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Purpose: To evaluate the intrasession repeatability and validity of posterior corneal curvature and astigmatism measurements provided by a color light-emitting diode reflection topography system in healthy eyes. Methods: A total of 40 healthy eyes of 40 patients (age, 16–66 years) were enrolled. A complete eye examination was performed in all cases including posterior topographic analysis with two systems: the Scheimpflug-based system (Pentacam; Oculus Optikgeräte GmbH, Wetzlar, Germany) and the Cassini system (i-Optics; Ophthec, The Hague, The Netherlands). With this last system, three consecutive measurements were taken to assess the level of intrasession repeatability (within-subject standard deviation, Sw; intraclass correlation coefficient). The Bland & Altman analysis was used to evaluate the interchangeability of both devices. Results: The Sw was ⩽0.06 mm for all posterior corneal radius measurements, with intraclass correlation coefficient of ⩾0.960. The Sw for the magnitude of astigmatism, J0, and J45 were 0.15, 0.04, and 0.04 D, respectively, with intraclass correlation coefficient values of 0.876, 0.897, and 0.840, respectively. Statistically significant differences between devices were found in all parameters evaluated (p ⩽ 0.025). The interchangeability analysis revealed the presence of clinically relevant limits of agreement for the flattest (0.03 to 0.50 mm) and steepest posterior corneal radii (–0.01 to 0.39 mm). In contrast, limits of agreements were not clinically relevant for the magnitude of posterior astigmatism (–0.17 to 0.27 D) and their power vector components (–0.11 to 0.15 D). Conclusion: The Cassini system provides consistent measures of posterior corneal curvature and astigmatism in healthy eyes, but only measures of posterior astigmatism can be considered as interchangeable with those provided by the Pentacam.

International audience; Titan was a mostly unknown world prior to the Cassini spacecraft’s arrival in July 2004. We review the major scientific advances made by Cassini’s Titan Radar Mapper (RADAR) during 13 years of Cassini’s exploration of Saturn and its moons. RADAR measurements revealed Titan’s surface geology, observed lakes and seas of mostly liquid methane in the polar regions, measured the depth of several lakes and seas, detected temporal changes on its surface, and provided key evidence that Titan contains an interior ocean. As a result of the Cassini mission, Titan has gone from an uncharted world to one that exhibits a variety of Earth-like geologic processes and surface-atmosphere interactions. Titan has also joined the ranks of “ocean worlds” along with Enceladus and Europa, which are prime targets for astrobiological research.

Background: The objective of this study was to compare the central corneal curvature and astigmatism measurements obtained with three different systems in healthy eyes and to assess the level of interchangeability between them. Methods: This was a comparative study examining 30 healthy eyes of 30 patients (age 15–53 years). A complete eye examination was performed in all cases including analysis of anterior corneal curvature and astigmatism with three devices: the colour‐LED topography system Cassini (i‐Optics) (CAS), the Scheimpflug‐based system Pentacam (Oculus Optikgeräte) (PTC) and the optical biometer IOL‐Master 500 (Carl Zeiss Meditec) (IOLM). Differences between devices in terms of curvature in the flattest (flat K) and steepest meridians (steep K) as well as in the magnitude (AST) and power vector components of astigmatism (J0 and J45) were evaluated. The interchangeability between devices was evaluated with the Bland–Altman method. Results: Statistically significant differences between devices were found in steep K and flat K (p

