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The origin of the Martian satellites presents a puzzle of long standing. Addressing the composition of Phobos will help constrain theories of its formation. Visible and near-infrared spectra of Phobos lack deep absorption features, making the compositional interpretation a tricky task. PFS/MEx and TES/MGS observations in the thermal infrared show several spectral features that can be used to investigate the composition of the surface. Our results show that the majority of the spectra are consistent with the presence of phyllosilicates, particularly in the area northeast of Stickney. This area corresponds to the “blue” region as defined by Murchie et al. (1999) . Analysis of PFS and TES observations in the “red” region defined by Murchie et al. (1999) are consistent with tectosilicates, especially feldspars/feldspathoids. We discuss several physical and chemical mechanisms that can act to eliminate or reduce the strength of bands in the VIS/NIR spectra, with possibly little or no effect in the mid-IR. Comparison of the TES and PFS data to the meteorites shows that no class of chondritic meteorites provide significant agreement with the spectral features observed. The lack of consistency of the PFS and TES spectra to analogs of ultraprimitive materials (organic residues) suggests that an origin via capture of a transneptunian object is not supported by these observations, although it cannot be completely ruled out. Derived surface temperatures from PFS and TES data are in very good agreement with brightness temperatures derived from Viking orbiter measurements, Earth-based observations, and values predicted by numerical models. Our results show that the surface temperature of Phobos varies with solar incidence angle and heliocentric distance, reconciling the different results. We collect and summarize the compositional clues for the origin of Phobos discussed in this paper, including our results. Currently, the most likely scenario is the in-situ formation of Phobos, although a capture of achrondrite-like meteorites is not ruled out.

The recent identification of large deposits of sulphates by remote sensing and in situ observations has been considered evidence of the past presence of liquid water on Mars. Here we report the unambiguous detection of diverse phyllosilicates, a family of aqueous alteration products, on the basis of observations by the OMEGA imaging spectrometer on board the Mars Express spacecraft. These minerals are mainly associated with Noachian outcrops, which is consistent with an early active hydrological system, sustaining the long-term contact of igneous minerals with liquid water. We infer that the two main families of hydrated alteration products detected-phyllosilicates and sulphates--result from different formation processes. These occurred during two distinct climatic episodes: an early Noachian Mars, resulting in the formation of hydrated silicates, followed by a more acidic environment, in which sulphates formed.

This paper presents in situ observational evidence from the Cluster Ion Spectrometer (CIS) on Cluster of injected solar wind "plasma clouds" protruding into the day-side high-latitude magnetopause. The plasma clouds, presumably injected by a transient process through the day-side magnetopause, show characteristics implying a generation mechanism denoted impulsive penetration (Lemaire and Roth, 1978). The injected plasma clouds, hereafter termed "plasma transfer events", (PTEs), (Woch and Lundin, 1991), are temporal in nature and relatively limited in size. They are initially moving inward with a high velocity and a magnetic signature that makes them essentially indistinguishable from regular magnetosheath encounters. Once inside the magnetosphere, however, PTEs are more easily distinguished from magnetopause encounters. The PTEs may still be moving while embedded in an isotropic background of energetic trapped particles but, once inside the magnetosphere, they expand along magnetic field lines. However, they frequently have a significant transverse drift component as well. The drift is localised, thus constituting an excess momentum/motional emf generating electric fields and currents. The induced emf also acts locally, accelerating a pre-existing cold plasma (e.g. Sauvaud et al., 2001). Observations of PTE-signatures range from "active" (strong transverse flow, magnetic turbulence, electric current, local plasma acceleration) to "evanescent" (weak flow, weak current signature). PTEs appear to occur independently of Interplanetary Magnetic Field (IMF) Bz in the vicinity of the polar cusp region, which is consistent with observations of transient plasma injections observed with mid- and high-altitude satellites (e.g. Woch and Lundin, 1992; Stenuit et al., 2001). However the characteristics of PTEs in the magnetosphere boundary layer differ for southward and northward IMF. The Cluster data available up to now indicate that PTEs penetrate deeper into the magnetosphere for northward IMF than for southward IMF. This may or may not mark a difference in nature between PTEs observed for southward and northward IMF. Considering that flux transfer events (FTEs), (Russell and Elphic, 1979), are observed for southward IMF or when the IMF is oriented such that antiparallel merging may occur, it seems likely that PTEs observed for southward IMF are related to FTEs.Key words. Magnetospheric physics (magnetopause, cusp, and boundary layers; magnetosphere-ionosphere interactions; solar-wind magnetosphere interactions)

