TY - JOUR A1 - Lecourieux, Fatma A1 - Kappel, Christian A1 - Lecourieux, David A1 - Serrano, Alejandra A1 - Torres, Elizabeth A1 - Arce-Johnson, Patricio A1 - Delrot, Serge T1 - An update on sugar transport and signalling in grapevine JF - Journal of experimental botany N2 - In addition to their role as a source of reduced carbon, sugars may directly or indirectly control a wide range of activities in plant cells, through transcriptional and post-translational regulation. This control has been studied in detail using Arabidopsis thaliana, where genetic analysis offers many possibilities. Much less is known about perennial woody species. For several years, various aspects of sugar sensing and signalling have been investigated in the grape (Vitis vinifera L.) berry, an organ that accumulates high concentrations of hexoses in the vacuoles of flesh cells. Here we review various aspects of this topic: the molecular basis of sugar transport and its regulation by sugars in grapevine; the functional analysis of several sugar-induced genes; the effects of some biotic and abiotic stresses on the sugar content of the berry; and finally the effects of exogenous sugar supply on the ripening process in field conditions. A picture of complex feedback and multiprocess regulation emerges from these data. KW - Fruit biology KW - grapevine KW - signalling KW - stress KW - sugar KW - transport Y1 - 2014 U6 - https://doi.org/10.1093/jxb/ert394 SN - 0022-0957 SN - 1460-2431 VL - 65 IS - 3 SP - 821 EP - 832 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Nicolas, Philippe A1 - Lecourieux, David A1 - Kappel, Christian A1 - Cluzet, Stephanie A1 - Cramer, Grant A1 - Delrot, Serge A1 - Lecourieux, Fatma T1 - The basic leucine zipper transcription factor abscisic acid responseelement-binding factor 2 is an important transcriptional regulator ofabscisic acid-dependent grape berry ripening processes JF - Plant physiology : an international journal devoted to physiology, biochemistry, cellular and molecular biology, biophysics and environmental biology of plants N2 - In grape (Vitis vinifera), abscisic acid (ABA) accumulates during fruit ripening and is thought to play a pivotal role in this process, but the molecular basis of this control is poorly understood. This work characterizes ABSCISIC ACID RESPONSE ELEMENT-BINDING FACTOR2 (VvABF2), a grape basic leucine zipper transcription factor belonging to a phylogenetic subgroup previously shown to be involved in ABA and abiotic stress signaling in other plant species. VvABF2 transcripts mainly accumulated in the berry, from the onset of ripening to the harvesting stage, and were up-regulated by ABA. Microarray analysis of transgenic grape cells overexpressing VvABF2 showed that this transcription factor up-regulates and/or modifies existing networks related to ABA responses. In addition, grape cells overexpressing VvABF2 exhibited enhanced responses to ABA treatment compared with control cells. Among the VvABF2-mediated responses highlighted in this study, the synthesis of phenolic compounds and cell wall softening were the most strongly affected. VvABF2 overexpression strongly increased the accumulation of stilbenes that play a role in plant defense and human health (resveratrol and piceid). In addition, the firmness of fruits from tomato (Solanum lycopersicum) plants overexpressing VvABF2 was strongly reduced. These data indicate that VvABF2 is an important transcriptional regulator of ABA-dependent grape berry ripening. Y1 - 2014 U6 - https://doi.org/10.1104/pp.113.231977 SN - 0032-0889 SN - 1532-2548 VL - 164 IS - 1 SP - 365 EP - 383 PB - American Society of Plant Physiologists CY - Rockville ER - TY - THES A1 - Kappel, David T1 - Multi-spectrum retrieval of maps of Venus' surface emissivity in the infrared T1 - Multispektrum-Retrieval von Karten der Oberflächenemissivität der Venus im Infrarotbereich N2 - The main goal of this cumulative thesis is the derivation of surface emissivity data in the infrared from radiance measurements of Venus. Since these data are diagnostic of the chemical composition and grain size of the surface material, they can help to improve knowledge of the planet’s geology. Spectrally resolved images of nightside emissions in the range 1.0-5.1 μm were recently