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| PEP Assessment Study - Internal Final Presentation |
The assessment study of Planetary Entry Probes (PEP) for Venus and three of the outer planets (Saturn, Uranus, and Neptune) has been performed at ESA's Concurrent Design Facility (CDF) and ran from 14 April to 30 June 2010. The internal final presentation has been prepared by the PEP/CDF team and summarizes the outcome of the PEP assessment study. This presentation can be downloaded below as a PDF (link to publication).
Contents of the presentation:
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| - | Introduction | | - | Systems | | - | Mission analysis | | - | Aerothermodynamics | | - | Thermal | | - | Entry, Descent & Landing | | - | Payload | | - | Configuration | | - | Structures | | - | Mechanisms |
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| - | Guidance & Navigation Control | | - | Power | | - | Communications | | - | Data Handling System | | - | Ground Segment & Operations | | - | Programmatics/ AIV | | - | Risk | | - | Annex I: Atmospheric Models
for Outer Planets |
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A summary of the PEP study is on the "Planetary Entry Probes (PEP)" page, linked form the right-hand menu. |
| Publication date: 30 Jun 2010 |
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| Detection of hydrated silicates in crustal outcrops in the northern plains of Mars |
| The composition of the ancient martian crust is a key ingredient in deciphering the environment and evolution of early Mars. We present an analysis of the composition of large craters in the martian northern plains based on data from spaceborne imaging spectrometers. Nine of the craters have excavated assemblages of phyllosilicates from ancient, Noachian crust buried beneath the plains' cover. The phyllosilicates are indistinguishable from those exposed in widespread locations in the southern highlands, demonstrating that liquid water once altered both hemispheres of Mars. |
| Publication date: 24 Jun 2010 |
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| INTEGRAL/IBIS 7-year All-Sky Hard X-Ray Survey – Part II: Catalog of Sources |
| This paper is the second in a series devoted to the hard X-ray (17-60 keV) whole sky survey performed by the INTEGRAL observatory over seven years. Here we present a catalog of detected sources which includes 521 objects, 449 of which exceed a 5 sigma detection threshold on the time-averaged map of the sky, and 53 were detected in various subsamples of exposures. Among the identified sources with known and suspected nature, 262 are Galactic (101 low-mass X-ray binaries, 95 high-mass X-ray binaries, 36 cataclysmic variables, and 30 of other types) and 219 are extragalactic, including 214 active galactic nuclei (AGNs), 4 galaxy clusters, and galaxy ESO 389-G 002. The extragalactic (|b|>5 deg) and Galactic (|b|<5 deg) persistently detected source samples are of high identification completeness (respectively ~96% and ~94%) and valuable for population studies. |
| Publication date: 23 Jun 2010 |
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| The thermal structure of Venusian night-time mesosphere as observed by VIRTIS-Venus Express |
The mapping IR channel of the Visual and Infrared Thermal Imaging Spectrometer (VIRTIS-M) on board the Venus Express spacecraft observes the CO2 band at 4.3 ¼m at a spectral resolution adequate to retrieve the atmospheric temperature profiles in the 65-96 km altitude range.
Observations acquired in the period June 2006 - July 2008 were used to derive average temperature fields as a function of latitude, subsolar longitude (i.e.: local time, LT) and pressure. Coverage presented here is limited to the nighttime because of the adverse effects of daytime non-LTE emission on the retrieval procedure, and to southernmost latitudes because of the orientation of the Venus-Express orbit. Maps of air temperature variability are also presented as the standard deviation of the population included in each averaging bin.
At the 100 mbar level (about 65 km above the reference surface) temperatures tend to decrease from the evening to the morning side, despite a local maximum observed around 20-21LT. The cold collar is evident around 65S, with a minimum temperature at 3LT. Moving to higher altitudes, local time trends become less evident at 12.6 mbar (about 75 km) where the temperature monotonically increases from middle-latitudes to the southern pole. Nonetheless, at this pressure level, two weaker local time temperature minima are observed at 23LT and 2LT equatorward of 60S. Local time trends in temperature reverse about 85 km, where the morning side is the warmer.