Purpose To evaluate the intrasession repeatability of anterior corneal topographic and aberrometric measurements provided by a color-LED topographer as well as their interchangeability with those provided by a Scheimpflug-based system in healthy eyes. Methods Thirty-five healthy eyes of 35 patients (age, 16–66 years) were enrolled. A complete eye examination was performed in all cases including a complete corneal analysis with the Scheimpflug-based system Pentacam (Oculus Optikgeräte) (one measurement) and the Cassini system (i-Optics) (three consecutive measurements). Intrasession repeatability of the Cassini measurements was assessed with the within-subject standard deviation (Sw) and the intraclass correlation coefficient (ICC). The Bland-Altman analysis was used to evaluate the agreement between both devices. Results Mean Sw for keratometric readings was 0.02 mm (ICC ≥ 0.992), ranging between 0.16 and 0.05 D (ICC 0.930–0.978) for anterior and total astigmatic measurements. Mean Sw for asphericity and corneal diameter were 0.06 (ICC 0.926) and 0.03 mm (IC 0.997), respectively. Aberrometric parameters showed ICCs ≥ 0.816, except for Z42 (ICC 0.741) and Z44 (ICC 0.544). When comparing devices, statistically significant differences were found for most of topographic and aberrometric data (p ≤ 0.044). Likewise, ranges of agreement between devices were clinically relevant (keratometry > 0.06 mm; total astigmatic components > 0.69 D; asphericity 0.35; second-, third-, and fourth-order Zernike terms, more than 0.20, 0.13, and 0.01 μm, respectively). Conclusions Consistent anterior corneal topographic, total corneal astigmatic, and aberrometric measurements are obtained with color-LED topography in healthy eyes, which are not interchangeable with those provided by the Scheimpflug-based topography. The author David P Piñero has been supported by the Ministry of Economy, Industry and Competitiveness of Spain within the program Ramón y Cajal, RYC-2016-20471.

Stéphane Baciocchi, Bertrand Duménieu et Claude Motte, du Centre de Recherches Historiques de l’EHESS, présentent l’édition numérique (disponible en accès libre sur le site GeoHistoricalData) et papier (réalisée par l’IGN), de la feuille 52 de la carte de Cassini.

Vincent Flauraud, historien (CHEC), et Julien Chadeyron, cartographe (UCA), exposent, durant cet atelier de recherche, le travail intellectuel et technique mené pour cartographier les paroisses concordataires en Auvergne.

The Cassini RADAR altimeter has provided broad-scale surface topography data for Saturn’s largest moon Titan. Herein, we adapt the delay/Doppler algorithm to take into account Cassini geometries and antenna mispointing usually occurring during hyperbolic Titan flybys. The proposed algorithm allows up to tenfold improvement in the along-track resolution. Preliminary results are provided that show how the improved topography presented herein can advance our understanding of Titan’s surface characteristics.

Pierre Boivin, chercheur au Laboratoire Magmas et Volcans (UCA), fait part de ses observations et questionnements concernant la représentation des volcans sur la feuille 52 de la carte de Cassini. Il la compare à d’autres cartes de la même période.

The nature and structure of the observed east-west flows on Jupiter and Saturn has been one of the longest-lasting mysteries in planetary science. This mystery has been recently unraveled due to the accurate gravity measurements provided by the Juno mission to Jupiter and the Grand Finale of the Cassini mission to Saturn. These two experiments, which coincidentally happened around the same time, allowed determination of the vertical and meridional profiles of the zonal flows on both planets. This paper reviews the topic of zonal jets on the gas giants in light of the new data from these two experiments. The gravity measurements not only allow the depth of the jets to be constrained, yielding the inference that the jets extend roughly 3000 and 9000 km below the observed clouds on Jupiter and Saturn, respectively, but also provide insights into the mechanisms controlling these zonal flows. Specifically, for both planets this depth corresponds to the depth where electrical conductivity is within an order of magnitude of 1 S/m, implying that the magnetic field likely plays a key role in damping the zonal flows., Comment: Submitted to Space Science Reviews. Part of ISSI special collection on Diversity of Atmospheres

Jean-Michel Delaveau, géographe (UCA), propose une (re)découverte du bassin hydrographique de la région de Clermont-Ferrand en comparant les données géohistoriques de la carte de Cassini et des représentations actuelles.