acquired by the InfraRed Mapping channel of the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS-M-IR) aboard ESA’s Venus EXpress (VEX). Surface and deep atmospheric thermal emissions in this spectral range are strongly obscured by the extremely opaque atmosphere, but three narrow spectral windows at 1.02, 1.10, and 1.18 μm allow the sounding of the surface. Additional windows between 1.3 and 2.6 μm provide information on atmospheric parameters that is required to interpret the surface signals. Quantitative data on surface and atmosphere can be retrieved from the measured spectra by comparing them to simulated spectra. A numerical radiative transfer model is used in this work to simulate the observable radiation as a function of atmospheric, surface, and instrumental parameters. It is a line-by-line model taking into account thermal emissions by surface and atmosphere as well as absorption and multiple scattering by gases and clouds. The VIRTIS-M-IR measurements are first preprocessed to obtain an optimal data basis for the subsequent steps. In this process, a detailed detector responsivity analysis enables the optimization of the data consistency. The measurement data have a relatively low spectral information content, and different parameter vectors can describe the same measured spectrum equally well. A usual method to regularize the retrieval of the wanted parameters from a measured spectrum is to take into account a priori mean values and standard deviations of the parameters to be retrieved. This decreases the probability to obtain unreasonable parameter values. The multi-spectrum retrieval algorithm MSR is developed to additionally consider physically realistic spatial and temporal a priori correlations between retrieval parameters describing different measurements. Neglecting geologic activity, MSR also allows the retrieval of an emissivity map as a parameter vector that is common to several spectrally resolved images that cover the same surface target. Even applying MSR, it is difficult to obtain reliable emissivity maps in absolute values. A detailed retrieval error analysis based on synthetic spectra reveals that this is mainly due to interferences from parameters that cannot be derived from the spectra themselves, but that have to be set to assumed values to enable the radiative transfer simulations. The MSR retrieval of emissivity maps relative to a fixed emissivity is shown to effectively avoid most emissivity retrieval errors. Relative emissivity maps at 1.02, 1.10, and 1.18 μm are finally derived from many VIRTIS-M-IR measurements that cover a surface target at Themis Regio. They are interpreted as spatial variations relative to an assumed emissivity mean of the target. It is verified that the maps are largely independent of the choice of many interfering parameters as well as the utilized measurement data set. These are the first Venus IR emissivity data maps based on a consistent application of a full radiative transfer simulation and a retrieval algorithm that respects a priori information. The maps are sufficiently reliable for future geologic interpretations. N2 - Das Hauptziel dieser publikationsbasierten Dissertation ist die Ableitung von Oberflächenemissivitäts-Daten im Infraroten aus Radianzmessungen der Venus. Da diese Daten diagnostisch bezüglich chemischer Zusammensetzung und Korngröße des Oberflächenmaterials sind, können sie zur Erweiterung des Wissens über die Geologie des Planeten beitragen. Spektral aufgelöste Bilder von nachtseitigen Emissionen im Bereich 1.0-5.1 µm wurden kürzlich durch den Infrarot-Kartierungskanal des Abbildenden Spektrometers im Sichtbaren und Infraroten Bereich (VIRTIS-M-IR) an Bord der ESA-Sonde Venus Express (VEX) gewonnen. Die thermischen Emissionen der Oberfläche sowie der tiefen Atmosphäre werden in diesem Spektralbereich stark durch die extrem licht-undurchlässige Atmosphäre verschleiert, aber drei schmale spektrale Fenster bei 1.02, 1.10 und 1.18 µm ermöglichen die Sondierung der Oberfläche. Weitere Fenster zwischen 1.3 und 2.6 µm liefern Informationen über atmosphärische Parameter, die benötigt werden, um die Oberflächensignale zu interpretieren. Quantitative Daten von Oberfläche und Atmosphäre können von den gemessenen Spektren durch Vergleiche