Model of Dust Thermal Emission of Comet 67p-Churyumov-Gerasimenko for the Rosetta-MIRO Instrument

The ESA's Rosetta spacecraft will arrive at comet 67P/Churyumov-Gerasimenko in 2014. The study of gas and dust emission is primary objective of several instruments on the Rosetta spacecraft, including the Microwave Instrument for the Rosetta Orbiter (MIRO). We developed a model of dust thermal emission to estimate the detectability of dust in the vicinity of the nucleus with MIRO. Our model computes the power received by the MIRO antenna in limb viewing as a function of the geometry of the observations and the physical properties of the grains. We show that detection in the millimeter and submillimeter channels can be achieved near perihelion

Model for the architecture of caveolae based on a flexible, net-like assembly of Cavin1 and Caveolin discs.

Caveolae are invaginated plasma membrane domains involved in mechanosensing, signaling, endocytosis, and membrane homeostasis. Oligomers of membrane-embedded caveolins and peripherally attached cavins form the caveolar coat whose structure has remained elusive. Here, purified Cavin1 60S complexes were analyzed structurally in solution and after liposome reconstitution by electron cryotomography. Cavin1 adopted a flexible, net-like protein mesh able to form polyhedral lattices on phosphatidylserine-containing vesicles. Mutating the two coiled-coil domains in Cavin1 revealed that they mediate distinct assembly steps during 60S complex formation. The organization of the cavin coat corresponded to a polyhedral nano-net held together by coiled-coil segments. Positive residues around the C-terminal coiled-coil domain were required for membrane binding. Purified caveolin 8S oligomers assumed disc-shaped arrangements of sizes that are consistent with the discs occupying the faces in the caveolar polyhedra. Polygonal caveolar membrane profiles were revealed in tomograms of native caveolae inside cells. We propose a model with a regular dodecahedron as structural basis for the caveolae architecture

Orthoparamyxovirinae C Proteins Have a Common Origin and a Common Structural Organization

The protein C is a small viral protein encoded in an overlapping frame of the P gene in the subfamily Orthoparamyxovirinae. This protein, expressed by alternative translation initiation, is a virulence factor that regulates viral transcription, replication, and production of defective interfering RNA, interferes with the host-cell innate immunity systems and supports the assembly of viral particles and budding. We expressed and purified full-length and an N-terminally truncated C protein from Tupaia paramyxovirus (TupV) C protein (genus Narmovirus). We solved the crystal structure of the C-terminal part of TupV C protein at a resolution of 2.4 Å and found that it is structurally similar to Sendai virus C protein, suggesting that despite undetectable sequence conservation, these proteins are homologous. We characterized both truncated and full-length proteins by SEC-MALLS and SEC-SAXS and described their solution structures by ensemble models. We established a mini-replicon assay for the related Nipah virus (NiV) and showed that TupV C inhibited the expression of NiV minigenome in a concentration-dependent manner as efficiently as the NiV C protein. A previous study found that the Orthoparamyxovirinae C proteins form two clusters without detectable sequence similarity, raising the question of whether they were homologous or instead had originated independently. Since TupV C and SeV C are representatives of these two clusters, our discovery that they have a similar structure indicates that all Orthoparamyxovirine C proteins are homologous. Our results also imply that, strikingly, a STAT1-binding site is encoded by exactly the same RNA region of the P/C gene across Paramyxovirinae, but in different reading frames (P or C), depending on which cluster they belong to.French Agence Nationale de la RechercheFond de la Recherche Médicale (FRM)Grenoble Instruct-ERIC centerFRISBIUniversity Grenoble Alpes graduate school (Ecoles Universitaires de Recherche)Peer Reviewe

Investigating the correlations between water coma emissions and active regions in comet 67P/ Churyumov-Gerasimenko

