| 1. |
- Bertini, Ivano, et al.
(author)
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Search for satellites near (21) Lutetia using OSIRIS/Rosetta images
- 2012
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In: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 66:1, s. 64-70
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Journal article (peer-reviewed)abstract
- On 2010 July 10 the ESA Rosetta mission flew by the large asteroid (21) Lutetia. One of the scientific goals of the onboard OSIRIS instrument was the search for satellites of the asteroid, with more than 20 images specifically dedicated to this topic. An observational campaign was devised with a selection of filters and exposure times tailored to maximize the possibility of detecting small companions and determining their bound orbits. Data were analyzed with suitable methods to remove cosmic ray hits and known background objects, in order to search for persistent detections of potential interesting flux sources. We found no unambiguous detections of a satellite larger than similar to 160 m inside the entire sphere of gravitational influence. Our search confirmed the absence of bound companions larger than similar to 30 m inside 20 primary radii. These limits are a factor of similar to 30 smaller than the values reported so far from large ground-based telescopes using adaptive optics and from the Hubble Space Telescope.
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| 2. |
- Cavalie, T., et al.
(author)
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Odin space telescope monitoring of water vapor in the stratosphere of Jupiter
- 2012
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In: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 61:1, s. 3-14
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Journal article (peer-reviewed)abstract
- The Odin space telescope has monitored the H2O (1(10)-1(01)) line in Jupiter's stratosphere over the 2003-2009 period. When comparing these data with previous spectra obtained with SWAS and Odin over the 1999-2002 period, we see no significant variations in the line-to-continuum ratio of the H2O line over the whole period. We have however tentatively identified a decrease by similar to 15% of the line-to-continuum ratio between 2002 and 2007-2009, indicating that there was less H2O in the stratosphere of Jupiter in 2007-2009 than anticipated. We have tested the IDP (interplanetary dust particles) and SL9 (Shoemaker-Levy 9) 1D time-dependent models presented in Cavalie et al. [2008, Observation of water vapor in the stratosphere 613 of Jupiter with the Odin space telescope. Planetary and Space Science 56,1573-1584]. We present a series of scenarios that lead to satisfactory fits of the whole data set (1999-2002 and 2003-2009 periods) based on IDP and SL9 models. The evolution of Jupiter's stratospheric H2O that we have tentatively observed has however to be confirmed by Herschel/HIFI observations. If the decrease of the line-to-continuum ratio is confirmed by future observations, it would be a direct evidence that Jupiter's H2O comes from SW. In addition, this study shows that new constraints on Jupiter's eddy diffusion coefficient profile could be obtained (in the pressure ranges that are probed) from the monitoring of SW species in its stratosphere.
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| 3. |
- Cremonese, G., et al.
(author)
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Techniques and methods in ground-based observation of Mercury
- 2010
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In: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 58:1-2, s. 61-78
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Journal article (peer-reviewed)abstract
- Modern telescopes and equipments have permitted excellent ground-based observations of Mercury, despite its proximity to the Sun. This is one of the main reasons why it has been observed using different techniques from high-resolution spectroscopy to high-resolution imaging from visible to infrared up to radio wavelengths. Because there is no obscuration from a thick atmosphere, the surface and exosphere have been imaged and the surface studied by infrared spectroscopy. This manuscript describes the techniques used to obtain information and new data of Mercury giving an overview of advantages and difficulties, and describes important scientific discoveries made with specific telescopic instrumentation.
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| 4. |
- Edberg, Niklas J. T., et al.
(author)
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Structured ionospheric outflow during the Cassini T55-T59 Titan flybys
- 2011
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In: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 59:8, s. 788-797
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Journal article (peer-reviewed)abstract
- During the final three of the five consecutive and similar Cassini Titan flybys T55-T59 we observe a region characterized by high plasma densities (electron densities of 1-8 cm(-3)) in the tail/nightside of Titan. This region is observed progressively farther downtail from pass to pass and is interpreted as a plume of ionospheric plasma escaping Titan, which appears steady in both location and time. The ions in this plasma plume are moving in the direction away from Titan and are a mixture of both light and heavy ions with composition revealing that their origin are in Titan's ionosphere, while the electrons are more isotropically distributed. Magnetic field measurements indicate the presence of a current sheet at the inner edge of this region. We discuss the mechanisms behind this outflow, and suggest that it could be caused by ambipolar diffusion, magnetic moment pumping or dispersive Alfven waves.
