Showing papers by "Japan Aerospace Exploration Agency published in 2017"

A high-accuracy map of global terrain elevations

Abstract: Spaceborne digital elevation models (DEMs) are a fundamental input for many geoscience studies, but they still include nonnegligible height errors Here we introduce a high-accuracy global DEM at 3″ resolution (~90 m at the equator) by eliminating major error components from existing DEMs We separated absolute bias, stripe noise, speckle noise, and tree height bias using multiple satellite data sets and filtering techniques After the error removal, land areas mapped with ±2 m or better vertical accuracy were increased from 39% to 58% Significant improvements were found in flat regions where height errors larger than topography variability, and landscapes such as river networks and hill-valley structures, became clearly represented We found the topography slope of previous DEMs was largely distorted in most of world major floodplains (eg, Ganges, Nile, Niger, and Mekong) and swamp forests (eg, Amazon, Congo, and Vasyugan) The newly developed DEM will enhance many geoscience applications which are terrain dependent

The Global Precipitation Measurement (GPM) Mission for Science and Society

Abstract: The GPM mission collects essential rain and snow data for scientific studies and societal benefit.

Hayabusa2 Mission Overview

Abstract: The Hayabusa2 mission journeys to C-type near-Earth asteroid (162173) Ryugu (1999 JU3) to observe and explore the 900 m-sized object, as well as return samples collected from the surface layer. The Haybusa2 spacecraft developed by Japan Aerospace Exploration Agency (JAXA) was successfully launched on December 3, 2014 by an H-IIA launch vehicle and performed an Earth swing-by on December 3, 2015 to set it on a course toward its target Ryugu. Hayabusa2 aims at increasing our knowledge of the early history and transfer processes of the solar system through deciphering memories recorded on Ryugu, especially about the origin of water and organic materials transferred to the Earth’s region. Hayabusa2 carries four remote-sensing instruments, a telescopic optical camera with seven colors (ONC-T), a laser altimeter (LIDAR), a near-infrared spectrometer covering the 3-μm absorption band (NIRS3), and a thermal infrared imager (TIR). It also has three small rovers of MINERVA-II and a small lander MASCOT (Mobile Asteroid Surface Scout) developed by German Aerospace Center (DLR) in cooperation with French space agency CNES. MASCOT has a wide angle imager (MasCam), a 6-band thermal radiator (MARA), a 3-axis magnetometer (MasMag), and a hyperspectral infrared microscope (MicrOmega). Further, Hayabusa2 has a sampling device (SMP), and impact experiment devices which consist of a small carry-on impactor (SCI) and a deployable camera (DCAM3). The interdisciplinary research using the data from these onboard and lander’s instruments and the analyses of returned samples are the key to success of the mission.

The status of DECIGO

Abstract: DECIGO (DECi-hertz Interferometer Gravitational wave Observatory) is the planned Japanese space gravitational wave antenna, aiming to detect gravitational waves from astrophysically and cosmologically significant sources mainly between 01 Hz and 10 Hz and thus to open a new window for gravitational wave astronomy and for the universe DECIGO will consists of three drag-free spacecraft arranged in an equilateral triangle with 1000 km arm lengths whose relative displacements are measured by a differential Fabry-Perot interferometer, and four units of triangular Fabry-Perot interferometers are arranged on heliocentric orbit around the sun DECIGO is vary ambitious mission, we plan to launch DECIGO in era of 2030s after precursor satellite mission, B-DECIGO B-DECIGO is essentially smaller version of DECIGO: B-DECIGO consists of three spacecraft arranged in an triangle with 100 km arm lengths orbiting 2000 km above the surface of the earth It is hoped that the launch date will be late 2020s for the present

Energy Spectrum of Cosmic-Ray Electron and Positron from 10 GeV to 3 TeV Observed with the Calorimetric Electron Telescope on the International Space Station

Abstract: First results of a cosmic-ray electron and positron spectrum from 10 GeV to 3 TeV is presented based upon observations with the CALET instrument on the International Space Station starting in October, 2015. Nearly a half million electron and positron events are included in the analysis. CALET is an all-calorimetric instrument with total vertical thickness of 30 ${X}_{0}$ and a fine imaging capability designed to achieve a large proton rejection and excellent energy resolution well into the TeV energy region. The observed energy spectrum over 30 GeV can be fit with a single power law with a spectral index of $\ensuremath{-}3.152\ifmmode\pm\else\textpm\fi{}0.016$ ($\text{stat}+\text{syst}$). Possible structure observed above 100 GeV requires further investigation with increased statistics and refined data analysis.

