Plasma convection in the low-latitude mantle of the near-earth magnetosphere

A detailed analysis of Geotail observations on June 1, 1997 provides evidence for the appearance of the plasma mantle at low-latitudes, Z_GSM 3 R_E for southward interplanetary magnetic field (IMF), and clarifies the characteristics of the plasma flow in the low-latitude mantle. The tailward flow speed in the mantle is 80 160 km/s, smaller than the flow speed (300 km/s) in the adjacent magnetosheath. The component of the velocity perpendicular to the magnetic field lines is predominantly poleward at speeds up to 60 km/s, and the convection tends to be stronger for |;B_Y|<|;B_Z| than for IMF |B_Y|>|B_Z|;. This polewardconvection can be interpreted as being driven by a J × B force operating on the field lines.     

Hypergravity suppresses bone resorption in ovariectomized rats

The effects of gravity on bone metabolism are unclear, and little has been reported about the effects of hypergravity on the mature skeleton. Since low gravity has been shown to decrease bone volume, we hypothesized that hypergravity increases bone volume. To clarify this hypothesis, adult female rats were ovariectomized and exposed to hypergravity (2.9G) using a centrifugation system. The rats were killed 28 days after the start of loading, and the distal femoral metaphysis of the rats was studied. Bone architecture was assessed by micro-computed tomography (micro-CT) and bone mineral density was measured using peripheral quantitative CT (pQCT). Hypergravity increased the trabecular bone volume of ovariectomized rats. Histomorphometric analyses revealed that hypergravity suppressed both bone formation and resorption and increased bone volume in ovariectomized rats.     

Auroral signatures of transient processes in the outer magnetosphere

We present an analysis of sporadic and recurrent injections of magnetospheric ions in the midnight auroral oval during substorms and of the associated ionospheric ion outflows. The source of plasma sheet precipitating ions is determined using a simple method, based on the measured relation between the ion inverse velocity and time (l = v × t). This method is applied here to two typical passes of the Interball-Auroral (IA) satellite at distances of 3 R_E above the auroral regions. Substorm related ion injections are shown to be mainly due to time of flight effects. In contrast with particle trajectory computations (Sauvaud et al., 1999), the inverse velocity method does not require magnetic and electric field models and can thus be used systematically for the detection of time of flight dispersed ion structures (TDIS). This allowed us to build a large database of TDIS events and to perform a statistical analysis of their spatial distribution. For the cases presented here the source region of the injected ions is found at radial distances from 18 to 30 R_E near the equatorial magnetosphere. At Interball altitudes ( 3 R_E), ion injections detected at the poleward boundary of the nighside auroral oval are associated with shear Alfvén waves superimposed over large-scale quasi-static current structures. We show that the most poleward TDIS are collocated with a large outflow of ionospheric H⁺ and O⁺ displaying pitch-angle distributions peaked in the pitch-angle range 90°–120°. These ions are thus accelerated perpendicularly to the magnetic field not only in the main auroral acceleration region but also up to at least 3 R_E. The expanding auroral bulge thus constitutes a significant source of H⁺ and O⁺ ions for the mid-tail magnetosphere.     

On the evolution of dust in the solar vicinity.

The analysis of interplanetary dust shows that the majority of particles in out-of-ecliptic regions comes from comets and also that near solar dust, in the ecliptic regions, results most probably largely from comets. The intense radiation flux in the solar vicinity is expected to cause strong modifications in the material composition and surface structure of interplanetary dust particles and hence the analysis of near solar dust provides interesting insights into the evolution of meteoritic, especially cometary materials. Because of the lack of in-situ measurements our present knowledge concerning these processes derives from remote sensing, i.e. observations of the solar F-corona. In particular these are observations of albedo, polarization and colour temperature given in terms of average particle properties. For example the analysis of near infra-red F-corona data points to the existence of a strong component of irregularly structured silicate particles, most probably of cometary origin. The data may indicate a subsequent sublimation of different particles or different constituents of the particles. Here we compare particle properties derived from F-corona observations with model calculations of single particle properties and discuss perspectives of future analysis of cometary dust in the interplanetary cloud.     

Dirty ice grains in comets

Based on the computed equilibrium temperature of evaporating dirty water-ice grains, dirty water-ice halo is examined, taking into account of a size dependence of terminal velocity of dust at P/Halley. It is found that due to an enhanced grain's temperature caused by dirtiness, icy halo cannot extend over 100 km from the nucleus when comet approaches inside a solar distance r of 1 AU. Therefore, it is unlikely that the ice bands in the near infrared wavelengths could be detected in the cometary coma at r<1 AU.     