Introduction du Séminaire Atlas historique (CHEC, UCA) GeoHistoricaldata (CRH, EHESS) consacré à l'édition et la valorisation de la feuille 52 de la carte de Cassini (Clermont). Jean-Philippe Luis (MSH Clermont-Ferrand), Stéphane Gomis (CHEC) et Maurizio Gribaudi (CRH) rappellent la genèse de cette collaboration entre l'UCA et l'EHESS ainsi que les enjeux de la vectorisation et de l'édition (IGN) réussies de la "feuille 52".

Dans cet atelier de recherche, Nathalie Abadie (IGN) présente la méthode mise en œuvre pour créer une base de connaissances sur les redécoupages administratifs durant la Révolution française. Elle prend l’exemple des paroisses constitutionnelles.

Saturn’s moon Titan has a dense nitrogen-rich atmosphere, with methane as its primary volatile. Titan’s atmosphere experiences an active chemistry that produces a haze of organic aerosols that settle to the surface and a dynamic climate in which hydrocarbons are cycled between clouds, rain and seas. Titan displays particularly energetic meteorology at equinox in equatorial regions, including sporadic and large methane storms. In 2009 and 2010, near Titan’s northern spring equinox, the Cassini spacecraft observed three distinctive and short-lived spectral brightenings close to the equator. Here, we show from analyses of Cassini spectral data, radiative transfer modelling and atmospheric simulations that the brightenings originate in the atmosphere and are consistent with formation from dust storms composed of micrometre-sized solid organic particles mobilized from underlying dune fields. Although the Huygens lander found evidence that dust can be kicked up locally from Titan’s surface, our findings suggest that dust can be suspended in Titan’s atmosphere at much larger spatial scale. Mobilization of dust and injection into the atmosphere would require dry conditions and unusually strong near-surface winds (about five times more than estimated ambient winds). Such strong winds are expected to occur in downbursts during rare equinoctial methane storms—consistent with the timing of the observed brightenings. Our findings imply that Titan—like Earth and Mars—has an active dust cycle, which suggests that Titan’s dune fields are actively evolving by aeolian processes. Saturn’s moon Titan may have an active dust cycle in equatorial regions driven by storm winds, Cassini observations consistent with dust suspension in Titan’s atmosphere suggest.

Between 2004 and 2017, spectral observations have been gathered by the Visual and Infrared Mapping Spectrometer (VIMS) on-board Cassini (Brown et al., 2004) during 23 Enceladus close encounters, in addition to more distant surveys. The objective of the present study is to produce a global hyperspectral mosaic of the complete VIMS data set of Enceladus in order to highlight spectral variations among the different geological units. This requires the selection of the best observations in terms of spatial resolution and illumination conditions. We have carried out a detailed investigation of the photometric behavior at several key wavelengths (1.35, 1.5, 1.65, 1.8, 2.0, 2.25, 2.55 and 3.6 ${\mu}$m), characteristics of the infrared spectra of water ice. We propose a new photometric function, based on the model of Shkuratov et al. (2011). When combined, corrected mosaics at different wavelengths reveal heterogeneous areas, in particular in the terrains surrounding the Tiger Stripes on the South Pole and in the northern hemisphere around 30{\deg}N, 90{\deg}W. Those areas appear mainly correlated to tectonized units, indicating an endogenous origin, potentially driven by seafloor hotspots., Comment: Erratum: Fix south polar grid longitudes in Figures 9 and 11

We examine and compare the magnetic field perturbations associated with field-aligned ionosphere-magnetosphere coupling currents at Saturn, observed by the Cassini spacecraft during two sequences of highly inclined orbits in 2006/2007 and 2008 under late southern summer conditions. These sequences explore the southern currents in the dawn-noon and midnight sectors, respectively, thus allowing investigation of possible origins of the local time (LT) asymmetry in auroral Saturn kilometric radiation (SKR) emissions, which peak in power at ~8 h LT in the dawn-noon sector. We first show that the dawn-noon field data generally have the same four-sheet current structure as found previously in the midnight data and that both are similarly modulated by “planetary period oscillation” (PPO) currents. We then separate the averaged PPO-independent (e.g., subcorotation) and PPO-related currents for both LT sectors by using the current system symmetry properties. Surprisingly, we find that the PPO-independent currents are essentially identical within uncertainties in the dawn-dusk and midnight sectors, thus providing no explanation for the LT dependence of the SKR emissions. The main PPO-related currents are, however, found to be slightly stronger and narrower in latitudinal width at dawn-noon than at midnight, leading to estimated precipitating electron powers, and hence emissions, that are on average a factor of ~1.3 larger at dawn-noon than at midnight, inadequate to account for the observed LT asymmetry in SKR power by a factor of ~2.7. Some other factors must also be involved, such as a LT asymmetry in the hot magnetospheric auroral source electron population.

