Publication archive

Publication archive

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.
Published: 01 December 2005
On March 31, 2001 at ~0635 UT when the CLUSTER constellation was near local midnight and at ~4 RE geocentric distance, sensors observed an energetic electron injection event associated with a strong (AE ~ 1200 nT) magnetospheric substorm. Geostationary spacecraft 1991-080 located at ~20 LT also saw an abrupt electron injection event at ~0630 UT and FAST spacecraft instruments (~19 LT) detected a powerful set of magnetic field, electric field, and energetic plasma signatures at ~0637 UT. The energetic neutral atom imaging experiments onboard the IMAGE spacecraft detected an injection of substorm-produced ions in the pre-midnight sector commencing at ~0630 UT. Electron injection signatures at the four separate CLUSTER locations allow us to infer the location, speed, and direction of the substorm injection boundary. Hence, the CLUSTER (and IMAGE) telescope-microscope combination is a long-sought realization of a major magnetospheric research objective and shows the power of localized multi-point measurements from CLUSTER.
Published: 20 September 2002
In this paper we report Cluster observation of a fast flow event in the plasma sheet associated with a small auroral substorm intensification at 1838 UT on August 12, 2001. Cluster, located in the plasma sheet, experienced significant thinning of the current sheet associated with a high-speed Earthward flow of 900 km s-1. By using the four spacecraft magnetic field data and a Harris-type current sheet model, it was estimated that the thickness of the current sheet changes from about 1 RE before the flow observation down to 400 km, i.e., close to the ion inertia length. In the vicinity of this thin current sheet there were also signatures of enhanced current density off the center of the neutral sheet, consistent with recent Geotail results.
Published: 14 December 2002
During the interval 0947-0951 UT on 1 October 2001, when Cluster was located at XGSM = -16.4 RE near ZGSM = 0 in the pre-midnight magnetotail, the Cluster barycenter crosses the neutral sheet four times. High speed proton flow, with reversal from tailward to Earthward, was detected during the crossings. Using a linear gradient/curl estimator technique we estimate current density and magnetic field curvature within the crossings. These observations exhibit the tailward passage of an X-line over the Cluster tetrahedron. These current sheet has a bifurcated structure in the regions of tailward and earthward flows and a flat and/or slightly bifurcated thin current sheet in between. A distinct quadrupolar Hall magnetic field component was observed.
Published: 11 June 2003
The daytime martian ionosphere has been observed as a two-layer structure with electron densities that peak at altitudes between about 110 and 130 kilometers. The Mars Express Orbiter Radio Science Experiment on the European Mars Express spacecraft observed, in 10 out of 120 electron density profiles, a third ionospheric layer at altitude ranges of 65 to 110 kilometers, where electron densities, on average, peaked at 0.8 x 1010 per cubic meter. Such a layer has been predicted to be permanent and continuous. Its origin has been attributed to ablation of meteors and charge exchange of magnesium and iron. Our observations imply that this layer is present sporadically and locally.
Published: 04 November 2005
Editors: C. P. Escoubet, Z.-X. Liu, and Z. Pu

This special issue of Annales Geophysicae presents the mission, the instruments and the first results of the Double Star programme. Double Star is the first mission in collaboration between China and ESA. Double Star has been a great opportunity for the European and Chinese scientists to enhance the knowledge of the Sun-Earth connection. Double Star, together with Cluster, brings six coordinated spacecraft to study small-, medium- and large-scale plasma processes in geospace. This is the first time that European instruments have been flown on a Chinese spacecraft as part of the payload.

