Advances in Geosciences

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The plasma environments of Mars and Venus have been explored by spacecraft, such as Mars 2, 3 and 5, Phobos 2, Mars Global Surveyor (MGS), Mars Express for planet Mars and Venera 9 and 10, Pioneer Venus Orbiter, Venus Express for planet Venus. Overall observations of plasma regions and their boundaries, in particular the bow shock, the magnetic pile-up boundary and the magnetic tail, show the solar wind interaction with these two planets to be rather similar. Mars and Venus are both considered as non-magnetic planets, compared with the Earth, in a sense that they do not possess any significant intrinsic magnetic field that could play a significant role in their interactions with the solar wind. At most, the magnetic anomalies discovered at Mars by MGS are thought to slightly influence the lower regions of the Martian ionosphere. Therefore, both Venus and Mars have principally comet-like induced magnetospheres and magnetotails as a result of the atmospheric mass loading and subsequent draping of passing interplanetary flux tubes. Nevertheless, there are many differences between the characteristics and space environment behaviors of the two telluric planets and a lot remains actually to be done, in terms of in situ measurements and modeling efforts, to fully understand how Venus and Mars interact with the interplanetary medium. The objective of the presentation is not to review all the aspects of these interactions but simply to compare the main characteristics of the Mars' and Venus' plasma environments and to highlight some similarities and differences between the interactions of these two non-magnetic planets with the solar wind as a function of solar wind dynamic pressure and solar activity.

Microwave observations of the temperature and wind in the middle atmosphere of Mars are compared with the results of simulations with the Martian general circulation model. The simulated global-mean mesospheric temperature during a northern summer solstice is ~10 K lower than in spring and autumn equinoxes, which is consistent with the James Clerk Maxwell Telescope observation in 1996–1997, although the absolute values are 30–40 K higher than in the observations. The wind velocity in the middle atmosphere in the model is comparable to the observations, except that the easterly wind in the afternoon is ~100ms⁻¹ weaker. A brief discussion for the discrepancies between the model and observation is provided.

Although it cannot provide direct and unambiguous information on the mineralogical composition of an asteroid surface, polarimetry is a very useful tool to get an improved understanding of parameters which are intimately related to surface composition and regolith structure. In recent times there has been a revival in the field of asteroid polarimetry, on the theoretical side, in relation to experimental simulations, and due to the activity of some teams who are engaged in extensive observational campaigns. Some new discoveries of objects exhibiting unprecedented polarimetric properties have been done. The above subjects are briefly reviewed.

SELenological and ENgineering Explorer (SELENE) is a Japanese lunar orbiter that will be launched in 2007. The main purpose of this satellite is to study the origin and evolution of the Moon by means of global mapping of element abundances, mineralogical composition, and surface geographical mapping from 100 km altitude. Plasma energy Angle and Composition Experiment (PACE) is one of the scientific instruments onboard the SELENE satellite. The scientific objectives of PACE are (1) to measure the ions sputtered from the lunar surface and the lunar atmosphere, (2) to measure the magnetic anomaly on the lunar surface using two electron spectrum analyzers (ESAs) and a magnetometer onboard SELENE simultaneously as an electron reflectometer, (3) to resolve the Moon–solar wind interaction, (4) to resolve the Moon–Earth's magnetosphere interaction, and (5) to observe the Earth's magnetotail. PACE consists of four sensors: ESA-S1, ESA-S2, ion mass analyzer (IMA), and ion energy analyzer (IEA). ESA-S1 and S2 measure the three-dimensional distribution function of low energy electrons below 15 keV, while IMA and IEA measure the three-dimensional distribution function of low energy ions below 28 keV/q.

The Solar-Sail Project has been investigated by JAXA as an engineering mission with a small orbiter into the Jovian orbit. This paper summarizes the basic design of this project and possible Jovian system studies by this opportunity.

The large-scale Jovian mission has been discussed as a long future plan since the 1970s, when the investigation of the future planetary exploration program started in Japan. The largest planet and its complex planetary system would be studied by several main objectives: (1) The structure of a gas planet: the internal and atmospheric structures of a gas planet which could not be a star. (2) The Jovian-type magnetosphere: the structure and processes of the largest and strongest magnetosphere in the solar system. (3) The structure, composition, and evolution of Jupiter and its satellite system. The small Jovian orbiter accompanied with the Solar-Sail Project will try to establish the technical feasibility of such future outer planet missions in Japan. The main objective is the second target, the Jovian magnetospheric and auroral studies with its limited payload resources.

