村上 豪

©2018. American Geophysical Union. All Rights Reserved. Embedded deep inside the huge magnetosphere of Jupiter, the moon Io has active volcanos. Jovian magnetospheric dynamics are driven by the expulsion of Iogenic plasma in the strongly magnetized, fast-rotating system and should vary in response to Io's volcanic activity. In early 2015 when various observations indicated an increase in volcanic activity, the EXCEED instrument onboard the Hisaki spacecraft continuously observed the Jovian magnetosphere via the aurora emission and the emission from the Io plasma torus. The plasma diagnosis of the enhanced Io plasma torus spectrum along with a physical chemistry model for deducing plasma parameters revealed a higher plasma density and a 2–4 times faster radial flow as compared with a volcanically quiet period. Aurora emissions reflecting midmagnetospheric activities showed multiple highly elevated brightness peaks about a month later. Long-term and continuous monitoring by Hisaki enabled the first comprehensive observations of the Jovian magnetosphere in response to Io's enhanced volcanic activity.

©2018. Johns Hopkins Applied Physics Laboratory. The relationship between electron energy flux and the characteristic energy of electron distributions in the main auroral loss cone bridges the gap between predictions made by theory and measurements just recently available from Juno. For decades such relationships have been inferred from remote sensing observations of the Jovian aurora, primarily from the Hubble Space Telescope, and also more recently from Hisaki. However, to infer these quantities, remote sensing techniques had to assume properties of the Jovian atmospheric structure—leading to uncertainties in their profile. Juno's arrival and subsequent auroral passes have allowed us to obtain these relationships unambiguously for the first time, when the spacecraft passes through the auroral acceleration region. Using Juno/Jupiter Energetic particle Detector Instrument (JEDI), an energetic particle instrument, we present these relationships for the 30-keV to 1-MeV electron population. Observations presented here show that the electron energy flux in the loss cone is a nonlinear function of the characteristic or mean electron energy and supports both the predictions from Knight (1973, https://doi.org/10.1016/0032-0633(73)90093-7) and magnetohydrodynamic turbulence acceleration theories (e.g., Saur et al., 2003, https://doi.org/10.1029/2002GL015761). Finally, we compare the in situ analyses of Juno with remote Hisaki observations and use them to help constrain Jupiter's atmospheric profile. We find a possible solution that provides the best agreement between these data sets is an atmospheric profile that more efficiently transports the hydrocarbons to higher altitudes. If this is correct, it supports the previously published idea (e.g., Parkinson et al., 2006, https://doi.org/10.1029/2005JE002539) that precipitating electrons increase the hydrocarbon eddy diffusion coefficients in the auroral regions.

©2018. American Geophysical Union. All Rights Reserved. The innermost Galilean satellite, Io, supplies a large amount of volcanic gasses to the Jovian magnetosphere. The fast rotation of Jupiter and the outward transport of ionized gasses are responsible for forming a huge and rotationally dominant magnetosphere. The plasma supply from the satellite has a key role in the characterization of the Jovian magnetosphere. In fact, significant variations of the plasma population in the inner magnetosphere caused by the volcanic eruptions in Io were found in early 2015, using a continuous data set of the Io plasma torus obtained from an extreme ultraviolet spectroscope onboard the Hisaki satellite. The time evolution of the Io plasma torus radial distribution showed that the outward transport of plasma through 8 RJ from Jupiter was enhanced for approximately 2 months (from the end of January to the beginning of April 2015). Intense short-lived auroral brightenings––which represent transient energy releases in the outer part of the magnetosphere—occurred frequently during this period. The short-lived auroral brightenings accompanied well-defined sporadic enhancements of the ion brightness in the plasma torus, indicating a rapid inward transport of energy from the outer part of the magnetosphere and the resultant enhancement of hot electron population in the inner magnetosphere. This evidently shows that the change in a plasma source in the inner magnetosphere affects a large-scale radial circulation of mass and energy in a rotationally dominant magnetosphere.

©2018. American Geophysical Union. All Rights Reserved. The sulfur and oxygen ions in the Io plasma torus (IPT), which is located at a distance of ~6 RJ from Jupiter, emit light in various wavelength regions. In particular, radiative cooling in the ultraviolet wavelength range plays an important role in the energy balance of the Io torus, and it is important to explore the detailed spectral structure in the ultraviolet region. The ultraviolet spectrum of the IPT in the wavelength range 52.0–148.0 nm with a resolution of 0.3–0.4 nm was obtained by Extreme Ultraviolet Spectroscope for Exospheric Dynamics on the Hisaki satellite. Owing to its instrument performance and long integration time, 10 emission lines from the IPT were detected for the first time. By summarizing previous observations and using the results obtained by Extreme Ultraviolet Spectroscope for Exospheric Dynamics, we updated the term diagrams for S II, S III, and S IV emissions from the IPT. Four excited levels in the IPT were detected for the first time. Detection of the emission lines may improve the estimation accuracy of the fraction of hot electron density using the atomic data.