The Undifferentiated Plains on Titan, first mapped by Lopes et al. (Lopes, R.M.C. et al., 2010. Icarus, 205, 540–588), are vast expanses of terrains that appear radar-dark and fairly uniform in Cassini Synthetic Aperture Radar (SAR) images. As a result, these terrains are often referred to as “blandlands”. While the interpretation of several other geologic units on Titan – such as dunes, lakes, and well-preserved impact craters – has been relatively straightforward, the origin of the Undifferentiated Plains has remained elusive. SAR images show that these “blandlands” are mostly found at mid-latitudes and appear relatively featureless at radar wavelengths, with no major topographic features. Their gradational boundaries and paucity of recognizable features in SAR data make geologic interpretation particularly challenging. We have mapped the distribution of these terrains using SAR swaths up to flyby T92 (July 2013), which cover >50% of Titan’s surface. We compared SAR images with other data sets where available, including topography derived from the SARTopo method and stereo DEMs, the response from RADAR radiometry, hyperspectral imaging data from Cassini’s Visual and Infrared Mapping Spectrometer (VIMS), and near infrared imaging from the Imaging Science Subsystem (ISS). We examined and evaluated different formation mechanisms, including (i) cryovolcanic origin, consisting of overlapping flows of low relief or (ii) sedimentary origins, resulting from fluvial/lacustrine or aeolian deposition, or accumulation of photolysis products created in the atmosphere. Our analysis indicates that the Undifferentiated Plains unit is consistent with a composition predominantly containing organic rather than icy materials and formed by depositional and/or sedimentary processes. We conclude that aeolian processes played a major part in the formation of the Undifferentiated Plains; however, other processes (fluvial, deposition of photolysis products) are likely to have contributed, possibly in differing proportions depending on location.

By applying a hybrid (kinetic ions and fluid electrons) simulation code, we study the plasma environment of Saturn´s largest moon Titan during Cassini´s T96 flyby on 1 December 2013. The T96 encounter marks the only observed event of the entire Cassini mission where Titan was located in the supersonic solar wind in front of Saturn´s bow shock. Our simulations can quantitatively reproduce the key features of Cassini magnetic field and electron density observations during this encounter. We demonstrate that the large-scale features of Titan´s induced magnetosphere during T96 can be described in terms of a steady state interaction with a high-pressure solar wind flow. About 40 min before the encounter, Cassini observed a rotation of the incident solar wind magnetic field by almost 90°. We provide strong evidence that this rotation left a bundle of fossilized magnetic field lines in Titan´s ionosphere that was subsequently detected by the spacecraft. Fil: Feyerabend, Moritz. Georgia Institute Of Techology; Estados Unidos Fil: Simon, Sven. Georgia Institute Of Techology; Estados Unidos Fil: Neubauer, Fritz M.. Universitat Zu Köln; Alemania Fil: Motschmann, Uwe. Deutsches Zentrum Fur Luft- Und Raumfahrt; Alemania. Technische Universitat Braunschweig; Alemania Fil: Bertucci, Cesar. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Edberg, Niklas J. T.. Instiutet For Rymdfysik; Suecia Fil: Hospodarsky, George B.. University Of Iowa; Estados Unidos Fil: Kurth, William S.. University Of Iowa; Estados Unidos

