ESA Science & Technology - Publication Archive

We present energetic neutral atom (ENA) images in the energy range 45 to 50 keV for H and 92 to 138 keV for O measured by the Neutral Atom Detector Unit (NUADU) onboard Double Star TC-2 during a geomagnetic storm on 8 May 2005. We compare the ion fluxes deduced from inversion of the NUADU image with those calculated using the Comprehensive Ring Current Model (CRCM). This comparison shows that the two approaches are consistent when used to derive the configuration of the corresponding global ion distribution and the peak ion fluxes. The deduced peak ion flux is located in the premidnight sector at 1540 UT, while the deduced ion peak flux is located in the midnight sector at 1610 UT. There are strong ion fluxes in the region between L = 2 and L = 4 which form a closed loop configuration. The ion peak flux is about 2.2×10⁶/cm²/sr/keV/s. The deduced ion distribution agrees well with the NUADU measurement. The agreement between the inverted ion distributions and the CRCM results give us confidence in applying our ENA imaging and modeling techniques to the study of the evolution of the inner magnetosphere plasma distribution and the global dynamics of the ring current during magnetic storms.

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.]

We study the plasma turbulence, at scales larger than the ion inertial length scale, downstream of a quasiparallel bow shock using Cluster multispacecraft measurements. We show that turbulence is intermittent and well described by the extended structure function model, which takes into account the spatial inhomogeneity of the cascade rate. For the first time we use multispacecraft observations to characterize the evolution of magnetosheath turbulence, particularly its intermittency, as a function of the distance from the bow shock. The intermittency significantly changes over the distance of the order of 100 ion inertial lengths, being increasingly stronger and anisotropic away from the bow shock.

This document describes the detailed scientific requirements for the Marco Polo mission. These requirements are derived from discussions by the Science Study Team (SST) of the Marco Polo study and is based on the scientific objectives as described in the Marco Polo Proposal to ESA's Cosmic Vision programme (RD 01). [This is an abbreviated version of the original document abstract.]

This Payload Definition Document (PDD) is a compilation of the Cross-Scale strawman payload requirements and of their related reference design. The PDD plays a key role in defining the resources required by the Cross-Scale instruments and in providing the information necessary to conduct the mission assessment study and the preliminary spacecraft design. [This is an abbreviated version of the original document abstract.]

We report measurements of night-side airglow emission in the atmosphere of Venus in the OH (2-0), OH (1-0), O2(a-X) (0-1), and O2(a-X) (0-0) bands. This is the first detection of the first three of these airglow emissions on another planet. These observations provide the most direct observational constraints to date on H, OH, and O3, key species in the chemistry of Venus' upper atmosphere. (This is an abbreviated abstract from the paper "First detection of hydroxyl in the atmosphere of Venus", by Piccioni et al, published in Astronomy & Astrophysics, A&A 483, L29-L33 (2008))

CMOS-APS imaging detectors open new opportunities for remote sensing in solar physics beyond what classical CCDs can provide, offering far less power consumption, simpler electronics, better radiation hardness, and the possibility of avoiding a mechanical shutter. The SWAP telescope onboard the PROBA2 technology demonstration satellite of the European Space Agency will be the first actual implementation of a CMOS-APS detector for solar physics in orbit. One of the goals of the SWAP project is precisely to acquire experience with the CMOS-APS technology in a real-live space science context. Such a precursor mission is essential in the preparation of missions such as Solar Orbiter where the extra CMOS-APS functionalities will be hard requirements. The current paper concentrates on specific CMOS-APS issues that were identified during the SWAP preflight calibration measurements. We will discuss the different readout possibilities that the CMOS-APS detector of SWAP provides and their associated pros and cons. In particular we describe the image lag effect, which results in a contamination of each image with a remnant of the previous image. We have characterised this effect for the specific SWAP implementation and we conclude with a strategy on how to successfully circumvent the problem and actually take benefit of it for solar monitoring.