Hitomi Constraints on the 3.5 keV Line in the Perseus Galaxy Cluster

Abstract: High-resolution X-ray spectroscopy with Hitomi was expected to resolve the origin of the faint unidentified $E\approx 3.5\,\mathrm{keV}$ emission line reported in several low-resolution studies of various massive systems, such as galaxies and clusters, including the Perseus cluster. We have analyzed the Hitomi first-light observation of the Perseus cluster. The emission line expected for Perseus based on the XMM-Newton signal from the large cluster sample under the dark matter decay scenario is too faint to be detectable in the Hitomi data. However, the previously reported 3.5 keV flux from Perseus was anomalously high compared to the sample-based prediction. We find no unidentified line at the reported high flux level. Taking into account the XMM measurement uncertainties for this region, the inconsistency with Hitomi is at a 99% significance for a broad dark matter line and at 99.7% for a narrow line from the gas. We do not find anomalously high fluxes of the nearby faint K line or the Ar satellite line that were proposed as explanations for the earlier 3.5 keV detections. We do find a hint of a broad excess near the energies of high-n transitions of S xvi ($E\simeq 3.44\,\mathrm{keV}$ rest-frame)—a possible signature of charge exchange in the molecular nebula and another proposed explanation for the unidentified line. While its energy is consistent with XMM pn detections, it is unlikely to explain the MOS signal. A confirmation of this interesting feature has to wait for a more sensitive observation with a future calorimeter experiment.

The JCMT BISTRO Survey: The Magnetic Field Strength in the Orion A Filament

Abstract: The James Clerk Maxwell Telescope is operated by the East Asian Observatory on behalf of The National Astronomical Observatory of Japan, Academia Sinica Institute of Astronomy and Astrophysics, the Korea Astronomy and Space Science Institute, the National Astronomical Observatories of China, and the Chinese Academy of Sciences (Grant No. XDB09000000), with additional funding support from the Science and Technology Facilities Council of the United Kingdom and participating universities in the United Kingdom and Canada. The James Clerk Maxwell Telescope has historically been operated by the Joint Astronomy Centre on behalf of the Science and Technology Facilities Council of the United Kingdom, the National Research Council of Canada, and the Netherlands Organization for Scientific Research. Additional funds for the construction of SCUBA-2 and POL-2 were provided by the Canada Foundation for Innovation. The data used in this paper were taken under project codes M16AL004, M15BEC02, and MJLSG32. K.P. and D.W.T. would like to acknowledge support from the Science and Technology Facilities Council (STFC) under grant numbers ST/K002023/1 and ST/M000877/1 while this research was carried out. Partial salary support for A.P. was provided by a Canadian Institute for Theoretical Astrophysics (CITA) National Fellowship. C.W.L. and W.K. were supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (C.W.L.: NRF-2016R1A2B4012593) and the Ministry of Science, ICT & Future Planning (W.K.: NRF-2016R1C1B2013642). J.C.M. acknowledges support from the European Research Council under the European Community's Horizon 2020 framework program (2014–2020) via the ERC Consolidator grant "From Cloud to Star Formation (CSF)" (project number 648505). S.P.L. is thankful for the support of the Ministry of Science and Technology (MoST) of Taiwan through grant Nos. 105-2119-M-007-024 and 106-2119-M-007-021-MY3. K.Q. acknowledges the support from National Natural Science Foundation of China (NSFC) through grant Nos. NSFC 11473011 and NSFC 11590781.The Starlink software (Currie et al. 2014) is supported by the East Asian Observatory. This research used the services of the Canadian Advanced Network for Astronomy Research (CANFAR) which in turn is supported by CANARIE, Compute Canada, University of Victoria, the National Research Council of Canada, and the Canadian Space Agency. This research used the facilities of the Canadian Astronomy Data Centre operated by the National Research Council of Canada with the support of the Canadian Space Agency. This research has made use of the NASA Astrophysics Data System. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

