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| Location and size of the global source region of whistler mode chorus |
| 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. |
| Publication date: 31 Mar 2010 |
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| The LISA Pathfinder Mission - Tracing Einstein's Geodesics in Space |
| 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. |
| Publication date: 31 Mar 2010 |
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| ULF waves associated with the periodical high speed flows in magnetotail plasma sheet |
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| Publication date: 31 Mar 2010 |
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| ESM Assessment Study - Internal Final Presentation |
| 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:
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Overview / Agenda
- System Presentation
- Payload Instruments (Telescope; Instruments; Detectors)
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Discipline presentations (AOCS; Configuration; Structures; Thermal; Propulsion; Power; DHS; GS/OPS; Communications; Programmatics; Risk)
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Conclusions
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| Publication date: 26 Mar 2010 |
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| Star-galaxy separation by far-infrared color-color diagrams for the AKARI FIS All-Sky Survey (Bright Source Catalogue version beta-1) |
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. |
| Publication date: 24 Mar 2010 |
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| An XMM-Newton survey of the soft X-ray background. I. The O VII and O VIII lines between l = 120° and l = 240° |
| [Abbreviated abstract] We present measurements of the soft X-ray background (SXRB) O VII and O VIII intensity between l = 120° and l = 240°, the first results of a survey of the SXRB using archival XMM-Newton observations. |
| Publication date: 23 Mar 2010 |
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| A Roadmap for Exoplanets (draft document) |
| 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). |
| Publication date: 22 Mar 2010 |
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| An Evolving View of Saturn's Dynamic Rings |
| 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. |
| Publication date: 19 Mar 2010 |
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| Saturn: Atmosphere, Ionosphere, and Magnetosphere |
| 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? |
| Publication date: 19 Mar 2010 |
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| A transiting giant planet with a temperature between 250 K and 430 K |
| 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. |
| Publication date: 18 Mar 2010 |
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| James Webb Space Telescope Studies of Dark Energy |
| The Hubble Space Telescope (HST) has contributed significantly to studies of dark energy. It was used to find the first evidence of deceleration at z=1.8 (Riess et al. 2001) through the serendipitous discovery of a type 1a supernova (SNIa) in the Hubble Deep Field. The discovery of deceleration at z>1 was confirmation that the apparent acceleration at low redshift (Riess et al. 1998; Perlmutter et al. 1999)
was due to dark energy rather than observational or astrophysical effects such as systematic errors, evolution in the SNIa population or intergalactic dust. The GOODS project and associated follow-up discovered 21 SNIa, expanding on this result (Riess et al. 2007). HST has also been used to constrain cosmological parameters and dark energy through weak lensing measurements in the COSMOS survey (Massey et al 2007; Schrabback et al 2009) and strong gravitational lensing with measured time delays (Suyu et al 2010). |
| Publication date: 18 Mar 2010 |
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| Notching during random vibration test based on interface forces - The JWST NIRSpec experience |
| Force limited vibration was used during the sine and random qualification tests of the NIRSpec instrument, to limit stresses in the brittle structure while demonstrating adequate qualification with regard to the environmental flight conditions. First, NASA provided a force limit curve based on their internal 'Semi-Empirical Method'. Then, strain gages were mounted on the legs of the kinematic mounts to recover interface forces during the vibration test. Two different methods were then used to determine the notches: one called the 'Apparent Mass' method that is based on sine sweep signatures and another one based on direct force measurement in the time domain during random test. The second method resulted in the most effective notch determination, allowing the justification of the notches in real time with high accuracy. The resulting RMS forces are well below the forces corresponding to static design loads that is a more conventional method. |
| Publication date: 18 Mar 2010 |
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| Gravity Field, Shape, and Moment of Inertia of Titan |
| 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. |
| Publication date: 12 Mar 2010 |
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| Deviations from a uniform period spacing of gravity modes in a massive star |
| 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. |
| Publication date: 11 Mar 2010 |
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| Cusp as a source for oxygen in the plasma sheet during geomagnetic storms |
| 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. |
| Publication date: 09 Mar 2010 |
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| JWST Planetary Observations within the Solar System |
| JWST provides capabilities unmatched by other telescopic facilities in the near to mid
infrared part of the electromagnetic spectrum. Its combination of broad wavelength
range, high sensitivity and near diffraction-limited imaging around two microns
wavelength make it a high value facility for a variety of Solar System targets. Beyond
Neptune, a class of cold, large bodies that include Pluto, Triton and Eris exhibits surface
deposits of nitrogen, methane, and other molecules that are poorly observed from the
ground, but for which JWST might provide spectral mapping at high sensitivity and
spatial resolution difficult to match with the current generation of ground-based
observatories. The observatory will also provide unique sensitivity in a variety of near
and mid infrared windows for observing relatively deep into the atmospheres of Uranus
and Neptune, searching there for minor species. It will examine the Jovian aurora in a
wavelength regime where the background atmosphere is dark. Special provision of a subarray
observing strategy may allow observation of Jupiter and Saturn over a larger
wavelength range despite their large surface brightnesses, allowing for detailed
observation of transient phenomena including large scale storms and impact-generation
disturbances. JWSTs observations of Saturns moon Titan will overlap with and go
beyond the 2017 end-of-mission for Cassini, providing an important extension to the
time-series of meteorological studies for much of northern hemisphere summer. It will
overlap with a number of other planetary missions to targets for which JWST can make
unique types of observations. JWST provides a platform for linking solar system and
extrasolar planet studies through its unique observational capabilities in both arenas. |
| Publication date: 09 Mar 2010 |
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| Science Requirements Document for Euclid |
| This document provides the top level science requirements and the implied top level payload and
mission requirements for Euclid, ESA's mission to map the dark Universe. Euclid will tightly constrain the dark energy equation of state and address key cosmological questions.
This Issue 4 of the Science Requirements Document (SciRD) will be the basis for the Euclid mission and payload design during the Definition Phase.
[This is an abbreviated version of the original document abstract.] |
| Publication date: 05 Mar 2010 |
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| New astrometric observations of Phobos with the SRC on Mars Express |
| Aims. New astrometric measurements for Phobos are reported on the basis of 69 SRC (Super Resolution Channel) images obtained during 28 Mars Express Phobos flybys executed between 2004 and 2007.
Methods. The measurements have been made using a newly developed technique that involves positional measurements of surface control points and verification of camera pointing by background stars.
Results. The astrometric positions are in excellent agreement with currently available Phobos orbit models. However, we find remaining systematic offsets of 1.5-2.6 km such that Phobos is ahead of its predicted position along the track.
Conclusions. Our observations will be a basis for further improvements in the Phobos ephemeris. The methods that we have developed will be useful for the astrometric tracking of planetary or asteroidal targets and spacecraft optical navigation in future planetary missions. |
| Publication date: 25 Feb 2010 |
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| ESA Bulletin 137 - The First European Asteroid Flyby |
| The first flyby of an asteroid by a European spacecraft was a major success, both from the scientific and engineering points of view. This was the first planned scientific objective of ESA's Rosetta mission, and the optical navigation campaign, performed for the first time in Europe, gave results well beyond expectations. |
| Publication date: 15 Feb 2010 |
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| ESA Bulletin 137: ESA's 'billion-pixel' camera - The challenges of the Gaia mission |
| Gaia is ESA's global space astrometry mission,
designed to map one thousand million stars and
hundreds of thousands of other celestial objects in
our galaxy, so its camera will have to be something
truly special. |
| Publication date: 15 Feb 2010 |
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