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The Miniaturised Mossbauer Spectrometers MIMOS II on board the two Mars Exploration Rovers (MER) have now been collecting valuable scientific data for more than five years. Mossbauer Spectrometers are part of two future missions: Phobos Grunt (Russian Space Agency) and a joint ESA—NASA Rover in 2018. The new advanced MIMOS IIA instrument described in this paper uses Silicon Drift Detectors (SDD) allowing also X-ray fluorescence chemical analysis (XRF) simultaneously to Mossbauer acquisitions. This paper highlights the features and technological improvements of the new spectrometer MIMOS IIA.

The Kaguya gamma-ray spectrometer (KGRS) has great potential to precisely determine the absolute abundances of natural radioactive elements K, Th and U on the lunar surface because of its excellent spectroscopic performance. In order to achieve the best performance of the KGRS, it is important to know the spatial response function (SRF) that describes the directional sensitivity of the KGRS. The SRF is derived by a series of Monte Carlo simulations of gamma-ray transport in the sensor of the KGRS using the full-fledged simulation model of the KGRS, and is studied in detail. In this paper, the method for deriving absolute abundance of natural radioactive elements based on the SRF is described for the analysis of KGRS data, which is also applicable to any gamma-ray remote sensings. In the preliminary analysis of KGRS data, we determined the absolute abundances of K and Th on the lunar surface without using any previous knowledge of chemical information gained from Apollo samples, lunar meteorites and/or previous lunar remote sensings. The results are compared with the previous measurements and the difference and the correspondence are discussed. Future detailed analysis of KGRS data will provide new and more precise maps of K, Th and U on the lunar surface.

The high precision gamma-ray spectrometer (GRS) is scheduled to be launched on the lunar polar orbiter of the SELENE mission in 2007. The GRS consists of a large Ge crystal as a main detector and massive bismuth germanate crystals as an anticoincidence detector. A Stirling cryocooler was adopted in cooling the Ge detector. The flight model of SELENE GRS has been completed and an energy resolution of 3.0 keV (FWHM) at 1.332 MeV has been achieved. The spectrometer aims to observe nuclear line gamma rays emitted from the lunar surface in a wide energy range from 100 keV to 12 MeV for one year and more to obtain chemical composition on the entire lunar surface. The gamma-ray data enable us to study lunar geoscience problems including crust and mantle composition, and volatile reservoirs at polar regions.

Assuming different abundances of the Apollo lunar soil samples and the average spectrum of galactic cosmic ray protons, energy spectra of neutrons and gamma rays and emission rates of gamma-ray lines from major elements have been estimated by using the reviewed Monte Carlo simulation library Geant4 and nuclear data. Previously, such libraries were not able to reproduce gamma-ray lines properly for the planetary application. Results clearly show that the emission rate of gamma rays heavily depends not only on the chemical abundance but also neutron flux within the lunar subsurface. While the intensities of gamma-ray lines are mostly proportional to elemental abundances, the intensity per unit elemental abundance can vary. Such a complex correlation is attributed to the change in neutron flux within the lunar subsurface and petrological restriction of elemental variation.

High-purity germanium (HPGe) detectors used in space for gamma-ray spectroscopy in astrophysics and planetary exploration are known to be damaged by energetic particles. For interplanetary missions close to the Sun such as Messenger or BepiColombo to explore planet Mercury, solar protons represent an important source of damage. In this work, irradiation tests were performed on two large-volume coaxial n-type HPGe detectors with mono-energetic beams of 50-60 MeV protons. One of the detectors, designed for spatial applications, was incrementally exposed to a proton fluence up to 7.5 x 1010 p/cm2 and the other to a unique fluence of 10(10) p/cm(2.) The results showed that the degradation of the energy resolution appeared for fluences higher than 5 x 108 p/cm(2). Moreover, a loss in detection efficiency was observed for fluences above 1010 p/cm(2). Annealings above 80 degrees C allowed the recovery of the initial resolution but not the initial efficiency. By extrapolating the results beyond the experimental conditions, this study also establishes the limits for the use of spaceborne HPGc detectors in harsh low-energy proton environment. (c) 2006 Elsevier B.V. All rights reserved.