The European space Agency (ESA) undertook a bold experiment with the Mars Express mission: to develop rapidly a low cost platform for planetary exploration. The myriad scientific achievements of this mission prove the success of the experiment. ESA took a second bold step by adapting the Mars platform for the Venus Express mission, and doing so rapidly and most cost-effectively. While the differences in Venus and Mars necessitated several changes in instrumentation, there are many objectives that remain the same at the two planets. When we issued a call to the MEX and VEX communities for a volume of brief articles covering the latest results from these two missions, the response from those examining the interaction of the solar wind and energetic particles with the planets was most swift. The authors were asked to keep their presentations to four published pages. The guest editor in turn attempted to shepherd these papers through the reviewing process quickly. In those instances where the editor had a conflict of interest, R. J. Strangeway assumed the duties of the editor.

The articles that passed review before the press deadline are included therein. They include discussions of the various plasma boundaries at Venus and Mars, the nature of their plasma environments, the discovery of energetic neutral particles, the configuration of the magnetic field near the planets, space weather and the loss of atmosphere. Papers included contain both modeling and observational work and are written by some of the newest members of the community as well as many of the veteran research scientists. We especially thank the referees of these papers who responded promptly to help speed these early results to the readers of Planetary and Space Science.

On the 18th of August 2002, during a crossing of the near-Earth plasma sheet Cluster observed an ion flow burst, caused by a near-Earth reconnection event. Cluster observed a tailward bulk flow which reverse to earthward flow, indicating a close passage of the diffusion region. We show that reversals in B_Z and B_Y are consistent with reconnection. During the event, a short duration burst of electrons in the range of a few keV up to more than 100 keV are observed streaming away from the reconnection region. The accelerated electrons were aligned with the magnetic field, streaming tailward, and were observed simultaneously by all four spacecraft located on both the northern and southern side of the current sheet. The four Cluster spacecraft, separated by ~3700 km, observe the electrons for a time period of ~60 s, indicating the burst to be a temporal rather than localized feature. A second burst of tailward accelerated electrons observed for ~40 s was observed by Cluster 1 and 2 upon entering the earthward outflow region. The second beam thus appear to be directed toward the X-line. The flux levels of the energetic electron bursts exceed those of the ambient plasma sheet by a factor 2-4. In general, the highest energetic electron fluxes during this event were observed in the earthward outflow region. Observations indicate that reconnection operates on closed plasma sheet field lines in this event and does not reach lobe field lines.

Using Hubble Space Telescope (HST) and Spitzer IRAC imaging, we report the discovery of a very bright strongly lensed Lyman break galaxy (LBG) candidate at z ~ 7.6 in the field of the massive galaxy cluster Abell 1689 (z=0.18). The galaxy candidate, which we refer to as A1689-zD1, shows a strong z₈₅₀-J₁₁₀ break of at least 2.2 mag and is completely undetected (<1 sigma) in HST Advanced Camera for Surveys (ACS) g₄₇₅, r₆₂₅, i₇₇₅, and z₈₅₀ data. These properties, combined with the very blue J₁₁₀-H₁₆₀ and H₁₆₀-4.5 micron colors, are exactly the properties of an z ~ 7.6 LBG, and can only be reasonably fit by a star-forming galaxy at z=7.6±0.4 (Chi_mu-square=1.1). Attempts to reproduce these properties with a model galaxy at z < 4 yield particularly poor fits (Chi_mu-square=25). A1689-zD1 has an observed (lensed) magnitude of 24.7 AB (8 sigma) in the NICMOS H₁₆₀ band and is 1.3 mag brighter than the brightest known z₈₅₀-dropout galaxy. When corrected for the cluster magnification of ~9.3 at z~7.6, the candidate has an intrinsic magnitude of H₁₆₀=27.1 AB, or about an L* galaxy at z~7.6. The source-plane deprojection shows that the star formation is occurring in compact knots of size <~300 pc. The best-fit stellar population synthesis models yield a median redshift of 7.6, stellar masses (1.6-3.9)×10⁹ M_solar, stellar ages 45-320 Myr, star formation rates <~7.6 M_solar yr^-1, and low reddening with A_V<=0.3. These properties are generally similar to those of LBGs found at z~5-6. The inferred stellar ages suggest a formation redshift of z~8-10 (t<~0.63Gyr). A1689-zD1 is the brightest observed, highly reliable z>7.0 galaxy candidate found to date.