mit simulierten Spektren abgeleitet werden. In dieser Arbeit wird ein numerisches Strahlungstransportmodell verwendet, um die beobachtbare Strahlung als Funktion von Atmosphären-, Oberflächen-, und Instrumentenparametern zu simulieren. Es ist ein Linie-für-Linie-Modell und berücksichtigt sowohl thermische Emissionen der Oberfläche und Atmosphäre, als auch Absorption und Mehrfachstreuung durch Gase und Wolken. Die VIRTIS-M-IR-Messungen werden zunächst vorverarbeitet, um eine optimale Datenbasis für die nachfolgenden Schritte zu erhalten. Eine detaillierte Analyse des Detektoransprechvermögens ermöglicht dabei die Optimierung der Datenkonsistenz. Die Messdaten haben einen vergleichsweise geringen spektralen Informationsgehalt, und verschiedene Parametervektoren können ein- und dasselbe gemessene Spektrum gleich gut beschreiben. Eine übliche Maßnahme, das Retrieval der gesuchten Parameter aus einem gemessenem Spektrum zu regularisieren, ist die Berücksichtigung von a-priori-Mittelwerten und -Standardabweichungen der zu bestimmenden Parameter. Dadurch wird die Wahrscheinlichkeit verringert, unrealistische Parameterwerte zu erhalten. Es wird der Multispektrum-Retrieval-Algorithmus MSR entwickelt, um zusätzlich physikalisch realistische räumliche und zeitliche a-priori-Korrelationen zwischen Retrievalparametern, die verschiedene Messungen beschreiben, berücksichtigen zu können. Vernachlässigt man geologische Aktivität, kann mittels MSR auch eine Emissivitätskarte in Form eines Parametervektors bestimmt werden, der verschiedenen spektral aufgelösten, denselben Oberflächenbereich überdeckenden Bildern gemeinsam ist. Selbst bei Anwendung von MSR ist es schwierig, verlässliche Karten für die Absolutwerte der Emissivität zu erhalten. Eine detaillierte Retrieval-Fehleranalyse, die auf synthetischen Spektren beruht, zeigt, dass dies hauptsächlich an Interferenzen von Parametern liegt, die nicht aus den Spektren selbst hergeleitet werden können. Um dennoch die Strahlungstransportsimulationen zu ermöglichen, müssen diese Parameter auf angenommene Werte gesetzt werden. Es wird nachgewiesen, dass durch ein MSR-Retrieval von Emissivitätskarten relativ zu einer festen Emissivität die meisten Fehler bei der Emissivitätsbestimmung effizient vermieden werden können. Abschließend werden relative Emissivitätskarten bei 1.02, 1.10 und 1.18 µm aus vielen VIRTIS-M-IR-Messungen bestimmt, die einen Oberflächenbereich in der Themis Regio überdecken. Diese Karten werden als räumliche Variationen relativ zu einer angenommenen mittleren Emissivität des Oberflächenbereichs interpretiert. Es wird nachgewiesen, dass die Karten von der Wahl vieler interferierender Parameter sowie von der Auswahl der zugrunde liegenden Messungen weitgehend unabhängig sind. Dieses sind die ersten Karten von Emissivitätsdaten der Venus im Infrarotbereich auf Basis der konsistenten Anwendung einer umfassenden Strahlungstransportsimulation und eines Retrievalalgorithmus, der a priori Informationen berücksichtigt. Die Karten sind hinreichend zuverlässig für zukünftige geologische Interpretationen. KW - Venus Express KW - VIRTIS KW - surface emissivity KW - infrared KW - radiative transfer KW - retrieval KW - multi-spectrum regularization KW - Venus Express KW - VIRTIS KW - Oberflächenemissivität KW - Infrarot KW - Strahlungstransport KW - Retrieval KW - Multi-Spektrum-Regularisierung Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-85301 ER - TY - JOUR A1 - Kappel, David A1 - Arnold, Gabriele A1 - Haus, Rainer T1 - Multi-spectrum retrieval of Venus IR surface emissivity maps from VIRTIS/VEX nightside measurements at Themis Regio JF - Icarus : international journal of solar system studies N2 - Renormalized emissivity maps of Themis Regio at the three surface windows are determined from 64 measurement repetitions. Retrieval errors are estimated by a statistical evaluation of maps derived from various disjoint selections of spectra and using different assumptions on the interfering parameters. Double standard deviation errors for the three surface windows amount to 3%, 8%, and 4%, respectively, allowing geologic interpretation. A comparison to results from an earlier error analysis based on synthetic spectra shows that unconsidered time variations of interfering