Studies of Saturn's magnetosphere with the Cassini mission have established the importance of Enceladus as the dominant mass source for Saturn's magnetosphere. It is well known that the ionosphere is an important mass source at Earth during periods of intense geomagnetic activity, but lesser attention has been dedicated to study the ionospheric mass source at Saturn. In this paper we describe a case study of data from Saturn's magnetotail, when Cassini was located at ≃ 2200 h Saturn local time at 36 R S from Saturn. During several entries into the magnetotail lobe, tailward flowing cold electrons and a cold ion beam were observed directly adjacent to the plasma sheet and extending deeper into the lobe. The electrons and ions appear to be dispersed, dropping to lower energies with time. The composition of both the plasma sheet and lobe ions show very low fluxes (sometimes zero within measurement error) of water group ions. The magnetic field has a swept‐forward configuration which is atypical for this region, and the total magnetic field strength is larger than expected at this distance from the planet. Ultraviolet auroral observations show a dawn brightening, and upstream heliospheric models suggest that the magnetosphere is being compressed by a region of high solar wind ram pressure. We interpret this event as the observation of ionospheric outflow in Saturn's magnetotail. We estimate a number flux between (2.95 ± 0.43) × 109 and (1.43 ± 0.21) × 1010 cm−2 s−1, 1 or about 2 orders of magnitude larger than suggested by steady state MHD models, with a mass source between 1.4 ×102 and 1.1 ×103 kg/s. After considering several configurations for the active atmospheric regions, we consider as most probable the main auroral oval, with associated mass source between 49.7 ±13.4 and 239.8 ±64.8 kg/s for an average auroral oval, and 10 ±4 and 49 ±23 kg/s for the specific auroral oval morphology found during this event. It is not clear how much of this mass is trapped within the magnetosphere and how much is lost to the solar wind., Key Points Tailward observation of ionospheric plasma in the magnetotail lobeEvidence for simultaneous reconnection in the plasma sheetFirst observational estimate at Saturn of mass source rate from the ionosphere to the magnetotail

Radiation belts of MeV protons have been observed just outward of Saturn's main rings. During the final stages of the mission, the Cassini spacecraft will pass through the gap between the main rings and the planet. Based on how the known radiation belts of Saturn are formed, it is expected that MeV protons will be present in this gap and also bounce through the tenuous D ring right outside the gap. At least one model has suggested that the intensity of MeV protons near the planet could be much larger than in the known belts. We model this inner radiation belt using a technique developed earlier to understand Saturn's known radiation belts. We find that the inner belt is very different from the outer belts in the sense that its intensity is limited by the densities of the D ring and Saturn's upper atmosphere, not by radial diffusion and satellite absorption. The atmospheric density is relatively well constrained by EUV occultations. Based on that we predict an intensity in the gap region that is well below that of the known belts. It is more difficult to do the same for the region magnetically connected to the D ring since its density is poorly constrained. We find that the intensity in this region can be comparable to the known belts. Such intensities pose no hazard to the mission since Cassini would only experience these fluxes on timescales of minutes but might affect scientific measurements by decreasing the signal‐to‐contamination ratio of instruments., Key Points Intensity between Saturn and D ring is lower than in Saturn's proton beltsIntensity over the D ring might be comparable to Saturn's known beltsProton intensity is limited by neutral density, not diffusion as in known belts