A new chirp transform spectrometer (CTS) with a bandwidth of 400MHz and a spectral resolution of 100 kHz has been developed. The CTS is deviced using a digital chirp generator and a preprocessing unit based on a Complementary Metal Oxide Semiconductor (CMOS) and an Application-Specific Integrated Circuit (ASIC). A build in PC 104 computer handles the process control and the external communication via Ethernet and a Transistor-Transistor Logic (TTL) interface. The CTS has been applied to atmospheric science, i.e., a 25-K noise temperature, 22-GHz water vapor, and a 142-GHz ozone system. Astronomical observations have been performed using the Heinrich Hertz submillimeter telescope. In this paper, we describe the function of the CTS and provide information about its functional performance.

γ-Alumina nanoparticles with a polyhedral shape based on an octahedral shape were produced with a plasma field of Ar–O₂ gas mixture (Ar: 7Torr, O₂: 3Torr). The obtained infrared spectrum showed a characteristic strong absorption peak at 7.2 μm, which had never been previously observed in the alumina nanoparticles produced without a plasma field. The plasma field mainly affected the surfaces of the alumina nanoparticles and changed their morphology and gas adsorbability. The 7.2 μm, absorption peak derived from surface hydroxyl was considered to be due to the existence of activated Al in the alumina nanoparticles produced with a plasma field.

We have carried out photon irradiation study of naphthalene (C₁₀H₈), the smallest polycyclic aromatic hydrocarbon (PAH) in water and ammonia ice mixtures. Photons provided by a synchrotron radiation light source in two broad-band energy ranges in the ultraviolet/near extreme ultraviolet (4–20 eV) and the extreme ultraviolet (13–45 eV) ranges were used for the irradiation of H₂O+NH₃+C₁₀H₈ = 1:1:1 ice mixtures at 15K. We could identify several photo-products, namely CH₄, C₂H₆, C₃H₈, CO, CO₂, HNCO, OCN⁻, and probably quinoline (C₉H₇N) and phenanthridine (C₁₃H₉N). We found that the light hydrocarbons are preferably produced for the ice mixture subjected to 4–20 eV photons. However, the production yields of CO, CO₂, and OCN⁻ species seem to be higher for the mixture subjected to EUV photons (13–45 eV). Therefore, naphthalene and its photo-products appear to be more efficiently destroyed when high energy photons (E > 20 eV) are used. This has important consequences on the photochemical evolution of PAHs in astrophysical environments.

By making a carbon rod covered with Ti on the surface without exposure to air, TiC grains less than 10nm in diameter were predominantly produced. The introduction of a small amount of oxygen in Ar gas (partial pressure 1/1000), allowed the continuous formation of TiO₂ and TiO–TiC. The infrared spectra of TiO₂, TiO, and TiC were measured. An absorption feature attributed to TiO phase in oxidized TiC grains showed a characteristic peak at 14.7 μm.

Experimental measurements of the destruction yields of NH₃ have been carried out by extreme ultraviolet–vacuum ultraviolet (EUV–VUV) photolysis of cosmic ices containing NH₃. The ice systems studied in the present work include pure NH₃ ices and icy mixtures of NH₃ with CO, H₂O, and CH₄ at a temperature of 10K. A tunable intense synchrotron radiation light source, available at the National Synchrotron Radiation Research Center, Hsinchu, Taiwan, was employed to provide the required EUV–VUV photons. In this study, the photon wavelengths used to irradiate the icy samples were mainly selected to center on the prominent solar lines, namely, the 30.4, 58.4 and 121.6 nm. The photodestruction yields of NH₃ in the presently studied ice mixtures are typically higher than 0.5 and can be higher than unity, a very efficient ice photochemical process.

The crystalline grain formation of perovskite (CaTiO₃) by the coalescence due to grain–grain collisions between TiO₂ and CaO grains in smoke has been demonstrated. Spherical grains with diameters of 100–200 nm were produced. A large quantity of perovskite grains were also produced by the condensation from CaTiO₃ vapor evaporated in selecting Ar gas pressure of 10 Torr. These grains contained the WO₃ crystal in the center by the peritectic reaction. The perovskite grains showed significant peaks at 14.4 and 21.9 μm in the optical spectra.

The crystallization of amorphous Mg-bearing silicate grains into Mg₂SiO₄ crystal covered with a thin carbon layer was directly observed by in-situ transmission electron microscopy. The temperature of crystallization of the sample was observed to be 200°C lower than that of the sample without the carbon layer. The graphitization energy of the surface amorphous carbon layer with the mean thickness of 10 nm accelerated the crystallization of the central amorphous Mg-bearing silicate grain of 100 nm order. Sample results for crystallization at room temperature are presented.

Spinel particles containing Mg of different amounts were obtained by flash gas evaporation from different mixture powders of Mg and Al in a mixture gas of argon and oxygen. By decreasing Mg content, the shape of the particles was changed from cubic, octahedral, elliptical to spherical. The characteristic spectra among these produced particles are indicated. The difference between the observed peak positions and the calculated absorption positions was discussed in terms of the effect of the spinel phase on shape.