Published: 08 November 2005
In this review, we report on some new aspects of magnetotail dynamics found in the data of the first traversal of the magnetotail by the Cluster quartet in summer and autumn 2001: (1) The electron drift instrument made the first direct measurements of tail lobe convection. The statistical data shows convection toward the center of the plasma sheet, with a clear dependence on the sign of the interplanetary magnetic field BZ component. Moreover, a dawn-dusk shear (if one compares convection in opposite lobes) for BY-dominated interplanetary field hints to an interconnection of open lobe field lines with the interplanetary medium. (2) At times the tail current sheet resembles a one-dimensional Harris sheet, which might get as thin as 500 km and may carry current densities as high as 20-40 nA m-2. (3) At other times, the current sheet may exhibit rapid kink-type flapping motion with vertical velocities of 50-100 km s-1. During these intervals the current sheet clearly exhibits a bifurcated structure, with two current density maxima around a region of much reduced current in the center of the plasma sheet.
Published: 30 November 2005
This paper presents the results of a statistical investigation into the nature of oblique wave propagation in the foreshock. Observations have shown that foreshock ULF waves tend to propagate obliquely to the background magnetic field. This is in contrast to theoretical work, which predicts that the growth rate of the mechanism responsible for the waves is maximized for parallel propagation, at least in the linear regime in homogenous plasma. Here we use data from the Cluster mission to study in detail the oblique propagation of a particular class of foreshock ULF wave, the 30 s quasi-monochromatic wave. We find that these waves persistently propagate at oblique angles to the magnetic field. Over the whole data set, the average value of thetakB was found to be 21 ± 14°. Oblique propagation is observed even when the interplanetary magnetic field (IMF) cone angle is small, such that the convective component of the solar wind velocity, vExB, is comparable to the wave speed. In this subset of the data, the mean value of thetakB was 12.9 ± 7.1°. In the subset of data for which the IMF cone angle exceeded 45°, the mean value of thetakB was 19.5 ± 10.7°. When the angle between the IMF and the x geocentric solar ecliptic (GSE) direction (i.e., the solar wind vector) is large, the wave k vectors tend to be confined in the plane defined by the x GSE direction and the magnetic field and a systematic deflection is observed. The dependence of thetakB on vExB is also studied.
Published: 26 November 2005
We present initial results from a statistical study of Cluster multispacecraft flux transfer event (FTE) observations at the high-latitude magnetopause and low-latitude flanks from February 2001 to June 2003. Cluster FTEs are observed at both the high-latitude magnetopause and low-latitude flanks for both southward and northward IMF. Among the 1222 FTEs, 36%, 20%, 14%, and 30% are seen by one, two, three, and four Cluster satellites, respectively. There are 73% (27%) of the FTEs observed outside (inside) the magnetopause, which might be caused by the motion of FTEs toward the magnetosheath when they propagate from subsolar magnetopause to the midlatitude and high-latitude magnetopause and low-latitude flanks. We obtain an average FTE separation time of 7.09 min, which is at the lower end of the previous results. The mean BN peak-peak magnitude of Cluster FTEs is significantly larger than that from low-latitude FTE studies. FTE BN peak-peak magnitude clearly increases with increasing absolute magnetic latitude (MLAT), it has a weaker dependence on magnetic local time (MLT) with a peak near the magnetic local noon, and it has a complex dependence on Earth dipole tilt with a peak at around zero. FTE periodic behavior is found to be controlled by MLT, with a general increase of FTE separation time with increasing MLT, and by Earth dipole tilt, with a peak FTE separation time at around zero Earth dipole tilt. There is no clear dependence of FTE separation time on MLAT. There is a weak increase of FTE BN peak-peak magnitude with increasing FTE separation time, and we see no clear dependence of it on FTE BN peak-peak time. When no FTE identification thresholds are used, more accurate calculations of some FTE statistical parameters, including the mean BN peak-peak time, can be obtained. Further, comparing results with different thresholds can help obtain useful information about FTEs.
Published: 26 November 2005
We report the results of two XMM-Newton observations of the ultra-compact low-mass X-ray binary 4U 1850-087 located in the galactic globular cluster NGC6712. A broad emission feature at 0.7 keV was detected in an earlier ASCA observation and explained as the result of an unusual Ne/O abundance ratio in the absorbing material local to the source. We find no evidence for this feature and derive Ne/O ratios in the range 0.14-0.21, consistent with that of the interstellar medium. During the second observation, when the source was ~10% more luminous, there is some evidence for a slightly higher Ne/O ratio and additional absorption. Changes in the Ne/O abundance ratio have been detected from another ultra-compact binary, 4U 1543-624. We propose that these changes result from an X-ay induced wind which is evaporated from an O and Ne rich degenerate donor. As the source X-ray intensity increases so does the amount of evaporation and hence the column densities and abundance ratio of Ne and O.
Published: 21 November 2005
...Looking back over the events of the past year, 2004 was another great year for space science. The success of the Huygens probe and its exploration of the atmosphere and surface of Saturn's largest moon Titan is a mangnificent achievement for Europea science and technology. The Rosetta spacecraft launched on 2 March by an Ariane-5 from Kourou is now well into its 10-year flight to the comet Churyumov-Gerasimenko. Smart-1, Europea's first lunar mission arraived in orbit around the Moon after its thirteen-month journey. Mars Express, which has been in polar orbit around mars since 2003, delivered stunning pictures of the planet's surface. Europe, the Agency and all of its Member States can be proud of these great schievements...
Per Tegnér, Chairman of Council
Published: 01 October 2005
  • Foreword
    - 4th Announcement of Opportunity (AO-4)
    - The INTEGRAL Users Group
  • INTEGRAL Mission Status
  • Science Highlights
  • Galactic Bulge Monitoring Program
  • Science Operations - Highlights
  • The ISOC Science Data Archive
  • The 6th INTEGRAL workshop
  • Outreach
  • ISOC now at ESAC
  • Contact INTEGRAL science operations
Published: 15 November 2005
This issue of the ESA Bulletin takes an in-depth look at the Venus Express mission. The successful launch, the mission, the spacecraft, the science return, as well as the ground segment and mission operations are featured.
Published: 15 November 2005

