Publication archive

Publication archive

The downstream region of a collisionless quasiparallel shock is structured containing bulk flows with high kinetic energy density from a previously unidentified source. We present Cluster multispacecraft measurements of this type of supermagnetosonic jet as well as of a weak secondary shock front within the sheath, that allow us to propose the following generation mechanism for the jets: The local curvature variations inherent to quasiparallel shocks can create fast, deflected jets accompanied by density variations in the downstream region. If the speed of the jet is super(magneto)sonic in the reference frame of the obstacle, a second shock front forms in the sheath closer to the obstacle. Our results can be applied to collisionless quasiparallel shocks in many plasma environments.
Published: 20 April 2010
The questions of whether or not Venus is geologically active and how the planet has resurfaced over the last billion years have major implications for interior dynamics and climate change. Nine 'hot spots', areas analogous to Hawaii with volcanism, broad topographic rises, and large positive gravity anomalies suggesting mantle plumes at depth, have been identified as possibly active. This study uses variations in thermal emissivity of the surface by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on the ESA Venus Express spacecraft to identify compositional differences in lava flows at three hot spots. The anomalies are interpreted as a lack of surface weathering. We estimate the flows to be younger than 250 ky, and probably much younger, indicating that Venus is actively resurfacing.
Published: 09 April 2010
Document id: cR-SPO-SummaryReport

An ESA TRP activity was carried out by cosine Research (NL), Micronit (NL), Kayser-Threde (DE), SRON (NL), DTU (DK) and MPE (DE) with the goal of improving the angular resolution of Silicon Pore X-ray Optics. Silicon Pore Optics is the European baseline mirror technology for the International X-ray Observatory (IXO), one of the three L-class mission candidates under the Cosmic Vision 2015-2025 program.

This ESA TRP funded activity, 'High Performance X-Ray Optics', started late 2007. The entire production chain of these light-weight and modular X-ray optics has been reviewed, improved, demonstrated and tested, from silicon plate manufacture, over ribbing, dicing, wedging, coating, stacking, assembly and integration up to petal level.

Published: 03 April 2010
LISA Pathfinder, formerly known as SMART-2, is the second of the European Space Agency's Small Missions for Advance Research and Technology, and is designed to pave the way for the joint ESA/NASA Laser Interferometer Space Antenna (LISA) mission, by testing the core assumption of gravitational wave detection and general relativity: that free particles follow geodesics. The new technologies to be demonstrated in a space environment include: inertial sensors, high precision laser interferometry to free floating mirrors, and micro-Newton proportional thrusters. LISA Pathfinder will be launched on a dedicated launch vehicle in late 2011 into a low Earth orbit. By a transfer trajectory, the sciencecraft will enter its final orbit around the first Sun-Earth Lagrange point. First science results are expected approximately 3 months thereafter. Here, we give an overview of the mission including the technologies being demonstrated.
Published: 01 April 2010
We use multicomponent measurements of the four Cluster spacecraft and a backward ray tracing simulation to estimate the location and size of the global source of whistler mode chorus emissions in the magnetic equatorial plane. For the first time, analysis is made in a broad range of latitudes in both hemispheres along a single Cluster orbit. Our results show that for different time intervals, the sizes of the observed portions of the global chorus source region in the equatorial plane varied between 0.4 and 1.5 Earth radii. They were found at radial distances between 4.5 and 8.2 Earth radii during 2 h of measurements. Therefore, the superposed minimum width of the global source region of whistler mode chorus in the magnetic equatorial plane is approximately 4 Earth radii.
Published: 01 April 2010
We use multicomponent measurements of the four Cluster spacecraft and a backward ray tracing simulation to estimate the location and size of the global source of whistler mode chorus emissions in the magnetic equatorial plane. For the first time, analysis is made in a broad range of latitudes in both hemispheres along a single Cluster orbit. Our results show that for different time intervals, the sizes of the observed portions of the global chorus source region in the equatorial plane varied between 0.4 and 1.5 Earth radii. They were found at radial distances between 4.5 and 8.2 Earth radii during 2 h of measurements. Therefore, the superposed minimum width of the global source region of whistler mode chorus in the magnetic equatorial plane is approximately 4 Earth radii.
Published: 01 April 2010
The assessment study of an Exoplanet Spectroscopy Mission (ESM) has been performed at ESA's Concurrent Design Facility (CDF) and ran from mid-February to end-March 2010.

This internal final presentation has been prepared by the ESM/CDF team and summarizes the outcome of the ESM assessment study.