The thesis focused on the study of Jupiter's auroral radio emissions, produced close to the local electronic cyclotron frequency by Maser Cyclotron instability, powered by resonant electrons of energies of a few keV, accelerated along high magnetic field lines at high latitude.I first took over, validated and extended the simulation code ExPRES (Exoplanetary and Planetary Radio Emissions Simulator) developed at LESIA, which allows to produce dynamic spectra of visible radio emissions for a given observer. I performed a parametric study of simulations of radio emissions induced by Io in order to quantify the role of the main free parameters of the code (distribution function and energy of the electrons, magnetic field model, position of the active magnetic field line and altitude of the ionospheric cutoff). This study confirmed that Io emissions are correctly reproduced only when the radiation is oblique to the magnetic field lines, which is simulated by ExPRES through loss cone electronic distribution functions. I have also shown that (a) the parameters that mainly control the shape of the simulated emissions in the time-frequency plane are the magnetic field model and the electron energy, and that (b) the simulations are in excellent agreement with observations, with a time window of uncertainty of ± 2 hours.Using this code, I produced long-term simulations of radio emissions induced by Io, and those expected for Europa, Ganymede and Callisto. Comparing these simulations with several years of Jupiter observations recorded with the Voyager / PRA and Cassini / RPWS instruments (punctually supplemented by those of the Nançay decametric array), I proved the existence of radio emissions induced by Europa and Ganymede. The statistical study of these emissions allowed me to establish their average properties (extension in frequency, temporal variability, and occurrence). This result opens a new field of study, remotely and in the long-term, of the planet-satellite interactions other than Io-Jupiter.The comparison of these simulations with the Juno / Waves observations allowed me to unambiguously identify the radio emissions induced by Io, as well as their hemisphere of origin (without knowing their polarization, not measured by Juno / Waves), for an observer close to the equator (case of the Earth), as at higher latitudes. Thanks to these simulations, I have also shown that the emissions are visible only if the opening of the emission angle is greater than 70 ° ± 5 °.Finally, I began a statistical study of the spatial distribution of auroral radio sources traversed by the Juno probe. I thus mapped the sources of the various components (kilometer to HF) of Jovian radio broadcasts. Comparison with recent magnetic field models, as well as UV imagery (Juno / UVS and Hubble / STIS) allowed me to demonstrate a correlation of radio emissions with the main auroral oval.; La thèse a porté sur l’étude des émissions radio aurorales de Jupiter, produites proche de la fréquence cyclotron électronique locale par Instabilité Maser Cyclotron, alimentée par des électrons résonants d’énergies de quelques keV, accélérés le long des lignes de champ magnétique de haute latitude.J’ai tout d’abord repris, validé et étendu le code de simulation SERPE (Simulateur d’Émissions Radio Planétaire et Exo–planétaire) développé au LESIA, qui permet de produire des spectres dynamiques des émissions radio visibles pour un observateur donné. J’ai effectué une étude paramétrique des simulations des émissions radio induites par Io afin de quantifier le rôle des principaux paramètres libres du code (fonction de distribution et énergie des électrons, modèle de champ magnétique, position de la ligne de champ magnétique active et altitude de la coupure ionosphérique). Cette étude a confirmé que les émissions Io sont correctement reproduites seulement lorsque le rayonnement est oblique par rapport aux lignes de champ magnétique, ce qui est simulé par SERPE grâce à des fonctions de distribution électronique de type cône de perte. J’ai également montré que (a) les paramètres qui contrôlent principalement la forme des émissions simulées dans le plan temps-fréquence sont le modèle de champ magnétique et l’énergie des électrons, et que (b) les simulations sont en excellent accord avec les observations, moyennant une fenêtre d’incertitude temporelle de ±2 heures.À l’aide de ce code, j’ai réalisé des simulations au long cours des émissions radio induites par Io, et de celles attendues pour Europe, Ganymède et Callisto. En comparant ces simulations à plusieurs années d’observations de Jupiter enregistrées avec les instruments Voyager/PRA et Cassini/RPWS (ponctuellement complétées par celles du réseau décamétrique de Nançay), j’ai prouvé l’existence d’émissions radio induites par Europe et Ganymède. L’étude statistique de ces émissions m’a permis d’établir leur propriétés moyennes (extension en fréquence, variabilité temporelle, et occurrence). Ce résultat ouvre un nouveau champ d’étude à distance, et au long cours, des interactions planète–satellites autres que Io–Jupiter.La comparaison de ces simulations avec les observations Juno/Waves m’a permis d’identifier sans ambiguïté les émissions radio induites par Io, ainsi que leur hémisphère d’origine (sans connaitre leur polarisation, non–mesurée par Juno/Waves), pour un observateur proche de l’équateur (cas de la Terre), comme a des latitudes plus hautes. Grâce à ces simulations, j’ai également montré que les émissions sont visibles seulement si l’ouverture de l’angle d’émission est supérieure à 70°±5°.Enfin, j’ai entamé une étude statistique de la distribution spatiale des sources radio aurorales traversées par la sonde Juno. J’ai ainsi cartographié les sources des diverses composantes (kilométriques à décamétriques) des émissions radio joviennes. La comparaison avec des modèles de champ magnétique récents, ainsi qu’avec des images UV (Juno/UVS et Hubble/STIS) m’a permis de démontrer une corrélation des émissions radio avec l’ovale auroral principal.

