村上 豪

Microchannel plate (MCP) detectors have been widely used as two-dimensional photon counting devices on numerous space EUV (extreme ultraviolet) missions. Although there are other choices for EUV photon detectors, the characteristic features of MCP detectors such as their light weight, low dark current, and high spatial resolution make them more desirable for space applications than any other detector. In addition, it is known that the photocathode can be tailored to increase the quantum detection efficiency (QDE) especially for longer UV wavelengths (100-150 nm). There are many types of photocathode materials available, typically alkali halides. In this study, we report on the EUV (50-150 nm) QDE evaluations for MCPs that were coated with Au, MgF2, CsI, and KBr. We confirmed that CsI and KBr show 2-100 times higher QDEs than the bare photocathode MCPs, while Au and MgF2 show reduced QDEs. In addition, the optimal geometrical parameters for the CsI deposition were also studied experimentally. The best CsI thickness was found to be 150 nm, and it should be deposited on the inner wall of the channels only where the EUV photons initially impinge. We will also discuss the techniques and procedures for reducing the degradation of the photocathode while it is being prepared on the ground before being deployed in space, as adopted by JAXA's EXCEED mission which will be launched in 2013. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4746989]

BepiColombo, a mission of ESA (European Space Agency) in cooperation with JAXA (Japan Aerospace Exploration Agency), will explore Mercury, the planet closest to the Sun. BepiColombo will launch in 2014 on a journey lasting up to six and a half years; the data gathering phase should occupy a one year nominal mission, with a possible extension of another year. The data which will be brought back from the orbiters will tell us about the Hermean surface, atmospheric composition, and magnetospheric dynamics; it will also contribute to understanding the history and formation of terrestrial planets. The PHEBUS (Probing of Hermean Exosphere by Ultraviolet Spectroscopy) instrument will be flown on MPO: Mercury Planetary Orbiter, one of the two BepiColombo orbiters. The main purpose of the instrument is to reveal the composition and the distribution of the exosphere of Mercury through EUV (Extreme Ultraviolet: 55-155 nm) and FUV (Far Ultraviolet: 145-315 nm) measurements. A consortium composed of four main countries has been formed to build it. Japan provides the two detectors (EUV and FUV), Russia implements the scanning system, and France and Italy take charge of the overall design, assembly, test, integration, and also provide two small NUV (Near Ultraviolet) detectors (for the light from calcium and potassium molecules). An optical prototype of the EUV detector which is identical to the flight configuration has been manufactured and evaluated. In this paper, we show the first spectra results observed by the EUV channel optical prototype. We also describe the design of PHEBUS and discuss the possibility of detecting noble gases in Mercury's exosphere taking the experimental results so far into account. (C) 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.

The Io plasma torus is composed mainly of sulfur and oxygen ions and their compounds such as SO2+ derived from Io's volcanic activities, together with a background of electrons. In addition to those basic components, several in-situ observations have shown that a few percent of the electrons there have been excited to be as much as 100 times hotter than the background electrons. These hot electrons have a significant impact on the energy balance in the Jovian inner magnetosphere. However, their generation process has not yet been elucidated. One difficulty is that the available data all comes from in-situ observations, which cannot explore the temporal and spatial distributions explicitly. Therefore remote sensing, which could take a direct picture of the plasma dynamics is necessary. In order to clear up the hot electron problem, the Earth-orbiting EUV spectroscope, EXCEED will be launched in 2013. It is dedicated and optimized for observing the terrestrial planets. Because of its large effective area and the simplicity of the scientific target, better temporal resolution and more complete coverage for 10 plasma torus observation is expected. In this paper, the optical design and specifications of EXCEED are introduced. Furthermore, based on a feasibility study using the spectral diagnosis method, it is shown that EXCEED can determine the Io plasma torus parameters such as the electron density, temperatures, hot electron fraction and so on. The possibility of clearing up the hot electron problem through the EXCEED observations is also discussed. (C) 2012 Elsevier Ltd. All rights reserved.