atmospheric parameters are a major error source. Spatial variations of the 1.02 mu m surface emissivity of 20% that correspond to the difference between unweathered granitic and basaltic rocks would be easily detectable, but such variations are ruled out for the studied target area. Emissivity anomalies of up to 8% are detected at both 1.02 and 1.18 mu m. At present sensitivity, no anomalies are identified at 1.10 mu m, but anomalies exceeding the determined error level can be excluded. With single standard deviation significance, all three maps show interesting spatial emissivity variations. (C) 2015 Elsevier Inc. All rights reserved. KW - Venus, surface KW - Infrared observations KW - Radiative transfer Y1 - 2016 U6 - https://doi.org/10.1016/j.icarus.2015.10.014 SN - 0019-1035 SN - 1090-2643 VL - 265 SP - 42 EP - 62 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - Lecourieux, Fatma A1 - Kappel, Christian A1 - Pieri, Philippe A1 - Charon, Justine A1 - Pillet, Jeremy A1 - Hilbert, Ghislaine A1 - Renaud, Christel A1 - Gomes, Eric A1 - Delrot, Serge A1 - Lecourieux, David T1 - Dissecting the Biochemical and Transcriptomic Effects of a Locally Applied Heat Treatment on Developing Cabernet Sauvignon Grape Berries JF - Frontiers in plant science N2 - Reproductive development of grapevine and berry composition are both strongly influenced by temperature. To date, the molecular mechanisms involved in grapevine berries response to high temperatures are poorly understood. Unlike recent data that addressed the effects on berry development of elevated temperatures applied at the whole plant level, the present work particularly focuses on the fruit responses triggered by direct exposure to heat treatment (HT). In the context of climate change, this work focusing on temperature effect at the microclimate level is of particular interest as it can help to better understand the consequences of leaf removal (a common viticultural practice) on berry development. HT (+8 degrees C) was locally applied to clusters from Cabernet Sauvignon fruiting cuttings at three different developmental stages (middle green, veraison and middle ripening). Samples were collected 1, 7, and 14 days after treatment and used for metabolic and transcriptomic analyses. The results showed dramatic and specific biochemical and transcriptomic changes in heat exposed berries, depending on the developmental stage and the stress duration. When applied at the herbaceous stage, HT delayed the onset of veraison. Heating also strongly altered the berry concentration of amino acids and organic acids (e.g., phenylalanine, raminobutyric acid and malate) and decreased the anthocyanin content at maturity. These physiological alterations could be partly explained by the deep remodeling of transcriptome in heated berries. More than 7000 genes were deregulated in at least one of the nine experimental conditions. The most affected processes belong to the categories "stress responses," protein metabolism" and "secondary metabolism," highlighting the intrinsic capacity of grape berries to perceive HT and to build adaptive responses. Additionally, important changes in processes related to "transport," "hormone" and "cell wall" might contribute to the postponing of veraison. Finally, opposite effects depending on heating duration were observed for genes encoding enzymes of the general phenylpropanoid pathway, suggesting that the HI induced decrease in anthocyanin content may result from a combination of transcript abundance and product degradation. KW - grapevine KW - berry development KW - microclimate KW - high temperature KW - microarrays KW - metabolomics/metabolite profiling KW - climate change Y1 - 2017 U6 - https://doi.org/10.3389/fpls.2017.00053 SN - 1664-462X VL - 8 PB - Frontiers Research Foundation CY - Lausanne ER - TY - JOUR A1 - Rousseau, Batiste A1 - Erard, Stéphane A1 - Beck, P. A1 - Quirico, Eric A1 - Schmitt, B. A1 - Brissaud, O. A1 - Montes-Hernandez, G. A1 - Capaccioni, F. A1 - Filacchione, Gianrico A1 - Bockelee-Morvan, Dominique A1 - Leyrat, C. A1 - Ciarniello, M. A1 - Raponi, Andrea A1 - Kappel, David A1 - Arnold, G. A1 - Moroz, L. V. A1 - Palomba, Ernesto A1 - Tosi, Federico T1 - Laboratory simulations of the Vis-NIR spectra of comet 67P using