This thesis focused on the study of Jupiter’s auroral radio emissions, produced close to the local electronic cyclotron frequency by the Maser Cyclotron instability powered by resonant electrons of a few keV, accelerated along high magnetic field lines at high latitude.I first took over, validated and extended the simulation code ExPRES (Exoplanetary and Planetary Radio Emissions Simulator) developed at LESIA, which allows us to pro- duce dynamic spectra of auroral radio emissions visible for a given observer. I performed a parametric study of the simulations of radio emissions induced by Io in order to quantify the role of ExPRES free parameters (distribution function and energy of the electrons, magnetic field model, position of the active magnetic field line and altitude of the ionos- pheric cutoff). This study confirmed that Io emissions are correctly reproduced only when the radiation is oblique to the magnetic field lines, which is simulated by ExPRES through loss cone electronic distribution functions. I have also shown that (a) the parameters that mainly control the shape of the simulated emissions in the time-frequency plane are the magnetic field model and the electron energy, and that (b) the simulations are in excellent agreement with observations, with a time window of uncertainty of ±2 hours.Using this code, I produced long-term simulations of radio emissions induced by Io, and those expected for Europa, Ganymede and Callisto. Comparing these simulations with several years of Jupiter observations recorded with the Voyager / PRA and Cassini / RPWS instruments (punctually supplemented by those of the Nançay decameter array), I proved the existence of radio emissions induced by Europa and Ganymede. The statistical study of these signatures allowed me to measure their average properties (extension in frequency, temporal variability, and occurrence). This result opens a new field of study of planet-satellite interactions other than Io-Jupiter.The comparison of these simulations with the Juno / Waves observations allowed me to unambiguously identify the radio emissions induced by Io, as well as their hemisphere of origin (without knowing their polarization, not measured by Juno / Waves), for an observer close to the equator (case of the Earth) and at higher latitudes. Thanks to these simulations, I have also shown that the emissions are visible only if the opening of the emission angle is greater than 70 ̊± 5 ̊ and if the observer is in the same magnetic hemisphere as the sources.Finally, I began a statistical study of the spatial distribution of auroral radio sources traversed by the Juno probe. I thus mapped the sources of the various components (kilo- meter to HF) of Jovian radio broadcasts. Comparison with recent magnetic field models, as well as UV imagery (Juno / UVS and Hubble / STIS) allowed me to show that they are colocated with the main auroral oval.; La thèse a porté sur l’étude des émissions radio aurorales de Jupiter, produites proches de la fréquence cyclotron électronique locale par l’Instabilité Maser Cyclotron alimentée par des électrons résonants de quelques keV, accélérés le long des lignes de champ magné- tique de haute latitude.J’ai tout d’abord repris, validé et étendu le code de simulation SERPE (Simulateur d’Emissions Radio Planétaire et Exo-planétaire) développé au LESIA, qui permet de pro- duire des spectres dynamiques des émissions radio aurorales visibles pour un observateur donné. J’ai effectué une étude paramétrique des simulations des émissions radio induites par Io afin de quantifier le rôle des paramètres libres du code (fonction de distribution et énergie des électrons, modèle de champ magnétique, position de la ligne de champ ma- gnétique active et altitude de la coupure ionosphérique). Cette étude a confirmé que les émissions Io sont correctement reproduites seulement lorsque le rayonnement est oblique par rapport aux lignes de champ magnétique, ce qui est simulé par SERPE grâce à des fonctions de distribution électronique de type cône de perte. J’ai également montré que (a) les paramètres qui contrôlent principalement la forme des émissions simulées dans le plan temps-fréquence sont le modèle de champ magnétique et l’énergie des électrons, et que (b) les simulations sont en excellent accord avec les observations, moyennant une fenêtre d’incertitude temporelle de ±2 heures.À l’aide de ce code, j’ai réalisé des simulations au long cours des émissions radio in- duites par Io, et de celles attendues pour Europe, Ganymède et Callisto. En comparant ces simulations à plusieurs années d’observations de Jupiter enregistrées avec les instru- ments Voyager/PRA et Cassini/RPWS (ponctuellement complétées par celles du réseau décamétrique de Nançay), j’ai prouvé l’existence d’émissions radio induites par Europe et Ganymède. L’étude statistique de ces émissions m’a permis d’établir leur propriétés moyennes (extension en fréquence, variabilité temporelle, et occurrence). Ce résultat ouvre un nouveau champ d’étude à distance, et au long cours, des interactions planète–satellites autres que Io–Jupiter.La comparaison de ces simulations avec les observations Juno/Waves m’a permis d’identifier, sans ambiguïté, les émissions radio induites par Io, ainsi que leur hémisphère d’origine (sans connaitre leur polarisation, non–mesurée par Juno/Waves), pour un ob- servateur proche de l’équateur (cas de la Terre) et a des latitudes plus hautes. Grâce à ces simulations, j’ai également montré que les émissions sont visibles seulement si l’angle du feuillet conique d’émission est supérieure à 70 ̊±5 ̊et si l’observateur est situé dans le même hémisphère magnétique que les sources produisant l’émission.Enfin, j’ai entamé une étude statistique de la distribution spatiale des sources radio aurorales traversées par la sonde Juno. J’ai ainsi cartographié les sources des diverses com- posantes (kilométriques à décamétriques) des émissions radio joviennes. La comparaison avec des modèles de champs magnétiques récents, ainsi qu’avec des images UV (Juno/UVS et Hubble/STIS) m’a permis de montrer qu’elles étaient co–localisées avec l’ovale auroral principal.