The Venus Entry Probe study is one of the European Space Agency's (ESA) technology reference studies. It aims to identify; the technologies required to develop a low-cost, science-driven mission for in-situ exploration of the atmosphere of Venus, and the philosophy that can be adopted. The mission includes a science gathering spacecraft in an elliptical polar Venus orbit, a relay satellite in highly elliptical Venus orbit, and an atmospheric entry probe delivering a long duration aerobot (aerial robot) which will drop several microprobes during its operational phase.

The atmospheric entry sequence is initiated at 120 km altitude and an entry velocity of 9.8 kms-1. Once the velocity has reduced to 15 ms-1 the aerobot is deployed. This consists of a gondola and balloon and has a floating mass of 32 kg (which includes 8 kg of science instruments and microprobes). To avoid Venus' crushing surface pressure and high temperature an equilibrium float altitude of around 55 km has been baselined. The aerobot will circumnavigate Venus several times over a 15-22 lifetime analysing the Venusian middle cloud layer. Science data will be returned at 2.5 kbps over the mission duration. At scientifically interesting locations 15 drop-sondes will be released.

This paper focuses on the final mission design with particular emphasis on system level trade-offs including the balloon and pressurisation system, communications architecture, power system, design for mission lifetime in a hostile and acidic environment. It discusses the system design, design drivers and presents an overview of the innovative mission-enabling and mission-enhancing technologies.

Published: 22 October 2005
The concept of Technology Reference Studies (TRS), set up by ESA's Science Payload and Advanced Concepts Office (SCI-A) to focus the development of strategically important technologies of likely relevance to future science missions, has already been introduced in 2004 at the 55th IAC in Vancouver[1].

Significant progress in the definition of the mission concepts and related technology requirements has been achieved since then. At the present time the Planetary Exploration Studies Section of SCI-A has finished the study of the first four TRSs, the Venus Entry Probe (VEP), the Jupiter Minisat Explorer (JME), the Deimos Sample Return (DSR) and the Interstellar Heliopause Probe (IHP). Current study activities are now focusing on the extension of the Jovian Explorer scenario towards magnetospheric and atmospheric investigations by means of additional orbiter(s) and entry probes. New introduced concepts deal with cross-scale constellation (CSM) of up to 12 spacecrafts to further explore the Earth magnetosphere and a Near Earth Asteroid Sample Return (ASR).

All TRS mission profiles are based on small spacecraft, with miniaturized highly integrated payload suites (HIPS) and launched on Soyuz Fregat-2B (SF-2B) as baseline. TRSs are set up to provide thematic context for technology development based on feasible mission concepts, which may be also used by the scientific community as embryonic building blocks for future mission proposals. This paper describes the current status of the new concepts under study (CSM, JEP, ASR) and the final results of the first four TRSs (JME, DSR, VEP and IHP) in further detail.