The extreme ultraviolet (EUV) telescope EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) onboard the Japan's small satellite SPRINT-A will be launched in August 2013. The EXCEED instrument will observe tenuous gases and plasmas around the planets in the solar system (e.g., Mercury, Venus, Mars, Jupiter, and Saturn). The EXCEED instrument is designed to have a spectral range of 60-145 nm with a spectral resolution of 0.4-1.0 nm. The instrument has a field of view of 400 '' x 140 '' (maximum), and the attitude fluctuations are stabilized within +/- 5 ''. The optics of the instrument consists of an entrance mirror with a diameter of 200 mm, three types of slits, two types of filters, a laminar type grating, and a 5-stage microchannel plate assembly with a resistive anode encoder. In this paper, we report the general mission overview, the instrumentations, and the results of ground calibrations.

The Io plasma torus is composed mainly of sulfur and oxygen ions and their compounds, together with a background of electrons. In addition to those basic components, several in situ observations have shown that a small percentage of the electrons there have been excited to be as much as 100 times hotter than the background electrons. They have a significant impact on the energy balance in the Jovian inner magnetosphere. However, their generation process has not yet been clarified. One difficulty is that the available data about the hot electrons all come from in situ observations which cannot explore the temporal and spatial distributions explicitly. Therefore, remote sensing which can take a direct picture of the plasma dynamics is necessary in order to clarify the hot electron problem. In this study, a plasma diagnosis method was used for the Io plasma torus EUV spectra taken from the Cassini spacecraft. Agreement with previous observations confirmed the background electron temperature and ion compositions as determined by our model. In addition, the available data are matched even better when the model is run with a hot electron component. This consistent confirmation by remote sensing is a first. Because of the limited temporal resolution and observational coverage, the results could not be used to explain the generation process of the hot electrons. However, we expect that this method will be useful in studying the hot electron generation process when data from future missions with better temporal resolution and more complete coverage become available.

The Io plasma torus is composed mainly of sulfur and oxygen ions and their compounds, together with a background of electrons. In addition to those basic components, several in situ observations have shown that a small percentage of the electrons there have been excited to be as much as 100 times hotter than the background electrons. They have a significant impact on the energy balance in the Jovian inner magnetosphere. However, their generation process has not yet been clarified. One difficulty is that the available data about the hot electrons all come from in situ observations which cannot explore the temporal and spatial distributions explicitly. Therefore, remote sensing which can take a direct picture of the plasma dynamics is necessary in order to clarify the hot electron problem. In this study, a plasma diagnosis method was used for the Io plasma torus EUV spectra taken from the Cassini spacecraft. Agreement with previous observations confirmed the background electron temperature and ion compositions as determined by our model. In addition, the available data are matched even better when the model is run with a hot electron component. This consistent confirmation by remote sensing is a first. Because of the limited temporal resolution and observational coverage, the results could not be used to explain the generation process of the hot electrons. However, we expect that this method will be useful in studying the hot electron generation process when data from future missions with better temporal resolution and more complete coverage become available. Copyright 2011 by the American Geophysical Union.

We have succeeded in imaging of the terrestrial plasmasphere by the Telescope of Extreme Ultraviolet (TEX) aboard Japan's lunar orbiter KAGUYA. The view afforded by the KAGUYA orbit encompasses the plasma 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. This is the world first image of the plasmasphere from the moon.

An earth–orbiting extreme ultraviolet (EUV) spectroscopic mission, EXtreme ultraviolet speCtroscope for ExosphEric Dynamics explore (EXCEED) that will be launched in2012 is now under development. The EXCEED mission will carry out out–of–atmosphere observations of EUV (60–145 nm) emissions from tenuous plasmas around the planets (Mercury, Mars, Venus, and Jupiter). In this paper, we will introducethe general mission overview, the instrument, and the scientific targets.

