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The SPICAM experiment onboard the Mars-Express spacecraft includes sounding the Martian atmosphere in the ultra-violet (118–320 nm) and near IR (1–1.7 μm) ranges. The infrared spectrometer operates in the range of 1–1.7 μm with a... more
The SPICAM experiment onboard the Mars-Express spacecraft includes sounding the Martian atmosphere in the ultra-violet (118–320 nm) and near IR (1–1.7 μm) ranges. The infrared spectrometer operates in the range of 1–1.7 μm with a resolution of 3.5 cm−1 in the mode of nadir observations and solar and stellar occulations. This paper is devoted to analyzing the basic results of
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ABSTRACT The vertical distribution of water vapor in the atmosphere of Mars is a crucial, and sometimes the only, diagnostics of several important processes for the hydrological cycle of the planet. Up to now, however, water vapor... more
ABSTRACT The vertical distribution of water vapor in the atmosphere of Mars is a crucial, and sometimes the only, diagnostics of several important processes for the hydrological cycle of the planet. Up to now, however, water vapor vertical profiles have been directly observed only by ISM/Phobos, with very limited spatial and temporal coverage (Rodin et al. 1997). Our current knowledge relies above all on General Circulation Models, which employ strong assumptions. The H2O vertical profile is considered to be mainly controlled by atmospheric temperature, through saturation physics, and it is usually schematized as a step function: well-mixed below the saturation height and abruptly declining to zero above it. In this work we test the current vertical knowledge of water vapor by analyzing the SPICAM dataset. The SPICAM spectrometer onboard Mars Express is perfectly suited to study the vertical structure of Mars’ atmosphere, thanks to its solar and stellar occultation mode of observation both in IR and UV (Lebonnois et al. 2006, Fedorova et al. 2009). It has been monitoring the planet for more than three Martian years, providing a series of measurements unprecedented for quality and spatial and temporal coverage. In particular, solar occultations in the IR channel allows the simultaneous retrieval of H2O, CO2 and aerosols atmospheric profiles. The evolution and behavior of the vertical distribution of gaseous H2O for a whole Martian year will be shown, and the discrepancies with GCM predictions will be highlighted. Particular attention will be devoted to describe and explain the behavior regarding the saturation state of the atmosphere. The interaction between the water and dust cycles will be examined, thanks to the simultaneous observations of water and aerosols. The observations trace a consistent picture of the vertical behavior of water vapor. They point towards a new paradigm, which stresses the importance of water-dust interactions with respect to the role of atmospheric thermal structure. References: Fedorova A. et al - Icarus, vol. 200, p. 96-117 (2009) Lebonnois S. et al. - JGR, vol. 111 E9 (2006) Rodin A. et al. - Icarus, vol. 125, p. 212-229 (1997)
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Since May 2006, the Venus-Express spacecraft is in its nominal orbit around VENUS and the SPICAV optical package has begun to acquire spectra. The SOIR extension to SPICAV is an echelle spectrometer associated to an AOTF (Acousto-Optical... more
Since May 2006, the Venus-Express spacecraft is in its nominal orbit around VENUS and the SPICAV optical package has begun to acquire spectra. The SOIR extension to SPICAV is an echelle spectrometer associated to an AOTF (Acousto-Optical Tunable Filter) for the order selection, which performs solar occultation measurements in the IR region (2.2-4.3 µm) at a resolution of 0.1 cm-1
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CO2 is the major constituent of the atmosphere of Venus. Absorption lines due to its 12C16O18O isotopologue have been observed for the first time in Venus spectra in the 2930–3015cm−1 spectral region, where the HITRAN database does not... more
CO2 is the major constituent of the atmosphere of Venus. Absorption lines due to its 12C16O18O isotopologue have been observed for the first time in Venus spectra in the 2930–3015cm−1 spectral region, where the HITRAN database does not contain any line from this isotopologue. The measurements were performed by the SOIR instrument, which is part of the SPICAV/SOIR instrument on board the Venus Express mission of ESA. SOIR measured the atmospheric transmission of the upper atmosphere of Venus (z>70km) by performing a solar occultation experiment using the atmosphere as a gigantic absorption cell. The identification of this newly observed band was first made recently from Mars atmosphere observations by US colleagues. We have made independent theoretical calculations of the positions of the lines of this new 01111–00001 absorption band, which coincide perfectly with the positions of the observed lines. Assuming an oxygen isotopic ratio similar to the one measured previously in the lower atmosphere of Venus, the line strengths of each observed line are deduced and listed.