ISHTAR or VENUS ORBITER is a mission to Venus similar to the mission Mars Express to Mars, with the use, possibly, of the same spacecraft and subsystems. This mission has been proposed to ESA for a feasibility study as a small mission (F2, F3). We shall describe here briefly the scientific objectives of the mission, and how could be implemented. The scientific objectives of the mission are evenly distributed in three broad areas: atmospheric science, planetary interior and surface, and interaction with the solar wind. Ishtar will study the surface and the atmosphere of the planet by making use of remote sensing instruments, and, if possible, by a descending meteorological balloon/lander. The model payload of the orbiter should include an Imaging Spectrometer, a Fourier Spectrometer, a Radar imaging/altimeter, a UV spectrometer and a Plasma Package studying also the Energetic Neutral Atoms population resulting from the plasma interaction with the planetary atmosphere.

This paper presents the first observations with Cluster of a very dense population of thermal ionospheric ions (H+, He+, O+) locally "accelerated" perpendicularly to the local magnetic field in a region adjacent to the magnetopause and on its magnetospheric side. The observation periods follow a long period of very weak magnetic activity. Recurrent motions of the magnetopause are, in the presented cases, unexpectedly associated with the appearance inside closed field lines of recurrent energy structures of ionospheric ions with energies in the 5 eV to ~1000 eV range. The heaviest ions were detected with the highest energies. Here, the ion behaviour is interpreted as resulting from local electric field enhancements/decreases which adiabatically enhance/lower the bulk energy of a local dense thermal ion population. This drift effect, which is directly linked to magnetopause motions caused by pressure changes, allows for the thermal ions to overcome the satellite potential and be detected by the suprathermal CIS Cluster experiment. When fast flowing, i.e. when detectable, the density (~ 1 cm-3) of these ions from a terrestrial origin is (in the cases presented here) largely higher than the local density of ions from magnetospheric/plasma sheet origin which poses again the question of the relative importance of solar and ionospheric sources for the magnetospheric plasma even during very quiet magnetic conditions.Key words. Ionosphere (planetary ionosphere; plasma convection) Magnetospheric physics (magnetopause, cusp and boundary layers)

The plasma-wave experiment ASPI (analysis of spectra of plasma waves and instabilities) on board the INTERBALL spacecraft is a combined wave diagnostics experiment. It performs measurements of the DC and AC magnetic field vector by flux-gate and search-coil sensors, the DC and AC electric field vector by Langmuir double probes and the plasma current by Langmuir split probe. Preliminary data analysis shows the low noise levels of the sensors and the compatibility of new data with the results of previous missions. During several months of in-orbit operation a rich collection of data was acquired, examples of which at the magnetopause and plasma sheet are presented in second part of the paper.

In this paper we present some results concerning the Aristarchus plateau and Mounts Harbinger regions. The study was conducted using an imaging spectrometer in the 0.4–1.1 μm spectral range at the 1.5 meters Sierra Nevada Observatory telescope. We report the albedo, the UV-VIS continuum and 0.9–1 μm absorption band maps, showing the complex pattern of Aristarchus crater ejecta and the distribution of surrounding materials. The extension of the dark mantling deposits present on Aristarchus plateau is well shown from our data, appearing very red and with a uniform distribution of the 0.9–1 μm band.

The aim of this retrospective study is to compare the different surgical approaches in obstructing colo-rectal cancer in terms of mortality, morbidity and quality of life.We observed 379 patients with colorectal cancer, 354 of which underwent surgical treatment, 189 M (53.4%) and 165 F (46.6%), with a median age of 72.6 years. Complicated tumors were 150 (42.4%), with 126 obstructions (84%). For 95 obstructing left-sided colorectal cancers we performed: 9 defunctioning colostomies; 62 two-stages operations: 55 Hartmann's procedures, 5 primary anastomosis with colostomy; 2 primary anastomosis with on table wash-out and ileostomy; 24 single-stage operations: 17 primary anastomosis with on table wash-out and 7 colectomy.The overall operative mortality rate was 8.7% (11/126). The overall leak rate was 8% (5/62), 12.9% (4/31) in left colon and 3.2% (1/31) in right colon, all treated conservatively. The wound infection rate was 23.8% (30/126).Obstructing colo-rectal cancer is associated with a high operative mortality and a worse prognosis. Defunctioning colostomy can be regarded as a valid option only in extreme circumstances. Hartmann's operation has indicated in case of metastatic disease, unsure anastomosis, simultaneous colonic perforation. The gold-standard is primary anastomosis, as colonic resection with on table wash-out or subtotal/total colectomy, in case of largely distended colon or synchronous lesions.