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| 5. |
- Gamier, P., et al.
(author)
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Deriving the characteristics of warm electrons (100-500 eV) in the magnetosphere of Saturn with the Cassini Langmuir probe
- 2014
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In: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 104, s. 173-184
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Journal article (peer-reviewed)abstract
- Though Langmuir probes (LP) are designed to investigate cold plasma regions (e.g. ionospheres), a recent analysis revealed a strong sensitivity of the Cassini LP measurements to hundreds of eV electrons. These warm electrons impact the surface of the probe and generate a significant current of secondary electrons, that impacts both the DC level and the slope of the current-voltage curve of the LP (for negative potentials) through energetic contributions that may be modeled with a reasonable precision. We show here how to derive information about the incident warm electrons from the analysis of these energetic contributions, in the regions where the cold plasma component is small with an average temperature in the range similar to [100-500] eV. First, modeling the energetic contributions (based on the incident electron flux given by a single anode of the CAPS spectrometer) allows us to provide information about the pitch angle anisotropies of the incident hundreds of eV electrons. The modeling reveals indeed sometimes a large variability of the estimated maximum secondary electron yield (which is a constant for a surface material) needed to reproduce the observations. Such dispersions give evidence for strong pitch angle anisotropies of the incident electrons, and using a functional form of the pitch angle distribution even allows us to derive the real peak angle of the distribution. Second, rough estimates of the total electron temperature may be derived in the regions where the warm electrons are dominant and thus strongly influence the LP observations, i.e. when the average electron temperature is in the range similar to [100-500] eV. These regions may be identified from the LP observations through large positive values of the current-voltage slope at negative potentials. The estimated temperature may then be used to derive the electron density in the same region, with estimated densities between similar to 0.1 and a few particles/cm(3) (cc). The derived densities are in better agreement with the CAPS measurements than the values derived from the proxy technique (Morooka et al., 2009) based on the floating potential of the LP. Both the electron temperature and the density estimates lie outside the classical capabilities of the LP, which are essentially n(e) > 5 cc and T-e <5 eV at Saturn. This approximate derivation technique may be used in the regions where the cold plasma component is small with an average temperature in the range similar to [100-500] eV, which occurs often in the L range 6.4-9.4 R-S when Cassini is off the equator, but may occur anywhere in the magnetosphere. This technique may be all the more interesting since the CAPS instrument was shut down, and, though it cannot replace the CAPS instrument, the technique can provide useful information about the electron moments, with probably even better estimates than CAPS in some cases (when the plasma is strongly anisotropic). Finally, a simple modeling approach allows us to predict the impact of the energetic contributions on LP measurements in any plasma environment whose characteristics (density, temperature, etc.) are known. LP observations may thus be influenced by warm electrons in several planetary plasma regions in the solar system, and ambient magnetospheric electron density and temperature could be estimated in some of them (e.g. around several galilean satellites) through the use of Langmuir probes.
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| 6. |
- Garnier, P., et al.
(author)
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Statistical analysis of the energetic ion and ENA data for the Titan environment
- 2010
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In: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 58:14-15, s. 1811-1822
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Journal article (peer-reviewed)abstract
- The MIMI experiment (Magnetosphere Imaging Instrument) onboard Cassini is dedicated to the study of energetic particles, with in particular LEMMS analyzing charged particles, or the INCA detector which can image the Energetic Neutral Atoms produced by charge exchange collisions between cold neutrals and energetic ions. The MIMI experiment is thus well adapted to the study of the interaction between the Titan nitrogen rich atmosphere and the energetic Saturnian magnetospheric plasma. We analyze here the energetic protons at the Titan orbit crossings before January 2008 (MIMI-LEMMS data; 27-255 key), which are very dynamic, with tri-modal flux spectra and probably quasi-isotropic pitch angle distributions. We provide statistical parameters for the proton fluxes, leading to estimates of the average energy deposition into Titan's atmosphere, before we discuss the possible influence of Titan on the magnetopause. We then analyze the H ENA images (24-55 key) during the Titan flybys before June 2006 to obtain a better diagnostic of the Titan interaction: the ENAs variability is mostly related to the magnetospheric variability (the exosphere being roughly stable) or the distance from the moon, the ENAs halo around Titan is very stable (corresponding to a lower limit for ENAs emission at the exobase), and strong asymmetries are observed, due to finite gyroradii effects for the parent ions.
