Publication archive

Publication archive

Jets of water ice from surface fractures near the south pole of Saturn's icy moon Enceladus produce a plume of gas and particles. The source of the jets may be a liquid water region under the ice shell - as suggested most recently by the discovery of salts in E-ring particles derived from the plume - or warm ice that is heated, causing dissociation of clathrate hydrates. Here we report that ammonia is present in the plume, along with various organic compounds, deuterium and, very probably, 40Ar. The presence of ammonia provides strong evidence for the existence of at least some liquid water, given that temperatures in excess of 180 K have been measured near the fractures from which the jets emanate. We conclude, from the overall composition of the material, that the plume derives from both a liquid reservoir (or from ice that in recent geological time has been in contact with such a reservoir) as well as from degassing, volatile-charged ice.
Published: 24 July 2009
In this article, we study the velocity distribution, density, duration, and energy transport of earthward flow bursts in the inner plasma sheet (IPS) during three substorm phases using the data of Cluster in 2001 and 2002. The mean peak velocity of earthward flow bursts in recovery phases (390 km/s) is smaller than those in growth and expansion phases (490 and 520 km/s). The super earthward flow bursts (V > 1000 km/s) appear more frequently in the expansion phase. The average ion density of earthward flow bursts in the recovery phase is 0.14 cm-3, much smaller than those in growth and expansion phases (0.28 and 0.21 cm-3), indicating that lobe reconnections most likely occur in the recovery phase. The average durations of earthward flow bursts in recovery phase are 48 s, smaller than those in growth and expansion phases (99 and 103 s), suggesting that the reconnections occurring in recovery phase are rather short-lived. The earthward flow bursts in the expansion phase have largest capability of the transport of energy, about 7 times that in the recovery phase. Thus the earthward flow bursts in the expansion phase can produce largest impact effects to the inner magnetosphere.
Published: 17 July 2009
Edited by Dr. Angelo Pio Rossi and Dr. Olivier Witasse. This Special Issue of Planetary and Space Science contains 15 papers; the majority of which were presented at the European Mars Science and Exploration Conference (EMSEC) - Mars Express & ExoMars. There are several geoscience-related contributions covering volcanic, hydrologic, stratigraphic and geomorphologic investigations. The EMSEC conference was held 12-16 November 2007 at ESA ESTEC, Noordwijk, The Netherlands (see right-hand menu for conference programme).
Published: 16 July 2009
Executive Summary of the mission study by EADS Astrium (Ref: CS.ASU.TN.ES). Cross-Scale is a mission that both builds on the advances from previous spacecraft missions like Cluster and also pushes the frontiers of knowledge in terms of magnetospheric dynamics, energy processes and couplings across different spatial and temporal scales. This is done by simultaneously measuring a minimum of two plasma scales (electron and ion scales in year 1 and then ion and fluid scales afterwards) with 7 spacecraft in two nested tetrahedral constellations (with a common apex), over a 5 year period. This document provides a concise summary of the findings from the ESA contract awarded to the Astrium Ltd study team, for the "System Design of the Cross-Scale Mission".
Published: 04 July 2009
Executive Summary of the mission study by the consortium led by Thales Alenia Space, including Deimos and OHB (Ref: CS-TAS-TN-100350224F). The Consortium led by Thales Alenia Space, including Deimos and OHB, has completed the Assessment Phase contract "System Design of the Cross-Scale Mission" awarded by ESA. The expertise of the Consortium has allowed analysing the requirements, trading options extensively and selecting a baseline design that has been defined in detail and justified by a comprehensive set of analyses. The robust solution not only fully complies with the requirements, but also implements high TRL and strong design-to-schedule dispositions that lead to safer programmatics, to the maximization of the mass production effect and to the mastery of costs. The technical, schedule and cost elements produced will enable ESA to assess the Cross-Scale Mission in the frame of its Cosmic Vision selection process.
Published: 04 July 2009
Ultraluminous X-ray sources are extragalactic objects located outside the nucleus of the host galaxy with bolometric luminosities exceeding 1039 erg s-1. These extreme luminosities - if the emission is isotropic and below the theoretical (Eddington) limit, where the radiation pressure is balanced by the gravitational pressure - imply the presence of an accreting black hole with a mass of ~ 10²-105 solar masses. The existence of such intermediate-mass black holes is in dispute, and though many candidates have been proposed, none are widely accepted as definitive. Here we report the detection of a variable X-ray source with a maximum 0.2-10 keV luminosity of up to 1.1 x 1042 erg s-1 in the edge-on spiral galaxy ESO 243-49, with an implied conservative lower limit for the mass of the black hole of 500 solar masses.