Extreme ultraviolet (EUV) spectra of Venus in the wavelength range 520−1480 Å with 3−4 Å resolutions were obtained in March 2014 by an EUV imaging spectrometer EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) on the HISAKI spacecraft. Due to its high sensitivity and long exposure time, many new emission lines and bands were identified. Already known emissions such as the O II 834 Å O I 989 Å HILy−β1026 Å and the C I 1277 Å lines (Broadfoot et al., 1974 Bertaux et al., 1980 Feldman et al., 2000) are also detected in the EXCEED spectrum. In addition, N2 band systems such as the Lyman-Birge-Hopfield (a1Πg−X1Σg +) (2, 0), (2, 1), (3, 1), (3, 2) and (5, 3) bands, the Birge-Hopfield (b1Πu−X1Σg +) (1, 3) band, and the Carroll-Yoshino (c4 ′ 1Σu +−X1Σg +) (0, 0) and (0, 1) bands together are identified for the first time in the Venusian airglow. We also identified the CO Hopfield-Birge (B1Σ+−X1Σ+) (1, 0) band in addition to the already known (0, 0) band, and the CO Hopfield-Birge (C1Σ+−X1Σ+) (0, 1), (0, 2) bands in addition to the already known (0, 0) band (Feldman et al., 2000 Gérard et al., 2011).

©2018. American Geophysical Union. All Rights Reserved. We report on the spatial distribution of a neutral oxygen cloud surrounding Jupiter's moon Io and along Io's orbit observed by the Hisaki satellite. Atomic oxygen and sulfur in Io's atmosphere escape from the exosphere mainly through atmospheric sputtering. Some of the neutral atoms escape from Io's gravitational sphere and form neutral clouds around Jupiter. The extreme ultraviolet spectrograph called EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) installed on the Japan Aerospace Exploration Agency's Hisaki satellite observed the Io plasma torus continuously in 2014–2015, and we derived the spatial distribution of atomic oxygen emissions at 130.4 nm. The results show that Io's oxygen cloud is composed of two regions, namely, a dense region near Io and a diffuse region with a longitudinally homogeneous distribution along Io's orbit. The dense region mainly extends on the leading side of Io and inside of Io's orbit. The emissions spread out to 7.6 Jupiter radii (RJ). Based on Hisaki observations, we estimated the radial distribution of the atomic oxygen number density and oxygen ion source rate. The peak atomic oxygen number density is 80 cm−3, which is spread 1.2 RJ in the north-south direction. We found more oxygen atoms inside Io's orbit than a previous study. We estimated the total oxygen ion source rate to be 410 kg/s, which is consistent with the value derived from a previous study that used a physical chemistry model based on Hisaki observations of ultraviolet emission ions in the Io plasma torus.

The production and transport of plasma mass are essential processes in the dynamics of planetary magnetospheres. At Jupiter, it is hypothesized that Io's volcanic plasma carried out of the plasma torus is transported radially outward in the rotating magnetosphere and is recurrently ejected as plasmoid via tail reconnection. The plasmoid ejection is likely associated with particle energization, radial plasma flow, and transient auroral emissions. However, it has not been demonstrated that plasmoid ejection is sensitive to mass loading because of the lack of simultaneous observations of both processes. We report the response of plasmoid ejection to mass loading during large volcanic eruptions at Io in 2015. Response of the transient aurora to the mass loading rate was investigated based on a combination of Hisaki satellite monitoring and a newly developed analytic model. We found that the transient aurora frequently recurred at a 2–6 day period in response to a mass loading increase from 0.3 to 0.5 t/s. In general, the recurrence of the transient aurora was not significantly correlated with the solar wind, although there was an exceptional event with a maximum emission power of ~10 TW after the solar wind shock arrival. The recurrence of plasmoid ejection requires the precondition that an amount comparable to the total mass of magnetosphere, ~1.5 Mt, is accumulated in the magnetosphere. A plasmoid mass of more than 0.1 Mt is necessary in case that the plasmoid ejection is the only process for mass release.

In has an atmosphere produced by volcanism and sublimation of frosts deposited around active volcanoes. However, the time variation of atomic oxygen escaping Io's atmosphere is not well known. In this paper, we show a significant increase in atomic oxygen around to during a volcanic event. Brightening of Io's extended sodium nebula was observed in the spring of 2015. We used the Hisaki satellite to investigate the time variation of atomic oxygen emission around lo during the same period. This investigation reveals that the duration of atomic oxygen brightness increases from a volcanically quiet level to a maximum level during the same approximate time period of 30 days as the observed sodium brightness. On the other hand, the recovery of the atomic oxygen brightness from the maximum to the quiet level (60 days) was longer than that of the sodium nebula decreasing (40 days). Additionally, a dawn-dusk asymmetry of the atomic oxygen emission is observed. (C) 2017 Elsevier Inc. All rights reserved.