FOREST unbiased Galactic plane imaging survey with the Nobeyama 45 m telescope (FUGIN). I. Project overview and initial results

Abstract: The FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) project is one of the legacy projects using the new multi-beam FOREST receiver installed on the Nobeyama 45-m telescope. This project aims to investigate the distribution, kinematics, and physical properties of both diffuse and dense molecular gas in the Galaxy at once by observing 12CO, 13CO, and C18O J=1-0 lines simultaneously. The mapping regions are a part of the 1st quadrant (10d < l < 50d, |b| < 1d) and the 3rd quadrant (198d < l <236d, |b| < 1d) of the Galaxy, where spiral arms, bar structure, and the molecular gas ring are included. This survey achieves the highest angular resolution to date (~20") for the Galactic plane survey in the CO J=1-0 lines, which makes it possible to find dense clumps located farther away than the previous surveys. FUGIN will provide us with an invaluable dataset for investigating the physics of the galactic interstellar medium (ISM), particularly the evolution of interstellar gas covering galactic scale structures to the internal structures of giant molecular clouds, such as small filament/clump/core. We present an overview of the FUGIN project, observation plan, and initial results, which reveal wide-field and detailed structures of molecular clouds, such as entangled filaments that have not been obvious in previous surveys, and large-scale kinematics of molecular gas such as spiral arms.

Large stationary gravity wave in the atmosphere of Venus

Abstract: The planet Venus is covered by thick clouds of sulfuric acid that move westwards because the entire upper atmosphere rotates much faster than the planet itself. At the cloud tops, about 65 km in altitude, small-scale features are predominantly carried by the background wind at speeds of approximately 100 m s−1. In contrast, planetary-scale atmospheric features have been observed to move slightly faster or slower than the background wind, a phenomenon that has been interpreted to reflect the propagation of planetary-scale waves. Here we report the detection of an interhemispheric bow-shaped structure stretching 10,000 km across at the cloud-top level of Venus in middle infrared and ultraviolet images from the Japanese orbiter Akatsuki. Over several days of observation, the bow-shaped structure remained relatively fixed in position above the highland on the slowly rotating surface, despite the background atmospheric super rotation. We suggest that the bow-shaped structure is the result of an atmospheric gravity wave generated in the lower atmosphere by mountain topography that then propagated upwards. Numerical simulations provide preliminary support for this interpretation, but the formation and propagation of a mountain gravity wave remain difficult to reconcile with assumed near-surface conditions on Venus. We suggest that winds in the deep atmosphere may be spatially or temporally more variable than previously thought. The upper atmosphere of Venus rotates much faster than the planet itself. An anomalous stationary structure observed by the Akatsuki mission at the cloud tops of Venus could be an atmospheric gravity wave induced by mountain topography below.

First Results from BISTRO : A SCUBA-2 Polarimeter Survey of the Gould Belt

Abstract: We present the first results from the B-fields In STar-forming Region Observations (BISTRO) survey, using the Sub-millimetre Common-User Bolometer Array 2 camera, with its associated polarimeter (POL-2), on the James Clerk Maxwell Telescope in Hawaii. We discuss the survey's aims and objectives. We describe the rationale behind the survey, and the questions that the survey will aim to answer. The most important of these is the role of magnetic fields in the star formation process on the scale of individual filaments and cores in dense regions. We describe the data acquisition and reduction processes for POL-2, demonstrating both repeatability and consistency with previous data. We present a first-look analysis of the first results from the BISTRO survey in the OMC 1 region. We see that the magnetic field lies approximately perpendicular to the famous "integral filament" in the densest regions of that filament. Furthermore, we see an "hourglass" magnetic field morphology extending beyond the densest region of the integral filament into the less-dense surrounding material, and discuss possible causes for this. We also discuss the more complex morphology seen along the Orion Bar region. We examine the morphology of the field along the lower-density northeastern filament. We find consistency with previous theoretical models that predict magnetic fields lying parallel to low-density, non-self-gravitating filaments, and perpendicular to higher-density, self-gravitating filaments.