The Alpha Particle X-Ray Spectrometer (APXS) is a small instrument to determine the elemental composition of a given sample. For the ESA Rosetta mission, the periodical comet 67P/Churyumov-Gerasimenko was selected as the target comet, where the lander PHILAE (after landing) will carry out in-situ observations. One of the instruments onboard is the APXS to make measurements on the landing site. The APXS science goal is to provide basic compositional data of the comet surface. As comets consist of a mixture of ice and dust, the dust component can be characterized and compared with known meteoritic compositions. Various element ratios can be used to evaluate whether chemical fractionations occurred in cometary material by comparing them with known chondritic material. To enable observations of the local environment, APXS measurements of several spots on the surface and one spot as function of temperature can be made. Repetitive measurements as function of heliocentric distance can elucidate thermal processes at work. By measuring samples that were obtained by drilling subsurface material can be analyzed. The accumulated APXS data can be used to shed light on state, evolution, and origin of 67P/Churyumov- Gerasimenko.

Neutron spectroscopy is a new way to study planetary bodies that have sufficiently thin atmospheres. This technique was demonstrated for the first time with Lunar Prospector around the Moon. Here, we report results for moderated neutrons having energies from 0 to 500 keV that were measured using the anti-coincidence shield (ACS) of the gamma-ray spectrometer. We describe the detection method, followed by data reduction with an emphasis on each data processing step; most steps rely on in-flight calibrations. The behavior of the ACS is well known regarding the measurement of moderated neutrons. We present a map of 0– 500 keV neutrons over the whole Moon with a spatial resolution of ∼60 km . Statistical errors per pixel are less than 2%. The resulting map includes information about the hydrogen content, concentrations of Fe, Ti, traces of Sm and Gd, and the atomic mass of the regolith. These data complement other neutron products of Lunar Prospector, namely thermal (0– 0.4 eV ), epithermal (0.4– 100 eV ) and fast (0.5– 8 MeV ) neutrons. The previous unexplored region between 100 eV and 500 keV reveals several high counting rate regions that are also visible in epithermal neutron data.

The Japanese lunar polar orbiter SELENE carries a gamma-ray spectrometer which uses a high-purity Ge detector cooled to 80-90 K by a Stirling mechanical cooler. The Gamma-Ray Spectrometer (GRS) consists of a large volume n-type Ge detector (252 cc) as the main detector and bismuth-germanate (BGO) and plastic scintillators as an active shielding. The engineering model still maintains excellent energy resolution even after severe vibration testing. The Gamma-Ray Spectrometer will globally map of the Moon for the major elements of O, Mg, Al, Si, Ti, Fe, etc. and natural radioisotopes of K, Th and U with a high precision. The energy resolution of the GRS is such that it would identify prompt gamma-ray line from hydrogen and the location and the amount of ice, if it exists at the polar regions.

We present the first report dedicated to 0.6–8 MeV neutrons measured by the Lunar Prospector gamma-ray spectrometer. The period of data collection extends from January 1998 to July 1999; the spacecraft altitude varied between 15 km and 140 km. Maps are at a 2° × 2° equal-area resolution. They show high counts and high variability for the mare and, low counts and low variability for the highlands. Such variability is due to differences of Fe and Ti concentrations in the lunar regolith, plus other elements with lesser effect that have not yet been included in our calculations. Assuming that only FeO and TiO2 concentrations are responsible for the fast neutron structures, fluxes are 2.7 times more sensitive to FeO than to TiO2. The statistical resolutions are 1.3% in FeO and 3.5% in TiO2. No discrimination of FeO is possible below 6.5%. Results are supported by numerical simulations. We also present the first lunar neutron spectrum over 16 channels between 0.6 and 8 MeV. Ninety-five percent of the counts are below ∼4.5 MeV. In flux units the spectrum peaks at ∼1.5 MeV. Its shape agrees with numerical simulations.

A sharp decline in electron fluxes is observed in the Mars Global Surveyor Electron Reflectometer data in conjunction with the magnetic pileup boundary. We examine the characteristics of the evolution of the electron distribution function for one orbit. We determine that the spectra can best be explained by electron impact ionization of oxygen and hydrogen. To reproduce the observed spectral evolution, we construct a model of the effects of electron impact ionization on the electron distribution function as a flow element encounters the neutral atmosphere. Using the observed post-shock electron distribution function, we are able to reproduce the observed flux attenuation. We conclude that electron impact ionization is the physical mechanism responsible for the spectral feature.