The EXCEED mission is an Earth-orbiting extreme ultraviolet (EUV) spectroscopic mission and the first in the SPRINT series being developed by ISAS/JAXA. EUV spectroscopy is suitable for observing tenuous gases and plasmas around planets in the solar system (e.g., Mercury, Venus, Mars, Jupiter, and Saturn). One of the primary observation targets is Jupiter, whose magnetospheric plasma dynamics is dominated by planetary rotation. In the EUV range, a number of emission lines originate from plasmas distributed in Jupiter's inner magnetosphere. The EXCEED spectrograph is designed to have a wavelength range of 55–145 nm with minimum spectral resolution of 0.4 nm, enabling the electrontemperature and ion composition in the inner magnetosphere to be determined. Thespectrograph slits have a field of view of 400 × 140 arc-seconds (maximum), and an onboard target guide camera is used to stabilize attitude fluctuations to within ±5 arc-seconds. With a large primary mirror (diameter: 20 cm) and high detection efficiencies (1–3%), EXCEED will measure Io plasma torus emission distributions with a good signal-to-noise ratio using an exposure time of 50 minutes and achieving spatial resolution of 20arc-seconds. The previous observation of plasmas in the inner magnetosphere and the aurora with an EUV spectrograph was done by the Cassini spacecraft over a period of a few months. We re-examined the data obtained by the UVIS instrument to clarify the scientific objectives for the EXCEED mission. The UVIS observation sometimes showed sudden brightening in both the aurora and the Io plasma torus with a timescale from several hours to a few tens of hours. From the reanalysis of the UVIS dataas well as radio waves (Cassini/RPWS) and the interplanetary magnetic field (Galileo/MAG) data, we found that thebrightening events were related to a large-scale structure inthe solar wind. However, because the Cassini observations had a lack of continuity due to the intermittent observation mode, it is difficult to make a definitive relation between the aurora and the plasma emissions in the inner magnetosphere. EXCEED plans to observe the variations in the aurora and in the radial structures of plasma emissions andshould reveal the relationship between them in detail. The EXCEED observations are expected to investigate the radial plasma and energy transport processes in the rotation-driven magnetosphere.

At the end of previous century, we succeeded to image the Earth's plasmasphere from the space by EUV spectral range. Then, spacecraft missions were carried out to image the terrestrial EUV emissions. The extreme ultraviolet imagers (EUVIs) on the international space station (ISS) will be launched in 2012. At the altitude of approximately 400 km, two telescopes direct toward the Earth's limb to look the ionosphere and plasmasphere from the inside-out. One telescope detects the terrestrial EUV emission at O + (83.4 nm), and the other is He + (30.4 nm). These two EUV emissions are solar-scattered by ionized oxygen and helium, respectively. The maximum spatial and time resolutions are 0.1 degree and 1 minute, respectively. Our observation methods will become standard to probe the Earth's upper atmosphere. © 2011 The Institute of Electrical Engineers of Japan.

EXtreme ultraviolet spectrosCope for ExosphEric Dynamics (EXCEED) will carry out the extreme ultraviolet (EUV) spectroscopic imaging observations from earth orbit. It clarifies the plasma distributions and compositions around the various planets and examines the interactions with the solar wind. Observations should be carried out at high altitude so that the earth's atmospheric absorption is free. Our spectral range is from 60 to 145 nm and the spectral resolution is 0.3 to 1 nm (FWHM). The mission is planned to be launched in 2013, beginning of the next period of solar maximum. In this paper, we will introduce the general mission overview, scientific objectives and development of instrument.

Resonant scattering of the lunar sodium exosphere was measured from the lunar orbiter SELENE (Kaguya) from December 2008 to June 2009. Variations in line-of-sight integrated intensity measured on the night-side hemisphere of the Moon could be described as a spherical symmetric distribution of the sodium exosphere with a temperature of 2400-6000 K. Average surface density of sodium atoms in February is well above that in the other months by about 30%. A clear variation in surface density related to the Moon's passage across the Earth's magnetotail could not be seen, although sodium density gradually decreased (by 20 +/- 8%) during periods from the first through the last quarter of two lunar cycles. These results suggest that the supra-thermal components of the sodium exosphere are not mainly produced by classical sputtering of solar wind. The variation in sodium density (which depends on lunar-phase angle) is possibly explained by the presence of an inhomogeneous source distribution of photon-stimulated desorption (PSD) on the surface. (c) 2010 Elsevier Ltd. All rights reserved.