Summary Data from the Sixth AIAA CFD Drag Prediction Workshop: CRM Cases

Abstract: Results from the Sixth AIAA CFD Drag Prediction Workshop Cases 2 to 5 are presented. These cases focused on force/moment and pressure predictions for the NASA Common Research Model wing–body and wi...

Preflight Calibration Test Results for Optical Navigation Camera Telescope (ONC-T) Onboard the Hayabusa2 Spacecraft

Abstract: The optical navigation camera telescope (ONC-T) is a telescopic framing camera with seven colors onboard the Hayabusa2 spacecraft launched on December 3, 2014. The main objectives of this instrument are to optically navigate the spacecraft to asteroid Ryugu and to conduct multi-band mapping the asteroid. We conducted performance tests of the instrument before its installation on the spacecraft. We evaluated the dark current and bias level, obtained data on the dependency of the dark current on the temperature of the charge-coupled device (CCD). The bias level depends strongly on the temperature of the electronics package but only weakly on the CCD temperature. The dark-reference data, which is obtained simultaneously with observation data, can be used for estimation of the dark current and bias level. A long front hood is used for ONC-T to reduce the stray light at the expense of flatness in the peripheral area of the field of view (FOV). The central area in FOV has a flat sensitivity, and the limb darkening has been measured with an integrating sphere. The ONC-T has a wheel with seven bandpass filters and a panchromatic glass window. We measured the spectral sensitivity using an integrating sphere and obtained the sensitivity of all the pixels. We also measured the point-spread function using a star simulator. Measurement results indicate that the full width at half maximum is less than two pixels for all the bandpass filters and in the temperature range expected in the mission phase except for short periods of time during touchdowns.

New Spectral Evidence of an Unaccounted Component of the Near-infrared Extragalactic Background Light from the CIBER

Abstract: The extragalactic background light (EBL) captures the total integrated emission from stars and galaxies throughout the cosmic history. The amplitude of the near-infrared EBL from space absolute photometry observations has been controversial and depends strongly on the modeling and subtraction of the zodiacal light (ZL) foreground. We report the first measurement of the diffuse background spectrum at 0.8–1.7 μm from the CIBER experiment. The observations were obtained with an absolute spectrometer over two flights in multiple sky fields to enable the subtraction of ZL, stars, terrestrial emission, and diffuse Galactic light. After subtracting foregrounds and accounting for systematic errors, we find the nominal EBL brightness, assuming the Kelsall ZL model, is 42.7^(+11.9)_(-10.6) nW m^(−2) sr^(−1) at 1.4 μm. We also analyzed the data using the Wright ZL model, which results in a worse statistical fit to the data and an unphysical EBL, falling below the known background light from galaxies at λ < 1.3 μm. Using a model-independent analysis based on the minimum EBL brightness, we find an EBL brightness of 28.7^(+5.1)_(-3.3) nWm^(−2) sr^(−1) at 1.4 μm. While the derived EBL amplitude strongly depends on the ZL model, we find that we cannot fit the spectral data to ZL, Galactic emission, and EBL from solely integrated galactic light from galaxy counts. The results require a new diffuse component, such as an additional foreground or an excess EBL with a redder spectrum than that of ZL.

Ground-based instruments of the PWING project to investigate dynamics of the inner magnetosphere at subauroral latitudes as a part of the ERG-ground coordinated observation network

