Publication archive

Publication archive

On 16 March 2005, the Cluster spacecraft crossed a shock almost at the transition between the quasi-perpendicular and quasi-parallel regimes (ThetaBn = 46°) preceded by an upstream low-frequency (~0.02 Hz in the spacecraft frame) wave train observed for more than 10 mn. The wave semicycle nearest to the shock was found to grow in time, steepen and reflect an increasing fraction of the incoming ions. This gives strong indication that this pulsation is becoming a new shock front, standing ~5lambdap upstream of the main front and growing to shock-like amplitude on a timescale of ~35 Omegap. Downstream of the main shock transition, remnants of an older front are found indicating that the reformation is cyclic. This provides a unique example where the dynamics of shock reformation can be sequentially followed. The process shares many characteristics with simulations of reforming quasi-parallel shocks.
Published: 25 November 2009
The variability of energetic electron fluxes (>40 keV) within the plasma sheet is explored using measurements from the Cluster spacecraft from 2001 through 2005. Only cases where the spacecraft remains inside the plasma sheet throughout the event are considered. Interesting cases were found using a combination of automated methods and visual inspection. Events are classified into 4 main types: (1) plasma sheet empty of energetic electrons; (2) decreasing plasma sheet energetic electron fluxes; (3) increasing plasma sheet energetic electron fluxes; and (4) sharp (rising and falling) variations in plasma sheet energetic electron fluxes during a single plasma sheet crossing. Case studies are presented for each type of event. The time it takes to fill/empty the plasma sheet of energetic electrons is quantified based on these events. Extreme events, most of which are associated with enhanced geomagnetic activity, showed that energetic electrons in the plasma sheet can vary up to several orders of magnitude. Interestingly, the energetic electron fluxes inside the plasma sheet can still undergo rapid variations when the solar wind is calm and geomagnetic activity is low.
Published: 18 November 2009
We report an all-sky image of energetic neutral atoms (ENAs) >6 kilo-electron volts produced by energetic protons occupying the region (heliosheath) between the boundary of the extended solar atmosphere and the local interstellar medium (LISM). The map obtained by the Ion and Neutral Camera (INCA) onboard Cassini reveals a broad belt of energetic protons whose nonthermal pressure is comparable to that of the local interstellar magnetic field. The belt, centered at ~260° ecliptic longitude extending from north to south and looping back through ~80°, appears to be ordered by the local interstellar magnetic field. The shape revealed by the ENA image does not conform to current models, wherein the heliosphere resembles a cometlike figure aligned in the direction of Sun's travel through the LISM.
Published: 13 November 2009
Aims. In order to discover new X-ray transients, the data taken by XMM-Newton as it slews between targets are being processed and cross-correlated with other X-ray observations.
Methods. A bright source, XMMSL1 J060636.2-694933, was detected on 18 July 2006 at a position where no previous X-ray source had been seen. The XMM-Newton slew data, plus follow-up dedicated XMM-Newton and Swift observations, plus optical data acquired with the Magellan Clay telescope, and archival All-Sky Automated Survey (ASAS) data were used to classify the new object, and to investigate its properties.
Results. No XMM-Newton slew X-ray counts are detected above 1 keV and the source is seen to be over five hundred times brighter than the ROSAT All-Sky Survey upper limit at that position. The line-rich optical spectrum acquired with the Magellan telescope allows the object to be classified as an A0 auroral phase nova, and the soft X-ray spectrum indicates that the nova was in a super-soft source state in the X-ray decline seen in the follow-up X-ray observations. The archival ASAS data suggests that the nova at onset (Oct 2005) was a "very fast" nova, and an estimate of its distance is consistent with the nova being situated within the LMC.
Conclusions. With the discovery presented here of a new classical nova in the LMC, it is clear that XMM-Newton slew data are continuing to offer a powerful opportunity to find new X-ray transient objects.
Published: 08 November 2009
Abstract: We develop a model for estimating solar total irradiance since 1600 AD using the sunspot number record as input, since this is the only intrinsic record of solar activity extending back far enough in time. Sunspot number is strongly correlated, albeit nonlinearly with the 10.7-cm radio flux (F 10.7), which forms a continuous record back to 1947. This enables the nonlinear relationship to be estimated with usable accuracy and shows that relationship to be consistent over multiple solar activity cycles. From the sunspot number record we estimate 10.7 values back to 1600 AD. 10.7 is linearly correlated with the total amount of magnetic flux in active regions, and we use it as input to a simple cascade model for the other magnetic flux components. The irradiance record is estimated by using these magnetic flux components plus a very rudimentary model for the modulation of energy flow to the photosphere by the subphotospheric magnetic flux reservoir feeding the photospheric magnetic structures. Including a Monte Carlo analysis of the consequences of measurement and fitting errors, the model indicates the mean irradiance during the Maunder Minimum was about 1 ± 0.4 W /m2 lower than the mean irradiance over the last solar activity cycle.
Published: 20 November 2007
During the solar minimum of 2008, the value of total solar irradiance at 1 AU (TSI) was more than 0.2 Wm/2 lower than during the last minimum in 1996, indicating for the first time a directly observed long-term change. In contrast, chromospheric indices and hence solar UV irradiance do not exhibit a similar change. Comparison of TSI with other activity parameters indicates that only the open solar magnetic field, BR, observed from satellites at 1 AU show a similar long-term behaviour. The values at the minima correlate well and the linear fit provides a direct physical relationship between TSI and BR during the minimum times. This correlation allows an unambiguous reconstruction of TSI back in time, provided the open solar magnetic field can be determined from e.g. geomagnetic indices or cosmogenic radionucleides. Since the solar UV irradiance has no long-term trend, the mechanism for the secular change of TSI must differ from the effect of surface magnetism, as manifested by sunspots, faculae, and network which indeed explain well the intra-cycle variability of both total and spectral irradiance. The long-term trend of TSI is most probably caused by a global temperature change of the Sun that does not influence the UV irradiance in the same way as the surface magnetic fields.
Published: 05 November 2009