A statistical study comparing the plasmapause location determined using extreme ultraviolet (EUV) and cross-phase measurements was performed over 50 days in May-July 2000 and 1 day in May 2008. In EUV images the plasmapause location was estimated using the sharp gradient in the brightness of 30.4 nm He+ emission. We have taken EUV images obtained by the IMAGE and the Kaguya satellites, which were operated in a solar maximum and minimum periods, respectively. In the ground-based cross-phase measurement, the plasmapause was defined as a steep drop of mass density in its radial profile. Mass density was inferred from the eigenfrequency of field line resonances in the ULF band (similar to 1-1000 mHz), which was deduced from geomagnetic field data using cross-phase analysis. The two measurements of the plasmapause have been compared in a same meridian at the same time and very good agreement was found in 18 of 19 events. Our result clearly indicates that the He+ and mass density plasmapause are usually detected at the same place with the error range of +/- 0.4 R-E. In only one event, the He+ and the mass density defined plasmapauses were not colocated. This event may be due to the difference of refilling time between He+ and other dominant species.

We have developed a high-resolution imaging detector with five microchannel plates (MCPs) in a set of V and Z stacks and a resistive anode encoder (RAE) for future space applications. In a position-sensitive system with a RAE, the spatial resolution depends on the signal-to-noise ratios at the anode terminals. Therefore, a high and stable electron gain of MCPs allows the position determination of each photoelectron event with a high spatial resolution. We investigated the effect of the potentials applied to the detector on the pulse height distribution (PHD) and the spatial resolution by means of calculations and experiments. The calculations showed that the negative interstack potential reduced the size of the electron cloud at the Z-stack input by similar to 80%. The result suggests that, under such a condition, the Z-stack MCP is operated in the completely saturated mode and exhibits a narrow PHD. On the other hand, in the measurements, applying the negative interstack potential reduced the width of the PHD by similar to 60%. As a result, the spatial resolution of 45 mu m, corresponding to 480 x 480 pixels, was achieved. The results enable us to optimize and apply the technique to future missions. (c) 2010 Optical Society of America

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.

A statistical study comparing the plasmapause location determined using extreme ultraviolet (EUV) and cross-phase measurements was performed over 50 days in May-July 2000 and 1 day in May 2008. In EUV images the plasmapause location was estimated using the sharp gradient in the brightness of 30.4 nm He+ emission. We have taken EUV images obtained by the IMAGE and the Kaguya satellites, which were operated in a solar maximum and minimum periods, respectively. In the ground-based cross-phase measurement, the plasmapause was defined as a steep drop of mass density in its radial profile. Mass density was inferred from the eigenfrequency of field line resonances in the ULF band (∼1-1000 mHz), which was deduced from geomagnetic field data using cross-phase analysis. The two measurements of the plasmapause have been compared in a same meridian at the same time and very good agreement was found in 18 of 19 events. Our result clearly indicates that the He+ and mass density plasmapause are usually detected at the same place with the error range of ± 0.4 RE. In only one event, the He+ and the mass density defined plasmapauses were not colocated. This event may be due to the difference of refilling time between He+ and other dominant species. Copyright © 2010 by the American Geophysical Union.

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.