A new goldfish model to evaluate pharmacokinetic and pharmacodynamic effects of drugs used for motion sickness in different gravity loads.

This paper proposes a new goldfish model to predict pharmacodynamic/pharmacokinetic effects of drugs used to treat motion sickness administered in differing gravity loads. The assumption of these experiments is that the vestibular system is dominant in producing motion sickness and that the visual system is secondary or of small import in the production of motion sickness. Studies will evaluate the parameter of gravity and the contribution of vision to the role of the neurovestibular system in the initiation of motion sickness with and without pharmacologic agents. Promethazine will be studied first. A comparison of data obtained in different groups of goldfish will be done (normal vs. acutely and chronically bilaterally blinded vs. sham operated). Some fish will be bilaterally blinded 10 months prior to initiation of the experiment (designated the chronically bilaterally blinded group of goldfish) to evaluate the neuroplasticity of the nervous system and the associated return of neurovestibular function. Data will be obtained under differing gravity loads with and without a pharmacological agent for motion sickness. Experiments will differentiate pharmacological effects on vision vs. neurovestibular input to motion sickness. Comparison of data obtained in the normal fish and in acutely and chronically bilaterally blinded fish with those obtained in fish with intact and denervated otoliths will differentiate if the visual or neurovestibular system is dominant in response to altered gravity and/or drugs. Experiments will contribute to validation of the goldfish as a model for humans since plasticity of the central nervous system allows astronauts to adapt to the altered visual stimulus conditions of 0-g. Space motion sickness may occur until such an adaptation is achieved.     

Dust Near The Sun

We review the current knowledge and understanding of dust in the inner solar system. The major sources of the dust population in the inner solar system are comets and asteroids, but the relative contributions of these sources are not quantified. The production processes inward from 1 AU are: Poynting-Robertson deceleration of particles outside of 1 AU, fragmentation into dust due to particle-particle collisions, and direct dust production from comets. The loss processes are: dust collisional fragmentation, sublimation, radiation pressure acceleration, sputtering, and rotational bursting. These loss processes as well as dust surface processes release dust compounds in the ambient interplanetary medium. Between 1 and 0.1 AU the dust number densities and fluxes can be described by inward extrapolation of 1 AU measurements, assuming radial dependences that describe particles in close to circular orbits. Observations have confirmed the general accuracy of these assumptions for regions within 30° latitude of the ecliptic plane. The dust densities are considerably lower above the solar poles but Lorentz forces can lift particles of sizes < 5 μm to high latitudes and produce a random distribution of small grains that varies with the solar magnetic field. Also long-period comets are a source of out-of-ecliptic particles. Under present conditions no prominent dust ring exists near the Sun. We discuss the recent observations of sungrazing comets. Future in-situ experiments should measure the complex dynamics of small dust particles, identify the contribution of cometary dust to the inner-solar-system dust cloud, and determine dust interactions in the ambient interplanetary medium. The combination of in-situ dust measurements with particle and field measurements is recommended.     

The BepiColombo/MMO model payload and operation plan

The Institute of Space and Astronautical Science (ISAS) of Japan plans to contribute the Mercury Magnetospheric Orbiter (MMO) to the BepiColombo program, the ESA Cornerstone mission to the planet Mercury. The principal objective of the MMO is to study the magnetic field and magnetosphere of Mercury. The ISAS Mercury exploration working group has performed the definition study of the MMO mission in cooperation with the ESA/ESTEC BepiColombo project team. This paper briefly reviews the scientific objectives, and describes the model payload and its operation plan.     

Possible Suzaku detection of non-thermal X-ray signals from a rotating magnetized white dwarf

Although rotating neutron stars (NSs) have been regarded as being textbook examples of astrophysical particle acceleration sites for decades, details of the acceleration mechanism remain a mystery; for example, we cannot yet observationally distinguish “polar cap” models from “outer gap” models. To solve the model degeneracy, it is useful to study similar systems with much different physical parameters. Strongly magnetized white dwarfs (WDs) are ideal for this purpose, because they have essentially the same system geometry as NSs, but differ largely from NSs in the system parameters, including the size, magnetic field, and the rotation velocity, with the induced electric field expected to reach 10¹³–10¹⁴ eV. Based on this idea, the best candidate among WDs, AE Aquarii, was observed with the fifth Japaneses X-ray satellite, Suzaku. The hard X-ray detector (HXD) on-board Suzaku has the highest sensitivity in the hard X-ray band over 10 keV. A marginal detection in the hard X-ray band was achieved with the HXD, and was separated from the thermal emission. The flux corresponds to about 0.02% of its spin-down energy. If the signal is real, this observation must be a first case of the detection of non-thermal emission from WDs.