The variability at the 100 mbar level is maximum around 80S and stronger toward the morning side. Moving to higher altitudes, the morning side always shows the stronger variability. Southward of 60S, standard deviation presents minimum values around 12.6 mbar for all the local times. |
| Publication date: 22 Jun 2010 |
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| A relativistically broadened O VIII Ly-alpha line in the ultra-compact X-ray binary 4U 0614+091 |
| Ultra-compact X-ray binaries consist of a neutron star or black hole that accretes material from a white dwarf-donor star. The ultra-compact nature is expressed in very short orbital periods of less than 1 hour. In the case of 4U 0614+091 oxygen-rich material from a CO or ONe white dwarf is flowing to the neutron star. This oxygen-rich disc can reflect X-rays emitted by the neutron star giving a characteristic emission spectrum. We have analyzed high-resolution RGS and broad band EPIC spectra of 4U 0614+091 obtained by the XMM-Newton satellite. We detect a broad emission feature at ~0.7 keV in both instruments, which cannot be explained by unusual abundances of oxygen and neon in the line of sight, as proposed before in the literature. We interpret this feature as O VIII Ly-alpha emission caused by reflection of X-rays off highly ionized oxygen, in the strong gravitational field close to the neutron star. |
| Publication date: 21 Jun 2010 |
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| Superrotation of Venus' atmosphere analyzed with a full general circulation model |
| A general circulation model (GCM) has been developed for the Venus atmosphere, from the surface up to 100 km altitude, based on the GCM developed for Earth at our laboratory. Key features of this new GCM include topography, diurnal cycle, dependence of the specific heat on temperature, and a consistent radiative transfer module based on net exchange rate matrices. This allows a consistent computation of the temperature field, in contrast to previous GCMs of Venus atmosphere that used simplified temperature forcing. The circulation is analyzed after 350 Venus days (111 Earth years). Superrotation is obtained above roughly 40 km altitude. Below, the zonal wind remains very small compared to observed values, which is a major pending question. The meridional circulation consists of equator-to-pole cells, the dominant one being located within the cloud layers. The modeled temperature structure is globally consistent with observations, though discrepancies persist in the stability of the lowest layers and equator-pole temperature contrast within the clouds (10 K in the model compared to the observed 40 K). In agreement with observational data, a convective layer is found between the base of the clouds (around 47 km) and the middle of the clouds (55-60 km altitude). The transport of angular momentum is analyzed, and comparison between the reference simulation and a simulation without diurnal cycle illustrates the role played by thermal tides in the equatorial region. Without diurnal cycle, the Gierasch-Rossow-Williams mechanism controls angular momentum transport. The diurnal tides add a significant downward transport of momentum in the equatorial region, causing low latitude momentum accumulation. |
| Publication date: 12 Jun 2010 |
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| Puzzling asteroid 21 Lutetia: our knowledge prior to the Rosetta fly-by |
| Aims. A wide observational campaign was carried out in 2004-2009 that aimed to complete the ground-based investigation of Lutetia prior to the Rosetta fly-by in July 2010.
