Publication archive

Publication archive

We report a periodicity of ~1 day in the highly elevated X-ray emission from the protostar V1647 Ori during its two recent multiple-year outbursts of mass accretion. This periodicity is indicative of protostellar rotation at near-break-up speed. Modeling of the phased X-ray light curve indicates that the high-temperature (~50 MK), X-ray-emitting plasma, which is most likely heated by accretion-induced magnetic reconnection, resides in dense ( >~5 × 1010 cm-3), pancake-shaped magnetic footprints where the accretion stream feeds the newborn star. The sustained X-ray periodicity of V1647 Ori demonstrates that such protostellar magnetospheric accretion configurations can be stable over timescales of years.
Published: 21 July 2012
We present new constraints on the star formation histories of the ultra-faint dwarf (UFD) galaxies, using deep photometry obtained with the Hubble Space Telescope (HST). A galaxy class recently discovered in the Sloan Digital Sky Survey, the UFDs appear to be an extension of the classical dwarf spheroidals to low luminosities, offering a new front in efforts to understand the missing satellite problem. They are the least luminous, most dark-matter-dominated, and least chemically evolved galaxies known. Our HST survey of six UFDs seeks to determine if these galaxies are true fossils from the early universe. We present here the preliminary analysis of three UFD galaxies: Hercules, Leo IV, and Ursa Major I. Classical dwarf spheroidals of the Local Group exhibit extended star formation histories, but these three Milky Way satellites are at least as old as the ancient globular cluster M92, with no evidence for intermediate-age populations. Their ages also appear to be synchronized to within ~1 Gyr of each other, as might be expected if their star formation was truncated by a global event, such as reionization.
Published: 02 June 2012
The loss of relativistic electrons from the Earth's radiation belts can be described in terms of the quasi-linear pitch angle diffusion by cyclotron-resonant waves, provided that their frequency spectrum is broad enough. Chorus waves at large wave-normal angles with respect to the magnetic field are often present in CLUSTER and THEMIS measurements in the outer belt at moderate to high latitudes. An approximate analytical formulation of diffusion coefficients has been derived in the low-frequency limit, leading to a simplified analytical expression of diffusion coefficients and lifetimes for energetic trapped electrons. Large values of the wave-normal angles between the Gendrin and resonance angles are shown to induce important increases in diffusion, thereby strongly reducing the particle lifetimes (by almost two orders of magnitude). The analytical diffusion coefficients and lifetimes obtained here are found to be in a good agreement with full numerical calculations based on CLUSTER chorus waves measurements in the outer belt for electron energies ranging from 100 keV to 2 MeV. Such very oblique chorus waves could contribute to a predominantly perpendicular anisotropy of the global equatorial electron population on the dayside and to a relative isotropization at low energy under disturbed conditions. It is also suggested that they might play a significant role in pulsating auroras.
Published: 01 July 2012

The 39th meeting of the Committee on Space Research (COSPAR) was held 14-22 July 2012 in Mysore, India.

This report to COSPAR on the scientific activities of the European Space Agency was written by members of the Directorate of Earth Observation, the Directorate of Human Spaceflight and Operations and the Directorate of Science and Robotic Exploration.

Contents:

  • Foreword by Jean-Jacques Dordain, Director General, ESA
  • Earth Observation
    1. Introduction
    2. The Living Planet Programme
    3. The Earth Explorer Missions
    4. ERS and Envisat
  • Human Spaceflight and Operations
    1. Introduction
    2. Overview: Columbus and ISS Facilities
    3. Funding Europe's ISS Research: ELIPS
    4. Research on the ISS
    5. Ongoing Research Using Other Platforms
    6. Projects under Development
  • Science and Robotic Exploration
    1. Introduction
    2. Missions in Operation
    3. Missions in the Post-Operations and Archiving Phases
    4. Projects under Development
    5. Missions under Study
Published: 01 July 2012
Published online on 28 June 2012

We have detected in Cassini data the signature of the periodic tidal stresses within Titan driven by the eccentricity (e = 0.028) of its 16-day orbit around Saturn. Precise measurements of the acceleration of the Cassini spacecraft during six close flybys between 2006 and 2011 have revealed that Titan responds to the variable tidal field exerted by Saturn with periodic changes of its quadrupole gravity, at about 4% of the static value. Two independent determinations of the corresponding degree-2 Love number yield k2 = 0.589 ± 0.150 and k2 = 0.637 ± 0.224 (2-sigma). Such a large response to the tidal field requires that Titan's interior is deformable over time scales of the orbital period, in a way that is consistent with a global ocean at depth.