sub-mu m sized cosmochemical analogues JF - Icarus : international journal of solar system studies N2 - Laboratory spectral measurements of relevant analogue materials were performed in the framework of the Rosetta mission in order to explain the surface spectral properties of comet 67P. Fine powders of coal, iron sulphides, silicates and their mixtures were prepared and their spectra measured in the Vis-IR range. These spectra are compared to a reference spectrum of 67P nucleus obtained with the VIRTIS/Rosetta instrument up to 2.7 mu m, excluding the organics band centred at 3.2 mu m. The species used are known to be chemical analogues for cometary materials which could be present at the surface of 67P. Grain sizes of the powders range from tens of nanometres to hundreds of micrometres. Some of the mixtures studied here actually reach the very low reflectance level observed by VIRTIS on 67P. The best match is provided by a mixture of sub-micron coal, pyrrhotite, and silicates. Grain sizes are in agreement with the sizes of the dust particles detected by the GIADA, MIDAS and COSIMA instruments on board Rosetta. The coal used in the experiment is responsible for the spectral slope in the visible and infrared ranges. Pyrrhotite, which is strongly absorbing, is responsible for the low albedo observed in the NIR. The darkest components dominate the spectra, especially within intimate mixtures. Depending on sample preparation, pyrrhotite can coat the coal and silicate aggregates. Such coating effects can affect the spectra as much as particle size. In contrast, silicates seem to play a minor role. (c) 2017 Elsevier Inc. All rights reserved. KW - Comets KW - Comets nucleus KW - Comets composition KW - Spectroscopy KW - Experimental techniques Y1 - 2018 U6 - https://doi.org/10.1016/j.icarus.2017.10.015 SN - 0019-1035 SN - 1090-2643 VL - 306 SP - 306 EP - 318 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - Rinaldi, G. A1 - Formisano, M. A1 - Kappel, David A1 - Capaccioni, F. A1 - Bockelee-Morvan, D. A1 - Cheng, Y-C A1 - Vincent, J-B A1 - Deshapriya, P. A1 - Arnold, G. A1 - Capria, M. T. A1 - Ciarniello, M. A1 - De Sanctis, M. C. A1 - Doose, L. A1 - Erard, S. A1 - Federico, C. A1 - Filacchione, G. A1 - Fink, U. A1 - Leyrat, C. A1 - Longobardo, A. A1 - Magni, G. A1 - Mighorini, A. A1 - Mottola, S. A1 - Naletto, G. A1 - Raponi, A. A1 - Taylor, F. A1 - Tosi, F. A1 - Tozzi, G. P. A1 - Salatti, M. T1 - Analysis of night-side dust activity on comet 67P observed by VIRTIS-M BT - a new method to constrain the thermal inertia on the surface JF - Astronomy and astrophysics : an international weekly journal N2 - On 2015 July 18, near perihelion at a heliocentric distance of 1.28 au, the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-M) on board the Rosetta spacecraft had the opportunity of observing dust activity in the inner coma with a view of the night side (shadowed side) of comet 67P/Churyumov-Gerasimenko. At the time of the measurements we present here, we observe a dust plume that originates on the far side of the nucleus. We are able to identify the approximate location of its source at the boundary between the Hapi and Anuket regions, and we find that it has been in darkness for some hours before the observation. Assuming that this time span is equal to the conductive time scale, we obtain a thermal inertia in the range 25-36 W K-1 m(-2) s(-1/2). These thermal inertia values can be used to verify with a 3D finite-element method (REM) numerical code whether the surface and subsurface temperatures agree with the values found in the literature. We explored three different configurations: (1) a layer of water ice mixed with dust beneath a dust mantle of 5 mm with thermal inertia of 36 J m(-2) K-1 S-0.5 ; (2) the same structure, but with thermal inertia of 100 J m(-2) K-1 S-0.5; (3) an ice-dust mixture that is directly exposed. Of these three configurations, the first seems to be the most reasonable, both for the low thermal inertia and for the agreement with the surface and subsurface temperatures that have been found for the comet 67P/Churyumov-Gerasimenko. The spectral properties of the plume show that the visible dust color ranged from 16 +/- 4.8%/100 nm to 13 +/- 2.6%/100 nm, indicating that this plume has no