Akira Miura
A5057550153- Ionosphere and magnetosphere dynamics
- Astro and Planetary Science
- Solar and Space Plasma Dynamics
- Planetary Science and Exploration
- Geomagnetism and Paleomagnetism Studies
- Magnetic confinement fusion research
- Space Satellite Systems and Control
- Isotope Analysis in Ecology
- Earthquake Detection and Analysis
- Fluid Dynamics and Turbulent Flows
- Geology and Paleoclimatology Research
- Inertial Sensor and Navigation
- Organic and Molecular Conductors Research
- Geological and Geochemical Analysis
- earthquake and tectonic studies
- Spacecraft Design and Technology
- Geophysics and Gravity Measurements
- Magnetism in coordination complexes
- Metal Extraction and Bioleaching
- Satellite Communication Systems
- Atmospheric and Environmental Gas Dynamics
- Calibration and Measurement Techniques
- Extraction and Separation Processes
- Atmospheric Ozone and Climate
- Lipid Membrane Structure and Behavior
Osaka Ohtani University
2024
Japan Aerospace Exploration Agency
2005-2023
Institute of Space and Astronautical Science
2001-2023
The Graduate University for Advanced Studies, SOKENDAI
2020-2022
Hitachi (Japan)
2008-2021
The University of Tokyo
1989-2013
Tokyo University of Science
1990-2013
Kitami Institute of Technology
2013
Tohoku University
1985-2011
Planetary Science Institute
1982-2011
A general stability analysis is performed for the Kelvin‐Helmholtz instability in sheared magnetohydrodynamic flow of finite thickness a compressible plasma. The allows arbitrary orientation magnetic field B 0 , velocity v and wave vector k plane perpendicular to gradient, no restrictions are imposed on sound or Alfvén Mach numbers. problem reduced solution single second‐order differential equation, which includes gravitational term represent coupling between mode interchange mode. In...
A magnetohydrodynamic simulation of Kelvin‐Helmholtz instabilities in a compressible plasma has been performed for parallel ( v 0 ∥ B ) and transverse ⊥ configurations, modeling high‐latitude (or downstream flanks) dayside low‐latitude magnetospheric boundaries. In the configuration, super‐Alfvénic transsonic shear flow (with 2 < M = V / υ 4 s c 1, where is total jump velocity across layer) leads to an oscillation layer, which bends initial uniform magnetic field. With hyper‐Alfvénic >...
The Hayabusa2 spacecraft investigated the small asteroid Ryugu, which has a rubble-pile structure. We describe an impact experiment on Ryugu using Hayabusa2's Small Carry-on Impactor. produced artificial crater with diameter >10 meters, semicircular shape, elevated rim, and central pit. Images of resulting ejecta were recorded by Deployable CAMera 3 for >8 minutes, showing growth curtain (the outer edge ejecta) deposition onto surface. was asymmetric heterogeneous it never fully detached...
Abstract C-type asteroids 1 are considered to be primitive small Solar System bodies enriched in water and organics, providing clues the origin evolution of building blocks life. asteroid 162173 Ryugu has been characterized by remote sensing 2–7 on-asteroid measurements 8,9 with Hayabusa2 (ref. 10 ). However, ground truth provided laboratory analysis returned samples is invaluable determine fine properties other planetary bodies. We report preliminary results analyses on from particle size...
Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples the asteroid (162173) Ryugu were retrieved by Hayabusa2 spacecraft. We measured mineralogy and bulk chemical isotopic compositions samples. The samples mainly composed materials similar those carbonaceous chondrite meteorites, particularly CI (Ivuna-type) group. consist predominantly minerals formed in aqueous fluid on a parent planetesimal. primary altered fluids at temperature 37° ± 10°C, about...
Collecting a sample of asteroid Ryugu The Hayabusa2 spacecraft recently traveled to the nearby carbonaceous collect samples and return them Earth for laboratory analysis. Morota et al. describe Hayabusa2's first collection, taken during brief touchdown on Ryugu's surface. Close-up images video sampling process allowed authors investigate surface colors morphology small scale. Relating these craters stratigraphy constrains evolution Ryugu. conclude that experienced prior period strong solar...
The Hayabusa2 spacecraft collected samples from the surface of carbonaceous near-Earth asteroid (162173) Ryugu and brought them to Earth. were expected contain organic molecules, which record processes that occurred in early Solar System. We analyzed molecules extracted samples. identified a variety containing atoms CHNOS, formed by methylation, hydration, hydroxylation, sulfurization reactions. Amino acids, aliphatic amines, carboxylic polycyclic aromatic hydrocarbons, nitrogen-heterocyclic...
Presented here are the observations and interpretations from a comprehensive analysis of 16 representative particles returned C-type asteroid Ryugu by Hayabusa2 mission. On average consist 50% phyllosilicate matrix, 41% porosity 9% minor phases, including organic matter. The abundances 70 elements in close agreement with those CI chondrites. Bulk show higher δ18O, Δ17O, ε54Cr values than As such, sampled most primitive least-thermally processed protosolar nebula reservoirs. Such finding is...
The Hayabusa2 spacecraft investigated the C-type (carbonaceous) asteroid (162173) Ryugu. mission performed two landing operations to collect samples of surface and subsurface material, latter exposed by an artificial impact. We present images second touchdown site, finding that ejecta from impact crater was at sample location. Surface pebbles both sites show morphological variations ranging rugged smooth, similar Ryugu's boulders, shapes quasi-spherical flattened. were returned Earth on 6...