We have succeeded in observations by the Telescope of Extreme Ultraviolet (TEX) aboard Japan's lunar orbiter KAGUYA to characterize the evolution of the Earth's plasmasphere. The view afforded by the KAGUYA orbit encompasses the plasma distribution in a single exposure, enabling us to examine for the first time the globally-averaged properties of the plasmasphere from the side (meridian) view. We focus on a study period that began with a likely moderate erosion event of plasma patches in a geomagnetically disturbed period, and follow refilling of plasma from the upper ionosphere. The Earth's plasmasphere grew up to saturated level at the rate of approximately 1,600 km per day to 4,800 km per day on the equatorial plane. From the “side view” of the Earth, a specific magnetic flux tube with cold dense plasmas was seen and likely moved to outer magnetosphere, even while geomagnetic activity was low. From the moon, we are studying the terrestrial plasmas in the vicinity of the Earth. This is called “Geoscience from the Moon”.

An earth-orbiting Extreme Ultraviolet spectroscopic mission, EXtreme ultraviolet spectrosCope for ExosphEric Dynamics explore (EXCEED) that will be launched in 2012 is now under development. The EXCEED mission will carry out observations of Extreme Ultraviolet (EUV) emissions from tenuous plasmas around the planets. It is essential for planetary EUV spectroscopy to avoid the Earth’s atmospheric absorption, therefore it should be mandatory to observe above the Earth’s atmosphere. In this paper, we will introduce the general mission overview, the instrument, and the scientific targets.

The Mercury Sodium Atmosphere Spectral Imager (MSASI) on the Mercury Magnetospheric Orbiter (MMO) of the JAXA/ESA Bepi-Colombo (BC) Mission will address a range of fundamental scientific questions pertaining to Mercury's exosphere. The measurements will provide new information on regolith-exosphere-magnetosphere coupling as well as new understanding of the dynamics governing the exosphere bounded by the planetary surface, the solar wind and interplanetary space. MSASI is a high-dispersion visible spectrometer working in the spectral region near the sodium D(2) emission (589 nm), a major constituent of the Mercury exosphere. A single high-resolution Fabry-Perot etalon is used in combination with a narrow-band interference filter to achieve a compact and efficient instrument design. The etalon and filter are extremely stable with respect to long-term aging and temperature variations. Full-disk images of the planet are obtained by means of a single-axis scanning mirror in combination with the spin of the MMO spacecraft. This paper presents an overview of the MSASI and the design of the Fabry-Perot interferometer used as its spectral analyser. It is concluded that: (1) The MSASI optical design is practical and can be implemented without new or critical technology developments. (2) The thermally stable etalon design is based on concepts, designs and materials that have a good space heritage. (3) The MSASI instrument will achieve a high signal-to-noise ratio (SNR) (> 10) in the range of 2K-10M Rayleigh. (C) 2008 Elsevier Ltd. All rights reserved.

An Earth-orbiting small satellite "EXtreme ultraviolet spectrosCope for ExosphEric Dynamics" (EXCEED) which will be launched in 2012 is under development. The mission will carry out spectroscopic and imaging observation of EUV (Extreme Ultraviolet: 60145 nm) emissions from tenuous plasmas around the planets (Venus, Mars, Mercury, and Jupiter). It is essential for EUV observation to put on an observing site outside the Earth's atmosphere to avoid the absorption. It is also essential that the detection efficiency must be very high in order to catch the faint signals from those targets. In this mission, we employ cesium iodide coated microchannel plate as a 2 dimensional photon counting devise which shows 1.5-50 times higher quantum detection efficiency comparing with the bared one. We coat the surface of the grating and entrance mirror with silicon carbides by the chemical vapor deposition method in order to archive the high diffraction efficiency and reflectivity. The whole spectrometer is shielded by the 2 mm thick stainless steel to prevent the contamination caused by the high energy electrons from the inner radiation belt. In this paper, we will introduce the mission overview, its instrument, and their performance. (C) 2009 COSPAR. Published by 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.

The BepiColombo is an international Mercury exploring mission which will be launched in 2014 and reach the planet in 2020. In this paper, we show the development status of the extreme ultraviolet (50-155 nm) detector for the mission. We have optimized the geometry of the micro channel plate that can achieve highest quantum detection efficiency. Furthermore, we have evaluated the quantum detection efficiencies of cesium iodide-coated micro channel plate which have been exposed to the air or dry nitrogen, in order to determine the treatment procedure to prevent performance degradation until the launch.

