Publication archive

Publication archive

The spectral reflectivity of asteroid surfaces over the wavelength range of 0.3 to 1.1 micron can be used to classify these objects into several broad groups with similar spectral characteristics. The three most recently developed taxonomies group the asteroids into 9, 11, or 14 different clases, depending on the technique used to perform the analysis. The distribution of the taxonomic classes shows that darker and redder objects become more dominant at larger heliocentric distances, while the rare asteroid types are found more frequently among the small objects of the planet-crossing population.
Published: 01 January 1989

Beyond their intrinsic interest, ground-based observations have proven their usefulness in supporting spacecraft observations of Solar System bodies. Probably the most spectacular illustration ever was provided during the descent of the Huygens Probe on Titan, when the radio astronomy segment detected the "channel A" carrier signal from Huygens and allowed the recovery of the Doppler Wind Experiment that had been compromised by the failure of the corresponding Cassini channel (Lebreton et al., 2005). Furthermore, ground-based science observations performed during or around the Huygens mission provided new, complementary information on Titan's atmosphere and surface, helping to put the Huygens observations into context (Witasse et al., 2006). Another example of a successful ground-based campaign is the Deep Impact event, when numerous Earth-based and Earth-orbiting observatories monitored comet 9P/Tempel 1 when it was hit by the impactor (Meech et al., 2005).

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Published: 16 August 2008
This Cross-Scale summary report provides a summary of the system design study carried out by industry (Deimos Space S.L. as prime, Thales Alenia Space and ONERA as sub-contractors) under ESA contract between May 2006 and June 2007. The first phase of the system design study consisted of a mission architecture trade. Key trades on the mission architecture included orbits, number of spacecraft, payload suites, deployment strategy, and orbit optimization. The second phase consisted of an assessment of the spacecraft design, ground segment requirements and programmatics.
Published: 06 December 2007
An important problem in space physics still not understood well is how the solar wind enters the Earth's magnetosphere. Evidence is presented that transient solar wind particles produced by solar disturbances can appear in the Earth's mid-altitude (~5 RE geocentric) cusps with densities nearly equal to those in the magnetosheath. That these are magnetosheath particles is established by showing they have the same "flattop" electron distributions as magnetosheath electrons behind the bow shock. The transient ions are moving parallel to the magnetic field (B) toward Earth and often coexist with ionospheric particles that are flowing out. The accompanying waves include electromagnetic and broadband electrostatic noise emissions and Bernstein mode waves. Phase-space distributions show a mixture of hot and cold electrons and multiple ion species including field-aligned ionospheric O+ beams.
Published: 12 August 2008
This paper reports for the first time the identification of a magnetic structure around a magnetic null in a magnetic reconnection region in the magnetotail. Magnetic reconnection is one of the fundamental processes in astrophysical and solar-terrestrial plasmas. Though the concept of reconnection has been studied for many years, the process that really occurs has not been fully revealed by direct measurements. In particular, the lack of a description of three-dimensional (3-D) reconnecting magnetic field from observations makes the task more difficult. The Cluster spacecraft array provide an opportunity to reconstruct the 3-D magnetic reconnection structure based on magnetic field vectors simultaneously measured at four positions. The identification of this structure comes from a new method of analysis of in situ measurements proposed here. Applying a fitting model of 10 spherical harmonic functions and a Harris current sheet function, plus a constant field, we reconstruct a 3-D magnetic field configuration around the magnetic null in an reconnection event observed by Cluster in the geo-magnetotail.
Published: 09 August 2008
Magnetic reconnection is an important process in astrophysical, space and laboratory plasmas. The magnetic null pair structure is theoretically suggested to be a crucial feature of the three-dimensional magnetic reconnection. The physics around the null pair, however, has not been explored in combination with the magnetic field configuration deduced from in situ observations. Here, we report the identification of the configuration around a null pair and simultaneous electron dynamics near one null of the pair, observed by four Cluster spacecraft in the geo-magnetotail. Further, we propose a new scenario of electron dynamics in the null region, suggesting that electrons are temporarily trapped in the central reconnection region including electron diffusion region resulting in an electron density peak, accelerated possibly by parallel electric field and electron pressure gradient, and reflected from the magnetic cusp mirrors leading to the bi-directional energetic electron beams, which excite the observed high frequency electrostatic waves.
Published: 30 July 2008
Plasmaspheric plumes have been routinely observed by the four Cluster spacecraft. This paper presents a statistical analysis of plumes observed during five years (from 1 February 2001 to 1 February 2006) based on four-point measurements of the plasmasphere (outside 4 Earth radii) as it is sampled by the spacecraft in a narrow local time sector before and after perigee. Plasmaspheric plumes can be identified from electron density profiles derived from the electron plasma frequency determined by the WHISPER wave sounder onboard Cluster. As the WHISPER instrument has a limited frequency range (2-80 kHz) only plumes with densities below 80 cm-3 can be identified in this way. Their occurrence is studied as a function of several geomagnetic indices (Kp, am and Dst). Their transverse equatorial size, magnetic local time distribution, L position and density variation are discussed. Plasmaspheric plumes are observed mostly for moderate Kp and never for small Dst. They are found mainly in the afternoon and pre-midnight MLT sectors. Comparisons are also made between the density profiles of the plumes as they are crossed on the in- and outbound legs of the orbit, before and after perigee crossing, respectively.
Published: 07 August 2008
The fraction of stellar mass contained in globular clusters (GCs), also measured by number as the specific frequency, is a fundamental quantity that reflects both a galaxy's early star formation and its entire merging history. We present specific frequencies, luminosities, and mass fractions for the globular cluster systems of 100 early-type galaxies in the ACS Virgo Cluster Survey, the largest homogeneous catalog of its kind.

