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| Detection of negative ions in the deep ionosphere of Titan during the Cassini T70 flyby |
| 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. |
| Publication date: 16 May 2012 |
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| Geologic interpretation of the near-infrared images of the surface taken by the Venus Monitoring Camera, Venus Express |
| 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. |
| Publication date: 16 May 2012 |
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| Characterization of hydrated silicate-bearing outcrops in Tyrrhena Terra, Mars: Implications to the alteration history of Mars |
| 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.] |
| Publication date: 15 May 2012 |
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| Herschel far-infrared observations of the Carina Nebula complex. I. Introduction and global cloud structure |
| 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.] |
| Publication date: 14 May 2012 |
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| The suppression of star formation by powerful active galactic nuclei |
| 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. |
| Publication date: 10 May 2012 |
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| Magnetic Reconnection in the Near Venusian Magnetotail |
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. |
| Publication date: 04 May 2012 |
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| JUICE Science Requirement Matrix |
| This document lists the JUICE mission's science objectives and the corresponding investigations, plus the necessary measurements (and instruments) to achieve these objectives. |
| Publication date: 02 May 2012 |
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