Vibrational emission lines of H2O and CO2 at 2.67 and 4.27 μm, respectively, were identified by the VIRTIS spectrometer (Bockelée-Morvan et al., 2015; Migliorini et al., 2016; Fink et al., 2016) and mapped from the surface up to about 10 km altitude with a spatial resolution on the order of tens of meters per pixel (Migliorini et al., 2016).Data acquired in April 2015 with the VIRTIS spectrometer on board the Rosetta mission, provided information on the possible correlation between the H2O emission in the inner coma and the exposed water deposits detected in the Hapi region on the 67P/Churyumov-Gerasimenko surface (Migliorini et al., 2106; De Sanctis et al., 2015). Further bright spots attributed to exposed water ice have been identified in other regions by OSIRIS at visible wavelengths (Pommerol, et al., 2015) and confirmed in the infrared by VIRTIS-M in the Imothep region (Filacchione et al., 2016). The small dimensions of these icy spots - approximately 100x100 m (Filacchione et al., 2016) - and the relatively small amount of water ice (about 5%) make uncertain the correlation with the strong emissions in the coma.However, VIRTIS data show that the distribution of jet-like emissions seems to follow the distribution of cliffs and exposed areas identified in the North hemisphere with OSIRIS camera (Vincent et al., 2015). These areas are mainly concentrated in correspondence of comet's rough terrains, while a lack of active regions is observed in the comet's neck. Nevertheless, strong H2O emission is observed above the neck with VIRTIS. This might be a consequence of gas jets that are originated in the surrounding of the neck but converging towards the neck itself. This gaseous activity is the main driver of the dust upwelling (Migliorini et al, 2016; Rinaldi et al., in preparation)In this paper, we investigate the relationship between H2O vapour observed with VIRTIS within 5 km from the 67P/C-G nucleus and the exposed regions identified by OSIRIS on the surface (in the timeframe March to April 2015) with an attempt to address possible variations with the heliocentric distance

Relationship between inner coma water emissions and ice deposits in comet 67P/Churyumov-Gerasimenko

Data acquired in April 2015 with the VIRTIS spectrometer on board the Rosetta mission provided information on the possible correlation between the H2O emission in the inner coma and the exposed water deposits detected in the Hapi region on the 67P/Churyumov-Gerasimenko surface (Migliorini et al. submitted). Further bright spots attributed to exposed water ice have been identified in other regions by OSIRIS at visible wavelengths (Pommerol, et al., 2015) and confirmed in the infrared by VIRTIS-M in the Imothep region (Filacchione et al., 2016). Furthermore, new water ice deposits have been identified in regions located both at the equator and at southern latitudes. These regions might be localised sources of water emissions in the inner coma of 67P/C-G. The present investigation seeks to identify the spatial and temporal correlations between the H2O emissions in the inner coma and the water ice rich deposits on the surface in order to identify the mechanisms operating at the surface-coma interface. It extends the study already carried out for a limited region located in the comet's neck, and identifies how the observed emissions and deposits evolve with the heliocentric distance, as observed by VIRTIS during the Rosetta escort phase mission

Mapping of thermal properties of comet 67P/C-G and temporal variations

The long-term evolution of the surfaces of comets depends mainly on the erosion rate that is driven by the thermal properties of the regolith and the sub-surface material. Following the diurnal and the seasonal thermal cycles, dust and gas are released progressively, increasing the erosion process. The amount of dust released depends on the surface and subsurface temperatures and thus on thermal inertia and bulk composition.The ESA's Rosetta spacecraft has followed the comet 67P/Churyumov-Gerasimenko over several months from 4 AU to 1.28 AU heliocentric distance, and the VIRTIS/Rosetta imaging infrared spectrometer was capable of detecting the thermal emission of the surface longward of 3 microns.The surface temperature was mapped over a large fraction of the nucleus and was previously used to derive thermal inertia of the main geomorphological units.In this presentation, we now focus on two different aspects: (1) We aim to present a complete detailed map of the thermal inertia by combining measurements of similar areas obtained at different viewing angles ; and (2) we track the evolution of the local thermal properties derived over months when the comet was moving towards perihelion. We then discuss and compare our results with the textural features observed at the surface

