@article{TosiCapaccioniCapriaetal.2019, author = {Tosi, Federico and Capaccioni, F. and Capria, M. T. and Mottola, Stefano and Zinzi, A. and Ciarniello, M. and Filacchione, G. and Hofstadter, M. and Fonti, S. and Formisano, M. and Kappel, David and K{\"u}hrt, E. and Leyrat, C. and Vincent, J-B and Arnold, G. and De Sanctis, M. C. and Longobardo, Andrea and Palomba, E. and Raponi, A. and Rousseau, Batiste and Schmitt, Bernard and Barucci, Maria Antonietta and Bellucci, Giancarlo and Benkhoff, Johannes and Bockelee-Morvan, D. and Cerroni, P. and Combe, J-Ph and Despan, D. and Erard, St{\´e}phane and Mancarella, F. and McCord, T. B. and Migliorini, Alessandra and Orofino, V and Piccioni, G.}, title = {The changing temperature of the nucleus of comet 67P induced by morphological and seasonal effects}, series = {Nature astronomy}, volume = {3}, journal = {Nature astronomy}, number = {7}, publisher = {Nature Publ. Group}, address = {London}, issn = {2397-3366}, doi = {10.1038/s41550-019-0740-0}, pages = {649 -- 658}, year = {2019}, abstract = {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}, language = {en} } @article{NicolasLecourieuxKappeletal.2014, author = {Nicolas, Philippe and Lecourieux, David and Kappel, Christian and Cluzet, Stephanie and Cramer, Grant and Delrot, Serge and Lecourieux, Fatma}, title = {The basic leucine zipper transcription factor abscisic acid responseelement-binding factor 2 is an important transcriptional regulator ofabscisic acid-dependent grape berry ripening processes}, series = {Plant physiology : an international journal devoted to physiology, biochemistry, cellular and molecular biology, biophysics and environmental biology of plants}, volume = {164}, journal = {Plant physiology : an international journal devoted to physiology, biochemistry, cellular and molecular biology, biophysics and environmental biology of plants}, number = {1}, publisher = {American Society of Plant Physiologists}, address = {Rockville}, issn = {0032-0889}, doi = {10.1104/pp.113.231977}, pages = {365 -- 383}, year = {2014}, abstract = {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.}, language = {en} } @article{KappelArnoldHaus2016, author = {Kappel, David and Arnold, Gabriele and Haus, Rainer}, title = {Multi-spectrum retrieval of Venus IR surface emissivity maps from VIRTIS/VEX nightside measurements at Themis Regio}, series = {Icarus : international journal of solar system studies}, volume = {265}, journal = {Icarus : international journal of solar system studies}, publisher = {Elsevier}, address = {San Diego}, issn = {0019-1035}, doi = {10.1016/j.icarus.2015.10.014}, pages = {42 -- 62}, year = {2016}, abstract = {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.}, language = {en} } @phdthesis{Kappel2015, author = {Kappel, David}, title = {Multi-spectrum retrieval of maps of Venus' surface emissivity in the infrared}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-85301}, school = {Universit{\"a}t Potsdam}, pages = {xix, 226}, year = {2015}, abstract = {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.}, language = {en} } @article{CiarnielloFulleRaponietal.2022, author = {Ciarniello, Mauro and Fulle, Marco and Raponi, Andrea and Filacchione, Gianrico and Capaccioni, Fabrizio and Rotundi, Alessandra and Rinaldi, Giovanna and Formisano, Michelangelo and Magni, Gianfranco and Tosi, Federico and De Sanctis, Maria Cristina and Capria, Maria Teresa and Longobardo, Andrea and Beck, Pierre and Fornasier, Sonia and Kappel, David and Mennella, Vito and Mottola, Stefano and Rousseau, Batiste and Arnold, Gabriele}, title = {Macro and micro structures of pebble-made cometary nuclei reconciled by seasonal evolution}, series = {Nature astronomy}, volume = {6}, journal = {Nature astronomy}, number = {5}, publisher = {Nature Research}, address = {Berlin}, issn = {2397-3366}, doi = {10.1038/s41550-022-01625-y}, pages = {546 -- 553}, year = {2022}, abstract = {Comets evolve due to sublimation of ices embedded inside porous dust, triggering dust emission (that is, erosion) followed by mass loss, mass redistribution and surface modifications. Surface changes were revealed by the Deep Impact and Stardust NExT missions for comet 9P/Tempel 1 (ref.