Publication archive

Publication archive

Venus, unlike Earth, is an extremely dry planet although both began with similar masses, distances from the Sun, and presumably water inventories. The high deuterium-to-hydrogen ratio in the venusian atmosphere relative to Earth's also indicates that the atmosphere has undergone significantly different evolution over the age of the Solar System. Present-day thermal escape is low for all atmospheric species. However, hydrogen can escape by means of collisions with hot atoms from ionospheric photochemistry, and although the bulk of O and O2 are gravitationally bound, heavy ions have been observed to escape through interaction with the solar wind. Nevertheless, their relative rates of escape, spatial distribution, and composition could not be determined from these previous measurements. Here we report Venus Express measurements showing that the dominant escaping ions are O+, He+ and H+. The escaping ions leave Venus through the plasma sheet (a central portion of the plasma wake) and in a boundary layer of the induced magnetosphere. The escape rate ratios are Q(H+)/Q(O+) = 1.9; Q(He+)/Q(O+) = 0.07. The first of these implies that the escape of H+ and O+, together with the estimated escape of neutral hydrogen and oxygen, currently takes place near the stoichometric ratio corresponding to water.
Published: 29 November 2007
Most stars form as members of large associations within dense, very cold (10-100 K) molecular clouds. The nearby giant molecular cloud in Orion hosts several thousand stars of ages less than a few million years, many of which are located in or around the famous Orion Nebula, a prominent gas structure illuminated and ionized by a small group of massive stars (the Trapezium). We present X-ray observations obtained with the X-ray Multi-Mirror satellite XMM-Newton revealing that a hot plasma with a temperature of 1.7-2.1 million K pervades the southwest extension of the nebula. The plasma flows into the adjacent interstellar medium. This X-ray outflow phenomenon must be widespread throughout our Galaxy
Published: 29 November 2007
Venus has thick clouds of H2SO4 aerosol particles extending from altitudes of 40 to 60 km. The 60-100 km region (the mesosphere) is a transition region between the 4 day retrograde superrotation at the top of the thick clouds and the solar-antisolar circulation in the thermosphere (above 100 km), which has upwelling over the subsolar point and transport to the nightside. The mesosphere has a light haze of variable optical thickness, with CO, SO2, HCl, HF, H2O and HDO as the most important minor gaseous constituents, but the vertical distribution of the haze and molecules is poorly known because previous descent probes began their measurements at or below 60 km. Here we report the detection of an extensive layer of warm air at altitudes 90-120 km on the night side that we interpret as the result of adiabatic heating during air subsidence. Such a strong temperature inversion was not expected, because the night side of Venus was otherwise so cold that it was named the 'cryosphere' above 100 km. We also measured the mesospheric distributions of HF, HCl, H2O and HDO. HCl is less abundant than reported 40 years ago. HDO/H2O is enhanced by a factor of 2.5 with respect to the lower atmosphere, and there is a general depletion of H2O around 80-90 km for which we have no explanation.
Published: 29 November 2007
The upper atmosphere of a planet is a transition region in which energy is transferred between the deeper atmosphere and outer space. Molecular emissions from the upper atmosphere (90-120 km altitude) of Venus can be used to investigate the energetics and to trace the circulation of this hitherto little-studied region. Previous spacecraft and ground-based observations of infrared emission from CO2, O2 and NO have established that photochemical and dynamic activity controls the structure of the upper atmosphere of Venus. These data, however, have left unresolved the precise altitude of the emission owing to a lack of data and of an adequate observing geometry. Here we report measurements of day-side CO2 non-local thermodynamic equilibrium emission at 4.3 m, extending from 90 to 120 km altitude, and of night-side O2 emission extending from 95 to 100 km. The CO2 emission peak occurs at 115 km and varies with solar zenith angle over a range of 10 km. This confirms previous modelling, and permits the beginning of a systematic study of the variability of the emission. The O2 peak emission happens at 96 km +- 1 km, which is consistent with three-body recombination of oxygen atoms transported from the day side by a global thermospheric sub-solar to anti-solar circulation, as previously predicted.
Published: 29 November 2007
Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright 'dipole' feature surrounded by a cold 'collar' at its north pole. The polar dipole is a 'double-eye' feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus' south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition.
Published: 29 November 2007
Venus is completely covered by a thick cloud layer, of which the upper part is composed of sulphuric acid and some unknown aerosols. The cloud tops are in fast retrograde rotation (super-rotation), but the factors responsible for this super-rotation are unknown. Here we report observations of Venus with the Venus Monitoring Camera on board the Venus Express spacecraft. We investigate both global and small-scale properties of the clouds, their temporal and latitudinal variations, and derive wind velocities. The southern polar region is highly variable and can change dramatically on timescales as short as one day, perhaps arising from the injection of SO2 into the mesosphere. The convective cells in the vicinity of the subsolar point are much smaller than previously inferred, which we interpret as indicating that they are confined to the upper cloud layer, contrary to previous conclusions but consistent with more recent study.
Published: 29 November 2007
Venus is Earth's near twin in mass and radius, and our nearest planetary neighbour, yet conditions there are very different in many respects. Its atmosphere, mostly composed of carbon dioxide, has a surface temperature and pressure far higher than those of Earth. Only traces of water are found, although it is likely that there was much more present in the past, possibly forming Earth-like oceans. Here we discuss how the first year of observations by Venus Express brings into focus the evolutionary paths by which the climates of two similar planets diverged from common beginnings to such extremes. These include a CO2-driven greenhouse effect, erosion of the atmosphere by solar particles and radiation, surface-atmosphere interactions, and atmospheric circulation regimes defined by differing planetary rotation rates.
Published: 29 November 2007

