractal dimension of compressed aggregates. Furthermore, we derive an ``equation of state'' of aggregates which reproduces the scaling law for compression. This equation of state would be useful to describe the density evolution of dust aggregates during their growth.
We examine planetesimal formation through direct dust growth. Our group showed that icy dust aggregates stick to each other at their collision for an impact velocity less than several tens m/sec. Thus it is worthwhile to examine planetesimal formation through direct dust growth. We compare the growth time of dust with the time scale of dust falling to the sun. As a result, we found that dust aggregates can grow before their falling if they settle to the mid-plane of gaseous disks. When dust aggregates grow to km-size, their self-gravity is effective and the mode of their growth would change to runaway.
A planetesimal is an object of 1-10 km in size, from which planets in our solar system are formed. The formation process of the planetesimal is still controversial. Gravitational instability of a dust rich sublayer is a convincing model for the formation mechanism of the planetesimal, but it requires the ratio of dust to gas surface density enhanced by 5-20 times over normal cosmic values. Many models are proposed to enhance the ratio to trigger the gravitational instability; dust concentration by turbulence eddies, magnetohydrodynamic turbulence, radial drift of dust aggregates, anticyclonic vortices, and photoevaporation by UV rays. Here I show capillary instability followed by the sintering of H2O ice is an effective mechanism to increase the ratio locally. Fragments from the surface of the dust aggregate stagnate around the heliocentric distance where the sintering proceeds. This mechanism straightforwardly increases the dust to gas surface density ratio by a factor of 10 or more enough to trigger the gravitational instability.
We studied the origin of short-period planets by numerical simulations. Many short-period Jovian or Neptunian planets are discovered outside of the solar system. One proposed mechanism for the formation of short-period planets is a slingshot model. In this model, a planet is scattered into shorter orbit by close encounters of the planets, and the dynamic tide from the central star makes the planet be short-period. We performed numerical simulations to test the efficiency of the slingshot model. Although the planet cannot be scattered into the short-orbit directly, we found that the Kozai mechanism effectively make the short-period planets, especially when more than three planets are left in the system. In our simulation, the short-period planets are formed at about 20-30% cases after the planet-planet scatterings.
We have investigated accretion of terrestrial planets from planetesimals around M dwarfs through N-body simulations including the effect of tidal interaction with disk gas. N-body simulations start from 5,000-10,000 planetesimals. Their self-gravity is calculated with GRAPE-6. Tidal damping of orbital eccentricity, inclination and semimajor axis is calculated with forces in equations of motion that are obtained by the linear theory. Because of the low luminosity of M dwarfs, their terrestrial planet regions are located near central stars (< 0.3AU) and habitable zones (HZ) are ~0.1AU. Accordingly, the formation of terrestrial planets around M dwarfs would differ from that around G dwarfs. Orbital decay due to the tidal interaction with disk gas (type I migration) and aerodynamical gas drag is much more efficient in such inner regions than that in HZs around solar-type stars. Furthermore, the terrestrial planet accretion would be affected by the disk inner edge (~ 0.05AU). Planetary embryos and planetesimals that migrate from outer regions pile up there and they would affect accretion in HZs. We will present preliminary results of N-body simulations.
In the last stage of the terrestrial planet formation, several giant impacts occur. Although the nature of giant impacts determines the final state of the terrestrial planets (number, mass, spin etc), all the previous N-body simulation of terrestrial planet formation have been based on the assumption of the perfect accretion. Agnor and Asphaug (2004) performed 48 SPH simulations for mutual collision of Mars-mass planets. They showed that the two protoplanets bounce and escape to infinity for collision with relatively faster impact velocity, and they estimated that more than roughly half of giant impact events are not coalescence events.To incorporate the effect of imperfect accretion into N-body simulations, we need to know the accretion condition for various types of giant impacts. Using the special purpose computers named micro-GRAPE6, we performed more than 1000 runs of impact SPH simulations. We formulated the boundary between coalition and rebound. We also formulated the mass(es) and orbit(s) of post-impact planet(s). We applied the above formulation to the impact events obtained by Kokubo et al. (2006), and 41% of giant impacts are not coalescence events.