Executive Summary of the mission study by EADS Astrium (Reference: MP.ASU.ES).

The Marco Polo Assessment Study under ESA contract led by Astrium Ltd has focused on an ESA-defined scenario, defining a feasible mission architecture for the mission and providing preliminary designs for the spacecraft and Earth Re-entry Capsule. Trade-offs have been carried out to determine the optimum launch and transfer strategy, proximity operations, and return strategy. In parallel the key-technologies for the mission have been assessed and the development requirements identified.

Published: 02 November 2009
Reference: SRE-PA/2009.069/Marco-Polo

This technical review report for the Marco Polo candidate mission presents the outcome of ESA's internal review of this M-class candidate mission in the Cosmic Vision 2015-2025 plan. The review was concluded at the end of the mission assessment phase and carried out in frame of the down-selection to 3 or 4 M-class missions, which will proceed to the definition phase. The main goal of this internal review was to identify the mission's critical issues and associated risks at technical, programmatic and financial level.

Published: 30 October 2009
The numerical simulations of the model equation governing the nonlinear dynamics of kinetic Alfvén waves in the intermediate-beta plasmas are performed. When the nonlinearity arises due to the ponderomotive force driven density perturbations of kinetic Alfvén waves, the model equation turns out to be a modified nonlinear Schrödinger equation. This has been solved numerically by using appropriate boundary conditions. The coherent, damped magnetic filaments with turbulent spectra have been observed. Our results reveal the interesting change in spectral index because of the damping effect. The steeper power spectra follow ~k-3.4 scaling. Using the Fokker-Planck equation with the new velocity space diffusion coefficient, we find the distribution function of energetic electrons in these turbulent structures. These turbulent structures can be responsible for plasma heating in Earth's magnetosphere.
Published: 28 October 2009

This A&A special issue is devoted to the CoRoT (Convection, Rotation & planetary Transits) space mission. Launched on 27 December 2006, the satellite moves in a polar circular orbit, and the CCD camera of its 27-cm telescope measures stellar-brightness variations with µmag precision in equatorial fields close to the galactic plane.