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| 7. |
- Gulkis, S., et al.
(author)
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Millimeter and submillimeter measurements of asteroid (2867) Steins during the Rosetta fly-by
- 2010
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In: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 58:9, s. 1077-1087
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Journal article (peer-reviewed)abstract
- The European Space Agency Rosetta Spacecraft passed within 803 km of the main belt asteroid (2867) Steins on 5 September 2008. The Rosetta Spacecraft carries a number of scientific instruments including a millimeter and submillimeter radiometer and spectrometer. The instrument, named MIRO (Microwave Instrument for the Rosetta Orbiter), consists of a 30-cm diameter, offset parabolic reflector telescope followed by two heterodyne receivers. Center-band operating frequencies of the receivers are near 190 GHz (1.6 mm) and 562 GHz (0.53 mm). Broadband continuum channels are implemented in both frequency bands for the measurement of near surface temperatures and temperature gradients. A 4096 channel CTS (chirp transform spectrometer) having 180 MHz total bandwidth and similar to 44 kHz resolution is also connected to the submillimeter receiver. We present the continuum observations of asteroid (2867) Steins obtained during the fly-by with the MIRO instrument. Spectroscopic data were also collected during the fly-by using the MIRO spectrometer fixed-tuned to rotational lines of several molecules. Results of the spectroscopic investigation will be the topic of a separate publication. Comparative thermal models and radiative transfer calculations for Steins are presented. Emissivities of Steins were determined to be 0.6-0.7 and 0.85-0.9 at wavelengths of 0.53 and 1.6 mm, respectively. The thermal inertia of Steins was estimated to be in the range 450-850 J/(m(2) s(0.5) K). Assuming that the emissivity of Steins is determined by the Fresnel reflection coefficients of the surface material, the area-averaged dielectric constant of the surface material is in the range 4-20. These values are rock-like, and are unlike the powdered-regolith surface of the Moon.
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| 8. |
- Gustafsson, Georg, et al.
(author)
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Electron temperatures in Saturn's plasma disc
- 2010
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In: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 58:7-8, s. 1018-1025
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Journal article (peer-reviewed)abstract
- We present new results concerning electron temperature (T-e) mapping in the inner magnetosphere of Saturn ( < 7 R-s). The data are obtained by the Langmuir Probe (LP) instrument of the Radio and Plasma Wave Science (RPWS) investigation on board Cassini. The study is based on the fourteen first orbits around Saturn, and focus is on cold ( < 10 eV) and dense ( > 5 cm(-3)) electron populations in the inner plasma torus (plasma disc). Apart from a general increase with distance from Saturn and away from the equatorial plane (latitude), we identify a possibly anisotropic electron temperature in the plasma disc, as well as the presence of photoelectrons from the spacecraft or E-ring dust particles. A polytropic index of gamma approximate to +0.4 is determined from the observations, which can be used in theoretical models of the plasma disc. We also infer local variations in T-e near the equatorial plane, where the E-ring of dusty plasma and enhancements of water rich neutral gas exist, and determine constraints on the energy source required to heat the electrons in the plasma disc. We suggest that Joule heating or heating by low-frequency plasma waves as well as cooling by neutral gas and E-ring dust are involved in the energy balance, together with Coulomb collision heating by co-rotating ions.
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| 9. |
- Hansen-Goos, H., et al.
(author)
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On the edge of habitability and the extremes of liquidity
- 2014
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In: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 98:Special Issue: SI, s. 169-181
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Journal article (peer-reviewed)abstract
- The physical and biological mechanisms that extend the equilibrium domain of liquid water into the ice region of the bulk phase diagram are examined in view of their importance for the enhancement of planetary habitability. The physical phenomena studied are the premelting of ice, which allows for films of liquid water at temperatures well below freezing, and the wetting of hygroscopic salts with the persistence of briny films even for thermodynamic conditions remote from those of bulk liquid water. Organisms are known to produce a variety of frost-suppressing substances, one of which, the anti-freeze protein, is described here. In this article, we provide a synthesis of theoretical and experimental studies whilst extending ideas into new territory as we address the question of habitability. (C) 2013 Elsevier Ltd. All rights reserved.
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| 10. |
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