Published: 03 July 2009
The number and complexity of systems that control Space Science Missions continues to increase. As a result, it is desirable to improve the efficiency of these systems and, in particular, their performance and their productivity. In this paper, we set out a strategy to achieve this goal. In order to talk about improving the Performance and Productivity of a system we need to discuss the functional architecture of the system. In order to make progress, our strategy is to develop a generic methodology that decomposes the functional architecture of a Space Science Mission System and uses this decomposition to identify areas where improvements can be made. This paper concentrates on the decomposition of one specific component, namely the Plan Management System. The purpose of the Plan Management System is to produce an operation plan that contains the directives that will operate the various nodes, i.e. physical parts, of the system such as the ground stations, the spacecraft, the instruments, or even human beings (when these are following specific instructions). In order to be generic, the decomposition of the Plan Management System must make no assumptions about the purpose and implementation choices that must ultimately be made. In order to describe a functional architecture, it must also make no assumptions about the nature and purpose of the nodes that the system will operate or the nodes on which it will run. In particular, it makes no assumptions as to whether the execution of the Plan Management System components is manual or automated or whether the functions will be executed on the ground or in space. -- Remainder of abstract is truncated --
Published: 02 June 2009
Saturn's moon Enceladus emits plumes of water vapour and ice particles from fractures near its south pole, suggesting the possibility of a subsurface ocean. These plume particles are the dominant source of Saturn's E ring. A previous in situ analysis of these particles concluded that the minor organic or siliceous components, identified in many ice grains, could be evidence for interaction between Enceladus' rocky core and liquid water. It was not clear, however, whether the liquid is still present today or whether it has frozen. Here we report the identification of a population of E-ring grains that are rich in sodium salts (0.5-2% by mass), which can arise only if the plumes originate from liquid water. The abundance of various salt components in these particles, as well as the inferred basic pH, exhibit a compelling similarity to the predicted composition of a subsurface Enceladus ocean in contact with its rock core. The plume vapour is expected to be free of atomic sodium. Thus, the absence of sodium from optical spectra is in good agreement with our results. In the E ring the upper limit for spectroscopy is insufficiently sensitive to detect the concentrations we found.
Published: 26 June 2009
The first meeting of the Fundamental Physics Roadmap Advisory Team was held on 2-3 June 2009. This report was prepared by the Chair and Secretary of the FPR-AT.
Published: 23 June 2009
Venus Express is the first European (ESA) mission to the planet Venus. Its main science goal is to carry out a global survey of the atmosphere, the plasma environment, and the surface of Venus from orbit. The payload consists of seven experiments. It includes a powerful suite of remote sensing imagers and spectrometers, instruments for in-situ investigation of the circumplanetary plasma and magnetic field, and a radio science experiment. The spacecraft, based on the Mars Express bus modified for the conditions at Venus, provides a versatile platform for nadir and limb observations as well as solar, stellar, and radio occultations. In April 2006 Venus Express was inserted in an elliptical polar orbit around Venus, with a pericentre height of ~250 km and apocentre distance of ~66000 km and an orbital period of 24 hours. The nominal mission lasted from June 4, 2006 till October 2, 2007, which corresponds to about two Venus sidereal days. Here we present an overview of the main results of the nominal mission, based on a set of papers recently published in Nature, Icarus, Planetary and Space Science, and Geophysical Research Letters.
Published: 23 June 2009
Seismology of stars provides insight into the physical mechanisms taking place in their interior, with modes of oscillation probing different layers. Low-amplitude acoustic oscillations excited by turbulent convection were detected four decades ago in the Sun and more recently in low-mass main-sequence stars. Using data gathered by the Convection Rotation and Planetary Transits mission, we report here on the detection of solar-like oscillations in a massive star, V1449 Aql, which is a known large-amplitude (beta Cephei) pulsator.
Published: 20 June 2009
In proceedings of the International Conference 'Future perspectives of space plasma and particle instrumentation and international collaborations', held 1-3 November 2006 in Tokyo, Japan.