The hydrogen exosphere constitutes the uppermost atmospheric layer of the Earth, and its shape may reflect the last stage of the atmospheric escape process. The distribution of hydrogen in the outer exosphere remains unobserved because outer geocoronal emissions are difficult to observe from within the exosphere. In this study, we used the Lyman Alpha Imaging Camera on board the Proximate Object Close Flyby with Optical Navigation spacecraft, located outside the exosphere, to obtain the first image of the entire geocorona that extends to more than 38 Earth radii. The observed emission intensity distribution can be reproduced using our analytical model that has three parameters: exobase temperature, exobase density, and solar radiation pressure, which implies that hot hydrogen production in the magnetized plasmasphere is not the dominant process shaping the outer hydrogen exosphere. However, the role of the magnetic effect in determining the total escape flux cannot be ruled out.

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 similar to 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 similar to 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. Plain Language Summary Jupiter's auroras (northern lights) are the brightest in the solar system, over a hundred times brighter than the Earth's. Auroras on Earth are driven by the solar wind, a million mile-per-hour stream of charged particles flowing away from the Sun, hitting the Earth's magnetic field, and stirring it around, but it is not known whether the solar wind causes any significant auroras on Jupiter. The main reason for this uncertainty is a lack of observations of the planet's auroras obtained while spacecraft have been near Jupiter and able to supply a full and continuous set of measurements of the solar wind and its accompanying magnetic field. In early mid-2016 Juno approached Jupiter, providing such an interplanetary data set, and we obtained over a month's worth of observations of Jupiter's auroras using the Hubble Space Telescope. We saw several solar wind storms, each causing auroral fireworks on Jupiter. We captured the most powerful auroras observed by Hubble to date, brightened main oval emissions, and flashing high-latitude patches of auroras during the solar wind storms. These results indicate that Jupiter's auroral response to the solar wind is more diverse than we previously have thought.

We report a dawn-dusk difference of periodic variations of oxygen EUV dayglow (OII 83.4 nm, OI 130.4 nm and OI 135.6 nm) in the upper atmosphere of Venus observed by the Hisaki spacecraft in 2015. Observations show that the periodic dayglow variations are mainly controlled by the solar EUV flux. Additionally, we observed characteristic similar to 1 day and similar to 4 day periodicities in the OI 135.6 nm brightness. The similar to 4 day periodicity was dominant on the duskside while the similar to 4 day periodicity was dominant on the dawnside. Although the driver of the similar to 1 day periodicity is still uncertain, we suggest that the similar to 4 day periodicity is caused by gravity waves that propagate from the middle atmosphere. The thermospheric subsolar-antisolar flow and the gravity waves dominantly enhance eddy diffusion on the dawnside, and the eddy diffusion coefficient changes every similar to 4 days due to large periodic modulations of wind velocity of the super-rotating atmosphere. Since the similar to 4 day modulations on the dawnside are not continuously observed, it is possible that there is an intermittent coupling between the thermosphere and middle atmosphere due to variations of wave source altitudes. Moreover, if there are variations of the wind velocity in the mesosphere or lower thermosphere, it is possible that gravity waves occasionally propagate to the thermosphere even on the duskside due to periodic disappearance of the critical level and the similar to 4 day periodic O atomic modulations occur. Thus, our observations imply that the similar to 4 day periodicity of the EUV dayglow may reflect the dynamics of the middle atmosphere of Venus. We also examined the effects of the solar wind on the dayglow variations by shifting the solar wind measurements from earth to Venus. We did not find clear correlations between them. However, since there are no local measurements of the solar wind at Venus, the effect of the solar wind on the dayglow is still uncertain. (C) 2016 Elsevier Inc. All rights reserved.

Jupiter's moon Io, which orbits deep inside the magnetosphere, is the most geologically active object in the solar system. Kurdalagon Patera, a volcano on Io, erupted in 2015 and became a substantial source of Jovian magnetospheric plasma. Based on Earth-orbiting spacecraft observations, Io plasma torus (IPT) exhibited the peak intensity (nearly double) of ionic sulfur emissions roughly 2 month later, followed by a decay phase. This environmental change provides a unique opportunity to determine how the more heavily loaded magnetosphere behaves. Indeed, the extreme ultraviolet spectroscope for exospheric dynamics onboard the Earth-orbiting spacecraft Hisaki witnessed the whole interval via aurora and IPT observations. A simple-minded idea would be that the centrifugal force acting on fast co-rotating magnetic flux tubes loaded with heavier contents intensifies their outward transport. At the same time, there must be increased inward convection to conserve the magnetic flux. The latter could be accompanied by (1) increased inward velocity of field lines, (2) increased frequency of inward transport events, (3) increased inward flux carried per event, or (4) combinations of them. The Hisaki observations showed that the densities of major ions in the IPT increased and roughly doubled compared with pre-eruption values. The hot electron fraction, which sustains the EUV radiation from the IPT, gradually increased on a timescale of days. Pairs of intensified aurora and IPT brightening due to the enhanced supply of hot electrons from the mid-magnetosphere to the IPT upon aurora explosions observed during both quiet and active times, enabled the study of the mid-magnetosphere/ IPT relationship. Hisaki observations under active Io conditions showed that: (1) the hot electron fraction in the torus gradually increased; (2) brightening pairs were more intense; (3) the energy supplied by the largest event maintained enhanced torus emission for less than a day; (4) the time delay of a torus brightening from a corresponding aurora intensification was roughly 11 h, that is, the same as during quiet times, suggesting that the inward convection speed of high-energy electrons does not change significantly.