This study uses two conjunctions between Cluster and Double Star TC-1 spacecraft together with global magnetohydrodynamic (MHD) simulations to investigate the large-scale configuration of magnetic reconnection at the dayside magnetopause. Both events involve southward interplanetary magnetic fields with significant B_y components. The first event occurred on 8 May 2004, while both spacecraft were exploring the dawn flank of the magnetosphere; TC-1 was skimming the magnetopause whereas Cluster was exploring higher latitudes. Results from a global MHD simulation show the formation of an equatorial merging line in the morning sector and suggest that the three-dimensional geometry of the merging region is mostly a radial juxtaposition of planes displaying X-type reconnection geometries. The second conjunction was on 6 April 2004. During this event, Cluster was located at high latitudes and close to the noon-midnight meridian, while TC-1 was exploring the dawnside at low latitudes. Analysis of the simulation reveals that both antiparallel and component merging occurred simultaneously. Three-dimensional rendering of the parallel electric field indicates that component merging initiated in the subsolar magnetopause. Simulation runs carried out using different parameters in the model suggest that the spread of the merging region depends on the local resistivity. The subsolar-merging region grows with increasing resistivity values and becomes patchy when a resistivity threshold is used. However, the region of component merging appears to remain spatially constrained to the subsolar region where stronger parallel electric fields occur and no clear connection with the antiparallel-merging regions is found for the range of parameters surveyed.

Observations of oscillations of temperature and wind in planetary atmospheres provide a means of generalizing models for atmospheric dynamics in a diverse set of planets in the Solar System and elsewhere. An equatorial oscillation similar to one in the Earth's atmosphere has been discovered in Jupiter. Here we report the existence of similar oscillations in Saturn's atmosphere, from an analysis of over two decades of spatially resolved observations of its 7.8-micron methane and 12.2-micron ethane stratospheric emissions, where we compare zonal-mean stratospheric brightness temperatures at planetographic latitudes of 3.6° and 15.5° in both the northern and the southern hemispheres. These results support the interpretation of vertical and meridional variability of temperatures in Saturn's stratosphere as a manifestation of a wave phenomenon similar to that on the Earth and in Jupiter. The period of this oscillation is 14.8 +- 1.2 terrestrial years, roughly half of Saturn's year, suggesting the influence of seasonal forcing, as is the case with the Earth's semi-annual oscillation.

Context: About half of the baryons in the local Universe are invisible and - according to simulations - their dominant fraction resides in filaments connecting clusters of galaxies in the form of low density gas with temperatures in the range of 10⁵ < T < 10⁷ K. This warm-hot intergalactic medium has never been detected indisputably using X-ray observations.
Aims: We aim to probe the low gas densities expected in the large-scale structure filaments by observing a filament connecting the massive clusters of galaxies A 222 and A 223 (z = 0.21), which has a favorable orientation approximately along our line-of-sight. This filament has been previously detected using weak lensing data and as an over-density of colour-selected galaxies.
Methods: We analyse X-ray images and spectra obtained from a deep observation (144 ks) of A 222/223 with XMM-Newton.
Results: We present observational evidence of X-ray emission from the filament connecting the two clusters. We detect the filament in the wavelet-decomposed soft-band (0.5-2.0 keV) X-ray image with a 5-sigma significance. Following the emission down to the 3-sigma significance level, the observed filament is ~1.2 Mpc wide. The temperature of the gas associated with the filament, determined from the spectra, is kT = 0.91±0.25 keV, and its emission measure corresponds to a baryon density of (3.4±1.3)×10^-5(l/15 Mpc)^-1/2 cm^-3, where l is the length of the filament along the line-of-sight. This density corresponds to a baryon over-density of rho/<rho_C> ~150. The properties of the gas in the filament are consistent with results of simulations of the densest and hottest parts of the warm-hot intergalactic medium.

