中村 正人

The Longwave Infrared Camera (LIR) is one of a suite of cameras onboard the Venus orbiter Akatsuki. It will take images of thermal radiation in the wavelength range of 8-12 mu m emitted by the Venus cloud tops. The use of an uncooled micro-bolometer array as an infrared image sensor makes LIR a lightweight, small and low-power consumption instrument with a required noise equivalent temperature difference of 0.3 K. Temperature and horizontal wind fields at the cloud-top will be retrieved for both dayside and nightside with equal quality. This will provide key observations to understand the mechanism of super rotation and the thermal budget of the planet. LIR will also monitor variations of the polar dipole and collar which are characteristic thermal features in the Venusian atmosphere. Mechanisms of the upper-cloud formation will be investigated using sequences of close-up images. The morphology of the nightside upper cloud will be studied in detail for the first time.

The Akatsuki spacecraft of Japan was launched on May 21, 2010. The spacecraft planned to enter a Venus-encircling near-equatorial orbit in December 7, 2010; however, the Venus orbit insertion maneuver has failed, and at present the spacecraft is orbiting the Sun. There is a possibility of conducting an orbit insertion maneuver again several years later. The main goal of the mission is to understand the Venusian atmospheric dynamics and cloud physics, with the explorations of the ground surface and the interplanetary dust also being the themes. The angular motion of the spacecraft is roughly synchronized with the zonal flow near the cloud base for roughly 20 hours centered at the apoapsis. Seen from this portion of the orbit, cloud features below the spacecraft continue to be observed over 20 hours, and thus the precise determination of atmospheric motions is possible. The onboard science instruments sense multiple height levels of the atmosphere to model the three-dimensional structure and dynamics. The lower clouds, the lower atmosphere and the surface are imaged by utilizing near-infrared windows. The cloud top structure is mapped by using scattered ultraviolet radiation and thermal infrared radiation. Lightning discharge is searched for by high speed sampling of lightning flashes. Night airglow is observed at visible wavelengths. Radio occultation complements the imaging observations principally by determining the vertical temperature structure.

MAP-PACE (MAgnetic field and Plasma experiment-Plasma energy Angle and Composition Experiment) on SELENE (Kaguya) has completed its ∼1.5-year observation of low-energy charged particles around the Moon. MAP-PACE consists of 4 sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2 measured the distribution function of low-energy electrons in the energy range 6 eV-9 keV and 9 eV-16 keV, respectively. IMA and IEA measured the distribution function of low-energy ions in the energy ranges 7 eV/q-28 keV/q and 7 eV/q-29 keV/q. All the sensors performed quite well as expected from the laboratory experiment carried out before launch. Since each sensor has a hemispherical field of view, two electron sensors and two ion sensors installed on the spacecraft panels opposite each other could cover the full 3-dimensional phase space of low-energy electrons and ions. One of the ion sensors IMA is an energy mass spectrometer. IMA measured mass-specific ion energy spectra that have never before been obtained at a 100 km altitude polar orbit around the Moon. The newly observed data show characteristic ion populations around the Moon. Besides the solar wind, MAP-PACE-IMA found four clearly distinguishable ion populations on the dayside of the Moon: (1) Solar wind protons backscattered at the lunar surface, (2) Solar wind protons reflected by magnetic anomalies on the lunar surface, (3) Reflected/backscattered protons picked-up by the solar wind, and (4) Ions originating from the lunar surface/lunar exosphere. © 2010 Springer Science+Business Media B.V.

The Telescope of Extreme Ultraviolet (TEX) aboard Japan's lunar orbiter Kaguya has succeeded in imaging of the plasmaspheric helium ions by detecting resonantly scattered emission at 30.4 nm. After the initial instrumental check was completed, TEX has been operated routinely, and EUV images from TEX have become available from the perspective of the lunar orbit. The view afforded by the Kaguya orbit encompasses the plasma (He+) distribution in a single exposure, enabling us to examine for the first time the globally averaged properties of the terrestrial plasmasphere from the "side" (meridian) perspective. In this paper we report the inward motion of the nightside plasmapause on 2 May 2008 as seen from this remote meridian view of the Earth. The southward turning of the IMF initiated the inward motion of the plasmapause, and the nightside plasmasphere shrunk at a rate of 0.2 Re/h. Simultaneous solar wind velocity measurements provide a possible explanation for the total radial displacement of the plasmasphere observed in the EUV images.