The global distribution of He+ in the topside ionosphere was investigated using data of the He+ resonant scattering emission at 30.4nm obtained by the Extreme Ultra Violet Imager (EUVI) onboard the International Space Station. The optical observation by EUVI from the low-Earth orbit provides He+ column density data above the altitude of 400km, presenting a unique opportunity to study the He+ distribution with a different perspective from that of past studies using data from in situ measurements. We analyzed data taken in 2013 and elucidated, for the first time, the seasonal, longitudinal, and latitudinal variations of the He+ column density in the dusk sector. It was found that the He+ column density in the winter hemisphere was about twice that in the summer hemisphere. In the December solstice season, the magnitude of this hemispheric asymmetry was large (small) in the longitudinal sector where the geomagnetic declination is eastward (westward). In the June solstice season, this relationship between the He+ distribution and the geomagnetic declination is reversed. In the equinox seasons, the He+ column densities in the two hemispheres are comparable at most longitudes. The seasonal and longitudinal dependence of the hemispheric asymmetry of the He+ distribution was attributed to the geomagnetic meridional neutral wind in the F region ionosphere. The neutral wind effect on the He+ distribution was examined with an empirical neutral wind model, and it was confirmed that the transport of ions in the topside ionosphere is predominantly affected by the F region neutral wind and the geomagnetic configuration.

In early 2014, continuous monitoring with the Hisaki satellite discovered transient auroral emission at Jupiter during a period when the solar wind was relatively quiet for a few days. Simultaneous imaging made by the Hubble Space Telescope (HST) suggested that the transient aurora is associated with a global magnetospheric disturbance that spans from the inner to outer magnetosphere. However, the temporal and spatial evolutions of the magnetospheric disturbance were not resolved because of the lack of continuous monitoring of the transient aurora simultaneously with the imaging. Here we report the coordinated observation of the aurora and plasma torus made by Hisaki and HST during the approach phase of the Juno spacecraft in mid-2016. On day 142, Hisaki detected a transient aurora with a maximum total H-2 emission power of similar to 8.5 TW. The simultaneous HST imaging was indicative of a large "dawn storm," which is associated with tail reconnection, at the onset of the transient aurora. The outer emission, which is associated with hot plasma injection in the inner magnetosphere, followed the dawn storm within less than two Jupiter rotations. The monitoring of the torus with Hisaki indicated that the hot plasma population increased in the torus during the transient aurora. These results imply that the magnetospheric disturbance is initiated via the tail reconnection and rapidly expands toward the inner magnetosphere, followed by the hot plasma injection reaching the plasma torus. This corresponds to the radially inward transport of the plasma and/or energy from the outer to the inner magnetosphere.

The Io plasma torus, situated in the Jovian inner magnetosphere (6-8Jovian radii from the planet) is filled with heavy ions and electrons, a large part of which are derived from Io's volcanos. The torus is the key area connecting the primary source of plasma (Io) with the midmagnetosphere (>10Jovian radii), where highly dynamic phenomena are taking place. Revealing the plasma behavior of the torus is a key factor in elucidating Jovian magnetospheric dynamics. A global picture of the Io plasma torus can be obtained via spectral diagnosis of remotely sensed ion emissions generated via electron impact excitation. Hisaki, an Earth-orbiting spacecraft equipped with an extreme ultraviolet spectrograph Extreme Ultraviolet Spectroscope for Exospheric Dynamics, has observed the torus at moderate spectral resolution. The data have been submitted to spectral analysis and physical chemistry modeling under the assumption of axial symmetry. Results from the investigation are radial profiles of several important parameters including electron density and temperature as well as ion abundances. The inward transport timescale of midmagnetospheric plasma is obtained to be 2-40h from the derived radial profile for the abundance of suprathermal electrons. The physical chemistry modeling results in a timescale for the outward transport of Io-derived plasma of around 30days. The ratio between inward and outward plasma speed (similar to 1%) is consistent with the occurrence rate of depleted flux tubes determined using in situ observations by instruments on the Galileo spacecraft.