Aims. In an attempt to catch new X-ray transients while they are still bright, the data taken by XMM-Newton as it slews between targets are being processed and cross-correlated with other X-ray observations as soon as the slew data appear in the XMM-Newton archive.
Methods. A bright source, XMMSL1 J070542.7-381442, was detected on 9 Oct. 2007 at a position where no previous X-ray source had been seen. The XMM slew data and optical data acquired with the Magellan Clay 6.5 m telescope were used to classify the new object.
Results. No XMM slew X-ray counts are detected above 1 keV and the source is seen to be 750 times brighter than the ROSAT All-Sky Survey upper limit at that position. The normally m_V ~ 16 star, USNO-A2.0 0450-03360039, which lies 3.5" from the X-ray position, was seen in our Magellan data to be very much enhanced in brightness. Our optical spectrum showed emission lines that identified the source as a nova in the auroral phase; hence, this optical source is undoubtedly the progenitor of the X-ray source - a new nova (now also known as V598 Pup). The X-ray spectrum indicates that the nova was in a super-soft state (with kT_eff ~ 35 eV). We estimate the distance to the nova to be ~ 3 kpc. Analysis of archival robotic optical survey data shows a rapid-decline light curve consistent with what is expected for a very fast nova.
Conclusions. The XMM-Newton slew data present a powerful opportunity to find new X-ray transient objects while they are still bright. Here we present the first such source discovered by the analysis of near real-time slew data.

Spacecraft potential measurements by the EFW electric field experiment on the Cluster satellites can be used to obtain plasma density estimates in regions barely accessible to other type of plasma experiments. Direct calibrations of the plasma density as a function of the measured potential difference between the spacecraft and the probes can be carried out in the solar wind, the magnetosheath, and the plasmashere by the use of CIS ion density and WHISPER electron density measurements. The spacecraft photoelectron characteristic (photoelectrons escaping to the plasma in current balance with collected ambient electrons) can be calculated from knowledge of the electron current to the spacecraft based on plasma density and electron temperature data from the above mentioned experiments and can be extended to more positive spacecraft potentials by CIS ion and the PEACE electron experiments in the plasma sheet. This characteristic enables determination of the electron density as a function of spacecraft potential over the polar caps and in the lobes of the magnetosphere, regions where other experiments on Cluster have intrinsic limitations. Data from 2001 to 2006 reveal that the photoelectron characteristics of the Cluster spacecraft as well as the electric field probes vary with the solar cycle and solar activity. The consequences for plasma density measurements are addressed. Typical examples are presented to demonstrate the use of this technique in a polar cap/lobe plasma.

The immediate effect of the rotation of the interplanetary magnetic field (IMF) from southward to northward on cusp precipitation has been rarely observed by a polar orbiting satellite in the past. The four Cluster spacecraft observed such an event on 23 September 2004 as they were crossing the polar cusp within 2-16 min from each other. Between the first three and the last spacecraft crossing the cusp, the IMF rotated from southward to northward with a dominant By (GSM) component. For the first time we can examine the changes in the particle precipitation immediately after such IMF change. The first two spacecraft observed typical IMF-southward ion dispersion, while the last one observed both an IMF-southward-like dispersion in the boundary layer and an IMF-northward dispersion in the cusp. After the IMF turning, the cusp is shown to have grown in size in both the poleward and equatorward directions. A three-dimensional magnetohydrodynamic simulation is used to determine the locations of the sources of the ions and the topology of the magnetic field during the event.