Methods. We obtained BVRI photometric and V-band polarimetric measurements over a wide range of phase angles, and visible and infrared spectra in the 0.4-2.4 micron range. We analyze them with previously published data to retrieve information about Lutetia's surface properties. Results. Values of lightcurve amplitudes, absolute magnitude, opposition effect, phase coefficient, and BVRI colors of Lutetia surface seen at near pole-on aspect are determined. We define more precisely parameters of polarization phase curve and show their distinct deviation from any other moderate-albedo asteroid. An indication of possible variations in both polarization and spectral data across the asteroid surface are found. To explain features found by different techniques, we propose that (i) Lutetia has a non-convex shape, probably due to a large crater, and heterogeneous surface properties probably related to surface morphology; (ii) at least part of the surface is covered by a fine-grained regolith of particle size smaller than 20 micron; (iii) the closest meteorite analogues of Lutetia's surface composition are particular types of carbonaceous chondrites, or Lutetia has specific surface composition that is not representative among studied meteorites. |
| Publication date: 03 Jun 2010 |
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| Electron acceleration signatures in the magnetotail associated with substorms |
| We present Cluster multisatellite observations of accelerated electrons in the near-Earth magnetotail associated with substorms. We found that the hardest electron energy spectra appear in the earliest stage of substorm expansion in the near-Earth tail region and that they gradually become softer during the events. Enhancement of the high-energy electron flux occurs generally associated with the bulk acceleration of ions (fast flow) and electrons. It is also shown that the high-energy electrons sometimes show preferential perpendicular acceleration associated with the temporal enhancement of the normal component of the magnetic field, and then the anisotropic distribution quickly becomes isotropic. During the dipolarization interval, in which no convection signature is observed, perpendicular flux drops to less than the initial value, and the parallel flux is more than the perpendicular flux. The results suggest that the electron acceleration mechanism is mostly consistent with adiabatic betatron acceleration, while Fermi acceleration is not clear in the high-energy part. The effect of the pitch angle scattering is also important. The dispersive signature of the high-energy electron flux indicates fast dawnward drift loss, namely, the three-dimensional effect of the limited plasma acceleration region. |
| Publication date: 21 May 2010 |
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| INTEGRAL/IBIS 7-year All-Sky Hard X-Ray Survey – Part I: Image Reconstruction |
| This paper is the first in a series devoted to the hard X-ray whole sky survey performed by the INTEGRAL observatory over seven years. Here we present an improved method for image reconstruction with the IBIS coded mask telescope. The main improvements are related to the suppression of systematic effects which strongly limit sensitivity in the region of the Galactic Plane (GP), especially in the crowded field of the Galactic Center (GC). We extended the IBIS/ISGRI background model to take into account the Galactic Ridge X-ray Emission (GRXE). To suppress residual systematic artifacts on a reconstructed sky image we applied nonparametric sky image filtering based on wavelet decomposition. The implemented modifications of the sky reconstruction method decrease the systematic noise in the ~20 Ms deep field of GC by ~44%, and practically remove it from the high-latitude sky images. New observational data sets, along with an improved reconstruction algorithm, allow us to conduct the hard X-ray survey with the best currently available minimal sensitivity 3.7E-12 erg/s/cm2 ~0.26 mCrab in the 17-60 keV band at a 5 sigma detection level. The survey covers 90% of the sky down to the flux limit of 6.2E-11 erg/s/cm2 (~4.32 mCrab) and 10% of the sky area down to the flux limit of 8.6E-12 erg/s/cm2 (~0.60 mCrab). |
| Publication date: 20 May 2010 |
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| XMM-Newton detection of two clusters of galaxies with strong SPT Sunyaev-Zel'dovich effect signatures |
We report on the discovery of two galaxy clusters, SPT-CL J2332-5358 and SPT-CL J2342-5411, in X-rays. These clusters were also independently detected through their Sunyaev-Zel'dovich effect by the South Pole Telescope, and in the optical band by the Southern Cosmology Survey. They are thus the first clusters detected under survey conditions by all major cluster search approaches. The X-ray detection is made within the frame of the XMM-BCS cluster survey utilizing a novel XMM-Newton mosaic-mode of observations.