Using electron and magnetic field data obtained from the Cluster satellites, we identify the spatial distribution of highly accelerated electron distributions up to 10 keV. They are generally isotropic and form flat-top distributions in the phase space. These distributions are observed in the vicinity of the X line associated with the quadrupole-like magnetic field and energetic ions, throughout the plasma sheet. In some cases, these distributions are quasi-stable, continuously observed for a few minutes with a stable Bz polarity and low current density in the center of the plasma sheet.

Published: 17 June 2009
In proceedings of the International Conference 'Future perspectives of space plasma and particle instrumentation and international collaborations', held 1-3 November 2006 in Tokyo, Japan.

With Cluster observations in the magnetotail, we study the dynamics of plasma sheet thinning and stretching in a typical growth phase event of September 12, 2001. The thinning and stretching proceed in parallel, with transient variations. The pre-onset value is Bz~1.5 nT, J~8 nA/m2. The current density increase is not accompanied with a corresponding number density increase. A large (>5 nT) guide field along the cross-tail current direction was registered. An embedded current sheet structure was detected and, therefore, caution is required if making thickness estimations.

Published: 17 June 2009
This ESA special publication is dedicated to the scientific investigations of Mars by Mars Express, giving a detailed overview of the scientific results of the mission so far.


Mars Express: Summary of Scientific Results
A. Chicarro, O.G. Witasse & A.P. Rossi
Scientific Instruments
HRSC: High Resolution Stereo Camera
G. Neukum, R. Jaumann and the Co-Investigator Team
OMEGA: Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité
J.-P. Bibring, Y. Langevin, F. Altieri et al.
MARSIS: Mars Advanced Radar for Subsurface and Ionospheric Sounding
J.J. Plaut, G. Picardi, T.W. Watters et al.
PFS: Planetary Fourier Spectrometer
V. Formisano, F. Angrilli, G. Arnold et al.
SPICAM: Spectroscopy for the Investigation of the Characteristics of the Atmospheric of Mars
J.-L. Bertaux, O. Korablev, D. Fonteyn et al.
ASPERA-3: Analyser of Space Plasmas and Energetic Neutral Atoms
R. Lundin, S. Barabash and the ASPERA-3 team
MaRS: Mars Express Radio Science Experiment
M. Pätzold, S. Tellmann, T. Andert et al.
Operations and Archiving
Mars Express Science Planning and Operations
R. Pischel & T. Zegers
Spacecraft and Payload Data Handling
J. Zender, F. Delhaise, C. Arviset et al.
Acronyms and Abbreviations279