Mercury possesses a weak, internal, global magnetic field that supports a small magnetosphere populated by charged particles originating from the solar wind, the planet's exosphere and surface layers. Mercury's exosphere is continuously refilled and eroded through a variety of chemical and physical processes acting in the planet's surface and environment. Using simultaneous two-point measurements from two satellites, ESA's future mission BepiColombo will offer an unprecedented opportunity to investigate magnetospheric and exospheric dynamics at Mercury as well as their interactions with solar radiation and interplanetary dust. The expected data will provide important insights into the evolution of a planet in close proximity of a star. Many payload instruments aboard the two spacecraft making up the mission will be completely, or partially, devoted to studying the close environment of the planet as well as the complex processes that govern it. Coordinated measurements by different onboard instruments will permit a wider range of scientific questions to be addressed than those that could be achieved by the individual instruments acting alone. Thus, an important feature of the BepiColombo mission is that simultaneous two-point measurements can be implemented at a location in space other than the Earth. These joint observations are of key importance because many phenomena in Mercury's environment are temporarily and spatially varying. In the present paper, we focus on some of the exciting scientific goals achievable during the BepiColombo mission through making coordinated observations. (C) 2008 Elsevier Ltd. All rights reserved.

Our understanding of plasmaspheric dynamics has increased in recent years largely due to the information generated during the IMAGE-EUV mission. Even though this successful mission has ended, we have succeeded in imaging the terrestrial helium ions (He(+)) by the Telescope of Extreme Ultraviolet (TEX) aboard the Japanese lunar orbiter KAGUYA by detecting resonantly scattered emission at 30.4 nm. The view afforded by the KAGUYA orbit encompasses the plasma (He(+)) distribution in a single exposure, enabling us to examine for the first time the globally averaged properties of the plasmasphere from the "side" (meridian) perspective. The TEX instrument observed a medium-scale density structure in the dawnside plasmasphere during a quiet period (1-2 June 2008). The meridian shape of the structure clearly agreed with the dipole magnetic field line. The TEX instrument also observed the structure in the plasmasphere co-rotating with a duration of 26 h, which is consistent with results from a number of recent studies derived from the IMAGE-EUV mission. These results confirm that the TEX instrument successfully obtained the spatial distribution and temporal variation of the plasmasphere.

PLANET-C (PLC) is the mission of Japan Aerospace Exploration Agency (JAXA) for Venus exploration. It is a successor of HAYABUSA in the history of Japanese deep space missions and is expected to be the first Japanese planetary orbiter. The spacecraft will be launched in the summer of 2010 from Tanegashima Space Center. The mission has demanded new onboard telecommunication instruments. Among them are X-band digital transponder, high gain flat antenna, and low gain wider field of view antenna. Through their developments, new technologies such as deep space regenerative ranging adapted for JAXA ground stations have been successfully incorporated into the PLC system. They are now raedy for their first space-borne demonstration. We will discuss these telecommunication technologies newly introduced for the PLC mission.

This paper presents, the operations scenario, specifically the initial phase operation, of the Attitude and Orbit Control System (AOCS) of PLANET-C: Venus Climate Orbiter Mission "AKATSUKI". AKATSUKI is the first exploration program from Japan to Earth's inferior planetary neighbor, Venus, and will be launched by an H-A vehicle on May 18th 2010 (Japan Standard Time: JST) from Kagoshima Space Center. AKATSUKI aims at understanding the atmospheric characteristics of Venus. To accomplish this mission, AKATSUKI has five camera instruments onboard to image ultraviolet and thermal infrared wavelengths, to detect lightning with a high-speed imager, and to observe the vertical structure of the atmosphere using radio science techniques. To achieve these objectives, AKATSUKI has four operation phases; such as launch and initial check, cruise, Venus orbit injection (VOI) and nominal Venus observation. The VOI phase is a particularly critical phase to enter equatorial elongated Venus orbit. To achieve this trajectory, AKATSUKI requires an AOCS with the tolerance for the stringent high temperature environment produced in the inferior planet. © 2010 SICE.