The present study makes the first scientific use of this operation mode. We estimate the X-ray spectroscopic temperature of SPT-CL J2332-5358 (at redshift z = 0.32) to be T = 9.3 [+3.3][-1.9] keV, implying a high mass, M500 = 8.8 ± 3.8 × 1014 solar masses. For SPT-CL J2342-5411, at z = 1.08, the available X-ray data do not allow us to directly estimate the temperature with good confidence. However, using our measured luminosity and scaling relations we estimate that T = 4.5 ± 1.3 keV and M500 = 1.9 ± 0.8 × 1014 solar masses. We find a good agreement between the X-ray masses and those estimated from the Sunyaev-Zel'dovich effect. |
| Publication date: 18 May 2010 |
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| Confirmation of X-ray absorption by warm-hot intergalactic medium in the sculptor wall |
| In a previous paper, we reported a 3 sigma detection of an absorption line from the warm-hot intergalactic medium (WHIM) using the Chandra and XMM X-ray grating spectra of the blazar H2356-309, the sight line of which intercepts the Sculptor Wall, a large-scale superstructure of galaxies at z ~ 0.03. To verify our initial detection, we obtained a deep (500 ks), follow-up exposure of H2356-309 as part of the Cycle-10 Chandra Large Project Program. From a joint analysis of the Cycle-10 and previous (Cycle-8) Chandra grating data we detect the redshifted O VII WHIM line at a significance level of 3.4 sigma, a substantial improvement over the 1.7 sigma level reported previously when using only the Cycle-8 data. The significance increases to 4.0 sigma when the existing XMM grating data are included in the analysis, thus confirming at higher significance the existence of the line at the redshift of the Sculptor Wall with an equivalent width of 28.5 ± 10.5 mÅ (90% confidence). We obtain a 90% lower limit on the O VII column density of 0.8 × 1016 cm-2 and a 90% upper limit on the Doppler b parameter of 460 km s-1. Assuming the absorber is uniformly distributed throughout the ~15 Mpc portion of the blazar's sight line that intercepts the Sculptor Wall, that the O VII column density is 2 × 1016 cm-2 (corresponding to b >~150 km-1where the inferred column density is only weakly dependent on b), and that the oxygen abundance is 0.1 solar, we estimate a baryon over-density of ~30 for the WHIM, which is consistent with the peak of the WHIM mass fraction predicted by cosmological simulations. The clear detection of O VII absorption in the Sculptor Wall demonstrates the viability of using current observatories to study WHIM in the X-ray absorption spectra of blazars behind known large-scale structures. |
| Publication date: 11 May 2010 |
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| Comparative investigation of the terrestrial and Venusian magnetopause: Kinetic modeling and experimental observations by Cluster and Venus Express |
| In June 2006 Venus Express crossed several times the outer boundary of Venus induced magnetosphere, its magnetosheath and its bow shock. During the same interval the Cluster spacecraft surveyed the dawn flank of the terrestrial magnetosphere, intersected the Earth's magnetopause and spent long time intervals in the magnetosheath. This configuration offers the opportunity to perform a joint investigation of the interface between Venus and Earth's outer plasma layers and the shocked solar wind. We discuss the kinetic structure of the magnetopause of both planets, its global characteristics and the effects on the interaction between the planetary plasma and the solar wind. A Vlasov equilibrium model is constructed for both planetary magnetopauses and provides good estimates of the magnetic field profile across the interface. The model is also in agreement with plasma data and evidence the role of planetary and solar wind ions on the spatial scale of the equilibrium magnetopause of the two planets. The main characteristics of the two magnetopauses are discussed and compared. |
| Publication date: 06 May 2010 |
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| Comparative investigation of the terrestrial and Venusian magnetopause: Kinetic modeling and experimental observations by Cluster and Venus Express |
| In June 2006 Venus Express crossed several times the outer boundary of Venus induced magnetosphere, its magnetosheath and its bow shock. During the same interval the Cluster spacecraft surveyed the dawn flank of the terrestrial magnetosphere, intersected the Earth's magnetopause and spent long time intervals in the magnetosheath. This configuration offers the opportunity to perform a joint investigation of the interface between Venus and Earth's outer plasma layers and the shocked solar wind. We discuss the kinetic structure of the magnetopause of both planets, its global characteristics and the effects on the interaction between the planetary plasma and the solar wind. A Vlasov equilibrium model is constructed for both planetary magnetopauses and provides good estimates of the magnetic field profile across the interface. The model is also in agreement with plasma data and evidence the role of planetary and solar wind ions on the spatial scale of the equilibrium magnetopause of the two planets. The main characteristics of the two magnetopauses are discussed and compared. |