Contents of the presentation:

  • Overview / Agenda
  • System Presentation
  • Payload Instruments (Telescope; Instruments; Detectors)
  • Discipline presentations (AOCS; Configuration; Structures; Thermal; Propulsion; Power; DHS; GS/OPS; Communications; Programmatics; Risk)
  • Conclusions
Published: 26 March 2010
Aims. To separate stars and galaxies in the far infrared AKARI All-Sky Survey data, we have selected a sample with the complete color information available in the low extinction regions of the sky and constructed color-color plots for these data. We looked for the method of separating stars and galaxies using the color information.
Methods. We performed an extensive search for the counterparts of these selected All-Sky Survey objects in the NED and SIMBAD databases. Among 5176 selected objects, we found 4272 galaxies, 382 other extragalactic objects, 349 Milky Way stars, 50 other Galactic objects, and 101 sources detected before in various wavelengths but of an unknown origin. Twenty-two sources were left unidentified. Then, we checked the colors of stars and galaxies in the far-infrared flux-color and color-color plots.
Results. In the resulting diagrams, stars form two clearly separated clouds. One of them is easily distinguished from galaxies and allows for a simple method of excluding a large part of stars using the far-infrared data. The other smaller branch, overplotting galaxies, consists of stars known to have an infrared excess, like Vega and some fainter stars discovered by IRAS or 2MASS. The color properties of these objects in any case make them very difficult to distinguish from galaxies.
Conclusions. We conclude that the FIR color-color diagrams allow for a high-quality star-galaxy separation.With the proposed simple method we can select more that 95% of galaxies rejecting at least 80% of stars.
Published: 24 March 2010
This draft version of "A Roadmap for Exoplanets" was prepared by the Exoplanet Roadmap Advisory Team (EPR-AT), an expert advisory team appointed by ESA. This is a working draft document that will be completed and revised after the "A Roadmap for Exoplanets" workshop (7-8 April 2010, University College London).
Published: 22 March 2010
The Cassini spacecraft has been in orbit around Saturn since 30 June 2004, yielding a wealth of data about the Saturn system. This review focuses on the atmosphere and magnetosphere and briefly outlines the state of our knowledge after the Cassini prime mission. The mission has addressed a host of fundamental questions: What processes control the physics, chemistry, and dynamics of the atmosphere? Where does the magnetospheric plasma come from? What are the physical processes coupling the ionosphere and magnetosphere? And, what are the rotation rates of Saturn's atmosphere and magnetosphere?
Published: 19 March 2010
We review our understanding of Saturn's rings after nearly 6 years of observations by the Cassini spacecraft. Saturn's rings are composed mostly of water ice but also contain an undetermined reddish contaminant. The rings exhibit a range of structure across many spatial scales; some of this involves the interplay of the fluid nature and the self-gravity of innumerable orbiting centimeter- to meter-sized particles, and the effects of several peripheral and embedded moonlets, but much remains unexplained. A few aspects of ring structure change on time scales as short as days. It remains unclear whether the vigorous evolutionary processes to which the rings are subject imply a much younger age than that of the solar system. Processes on view at Saturn have parallels in circumstellar disks.
Published: 19 March 2010
Of the over 400 known exoplanets, there are about 70 planets that transit their central star, a situation that permits the derivation of their basic parameters and facilitates investigations of their atmospheres. Some short-period planets, including the first terrestrial exoplanet (CoRoT-7b), have been discovered using a space mission designed to find smaller and more distant planets than can be seen from the ground. Here we report transit observations of CoRoT-9b, which orbits with a period of 95.274 days on a low eccentricity of 0.11 ± 0.04 around a solar-like star. Its periastron distance of 0.36 astronomical units is by far the largest of all transiting planets, yielding a 'temperate' photospheric temperature estimated to be between 250 and 430 K. Unlike previously known transiting planets, the present size of CoRoT-9b should not have been affected by tidal heat dissipation processes. Indeed, the planet is found to be well described by standard evolution models with an inferred interior composition consistent with that of Jupiter and Saturn.
Published: 18 March 2010
Precise radio tracking of the spacecraft Cassini has provided a determination of Titan's mass and gravity harmonics to degree 3. The quadrupole field is consistent with a hydrostatically relaxed body shaped by tidal and rotational effects. The inferred moment of inertia factor is about 0.34, implying incomplete differentiation, either in the sense of imperfect separation of rock from ice or a core in which a large amount of water remains chemically bound in silicates. The equilibrium figure is a triaxial ellipsoid whose semi-axes a, b, and c differ by 410 meters (a - c) and 103 meters (b - c). The nonhydrostatic geoid height variations (up to 19 meters) are small compared to the observed topographic anomalies of hundreds of meters, suggesting a high degree of compensation appropriate to a body that has warm ice at depth.
Published: 12 March 2010
The life of a star is dominantly determined by the physical processes in the stellar interior. Unfortunately, we still have a poor understanding of how the stellar gas mixes near the stellar core, preventing precise predictions of stellar evolution. The unknown nature of the mixing processes as well as the extent of the central mixed region is particularly problematic for massive stars. Oscillations in stars with masses a few times that of the Sun offer a unique opportunity to disentangle the nature of various mixing processes, through the distinct signature they leave on period spacings in the gravity mode spectrum. Here we report the detection of numerous gravity modes in a young star with a mass of about seven solar masses. The mean period spacing allows us to estimate the extent of the convective core, and the clear periodic deviation from the mean constrains the location of the chemical transition zone to be at about 10 per cent of the radius and rules out a clear-cut profile.
Published: 11 March 2010
We have used the ion composition data from the CIS/CODIF instrument on Cluster to determine how the O+ population in the plasma sheet and the adjacent lobes changes during geomagnetic storms. The Cluster trajectory, which moves over the polar cap, into the lobe, and then into the plasma sheet on each orbit, allows us to track the changes in O+ in these regions for a prestorm orbit, main-phase orbit, and recovery phase orbit. We find that changes in the O+ density and pressure in the plasma sheet are similar to those commonly observed in the ring current during a storm. The O+ is low prestorm. It increases by about a factor of 10 just prior to or during the early main phase of the storm, and is reduced, but usually not down to prestorm levels, in the recovery phase. The lobes contain tailward streaming O+ which originates in the "cleft ion fountain". During the storms main phase, this population also increases. A detailed look at the main-phase passes shows that a significant increase in the O+/H+ ratio is observed when this lobe population reaches the plasma sheet, and the tailward streaming O+ is observed continuously as the spacecraft moves from the lobe into the plasma sheet. The enhanced O+ in the lobe and the plasma sheet is observed for many hours during the storm. The inward convection of this population is likely a significant contributor to the storm time ring current.
Published: 09 March 2010
The eccentric orbit of Mars Express allows some close encounters with PHOBOS. Four observations were organized up to August 11, 2004. The spacecraft was put in a fixed inertial position, and Phobos was scanned from the orbital motion, crossing the slit of SPICAM UV imaging spectrometer in a few seconds. The distance was from 150 to 1900 km. Along the slit, five FOV of 10 x 1.3 arcmin each recorded the UV spectrum (110-310 nm, resolution 1.5 nm) of scattered solar light, resulting in 30 to 50 independent UV spectra at each encounter, and giving an unprecedented spatial resolution in UV. From the absolute calibration of SPICAM with star observations, the albedo may be determined as a function of wavelength and geography. Albedo markings were search for. The UV color (wavelength trend in the range 200-320 nm) was determined.Comparisons with previous measurements (in particular HST) will be discussed, with potential implications for mineralogy of Phobos.
Published: 11 November 2004