The main science goals of CoRoT are to discover exoplanets by the transit method and detect seismic waves in stars across the entire Hertzsprung-Russell diagram. Objectives also include the study of stellar activity, stellar rotation, and eclipsing multiple systems.The first results obtained with CoRoT in all these scientific areas are discussed in the pages of this special issue.

Published: 23 October 2009
The solar wind interaction with a planetary atmosphere produces a magnetosphere-like structure near the planet whether or not the planet has an intrinsic global magnetic field. In the case of planets like Venus or Mars, which have no global intrinsic magnetic field but possess a significant atmosphere, a magnetosphere is induced in the highly conducting ionosphere by the time-varying magnetic field carried by the solar wind. The induced magnetosphere at Venus and Mars is almost a "permanent" feature of the solar wind interaction. Here we report a Venus Express observation of the absence of the dayside part of the induced magnetosphere, when the interplanetary magnetic field (IMF) is nearly aligned with the solar wind flow. Using MHD simulations for this extreme IMF orientation, we examine the global interaction of the solar wind with Venus when the magnetic barrier disappears. Furthermore, we estimate the atmospheric loss under this extreme situation. While this solar wind aligned IMF interaction with a planet case is presently rare, and even rarer over solar system history, it might be an appropriate analogue of the interaction of a stellar wind with close-in exoplanet. Thus the solar wind interaction with Venus under this extreme condition might provide us a natural laboratory for studying the evolution of the atmospheres of "hot Jupiters" as well as close-in "terrestrial" planets.
Published: 27 October 2009
LISA Pathfinder (formerly known as SMART-2) is an ESA mission designed to pave the way for the joint ESA/NASA Laser Interferometer Space Antenna (LISA) mission by testing in-flight the critical technologies required for spaceborne gravitational wave detection; it will put two test masses in a nearperfect gravitational free fall, and control and measure their motion with an unprecedented accuracy. This is achieved through technology comprising inertial sensors, high-precision laser metrology, drag-free control and an ultraprecise micro-Newton propulsion system. The LISA Pathfinder mission is now in Phase C/Dthe Implementation Phase, and is due to be launched in 2010, with results on the performance of the system being available within 6 months thereafter.
Published: 08 June 2008
To investigate the universality of magnetic turbulence in space plasmas, we analyze seven time periods in the free solar wind under different plasma conditions. Three instruments on Cluster spacecraft operating in different frequency ranges give us the possibility to resolve spectra up to 300 Hz. We show that the spectra form a quasiuniversal spectrum following the Kolmogorov's law ~k-5/3 at MHD scales, a ~k-2.8 power law at ion scales, and an exponential ~exp[-sqrt(k rhoe)] at scales k rhoe~[0.1,1], where rhoe is the electron gyroradius. This is the first observation of an exponential magnetic spectrum in space plasmas that may indicate the onset of dissipation. We distinguish for the first time between the role of different spatial kinetic plasma scales and show that the electron Larmor radius plays the role of a dissipation scale in space plasma turbulence.
Published: 15 October 2009
Strong interplanetary shock interactions with the Earth's magnetosphere have great impacts on energetic particle dynamics in the magnetosphere. An interplanetary shock on 7 November 2004 (with the maximum solar wind dynamic pressure of ~70 nPa) was observed by the Cluster constellation to induce significant ULF waves in the plasmasphere boundary, and energetic electrons (up to 2 MeV) were almost simultaneously accelerated when the interplanetary shock impinged upon the magnetosphere. In this paper, the relationship between the energetic electron bursts and the large shock-induced ULF waves is studied. It is shown that the energetic electrons could be accelerated and decelerated by the observed ULF wave electric fields, and the distinct wave number of the poloidal and toroidal waves at different locations also indicates the different energy ranges of electrons resonating with these waves. For comparison, a rather weak interplanetary shock on 30 August 2001 (dynamic pressure ~2.7 nPa) is also investigated. It is found that interplanetary shocks or solar wind pressure pulses with even small dynamic pressure change can have a nonnegligible role in the radiation belt dynamics.
Published: 11 October 2009
This document is the Cross-Scale proposal submitted to ESA in response to the March 2007 "Cosmic Vision 2015-2025 Call for Proposals". It includes descriptions of the scientific objectives, mission profile, payload, spacecraft considerations, science operations and archiving, technology, programmatics and costs, communications and outreach of Cross-Scale.
Published: 29 June 2007
BepiColombo is an interdisciplinary mission to explore Mercury, the planet closest to the sun, carried out jointly between the European Space Agency and the Japanese Aerospace Exploration Agency. From dedicated orbits two spacecraft will be studying the planet and its environment. The scientific payload of both spacecraft will provide the detailed information necessary to understand the origin and evolution of the planet itself and its surrounding environment. The scientific objectives focus on a global characterization of Mercury through the investigation of its interior, surface, exosphere and magnetosphere. In addition, instrumentation onboard BepiColombo will be used to test Einstein's theory of general relativity. Major effort was put into optimizing the scientific return of the mission by defining a payload complement such that individual measurements can be interrelated and complement each other. This paper gives an in-depth overview of BepiColombo spacecraft composite and the mission profile. It describes the suite of scientific instruments on board of the two BepiColombo spacecraft and the science goals of the mission.
Published: 15 January 2010
The nonlinear kinetic theory is presented for the ion acoustic perturbations at the foot of the Earth's quasiperpendicular bow shock, that is characterized by weakly magnetized electrons and unmagnetized ions. The streaming ions, due to the reflection of the solar wind ions from the shock, provide the free energy source for the linear instability of the acoustic wave. In the fully nonlinear regime, a coherent localized solution is found in the form of a stationary ion hump, which is traveling with the velocity close to the phase velocity of the linear mode. The structure is supported by the nonlinearities coming from the increased population of the resonant beam ions, trapped in the self-consistent potential. As their size in the direction perpendicular to the local magnetic field is somewhat smaller that the electron Larmor radius and much larger that the Debye length, their spatial properties are determined by the effects of the magnetic field on weakly magnetized electrons. These coherent structures provide a theoretical explanation for the bipolar electric pulses, observed upstream of the shock by Polar and Cluster satellite missions.
Published: 06 October 2009
Reference: SRE/PA/2009/068