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. So far we adopted perfect accretion in which all collisions lead to accretion. In the present paper, we adopt imperfect accretion, in other words, accretion condition of protoplanets. We show the dependences of the mass and dynamical properties of assembled planets on the accretion models. Especially we focus on the spin velocity of planets, which is decreased by the imperfect accretion.
Planetesimals with great semimajor axes by planetary scattering form the spherical Oort cloud due to the Galactic tide. However, the distribution of the inclination is not isotropic. Passing stars, that have random-wark nature, may play an important role in producing an isotropic distribution of the inclination. Using the impulse approximation, we analytically examine the effects of stellar encounters on the orbital evolution of planetesimals. For the initial condition, we use a flat planetesimal disk on the ecliptic plane formed by planetary scattering.
Solar system has experienced planetary migration in its formation stage. To understand formation of Solar system, it is important to reveal the migration mechanism of planet. We investigate the planetary migration by using numerical calculations, and we found that changes of specific angular momentum of planetesimals are in inverse proportion to migration velocity of planet. This trend means planetadjusts its own migration velocity.
Trans-Neptunian objects (TNOs) orbit in the so called trans-Neptunian belt (or Edgeworth-Kuiper belt). These icy bodies represent the relics of planet accretion in the outer solar system. We investigated the structure of the trans-Neptunian belt by conducting extensive computer simulations (4-5Gyr) using tens of thousands of particles in planetesimal disks. After taking into account several observational constraints, we developed a model to explain the origin and evolution of the belt by considering a hypothetical outer planet (or planetoid) with tenths of Earth masses orbiting beyond about 100AU.An outer planet in a distant orbit in the scattered disk can explain the ancient trans-Neptunian belt excitation, the formation of an outer edge at ~48AU, the entire TNO resonant population, the formation of detached TNOs and many other features in a self-consistent way. Noteworthy, the results match very well up-to-date observations. The best constraints obtained from the model for the planetoid are: aP=100-170AU, qP>80AU, iP=30-50 degrees, albedo=0.1-0.3, and apparent magnitude mP=15~17mag at perihelion.In summary, our model with the existence of a distant massive planet successfully describes the trans-Neptunian belt architecture with an unprecedented level of details.
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.
Recent study (Chiang & Goldreich, 1997) implies 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. The competition of the collisional growth and the sublimation of icy planetesimals controls the abundance of H2O that survives until the formation of protoplanets. In addition, the internal structure and the thermal history of icy planetesimals will have strong effect on the water supply to the planets. In this study, we perform numerical simulation of the thermal history of icy planetesimals heated by short-lived radioactive elements such as 26Al to explorer the condition that allows the formation of hydrous minerals.
The theory of planetary accretion suggests that if the Earth is formed in the solar nebula gas, the primordial earth should capture the solar composition atmosphere. At that time, Ne included in the atmosphere voluminously dissolves into the magma ocean. However, the amount of dissolved Ne estimated from the captured atmospheric amount is inconsistent with that of Ne found on the present earth. In this study, we investigated the amount of Ne escaped from a mantle as atmosphere decreases at the time of nebula dissipation that had not been considered before. As a result, we found that a large amount of Ne could be escaped from the primordial earth with nebula dissipation and the amount of Ne remained on the Earth could be less than that of the past study.
Partitioning of atmophile elements among gas, silicate melt, and molten metallic iron within a growing earth is estimated by using a thermodynamic model based on Kuramoto and Matsui (1996, hereafter called KM96). It is thought that the origin of the atmosphere of the terrestrial planets are (1) capture of nebular gas, (2) degassing by collision of planetesimals before core formation, and (3) late-veneer atmosphere by accretion of oxidative planetesimals after core formation. On the other hand, Hashimoto et al. (2007) made a point of little effect of late-veneer to the formation of atmosphere of terrestrial planets and Genda and Abe (2003) gave suggestions that planetary atmosphere is likely not to thoroughly escape by Giant Impact. In this research, we focus attention on the case (2) that is considered to play a key role to atmosphere formation by modifying the model of KM96.KM96 didn't consider differentiation of iron settling and degassing. Therefore, we took into account the differentiation of three phases, and the effect of planetary accretion to consider more realistic condition.