Photometric correction for VIRTIS-M data of comet 67P/CG

VIRTIS, the Visible Infrared Thermal Imaging Spectrometer onboard the Rosetta orbiter [1], has acquired so far millions of spectra of the comet 67P/Churyumov-Gerasimenko [2]. The instrument is composed of two subsystems: a high-resolution channel (VIRTIS-H) which is a punctual spectrometer (2.0-5-0 µm) and the mapper (VIRTIS-M) able to produce hyper-spectral images of the target (0.25-5.1 µm). The huge amount of data produced by VIRTIS has been acquired under different observation and illumination conditions. This induces photometric effects on the measured signal that need to be quantified and removed, in order to characterize the intrinsic spectral variability of the surface. To achieve this task we computed a photometric correction from VIRTIS-M data (Ciarniello et al, 2015), starting from August 2014, when the nucleus was largely resolved (MTP006-MT007 observation sequences) by means of a simplified Hapke model [3]. The global surface single particle phase function (SPPF) and the single scattering albedo (SSA) are determined as well as the effect of sub-pixel roughness is discussed. Comparisons with photometric properties of other comets are shown. This work is supported by the Italian Space Agency (ASI. We acknowledge funding from French and German space agency. References 1- Coradini et al, SSR, 2007 2- Capaccioni et al., Science, in Press, 2015 3- Hapke, Theory of reflectance and emittance spectroscopy. Cambridge University Press, 2012 <P /

Etudes biophysiques et structurales du complexe de réplication des Rhabdoviridae: La phosphoprotéine et ses interactions avec la nucléoprotéine

Vesicular Stomatitis Virus (VSV) and Rabies Virus (RV) belong to the Rhabdoviridae family and are prototypic members of the genus Vesiculovirus and Lyssavirus, respectively. VSV and RV are envelopped, single stranded, negative sense RNA viruses, and their genome encode successively for five viral proteins including nucleoprotein (N) and phosphoprotein (P), which form, together with the viral RNA dependent RNA polymerase (L), the Rhabdoviridae transcription and replication complex. The aim of this work was to obtain structural information regarding the structure of phosphoprotein and of several of its fragments, free or in complex with N, in order to better understand the mechanisms involved in viral replication. The P protein interacts with N by forming two distinct types of complexes : the N-ARN-P complex results from the association of P with the N-RNA complex, which constitutes the active template for transcription and replication ; the N0-P complex arises from the attachment of P to a N0 molecule, thus preventing binding to non specific RNA and allowing for the specific encapsidation of newly synthesized genomes and antigenomes during viral replication. The data presented here reveals the modular organization of P dimers and highlights the intrinsically disordered character of its N-terminal region involved in N0 binding (PNTD). It is shown that the C-terminal domain of P (PCTD) is an autonomous folding unit that can bind to N-RNA complexes. The atomic scale modeling of P in solution shows that the protein behaves as a partially disordered, highly flexible multidomain protein. Additionally, we constructed a structural model of the interaction between N-RNA and P in silico, which was validated experimentally, and we solved the crystal structure of the N0-PNTD complex using X-Ray diffraction. The work presented here concerning the structure of P, free or in complex with N enhances our understanding of the role of P in the viral replication complex, and emphasizes the importance of structural disorder and conformational changes in the molecular recognition processes involving N and P. The structural models for the N-ARN-P and N0-P complexes also represent attractive new targets for the development of antiviral drugs.Le virus de la stomatite vésiculaire (VSV) et le virus de la rage (RV) appartiennent à la famille des Rhabdoviridae et sont les représentants prototypiques respectifs des genres Vesiculovirus et Lyssavirus. Ces virus sont enveloppés, et leur génome est composé d’une molécule d’ARN de polarité négative qui encode successivement cinq protéines virales dont la nucléoprotéine (N) et la phosphoprotéine (P), qui forment, avec l’ARN polymérase ARN dépendante virale (L), le complexe de transcription et de réplication des Rhabdoviridae. L’objectif de mon travail de thèse consistait à obtenir des informations structurales concernant la phosphoprotéine et plusieurs de ses fragments, à l’état libre en solution, ou en complexe avec N, et ce afin de mieux comprendre les mécanismes impliqués dans la multiplication virale. La protéine P interagit avec N en formant deux types de complexes distincts : le complexe N-ARN-P, résultant de l’association de P avec les complexes N-ARN, qui constituent la matrice utilisée pour la transcription et la réplication virale, et le complexe N0-P, qui correspond à la fixation par P d’une molécule de nucléoprotéine N0 monomérique, empêchant ainsi la fixation non spécifique de N à l’ARN et permettant l’encapsidation des génomes et anti-génomes néo-synthétisés lors de la réplication virale. Les travaux réalisés ont permis de mettre en évidence la nature modulaire des dimères de phosphoprotéine, et de caractériser la région N-terminale intrinsèquement désordonnée de P (PNTD) impliquée dans la fixation à N0. Nous avons montré que le domaine C-terminal impliqué dans la fixation à N-ARN (PCTD) constituait un module structural indépendant, et modélisé à l’échelle atomique la structure multi-domaine partiellement désordonnée de P en solution. Nous avons également construit un modèle atomique in silico de l’interaction entre N-ARN et P, validé expérimentalement, et enfin résolus par diffraction des rayons X la structure du complexe N0-PNTD à l’état cristallin. Les travaux présentés concernant la structure de la phosphoprotéine libre ou en complexe avec la nucléoprotéine permettent de mieux comprendre le rôle de P dans le complexe de réplication, et soulignent l’importance du désordre moléculaire et des changements conformationnels dans les processus de reconnaissance moléculaire impliquant N et P. Les modèles structuraux des complexes N-ARN-P et N0-P constituent par ailleurs des nouvelles cibles intéressantes pour le développement de composés antiviraux