PLANET-C, the spacecraft for Venus exploration developed in Japan Aerospace Exploration Agency (JAXA) is under careful construction for the coming launch in the summer of 2010. It is expected to be the first Japanese orbiter other than Earth and Moon. Some new onboard communication instruments to encourage PLANET-C ambitious missions have been developed since 2001. Among them are X-band digital transponder, slot array high gain flat antenna, and low gain wide field of view lens antenna, and X-band power amplifier. New technologies such as deep space regenerative ranging have been introduced and customized so as to fit the JAXA style. They are now successfully operated through the ground tests of PLANET-C and ready for flight qualification. The qualified products will be catalogued as standard components in deep space activities of JAXA for the next decade.

The Upper Atmosphere and Plasma Imager (UPI) was launched in 2007, and went to the moon. From the lunar orbit, two telescopes direct toward the Earth. The moon has no atmosphere, which leads no active emission near the spacecraft, thus we have a high quality image of the near-Earth environment. Moreover the moon orbits the Earth once a month and the Earth is observed from many different directions. This is called a "science from the Moon". The two telescopes are mounted on 2-axis gimbal system, Telescope of Extreme ultraviolet (TEX) and Telescope of Visible light (TVIS). TEX detects the O II (83.4nm) and He II (30.4nm) emissions scattered by ionized oxygen and helium, respectively. The targets of EUV imaging are the polar ionosphere, the polar wind, and the plasmasphere and the inner magnetosphere. The maximum spatial and time resolutions are 0.09 Re and 1 minute, respectively.

Aims. Following recent reports on spectroscopic observations by SWAN/SOHO suggesting that the flows of neutral interstellar helium and hydrogen in the inner heliosphere are slightly divergent, we tried to verify them on the basis of simultaneous photometric observations of heliospheric hydrogen and helium glows performed by a spacecraft located on an orbit between the Earth and Mars (which differs from the orbit of SWAN/SOHO). The observations were interpreted with the use of various independent models of interstellar hydrogen and helium in the inner heliosphere, evaluated over a mesh of parameters. Methods. The data might suggest that the upwind and downwind directions of interstellar H may differ by less than 180 degrees, which we interpret as due to a side shift of the secondary population of interstellar hydrogen, which might be due to a deformation of the outer heliosheath e.g. because of the action of interstellar magnetic field. The simulations we performed do not support the idea that the secondary population is significantly shifted to the side. Results. The upwind/downwind direction of interstellar hydrogen as derived from our observations agrees within the error bars with the upwind/downwind direction of interstellar helium and the error bars include both the upwind direction of interstellar helium, derived from in-situ observations of GAS/Ulysses, and the upwind direction of interstellar hydrogen, derived from observations of SWAN/SOHO.

Lightning activity in Venus has been a mystery for a long period, although many studies based on observations both by spacecraft and by ground-based telescope have been carried out. This situation may be attributed to the ambiguity of these evidential measurements. In order to conclude this controversial subject, we are developing a new type of lightning detector, LAC (Lightning and Airglow Camera), which will be onboard Planet-C (Venus Climate Orbiter: VCO). Planet-C will be launched in 2010 by JAXA. To distinguish an optical lightning flash from other pulsing noises, high-speed sampling at 50 kHz for each pixel, that enables us to investigate the time variation of each lightning flash phenomenon, is adopted. On the other hand, spatial resolution is not the first priority. For this purpose we developed a new type of APD (avalanche photo diode) array with a format of 8x8. A narrow band interference filter at wavelength of 777.4 nm (OI), which is the expected lightning color based on laboratory discharge experiment, is chosen for lightning measurement. LAC detects lightning flash with an optical intensity of average of Earth's lightning or less at a distance of 3 Rv. In this paper, firstly we describe the background of the Venus lightning study to locate our spacecraft project, and then introduce the mission details.