Retroperitoneal and subcapsular renal hematomas, following extracorporeal shock wave lithotripsy (ESWL) occur rarely, but the large number of this treatment performed has to be considered. The knowledge of risk factors, natural history and complications represents a crucial factor in the correct management of these lesions, that generally must be treated conservatively, monitoring clinical parameters and eco-TC diameters of the hematoma. Surgical approache is indicated only in case of haemodinamic instability not responsive to medical therapy and, after 1-2 months, to try to improve renal disfunction due to compression. In this paper we present a case of retroperitoneal hematoma after ESWL and review the literature, so as to define the management of these lesions.

Peutz-Jeghers syndrome is a rare autosomal dominantly inherited condition with an incidence of 1/120.000 liveborns, characterized by the presence of hamartomatous gastrointestinal polyps and mucocutaneous pigmentation. This syndrome predisposes to various clinical problems such as intussusception and cancer development in different loci (gastrointestinal tract, breast and ovary). For this reason, PJS patients should undergo a surveillance protocol of the genital and gastrointestinal apparatus. Therefore, the early diagnosis of PJS in at-risk family members is very important in preventing cancer development. Germline mutations within the LKB1 or Serine Threonine Kinase (STK11) gene, located on chromosome 19p13.3, are responsible for most cases of PJS so far studied. The existence of a second locus is suspected on chromosome 19q13.4 in a minority of families. The LKB1 gene, recently cloned, encodes the Serine Threonine Kinase LKB1 and is ubiquitously expressed. The identification of the disease-causing mutation in each family makes it possible to perform a presymptomatic diagnosis; therefore, only the mutation carriers will undergo the clinical surveillance program. In this paper, the case of a PJS patient who has been surgically treated is presented. The DNA screening of the LKB1 gene in this patient has led to the identification of the causing mutation. A critical review of the literature and is also presented as well as the proposal to establish an Italian Registry of PJS.

The surgical procedure is a crucial factor in preventing local recurrence in rectal cancer, and total mesorectal excision (TME) particularly is widely accepted as being associated with a decreased local recurrence rate. In this study, concerning 187 patients with rectal cancer, we compare conventional surgery, performed in 140 patients from 1979 to 1993, with a standardised TME procedure in 47 patients over the period from 1994 to 1998. The first group not treated by TME were operated on for 56 (40%) tumours of the upper rectum and 84 (60%) of the lower rectum; 35 (25%) were Dukes' A, 77 Dukes' B and 28 (20%) Dukes' C. 42 abdominoperineal amputations (30%) and 98 anterior resections (70%) were performed. The second group in which TME was performed comprised 17 (36%) tumours of the upper rectum and 30 (64%) of the lower rectum, 8 (17%) in stage I AJCC (Dukes' A), 16 (34%) in II (B) and 23 (49%) in III (C). 9 abdominoperineal amputations (19%) and 38 anterior resections (81%) were performed, 8 (21%) with an ultra-low anastomosis. In the first group of patients we observed 28 local recurrences (20%) and a 5-year disease-free survival in 50% of cases. In the second group we achieved a decreased rate of local recurrence (10.6%) which is about half that observed after conventional surgery, but there was no significant difference in survival. These data confirm the effectiveness of TME in reducing local recurrence rate, according to the literature; in future this procedure can get to reconsider the role of adjuvant therapy in the management of rectal cancer.

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.

Pancreatic cystadenomas must be considered in the differential diagnosis of all cystic neoplasms of the pancreas. On the basis of a clinical observation, the authors discuss the most important clinical and diagnostic findings of pancreatic cystadenomas with special regard for what concerns the mucinous type. The authors underline the extreme difficulty of a correct preoperative diagnosis and discuss, after a wide literature review, the utility and the validity of the various imaging, cytological and immunohistochemical preoperative diagnostic procedures. In most cases the final diagnostic confirmation comes from the histology on the resected specimen; therefore all cystic neoplasms, no matter their location within the gland, which are not clearly identified pre or intraoperatively, should be surgically treated and removed.