| Publication date: 06 May 2010 |
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| A&A special feature: Science with AKARI |
The May 2010 issue of Astronomy & Astrophysics is a special feature devoted to the new results obtained with the infrared satellite AKARI, a JAXA project with the participation of ESA. It includes 17 articles dealing with various subjects. Some papers are based on the AKARI all-sky survey, which has just been released. Others are dedicated to pointed observations of many astronomical targets from solar system bodies to distant galaxies. |
| Publication date: 01 May 2010 |
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| Supermagnetosonic Jets behind a Collisionless Quasiparallel Shock |
| 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. |
| Publication date: 19 Apr 2010 |
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| Inhomogeneities on the surface of 21 Lutetia, the asteroid target of the Rosetta mission - Ground-based results before the Rosetta fly-by |
Context. In July 2010 the ESA spacecraft Rosetta will fly by the main belt asteroid 21 Lutetia. Several observations of this asteroid have been performed so far, but its surface composition and nature are still a matter of debate. For a long time Lutetia was supposed to have a metallic nature due to its high IRAS albedo. Later on it has been suggested that the asteroid has a surface composition similar to primitive carbonaceous chondrite meteorites, while further observations proposed a possible genetic link with more evolved enstatite chondrite meteorites.
Aims. We performed visible spectroscopic observations of 21 Lutetia in November 2008 at the Telescopio Nazionale Galileo (TNG, La Palma, Spain) to make a decisive contribution to solving the conundrum of its nature.
Methods. Thirteen visible spectra were acquired at different rotational phases and subsequently analyzed.
Results. We confirm a narrow spectral feature at about 0.47-0.48 microns which was already found by Lazzarin et al. (2004, A&A, 425, L25) in the spectra of Lutetia. We also confirm an earlier find of Lazzarin et al. (2004), who detected a spectral feature at about 0.6 microns in one of their Lutetia's spectra. More remarkable is the difference of our spectra though, which exhibit different spectral slopes between 0.6 and 0.75 microns and, in particular, we found that up to 20% of the Lutetia surface could have flatter spectra.
Conclusions. We detected a variation of the spectral slopes at different rotational phases that could be interpreted as possibly due to differences in the chemical/mineralogical composition as well as to inhomogeneities of the structure of the Lutetia's surface (e.g., to craters or albedo spots) in the southern hemisphere.
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| Publication date: 15 Apr 2010 |
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| Link between EMIC waves in a plasmaspheric plume and a detached sub-auroral proton arc with observations of Cluster and IMAGE satellites, |
| In this paper, we report observations from a Cluster satellite showing that ULF wave occurred in the outer boundary of a plasmaspheric plume on September 4, 2005. The band of observed ULF waves is between the He+ ion gyrofrequency and O+ ion gyrofrequency at the equatorial plane, implying that those ULF waves can be identified as EMIC waves generated by ring current ions in the equatorial plane and strongly affected by rich cold He+ ions in plasmaspheric plumes. During the interval of observed EMIC waves, the footprint of Cluster SC3 lies in a subauroral proton arc observed by the IMAGE FUV instrument, demonstrating that the subauroral proton arc was caused by energetic ring current protons scattered into the loss cone under the Ring Current (RC)-EMIC interaction in the plasmaspheric plume. Therefore, the paper provides a direct proof that EMIC waves can be generated in the plasmaspheric plume and scatter RC ions to cause subauroral proton arcs. |
| Publication date: 13 Apr 2010 |
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| Recent hot-spot volcanism on Venus from VIRTIS emissivity data |
| 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. |
| Publication date: 08 Apr 2010 |
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| High-Performance X-ray Optics - Abstract and Summary report |
| 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. |
| Publication date: 02 Apr 2010 |
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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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