The Longwave Infrared Camera (LIR), which mounts an uncooled micro-bolometer array (UMBA), is under development for the Japanese Venus orbiter mission, PLANET-C. LIR detects thermal emission from the top of the sulfur dioxide cloud in a wavelength region 8-12 mu m to map the cloud-top temperature which is typically as low as 230 K. The requirement for the noise equivalent temperature difference (NETD) is 0.3 K. Images of blackbody targets in room temperature (similar to 300 K) and low temperature (similar to 230 K) have been acquired in a vacuum environment using a prototype model of LIR, showing that the NETD of 0.2 K and 0.8 K are achieved in similar to 300 K and -230 K, respectively. We expect that the requirement of NETD < 0.3 K for similar to 230 K targets will be achieved by averaging several tens of images which are acquired within a few minutes. The vibration test for the UMBA was also carried out and the result showed the UMBA survived without any pixel defects or malfunctions. The tolerance to high-energy protons was tested and verified using a commercial camera in which a same type of UMBA is mounted. Based on these results, a flight model is now being manufactured with minor modifications from the prototype.

MAP-PACE (MAgnetic field and Plasma experiment-Plasma energy Angle and Compostion Experiment) is one of the scientific instruments onboard the SELENE (SELenological and ENgineering Explorer) satellite. PACE consists of four sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2 measure the distribution function of low-energy electrons below 15 keV, while IMA and IEA measure the distribution function of low energy ions below 28 keV/q. Each sensor has a hemispherical field of view. Since SELENE is a three-axis stabilized spacecraft, a pair of electron sensors (ESA-S1 and S2) and a pair of ion sensors (IMA and IEA) are necessary for obtaining a three-dimensional distribution function of electrons and ions. The scientific objectives of PACE are (1) to measure the ions sputtered from the lunar surface and the lunar atmosphere, (2) to measure the magnetic anomaly on the lunar surface using two ESAs and a magnetometer onboard SELENE simultaneously as an electron reflectometer, (3) to resolve the Moon-solar wind interaction, (4) to resolve the Moon-Earth's magnetosphere interaction, and (5) to observe the Earth's magnetotail. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB.

The small intrinsic magnetic field of Mercury together with its proximity to the Sun makes the Hermean magnetosphere unique in the context of comparative magnetosphere study. The basic framework of the Hermean magnetosphere is believed to be the same as that of Earth. However, there exist various differences which cause new and exciting effects not present at Earth to appear. These new effects may force a substantial correction of our naïve predictions concerning the magnetosphere of Mercury. Here, we outline the predictions based on our experience at Earth and what effects can drastically change this picture. The basic structure of the magnetosphere is likely to be understood by scaling the Earth's case but its dynamic aspect is likely modified significantly by the smallness of the Hermean magnetosphere and the substantial presence of heavy ions coming from the planet's surface. © 2007 Springer Science+Business Media B.V.

The Venus Climate Orbiter mission (PLANET-C), one of the future planetary missions of Japan, aims at understanding the atmospheric circulation of Venus. Meteorological information will be obtained by globally mapping clouds and minor constituents successively with four cameras at ultraviolet and infrared wavelengths, detecting lightning with a high-speed imager, and observing the vertical structure of the atmosphere with radio science technique. The equatorial elongated orbit with westward revolution fits the observation of the movement and temporal variation of the atmosphere which as a whole rotates westward. The systematic, continuous imaging observations will provide us with an unprecedented large data set of the Venusian atmospheric dynamics. Additional targets of the mission are the exploration of the ground surface and the observation of zodiacal light. The mission will complement the ESA's Venus Express, which also explores the Venusian environment with different approaches. (C) 2007 Elsevier Ltd. All rights reserved.

The outcomes of asteroid collisional evolution are presently unclear: are most asteroids larger than 1 km size gravitational aggregates reaccreted from fragments of a parent body that was collisionally disrupted, while much smaller asteroids are collisional shards that were never completely disrupted? The 16 km mean diameter S-type asteroid 433 Eros, visited by the NEAR mission, has surface geology consistent with being a fractured shard. The Hayabusa spacecraft visited an S-asteroid smaller than 1 km, namely 25143 Itokawa. Here we report the first comparative analyses of Itokawa and Eros geology. Itokawa lacks a global lineament fabric, and its blocks, craters, and regolith are inconsistent with formation and evolution as a fractured shard, unlike Eros. Itokawa is not a scaled-down Eros, but formed by a distinct process of catastrophic disruption and reaccumulation.

Observation strategy and Digital Electronics unit of Japanese Planet-C, next Japanese Venus observation program is described and the adoptability of loss-lees data compression method, HEREW and JEPG2000 is discussed.