This technical review report for the Cross-Scale candidate mission presents the outcome of ESA's internal review of this M-class candidate mission in the Cosmic Vision 2015-2025 plan. The review was concluded at the end of the mission assessment phase and carried out in frame of the down-selection to 3 or 4 M-class missions, which will proceed to the definition phase. The main goal of this internal review was to identify the mission's critical issues and associated risks at technical, programmatic and financial level.

Published: 06 October 2009
Reference: SRE-PA/2009/90

This technical review report for the Solar Orbiter candidate mission presents the outcome of ESA's internal review of this M-class candidate mission in the Cosmic Vision 2015-2025 plan. The review was concluded at the end of the mission assessment phase and carried out in frame of the down-selection to 3 or 4 M-class missions, which will proceed to the definition phase. The main goal of this internal review was to identify the mission's critical issues and associated risks at technical, programmatic and financial level.

Note: This report has been superseded by the Solar Orbiter definition study report (Red Book), released in July 2011, which is linked from the right-hand menu.
Published: 01 October 2009
The Earth's magnetosphere is populated by particles originating from the solar wind and the terrestrial ionosphere. A substantial fraction of the plasma from these sources are convected through the magnetotail lobes. In this paper, we present a statistical study of convective plasma transport through the Earth's magnetotail lobes for various geomagnetic conditions. The results are based on a combination of density measurements from the Electric Field and Waves Experiment (EFW) and convection velocities from the Electron Drift Instrument (EDI) on board the Cluster spacecraft. The results show that variations in the plasma flow is primarily attributed to changes in the convection velocity, whereas the plasma density remains fairly constant and shows little correlation with geomagnetic activity. During disturbed conditions there is also an increased abundance of heavier ions, which combined with enhanced convection, cause an accentuation of the mass flow. The convective transport is much slower than the field aligned transport. A substantial amount of plasma therefore escape downtail without ever reaching the central plasma sheet.
Published: 29 September 2009
12-Apr-2024 18:10 UT

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