[This is an extract of the original abstract.]
Published: 02 June 2008
Intermittency is usually identified in turbulent flows as non-Gaussian tails of the probability density functions (PDFs) of the turbulent field derivatives. Here we investigate the role of phase coherence among the Fourier modes in creating intermittency in magnetized space plasmas using the technique of surrogate data. We apply the technique to two examples: (i) synthetic data and (ii) magnetic field fluctuations recorded in the terrestrial magnetosheath by the Cluster spacecraft. We use a set of four series of data, one observed and three surrogate, and their PDFs and moments (q<=4) as discriminating statistics. We show that the technique allows for detecting coherent structures and estimating their scales. We show furthermore that the phases, but not the amplitudes, create the non-Gaussian tails of the PDFs. We show also that the surrogate data used cannot account for asymmetries of the PDFs of the observed data. This enables us to confirm a scenario of turbulent cascade of mirror structures proposed in previous publications, by showing the existence of an approximately constant energy flux in the inertial range.
Published: 06 August 2008
We present detailed measurements of ion scale vortices of drift type coupled to Alfvén waves in an inhomogeneous and collisionless space magnetoplasma. The two free parameters of a dipolar vortex, intensity and spatial radius, are measured. The vortices are driven by a strong density gradient on a boundary layer with scale size of the same order as the vortex diameter. Observations of vortices off the gradient show that symmetry-breaking conditions in a real inhomogeneous plasma can lead not only to cross-field but also to cross-boundary anomalous transport of particles and energy.
Published: 05 August 2008
From June 1, 2004 to October 31, 2006, a total 465 high-speed flow events are observed by the TC-1 satellite in the near-Earth region (-13 RE < x < -9 RE, |Y|<10 RE, |Z|<5 RE). Based on the angle between the flow and the magnetic field, the high-speed flow events are further divided into two types, that is, field-aligned high-speed flow (FAHF) in the plasma sheet boundary and convective bursty bulk flow (BBF) in the center plasma sheet. Among the total 465 high-speed flow events, there are 371 FAHFs, and 94 BBFs. The CHF are mainly concentrated in the plasma sheet, the intersection angle between the flow and the magnetic field is larger, the magnetic field intensity is relatively weak. The FHF are mainly distributed near the boundary layer of the plasma sheet, the intersection angle between the flow and magnetic field is smaller, and the magnetic field intensity is relatively strong. The convective BBFs have an important effect on the substorm.
Published: 03 August 2008
ESA's report to the 37th COSPAR meeting (13-20 July 2008) covers the missions of the Science Programme of ESA. This section contains the report on the LISA Pathfinder mission.
Published: 02 July 2008
The present issue of Spatium is devoted to solar magnetism. Baffled by the thought that a hot gaseous Sun should have a magnetic field, such ideas came up only very late. It was George Ellery Hale who suggested solar magnetism in 1908. This edition of Spatium is a written version of the fascinating public lecture that was held by Professor Eugene Parker at the University of Bern on 23 January 2008, as part of the ISSI workshop on solar magnetism.
Published: 02 July 2008
Titan was once thought to have global oceans of light hydrocarbons on its surface, but after 40 close flybys of Titan by the Cassini spacecraft, it has become clear that no such oceans exist. There are, however, features similar to terrestrial lakes and seas, and widespread evidence for fluvial erosion, presumably driven by precipitation of liquid methane from Titan's dense, nitrogen-dominated atmosphere. Here we report infrared spectroscopic data, obtained by the Visual and Infrared Mapping Spectrometer (VIMS) on board the Cassini spacecraft, that strongly indicate that ethane, probably in liquid solution with methane, nitrogen and other low-molecular-mass hydrocarbons, is contained within Titan's Ontario Lacus.
Published: 01 August 2008
"Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation". Edited by Atad-Ettedgui, Eli; Lemke, Dietrich. Proceedings of the SPIE, Volume 7018, pp. 70180R-70180R-13 (2008)