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Research Interests: Physics, Remote Sensing, Astrobiology, Multidisciplinary, Composition, and 15 moreAstronomy, Atmospheres, Venus, Planet, GPS Radio Occultation, Spectrum, Infrared, Geophysical, IR Spectroscopy, Vertical Distribution, Sulfur Dioxide, Spectral Resolution, Direct Method, Occultation, and vertical structure
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The SOIR instrument performs solar occultation measurements in the IR region (2.2 - 4.3 mum) at a resolution of 0.12 cm-1, the highest on board Venus Express. It combines an echelle spectrometer and an AOTF (Acousto-Optical Tunable... more
The SOIR instrument performs solar occultation measurements in the IR region (2.2 - 4.3 mum) at a resolution of 0.12 cm-1, the highest on board Venus Express. It combines an echelle spectrometer and an AOTF (Acousto-Optical Tunable Filter) for the order selection. A brief description of the instrument and its in- flight measured performances will be presented. The wavelength range probed by SOIR allows a detailed chemical inventory of the Venus atmosphere above the cloud layer (65 to 150 km) with an emphasis on vertical distribution of the gases. In particular, measurements of HDO, H2O, HCl, HF, CO and CO2 vertical profiles have been routinely performed. Temperature retrieval will be described and tentative results presented. Aerosols extinction profiles are also simultaneously retrieved from the SOIR spectra. Some results for selected orbits will be investigated and discussed. It will be shown that size distribution can be addressed but only when considering all three channels of the SPICAV/SOIR instrument.
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ABSTRACT The experiment SOIR (Solar Occultation in the Infra-Red) - a part of the Venus Express mission - is performed for study of gaseous and aerosol vertical structure in Venus' mesosphere. The instrument of SOIR is an... more
ABSTRACT The experiment SOIR (Solar Occultation in the Infra-Red) - a part of the Venus Express mission - is performed for study of gaseous and aerosol vertical structure in Venus' mesosphere. The instrument of SOIR is an acousto-optical (AO) echelle spectrometer that operates at wavelengths 2.2-4.3 µm with high spectral resolution (lambda/∆lambda=30000). The spectrometer is capable to detect important minor gaseous constituents such as CO, SO2 , HCl, HF, H2 O and HDO at altitudes 65-110 km. Here we report results from some occultation sessions with observation of 4 µm SO2 band at latitudes 69o -88o N and 23o -30o N. It's the first time of SO2 vertical distribution retrieval above Venus' clouds by means of solar occultation. Since sulfur dioxide spectrum of transmission is measured on a background of abundant CO2 band, it is impossible to retrieve any separate SO2 line for observing and fitting. This fact forces us to do modeling of combined spectrum (CO2 *SO2 ) and to perform fitting with appropriate mixing ratio of SO2 by comparison between the combined model and a measured spectrum (point-by-point). As result, just a few points of a SO2 vertical profile can be detected clearly (0.1 ppm at high latitudes and 1 ppm at low latitudes at the altitude about 70 km). All the rest points provide upper limit of the gas' mixing ratio (0.05 ppm at 75 km and higher).
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ABSTRACT The SPICAV suite of instruments is composed of three separate channels: UV (110 to 320 nm), near-IR (0.7 to 1.7 mum) and the SOIR channel (2.3 to 4.4 mum). On specific opportunities, all three channels have operated... more
ABSTRACT The SPICAV suite of instruments is composed of three separate channels: UV (110 to 320 nm), near-IR (0.7 to 1.7 mum) and the SOIR channel (2.3 to 4.4 mum). On specific opportunities, all three channels have operated simultaneously during solar occultations and have provided almost contiguous spectral information from 0.11 to 4.4 mum. Occultation observations provide several advantages, in particular it does not require cross-calibrating the channels together as scientific analysis is based on relative measurements; i.e. atmospheric transmissions which are the ratio of spectra obtained at a given altitude where the atmosphere produces some attenuation onto that collected outside the atmosphere where the sun can be observed free of any absorption. Haze opacities are readily retrieved using Beer-Lambert's law and vertical distribution from 65 to 120 km is inferred using regular onion peeling technique. Over the interval covered by SPICAV/SOIR, the spectral behavior of haze particles can be fully and robustly evaluated since the size parameter varies by more than one order of magnitude. Extraction of extinction coefficients have been performed for all three channels, allowing derivation of size distribution parameters. Details on the observations made for each channel will be presented. Profiles exhibit peculiar wavy structures that suggest gravity wave vertical propagations or localized destruction processes. Size distribution results will be discussed, in particular the possibility for a multi-modal distribution potentially implying different processes of formation and destruction at work in the mesosphere of Venus.