The diode laser is often used as a reference source in an interferometer because its interferogram zero crossings allow for precise intervals to be used for sampling the measured interferogram. The diode laser side modes, the features of which depend on the laser's temperature and power, may generate extra sampling points. The number of extra sampling points is analytically evaluated, and the synthetic spectra are compared with those obtained experimentally using the Planetary Fourier Spectrometer. The conclusion is that the theoretical resolution is guaranteed in practice only when no more than one extra sampling point is generated. This is the case when either the diode laser side mode amplitudes are less than one half of the main mode amplitude or the distance in wave numbers between the side modes and the main mode times the maximum optical path difference is less than 1. Finally, once an appropriate diode laser has been chosen, the actual spectral resolution might be degraded by poor device-operating conditions.

The radial distance to the bow shock obtained in earlier studies is first reviewed. Recently, HEOS 2 data have provided an extensive exploration of the bow shock location away from the ecliptic plane. These shock crossings have been used to find with a least-squares technique a conic surface that best describes the shock. The limitation of HEOS 2 observations is discussed in relation to both usual and unusual locations fo the bow shock. It seems clear from ≈2000 shock crossings which have been examined that, when the interplanetary magnetic field has a southward component, the shock is closer to the Earth, by 1R E, than when it has a northward component.

A marginal stability criterion for ion acoustic waves is applied to the analysis of five thin bow shock crossings observed by OGO-5; the observations began with the satellite in the magnetosheath. The assumption of marginally stable ion acoustic wave generation in the shock ramp provides the basis for determining the thickness of the magnetic gradients for subcritical, quasi-perpendicular shock features.

The ISEE-B EGD solar-wind plasma experiment often observes heavy ions in the solar wind. Selecting two periods of quiet solar wind with no particles observed backstreaming from the Earth’s bow-shock, we show that different ion species follow similar trends in terms of changes in the bulk speed and changes in the particle number density. In particular, quiet-solar-wind ionic abundances in these two cases are (relative to H+)4He2+=(1”5)·10−2,3He2+=1.5·10−4, 0+6=(3”15)·10−4, O+7=3·10−4, Si=1·10−4, Fe=0.5·10−4. We show that, if4He2+ abundance increases, the same occurs for the Si, O+7 and O+6 abundances. Finally the O+6 density fluctuations seem to be anticorrelated with4He2+ density fluctuations.

The location of the forward boundary of the upstream wave region ahead of the earth's bow shock is investigated statistically using plasma and magnetic-field data obtained by Heos 1. The analysis is conducted on the assumption that the waves are produced by protons reflected from the bow shock and traveling upstream with an effective velocity equal to the product of a parameter, p, and the solar-wind bulk velocity. The data-reduction methods are summarized, and uncertainties in the determination of the value of p are discussed. It is found that the overall average boundary corresponds to a velocity of approximately twice the solar-wind velocity for protons reflected from the daytime sector of the bow shock. More refined analysis of the data shows that the value of p is approximately 1.6 near the subsolar point and greater than 2 along the daytime flanks of the bow shock.

The electric field experiment on board ISEE-1 had a special mode of operation in which bursts of very high time resolution measurements were stored and slowly read-out. This mode of operation allows us to study in detail the waveforms of the large amplitude electrostatic waves observed at the Earth's bow shock in a frequency range (10--500 Hz) not well covered previously. These waves appear to be correlated with two streams in the ion angular distribution. Our observations indicate, therefore, that the ion--ion stream instability is the dissipation mechanism of a collisionless fast quasi-perpendicular shock wave.

Measurements from six OGO-5 particle and field experiments are used to examine the structure of the earth's bow shock during a period of extremely high beta (the ratio of plasma thermal to magnetic energy density), as determined from simultaneous measurements of the upstream plasma on board the HEOS satellite. Even though the interplanetary field is nearly perpendicular to the shock normal, the shock is extremely turbulent. Large field increases are observed up to a factor of 20 above the upstream values. Ahead of these large enhancements, smaller magnetic effects accompanied by electrostatic noise, electron heating, and ion deflection are observed for several minutes. These observations suggest that a steady-state shock may not be able to form at very high beta. Further, they show that while the magnetic energy density may be relatively unimportant in the upstream flow, it can become very significant within the shock structure, and hence the magnetic field should not be ignored in theoretical treatments of very high beta shocks.