The magnetometer and electron reflectometer experiment (MAG/ER) on the Mars Global Surveyor (MGS) spacecraft has obtained magnetic field and electron data which indicates that the solar wind interaction with Mars is primarily an ionospheric-atmospheric interaction similar to that at Venus. However, the global-scale electric currents and resulting magnetic fields due to the interaction at Mars are locally interrupted or perturbed over distance scales of several hundred kilometers by the effects of paleomagnetic fields due to crustal remanence. In this paper we compare the Mars-solar wind interaction with the Venus-solar wind interaction by selecting MGS orbits which do not show significant magnetic perturbations due to crustal magnetic anomalies, and demonstrate that a number of phenomena characteristic of the Venus-solar wind interaction are also observable at Mars.

We review the current status of the development of Gamma-Ray Spectrometer (GRS) for the Lunar mission SELENE. The GRS instrument will measure gamma-rays in the energy range from 100 keV to 9 MeV. The instrument is a high-purity Ge detector surrounded by BGO and plastic scintillators which are operated as an anticoincidence shield, and is cooled by a Stirling cycle cryocooler. The primary objective is to provide global maps of the lunar composition. Measurements are anticipated for Fe, Ti, U, Th, K, Si, Mg, Al, O, Ca and Na over the entire lunar surface. The abundance of water ice in the permanently shaded craters at both the lunar poles will be measured with this instrument.

The MGS MAG/ER investigation provides vector measurements of the magnetic field and the ionospheric electron density near periapsis. The instrumentation consists of twin triaxial fluxgate magnetometers and a “top hat” electrostatic analyzer of electrons in the energy range of 1 eV to 20 keV. Results include extensive mapping of the detached bow shock wave in the solar wind, the nature and structure of the ionopause and magnetic pile-up boundaries. The most surprising result is the discovery of localized magnetic fields of planetary origin, presumably due to remanent crustal magnetization. Maximum fields measured while below the ionosphere exceed 300 nT. We present an initial study of one of these very localized fields and extrapolations to the Martian surface in the Acidalia planitia.

We present Wind spacecraft observations of solar impulsive electron events associated with locally generated Langmuir waves during solar type III radio bursts. The solar impulsive electrons had energies from ~600 eV to greater than 300 keV. Local Langmuir emissions associated with these fluxes generally coincided with the arrival of 2-12 keV electrons. A survey of 27 events over 1 yr shows that there were few occurrences of electron distributions (~96 s averaged) that were unstable to Langmuir waves and none that had a substantial growth rate (>3 × 10-2 s-1) or endured for more than 96 s. Intense solar impulsive electron events that occurred on 1995 April 2 are studied in detail. Marginally stable (plateaued) distributions occasionally coincided with a periods of local Langmuir emissions, but the electron distributions were otherwise stable. These observations suggest that kinetic processes were modifying the electron distribution but also suggest that processes other than one-dimensional quasilinear relaxation were involved. We find that solar impulsive electron distributions were often unstable to oblique waves, such as quasi-electrostatic whistler waves or electromagnetic ion cyclotron waves, suggesting that competition between Langmuir and oblique emissions may be important. There are several other features in the Wind spacecraft solar impulsive electron observations that are noteworthy. Nondispersive flux modulations were visible in many of the events (also visible in the published ISEE 3 data) in ~1-4 keV electrons, suggesting that a local hydromagnetic instability may have accompanied the lowest energy solar impulsive electron fluxes. The Wind data differ from the ISEE 3 data in the energy spectra of the electron events. ISEE 3 recorded few events with only high-energy (>10 keV) electron fluxes, whereas a survey of the Wind events shows a substantially higher ratio of high-energy events. The high-energy events were often associated with solar flares that could not have been magnetically well connected with the satellite.

A statistical investigation of the location of onset of intermediate and gyrating ion populations in the Earth's foreshock is presented based on Fixed Voltage Analyzer data from ISEE 1. This study reveals the existence of a spatial boundary for intermediate and gyrating ion populations that coincides with the reported ULF wave boundary. This boundary position in the Earth's foreshock depends strongly upon the magnetic cone angle θBX and appears well defined for relatively large cone angles, though not for small cone angles. As reported in a previous study of the ULF wave boundary, the position of the intermediate-gyrating ion boundary is not compatible with a fixed growth rate of the waves resulting from the interaction between a uniform beam and the ambient plasma. The present work examines the momentum associated with protons which travel along this boundary, and we show that the variation of the boundary position (or equivalently, the associated particle momentum) with the cone angle is related to classical acceleration mechanisms at the bow shock surface. The same functional behavior as a function of the cone angle is obtained for the momentum predicted by an acceleration model and for the particle momentum associated with the boundary. However, the model predicts systematically larger values of the momentum than the observation related values by a constant amount; we suggest that this difference may be due to some momentum exchange between the incident solar-wind population and the backstreaming particles through a wave-particle interaction resulting from a beam plasma instability.Key words. Intermediate ion boundary · Statistical investigation · Earth's foreshock · ISEE 1 spacecraft