Venus Express is the first dedicated mission to Venus in over a decade. It was built by the European Space Agency, launched from Baikonur on a Soyuz-Fregat launcher on 9 November 2005. It arrived at Venus on 11 April 2006 and is in a polar orbit, with a period of ~24 hours. Since arrival its suite of instruments has been collecting data on the atmosphere and magnetosphere. In this focus, eight Letters describe the results obtained so far, while a Progress paper by Svedhem et al. gives an overview of the mission.

Published: 28 November 2007
Titan's ionosphere contains a rich positive ion population including organic molecules. Here, using CAPS electron spectrometer data from sixteen Titan encounters, we reveal the existence of negative ions. These ions, with densities up to ~100 cm-3, are in mass groups of 10-30, 30-50, 50-80, 80-110, 110-200 and 200+ amu/charge. During one low encounter, negative ions with mass per charge as high as 10,000 amu/q are seen. Due to their unexpectedly high densities at ~950 km altitude, these negative ions must play a key role in the ion chemistry and they may be important in the formation of organic-rich aerosols (tholins) eventually falling to the surface.
Published: 28 November 2007
Scientific editor: R. Marsden
Editor: A. Wilson The report for the 36th COSPAR Meeting covers, as in previous issues, the missions of the Scientific Programme of ESA in the areas of astronomy, Solar System science and fundamental physics. This year's COSPAR meeting will take place only weeks before the end of the SMART-1 mission to the Moon, a technology project that provided the first European look at our natural satellite from lunar orbit.In October of this year, a new mission will be launched: COROT. ESA, together with a number of countries, is contributing to this unique, French-led project that will provide an insight into the interior of the stars, by means of the asteroseismology technique successfully applied by SOHO. COROT will also perform a systematic search for new extrasolar planets using photometric transits. The record number of ESA Science Programme missions in operation established at the time of the last report was maintained in 2006 (Huygens having been replaced in the list by Venus Express). Eleven different missions, involving 14 operating spacecraft, are providing excellent science to the worldwide scientific community. The Research and Scientific Support Department (RSSD) is responsible for the science operations of these missions and makes every effort to ensure the best possible science return. The Department also supports the realisation of approved projects in all phases of their development.
Published: 16 June 2006
Editors: A. Balogh, L.J. Lanzerotti, and S.T. Suess A principal objective of space research has been to increase understanding of the way the Sun changes through its 11-year sunspot cycle, and how these changes affect the space around the Sun - the heliosphere. "The Heliosphere through the Solar Activity Cycle" is the first book to describe and analyze ground and space-based data on the three-dimensional heliosphere taken as the Ulysses spacecraft made orbital passes of the Sun's north and south poles in 1994-1995 and again in 2000-2001. The chapters explain the many different aspects of changes in the heliosphere in response to solar activity, and describe the rise in solar activity from the last minimum in 1998 to its maximum in 2000, and its subsequent decline. "The Heliosphere through the Solar Activity Cycle" was written by leading scientists directly involved with the Ulysses mission and edited by André Balogh, Louis J. Lanzerotti, and Steven T. Suess. It provides the definitive discussion of the subject to date and looks forward to discoveries to be made by Ulysses and potential follow-on missions in the future.