Published: 28 July 2012
Reference: SRE-PA/2011-075/TN/PW

This document describes the Payload of STE-QUEST, a mission in the Fundamental Physics domain conceived to test to high accuracy the different aspects of the Einstein Equivalence Principle. This document derives directly from the STE-QUEST Science Requirements Document and STE-QUEST Mission Requirements Document. It also integrates elements included in the STE-QUEST proposal (and associated reference documents), the STE-QUEST CDF Study and the STE-QUEST Instruments Mid-Term Review datapackages.

This document provides the baseline description of the payload, its instruments, supporting units and interfaces, as defined at the beginning of the STE-QUEST assessment study. It shall be consolidated as part of the study and shall be formally updated at the end of it. This is the first revision of the document, following the completion and closure of the Instruments mid-term Review held in May 2011.

Published: 23 June 2012
Reference: ESA/SPC(2012)20, rev. 1

JUpiter ICy moons Explorer (JUICE) is an ESA-led L-class mission of the ESA's Cosmic Vision 2015-25 Programme. It aims at a comprehensive exploration of the Jovian system with particular emphasis on Jupiter, its environment, and Galilean moons Ganymede, Europa and Callisto by investigating them as planetary bodies and potential habitats.

The Science Management Plan (SMP) describes the approach that will be implemented to ensure the fulfilment of the scientific objectives of the JUICE mission and to optimise its scientific return, with special emphasis on payload procurement, science operation and data management.

Published: 21 June 2012
Published online 16 June 2012, in Online First

The Earth's bow shock is the most studied example of a collisionless shock in the solar system. It is also widely used to model or predict the behaviour at other astrophysical shock systems. Spacecraft observations, theoretical modelling and numerical simulations have led to a detailed understanding of the bow shock structure, the spatial organization of the components making up the shock interaction system, as well as fundamental shock processes such as particle heating and acceleration. In this paper we review the observations of accelerated ions at and upstream of the terrestrial bow shock and discuss the models and theories used to explain them. We describe the global morphology of the quasi-perpendicular and quasi-parallel shock regions and the foreshock. The acceleration processes for field-aligned beams and diffuse ion distribution types are discussed with connection to foreshock morphology and shock structure. The different possible mechanisms for extracting solar wind ions into the acceleration processes are also described. Despite several decades of study, there still remain some unsolved problems concerning ion acceleration at the bow shock, and we summarize these challenges.

Published: 17 June 2012

Cataloguing the night sky is an essential part of astronomy. Before astronomers can investigate a celestial object, they must know where to find it. Without this knowledge, astronomers would wander helplessly in what Galileo once termed a 'dark labyrinth'.

ESA's Gaia mission will create a detailed map of this labyrinth, finding clues to the origin, structure and evolution of our home galaxy, the Milky Way.

Contents:

  • The discovery machine
  • Stars as individuals and collectives
  • Our Solar System and others
  • How does Gaia work?
  • Building Gaia
  • Launch
  • The flood of data
Published: 16 June 2012
An analytical model of magnetosheath plasma flow is described and compared with a large dataset of magnetosheath ion flow velocity measurements from Cluster and THEMIS spacecraft. The model is based on previous works by Kobel and Flückiger (1994) and Génot et al. (2011) and has been modified to overcome the restrictions of these models on the shape of model magnetopause and bow shock. Our model is compatible with any parabolic bow shock model and arbitrary magnetopause model. The model is relatively simple to implement and computationally inexpensive, and its only inputs are upstream solar wind parameters. Comparison with observed data yields a good correspondence: median error in the direction of flow velocity is comparable with the instrumental error, and flow magnitude is predicted with a reasonable accuracy (relative error in flow speed was less than 25% for 86.5% of observations).
Published: 13 June 2012
The Milky Way galaxy has several components, such as the bulge, disk and halo. Unravelling the assembly history of these stellar populations is often restricted because of difficulties in measuring accurate ages for low-mass, hydrogen-burning stars. Unlike these progenitors, white dwarf stars, the 'cinders' of stellar evolution, are remarkably simple objects and their fundamental properties can be measured with little ambiguity. Here I report observations of newly formed white dwarf stars in the halo of the Milky Way, and a separate analysis of archival data in the well studied 12.5-billion-year-old globular cluster Messier 4. I measure the mass distribution of the remnant stars and invert the stellar evolution process to develop a mathematical relation that links this final stellar mass to the mass of their immediate progenitors, and therefore to the age of the parent population. By applying this technique to a small sample of four nearby and kinematically confirmed halo white dwarf stars, I calculate the age of local field halo stars to be 11.4 ± 0.7 billion years. The oldest globular clusters formed 13.5 billion years ago. Future observations of newly formed white dwarf stars in the halo could be used to reduce the uncertainty, and to probe relative differences between the formation times of the youngest globular clusters and the inner halo.
Published: 08 June 2012
Published online on 1 October 2011. To appear in a Special Issue of the journal, in press. We have analyzed Cluster magnetic field and plasma data during a high-altitude cusp crossing in 2003. The Cluster separation was ~5000 km and provided unique measurements of high energy particle properties both inside the DiaMagnetic Cavity (DMC) and surrounding magnetosheath. Most of the high energy electrons and protons had pitch angles of ~90 degrees in the cavity and the high energy particle intensities dropped as a function of distance from the cavity boundary. By assuming conservation of the first adiabatic invariant for the electrons our analysis indicates that most of the high-energy electrons in the diamagnetic cavity cannot directly originate from the magnetosheath or from the magnetosphere. Our test particle simulations in a local 3-D high-resolution MHD cusp model show that particles can gain up to 40 keV and their pitch angles become nearly 90 degrees in the local cusp geometry due to gradients in reconnection 'quasi-potential' agreeing with the Cluster RAPID observations. These results strongly support a local acceleration of particles in the cusp diamagnetic cavities.
Published: 06 June 2012
We present radio and plasma wave science (RPWS) Langmuir probe (LP) observations that give evidence for a population of heavy, negative ions at altitudes below 900 km in Titan's ionosphere during the Cassini T70 flyby. The negative ion density in this region is comparable to, or higher than, the electron density of 760 cm-3. Both positive and negative ions are moving with a velocity of at least a few hundred m s-1 relative to Titan. We show two limiting cases where we have analysed RPWS/LP ion measurements. The data can be interpreted as either that a population of negative ions with density comparable to the electron density is present, moving at a very high (>2 km s-1) velocity, or that the ion population is moving at a few hundred m s-1, but with a density an order of magnitude larger than the electron density in the same region.
Published: 17 May 2012
We analyze night-time near-infrared (NIR) thermal emission images of the Venus surface obtained with the 1-micron channel of the Venus Monitoring Camera onboard Venus Express. Comparison with the results of the Magellan radar survey and the model NIR images of the Beta-Phoebe region show that the night-time VMC images provide reliable information on spatial variations of the NIR surface emission. In this paper we consider if tessera terrain has the different NIR emissivity (and thus mineralogic composition) in comparison to the surrounding basaltic plains. This is done through the study of an area SW of Beta Regio where there is a massif of tessera terrain, Chimon-mana Tessera, surrounded by supposedly basaltic plains. Our analysis showed that 1-micron emissivity of tessera surface material is by 15-35% lower than that of relatively fresh supposedly basaltic lavas of plains and volcanic edifices. This is consistent with hypothesis that the tessera material is not basaltic, maybe felsic, that is in agreement with the results of analyses of VEX VIRTIS and Galileo NIMS data. If the felsic nature of venusian tesserae will be confirmed in further studies this may have important implications on geochemical environments in early history of Venus. We have found that the surface materials of plains in the study area are very variegated in their 1-micron emissivity, which probably reflects variability of degree of their chemical weathering. We have also found a possible decrease of the calculated emissivity at the top of Tuulikki Mons volcano which, if real, may be due to different (more felsic?) composition of volcanic products on the volcano summit.
Published: 17 May 2012
The Tyrrhena Terra region of Mars is studied with the imaging spectrometers OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) onboard Mars Express and CRISM (Compact Reconnaissance Infrared Spectrometer for Mars) onboard Mars Reconnaissance Orbiter, through the observation of tens of craters that impacted into this part of the martian highlands. The 175 detections of hydrated silicates are reported, mainly associated with ejecta blankets, crater walls and rims, and central up-lifts. Sizes of craters where hydrated silicates are detected are highly variable, diameters range from less than 1 km to 42 km. We report the presence of zeolites and phyllosilicates like prehnite, Mg-chlorite, Mg-rich smectites and mixed-layer chlorites-smectites and chlorite-vermiculite from comparison of hyperspectral infrared observations with laboratory spectra. These minerals are associated with fresh craters post-dating any aqueous activity. They likely represent ancient hydrated terrains excavated by the crater-forming impacts, and hence reveal the composition of the altered Noachian crust, although crater-related hydrothermal activity may have played a minor role for the largest craters (>20 km in diameter). Most detected minerals formed over relatively high temperatures (100-300 °C), likely due to aqueous alteration of the Noachian crust by regional low grade metamorphism from the Noachian thermal gradient and/or by extended hydrothermal systems associated with Noachian volcanism and ancient large impact craters. [Abstract abbreviated due to character limitations.]
Published: 16 May 2012
Context. The Carina Nebula represents one of the most massive star forming regions known in our Galaxy and displays a high level of feedback from the large number of very massive stars. While the stellar content is now well known from recent deep X-ray and near-infrared surveys, the properties of the clouds remained rather poorly studied until today. Methods. We used SPIRE and PACS onboard of Herschel to map the full spatial extent (~5.3 square-degrees) of the clouds in the Carina Nebula complex at wavelengths between 70 and 500 micron. We used here the 70 micron and 160 micron far-infrared maps to determine color temperatures and column densities, and to investigate the global properties of the gas and dust clouds in the complex. Results. Our Herschel maps show the far-infrared morphology of the clouds at unprecedented high angular resolution. The clouds show a very complex and filamentary structure that is dominated by the radiation and wind feedback from the massive stars. In most locations, the column density of the clouds is NH < 2 × 1022 cm-2 (corresponding to visual extinctions of AV < 10 mag); denser cloud structures are restricted to the massive cloud west of Tr 14 and the innermost parts of large pillars. Our temperature map shows a clear large-scale gradient from ~35-40 K in the central region to <20 K at the periphery and in the densest parts of individual pillars. The total mass of the clouds seen by Herschel in the central (1 degree radius) region is ~656 000 M_Sun. We also derive the global spectral energy distribution in the mid-infrared to mm wavelength range. A simple radiative transfer model suggests that the total mass of all the gas (including a warmer component that is not well traced by Herschel) in the central 1 degree radius region is ~890 000 M_Sun. [Abstract abbreviated due to character limitations.]
Published: 15 May 2012
Published online 9 May 2012