Abstract No. 1832

As a complement to Mars observations, Phobos spectral imaging was implemented in order to acquired compositional mapping with the prime objective to answer to the following questions:

  1. Is Phobos a "primitive" (undifferentiated) body, or is its mass sufficient for this small body to have suffered some degree of internal differentiation, so as to exhibit surface compositional variations reflecting variation with depth?
  2. Can one detect surface material containing either volatile or organic compounds ?
We will present an overview of the results acquired, and discuss them in terms of planetary differentiation.

Published: 10 March 2008

Abstract No. 2195

Of the many previous hypotheses concerning the origin of Phobos' grooves, most authorities agree that their formation is in some way connected with the creation of Stickney crater, at nearly 10 km diameter the largest crater on Phobos [1,2,3]. The principal argument for the Stickney association has been that the grooves form a pattern that is approximately radial to Stickney [1,2]. However, such hypotheses were based on incomplete mapping of the satellite, the largest poorly-imaged area being adjacent to Stickney's western rim. Much of the unknown region has now been imaged by HRSC, and we have assembled a new groove map from this and all other available imagery. The impression of grooves radial to Stickney can be seen to be an artefact of the previous coverage. East of Stickney this idea can be sustained, but west of it the pattern is tangential to the crater. The satellite-wide groove pattern can be seen to be centred not at Stickney, but at the leading apex of Phobos in its orbit (i.e. 90° long., 0° lat.). Groove orientations are quite independent of Stickney and bear no relation to it.

Published: 13 March 2006
The determination of the ephemeris of the Martian moons has benefited from observations of their plane-of-sky positions derived from images taken by cameras onboard spacecraft orbiting Mars. Images obtained by the Super Resolution Camera (SRC) onboard Mars Express (MEX) have been used to derive moon positions relative to Mars on the basis of a fit of a complete dynamical model of their motion around Mars. Since, these positions are computed from the relative position of the spacecraft when the images are taken, those positions need to be known as accurately as possible. An accurate MEX orbit is obtained by fitting two years of tracking data of the Mars Express Radio Science (MaRS) experiment onboard MEX. The average accuracy of the orbits has been estimated to be around 20-25 m. From these orbits, we have re-derived the positions of Phobos and Deimos at the epoch of the SRC observations and compared them with the positions derived by using the MEX orbits provided by the ESOC navigation team. After fit of the orbital model of Phobos and Deimos, the gain in precision in the Phobos position is roughly 30 m, corresponding to the estimated gain of accuracy of the MEX orbits. A new solution of the GM of the Martian moons has also been obtained from the accurate MEX orbits, which is consistent with previous solutions and, for Phobos, is more precise than the solution from the Mars Global Surveyor (MGS) and Mars Odyssey (ODY) tracking data. It will be further improved with data from MEX-Phobos closer encounters (at a distance less than 300 km). This study also demonstrates the advantage of combining observations of the moon positions from a spacecraft and from the Earth to assess the real accuracy of the spacecraft orbit. In turn, the natural satellite ephemerides can be improved and participate to a better knowledge of the origin and evolution of the Martian moons.
Published: 02 April 2008
14-Apr-2021 06:16 UT

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