Propriétés physiques des anneaux de Saturne : de CAMIRAS à la mission CASSINI.

This thesis presents a study of the rotational properties of particles in Saturn's A and C rings. The own rotation of particles is a dynamical key parameter which plays a role during mutual collisions. The distribution of the spin rate w depends indeed on relative speeds but also on the surface quality of regolith (porosity and roughness) and thus on the internal structure of particles. To constrain w, we need to interpret the thermal emission (function of thermal inertia Tau and w) of the disc according to the phase angle and the planetocentric longitude, as it is still impossible to observe particles separately. Azimuthal variations of temperature observed with various phases angles are modulated by the cooling of the particles, when they cross the shadow of the planet. The heating and cooling rates make it possible to measure thermal inertia, whereas the differences in temperature with the phase angle inform us on the anisotropy of emission associated with the spin rate. Azimuthal variations of temperature were observed in the mid-infrared, at weak phase angle with imagers CAMIRAS (CFHT) and VISIR (VLT), and at multiple phases angles with IRIS (Voyager) and CIRS (Cassini) spectrometers, offering respectively a total or partial azimuthal coverage. A thermal model of planetary ring made up of icy spherical particles in rotation and distributed according to a monolayer structure was developed to interpret the observed temperatures. It enables us to determine how the temperature of the disc, submitted to the multiple sources of heating (Sun, Saturn... etc), varies with the phase angle and the longitude according to the thermal properties of particles. The significant asymmetrycal emission to weak or strong phase shows that the largest particles, which contain a significant fraction of the C ring mass, have an average spin rate w/Omega =0.5±0.4.This result, obtained with the assumptions of a mono size distribution and a monolayer vertical structure, is compatible with results of dynamical simulations. The thermal inertia of the regolith in the C ring (Tau = 6.0 ± 4Jm-2K-1s-1/2) is 3 orders of magnitude weaker than that of the crystalline water ice, and confirms a very porous structure, probably generated by cracks on the surface of the particles. They are probably the consequence of the permanent patching due to the mutual collisions, or the forces of tensions related to the signi- ficant variations in temperature with each orbit. In addition to azimuthal variations in temperature of the A ring, related to the spin rate and the cooling of particles in the Saturn's shadow, a modulation of brightness temperature, correlated with variations of optical depth, is put. This variation could be highlighted by the observations of CIRS at multiple phases and is explained by the presence of gravitational instabilities known under the name of "wakes". The thermal emission of the A ring observed with VISIR, after the taking into account of CIRS observations, is similar to that coming from plane structures in which the particles form aggregates. The high angular resolution accessible with the VLT enabled us, for the first time, to measure the azimuthal variations of temperature in this ring and to deduce its thermal inertia from it. The found value (Tau = 4±3Jm-2K-1s-1/2), under the assumption of a monolayer plane structure, is virtually identical to that of the rings C and B, indicating a probably similar surface quality.Cette thèse présente une étude des propriétés rotationnelles des particules dans les anneaux A et C de Saturne. La rotation des particules sur elles mêmes est un des paramètres dynamiques clé qui entre en jeu au cours des collisions mutuelles. La distribution du spin w dépend en effet des vitesses relatives mais aussi de l'état de surface du régolite (porosité et rugosité) et donc de la structure interne des particules. La contrainte de w passe par l'interprétation de l'émission thermique (fonction de l'inertie thermique Tau et de w) du disque en fonction de l'angle de phase et de la longitude planétocentrique, car il n'est pas encore possible d'observer les particules individuellement. Les variations azimutales de température