Atomic hydrogen atoms in the terrestrial exosphere resonantly scatter solar Lyman alpha (121.6 nm) radiation, observed as the hydrogen geocorona. Measurements of scattered solar photons allow us to probe time-varying distributions of exospheric hydrogen atoms. The Hisaki satellite with the extreme ultraviolet spectrometer (EXtreme ultraviolet spectrosCope for ExosphEric Dynamics: EXCEED) was launched in September 2013. EXCEED acquires spectral images (52-148 nm) of the atmospheres/magnetospheres of planets from Earth orbit. Due to its low orbital altitude (similar to 1000 km), the images taken by the instrument also contain the geocoronal emissions. In this context, EXCEED has provided quasi-continuous remote sensing observations of the geocorona with high temporal resolution (similar to 1 min) since 2013. These observations provide a unique database to determine the long-term behavior of the exospheric density structure. In this paper, we report exospheric structural responses observed by EXCEED to geomagnetic disturbances. Several geomagnetic storms with decreases of Dst index occurred in February 2014 and the Lyman alpha column brightness on the night side of the Earth increased abruptly and temporarily by approximately 10%. Hisaki reveal that the time lag between the peaks of the magnetic activity and the changes in the Lyman alpha column brightness is found to be about 2 to 6h during storms. In order to interpret the observational results, we evaluate quantitatively the factors causing the increase. On the basis of these results, a coupling effect via charge exchange between the exosphere and plasmasphere causes variations of the exospheric density structure.

Because Jupiter's magnetosphere is huge and is rotationally dominated, solar wind influence on its inner part has been thought to be negligible. Meanwhile, dawn-dusk asymmetric features of this region have been reported. Presence of dawn-to-dusk electric field is one of the leading explanations of the asymmetry; however, the physical process of generating such an intense electric field still remains unclear. Here we present long and continuous monitoring of the extreme ultraviolet emissions from the Io plasma torus in Jupiter's inner magnetosphere made by the Hisaki satellite between December 2013 and March 2014. We found five occasions where the dusk/dawn brightness ratio was enhanced above 2.5 in response to rapid increase of the solar wind dynamic pressure. The enhancement is achieved as the dusk region brightens and the dawn region dims. The observation indicates that dawn-to-dusk electric field in the inner magnetosphere is enhanced under compressed conditions.

Observations by the extreme ultraviolet (EUV) imager on board the IMAGE spacecraft revealed that the formation of a sharp plasmapause occurs in the postmidnight sector soon (<1h) after the convection enhancement. These results cannot be explained simply by the conventional theory of the plasmapause formation that the plasmapause coincides with the last closed equipotential of the convection electric field superposed on the Earth's corotation electric field. However, due to the limitation that the EUV imager provides information on only the azimuthal distribution of the plasmapause, the formation mechanism still remains an open issue. Now global images of the plasmasphere from meridian perspective become available, thanks to the telescope of extreme ultraviolet (TEX) instrument on board the KAGUYA spacecraft. Here we studied the plasmapause formation mechanism by analyzing the sequential TEX images of an erosion event during the geomagnetic disturbance (Kp=5) on 1-2 May 2008. The temporal evolution of the plasmapause locations at postmidnight observed by TEX agreed with those predicted by the dynamic simulations based on the interchange mechanism. Furthermore, the He+ column density in the nightside plasmasphere decreased by similar to 30% only at the low latitudes (< 20 degrees) during the enhanced convection period. This suggests that the plasmapause formation occurs first near the equatorial region during a geomagnetic disturbance, and it agrees with the plasmapause formation mechanism based on the interchange instability. Although we cannot conclude exclusively for the interchange mechanism, this is the first study to present the plasmapause formation viewed from the meridian perspective.

One of the focal points of interest in Jovian magnetospheric physics is the transport of energy and particles into the inner region. While an explosive energy release event in the midmagnetosphere is manifested as an aurora transient, its connection to the inner part has not been investigated due to sparsity of observations. Here we take the advantage of long-term and quasi-continuous simultaneous monitoring of the polar aurora and the Io Plasma Torus (IPT) located in the inner magnetosphere by Extreme Ultraviolet Spectroscope for Exospheric Dynamics/ Hisaki. Studies on temporal characteristics over hours enable us to see slow (similar to 10 h) coupling between the middle and inner magnetosphere as well as to quantify the temperature of hot electrons in the IPT. We derive parameters that characterize the strong particle acceleration process.

While the Jovian magnetosphere is known to have the internal source for its activity, it is reported to be under the influence of the solar wind as well. Here we report the statistical relationship between the total power of the Jovian ultraviolet aurora and the solar wind properties found from long-term monitoring by the spectrometer EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) on board the Hisaki satellite. Superposed epoch analysis indicates that auroral total power increases when an enhanced solar wind dynamic pressure hits the magnetosphere. Furthermore, the auroral total power shows a positive correlation with the duration of a quiescent interval of the solar wind that is present before a rise in the dynamic pressure, more than with the amplitude of dynamic pressure increase. These statistical characteristics define the next step to unveil the physical mechanism of the solar wind control on the Jovian magnetospheric dynamics.