The PHEBUS (Probing of Hermean Exosphere By Ultraviolet Spectroscopy) instrument on Mercury Planetary Orbiter in the BepiColombo mission is a dual FUV-EUV spectrometer (EUV: 55-155 nm, FUV: 145-315 nm). We are now developing the compact detector system sensitive to FUV airglow emissions of the Mercury. The FUV detector is required to have high spatial resolution (512×512 pixels) so that the wavelength resolution of the PHEBUS instrument should be 2 nm at the FUV range. The FUV detector consists of a Cs₂Te photocathode, microchannel plates (MCPs), and a resistive anode encoder. In a position-sensitive system with a resistive anode encoder, the spatial resolution is determined by the signal-to-noise ratios at the anode terminals. Therefore, a high and stable electron gain of MCPs allows the position determination of each photoelectron event with high spatial resolution. We studied a method for achieving a high and stable electron gain. We fabricated a test model of the FUV detector incorporating a clamped pair of MCPs (V-stack) followed by a gap and a clamped triplet of MCPs (Z-stack) in cascade. We investigated the effect of the negative inter-stack potential on the PHD and the spatial resolution by means of calculation and experiments. As a result, the negative inter-stack potential made the electron gain more stable and the spatial resolution higher by ∼14%. In this paper we report the specific performance of the test model of the FUV detector.

The Upper Atmosphere and Plasma Imager (UPI) was placed in a lunar orbit in order to Study both the Moon and Earth. The UPI consists of two telescopes: a Telescope of Extreme Ultraviolet (TEX) and a Telescope of Visible Light (TVIS), which are both mounted on a two-axis gimbals system. The TVIS is equipped with fast catadioptric optics and a high-sensitivity CCD to image swift aurora and dark airglow ill the terrestrial upper atmosphere. TVIS has a field-of-view equivalent to the Earth's disk as seen from the Moon. The spatial resolution is about 30 km x 70 km on the Earth's surface at auroral latitudes. The observation wavelengths can be changed by selecting different bandpass filters. Using the images of the northern and Southern auroral ovals taken by TVIS, the intensities and shapes of the conjugate auroras will be quantitatively compared. Using the an-low imaging, medium- and large-scale ionospheric disturbances will be Studied. In this paper, the instrumental design and performance of TVIS are presented.

The first successful observations of resonant scattering emission from the lunar sodium exosphere were made from the lunar orbiter SELENE (Kaguya) using TVIS instruments during the period 17-19 December, 2008. The emission intensity of the NaD-line decreased by 12 +/- 6%, with an average value of 5.4 kR (kilorayleighs) in this period, which was preceded, by I day, by enhancement of the solar proton flux associated with a corotating interaction region. The results suggest that solar wind particles foster the diffusion of sodium atoms or ions in the lunar regolith up to the surface and that the time scale of the diffusion is a few tens of hours. The declining activity of the Geminid meteor shower is also one possible explanation for the decreasing sodium exosphere.

A rare, but normal, astronomical event occurred on November 9th 2006 (JST) as Mercury passed in front of the Sun from the perspective of the Earth. The abundance of the sodium vapor above the planet limb was observed by detecting an excess absorption in the solar sodium line D, during this event. The observation was performed with a 10-m spectrograph of Czerny-Turnar system at Domeless Solar Tower Telescope at the Hida Observatory in Japan. The excess absorption was red-shifted by 10 pm relative to the solar line, and was measured at the dawnside (eastside) and duskside (westside) of Mercury. Between the dawn and dusksides, an asymmetry of total sodium abundance was clearly identified. At the dawnside, the total sodium column density was 6.1 x 10(10) Na atoms/cm(2), while it was 4.1 x 10(10) Na atoms/cm(2) at the duskside. The investigation of dawn-dusk asymmetry of the sodium exosphere of Mercury is a clue to understand the release mechanism of sodium from the surface rock. Our result suggests that a thermal desorption is a main source process for sodium vapor in the vicinity of Mercury. (C) 2008 Elsevier Ltd. All rights reserved.