Contents

1.The heliosphere: Its origin and exploration
A. Balogh & L.J. Lanzerotti
2.Solar Cycle 23
D.H. Hathaway & S.T. Suess
3.The solar wind throughout the solar cycle
R. von Steiger
4.The global heliospheric magnetic field
E.J. Smith
5.Heliospheric energetic particle variations
D. Lario & M. Pick
6.Galactic and anomalous cosmic rays through the solar cycle: New insight from Ulysses
B. Heber & M.S. Potgieter
7.Overview: The heliosphere then and now
S.T. Suess
Published: 01 November 2007
The ESA Huygens probe performed a successful Entry, Descent, and Landing (EDL) sequence through Titan's dense atmosphere on January 14, 2005. During all three phases, i.e., the supersonic entry phase, the descent phase, as well as the impact and post impact phases, the probe performed measurements that were used for the reconstruction of its entry and descent trajectory. We first discuss the datasets relevant to the entry and descent trajectory reconstruction. We then provide an overview of the reconstruction strategy, and show preliminary results of the reconstructed entry and descent trajectory, including both position and velocity.
Published: 02 May 2006
Be stars remain a mystery since their discovery 140 years ago. The two presently most favored explanations for the Be phenomenon are the beating of non-radial pulsations and the presence of a magnetic field. In this paper we present the method used in the search for magnetic fields in Be stars, from indirect indicators to direct Zeeman detections, and the role of the magnetic field in the presence of circumstellar material (disk and clouds).
Published: 02 May 2005
Spontaneous formation of solitary wave structures has been observed in Earth's magnetopause, and is shown to be caused by the breakup of a zonal flow by the action of drift wave turbulence. Here we show matched observations and modeling of coherent, large-scale solitary electrostatic structures, generated during the interaction of short-scale drift wave turbulence and zonal flows at the Earth's magnetopause. The observations were made by the Cluster spacecraft and the numerical modeling was performed using the wave-kinetic approach to drift wave-zonal flow interactions. Good agreement between observations and simulations has been found, thus explaining the emergence of the observed solitary structures as well as confirming earlier theoretical predictions of their existence.
Published: 16 November 2007
The Ground-based Asteroseismology Uniform Database Interface (GAUDI) is the result of the preparatory work performed for the COROT satellite. In the data available in GAUDI we discovered 17 B-type stars that show emission in their Balmer lines and were not known to display such emission before, including at least 16 non-supergiant ones. We thus reclassify those stars as Be stars. These 17 new Be stars increase the number of Be stars in the field of view of COROT by ~25%, which is important for the target selection of the mission. Moreover, ~70% of the discovered Be stars are of late subtypes. Be stars have been mostly found among early subtypes until now, but this could be due to an observational bias. Finally, one of the discovered star is either a slowly rotating shell Be star or a Herbig Be star with a low vsini, which makes this star especially interesting.
Published: 21 January 2005
The equatorial Medusae Fossae Formation (MFF) is enigmatic and perhaps among the youngest geologic deposits on Mars. They are thought to be composed of volcanic ash, eolian sediments, or an ice-rich material analogous to polar layered deposits. The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) instrument aboard the Mars Express Spacecraft has detected nadir echoes offset in time-delay from the surface return in orbits over MFF material. These echoes are interpreted to be from the subsurface interface between the MFF material and the underlying terrain. The delay time between the MFF surface and subsurface echoes is consistent with massive deposits emplaced on generally planar lowlands materials with a real dielectric constant of ~2.9 ± 0.4. The real dielectric constant and the estimated dielectric losses are consistent with a substantial component of water ice. However, an anomalously low-density, ice-poor material cannot be ruled out. If ice-rich, the MFF must have a higher percentage of dust and sand than polar layered deposits. The volume of water in an ice-rich MFF deposit would be comparable to that of the south polar layered deposits.