Several upstream ion distributions having a gyrating signature have been identified with the 3DP/PESA-High analyser on board the WIND spacecraft. These distributions are observed at distances greater than 20 R E from the Earth's bow shock. The distributions are observed in association with low frequency waves propagating quasi-parallel to the background magnetic field. By estimating the bulk velocity of the gyrating ions, we have found that the waves resonate with the particles. The observation of gyrating ions at large distances from the shock suggests their local production, probably from field-aligned beam disruption.

We present detailed measurements from the WIND 3D Plasma and Energetic Particle experiment of electron distributions in the deep foreshock, well away from the foreshock boundaries. Both electrons escaping from the magnetosheath and solar wind electrons reflected by the strong magnetic field of the shock are observed. The loss cone angle that separates the reflected electrons from the escaping magnetosheath electrons can be determined as a function of electron energy. At lower energies, the loss cone angle increases because the cross-shock potential tends to pull electrons into the magnetosheath. The loss cone angle is typically ≲ 30° at energies ≳ 100 eV, corresponding to peak shock magnetic field to local magnetic field ratio of ≳ 5, while the loss cone variation with energy gives typical shock potentials of ∼85 V. Thus the measurements of back-streaming foreshock electrons can be used as a tool to remotely probe the characteristics of the bow shock.

On a rapid inward pass through the subsolar magnetosheath (MSH) and magnetopause (MP), the WIND spacecraft initially encountered a moderately-compressed low-magnetic shear MP (at a radial distance of 8.6 RE), followed by multiple crossings of a high-shear MP (at 8.2 RE). The large shear resulted from a southward turning of the external MSH field. Strong magnetic field pile-up, a plasma depletion layer (PDL), and plasma flow acceleration and rotation to become more perpendicular to the local magnetic field were observed in the MSH on approach to the low-shear MP. At the high-shear MP, magnetic reconnection flows were detected, and there are some indications that plasma depletion effects were weak or absent in the adjacent MSH. We attribute the changes in the MP and MSH properties to the sudden rotation of the MSH field direction. In essence, the structure of the MP regions under the unusually high solar wind ram pressure condition in this case does not seem to be qualitatively different from that observed under more typical (less compressed) conditions. Also similar to previous observations, the mirror mode is marginally unstable in the MSH proper, but is stable in the PDL. In this region, the proton temperature anisotropy is inversely correlated with βp∥. Finally, the electron distributions are observed to be anisotropic (Te⟂/Te∥ ∼1.3) throughout the entire MSH.

We present the first observation of a solar impulsive electron event spanning the entire solar wind-suprathermal particle energy range (few eV to hundreds of keV), obtained with the 3-D Plasma and Energetic Particle experiment on the WIND spacecraft. The electron energy spectrum fits to a power-law ∼ E−3 from ∼40 keV down to a peak at ≲ 1 keV, with significant flux detected down to ∼0.5 keV. Since the range of such low energy electrons in ionized hydrogen is much less than the column density of the corona, they must be accelerated high, ∼1 R⊙ (solar radius) above the photosphere, for typical active coronal density models.

Both Alpha Particle X-ray Spectrometer (APXS) and the Miniaturized Moessbauer Spectrometer (MIMOS II) have shown their performances in space missions and terrestrial applications. Taking advantage of the challenges of space missions both instruments have become very powerful tools, even small in mass and dimensions.

The three-dimensional electron spectrometer of the Reme plasma analyzer-complete positive ion, electron and ram negative ion measurements near comet Halley (RPA-COPERNIC) experiment aboard the Giotto spacecraft, although damaged during the comet Halley encounter in March 1986, has provided very new results during the encounter on July 10, 1992, with the weakly active comet Grigg-Skjellerup (G-S). The main characteristic features of the highly structured interaction region extending from approximately 26,500 km inbound to approximately 37,200 km outbound are presented. These results are compared to the results obtained by the same instrument during the Giotto comet Halley fly-by. Despite the large difference in the size of the interaction regions (approximately 60,000 km for G-S, approximately 2000,000 km for Halley) due to 2 orders of magnitude difference in cometary neutral gas production rate, there are striking similarities in the solar wind interactions with the two comets.

