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| Sodium salts in E-ring ice grains from an ocean below the surface of Enceladus |
| Saturn's moon Enceladus emits plumes of water vapour and ice particles from fractures near its south pole, suggesting the possibility of a subsurface ocean. These plume particles are the dominant source of Saturn's E ring. A previous in situ analysis of these particles concluded that the minor organic or siliceous components, identified in many ice grains, could be evidence for interaction between Enceladus' rocky core and liquid water. It was not clear, however, whether the liquid is still present today or whether it has frozen. Here we report the identification of a population of E-ring grains that are rich in sodium salts (0.5-2% by mass), which can arise only if the plumes originate from liquid water. The abundance of various salt components in these particles, as well as the inferred basic pH, exhibit a compelling similarity to the predicted composition of a subsurface Enceladus ocean in contact with its rock core. The plume vapour is expected to be free of atomic sodium. Thus, the absence of sodium from optical spectra is in good agreement with our results. In the E ring the upper limit for spectroscopy is insufficiently sensitive to detect the concentrations we found. |
| Publication date: 25 Jun 2009 |
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| Summary Report #1 |
| The first meeting of the Fundamental Physics Roadmap Advisory Team was held on 2-3 June 2009. This report was prepared by the Chair and Secretary of the FPR-AT. |
| Publication date: 22 Jun 2009 |
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| Venus express: Highlights of the nominal mission |
| Venus Express is the first European (ESA) mission to the planet Venus. Its main science goal is to carry out a global survey of the atmosphere, the plasma environment, and the surface of Venus from orbit. The payload consists of seven experiments. It includes a powerful suite of remote sensing imagers and spectrometers, instruments for in-situ investigation of the circumplanetary plasma and magnetic field, and a radio science experiment. The spacecraft, based on the Mars Express bus modified for the conditions at Venus, provides a versatile platform for nadir and limb observations as well as solar, stellar, and radio occultations. In April 2006 Venus Express was inserted in an elliptical polar orbit around Venus, with a pericentre height of ~250 km and apocentre distance of ~66000 km and an orbital period of 24 hours. The nominal mission lasted from June 4, 2006 till October 2, 2007, which corresponds to about two Venus sidereal days. Here we present an overview of the main results of the nominal mission, based on a set of papers recently published in Nature, Icarus, Planetary and Space Science, and Geophysical Research Letters. |
| Publication date: 22 Jun 2009 |
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| Solar-Like Oscillations in a Massive Star |
| Seismology of stars provides insight into the physical mechanisms taking place in their interior, with modes of oscillation probing different layers. Low-amplitude acoustic oscillations excited by turbulent convection were detected four decades ago in the Sun and more recently in low-mass main-sequence stars. Using data gathered by the Convection Rotation and Planetary Transits mission, we report here on the detection of solar-like oscillations in a massive star, V1449 Aql, which is a known large-amplitude (beta Cephei) pulsator. |
| Publication date: 19 Jun 2009 |
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| Multipoint observations of plasma distributions around an X line |
| In proceedings of the International Conference 'Future perspectives of space plasma and particle instrumentation and international collaborations', held 1-3 November 2006 in Tokyo, Japan.
Using electron and magnetic field data obtained from the Cluster satellites, we identify the spatial distribution of highly accelerated electron distributions up to 10 keV. They are generally isotropic and form flat-top distributions in the phase space. These distributions are observed in the vicinity of the X line associated with the quadrupole-like magnetic field and energetic ions, throughout the plasma sheet. In some cases, these distributions are quasi-stable, continuously observed for a few minutes with a stable Bz polarity and low current density in the center of the plasma sheet. |
| Publication date: 16 Jun 2009 |
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| Scales in a thinning plasma sheet |
| In proceedings of the International Conference 'Future perspectives of space plasma and particle instrumentation and international collaborations', held 1-3 November 2006 in Tokyo, Japan.