(1)), and a full inventory of the processes modifying cometary nuclei was provided by Rosetta while it escorted comet 67P/Churyumov-Gerasimenko for approximately two years(2-4). Such observations also showed puzzling water-ice-rich spots that stood out as patches optically brighter and spectrally bluer than the average cometary surfaces(5-9). These are up to tens of metres large and indicate macroscopic compositional dishomogeneities apparently in contrast with the structural homogeneity above centimetre scales of pebble-made nuclei(10). Here we show that the occurrence of blue patches determines the seasonal variability of the nucleus colour(4,11,12) and gives insight into the internal structure of comets. We define a new model that links the centimetre-sized pebbles composing the nucleus(10) and driving cometary activity(13,14) to metre-sized water-ice-enriched blocks embedded in a drier matrix. The emergence of blue patches is due to the matrix erosion driven by CO2-ice sublimation that exposes the water-ice-enriched blocks, which in turn are eroded by water-ice sublimation when exposed to sunlight. Our model explains the observed seasonal evolution of the nucleus and reconciles the available data at micro (sub-centimetre) and macro (metre) scales.}, language = {en} } @article{RousseauErardBecketal.2018, author = {Rousseau, Batiste and Erard, St{\´e}phane and Beck, P. and Quirico, Eric and Schmitt, B. and Brissaud, O. and Montes-Hernandez, G. and Capaccioni, F. and Filacchione, Gianrico and Bockelee-Morvan, Dominique and Leyrat, C. and Ciarniello, M. and Raponi, Andrea and Kappel, David and Arnold, G. and Moroz, L. V. and Palomba, Ernesto and Tosi, Federico}, title = {Laboratory simulations of the Vis-NIR spectra of comet 67P using sub-mu m sized cosmochemical analogues}, series = {Icarus : international journal of solar system studies}, volume = {306}, journal = {Icarus : international journal of solar system studies}, publisher = {Elsevier}, address = {San Diego}, organization = {VIRTIS Team}, issn = {0019-1035}, doi = {10.1016/j.icarus.2017.10.015}, pages = {306 -- 318}, year = {2018}, abstract = {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.}, language = {en} } @article{TubianaRinaldiGuettleretal.2019, author = {Tubiana, C. and Rinaldi, G. and Guettler, C. and Snodgrass, C. and Shi, X. and Hu, X. and Marschall, R. and Fulle, M. and Bockeele-Morvan, D. and Naletto, G. and Capaccioni, F. and Sierks, H. and Arnold, G. and Barucci, M. A. and Bertaux, J-L and Bertini, I and Bodewits, D. and Capria, M. T. and Ciarniello, M. and Cremonese, G. and Crovisier, J. and Da Deppo, V and Debei, S. and De Cecco, M. and Deller, J. and De Sanctis, M. C. and Davidsson, B. and Doose, L. and Erard, S. and Filacchione, G. and Fink, U. and Formisano, M. and Fornasier, S. and Gutierrez, P. J. and Ip, W-H and Ivanovski, S. and Kappel, David and Keller, H. U. and Kolokolova, L. and Koschny, D. and Krueger, H. and La Forgia, F. and Lamy, P. L. and Lara, L. M. and Lazzarin, M. and Levasseur-Regourd, A. C. and Lin, Z-Y and Longobardo, A. and Lopez-Moreno, J. J. and Marzari, F. and Migliorini, A. and Mottola, S. and Rodrigo, R. and Taylor, F. and Toth, I and Zakharov, V}, title = {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}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {630}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201834869}, pages = {14}, year = {2019}, abstract = {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.}, language = {en} } @article{LecourieuxKappelPierietal.2017, author = {Lecourieux, Fatma and Kappel, Christian and Pieri, Philippe and Charon, Justine and Pillet, Jeremy and Hilbert, Ghislaine and Renaud, Christel and Gomes, Eric and Delrot, Serge and Lecourieux, David}, title = {Dissecting the Biochemical and Transcriptomic Effects of a Locally Applied Heat Treatment on Developing Cabernet Sauvignon Grape Berries}, series = {Frontiers in plant science}, volume = {8}, journal = {Frontiers in plant science}, publisher = {Frontiers Research Foundation}, address = {Lausanne}, issn = {1664-462X}, doi = {10.3389/fpls.2017.00053}, pages = {23}, year = {2017}, abstract = {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.}, language = {en} } @article{KappelSachseHaacketal.2020, author = {Kappel, David and Sachse, Manuel and Haack, David and Otto, Katharina A.