We analyze the spectra measured by the Gamma Ray Spectrometer (GRS) on board the SELENE satellite orbiting the Moon. The spectra consist in 8192 energy channels ranging from 0 to 12 MeV and exhibiting lines of interest (O, Mg, Al, Si, Ti, Ca, Fe, K, Th, and U) superposed on a continuum. We have also analysed the data with various multivariate techniques, one of them being the Independent Component Analysis. We have used the JADE algorithm for our analysis that we focused in the energy range from 750 to 3000 keV. We identify at least three meaningful components. The first one is correlated to the Thorium map. The corresponding correlation coefficient spectrum exhibits the lines of Thorium, Potassium and Uranium. The second component is clearly correlated with the Iron as shown on its corresponding spectrum. Finally the third component seems to be related to the altitude of the spacecraft. This work shows that maps of elements such as iron will be available with the GRS data by a purely statistical analysis.

This is the post-print version of the final paper published in Planetary and Space Science. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2009 Elsevier B.V. The Chandrayaan-1 X-ray Spectrometer (C1XS) is a compact X-ray spectrometer for the Indian Space Research Organisation (ISRO) Chandrayaan-1 lunar mission. It exploits heritage from the D-CIXS instrument on ESA's SMART-1 mission. As a result of detailed developments to all aspects of the design, its performance as measured in the laboratory greatly surpasses that of D-CIXS. In comparison with SMART-1, Chandrayaan-1 is a science-oriented rather than a technology mission, leading to far more favourable conditions for science measurements. C1XS is designed to measure absolute and relative abundances of major rock-forming elements (principally Mg, Al, Si, Ca and Fe) in the lunar crust with spatial resolution ⩽25 FWHM km, and to achieve relative elemental abundances of better than 10%. ESA Science and Technology Research Programmes

The detection of negatively charged cometary ions in the inner coma of Comet Halley is reported. These ions are observed in three broad mass peaks at 7-19, 22-65, and 85-110 AMU, with densities reaching greater than about 1/cu cm, about 0.05/cu cm, and about 0.04/cu cm, respectively, at a distance of about 2300 km from the nucleus. The ion species thought to be present include O(-), OH(-), C(-), CH(-), CN(-) and heavier complex CHO molecular ions. As negative ions are easily destroyed by solar radiation at about 1 AU, an efficient production mechanism, so far unidentified, is required to account for the observed densities. The detection of negative ions in the coma near 1 AU implies that negative ions should also be present in similar neutral gas and dust environment farther away from the sun. If the negative-ion densities are large enough, they could play an important part in physical processes such as radiative transfer or charge exchange.

The gamma ray spectrometer (GRS) will be onboard the Japanese lunar polar orbiter SELENE, to be launched in 2004, to obtain the information of element abundance on the entire lunar surface. GRS consists of a high-purity Ge detector as a main detector, which is an n-type Ge crystal with a high detection efficiency of 60% encapsulated in an aluminum canister. In addition, BGO and plastic scintillators are employed for an anti-coincidence shield and for suppression of Compton photons and energetic ion backgrounds. GRS will be the first gamma ray spectrometer employing a Ge detector for the lunar mission. GRS adopted a Stirling cycle refrigerator, whose cooling capacity is 2.0 W at 80 K. The mechanical vibration from the cryosystem to the Ge detector is effectively reduced by the dual opposed pistons in the compressor and the flexible thermo-coupling link between the two components. An excellent energy resolution of

Unformatted article available at http://www.cesr.fr/spip.php?rubrique105; International audience; Planetary neutron leakage fluxes provide a measure of surface composition. However to be used in geological studies, a quantitative relationship between measured fluxes and surface composition is needed. The present work shows that neutron production is expected to be a function of the atomic mass, and that the fast leakage flux in the energy range between 0.6 and 8 MeV is linearly related to the average soil atomic mass. This result is consistent with laboratory measurements, and with Lunar Prospector observations of the Moon. When calibrated with returned lunar samples, this relationship is used to construct a map of the average atomic mass of lunar soils.