The Longwave Infrared Camera (LIR) onboard the first Japanese Venus mission, PLANET-C, or the Venus Climate Orbiter, operates in the middle infrared region with a single bandpass filter of 8-12 mu m, measuring thermal radiation emitted from the cloud tops of the Venusian atmosphere. A horizontal wind vector field at the cloud-top height will be retrieved by means of a cloud tracking method. In addition, absolute temperature will be determined with an accuracy of 3 K. Since solar irradiation scattered by the atmosphere is much weaker than the atmospheric thermal radiation, LIR can continuously monitor a hemispheric wind field independent of the local time of the apocenter throughout the mission life. Wind and temperature fields obtained by LIR will provide key parameters to solve climatological issues related to the Venusian atmosphere. The use of an uncooled micro-bolometer array (UMBA), which requires no cryogenic apparatus, as an image sensor contributes to the reduction of power consumption and the weight of the LIR imager. An instrumental field-of-view of 12 degrees is equal to the angle subtended by Venus when observed from a height of 9.5 Rv. The pixel field-of-view corresponds to a spatial resolution of 70 km viewed from the apocenter. A mechanical shutter functions not only as an optical shutter but also as a reference blackbody. The temperature stability of the sensor is especially important, because fluctuation of thermal radiation from the internal environment of the sensor itself causes background noise. Therefore, the temperature of the UMBA package is stabilized at 313 +/- 0.1 K with a feedback controlled Peltier cooler/heater, and a NETD of 0.3 K, which is required for this infrared imager, will be achieved. Flat field images are taken with the shutter closed several seconds before and after 1 s exposure for a Venus thermal image. After a Venus image is taken, the LIR imager takes a cold calibration image of deep space. This measurement sequence is repeated every two hours when the spacecraft is orbiting at apocenter. Image data are transmitted down to the Earth after onboard calibration and data compression by common digital electronics. (c) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

The ranging instrument aboard the Hayabusa spacecraft measured the surface topography of asteroid 25143 Itokawa and its mass. A typical rough area is similar in roughness to debris located on the interior wall of a large crater on asteroid 433 Eros, which suggests a surface structure on Itokawa similar to crater ejecta on Eros. The mass of Itokawa was estimated as (3.58 +/- 0.18) x 1010 kilograms, implying a bulk density of (1.95 +/- 0.14) grams per cubic centimeter for a volume of ( 1.84 +/- 0.09) x 10(7) cubic meters and a bulk porosity of similar to 40%, which is similar to that of angular sands, when assuming an LL ( low iron chondritic) meteorite composition. Combined with surface observations, these data indicate that Itokawa is the first subkilometer-sized small asteroid showing a rubble-pile body rather than a solid monolithic asteroid.

The Extreme Ultraviolet (XUV) scanner on board the Planet-B spacecraft observed the He I 58.4-nm emission of the local interstellar gas in interplanetary space during solar maximum. The spacecraft was in an interplanetary orbit with a perihelion of 1 AU and an aphelion of 1.5 AU and encountered the helium focusing cone at a longitude different from the position of the Earth during March and April of 2000. Numerical simulations of the XUV observation were carried out based on a hot model of the interstellar gas (Wu and Judge, 1979) and an empirical solar flux model (SOLAR2000) (Tobiska et al., 2000). In comparison with the XUV observations, we obtain an ionization rate of (2.3 ± 0.27) × 10-7/s and a line width of 0.0098 ± 0.0014 nm, corresponding to a velocity of 50 ± 7.2 km/s. However, the distribution of the interplanetary He I intensity indicates that the solar He I irradiance has an anisotropy in longitude and latitude. From the comparison between the XUV observation and alternative simulations with an anisotropy in the solar He I irradiance and with no anisotropy in the total ionization rate, the He I flux ratio toward the pole to within the ecliptic plane is estimated to be 0.61 ± 0.24. Therefore it is suggested that the ionization rate of helium atoms has similar anisotropies as the solar He I flux. Since the relationship between anisotropies of the ionization rate and the helium density is not linear, a three-dimensional and time-dependent approach is required for full understanding on the helium distribution in interplanetary space. Copyright 2006 by the American Geophysical Union.