The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2-6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 1044 ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expelling the interstellar medium of its host and transforming the galaxy's properties in a brief period of cosmic time.

Published: 11 May 2012
We present a local mesoscale model of the magnetospheric cusp region with high resolution (up to 300 km). We discuss the construction and implementation of the initial configuration and give a detailed description of the numerical simulation. An overview of simulation results for the case of strongly northward interplanetary magnetic field (IMF) is then presented and compared with data from Cluster 2 spacecraft from 14 February 2003. Results show a cusp diamagnetic cavity (CDC) with depth normal to the magnetospheric boundary on the order of 1-2 RE and a much larger extent of ~5-9 RE tangential to the boundary, bounded by a gradual inner boundary with the magnetospheric lobe and a more distinct exterior boundary with the magnetosheath. These results are qualitatively consistent with observational data.
Published: 07 May 2011

Published online 5 April 2012, in Science Express

Observations with the Venus Express magnetometer and low-energy particle detector revealed magnetic field and plasma behaviour in the near-Venus wake symptomatic of magnetic reconnection, a process that occurs in the Earth's magnetotail but is not expected in the magnetotail of a non-magnetized planet like Venus. On 15 May 2006, the plasma flow in this region was toward the planet and the magnetic field component transverse to the flow was reversed. Magnetic reconnection is a plasma process that changes the topology of the magnetic field and results in energy exchange between the magnetic field and the plasma. Thus, the energetics of the Venus magnetotail resembles that of the terrestrial tail where energy is stored and later released from the magnetic field to the plasma.

Published: 05 May 2012
This document lists the JUICE mission's science objectives and the corresponding investigations, plus the necessary measurements (and instruments) to achieve these objectives.
Published: 03 May 2012
23-Sep-2019 09:17 UT

ShortUrl Portlet

Shortcut URL

https://sci.esa.int/p/dAGeRrW