The dosimetric experiments Dose-M and Liulin as part of the more complex French-German-Bulgarian-Russian experiments for the investigation of the radiation environment for Mars-96 mission are described. The experiments will be realized with dosemeter-radiometer instruments, measuring absorbed dose in semiconductor detectors and the particle flux. Two detectors will be mounted on board the Mars-96 orbiter. Another detector will be on the guiderope of the mars-96 Aerostate station. The scientific aims of Dose-M and Liulin experiments are: Analysis of the absorbed dose and the flux on the path and around Mars behind different shielding. Study of the shielding characteristics of the Martian atmosphere from galactic and solar cosmic rays including solar proton events. Together with the French gamma-spectrometer and the German neutron detectors the investigation of the radiation environment on the surface of Mars and in the atmosphere up to 4000 m altitude will be conducted.

The high precision gamma-ray spectrometer (GRS) is carried on the first Japan's large-scaled lunar explorer, SELENE (KAGUYA) circling a polar orbit. The GRS consists of a large Ge crystal as a main detector and massive bismuth germanate crystals and a plastic scintillator as anticoincidence detectors. Since the successful launch on Sep. 14, 2007, radiation damage in the Ge detector has been induced from the incidence of energetic particles from space, which degraded its energy resolution. Then the Ge detector was annealed for 2 days at 85±5 K and the resolution is recovered to the level at the initial phase of the early observation. The special operations were conducted in December, 2008 in order to measure backgrounds gamma rays from the materials of the spacecraft body and the GRS instrument itself. The GRS data from the 100 km altitude reveal the global distribution of trace elements of Th and K on the Moon which delineates the distributions of KREEP component of lunar materials. Th and K-rich materials are concentrated around the Imbrium basin in Procellarum KREEP Terrane (PKT) and intermediately concentrated in South Pole–Aitken basin area on the farside. Results from special operations and observation are described and discussed.

Research Institute for Science and Engineering., Waseda Univ., Japan College of Health Science, Saitama Prefectural University,, Japan Inst. of Space and Astronautical Science, JAXA, Japan Nippon Medical School, Japan Dep. of Chemistry, Tokyo Metropolitan Univ., Japan National Institute of Polar Research, Japan Japan Agency for Marine-Earth Science and Technology, Japan Research Institute, Chiba Institute of Technology, Japan Centre d’Etude Spatiale des Rayonnements,Toulouse, France Dep. of Meteorites, Univ. of New Mexico, USA *nhasebe@waseda.jp

Immediately after the flybys at comet Halley by a fleet of spacecraft in 1986, Gringauz et al. (1986a) reported the detection by the Vega-2 spacecraft of a chemical and sharp plasma boundary, which they named the 'cometopause,' at a distance of about 1.6 x 10(exp 5) km from the nucleus. Gringauz and Verigin (1991) presented the 'cometopause' as a permanent feature of the solar wind - Halley type comet interaction at about 1 UA from the Sun. This permanent boundary presumably separates an upstream region dominated by the solar wind from the downstream region where heavy cometary ions dominate. We present here the analysis of the results of the Giotto positive ion cluster composition analyzer - Reme plasma analyzer (PICCA-RPA2) ion mass spectrometer and electron electrostatic analyzer - Reme plasma analyzer (EESA-RPA1) electron spectrometer data, which clearly show that there is no such boundary at comet Halley.

The magnetic fields experiment designed for the Mars Observer mission will provide definitive measurements of the Martian magnetic field from the transition and mapping orbits planned for the Mars Observer. The paper describes the instruments (which include a classical magnetometer and an electron reflection magnetometer) and techniques designed to investigate the nature of the Martian magnetic field and the Mars-solar wind interaction, the mapping of crustal magnetic fields, and studies of the Martian ionosphere, which are activities included in the Mars Observer mission objectives. Attention is also given to the flight software incorporated in the on-board data processor, and the procedures of data processing and analysis.

The Giotto probe's three-dimensional electron spectrometer has obtained data that illustrate the complex interactions between comet Halley and the solar wind. As Giotto approached the comet, it traversed several regions exhibiting different plasma characteristics: a large upstream region, a foreshock, a bow wave whose apex lies at about 400,000 km, a transition region, a region permanently and strongly contaminated by cometary ions, a collision pause, and various inner regions up to the inner coma, including a region of depleted hot plasma.