The purpose of this paper is to clarify how the average structure of the Venus nightside ionopause for solar zenith angles (SZA) greater than 90 degrees depends on (1) the direction and (2) the magnitude of the motional electric field of the solar wind. Plasma density structure in the Venus nightside ionosphere has been investigated by using data sets of the Pioneer Venus Orbiter observations. It is found that the distribution of the nightside ionopause locations is asymmetric with respect to the direction of the solar wind electric field, leaning opposite to the electric field vector. It is also found that the asymmetry is increasingly prominent as the magnitude of the motional electric field increases, while not so prominent for small field magnitude. This result suggests that the asymmetric ionopause location in the nightside is related to the acceleration of pickup ions.

[1] To understand magnetotail dynamics, it is essential to determine where magnetic reconnection takes place in the near-Earth magnetotail during substorms. The Geotail spacecraft thoroughly surveyed the near-Earth plasma sheet at radial distances of 10-31 RE during the years 1995-2003. Thirty-four clear reconnection events were identified using the criterion of strong electron acceleration. Various solar wind parameters prior to each reconnection event were examined in order to find the factor controlling the location of the magnetic reconnection site in the magnetotail. The same analyses were carried out for fast tailward flow events. The most important factor was determined to be the solar wind energy input, which can be expressed by - Vx × Bs, where Vx is the x component of the solar wind velocity and Bs is the southward component of the interplanetary magnetic field. It is likely that higher efficiency of energy input, rather than the total amount of energy input, primarily controls the location of magnetic reconnection magnetic reconnection takes place closer to the Earth when efficiency of energy input is higher. The effect of solar wind dynamic pressure is minor. The present result suggests that the tail magnetic reconnection location during substorms is controlled by solar cycle variations in the solar wind. Copyright 2005 by the American Geophysical Union.

Extreme and far ultraviolet imaging spectrometers will be boarded on the low-altitude satellite of the upcoming mercury mission (the BepiColombo mission) conducted by ISAS and ESA. The UV instrument, consisting of the two spectrometers with common electronics, aims at measuring, (1) emission lines from molecules, atoms and ions present in the Mercury's tenuous atmosphere, and (2) the reflectance spectrum of Mercury's surface. The instrument pursues a complete coverage in UV spectroscopy. The extreme UV spectrometer covers the spectral range of 30-150 rim with the field of view of 5.0 degree, and the spectrum from 130 run to 430 run is obtained by the far UV spectrometer. The extreme UV spectrometer employs a Mo/Si multi-layer coating to enhance its sensitivity at particular emission lines. This technology enables us to identify small ionospheric signals such as He II (30.4nm) and Na II (37.2nm), which the previous mission could not identify.

Japan's Venus Climate Orbiter (the Planet-C spacecraft) will be launched in 2008 and will reach an orbit in the ecliptic plane around Venus in 2009. We propose two eXtreme UltraViolet (XUV) imagers to take global two-dimensional snapshots of near-Venus space, including the Venus ionosphere and the interaction region between the solar wind plasma and the Venus ionospheric plasma, The imagers detect the resonantly scattering emissions of oxygen ions (0 11 83.4 nm) and atoms (0 1 130.3 nm), neutral helium (He 158.4 nm), and hydrogen (H Ly-alpha 121.6 nm). Scientific goals are to investigate mechanisms of momentum and mass transfer across the ionopause, of convection in the upper atmosphere and ionosphere, and of atmospheric escape. Especially, we emphasize that sequential images of the 0 11 83.4-nm emission will enable us to understand temporal evolution of the vortex produced by the Kelvin-Helmholtz (K-H) instability. Though the wave structure due to the K-H instability is generated also at the terrestrial magnetopause, oxygen ions are too tenuous to detect the emission. On the other hand, at the Venus ionopause oxygen ions have enough density to image the resonance emission, i.e., the Venus ionosphere plays a role as a space laboratory for plasma physics. (C) 2004 COSPAR. Published by Elsevier Ltd. All rights reserved.