Abstract Volatile and organic-rich C-type asteroids may have been one of the main sources Earth’s water. Our best insight into their chemistry is currently provided by carbonaceous chondritic meteorites, but meteorite record biased: only strongest types survive atmospheric entry are then modified interaction with terrestrial environment. Here we present results a detailed bulk microanalytical study pristine Ryugu particles, brought to Earth Hayabusa2 spacecraft. particles display close...
Samples of the carbonaceous asteroid (162173) Ryugu were collected and brought to Earth by Hayabusa2 spacecraft. We investigated macromolecular organic matter in samples found that it contains aromatic aliphatic carbon, ketone, carboxyl functional groups. The spectroscopic features are consistent with those chemically primitive chondrite meteorites experienced parent-body aqueous alteration (reactions liquid water). morphology carbon includes nanoglobules diffuse associated phyllosilicate...
It has recently been demonstrated, by means of a two‐dimensional MHD simulation, that finite thick velocity shear layer with super‐Alfvénic jump at the magnetospheric boundary is unstable to Kelvin‐Helmholtz (K‐H) instability no matter how large magnetosheath sonic Mach number ( M S ); result suggesting tail flank magnetosphere K‐H instability. In order investigate this consequence further, dependence development on studied in detail. For all numbers formed inside magnetopause, and it...
A two‐dimensional magnetohydrodynamic simulation of Kelvin‐Helmholtz instability at the terrestrial magnetospheric boundary is performed by including gradients plasma and magnetic field normal to dayside low‐latitude boundary. magnetopause current layer corrugated highly nonlinearly instability, a blob formed an interchange motion associated with instability. The magnetosheath flow momentum diffused into magnetosphere anomalous tangential (Reynolds plus Maxwell) stresses wide velocity just...
Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through collective process called space weathering. The return samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study space-weathering signatures on most abundant type inner solar system body: C-type asteroid, composed materials largely unchanged since formation...
The near-Earth carbonaceous asteroid (162173) Ryugu is expected to contain volatile chemical species that could provide information on the origin of Earth's volatiles. Samples were retrieved by Hayabusa2 spacecraft. We measured noble gas and nitrogen isotopes in samples found they are dominated presolar primordial components, incorporated during Solar System formation. Noble concentrations higher than those Ivuna-type (CI) chondrite meteorites. Several host phases isotopically distinct have...
Global simulation of auroral arcs is performed, based on the feedback theory (Sato, 1978), for a three‐dimensionally coupled ionosphere‐magnetosphere system which includes two pairs large‐scale Birkeland currents, polar cap electric fields, and day‐night asymmetry electron density distribution. Simulation results have shown that are formed in dark sector oval, more preferentially evening sector. They usually appear multiples with shape elongating east‐west direction, each arc being couple...
A linear eigenmode analysis of ballooning instability an Alfvén wave and a drift‐Alfvén is performed for curved magnetic field line configuration in finite‐β plasma to examine stability the tail sheet find generation mechanism diamagnetic storm time Pc 5 pulsations, which are characterized by large azimuthal mode number ( m >50). obtained from self‐consistent model pressure distributions, constructed on basis two‐dimensional equilibrium sheet. An equation solved along order obtain...
Simulation of the magnetohydrodynamic Kelvin-Helmholtz instability in a compressible plasma shows that super-Alfv\'enic shear flow parallel to magnetic field develops into small eddies, which strongly compress, twist, and hence amplify field, sub-fast (magnetosonic) transverse evolves fast shock. The anomalous viscosity due is important understanding viscous drag at solar-wind-magnetosphere interface.
The Hayabusa2 spacecraft returned to Earth from the asteroid 162173 Ryugu on 6 December 2020. One day after recovery, gas species retained in sample container were extracted and measured on-site stored collection bottles. consists of helium neon with an extraterrestrial 3 He/ 4 He 20 Ne/ 22 Ne ratios, along some contaminant terrestrial atmospheric gases. A mixture solar Earth’s is best explanation for composition. Fragmentation grains within discussed basis estimated amount indigenous size...
For a two-dimensional (2-D) transverse configuration, where the plasma motion occurs in 2-D plane to magnetic field, nonlinear evolution of magnetohydrodynamic (MHD) Kelvin–Helmholtz (K–H) instability is investigated by means MHD simulation for convective fast magnetosonic Mach number 0.35, which defined total jump flow velocity. The compressibility and nonzero baroclinic vector are shown violate conservation enstrophy configuration fluid motion. After saturation linearly fastest growing...
It is demonstrated by means of a MHD simulation that finite thick velocity shear layer with super‐Alfvénic jump unstable to the Kelvin‐Helmholtz (KH) instability no matter how large sonic Mach number, result suggesting tail flank boundary KH instability. For supersonic flow mode becomes damped‐oscillatory in magnetosheath. both subsonic and flows, energy flux density into magnetosphere enough replenish plasma low latitude tailward kinetic observed intensity. A significant fraction can reach...
Temporal evolution of a two‐dimensional electrostatic shear instability is numerically studied with special attention to rotational deformation auroral arcs and momentum transport across the magnetospheric boundary. It found that spatial structure growing vortex in good agreement small‐scale called ‘curl.’ An anomalous viscosity arising from be given approximately by 0.08 aV 0 , where characteristic distance over which flow velocity changes V . If we assume = 200 km 250 km/s at boundary,...