HEOS-2 low energy electron data (10 eV–3.7 keV) from the LPS Frascati plasma experiment have been used to identify three different magnetospheric electron populations. Magnetosheathlike electron energy spectra (35–50 eV) are characteristic of the plasma mantle, entry layer and cusps from the magnetopause down to 2–3 R E Plasma sheet electrons (energy > 1 keV) are found at all local times, with strong intensities in the early morning quadrant and weaker intensities in the afternoon quadrant. The plasma sheet shows a well defined inner edge at all local times and latitudes, the inner edge coinciding probably with the plasmapause. The plasma sheet does not reach the magnetopause, but it is separated from it by a boundary layer electron population that is very distinct from the other two electron populations, most electrons having energies 100–300 eV. We map these three electron populations from the magnetopause down to the high latitude near earth regions, by making use of the HEOS-2 low latitude inbound passes and the high latitude outbound passes (in Solar Magnetic ( SM ) coordinates). The boundary layer extends along the magnetopause up to 5–7 R E above the equator; at higher latitudes it follows the magnetic lines of force and it is found closer and closer to the earth, so that it has the same invariant latitudes of the system 1 currents observed by Iijima and Potemra (1976) in their region 1. The plasma sheet can be mapped into their region 2 and the cusp-entry layer-plasma mantle can be mapped into their cusp currents region. The boundary layer is observed for any Interplanetary Magnetic Field ( IMF ) direction. We speculate that magnetosheath particles penetrate into the magnetosphere everywhere along the magnetopause. The electron energization, however, is observed only in the boundary layer, on both dawn and dusk side and could be due to the polarization electric field at magnetopause generated by the magnetosheath plasma bulk motion in the region where such motion is roughly perpendicular to the magnetospheric magnetic field. The electron energization is absent in the regions (entry layer and plasma mantle) where the sheath plasma motion is roughly parallel or antiparallel to the magnetospheric magnetic field.

Bursts of energetic electrons (from >40keV up to 2MeV) as distinct from the magnetopause electron layer observed by Domingo et al. (1977) have been observed in the magnetosheath and in the solar wind by HEOS-2 at high-latitudes. Although these electrons are occasionally found close to the bow shock and simultaneously with low frequency (magnetosonic) upstream waves our observations strongly indicate that these electrons are of exterior cusp origin. Indeed, the flux intensity is highest in the exterior cusp region and decreases as the spacecraft moves away from it both tailward or upward. The energy spectrum becomes harder with increasing radial distance from the exterior cusp. The measured anisotropy indicates that the particles are propagating away from the exterior cusp. The magnetic field points to the exterior cusp region when these electrons are observed, being, for solar wind observations, centred at longitude 0° or 180° rather than along the spiral and in the magnetosheath, being usually different from the 90° or 270° orientation typical of that region. We exclude, therefore, that acceleration in the bow shock is the source of these particles because B is not tangent to the shock when bursts are observed. We have also found a one to one correlation between geomagnetic storms' recovery phases and intense, continuous observations of >40 keV electrons in the magnetosheath, while, on the other hand, during geomagnetically quiet (Dst) periods bursts are observed only if AE is much larger than average.

Nearly 2500 shock crossings from HEOS-1, HEOS-2 and 5 IMP spacecraft, covering most of the northern and part of the southern bow shock surface for X values X > − 20 RE, have been used to carry out a detailed study of the three-dimensional shape and location of the bow shock. The influence of the different solar wind conditions has been reduced by normalising the observed crossings to an average solar wind dynamical pressure (N0 = 9.4 cm−3, V0 = 450 km s−1). It has been shown that the shock surface is symmetric with respect to the ecliptic plane and intersects the coordinate axes at 11.9 RE (X), + 27.0 and − 22.9 RE (Y), + 23.9 and − 24.5 RE (Z) for the average dynamical pressure (N0 = 9.4 cm−3, V0 = 450km s−1, with M A = 9.3 , M MS = 6.1) . The observed aberration of the shock surface is 8.9° ± 1°, i.e. 5.1° larger than the aberration predicted from the Earth's motion. This asymmetry around the solar wind apparent direction is described by equation (6) for different Mach numbers MA and confirms the predictions of Walters [J. geophys. Res. 71, 1319 (1964)] and Michel [J. geophys. Res. 70, 1 (1965)]. The magnetosheath thickness is 3.3 RE along the X-axis, 11.4 RE (+ Y), 8.7 RE (− Y), 9.9 RE (+Z) and 10.9 RE along the negative Z axis.