Extreme and far ultraviolet imaging spectrometers are proposed for the low-altitude orbiter of the BepiColombo mission. The UV instrument, consisting of the two spectrometers with common electronics, aims at measuring (1) emission lines from molecules, atoms and ions present in the Mercury's tenuous atmosphere and (2) the reflectance spectrum of Mercury's surface. The instrument pursues a complete coverage in UV spectroscopy. The extreme UV spectrometer covers the spectral range of 30-150 nm with the field of view of 5.0degrees, and the spectrum from 130 to 430 nm is obtained by the far UV spectrometer. The extreme UV spectrometer employs multi-layer coating technology to enhance its sensitivity at particular emission lines. This technology enables us to identify small ionospheric signatures such as He II (30.4 nm) and Na II (37.2 nm), which could not be detected with conventional optics. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

The position and shape of the Gegenschein's maximum brightness provide information on the structure of the interplanetary dust cloud. We show that the asteroidal dust bands, extended near the anti-solar point, play an important role in determining both the position of the maximum brightness and the shape of the Gegenschein. After removing the asteroidal dust bands from an observation of the Gegenschein on November 2, 1997, it was found that the maximum brightness point shifted -0.4degrees in ecliptic latitude, i.e., to the south of the ecliptic plane, at an ecliptic longitude of 180degrees, in contrast to a latitude value of 0.1degrees when the dust bands were included. Furthermore, the part of the Gegenschein to the south of the ecliptic plane was brighter than the northern part at the time of observation. Referring to the cloud model of T. Kelsall et al. (1998, Astrophy. J. 508, 44-73), it can be estimated that the ascending node of the symmetry plane of the dust cloud is 57degrees(-3)(+7degrees). when its inclination is 2.03degrees -/+ 0.50degrees. (C) 2003 Elsevier Science (USA). All rights reserved.

[1] The EUV imagery of the plasmasphere was taken by the He II ( 304 Angstrom) scanner on 20-21 September 1998 after the first success on 9-10 September [Nakamura et al., 2000]. Total amount of the plasma seen in the outside of the plasmapause is inconsistent between the first and the second images, although geomagnetic and solar conditions are almost the same. These plasmas are directly filled from the ionosphere or continuously leak from the plasmasphere. We conclude that the contribution of the plasma leakage from the plasmasphere is as significant as the contribution of the direct filling from the ionosphere even under a quiet/moderate geomagnetic condition.

The spacecraft Geotail has observed the Hall current system in the vicinity of the magnetic reconnection site of the near-Earth magnetotail for substorm onsets. In the outermost region near the plasma sheet/tail lobe boundary, field-aligned currents flow out of the magnetic reconnection site. In the adjacent region, just inside the outflowing current layer, field-aligned currents flow into the magnetic reconnection site. Hence, the Hall current circuit forms a thin double-sheet structure near the separatrix layer. Copyright 2003 by the American Geophysical Union.

Recent in-situ plasma observations find that large amounts of O+ are escaping from the terrestrial ionosphere to the magnetosphere. Remote-sensing methods using the extreme ultraviolet (EUV) emission of O+ have been expected to be a powerful tool to provide a global perspective on the escaping processes. The overall picture is also very important for the practical use such as monitoring space weather. O+ ions resonantly scatter the solar photons with wavelength 83.4 nm. The key to the success of the observation is to prevent from detecting the H Ly-alpha line (121.6 nm), which is stronger than the predicted O II emission by four orders of magnitude. We have successfully detected O II emission from the uppermost part of the ionosphere using the sounding rocket SS-520-2 to investigate heavy ion escape from the. cusp/cleft region. This success demonstrates the capability of the remote-sensing method to take an instantaneous 2-dimensional image of the O+ distribution, and provides a way for optical observation of the magnetosphere. We plan to obtain O II images of the polar wind using the Telescope for EXtreme ultraviolet light, which is an upgrade version of the instrument for the sounding rocket, in the Upper atmosphere and Plasma Imager component (UPI-TEX) on the SELenological and ENgineering Explorer (SELENE). We refer to the feasibility of the O II If imagery from the lunar orbit satellite. (C) 2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

According to previous theories a large number of oxygen ions are not able to escape from the ionosphere to the magnetosphere due to its heavy mass and loss process in the upper atmosphere. Recent satellite observations, however, reveal that oxygen ions of the ionospheric origin exist in the magnetosphere, and that the outflow flux from the polar ionosphere is comparable to that of hydrogen ions, which have its light mass, during the high solar activity and the high geomagnetic activity. The distribution of oxygen ions provides the interpretation of the plasma transfer during the high activity, and gives us the effective information for monitoring the space weather. The remote-sensing method is useful for the measurement of the distribution of oxygen ions all over the magnetosphere. We advance development of new optics for the resonance scattering emission of oxygen ions.