}, title = {Discrete element modeling of boulder and cliff morphologies on comet 67P/Churyumov-Gerasimenko}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {641}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/201937152}, pages = {22}, year = {2020}, abstract = {Context: Even after the Rosetta mission, some of the mechanical parameters of comet 67P/Churyumov-Gerasimenko's surface material are not yet well constrained. These parameters are needed to improve our understanding of cometary activity or for planning sample return missions. Aims: We study some of the physical processes involved in the formation of selected surface features and investigate the mechanical and geometrical parameters involved. Methods: Applying the discrete element method (DEM) in a low-gravity environment, we numerically simulated the surface layer particle dynamics involved in the formation of selected morphological features. The material considered is a mixture of polydisperse ice and dust spheres with inter-particle forces given by the Hertz contact model, translational friction, rolling friction, cohesion from unsintered contacts, and optionally due to bonds from ice sintering. We determined a working set of parameters that enables the simulations to be reasonably realistic and investigated morphological changes due to modifications thereof. Results: The selected morphological features are reasonably well reproduced using model materials with a tensile strength on the order of 1-10 Pa. Increasing the diameters of the spherical particles decreases the material strength, and increasing the friction leads to a more brittle but somewhat stronger material. High friction is required to make the material sufficiently brittle to match observations, which points to the presence of very rough, even angular particles. Reasonable seismic activity does not suffice to trigger the collapses of cliffs without material heterogeneities or structural defects. Conclusions: DEM modeling can be a powerful tool to investigate mechanical parameters of cometary surface material. However, many uncertainties arise from our limited understanding of particle shapes, spatial configurations, and size distributions, all on multiple length scales. Further numerical work, in situ measurements, and sample return missions are needed to better understand the mechanics of cometary material and cometary activity.}, language = {en} } @article{SachseKappelTirschetal.2022, author = {Sachse, Manuel and Kappel, David and Tirsch, Daniela and Otto, Katharina A.}, title = {Discrete element modeling of aeolian-like morphologies on comet 67P/Churyumov-Gerasimenko}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {662}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {0004-6361}, doi = {10.1051/0004-6361/202141296}, pages = {15}, year = {2022}, abstract = {Context. Even after the Rosetta mission, some of the mechanical parameters of comet 67P/Churyumov-Gerasimenko's surface material are still not well constrained. They are needed to improve our understanding of cometary activity or for planning sample return procedures. Aims. We discuss the physical process dominating the formation of aeolian-like surface features in the form of moats and wind taillike bedforms around obstacles and investigate the mechanical and geometrical parameters involved. Methods. By applying the discrete element method (DEM) in a low-gravity environment, we numerically simulated the dynamics of the surface layer particles and the particle stream involved in the formation of aeolian-like morphological features. The material is composed of polydisperse spherical particles that consist of a mixture of dust and water ice, with interparticle forces given by the Hertz contact model, cohesion, friction, and rolling friction. We determined a working set of parameters that enables simulations to be reasonably realistic and investigated morphological changes when modifying these parameters. Results. The aeolian-like surface features are reasonably well reproduced using model materials with a tensile strength on the order of 0.1-1 Pa. Stronger materials and obstacles with round shapes impede the formation of a moat and a wind tail. The integrated dust flux required for the formation of moats and wind tails is on the order of 100 kg m(-2), which, based on the timescale of morphological changes inferred from Rosetta images, translates to a near-surface particle density on the order of 10(-6)-10(-4) kg m(-3). Conclusions. DEM modeling of the aeolian-like surface features reveals complex formation mechanisms that involve both deposition of ejected material and surface erosion. More numerical work and additional in situ measurements or sample return missions are needed to better investigate mechanical parameters of cometary surface material and to understand the mechanics of cometary activity.}, language = {en} }