Jupiter's auroral parameters are estimated from observations by a spectrometer EXCEED (Extreme Ultraviolet Spectroscope for Exospheric Dynamics) on board Japanese Aerospace Exploration Agency's Earth-orbiting planetary space telescope Hisaki. EXCEED provides continuous auroral spectra covering the wavelength range over 80-148nm from the whole northern polar region. The auroral electron energy is estimated using a hydrocarbon color ratio adopted for the wavelength range of EXCEED, and the emission power in the long wavelength range 138.5-144.8nm is used as an indicator of total emitted power before hydrocarbon absorption and auroral electron energy flux. The quasi-continuous observations by Hisaki provide the auroral electron parameters and their relation under different auroral activity levels. Short- (within < one planetary rotation) and long-term (> one planetary rotation) enhancements of auroral power accompany increases of the electron number flux rather than the electron energy variations. The relationships between the auroral electron energy (70-400keV) and flux (10(26)-10(27)/s, 0.08-0.9A/m(2)) estimated from the observations over a 40day interval are in agreement with field-aligned acceleration theory when incorporating probable magnetospheric parameters. Applying the electron acceleration theory to each observation point, we explore the magnetospheric source plasma variation during these power-enhanced events. Possible scenarios to explain the derived variations are (i) an adiabatic variation of the magnetospheric plasma under a magnetospheric compression and/or plasma injection, and (ii) a change of the dominant auroral component from the main emission (main aurora) to the emission at the open-closed boundary.

Temporal variation of Jupiter's northern aurora is detected using the Extreme Ultraviolet Spectroscope for Exospheric Dynamics (EXCEED) on board JAXA's Earth-orbiting planetary space telescope Hisaki. The wavelength coverage of EXCEED includes the H-2 Lyman and Werner bands at 80-148nm from the entire northern polar region. The prominent periodic modulation of the observed emission corresponds to the rotation of Jupiter's main auroral oval through the aperture, with additional superposed -50%-100% temporal variations. The hydrocarbon color ratio (CR) adopted for the wavelength range of EXCEED is defined as the ratio of the emission intensity in the long wavelength range of 138.5-144.8nm to that in the short wavelength range of 126.3-130nm. This CR varies with the planetary rotation phase. Short- (within one planetary rotation) and long-term (> one planetary rotation) enhancements of the auroral power are observed in both wavelength ranges and result in a small CR variation. The occurrence timing of the auroral power enhancement does not clearly depend on the central meridian longitude. Despite the limitations of the wavelength coverage and the large field of view of the observation, the auroral spectra and CR-brightness distribution measured using EXCEED are consistent with other observations.

Jupiter's X-ray auroral emission in the polar cap region results from particles which have undergone strong field-aligned acceleration into the ionosphere. The origin of precipitating ions and electrons and the time variability in the X-ray emission are essential to uncover the driving mechanism for the high-energy acceleration. The magnetospheric location of the source field line where the X-ray is generated is likely affected by the solar wind variability. However, these essential characteristics are still unknown because the long-term monitoring of the X-rays and contemporaneous solar wind variability has not been carried out. In April 2014, the first long-term multiwavelength monitoring of Jupiter's X-ray and EUV auroral emissions was made by the Chandra X-ray Observatory, XMM-Newton, and Hisaki satellite. We find that the X-ray count rates are positively correlated with the solar wind velocity and insignificantly with the dynamic pressure. Based on the magnetic field mapping model, a half of the X-ray auroral region was found to be open to the interplanetary space. The other half of the X-ray auroral source region is magnetically connected with the prenoon to postdusk sector in the outermost region of the magnetosphere, where the Kelvin-Helmholtz (KH) instability, magnetopause reconnection, and quasiperiodic particle injection potentially take place. We speculate that the high-energy auroral acceleration is associated with the KH instability and/or magnetopause reconnection. This association is expected to also occur in many other space plasma environments such as Saturn and other magnetized rotators.

<p>DESTINY: the Demonstration and Experiment of Space Technology for Interplanetary Voyage, which is a candidate mission of Epsilon Launch Vehicle, plans to execute scientific observations using instruments with the mass of up to about 10 kg on the transfer and Halo orbit of the sun to earth Lagrangian point L1/L2 or on the fly-by orbit of near earth objects (NEO). Potential scientific objects include in-situ observation and remote sensing from these space are solar system explorations, such as, the observations of plasma and energetic particles around the terrestrial magnetosphere, inter-planetary and inter-stellar dust, and NEO. It is also considered to be useful for the pilot observations for future infrared, gamma-ray, and cosmic-ray space astronomical telescope in the deep space. Applied missions of DESTINY will be able to go to deep space with higher mass of payloads. Using the Epsilon Launch Vehicle, it will convey instruments of up to 50 kg to the space between Venus and Mars. DESTINY launched by the improved launch vehicle with the power of M-V rocket will carry payloads of up to 200 kg into the orbit of Venus and Mars. In these phases, Explorations for Venus, Mars, and multiple NEO, and astronomical observations from the deep space observatory will be realized by low cost deep space missions.</p>