The NIRSpec OA (optical assembly) design largely relies on SiC components. The properties of the SiC material and very tight stability budgets required a dedicated development process. Starting from validation of design principles by breadboard testing, this paper describes the development process up to the SM test of the NIRSpec optical assembly. From breadboard testing the design of the mounting interface was established. The test programme also included gluing processes, torque free mounting of mirrors and verification of stability of friction joints. The basic design rules for the mirrors to cope with distortion of mirror surfaces due to bi-metallic bending effects and flatness deficiencies were derived. A modular design using 3 TMAs (Three Mirror Anastigmats) was followed for the OA. From the overall design, budget allocations and design loads for the TMAs were determined. The detailed design process was then driven by distortion budget allocations derived from optical analysis. Due to stringent stability requirements and high mechanical loads, most elements needed several design iterations to meet the budget allocations. Finally, distortions and displacements of the optical elements under the predictable in-orbit conditions were calculated and used in the optical model. The effects can be partially compensated by adjustment. The budget allocation was then revised to account for non-predictable effects only.
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Published: 26 July 2008
In "Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation", edited by Eli Atad-Ettedgui, Dietrich Lemke, Proc. of SPIE Vol. 7018, 701823, (2008), doi: 10.1117/12.789148

The JWST Mid-Infrared Instrument (MIRI) is designed to meet the JWST science requirements for mid-IR capabilities and includes an Imager MIRIM provided by CEA (France). A double-prism assembly (DPA) allows MIRIM to perform low-resolution spectroscopy. The MIRIM DPA shall meet a number of challenging requirements in terms of optical and mechanical constraints, especially severe optical tolerances, limited envelope and very high vibration loads. The University of Cologne (Germany) and the Centre Spatial de Liege (Belgium) are responsible for design, manufacturing, integration, and testing of the prism assembly. A companion paper (Fischer et al. 2008) is presenting the science drivers and mechanical design of the DPA, while this paper is focusing on optical manufacturing and overall verification processes. The first part of this paper describes the manufacturing of Zinc-sulphide and Germanium prisms and techniques to ensure an accurate positioning of the prisms in their holder. (1) The delicate manufacturing of Ge and ZnS materials and (2) the severe specifications on the bearing and optical surfaces flatness and the tolerance on the prism optical angles make this process innovating. The specifications verification is carried out using mechanical and optical measurements; the implemented techniques are described in this paper. The second part concerns the qualification program of the double-prism assembly, including the prisms, the holder and the prisms anti-reflective coatings qualification. Both predictions and actual test results are shown.

Published: 26 July 2008
In "High Energy, Optical, and Infrared Detectors for Astronomy III", edited by David A. Dorn, Andrew D. Holland, Proc. of SPIE Vol. 7021, 70210O, (2008), doi: 10.1117/12.789606

The Mid-Infrared Instrument (MIRI) is a 5 to 28 micron imager and spectrometer that is slated to fly aboard the JWST in 2013. Each of the flight arrays is a 1024x1024 pixel Si:As impurity band conductor detector array, developed by RaytheonVision Systems. JPL, in conjunction with the MIRI science team, has selected the three flight arrays along with their spares. We briefly summarize the development of these devices, then describe the measured performance of the flight arrays along with supplemental data from sister flight-like parts.

Published: 25 July 2008
Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation. Edited by Atad-Ettedgui, Eli; Lemke, Dietrich. Proceedings of the SPIE, Volume 7018, pp. 70181Y-70181Y-15 (2008)

The James Webb Space Telescope (JWST) mission is a collaborative project between the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Canadian Space Agency (CSA) and is considered as the successor to the Hubble Space Telescope (HST). The European contribution consists in providing the Ariane 5 launcher and two out of the four instruments: a combined mid-infrared camera/spectrograph (MIRI) and a near infrared spectrograph (NIRSpec). This article will address the mechanical aspects of NIRSpec by providing an overview of the design drivers and the related solutions for the structure, the thermal design and the mechanisms so as to achieve the required stringent optical performances. The industrial set-up and the project development status will also be presented.

Published: 24 July 2008
Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation. Edited by Atad-Ettedgui, Eli; Lemke, Dietrich. Proceedings of the SPIE, Volume 7018, pp. 701821-701821-12 (2008)

The Grating and Filter Wheel Mechanisms of the JWST NIRSpec instrument allow for reconfiguration of the spectrograph in space in a number of NIR sub-bands and spectral resolutions. Challenging requirements need to be met simultaneously including high launch loads, the large temperature shift to cryo-space, high position repeatability and minimum deformation of the mounted optics. The design concept of the NIRSpec wheel mechanisms is based on the ISOPHOT Filter Wheels but with significant enhancements to support much larger optics. A well-balanced set of design parameters was to be found and a considerable effort was spent to adjust the hardware within narrow tolerances.

Published: 24 July 2008
High Energy, Optical, and Infrared Detectors for Astronomy III. Edited by Dorn, David A.; Holland, Andrew D. Proceedings of the SPIE, Volume 7021, pp. 702127-702127-12 (2008)

We present interim results from the characterization test development for the Detector Subsystem of the Near-Infrared Spectrograph (NIRSpec). NIRSpec will be the primary near-infrared spectrograph on the James Webb Space Telescope (JWST). The Detector Subsystem consists of a Focal Plane Assembly containing two Teledyne HAWAII-2RG arrays, two Teledyne SIDECAR cryogenic application specific integrated circuits, and a warm Focal Plane Electronics box. The Detector Characterization Laboratory at NASA's Goddard Space Flight Center will perform the Detector Subsystem characterization tests. In this paper, we update the initial test results obtained with engineering grade components.

Published: 23 July 2008
25-Oct-2020 20:26 UT

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