detectable color gradient. The morphology of the plume can be classified as a narrow jet that has an estimated total ejected mass of between 6 and 19 tons when we assume size distribution indices between -2.5 and -3. KW - comets: general KW - comets: individual: 67P/Churyumov-Gerasimenko KW - infrared: planetary systems Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201834907 SN - 1432-0746 VL - 630 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Tubiana, C. A1 - Rinaldi, G. A1 - Guettler, C. A1 - Snodgrass, C. A1 - Shi, X. A1 - Hu, X. A1 - Marschall, R. A1 - Fulle, M. A1 - Bockeele-Morvan, D. A1 - Naletto, G. A1 - Capaccioni, F. A1 - Sierks, H. A1 - Arnold, G. A1 - Barucci, M. A. A1 - Bertaux, J-L A1 - Bertini, I A1 - Bodewits, D. A1 - Capria, M. T. A1 - Ciarniello, M. A1 - Cremonese, G. A1 - Crovisier, J. A1 - Da Deppo, V A1 - Debei, S. A1 - De Cecco, M. A1 - Deller, J. A1 - De Sanctis, M. C. A1 - Davidsson, B. A1 - Doose, L. A1 - Erard, S. A1 - Filacchione, G. A1 - Fink, U. A1 - Formisano, M. A1 - Fornasier, S. A1 - Gutierrez, P. J. A1 - Ip, W-H A1 - Ivanovski, S. A1 - Kappel, David A1 - Keller, H. U. A1 - Kolokolova, L. A1 - Koschny, D. A1 - Krueger, H. A1 - La Forgia, F. A1 - Lamy, P. L. A1 - Lara, L. M. A1 - Lazzarin, M. A1 - Levasseur-Regourd, A. C. A1 - Lin, Z-Y A1 - Longobardo, A. A1 - Lopez-Moreno, J. J. A1 - Marzari, F. A1 - Migliorini, A. A1 - Mottola, S. A1 - Rodrigo, R. A1 - Taylor, F. A1 - Toth, I A1 - Zakharov, V T1 - Diurnal variation of dust and gas production in comet 67P/Churyumov-Gerasimenko at the inbound equinox as seen by OSIRIS and VIRTIS-M on board Rosetta JF - Astronomy and astrophysics : an international weekly journal N2 - Context. On 27 April 2015, when comet 67P/Churyumov-Gerasimenko was at 1.76 au from the Sun and moving toward perihelion, the OSIRIS and VIRTIS-M instruments on board the Rosetta spacecraft simultaneously observed the evolving dust and gas coma during a complete rotation of the comet. Aims. We aim to characterize the spatial distribution of dust, H2O, and CO2 gas in the inner coma. To do this, we performed a quantitative analysis of the release of dust and gas and compared the observed H2O production rate with the rate we calculated using a thermophysical model. Methods. For this study we selected OSIRIS WAC images at 612 nm (dust) and VIRTIS-M image cubes at 612 nm, 2700 nm (H2O emission band), and 4200 nm (CO2 emission band). We measured the average signal in a circular annulus to study the spatial variation around the comet, and in a sector of the annulus to study temporal variation in the sunward direction with comet rotation, both at a fixed distance of 3.1 km from the comet center. Results. The spatial correlation between dust and water, both coming from the sunlit side of the comet, shows that water is the main driver of dust activity in this time period. The spatial distribution of CO2 is not correlated with water and dust. There is no strong temporal correlation between the dust brightness and water production rate as the comet rotates. The dust brightness shows a peak at 0 degrees subsolar longitude, which is not pronounced in the water production. At the same epoch, there is also a maximum in CO2 production. An excess of measured water production with respect to the value calculated using a simple thermophysical model is observed when the head lobe and regions of the southern hemisphere with strong seasonal variations are illuminated (subsolar longitude 270 degrees-50 degrees). A drastic decrease in dust production when the water production (both measured and from the model) displays a maximum occurs when typical northern consolidated regions are illuminated and the southern hemisphere regions with strong seasonal variations are instead in shadow (subsolar longitude 50 degrees-90 degrees). Possible explanations of these observations are presented and discussed. KW - comets: general KW - comets: individual: 67P/Churyumov-Gerasimenko KW - methods: data analysis Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201834869 SN - 1432-0746 VL - 630 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Tosi, Federico A1 - Capaccioni, F. A1 - Capria, M. T. A1 - Mottola, Stefano A1 - Zinzi, A. A1 - Ciarniello, M. A1 - Filacchione, G. A1 - Hofstadter, M. A1 - Fonti, S. A1 - Formisano, M. A1 - Kappel, David A1 - Kührt, E. A1 - Leyrat, C. A1 - Vincent, J-B A1 - Arnold, G. A1 - De Sanctis, M. C. A1 - Longobardo, Andrea A1 - Palomba, E. A1 - Raponi, A. A1 - Rousseau, Batiste A1 - Schmitt, Bernard A1 - Barucci, Maria Antonietta A1 - Bellucci, Giancarlo A1 - Benkhoff, Johannes A1 - Bockelee-Morvan, D. A1 - Cerroni, P. A1 - Combe, J-Ph A1 - Despan, D. A1 - Erard, Stéphane A1 - Mancarella, F. A1 - McCord, T. B. A1 - Migliorini, Alessandra A1 - Orofino, V A1 - Piccioni, G. T1 - The changing temperature of the nucleus of comet 67P induced by morphological and seasonal effects JF - Nature astronomy N2 - Knowledge of the surface temperature distribution on a comet’s nucleus and its temporal evolution at different timescales is key to constraining its thermophysical properties and understanding the physical processes that take place at and below the surface. Here we report on time-resolved maps of comet 67P/Churyumov–Gerasimenko retrieved on the basis of infrared data acquired by the Visible InfraRed and Thermal Imaging Spectrometer (VIRTIS) onboard the Rosetta orbiter in 2014, over a roughly two-month period in the pre-perihelion phase at heliocentric distances between 3.62 and 3.31 au from the Sun. We find that at a spatial resolution ≤15 m per pixel, the measured temperatures point out the major effect that self-heating, due to the complex shape of the nucleus, has on the diurnal temperature variation. The bilobate nucleus of comet 67P also induces daytime shadowing effects, which result in large thermal gradients. Over longer periods, VIRTIS-derived temperature values reveal seasonal changes driven by decreasing heliocentric distance combined with an increasing abundance of ice within the uppermost centimetre-thick layer, which implies the possibility of having a largely pristine nucleus interior already in the shallow subsurface Y1 - 2019 U6 - https://doi.org/10.1038/s41550-019-0740-0 SN - 2397-3366 VL - 3 IS - 7 SP - 649 EP - 658 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Filacchione, Gianrico A1 - Groussin, Olivier A1 - Herny, Clemence A1 - Kappel, David A1 - Mottola, Stefano A1 - Oklay, Nilda A1 - Pommerol, Antoine A1 - Wright, Ian A1 - Yoldi, Zurine A1 - Ciarniello, Mauro A1 - Moroz, Lyuba A1 - Raponi, Andrea T1 - Comet 67P/CG Nucleus Composition and Comparison to Other Comets JF - Space science reviews N2 - We review our current knowledge of comet 67P/Churyumov–Gerasimenko nucleus composition as inferred from measurements made by remote sensing and in-situ instruments aboard Rosetta orbiter and Philae lander. Spectrophotometric properties (albedos, color indexes and Hapke parameters) of 67P/CG derived by Rosetta are discussed in the context of other comets previously explored by space missions. Composed of an assemblage made of ices, organic materials and minerals, cometary nuclei exhibit very dark and red surfaces which can be described by means of spectrophotometric quantities and reproduced with laboratory measurements. The presence of surface water and carbon dioxide ices was found by Rosetta to occur at localized sites where the activity driven by solar input, gaseous condensation or exposure of pristine inner layers can maintain these species on the surface. Apart from these specific areas, 67P/CG’s surface appears remarkably uniform in composition with a predominance of organic materials and minerals. The organic compounds contain abundant hydroxyl group and a refractory macromolecular material bearing aliphatic and aromatic hydrocarbons. The mineral components are compatible with a mixture of silicates and fine-grained opaques, including Fe-sulfides, like troilite and pyrrhotite, and ammoniated salts. In the vicinity of the perihelion several active phenomena, including the erosion of surface layers, the localized activity in cliffs, fractures and pits, the collapse of overhangs and walls, the transfer and redeposition of dust, cause the evolution of the different regions of the nucleus by inducing color, composition and texture changes. KW - Comets KW - Composition KW - Ices KW - Organic matter KW - Minerals Y1 - 2019 U6 - https://doi.org/10.1007/s11214-019-0580-3 SN - 0038-6308 SN - 1572-9672 VL - 215 IS - 19 PB - Springer CY - Dordrecht ER -