The Antennae galaxies are the closest example of an ongoing major galaxy merger and, as such, represent a unique laboratory for furthering the understanding of the formation of exotic objects (e.g., tidal dwarf galaxies, ultraluminous X-ray sources, super stellar clusters). In a previous paper HST WFPC2 observations were used to demonstrate that the Antennae system might be at a distance considerably less than that conventionally assumed in the literature. Here we report new, much deeper HST ACS imaging that resolves the composite stellar populations and, most importantly, reveals a well-defined red giant branch. The tip of this red giant branch (TRGB) is unambiguously detected at I₀^TRGB=26.65+-0.09 mag. Adopting the most recent calibration of the luminosity of the TRGB then yields a distance modulus for the Antennae of (m-M)₀ = 30.62+-0.17 corresponding to a distance of 13.3+-1.0 Mpc. This is consistent with our earlier result, once the different calibrations for the standard candle are considered. We briefly discuss the implications of this now well-determined shorter distance.

We use the multi-spacecraft mission Cluster to make observational estimates of the local energy conversion across the dayside high-latitude magnetopause. The energy conversion is estimated during eleven complete magnetopause crossings under steady south-dawnward interplanetary magnetic field (IMF). We describe a new method to determine the reconnection rate from the magnitude of the local energy conversion. The reconnection rate as well as the energy conversion varies during the course of the eleven crossings and is typically much higher for the outbound crossings. This supports the previous interpretation that reconnection is continuous but its rate is modulated.

The objective of the paper is to asses the specific spectral scaling properties of magnetic reconnection associated fluctuations/turbulence at the earthward and tailward outflow regions observed simultaneously by the Cluster and Double Star (TC-2) spacecraft on 26 September 2005. Systematic comparisons of spectral characteristics, including variance anisotropy and scale-dependent spectral anisotropy features in wave vector space were possible due to the well-documented reconnection events, occurring between the positions of Cluster (X = - 14-16 R_e) and TC-2 (X = - 6.6 R_e). Another factor of key importance is that the magnetometers on the spacecraft are similar. The comparisons provide further evidence for asymmetry of physical processes in earthward/tailward reconnection outflow regions. Variance anisotropy and spectral anisotropy angles estimated from the multiscale magnetic fluctuations in the tailward outflow region show features which are characteristic for magnetohydrodynamic cascading turbulence in the presence of a local mean magnetic field. The multiscale magnetic fluctuations in the earthward outflow region are not only exhibiting more power, lack of variance, and scale-dependent anisotropies but also are having larger anisotropy angles. In this region the magnetic field is more dipolar and the main processes driving turbulence are flow breaking/mixing, perhaps combined with turbulence ageing and noncascade-related multiscale energy sources.

We report on Cluster observations of a thin current sheet interval under the presence of a strong |B_Y| during a fast earthward flow interval between 1655 UT and 1703 UT on 17 August 2003. The strong |B_Y| in the tail could be associated with a strong IMF |B_Y|, but the large fluctuations in B_Y, not seen in the IMF, suggest that a varying reconnection rate causes a varying transport of B_Y-dominated magnetic flux and/or a change in B_Y due to the Hall-current system. During the encounter of the high-speed flow, an intense current layer was observed around 1655:53 UT with a peak current density of 182 nA/m², the largest current density observed by the Cluster four-spacecraft magnetic field measurement in the magnetotail. The half width of this current layer was estimated to be ~290 km, which was comparable to the ion-inertia length. Its unique signature is that the strong current is mainly field-aligned current flowing close to the center of the plasma sheet. The event was associated with parallel heating of electrons with asymmetries, which suggests that electrons moving along the field lines can contribute to a strong dawn-to-dusk current when the magnetotail current sheet becomes sufficiently thin and active in a strong guide field case.