observées à différents angles de phase sont modulées par le refroidissement des particules à chaque orbite, lorsqu'elles traversent l'ombre de la planète. Les vitesses de réchauffement et de refroidissement permettent de mesurer l'inertie thermique, alors que les différences de température en fonction de l'angle de phase nous informent sur l'anisotropie d'émission associée au spin.Ces variations de température ont été observées dans l'infrarouge, à faible angle de phase avec les caméras CAMIRAS (CFHT) et VISIR (VLT), et à de multiples angles de phase avec les spectromètres IRIS (Voyager) et CIRS (Cassini), offrant respectivement une couverture azimutale totale ou partielle. Un modèle thermique d'anneau planétaire constitué de particules de glace sphériques en rotation et réparties suivant une structure monocouche a été développé pour interpréter les températures observées. Il permet de déterminer comment la température du disque, soumis aux multiples sources de chauffage (Soleil, Saturne...etc), varie avec l'angle de phase et la longitude en fonction des propriétés thermiques des particules.L'importante asymétrie d'émission à faible ou fort angle de phase montre que les plus grosses particules, qui contiennent une fraction importante de la masse de l'anneau C, ont une vitesse moyenne de rotation proche de la rotation Keplerienne Omega(w/Omega =0.5±0.4). Ce résultat, obtenu avec les hypothèses d'une distribution mono taille des particules, et suivant une structure monocouche, est compatible avec les résultats des simulations dynamiques. L'inertie thermique du régolite de l'anneau C (Tau = 6.0 ± 4Jm-2K-1s-1/2) est 3 ordres de grandeur plus faible que celle de la glace d'eau cristalline, et confirme une structure très poreuse, probablement engendrée par des fissures à la surface des particules. Elles sont probablement la conséquence du resurfaçage permanent dû aux collisions mutuelles, ou aux forces de tensions liées aux importantes variations de température à chaque orbite.Aux variations de température azimutales de l'anneau A liées au spin et au refroidissement des particules dans l'ombre de la planète, s'ajoute une modulation de température de brillance, corrélée avec la variation de profondeur optique. Cette variation a pu être mise en évidence par les observations de CIRS à de multiples angles de phase et s'explique par la présence d'instabilit és gravitationnelles connues sous le nom de " wakes ". L'émission thermique de l'anneau A observée avec VISIR, après la prise en compte des observations de CIRS, est similaire à celle provenant de structures planes dans lesquelles les particules forment des agrégats. La haute résolution angulaire accessible au VLT nous a permis, pour la première fois, de mesurer les variations azimutales de température dans cette région et d'en déduire son inertie thermique. La valeur trouvée (Tau = 4 ± 3Jm-2K-1s-1/2), sous l'hypothèse d'une structure plane monocouche, est sensiblement identique à celle des anneaux C et B, indiquant un état de surface probablement similaire

Probing Pluto’s underworld: Ice temperatures from microwave radiometry decoupled from surface conditions

International audiencePresent models admit a wide range of 2015 surface conditions at Pluto and Charon, where the atmospheric pressure may undergo dramatic seasonal variation and for which measurements are imminent from the New Horizons mission. One anticipated observation is the microwave brightness temperature, heretofore anticipated as indicating surface conditions relevant to surface-atmosphere equilibrium. However, drawing on recent experience with Cassini observations at Iapetus and Titan, we call attention to the large electrical skin depth of outer solar system materials such as methane, nitrogen or water ice, such that this observation may indicate temperatures averaged over depths of several or tens of meters beneath the surface. Using a seasonally-forced thermal model to determine microwave emission we predict that the southern hemisphere observations (in polar night) of New Horizons in July 2015 will suggest effective temperatures of ∼40 K, reflecting deep heat buried over the last century of summer, even if the atmospheric pressure suggests that the surface nitrogen frost point may be much lower