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... BIRA-IASB), Brussels, Belgium), AG(Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium), AH(LATMOS, CNRS, Solar System Exploration, Verrières-le-buisson Cedex, France (denis.belyaev@latmos.ipsl.fr)). Publication: EGU... more
... BIRA-IASB), Brussels, Belgium), AG(Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium), AH(LATMOS, CNRS, Solar System Exploration, Verrières-le-buisson Cedex, France (denis.belyaev@latmos.ipsl.fr)). Publication: EGU General Assembly 2010, held 2-7 ...
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Abstract SPICAV (SPectroscopy for the Investigation of the Characteristics of the Atmosphere of Venus) is a suite of three spectrometers in the UV and IR range with a total mass of 12.3 kg flying on Venus Express orbiter, dedicated to the... more
Abstract SPICAV (SPectroscopy for the Investigation of the Characteristics of the Atmosphere of Venus) is a suite of three spectrometers in the UV and IR range with a total mass of 12.3 kg flying on Venus Express orbiter, dedicated to the study of the atmosphere ...
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The SPICAV instrument onboard the Venus Express spacecraft is a multi-channel suite covering the far ultraviolet to the mid-infrared. In this presentation, we will focus on the results obtained by the UV channel during stellar... more
The SPICAV instrument onboard the Venus Express spacecraft is a multi-channel suite covering the far ultraviolet to the mid-infrared. In this presentation, we will focus on the results obtained by the UV channel during stellar occultations observations. Stellar occultation technique possesses well-known advantages: self-calibration, low sensitivity to instrument aging, simple laws of radiative transfer. In addition, occultation with stars permit
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The factors shaping cometary nuclei are still largely unknown, but could be the result of concurrent effects of evolutionary and primordial processes. The peculiar bilobed shape of comet 67P/Churyumov-Gerasimenko may be the result of the... more
The factors shaping cometary nuclei are still largely unknown, but could be the result of concurrent effects of evolutionary and primordial processes. The peculiar bilobed shape of comet 67P/Churyumov-Gerasimenko may be the result of the fusion of two objects that were once separate or the result of a localized excavation by outgassing at the interface between the two lobes. Here we report that the comet's major lobe is enveloped by a nearly continuous set of strata, up to 650 metres thick, which are independent of an analogous stratified envelope on the minor lobe. Gravity vectors computed for the two lobes separately are closer to perpendicular to the strata than those calculated for the entire nucleus and adjacent to the neck separating the two lobes. Therefore comet 67P/Churyumov-Gerasimenko is an accreted body of two distinct objects with…
Research Interests: Physics, Medicine, Multidisciplinary, Nature, Solar System, and 3 moreComet, Nucleus, and Outgassing
Pits have been observed on many cometary nuclei mapped by spacecraft. It has been argued that cometary pits are a signature of endogenic activity, rather than impact craters such as those on planetary and asteroid surfaces. Impact... more
Pits have been observed on many cometary nuclei mapped by spacecraft. It has been argued that cometary pits are a signature of endogenic activity, rather than impact craters such as those on planetary and asteroid surfaces. Impact experiments and models cannot reproduce the shapes of most of the observed cometary pits, and the predicted collision rates imply that few of the pits are related to impacts. Alternative mechanisms like explosive activity have been suggested, but the driving process remains unknown. Here we report that pits on comet 67P/Churyumov-Gerasimenko are active, and probably created by a sinkhole process, possibly accompanied by outbursts. We argue that after formation, pits expand slowly in diameter, owing to sublimation-driven retreat of the walls. Therefore, pits characterize how eroded the surface is: a fresh cometary surface will have a ragged structure with many pits, while an evolved surface will look smoother. The size and spatial distribution of pits imply...