Abstract: The plasmas (electrons and ions) in the inner magnetosphere have wide energy ranges from electron volts to mega-electron volts (MeV). These plasmas rotate around the Earth longitudinally due to the gradient and curvature of the geomagnetic field and by the co-rotation motion with timescales from several tens of hours to less than 10 min. They interact with plasma waves at frequencies of mHz to kHz mainly in the equatorial plane of the magnetosphere, obtain energies up to MeV, and are lost into the ionosphere. In order to provide the global distribution and quantitative evaluation of the dynamical variation of these plasmas and waves in the inner magnetosphere, the PWING project (study of dynamical variation of particles and waves in the inner magnetosphere using ground-based network observations, http://www.isee.nagoya-u.ac.jp/dimr/PWING/ ) has been carried out since April 2016. This paper describes the stations and instrumentation of the PWING project. We operate all-sky airglow/aurora imagers, 64-Hz sampling induction magnetometers, 40-kHz sampling loop antennas, and 64-Hz sampling riometers at eight stations at subauroral latitudes (~ 60° geomagnetic latitude) in the northern hemisphere, as well as 100-Hz sampling EMCCD cameras at three stations. These stations are distributed longitudinally in Canada, Iceland, Finland, Russia, and Alaska to obtain the longitudinal distribution of plasmas and waves in the inner magnetosphere. This PWING longitudinal network has been developed as a part of the ERG (Arase)-ground coordinated observation network. The ERG (Arase) satellite was launched on December 20, 2016, and has been in full operation since March 2017. We will combine these ground network observations with the ERG (Arase) satellite and global modeling studies. These comprehensive datasets will contribute to the investigation of dynamical variation of particles and waves in the inner magnetosphere, which is one of the most important research topics in recent space physics, and the outcome of our research will improve safe and secure use of geospace around the Earth.

Thermal conductivity model for powdered materials under vacuum based on experimental studies

Abstract: The thermal conductivity of powdered media is characteristically very low in vacuum, and is effectively dependent on many parameters of their constituent particles and packing structure. Understanding of the heat transfer mechanism within powder layers in vacuum and theoretical modeling of their thermal conductivity are of great importance for several scientific and engineering problems. In this paper, we report the results of systematic thermal conductivity measurements of powdered media of varied particle size, porosity, and temperature under vacuum using glass beads as a model material. Based on the obtained experimental data, we investigated the heat transfer mechanism in powdered media in detail, and constructed a new theoretical thermal conductivity model for the vacuum condition. This model enables an absolute thermal conductivity to be calculated for a powder with the input of a set of powder parameters including particle size, porosity, temperature, and compressional stress or gravity, and vice v...

A Data-Driven Health Monitoring Method for Satellite Housekeeping Data Based on Probabilistic Clustering and Dimensionality Reduction

Abstract: In the operation of artificial satellites, it is very important to monitor the health status of the systems and detect any symptoms of anomalies in the housekeeping data as soon as possible. Recently, the data-driven approach to the system monitoring problem, in which statistical machine learning techniques are applied to the large amount of measurement data collected in the past, has attracted considerable attention. In this paper, we propose a new data-driven health monitoring and anomaly detection method for artificial satellites based on probabilistic dimensionality reduction and clustering, taking into consideration the miscellaneous characteristics of the spacecraft housekeeping data. We applied our method to the telemetry data of the small demonstration satellite 4 (SDS-4) of the Japan Aerospace Exploration Agency (JAXA) and evaluated its effectiveness. The results show that the proposed system provides satellite operators with valuable information for understanding the health status of the system and inferring the causes of anomalies.

FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) I: Project Overview and Initial Results

Abstract: The FOREST Unbiased Galactic plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) project is one of the legacy projects using the new multi-beam FOREST receiver installed on the Nobeyama 45-m telescope. This project aims to investigate the distribution, kinematics, and physical properties of both diffuse and dense molecular gas in the Galaxy at once by observing 12CO, 13CO, and C18O J=1-0 lines simultaneously. The mapping regions are a part of the 1st quadrant (10d < l < 50d, |b| < 1d) and the 3rd quadrant (198d < l <236d, |b| < 1d) of the Galaxy, where spiral arms, bar structure, and the molecular gas ring are included. This survey achieves the highest angular resolution to date (~20") for the Galactic plane survey in the CO J=1-0 lines, which makes it possible to find dense clumps located farther away than the previous surveys. FUGIN will provide us with an invaluable dataset for investigating the physics of the galactic interstellar medium (ISM), particularly the evolution of interstellar gas covering galactic scale structures to the internal structures of giant molecular clouds, such as small filament/clump/core. We present an overview of the FUGIN project, observation plan, and initial results, which reveal wide-field and detailed structures of molecular clouds, such as entangled filaments that have not been obvious in previous surveys, and large-scale kinematics of molecular gas such as spiral arms.