Published: 22 October 2005
The Solar Orbiter mission is part of ESA's science program, Cosmic Vision 2020. It will explore the innermost regions of the heliosphere from high heliopsheric latitudes. From a distance of about 0.23AU and a max inclination of about 35 degrees with respect to the Sun's equator the Solar Orbiter will perform high resolution imagery of the sun and in-situ measurements of the heliosphere. At its closest distance to the Sun the spacecraft will experience a sun flux of approximately 28000W/m2. To protect the spacecraft bus from this flux a sun shield is used. The shield requires innovative design and materials in order to keep both the radiated and conducted heat to a minimum. Additionally, all sun exposed elements such as the high gain antenna and the solar arrays need to be designed for surviving the intense sun flux. This paper will outline the work done on the Solar Orbiter thermal design during its assessment phase. A description of the technical challenges for the overall thermal control system will be given and some of the trade-offs will be discussed. Furthermore, a feasible heat shield design will be presented together with current solutions towards test and verification of the overall system.
Published: 10 November 2005
The Solar Orbiter mission is part of ESA's Cosmic Vision science program. In the last year this mission has been studied in an assessment phase aiming at demonstrating technical feasibility and defining the mission at systems level. The Solar Orbiter will explore the innermost regions of the heliosphere from high heliopsheric latitudes. It will reach a distance of 0.22 AU from the Sun and obtain an inclination of 35 degrees with respect to the Sun's equator. In these areas a series of insitu and remote sensing measurements will be performed, providing first time in-situ measurements of regions so close to the Sun and at the same time provide arcsec resolution imagery. Additionally, the Solar Orbiter will provide the first ever out-of-the-ecliptic imaging and spectroscopic observations of the Sun's poles. Two mission profiles have been studied during the assessment; one utilizing solar electric propulsion and one using chemical propulsion. Both these scenarios will be discussed in this paper and the respective spacecraft design and the current Strawman payload will be presented. The strong link to BepiColombo through reuse of components will be outlined and specific technology development needs for the Solar Orbiter will be described.
Published: 10 November 2005
Previous Cluster observations have shown that the flapping motions of the Earth's magnetotail are of internal origin and that kink-like waves are emitted from the central part of the tail and propagate toward the tail flanks. The newly launched Double Star Program (DSP) TC-1 satellite allows us to investigate neutral sheet at 10-13 Re in the tail. Using conjunctions with Cluster we will have simultaneous observations at 10-13 and 16-19 Re of these flapping motions. In this paper, we present the first results of neutral sheet oscillations observed by the Cluster and Double Star satellites on 5 August 2004.
Published: 08 November 2005
We present Cluster and Double Star-1 (TC-1) observations from a close magnetic conjunction on 8 May 2004. The five spacecraft were on the dawnside flank of the magnetosphere, with TC-1 located near the equatorial plane and Cluster at higher geographic latitudes in the Southern Hemisphere. TC-1, at its apogee, skimmed the magnetopause for almost 8h (between 08:00-16:00 UT). Flux Transfer Events (FTEs), moving southward/tailward from the reconnection site, were observed by TC-1 throughout almost all of the period. Cluster, travelling on a mainly dawn-dusk trajectory, crossed the magnetopause at around 10:30 UT in the same Magnetic Local Time (MLT) sector as TC-1 and remained close to the magnetopause boundary layer in the Southern Hemisphere. The four Cluster spacecraft observed FTEs for a period of 6.5h between 07:30 and 14:00 UT. The very clear signatures and the finite transverse sizes of the FTEs observed by TC-1 and Cluster imply that, during this event, sporadic reconnection occurred. From the properties of these FTEs, the reconnection site was located northward of both TC-1 and Cluster on the dawn flank of the magnetosphere. Reconnection occurred between draped magnetosheath and closed magnetospheric field lines. Despite variable interplanetary magnetic field (IMF) conditions and IMF-Bz turnings, the IMF clock angle remained greater than 70° and the location site appeared to remain relatively stable in position during the whole period. This result is in agreement with previous studies which reported that the dayside reconnection remained active for an IMF clock angle greater than 70°. The simultaneous observation of FTEs at both Cluster and TC-1, separated by 2h in MLT, implies that the reconnection site on the magnetopause must have been extended over several hours in MLT.
Published: 08 November 2005
We present the study of one year of INTEGRAL data on the neutron star low mass X-ray binary GX 5-1. Thanks to the excellent angular resolution and sensitivity of INTEGRAL, we are able to obtain a high quality spectrum of GX 5-1 from ~5 keV to ~100 keV, for the first time without contamination from the nearby black hole candidate GRS 1758-258 above 20 keV. During our observations, GX 5-1 was mostly found in the horizontal and normal branch of its hardness intensity diagram. A clear hard X-ray emission is observed above ~30 keV which exceeds the exponential cut-off spectrum expected from lower energies. This spectral flattening may have the same origin of the hard components observed in other Z sources as it shares the property of being characteristic to the horizontal branch. The hard excess is explained by introducing Compton up-scattering of soft photons from the neutron star surface due to a thin hot plasma expected in the boundary layer. The spectral changes of GX 5-1 downward along the 'Z' pattern in the hardness intensity diagram can be well described in terms of monotonical decrease of the neutron star surface temperature. This may be a consequence of the gradual expansion of the boundary layer as the mass accretion rate increases.
Published: 01 November 2005
23-Sep-2020 07:05 UT

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