Using the Extreme Ultraviolet Spectroscope for Exospheric Dynamics (EXCEED) aboard Hisaki and the Solar Extreme Ultraviolet Monitor on the Solar and Heliospheric Observatory, we investigate variations of the extreme ultraviolet (EUV) dayglow brightness for OII 83.4nm, OI 130.4nm, and OI 135.6nm in the Venusian upper atmosphere observed in March-April (period 1), April-May (period 2), and June-July (period 3) in 2014. The result shows that characteristic periodicities exist in the dayglow variations other than the 27day solar rotational effect of the solar EUV flux: 1.8, 2.8, 3.1, 4.5, and 9.9day in period 1; 1.1day in period 2; and 1.0 and 11day in period 3. Many of these periodicities are consistent with previous observations and theory. We suggest these periodicities are related to density oscillations of oxygen atoms or photoelectrons in the thermosphere. The cause of these periodicities is still uncertain, but planetary-scale waves and/or gravity waves propagating from the middle atmosphere, and/or minor periodic variations of the solar EUV radiation flux may play a role. Effects of the solar wind parameters (velocity, dynamic pressure, and interplanetary magnetic field's intensity) on the dayglow variations are also investigated using the Analyser of Space Plasma and Energetic Atoms (ASPERA-4) and magnetometer aboard Venus Express. Although clear correlation with the dayglow variations is not found, their minor periodicities are similar to the dayglow periodicities. Contribution of the solar wind to the dayglow remains still unknown, but the solar wind parameters might affect the dayglow variations.

Io-correlated brightness change in the Io plasma torus (IPT) was discovered by the Voyager spacecraft, showing evidence of local electron heating around Io. However, its detailed properties and the cause of electron heating are still open issues. The extreme ultraviolet spectrograph on board the HISAKI satellite continuously observed the IPT from the end of December 2013 to the middle of January 2014. The variation in the IPT brightness showed that clear periodicity associated with Io's orbital period (42 h) and that the bright region was located downstream of Io. The amplitude of the periodic variation was larger at short wavelengths than at long wavelengths. From spectral analyses, we found that Io-correlated brightening is caused by the increase in the hot electron population in the region downstream of Io. We also found that the brightness depends on the system III longitude and found primary and secondary peaks in the longitude ranges of 100-130 degrees and 250-340 degrees, respectively. Io's orbit crosses the center of the IPT around these longitudes. This longitude dependence suggests that the electron heating process is related to the plasma density around Io. The total radiated power from the IPT in January 2014 was estimated to be 1.4 TW in the wavelength range from 60 to 145 nm. The Io-correlated component produced 10% of this total radiated power. The interaction between Io and the IPT continuously produces a large amount of energy around Io, and 140 GW of that energy is immediately converted to hot electron production in the IPT.

Jupiter's auroral emissions reveal energy transport and dissipation through the planet's giant magnetosphere. While the main auroral emission is internally driven by planetary rotation in the steady state, transient brightenings are generally thought to be triggered by compression by the external solar wind. Here we present evidence provided by the new Hisaki spacecraft and the Hubble Space Telescope that shows that such brightening of Jupiter's aurora can in fact be internally driven. The brightening has an excess power up to similar to 550 GW. Intense emission appears from the polar cap region down to latitudes around Io's footprint aurora, suggesting a rapid energy input into the polar region by the internal plasma circulation process.

HISAKI (SPRINT-A) satellite is an earth-orbiting Extreme UltraViolet (EUV) spectroscopic mission and launched on 14 Sep. 2013 by the launch vehicle Epsilon-1. Extreme ultraviolet spectroscope (EXCEED) onboard the satellite will investigate plasma dynamics in Jupiter's inner magnetosphere and atmospheric escape from Venus and Mars. EUV spectroscopy is useful to measure electron density and temperature and ion composition in plasma environment. EXCEED also has an advantage to measure spatial distribution of plasmas around the planets. To measure radial plasma distribution in the Jovian inner magnetosphere and plasma emissions from ionosphere, exosphere and tail separately (for Venus and Mars), the pointing accuracy of the spectroscope should be smaller than spatial structures of interest (20 arc-seconds). For satellites in the low earth orbit (LEO), the pointing displacement is generally caused by change of alignment between the satellite bus module and the telescope due to the changing thermal inputs from the Sun and Earth. The HISAKI satellite is designed to compensate the displacement by tracking the target with using a Field-Of-View (FOV) guiding camera. Initial checkout of the attitude control for the EXCEED observation shows that pointing accuracy kept within 2 arc-seconds in a case of "track mode" which is used for Jupiter observation. For observations of Mercury, Venus, Mars, and Saturn, the entire disk will be guided inside slit to observe plasma around the planets. Since the FOV camera does not capture the disk in this case, the satellite uses a star tracker (STT) to hold the attitude ("hold mode"). Pointing accuracy during this mode has been 20-25 arc-seconds. It has been confirmed that the attitude control works well as designed.