Response of Jupiter's auroras to conditions in the interplanetary medium as measured by the Hubble Space Telescope and Juno

Abstract: We present the first comparison of Jupiter's auroral morphology with an extended, continuous and complete set of near-Jupiter interplanetary data, revealing the response of Jupiter's auroras to the interplanetary conditions. We show that for ∼1-3 days following compression region onset the planet's main emission brightened. A duskside poleward region also brightened during compressions, as well as during shallow rarefaction conditions at the start of the program. The power emitted from the noon active region did not exhibit dependence on any interplanetary parameter, though the morphology typically differed between rarefactions and compressions. The auroras equatorward of the main emission brightened over ∼10 days following an interval of increased volcanic activity on Io. These results show that the dependence of Jupiter's magnetosphere and auroras on the interplanetary conditions are more diverse than previously thought.

Detection of Intact Lava Tubes at Marius Hills on the Moon by SELENE (Kaguya) Lunar Radar Sounder

Abstract: Intact lunar lava tubes offer a pristine environment to conduct scientific examination of the Moon's composition and potentially serve as secure shelters for humans and instruments. We investigated the SELENE Lunar Radar Sounder (LRS) data at locations close to the Marius Hills Hole (MHH), a skylight potentially leading to an intact lava tube, and found a distinctive echo pattern exhibiting a precipitous decrease in echo power, subsequently followed by a large second echo peak that may be evidence for the existence of a lava tube. The search area was further expanded to 13.00–15.00°N, 301.85–304.01°E around the MHH, and similar LRS echo patterns were observed at several locations. Most of the locations are in regions of underground mass deficit suggested by GRAIL gravity data analysis. Some of the observed echo patterns are along rille A, where the MHH was discovered, or on the southwest underground extension of the rille.

Initial performance of the radio occultation experiment in the Venus orbiter mission Akatsuki

Abstract: After the arrival of Akatsuki spacecraft of Japan Aerospace Exploration Agency at Venus in December 2015, the radio occultation experiment, termed RS (Radio Science), obtained 19 vertical profiles of the Venusian atmosphere by April 2017. An onboard ultra-stable oscillator is used to generate stable X-band downlink signals needed for the experiment. The quantities to be retrieved are the atmospheric pressure, the temperature, the sulfuric acid vapor mixing ratio, and the electron density. Temperature profiles were successfully obtained down to ~ 38 km altitude and show distinct atmospheric structures depending on the altitude. The overall structure is close to the previous observations, suggesting a remarkable stability of the thermal structure. Local time-dependent features are seen within and above the clouds, which is located around 48–70 km altitude. The H2SO4 vapor density roughly follows the saturation curve at cloud heights, suggesting equilibrium with cloud particles. The ionospheric electron density profiles are also successfully retrieved, showing distinct local time dependence. Akatsuki RS mainly probes the low and middle latitude regions thanks to the near-equatorial orbit in contrast to the previous radio occultation experiments using polar orbiters. Studies based on combined analyses of RS and optical imaging data are ongoing.

Thermal Infrared Imaging Experiments of C-Type Asteroid 162173 Ryugu on Hayabusa2

Abstract: The thermal infrared imager TIR onboard Hayabusa2 has been developed to investigate thermo-physical properties of C-type, near-Earth asteroid 162173 Ryugu. TIR is one of the remote science instruments on Hayabusa2 designed to understand the nature of a volatile-rich solar system small body, but it also has significant mission objectives to provide information on surface physical properties and conditions for sampling site selection as well as the assessment of safe landing operations. TIR is based on a two-dimensional uncooled micro-bolometer array inherited from the Longwave Infrared Camera LIR on Akatsuki (Fukuhara et al., 2011). TIR takes images of thermal infrared emission in 8 to 12 μm with a field of view of 16×12∘ and a spatial resolution of 0.05∘ per pixel. TIR covers the temperature range from 150 to 460 K, including the well calibrated range from 230 to 420 K. Temperature accuracy is within 2 K or better for summed images, and the relative accuracy or noise equivalent temperature difference (NETD) at each of pixels is 0.4 K or lower for the well-calibrated temperature range. TIR takes a couple of images with shutter open and closed, the corresponding dark frame, and provides a true thermal image by dark frame subtraction. Data processing involves summation of multiple images, image processing including the StarPixel compression (Hihara et al., 2014), and transfer to the data recorder in the spacecraft digital electronics (DE). We report the scientific and mission objectives of TIR, the requirements and constraints for the instrument specifications, the designed instrumentation and the pre-flight and in-flight performances of TIR, as well as its observation plan during the Hayabusa2 mission.