Results of recent satellite observations indicate that a large amount of O+ are escaping from the terrestrial ionosphere into the magnetosphere. However, either the global distribution or the temporal variation of such O+ escape has not been understood well yet. A 2-Dimensional observation of oxygen ion emission (e.g., O II 83.4 nm) provides crucial information on the oxygen escape processes. In order to establish the basic technology required for such a 2-D (i.e., imaging) observation, we have developed an eXtreme Ultra-Violet (XUV) sensor sensitive to the O II 83.4-nm emission. In this study we present recent results of the observation of O+ ion escape from the ionosphere in the polar cap region using our XUV sensor carried by the sounding rocket SS-520-2. The XUV sensor successfully obtained an altitudinal profile of the intensity of the O II emission from 150 km through 1100 km of altitudes and detected 5-6 Rayleighs of the O II emission from the uppermost part of the ionosphere. The observation suggests that O+ ions convected from the cusp/cleft region exist over the polar ionosphere.

We present the first evidence of a cometary dust trail in optical wavelengths along the orbit of 22P/Kopff, observed when the parent comet was at a heliocentric distance of 3.01 AU. We find that the surface brightness and the width of the trail become, respectively, fainter and wider as the distance from the comet nucleus increases, except for a region with delta mean anomaly DeltaMAless than or equal to0.degrees02. This suggests that the majority of the centimeter-sized dust particles were ejected before the comet's previous perihelion passage and that they spread due to their initial velocity with respect to the comet. By comparing this trail with the IRAS data at wavelengths of 12 and 25 mum, we infer that the trail is composed of very low albedo particles (similar to0.01).

The visualization of the inner magnetosphere is a long-cherished goal in magnetospheric physics. This goal was recently achieved with the He II (304 Angstrom) image of the inner magnetosphere by using the EUV scanner on board the Planet-B spacecraft (Nakamura et al., 2000). However, our understanding of the inner magnetosphere in relation to these images has not been assessed. The two-dimensional (2-D) EUV image is difficult to interpret, as it is necessary to infer the three-dimensional (3-D) spatial information of the inner magnetosphere from the 2-D remote sensing data. We examine our present knowledge of the inner magnetosphere and compare simulated 2-D images with the real EUV image. We conclude that an empirical model that assumes conventional E x B flows and combines the diffusive equilibrium model of Chin et al. (1979) and the Weimer (1995) electric potential and Tsyganenko (1989) magnetic field models is in good agreement with the EUV image only within the Earth-dominated flow regime. Furthermore, the model gives a better fit to the EUV image data, by assuming the convection-dominated flow regime to be filled with ionospheric He+ at a filling rate of 1.2(.)(6.6/L)-3.0 (He(+)ions cm(-3) d(-1)), instead of the well-known L-4 density dependence on flux tube volume.

We have developed a lightweight, compact, and highly sensitive Extreme ultraviolet (EUV) photometer for a space-borne instrument. The photometer is onboard Japan's Mars orbiter, Planet-B, which was successfully launched on July 4, 1998, and stayed in the parking orbits around the Earth for 6 months. The new photometer is designed for studying the spatial distribution of helium ions and atoms by detecting He Il (304 Angstrom) and He I (584 Angstrom), which are major emission lines detectable around a planet. The photometer is a type of normal-incidence telescope that consists of a mirror, filters, and a detector. The mirror employs a new technology of a molybdenum/silicon multilayer coating and is designed to have peak reflectivity at 304 Angstrom. The photometer is capable of taking two-dimensional images by using the spin and orbital motions of the spacecraft. There are open questions concerning the Earth's plasmasphere and plasma sheet that cannot be resolved by in situ observations alone (e.g., global shape of the plasmasphere and cold ions in the plasma sheet). Our observations with the EUV photometer over a reasonable number of orbits will answer them. The photometer also shows an outstanding performance of measuring the Martian helium.