With Cluster observations in the magnetotail, we study the dynamics of plasma sheet thinning and stretching in a typical growth phase event of September 12, 2001. The thinning and stretching proceed in parallel, with transient variations. The pre-onset value is Bz~1.5 nT, J~8 nA/m2. The current density increase is not accompanied with a corresponding number density increase. A large (>5 nT) guide field along the cross-tail current direction was registered. An embedded current sheet structure was detected and, therefore, caution is required if making thickness estimations. |
| Publication date: 16 Jun 2009 |
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Mars Express
The Scientific Investigations |
| This ESA special publication is dedicated to the scientific investigations of Mars by Mars Express, giving a detailed overview of the scientific results of the mission so far.
Contents:
| Foreword |
| Overview |
Mars Express: Summary of Scientific Results
A. Chicarro, O.G. Witasse & A.P. Rossi | 1 |
| Scientific Instruments |
HRSC: High Resolution Stereo Camera
G. Neukum, R. Jaumann and the Co-Investigator Team | 15 |
OMEGA: Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité
J.-P. Bibring, Y. Langevin, F. Altieri et al. | 75 |
MARSIS: Mars Advanced Radar for Subsurface and Ionospheric Sounding
J.J. Plaut, G. Picardi, T.W. Watters et al. | 97 |
PFS: Planetary Fourier Spectrometer
V. Formisano, F. Angrilli, G. Arnold et al. | 115 |
SPICAM: Spectroscopy for the Investigation of the Characteristics of the Atmospheric of Mars
J.-L. Bertaux, O. Korablev, D. Fonteyn et al. | 139 |
ASPERA-3: Analyser of Space Plasmas and Energetic Neutral Atoms
R. Lundin, S. Barabash and the ASPERA-3 team | 199 |
MaRS: Mars Express Radio Science Experiment
M. Pätzold, S. Tellmann, T. Andert et al. | 217 |
| Operations and Archiving |
Mars Express Science Planning and Operations
R. Pischel & T. Zegers | 249 |
Spacecraft and Payload Data Handling
J. Zender, F. Delhaise, C. Arviset et al. | 257 |
| Acronyms and Abbreviations | 279 |
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| Publication date: 15 Jun 2009 |
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| X-ray fluorescence observations of the moon by SMART-1/D-CIXS and the first detection of Ti Kα from the lunar surface |
| The demonstration of a compact imaging X-ray spectrometer (D-CIXS), which flew on ESA's SMART-1 mission to the Moon (Racca et al., 2001; Foing et al., 2006), was designed to test innovative new technologies for orbital X-ray fluorescence spectroscopy. D-CIXS conducted observations of the lunar surface from January 2005 until SMART-1 impacted the Moon in September 2006. Here, we present scientific observations made during two solar flare events and show the first detection of Titanium K-alpha from the lunar surface. We discuss the geological implications of these results. We also discuss how experience from D-CIXS has aided the design of a similar instrument (Chandrayaan-1 X-ray Spectrometer [C1XS]) that was launched on the 22nd October 2008 on India's Chandrayaan-1 mission to the Moon. |
| Publication date: 15 Jun 2009 |
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| SMART-1 results and targets for LRO |
| Presented at the Lunar Reconnaissance Orbiter Science Targeting Meeting, 9-11 June 2009 We propose number of targets observed
with SMART-1 for follow-up studies with LRO. We
shall also discuss SMART-1 lunar highlights relevant
for science and exploration, in relation with
LRO/LCROSS and future lander missions. |
| Publication date: 12 Jun 2009 |
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| Evidence of a Cascade and Dissipation of Solar-Wind Turbulence at the Electron Gyroscale |
| We report the first direct determination of the dissipation range of magnetofluid turbulence in the solar wind at the electron scales. Combining high resolution magnetic and electric field data of the Cluster spacecraft, we computed the spectrum of turbulence and found two distinct breakpoints in the magnetic spectrum at 0.4 and 35 Hz, which correspond, respectively, to the Doppler-shifted proton and electron gyroscales, frho_p and frho_e. Below frho_p, the spectrum follows a Kolmogorov scaling f -1.62, typical of spectra observed at 1 AU. Above frho_p, a second inertial range is formed with a scaling f -2.3 down to frho_e. Above frho_e, the spectrum has a steeper power law ~f 4.1 down to the noise level of the instrument. We interpret this as the dissipation range and show a remarkable agreement with theoretical predictions of a quasi-two-dimensional cascade into Kinetic Alfvén Waves (KAW). |
| Publication date: 10 Jun 2009 |
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| On the numerical modelling of VLF chorus dynamical spectra |