Hayabusa-2 mission target asteroid 162173 Ryugu (1999 JU3): Searching for the object's spin-axis orientation

Abstract: The JAXA Hayabusa-2 mission was approved in 2010 and launched on December 3, 2014. The spacecraft will arrive at the near-Earth asteroid 162173 Ryugu (1999 JU3 ) in 2018 where it will perform a survey, land and obtainsurface material, then depart in December 2019 and return to Earth in December 2020. We observed Ryugu with the Herschel Space Observatory in April 2012 at far-infrared thermal wavelengths, supported by several ground-based observations to obtain optical lightcurves. We reanalysed previously published Subaru-COMICS and AKARI-IRC observations and merged them with a Spitzer -IRS data set. In addition, we used a large set of Spitzer -IRAC observations obtained in the period January to May, 2013. The data set includes two complete rotational lightcurves and a series of ten “point-and-shoot” observations, all at 3.6 and 4.5 μ m. The almost spherical shape of the target together with the insufficient lightcurve quality forced us to combine radiometric and lightcurve inversion techniques in different ways to find the object’s spin-axis orientation, its shape and to improve the quality of the key physical and thermal parameters. Handling thermal data in inversion techniques remains challenging: thermal inertia, roughness or local structures influence the temperature distribution on the surface. The constraints for size, spin or thermal properties therefore heavily depend on the wavelengths of the observations. We find that the solution which best matches our data sets leads to this C class asteroid having a retrograde rotation with a spin-axis orientation of (λ = 310°−340°; β = −40° ± ~ 15°) in ecliptic coordinates, an effective diameter (of an equal-volume sphere) of 850 to 880 m, a geometric albedo of 0.044 to 0.050 and a thermal inertia in the range 150 to 300 J m-2 s-0.5 K-1 . Based on estimated thermal conductivities of the top-layer surface in the range 0.1 to 0.6 W K-1 m-1 , we calculated that the grain sizes are approximately equal to between 1 and 10 mm. The finely constrained values for this asteroid serve as a “design reference model”, which is currently used for various planning, operational and modelling purposes by the Hayabusa-2 team.

The implications of the surprising existence of a large, massive CO disk in a distant protocluster

Abstract: It is not yet known if the properties of molecular gas in distant protocluster galaxies are significantly affected by their environment as galaxies are in local clusters. Through a deep, 64 h of effective on-source integration with the Australian Telescope Compact Array (ATCA), we discovered a massive, Mmol = 2.0 ± 0.2× 1011 M⊙, extended, ~40 kpc, CO(1–0)-emitting disk in the protocluster surrounding the radio galaxy, MRC 1138−262. The galaxy, at zCO = 2.1478, is a clumpy, massive disk galaxy, M∗ ~ 5 × 1011 M⊙, which lies 250 kpc in projection from MRC 1138−262 and is a known Hα emitter, named HAE229. This source has a molecular gas fraction of ~30%. The CO emission has a kinematic gradient along its major axis, centered on the highest surface brightness rest-frame optical emission, consistent with HAE229 being a rotating disk. Surprisingly, a significant fraction of the CO emission lies outside of the UV/optical emission. In spite of this, HAE229 follows the same relation between star-formation rate and molecular gas mass as normal field galaxies. HAE229 is the first CO (1–0) detection of an ordinary, star-forming galaxy in a protocluster. We compare a sample of cluster members at z > 0.4 thatare detected in low-order CO transitions, with a similar sample of sources drawn from the field. We confirm findings that the CO-luminosity and full-width at half maximum are correlated in starbursts and show that this relation is valid for normal high-z galaxies as well as for those in overdensities. We do not find a clear dichotomy in the integrated Schmidt-Kennicutt relation for protocluster and field galaxies. Our results suggest that environment does not have an impact on the “star-formation efficiency” or the molecular gas content of high-redshift galaxies. Not finding any environmental dependence in these characteristics, especially for such an extended CO disk, suggests that environmentally-specific processes such as ram pressure stripping do not operate efficiently in (proto)clusters.