A vibrating capacity (a metallic membrane excited by a piezoelectric ceramic) has been studied to measure low charge values. After studying several devices, the use of a low-noise amplifier has allowed us to measure a minimum charge of 103 electron charges. This sensitivity, together with the low mass, low power, strong mechanical characteristics make the device useful for space application.

Preliminary results from the JPA instrument on Giotto indicate that Comet Halley, even on the flanks, has a bow shock which moves backwards and forwards over the spacecraft. To understand the structure properly will require more detailed investigation of the relationships between three particle populations, cometary ions, solar wind ions and electrons.

Bursts of energetic electrons (from 40 keV up to 2 MeV) have been observed in the magnetosheath and in the solar wind by HEOS 2 at high latitudes. These bursts are not associated with the magnetopause layer observed by Domingoet al. Although these electrons are occasionally found close to the bow shock and simultaneously with low-frequency (magnetosonic) upstream waves, our observations strongly indicate that these electrons are of cusp origin. Indeed, the flux intensity is highest in the exterior-cusp region and decreases as the spacecraft moves away from it both tailward and upward. The energy spectrum becomes harder with increasing radial distance from the exterior cusp. The measured anisotropy indicates that the particles are propagating away from the exterior cusp. The local magnetic field points to the exterior-cusp region at times when these electron bursts are observed. When in the interplanetary medium, it is pointed around 0° or 180° rather than along the spiral and, when in the magnetosheath, it is directed towards the cusp identation rather than towards 90° or 270°, which are the most common azimuthal angles observed in the magnetosheath. We exclude, therefore, that acceleration in the bow shock is the source of these particles.

Many different low-frequency waves are observed close to the Earth's bow shock; a short review is given here. Upstream of the shock backstreaming protons generate (by interacting with the solar wind) circularly polarized magnetosonic waves. These waves are convected by the solar wind toward the shock itself. Backstreaming electrons appear to generate (locally upstream) low-frequency whistler waves which are also convected downstream. Related to the magnetosonic waves but generated, perhaps, by backstreaming electrons, low-frequency whistler wave «packets» with well-defined temporal shapes are observed (trailing peak amplitude and decaying in several wave cycles are seen by the satellites). These phenomena are not present for all different values of β,\(\widehat{Bn}\) andM MS. For a laminar shock, upstream standing whistler waves in very good agreement with the theory have been observed. In the shock layer all frequencies appear to be excited, but much energy seems to be in the midfrequency whistler waves, and this energy seems to increase when\(\widehat{Bn}\) goes from (20⋎30)° (quasi-parallel configurations) to (70⋎80)° (quasi-perpendicular configurations). On the contrary, downstream large-amplitude low-frequency fluctuations appear to be much enhanced in quasi-parallel structures and are reduced in quasi-perpendicular structures. Another kind of very-large-amplitude low-frequency oscillations appears both upstream and downstream of the shock main ramp when the dissipation length becomes longer than the dispersion length. In these cases we may, perhaps, talk of damped solitons.

A statistical study of correlated observations of plasma, energetic (>40 keV) electrons and magnetic fields on HEOS-2 in the outer dayside magnetosphere and magnetosheath has been performed. We find that on the dayside magnetosphere the occurrence of plasma inside the magnetopause is anti-correlated with the appearance of energetic electrons in the magnetosheath. A mechanism is derived that attempts to explain how plasma may penetrate across the magnetopause into the magnetosphere and how energetic electrons may escape from the (pseudo) trapping region in the dayside magnetosphere into the magnetosheath. The mechanism is an E × B drift across the magnetopause. The drift is directed inward or outward depending on the direction of the electric field E at the magnetopause.

An instrument to measure the three-dimensional energy distribution of positive ions in order to study the interaction between the solar wind and ionized Halley cometary particles was designed. Two sensors measure the distribution from 10 eV to 20 keV once per spacecraft spin and the distribution from 90 eV to 90 keV, with coarse mass discrimination, once every 32 spins. The instrument was turned on September 8, 1985. The performance throughout all testing was nominal. The spacecraft was greater than 10 million km from the earth in the solar wind. The only population identified is the solar wind. The Fast Ion Sensor follows solar wind variations with its autoranging capability. The Implanted Ion Sensor identifies higher mass ions such as O(6+) and O(5+) in the solar wind.