We examine the effect of mantle heat source distribution on the thermal evolution of Mercury. The radioactive elements, which are incompatible elements, are likely to be enriched in the crust. While Earth's crustal material partly returns to the mantle by the plate motion, Mercury's crustal elements are likely to be retained because of the lack of plate motion. This implies that Mercury's mantle has less heat sources and secular cooling may be more efficient. We calculate Mercury's thermalhistory by using mixing length theory and compare the highlydifferentiated mantle model with the homogeneous mantle model.
The origin and thermal evolution of iron meteorites are important topic to study since they are one of the most oldest material in the solar system we can obtain. According to analysis of isotopic chronology system, they have been separated from silicate within a few myr after CAI formation. On the other hand, Widmanstätten patterns tell us the cooling rate at around 800K. In this study, we construct a develop model on thermal evolution of planets with ra-dius of 1—100km taking into account melting and silicate-metal separation. Our results show metallic core formed as long as the size of silicate grains is larger than 50μm, and cooling rate as slow as 100 K/myr is achieved if the radius of planet is larger than about 20 km.
The study is presented to analyze the temporal change of conduction heat transfer in the real earth from a prescribed high uniform temperature based on the thermal radiation cooling of surface boundary. Both the multi-spherical shell structure and the latent heat release due to solidification are taken into consideration. The feasibility and/or the effect of mantle convection on the thermal structure of the earth are discussed in a simplified plane parallel system.
Hypervelocity impacts on anhydrite (CaSO4) induce degassing of SO2. Degassed SO2 is released into the atmosphere of planets and is thought to play an important role in controlling the surface environment of planets. For example, sulfate aerosols produced from SO2 were thought to block the sunlight and invoke the mass extinction at 65 Ma Cretaceous/Tertiary boundary (K/T boundary). However, it is suggested that these SO2 back-reacts with CaO into CaSO4 (i.e., SO2+1/2O2+CaO->CaSO4) in impact-induced vapor clouds soon after degassing. In this case, the amount of SO2 released into the atmosphere decreases. Impact-induced vapor clouds larger than the atmospheric scale height cool by adiabatic expansion and reach the temperature-pressure state where the back-reaction of SO2 and CaO is thermodynamically possible. However, if the reaction rate is slower than the cooling rate of vapor clouds, the back-reaction is inhibited kinetically. In this study we determine the reaction rate of the back-reaction SO2+1/2O2+CaO->CaSO4. Then, we compare the reaction rate and the cooling rate of the impact-induced vapor clouds to examine whether the back-reaction really occur. The results show that the back-reaction occurs in K/T-scale vapor clouds and that more than 40% of SO2 are consumed.
Meteorite impacts on the Earth induce the release of a huge amount of climatically active gases from the impacting body and crustal material under very high temperature and pressure condition. Here, we focused on the impact-induced degassing from carbonate minerals which is abundant on the Earth. Previous researches have assumed that impact-induced gas from carbonate is wholly CO2 [e.g. O'Keefe and Ahrens, 1989]. However, there is a prospect that the gas from carbonate contains CO which is stable under high temperature. The release of CO and its atmospheric chemical reactions may cause the increase of tropospheric ozone which has intensive greenhouse effect. Hence, when we consider the climatic effects caused by impact-induced gases from carbonate, it is very crucial problem whether the gas is CO or CO2. Now we conducted the impact-degassing experiments using a laser gun and specified the molecular species of impact-induced gas from carbonate.
Devolatilization from rock caused by hypervelocity impacts is believed to have played important roles on early atmosphere formation and the evolution of surface environments of terrestrial planets. In order to apply the results of laboratory experiments to planetary scale impacts, we need to understand detailed physical and chemical process and to establish the scaling law of impact-induced devolatilization. In this talk, we show the result of shock recovery experiment using calcite. The result suggests that the devolatilization from calcite occurs during the release of pressure.
Neutron is a storong probe for material sciences at high pressure, especially for hydrogen compounds. Thus it is the most desirable probe to analyze the property of ices at high pressure. A spallation neutron source of new generation is now being constructed in Tokai, Ibaragi Pref. as a part of the J-PARC project. Examples of scientific problems on ice sciences at high pressure are proposed, which will be newly revealed with this powerful neutron source.