Turbulent mass transfer caused by vortex induced reconnection in collisionless magnetospheric plasmas.

Abstract: Magnetic reconnection is believed to be the main driver to transport solar wind into the Earth's magnetosphere when the magnetopause features a large magnetic shear. However, even when the magnetic shear is too small for spontaneous reconnection, the Kelvin-Helmholtz instability driven by a super-Alfvenic velocity shear is expected to facilitate the transport. Although previous kinetic simulations have demonstrated that the non-linear vortex flows from the Kelvin-Helmholtz instability gives rise to vortex-induced reconnection and resulting plasma transport, the system sizes of these simulations were too small to allow the reconnection to evolve much beyond the electron scale as recently observed by the Magnetospheric Multiscale (MMS) spacecraft. Here, based on a large-scale kinetic simulation and its comparison with MMS observations, we show for the first time that ion-scale jets from vortex-induced reconnection rapidly decay through self-generated turbulence, leading to a mass transfer rate nearly one order higher than previous expectations for the Kelvin-Helmholtz instability.

Burst-Mode Frequency Effects of Dielectric Barrier Discharge Plasma Actuator for Separation Control

Abstract: The various separation control mechanisms of burst-mode actuation with a dielectric barrier discharge plasma actuator were experimentally investigated in this study. The control of the separated fl...

Measurement of the EBL spectral energy distribution using the VHE $\gamma$-ray spectra of H.E.S.S. blazars

Abstract: Very high-energy γ rays (VHE, E ≳ 100 GeV) propagating over cosmological distances can interact with the low-energy photons of the extragalactic background light (EBL) and produce electron-positron pairs. The transparency of the Universe to VHE γ rays is then directly related to the spectral energy distribution (SED) of the EBL. The observation of features in the VHE energy spectra of extragalactic sources allows the EBL to be measured, which otherwise is very difficult. An EBL model-independent measurement of the EBL SED with the H.E.S.S. array of Cherenkov telescopes is presented. It was obtained by extracting the EBL absorption signal from the reanalysis of high-quality spectra of blazars. From H.E.S.S. data alone the EBL signature is detected at a significance of 9.5σ, and the intensity of the EBL obtained in different spectral bands is presented together with the associated γ-ray horizon. Key words: gamma rays: galaxies / BL Lacertae objects: general / cosmic background radiation / infrared: diffuse background† Deceased.⋆ Corresponding authors: H.E.S.S. Collaboration, e-mail: contact.hess@hess-experiment.eu

Hayabusa2 Sampler: Collection of Asteroidal Surface Material

Abstract: Japan Aerospace Exploration Agency (JAXA) launched the asteroid exploration probe “Hayabusa2” in December 3rd, 2014, following the 1st Hayabusa mission. With technological and scientific improvements from the Hayabusa probe, we plan to visit the C-type asteroid 162137 Ryugu (1999 JU3), and to sample surface materials of the C-type asteroid that is likely to be different from the S-type asteroid Itokawa and contain more pristine materials, including organic matter and/or hydrated minerals, than S-type asteroids. We developed the Hayabusa2 sampler to collect a minimum of 100 mg of surface samples including several mm-sized particles at three surface locations without any severe terrestrial contamination. The basic configuration of the sampler design is mainly as same as the 1st Hayabusa (Yano et al. in Science, 312(5778):1350–1353, 2006), with several minor but important modifications based on lessons learned from the Hayabusa to fulfill the scientific requirements and to raise the scientific value of the returned samples. In this paper, we will report the details of the sampling system of Hayabusa2 with results of performance tests during the development and the current status of the sampling system.