Published: 16 November 2007
We present multi-wavelength observations of stellar features in the HI tidal bridge connecting M81 and M82 in the region called Arp's Loop. We identify eight young star-forming regions from Galaxy Evolution Explorer ultraviolet observations. Four of these objects are also detected at HI. We determine the basic star formation history of Arp's Loop using F475W and F814W images obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope. We find both a young (< 10 Myr) and an old (> 1 Gyr) stellar population with a similar spatial distribution and a metallicity Z ~ 0.004. We suggest that the old stellar population was formed in the stellar disk of M82 and/or M81 and ejected into the intergalactic medium during a tidal passage (~ 200-300 Myr ago), whereas the young UV-bright stars have formed in the tidal debris. The UV luminosities of the eight objects are modest and typical of small clusters or OB associations. The tidal bridge between M81-M82 therefore appears to be intermediate between the very low levels of star formation seen in the Magellanic bridge and actively star-forming tidal tails associated with major galaxy mergers.
Published: 16 November 2007
Mars Express arrived at its destination in December 2003 to probe every facet of the Red Planet, from the interior to the ionosphere, in unprecedented detail. In addition to these global studies, the mission's unifying theme is the search for water in its various forms everywhere on the planet. The mission has been extended into 2009, and could last even longer.
Published: 15 November 2007
In the course of Gaia's 5-year astronomical survey, the equivalent of around 20 000 DVDs of raw information on our Galaxy will be harvested and transmitted to Earth. Sophisticated processing is needed to distill this flood of complex data into the final Gaia Catalogue of about 1000 million celestial objects. A group of more than 300 European scientists and software developers is rising to the challenge: the Data Processing and Analysis Consortium is already preparing for Gaia's launch in 2011.
Published: 15 November 2007
We present results of an all-sky hard X-ray survey based on almost four years of observations with the IBIS telescope onboard the INTEGRAL observatory. The dead time-corrected exposure of the survey is ~33 Ms. Approximately 12% and 80% of the sky has been covered to limiting fluxes lower than 1 and 5 mCrab, respectively. Our catalog of detected sources includes 403 objects, 316 of which exceed a 5-sigma detection threshold on the time-averaged map of the sky, and the rest were detected in various subsamples of exposures. Among the identified sources, 219 are Galactic (90 low-mass X-ray binaries, 76 high-mass X-ray binaries, 21 cataclysmic variables, 6 coronally active stars, and other types) and 137 are extragalactic, including 130 active galactic nuclei (AGNs) and 3 galaxy clusters. We derived number-flux functions of AGNs and Galactic sources. The log N-log S relation of non-blazar AGNs is based on 68 sources located at Galactic latitudes |b| > 5°, where the survey is characterized by high identification completeness, with fluxes higher than Slim = 1.1 × 10-11 erg s-1 cm-2 (~0.8 mCrab) in the 17-60 keV energy band. The cumulative AGN number-flux function can be described by a power law with a slope of 1.62 ± 0.15 and normalization of (5.7±0.7) × 10-3 sources per deg² at fluxes > 1.43 × 10-11 erg s-1 cm-2 (>1 mCrab). Those AGNs with fluxes higher than Slim make up ~1% of the cosmic X-ray background at 17-60 keV. We present evidence of strong inhomogeneity in the spatial distribution of nearby (<70 Mpc) AGNs, which reflects the large-scale structure in the local Universe.
Published: 15 November 2007
25-Oct-2020 20:18 UT

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