| This paper presents a study of the use of a one-dimensional Vlasov Hybrid Simulation (VHS) computer code to simulate the dynamical spectra (i.e. frequency versus time spectrograms) of ELF/VLF chorus signals (from ~a fraction to ~10 kHz). Recently excellent measurements of chorus have been made in the source region close to the geomagnetic equator aboard the four spacecraft Cluster mission. Using Cluster data for wave amplitude, which is up to 300 pT, local gyrofrequency, cold plasma density, and L-shell, observed chorus signals are reproduced with remarkable fidelity and, in particular, sweep rates in the range 1-10 kHz result as observed. Further, we find that the sweep rate is a falling function of increasing cold plasma density, again in accord with observations. Finally, we have satisfactorily simulated the rather rare falling frequency elements of chorus which are sometimes observed aboard Cluster in the generation region. For both rising and falling chorus we have presented detailed structural analyses of the generation regions. The main contributor to the frequency sweep rate is primarily the establishment of wave number/frequency gradients across the generation region by the out of phase component of the resonant particle current. The secondary contributor is the shortening of the wavelength of resonant particle current relative to that of the wave field. In view of the close agreement between observation and simulation, we conclude that nonlinear electron cyclotron resonance is indeed the mechanism underlying the generation of chorus signals just outside the plasmasphere. |
| Publication date: 08 Jun 2009 |
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| The Jet Heated X-Ray Filament in the Centaurus A Northern Middle Radio Lobe |
| We present results from a 40 ks XMM-Newton observation of the X-ray filament coincident with the southeast edge of the Centaurus A Northern Middle Radio Lobe (NML). We find that the X-ray filament consists of five spatially resolved X-ray knots embedded in a continuous diffuse bridge. The spectrum of each knot is well fitted by a thermal model with temperatures ranging from 0.3 to 0.7 keV and subsolar elemental abundances. In four of the five knots, nonthermal models are a poor fit to the spectra, conclusively ruling out synchrotron or IC/CMB mechanisms for their emission. The internal pressures of the knots exceed that of the ambient interstellar medium or the equipartition pressure of the NML by more than an order of magnitude, demonstrating that they must be short lived (~3 × 106 yr). Based on energetic arguments, it is implausible that these knots have been ionized by the beamed flux from the active galactic nucleus of Cen A or that they have been shock heated by supersonic inflation of the NML. In our view, the most viable scenario for the origin of the X-ray knots is that they are the result of cold gas shock heated by a direct interaction with the jet. The most plausible model of the NML is that it is a bubble from a previous nuclear outburst that is being re-energized by the current outburst. The northeast inner lobe and the large-scale jet are lossless channels through which the jet material rapidly travels to the NML in this scenario. We also report the discovery of a large-scale (at least 35 kpc radius) gas halo around Cen A. |
| Publication date: 05 Jun 2009 |
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| Global circulation as the main source of cloud activity on Titan |
| Clouds on Titan result from the condensation of methane and ethane and, as on other planets, are primarily structured by circulation of the atmosphere. At present, cloud activity mainly occurs in the southern (summer) hemisphere, arising near the pole and at mid-latitudes from cumulus updrafts triggered by surface heating and/or local methane sources, and at the north (winter) pole, resulting from the subsidence and condensation of ethane-rich air into the colder troposphere. General circulation models predict that this distribution should change with the seasons on a 15-year timescale, and that clouds should develop under certain circumstances at temperate latitudes (40°) in the winter hemisphere. The models, however, have hitherto been poorly constrained and their long-term predictions have not yet been observationally verified. Here we report that the global spatial cloud coverage on Titan is in general agreement with the models, confirming that cloud activity is mainly controlled by the global circulation. The non-detection of clouds at latitude 40° N and the persistence of the southern clouds while the southern summer is ending are, however, both contrary to predictions. This suggests that Titan's equator-to-pole thermal contrast is overestimated in the models and that its atmosphere responds to the seasonal forcing with a greater inertia than expected. |
| Publication date: 04 Jun 2009 |
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