We present the results of mid-infrared N-band spectroscopy of the Herbig Ae/Be system MWC1080 using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on board the 8 m Subaru Telescope. The MWC1080 has a geometry such that the diffuse nebulous structures surround the central Herbig B0 type star. We focus on the properties of polycyclic aromatic hydrocarbons (PAHs) and PAH-like species, which are thought to be the carriers of the unidentified infrared (UIR) bands in such environments. A series of UIR bands at 8.6, 11.0, 11.2, and 12.7 μm is detected throughout the system and we find a clear increase in the UIR 11.0 μm/11.2 μm ratio in the vicinity of the central star. Since the UIR 11.0 μm feature is attributed to a solo-CH out-of-plane wagging mode of cationic PAHs while the UIR 11.2 μm feature to a solo-CH out-of-plane bending mode of neutral PAHs, the large 11.0 μm/11.2 μm ratio directly indicates a promotion of the ionization of PAHs near the central star.

Mainly based on our previous results, this article evaluates the presence of solid organic matter of prebiotic interest in space: from the carbon grains observed toward diffuse interstellar clouds and the organic grain mantles made from ice processing that are likely present in dense interstellar clouds and circumstellar regions, to the carbon component of solar system objects that could have delivered organic species to the early Earth [comets, meteorites, and interplanetary dust particles (IDPs)]. Here the term organic is attributed to hydrocarbon materials rich in O and N that contain prebiotic species or their precursors, and are therefore interesting for astrobiology. Organic residues made in the laboratory from ice ultraviolet-photoprocessing under simulated interstellar conditions are used as representative of organic matter and compared by means of infrared and Raman spectroscopy to carbon-bearing extraterrestrial samples. It is observed that the carbon bulk in grains of the diffuse interstellar medium, carbonaceous chondrites, and the IDPs collected in the stratosphere consists of amorphous carbon, with at most a small percent of organic matter. On the other hand, about 50% of the carbon component in comet Halley is made of organics that formed in the interstellar/circumstellar medium in the absence of liquid water. The characterization of cometary organic matter is therefore vital to constrain the contribution of extraterrestrial matter to the origin of life on Earth.

This paper reports on the ongoing development of a balloon-borne telescope system for remote sensing of planetary atmospheres and plasmas. In this system, a Schmidt–Cassegrain telescope with a 300-mm clear aperture is mounted on a gondola whose attitude is controlled by control moment gyros, an active decoupling motor, and a Sun sensor. The gondola can float in the stratosphere for periods in excess of 1 week. A pointing stability of 10 arcsec/s will be achieved via the cooperative operation of the following three-stage pointing devices: a gondola-attitude control system, two-axis telescope gimbals for coarse guiding, and a tip/tilt mirror mount for guiding error correction. The first target for the system is Venus. Wind vectors in the Venusian upper atmosphere will be derived from the tracking of cloud patterns observed in the ultraviolet and near-infrared regions. An experiment designed to test the system performance is scheduled to take place in Japan during June 2007, and a long-duration flight in the Arctic is scheduled for 2008.

A new era of lunar explorations is coming by two Japanese missions to the Moon: SELENE and Lunar-A. SELENE will execute the global mappings of the Moon, make technical demonstrations, and acquire the lunar data for future explorations. Fifteen mission instruments on SELENE will observe chemical elements, mineralogical distributions, surface structures, surface environments, gravity fields, and images for outreaches. They will provide wide knowledge of phenomena on the Moon to elucidate its origin and evolution, and also yield information to comprehend the interplanetary space of the solar system. SELENE is at the stage of the satellite integration and environment tests for all the systems in 2006, and is scheduled to be launched in the summer in 2007. Lunar-A is a spacecraft which provides two penetrators into the lunar surface to elucidate structures and compositions of the lunar interior with seismological and heat-flow data. The final confirmation for the penetrator system is ongoing in 2006.

We have examined a strategic plan for the integrated sciences of Japanese lunar exploration projects, and designed four stages for the definite accomplishment of the sciences of the Moon by: drawing two-dimensional maps, drawing three-dimensional subsurface structures, joint studies of special topics, and those of advanced topics.

Radiation protection has evolved from pen and pencil studies using tables of cross sections and of mathematical function to large and complex codes written and maintained by highly skilled teams. The author's pilgrimage through this process; from his pen and pencil days while on Eniwetak Atoll in 1956 to spherical-harmonics transport codes, the use of discrete ordinate and Monte Carlo codes to an analytical transport code for the calculation of cosmicray transport through solar-system atmospheres and finally to a Monte Carlo code to treat cosmic-ray transport through the heliosphere will be described. The application of these calculations include the radiation from radioactive fallout, beta-ray transport, accelerator shielding, hospital physics, cosmic-ray ionization, cosmogenic isotope production, the radiation dose to air crews and space crews, and cosmic-ray fluxes to space craft. Some examples of the results of these calculations will be given.