Published: 16 June 2009
We report the first direct determination of the dissipation range of magnetofluid turbulence in the solar wind at the electron scales. Combining high resolution magnetic and electric field data of the Cluster spacecraft, we computed the spectrum of turbulence and found two distinct breakpoints in the magnetic spectrum at 0.4 and 35 Hz, which correspond, respectively, to the Doppler-shifted proton and electron gyroscales, frho_p and frho_e. Below frho_p, the spectrum follows a Kolmogorov scaling f -1.62, typical of spectra observed at 1 AU. Above frho_p, a second inertial range is formed with a scaling f -2.3 down to frho_e. Above frho_e, the spectrum has a steeper power law ~f 4.1 down to the noise level of the instrument. We interpret this as the dissipation range and show a remarkable agreement with theoretical predictions of a quasi-two-dimensional cascade into Kinetic Alfvén Waves (KAW).
Published: 11 June 2009
This paper presents a study of the use of a one-dimensional Vlasov Hybrid Simulation (VHS) computer code to simulate the dynamical spectra (i.e. frequency versus time spectrograms) of ELF/VLF chorus signals (from ~a fraction to ~10 kHz). Recently excellent measurements of chorus have been made in the source region close to the geomagnetic equator aboard the four spacecraft Cluster mission. Using Cluster data for wave amplitude, which is up to 300 pT, local gyrofrequency, cold plasma density, and L-shell, observed chorus signals are reproduced with remarkable fidelity and, in particular, sweep rates in the range 1-10 kHz result as observed. Further, we find that the sweep rate is a falling function of increasing cold plasma density, again in accord with observations. Finally, we have satisfactorily simulated the rather rare falling frequency elements of chorus which are sometimes observed aboard Cluster in the generation region. For both rising and falling chorus we have presented detailed structural analyses of the generation regions. The main contributor to the frequency sweep rate is primarily the establishment of wave number/frequency gradients across the generation region by the out of phase component of the resonant particle current. The secondary contributor is the shortening of the wavelength of resonant particle current relative to that of the wave field. In view of the close agreement between observation and simulation, we conclude that nonlinear electron cyclotron resonance is indeed the mechanism underlying the generation of chorus signals just outside the plasmasphere.
Published: 09 June 2009
We present results from a 40 ks XMM-Newton observation of the X-ray filament coincident with the southeast edge of the Centaurus A Northern Middle Radio Lobe (NML). We find that the X-ray filament consists of five spatially resolved X-ray knots embedded in a continuous diffuse bridge. The spectrum of each knot is well fitted by a thermal model with temperatures ranging from 0.3 to 0.7 keV and subsolar elemental abundances. In four of the five knots, nonthermal models are a poor fit to the spectra, conclusively ruling out synchrotron or IC/CMB mechanisms for their emission. The internal pressures of the knots exceed that of the ambient interstellar medium or the equipartition pressure of the NML by more than an order of magnitude, demonstrating that they must be short lived (~3 × 106 yr). Based on energetic arguments, it is implausible that these knots have been ionized by the beamed flux from the active galactic nucleus of Cen A or that they have been shock heated by supersonic inflation of the NML. In our view, the most viable scenario for the origin of the X-ray knots is that they are the result of cold gas shock heated by a direct interaction with the jet. The most plausible model of the NML is that it is a bubble from a previous nuclear outburst that is being re-energized by the current outburst. The northeast inner lobe and the large-scale jet are lossless channels through which the jet material rapidly travels to the NML in this scenario. We also report the discovery of a large-scale (at least 35 kpc radius) gas halo around Cen A.
Published: 06 June 2009
Clouds on Titan result from the condensation of methane and ethane and, as on other planets, are primarily structured by circulation of the atmosphere. At present, cloud activity mainly occurs in the southern (summer) hemisphere, arising near the pole and at mid-latitudes from cumulus updrafts triggered by surface heating and/or local methane sources, and at the north (winter) pole, resulting from the subsidence and condensation of ethane-rich air into the colder troposphere. General circulation models predict that this distribution should change with the seasons on a 15-year timescale, and that clouds should develop under certain circumstances at temperate latitudes (40°) in the winter hemisphere. The models, however, have hitherto been poorly constrained and their long-term predictions have not yet been observationally verified. Here we report that the global spatial cloud coverage on Titan is in general agreement with the models, confirming that cloud activity is mainly controlled by the global circulation. The non-detection of clouds at latitude 40° N and the persistence of the southern clouds while the southern summer is ending are, however, both contrary to predictions. This suggests that Titan's equator-to-pole thermal contrast is overestimated in the models and that its atmosphere responds to the seasonal forcing with a greater inertia than expected.
Published: 05 June 2009
Hot Jupiters are a class of extrasolar planet that orbit their parent stars at very short distances. They are expected to be tidally locked, which can lead to a large temperature difference between their daysides and nightsides. Infrared observations of eclipsing systems have yielded dayside temperatures for a number of transiting planets. The day-night contrast of the transiting extrasolar planet HD 189733b was 'mapped' using infrared observations. It is expected that the contrast between the daysides and nightsides of hot Jupiters is much higher at visual wavelengths, shorter than that of the peak emission, and could be further enhanced by reflected stellar light. Here we report the analysis of optical photometric data obtained over 36 planetary orbits of the transiting hot Jupiter CoRoT-1b. The data are consistent with the nightside hemisphere of the planet being entirely black, with the dayside flux dominating the optical phase curve. This means that at optical wavelengths the planet's phase variation is just as we see it for the interior planets in the Solar System. The data allow for only a small fraction of reflected light, corresponding to a geometric albedo of <0.20.
Published: 29 May 2009
Since the discovery of the first broad iron-K line in 1995 from the Seyfert Galaxy MCG 6-30-15, broad iron-K lines have been found in several other Seyfert galaxies, from accreting stellar mass black holes and even from accreting neutron stars. The iron-K line is prominent in the reflection spectrum created by the hard X-ray continuum irradiating dense accreting matter. Relativistic distortion of the line makes it sensitive to the strong gravity and spin of the black hole. The accompanying iron-L line emission should be detectable when the iron abundance is high. Here we report the first discovery of both iron-K and L emission, using XMM-Newton observations of the Narrow-Line Seyfert 1 Galaxy 1H 0707-495. The bright Fe-L emission has enabled us, for the first time, to detect a reverberation lag of 30 s between the direct X-ray continuum and its reflection from matter falling into the hole. The observed reverberation timescale is comparable to the light-crossing time of the innermost radii around a supermassive black hole. The combination of spectral and timing data on 1H 0707-495 provides strong evidence that we are witnessing emission from matter within a gravitational radius, or a fraction of a light-minute, from the event horizon of a rapidly-spinning, massive black hole.
Published: 29 May 2009
27-May-2024 18:07 UT

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