The Mercury's Sodium Atmosphere Spectral Imager (MSASI) on BepiColombo (BC) will address a range of fundamental scientific questions pertaining to Mercury's exosphere. The measurements will provide new information on regolith-exosphere-magnetosphere coupling as well as new understanding of the dynamics governing the exosphere bounded by the planetary surface, the solar wind and interplanetary space. MSASI is a high-dispersion visible spectrometer working in the spectral range around sodium D2 emission (589 nm). A tandem Fabry-Perot etalon is used to achieve a compact design. We presents a design of the spectral analyzer using Fabry-Perot interferometer. We conclude that: (1) The MSASI optical design is practical and can be implemented without new or critical technology developments; (2) The thermally-tuned etalon design is based on concepts, designs and materials that have good space heritage. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

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

An ultraviolet spectrometer, PHEBUS (Probing of Hermean Exosphere by Ultraviolet Spectroscopy) that is loaded onto the Mercury Planetary Orbiter in the BepiColombo mission is under development. The instrument, basically consisting of two spectrophotometers (EUV: 50-150 nm, FUV: 145-330 nm) and one scanning mirror, aims at measuring emission lines from molecules, atoms and ions present in the tenuous atmosphere of Mercury. The detectors employ microchannel plates as 2-D photon-counting devices. In order to enhance the quantum detection efficiencies, the surface of the top microchannel plates of EUV detector is covered with photocathode. This method enables us to identify weak atmospheric signatures such as neon (73.5 nm) and argon (104.8 nm), which could not be detected with conventional detector systems. This paper presents measurements of the performance characteristics of potassium bromide and esium iodide photocathodes, which have been evaluated for use in the EUV channel. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

The Mercury's sodium atmosphere spectral imager (MSASI) on BepiColombo (BC) will address a range of fundamental scientific questions pertaining to Mercury's exosphere. The measurements will provide new information on regolith-exosphere-magnetosphere coupling as well as new understanding of the dynamics governing the exosphere bounded by the planetary surface, the solar wind and interplanetary space. MSASI is a high-dispersion visible spectrometer working in the spectral range around sodium D2 emission (589 nm). A tandem Fabry-Perot etalon is used to achieve a compact design. A one-degree-of-freedom scanning mirror is employed to obtain full-disk images of the planet. This paper presents an overview of the MSASI and the design of its spectral analyzer, which uses a Fabry-Perot interferometer. We conclude that: (1) The MSASI optical design is practical and can be implemented without new or critical technology developments. (2) The thermally tuned etalon design is based on concepts, designs and materials that have good space heritage. (3) The MSASI instrument achieves a high SNR (> 10) in the range of 2k-10 MRayleigh. (C) 2007 Elsevier Ltd. All rights reserved.

[1] We statistically examined the plasmapause response to the southward turning of the interplanetary magnetic field ( IMF) using sequential global images of the plasmasphere, in order to understand how the convection electric field propagates to the inner magnetosphere. The extreme ultraviolet (EUV) imager on the Imager for Magnetopause- to-Aurora Global Exploration satellite clearly observed inward motion of the plasmapause driven by the southward turning of the IMF. We surveyed the EUV data in the 2000 - 2001 period and found 16 events. Using the sequential EUV images, we calculated the plasmapause radial velocity, and then estimated the time development of the convection electric field at the plasmapause (E-pp). E-pp and the solar wind electric field derived from the measurement by the ACE satellite had very similar variations each other, but there surely was a time lag. Consequently, our research indicates that the plasmapause response to the southward turning of the IMF takes 10 - 30 min. This timescale suggests that the convection electric field penetrates from the magnetopause to the inner magnetosphere through the ionosphere.