Two and six keV electron and proton data obtained by the FVA detector onboard ISEE 1 and 2 in the upstream region near apogee are analyzed. Tracing back electron and ion fluxes shows that electrons are present in a region of space near the boundary inside the foreshock, and that diffuse and intermediate ions do not directly issue from the bow shock surface. Using the assumptions that they result from the scattering of an initial population with no magnetic moment (μ=0), and that their mean energy is conserved through a diffusion process, we get a clear organisation of the data. Protons are present in a broad region of space inside the foreshock but appear at greater distances from the boundary when the spacecraft is near apogee. It is thought that these protons have their origin in the scattered beam-like distributions produced at the shock surface.

Among the plasma discontinuities detected by the Giotto spacecraft around Comet P/Halley, the magnetic pile-up boundary, located at about 135,000 km from the nucleus, has a sharpness which was not foreseen by theoretical models. At this boundary, which marks the beginning of the region where the field lines draped around the nucleus have been piled up, the magnetic field jumps sharply. Electron measurements provided by the RPA experiment show that a clear plasma discontinuity coincides with this magnetic feature. Significant changes occur here in the suprathermal electron distribution function. A magneto-plasma sheet is clearly defined after the boundary. Inside this sheet, close correlations exist between the parameters describing the magnetic field and the electron population. The polytropic equation of state governing the suprathermal electrons in the sheet has been deduced from RPA measurements. Some implications of this law are discussed.

THE study of γ-ray emission from planets with a thin atmosphere allows a rough estimation of the chemical composition of their surface to be made. The first attempt to make orbital measurements of the -γ-ray flux from Mars was made by the Soviet spacecraft Mars 5 (ref. 1). Here we present results from the -γ-ray APEX experiment on board Phobos 2. We have measured the y-ray albedo of the martian surface. This albedo appears as a large continuum between a few hundred keV and 8 MeV corresponding to a source intensity of 5 photons cm-2 s-1 2Φ-l (estimated in the 150–1500 keV energy range). There is also evidence for a 511-keV annihilation emission and for a broad contribution of probable nuclear lines between 4 and 7 MeV.

The heavy ion analyzer, RPA2-PICCA, on board the Giotto spacecraft detected an increase in the densities of cometary ions within a cometocentric distance of 150 000 km. The composition of cometary ions changed dramatically as the comet’s nucleus was approached, but it was clearly dominated by the water group. The second and third most abundant ions identified were associated with the CO- or S-group and the CO2-group, respectively. Ions of larger atomic mass units were also present closer to the comet, and they possibly correspond to sulphur compounds and/or various hydrocarbons. Radial profiles of various groups of heavy ions and certain abundance ratios are presented. The peak density for all mass groups was detected at a cometocentric distance of ~ 11 000 km. A distinct boundary, where the ion velocity and temperature dropped significantly, was identified at about 27 000 km.

The Giotto RPA-COPERNIC plasma experiment identified several regions in which the solar wind interaction with the cometary plasma displayed characteristic features: Beginning ~ 4.6 106 km from the comet there is an upstream region with sporadic connection to the comet An electron foreshock is present up to 2.5 105 km away from the bow shock A bow shock is detected at 1.15 106 km Between the bow shock and the cometopause the outer regions can be divided into 3 parts A cometopause is found at ~ 1.35 105 km and a density decrease is detected at ~ 4.5 104 km from the comet. The detailed plasma features associated with these regions are successively described.

On board the four Cluster spacecraft, the Cluster Ion Spectrometry (CIS) experiment measures the full, three-dimensional ion distribution of the major magnetospheric ions (H+, He+, He++, and O+) from the thermal energies to about 40 keV/e. The experiment consists of two different instruments: a COmposition and DIstribution Function analyser (CIS1/CODIF), giving the mass per charge composition with medium (22.5°) angular resolution, and a Hot Ion Analyser (CIS2/HIA), which does not offer mass resolution but has a better angular resolution (5.6°) that is adequate for ion beam and solar wind measurements. Each analyser has two different sensitivities in order to increase the dynamic range. First tests of the instruments (commissioning activities) were achieved from early September 2000 to mid January 2001, and the operation phase began on 1 February 2001. In this paper, first results of the CIS instruments are presented showing the high level performances and capabilities of the instruments. Good examples of data were obtained in the central plasma sheet, magnetopause crossings, magnetosheath, solar wind and cusp measurements. Observations in the auroral regions could also be obtained with the Cluster spacecraft at radial distances of 4–6 Earth radii. These results show the tremendous interest of multispacecraft measurements with identical instruments and open a new area in magnetospheric and solar wind-magnetosphere interaction physics.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetopheric configuration and dynamics; solar wind - magnetosphere interactions)