The Sprint-A satellite with the EUV spectrometer (Extreme Ultraviolet Spectroscope for Exospheric Dynamics: EXCEED) was launched in September 2013 by the Epsilon rocket. Now it is orbiting around the Earth (954.05 km x 1156.87 km orbit; the period is 104 minutes) and one has started a broad and varied observation program. With an effective area of more than 1 cm(2) and well-calibrated sensitivity in space, the EUV spectrometer will produce spectral images (520-1480 angstrom) of the atmospheres/magnetospheres of several planets (Mercury, Venus, Mars, Jupiter, and Saturn) from the Earth's orbit. At the first day of the observation, EUV emissions from the Io plasma torus (mainly sulfur ions) and aurora (H-2 Lyman and Werner bands) of Jupiter have been identified. Continuous 3-month measurement for Io's plasma torus and aurora is planned to witness the sporadic and sudden brightening events occurring on one or both regions. For Venus, the Fourth Positive (A(1)Pi-X-1 Sigma(+)) system of CO and some yet known emissions of the atmosphere were identified even though the exposure was short (8-min). Long-term exposure from April to June (for approximately 2 months) will visualize the Venusian ionosphere and tail in the EUV spectral range. Saturn and Mars are the next targets.

Jupiter's magnetosphere is a strong particle accelerator that contains ultrarelativistic electrons in its inner part. They are thought to be accelerated by whistler-mode waves excited by anisotropic hot electrons (&gt;10 kiloelectron volts) injected from the outer magnetosphere. However, electron transportation in the inner magnetosphere is not well understood. By analyzing the extreme ultraviolet line emission from the inner magnetosphere, we show evidence for global inward transport of flux tubes containing hot plasma. High-spectral-resolution scanning observations of the Io plasma torus in the inner magnetosphere enable us to generate radial profiles of the hot electron fraction. It gradually decreases with decreasing radial distance, despite the short collisional time scale that should thermalize them rapidly. This indicates a fast and continuous resupply of hot electrons responsible for exciting the whistler-mode waves.

The extreme ultraviolet spectroscope EXtrem ultraviolet spetrosCope for ExosphEric Dynamics (EXCEED) on board the SPRINT-A mission will be launched in the summer of 2013 by the new Japanese solid propulsion rocket Epsilon as its first attempt, and it will orbit around the Earth with an orbital altitude of around 1000 km. EXCEED is dedicated to and optimized for observing the terrestrial planets Mercury, Venus and Mars, as well as Jupiter for several years. The instrument consists of an off axis parabolic entrance mirror, switchable slits with multiple filters and shapes, a toroidal grating, and a photon counting detector, together with a field of view guiding camera. The design goal is to achieve a large effective area but with high spatial and spectral resolution. In this paper, the performance of each optical component will be described as determined from the results of test evaluation of flight models. In addition, the results of the optical calibration of the overall instrument are also shown. As a result, the spectral resolution of EXCEED is found to be 0.3-0.5 nm Full Width at Half Maximum (FWHM) over the entire spectral band (52-148 nm) and the spatial resolution achieve was 10 ''. The evaluated effective area is around 3 cm(2). Based on these specifications, the possibility of EXCEED detecting atmospheric ions or atoms around Mercury, Venus, and Mars will be discussed. In addition, we estimate the spectra that might be detected from the Io plasma torus around Jupiter for various hypothetical plasma parameters. (C) 2013 Elsevier Ltd. All rights reserved.

The Telescope of Extreme Ultraviolet (TEX) onboard Japan's lunar orbiter KAGUYA provided the first sequential images of the Earth's plasmasphere from the "side" (meridian) view. The TEX instrument obtained the global distribution of the terrestrial helium ions (He+) by detecting resonantly scattered emission at 30.4 nm. One of the most striking features of the plasmasphere found by TEX is an arc-shaped structure of enhanced brightness, which we call a "plasmaspheric filament". In the TEX image on 2 June 2008, the filament structure was clearly aligned to the dipole magnetic field line of L = 3.7 at 7.3 magnetic local time. Our analysis suggests that the filament represents an isolated flux tube filled with four times higher He + density than its neighbors. We found four events of plasmaspheric filament in the images obtained between March and June 2008, and in all four events, the geomagnetic activity was quite low. The plasmaspheric filament in the TEX image is the first evidence that a "finger" structure seen in the IMAGE-EUV image is the projection of an isolated flux tube. © 2013. American Geophysical Union. All Rights Reserved.