Research Interests: Geology, Astrobiology, Medicine, Multidisciplinary, Nature, and 3 moreImpact Crater, Comet, and Sinkhole
Images of comet 67P/Churyumov-Gerasimenko acquired by the OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) imaging system onboard the European Space Agency's Rosetta spacecraft at scales of better than 0.8 meter per... more
Images of comet 67P/Churyumov-Gerasimenko acquired by the OSIRIS (Optical, Spectroscopic and Infrared Remote Imaging System) imaging system onboard the European Space Agency's Rosetta spacecraft at scales of better than 0.8 meter per pixel show a wide variety of different structures and textures. The data show the importance of airfall, surface dust transport, mass wasting, and insolation weathering for cometary surface evolution, and they offer some support for subsurface fluidization models and mass loss through the ejection of large chunks of material.
Research Interests: Geology, Physics, Science, Medicine, Multidisciplinary, and 5 moreInsolation, Osiris, Comet, Spacecraft, and Mass Wasting
Images from the OSIRIS scientific imaging system onboard Rosetta show that the nucleus of 67P/Churyumov-Gerasimenko consists of two lobes connected by a short neck. The nucleus has a bulk density less than half that of water. Activity at... more
Images from the OSIRIS scientific imaging system onboard Rosetta show that the nucleus of 67P/Churyumov-Gerasimenko consists of two lobes connected by a short neck. The nucleus has a bulk density less than half that of water. Activity at a distance from the Sun of >3 astronomical units is predominantly from the neck, where jets have been seen consistently. The nucleus rotates about the principal axis of momentum. The surface morphology suggests that the removal of larger volumes of material, possibly via explosive release of subsurface pressure or via creation of overhangs by sublimation, may be a major mass loss process. The shape raises the question of whether the two lobes represent a contact binary formed 4.5 billion years ago, or a single body where a gap has evolved via mass loss.
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Smooth Space Pebble In September 2008, on its way to meet comet 67P/Churyumov-Gerasimenko, the Rosetta spacecraft flew by asteroid Steins, a member of a very rare class of asteroids that had never been observed closely by spacecraft.... more
Smooth Space Pebble In September 2008, on its way to meet comet 67P/Churyumov-Gerasimenko, the Rosetta spacecraft flew by asteroid Steins, a member of a very rare class of asteroids that had never been observed closely by spacecraft. Keller et al. (p. 190 ) analyzed the images to generate a reconstruction of the asteroid's shape. Steins is oblate with an effective spherical diameter of 5.3 kilometers, and it lacks small craters, which may have been erased by surface reshaping. Indeed, Steins's shape resembles that of a body that was spun-up by the YORP effect—a torque produced by incident sunlight, which can alter the rotation rate of a small body—that causes material to slide toward the equator. This effect may have produced Steins's distinctive diamond-like shape.
Research Interests: Physics, Astrobiology, Science, Medicine, Multidisciplinary, and 7 moreOsiris, South Pole, Infrared, Comet, Spacecraft, Asteroid, and imaging system
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We present an analysis of observations of Venus made with the UVES instrument (Ultraviolet and Visual Echelle Spectrograph) at ESO's Very Large Telescope (VLT). The observations were carried out in May and June 2007 with the aim of... more
We present an analysis of observations of Venus made with the UVES instrument (Ultraviolet and Visual Echelle Spectrograph) at ESO's Very Large Telescope (VLT). The observations were carried out in May and June 2007 with the aim of characterizing the zonal wind flow in the atmosphere of Venus during the nominal mission phase of Venus Express. Doppler velocimetry measurements are
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After one year of almost flawless operation on board the SOHO spacecraft poised at L1 Lagrange point, we report the main features of SWAN observations. SWAN is mainly dedicated to the monitoring of the latitude distribution of the solar... more
After one year of almost flawless operation on board the SOHO spacecraft poised at L1 Lagrange point, we report the main features of SWAN observations. SWAN is mainly dedicated to the monitoring of the latitude distribution of the solar wind by the Lα method. Maps of sky Lα emissions were recorded througout the year. The region of maximum emission, located
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The SWAN instrument on board SOHO is a Lyman-α (Lα) photometer able to map the sky intensity with a resolution of 1°, and a capability of microstepping (0.1°). SWAN is primarily devoted to the study of the large scale distribution of... more
The SWAN instrument on board SOHO is a Lyman-α (Lα) photometer able to map the sky intensity with a resolution of 1°, and a capability of microstepping (0.1°). SWAN is primarily devoted to the study of the large scale distribution of solar wind from its imprints on the interplanetary sky background, but was in addition extensively used to map the