The Mars Odyssey Gamma-Ray Spectrometer is a suite of three different instruments, a gamma subsystem (GS), a neutron spectrometer, and a high-energy neutron detector, working together to collect data that will permit the mapping of elemental concentrations on the surface of Mars. The instruments are complimentary in that the neutron instruments have greater sensitivity to low amounts of hydrogen, but their signals saturate as the hydrogen content gets high. The hydrogen signal in the GS, on the other hand, does not saturate at high hydrogen contents and is sensitive to small differences in hydrogen content even when hydrogen is very abundant. The hydrogen signal in the neutron instruments and the GS have a different dependence on depth, and thus by combining both data sets we can infer not only the amount of hydrogen, but constrain its distribution with depth. In addition to hydrogen, the GS determines the abundances of several other elements. The instruments, the basis of the technique, and the data processing requirements are described as are some expected applications of the data to scientific problems.

The high-precision gamma-ray spectrometer (GRS) on the lunar polar orbiter SELENE is designed to measure 200 keV—12 MeV gamma rays in order to determine elemental compositions of the lunar surface. The GRS consists of a large germanium (Ge) crystal as a main detector and a massive bismuth germanate crystal and a plastic scintillator as anticoincidence detectors. The Ge detector is cooled by a Stirling cryocooler with its compressor attached to a passive radiator facing the cold space. The cooling system maintains the Ge detector below 90 K during the observation. The flight model of the GRS has achieved an energy resolution of 3.0 keV (FWHM) at 1333 keV. Energy spectra obtained by the GRS will show sharp gamma-ray lines whose energies identify the elements and whose intensities determine the concentrations of the elements, permitting global mapping of the elemental abundances in the sub-surface of the Moon. The elemental maps obtained by the GRS with such high-energy resolution enable us to study lunar geoscience problems.

The high precision gamma-ray spectrometer (GRS) is carried on the first Japan's large-scaled lunar explorer, SELENE (KAGUYA), successfully launched by the H-IIA rocket on Sep. 14, 2007. The GRS consists of a large Ge crystal as a main detector and massive bismuth germanate crystals and a plastic scintillator as anticoincidence detectors. After a series of initial health check of the GRS, it started a regular observation on December 21, 2007. Energy spectra including many clear peaks of major elements and trace elements on the lunar surface have been measured by the GRS. Global measurement of thorium counting rate on the lunar surface is presented. The region showing the highest count rate of thorium extends from Kepler to Fra Mauro region in the Procellarum. And Apennine Bench and Aristillus region and the northwestern region of Mare Imbrium are high in thorium count rate. Second high count rate region is located in the South Pole-Aitken basin of the farside. Arago and Compton/Belkovich craters are also e...

The Japanese lunar explorer SELENE was launched from Tanegashima Space Center on September 14, 2007. It consists of a main orbiter KAGUYA at 100 km altitude and two daughter satellites (relay satellite OKINA and VRAD satellite OUNA) with 14 scientific instruments. The high precision gamma-ray spectrometer (GRS) on KAGUYA measures 200 keV–12 MeV gamma rays to determine the elemental composition of the lunar surface. The GRS is composed of a large Ge crystal as a main detector and massive bismuth germinate (BGO) crystals and a plastic scintillator as anticoincidence detectors. The Ge detector is cooled by a Stirling cryocooler below 90 K during the observation. After successful launch of the spacecraft and initial checkouts, the GRS started the nominal observation on December 21, 2007, and the temperatures and counting rates of the GRS were confirmed to be stable. Energy spectra of gamma rays with a good energy resolution are being obtained over the lunar surface, which will allow us to make global maps of ...

The heavy ion analyzer (PICCA) on board the Giotto spacecraft was used to determine the composition of positively charged ions in the environment of Comet Halley. Here it is argued that a distinct peak at 37 amu, observed in the mass spectrum inside the ionopause, is due to C3H(+). It is further argued that the dominant source of this ion, as well as the earlier identified ion (C3H3(+) at 39 amu), is not the cometary nucleus but is rather the circum-nuclear halo of the so-called CHON dust particles observed at the comet. 22 refs.