We report on a set of clear and abrupt decreases in the high-frequency boundary of whistler mode emissions detected by Cassini at high latitudes (about +/- 40 degrees) during the low-altitude proximal flybys of Saturn. These abrupt decreases or dropouts have start and stop locations that correspond to L shells at the edges of the A and B rings. Langmuir probe measurements can confirm, in some cases, that the abrupt decrease in the high-frequency whistler mode boundary is associated with a corresponding abrupt electron density dropout over evacuated field lines connected to the A and B rings. Wideband data also reveal electron plasma oscillations and whistler mode cutoffs consistent with a low-density plasma in the region. The observation of the electron density dropout along ring-connecting field lines suggests that strong ambipolar forces are operating, drawing cold ionospheric ions outward to fill the flux tubes. There is an analog with the refilling of flux tubes in the terrestrial plasmasphere. We suggest that the ring-connected electron density dropouts observed between 1.1 and 1.3 R-s are connected to the low-density ring plasma cavity observed overtop the A and B rings during the 2004 Saturn orbital insertion pass. Plain Language Summary We present Cassini observations during the close passes by the planet Saturn indicating that plasma on magnetic field lines that pass through the A and B rings is of anomalously low density. These observations are consistent with the Saturn orbit insertion observations of a plasma cavity located at equatorial regions overtop the dense B ring. Using a terrestrial analogy, we suggest that the low-density conditions overtop the rings create an electrical force, called an ambipolar electric field that draws plasma out of the ionosphere in an attempt to replenish the plasma void found at equatorial regions.

We investigate the azimuthal magnetic field signatures associated with high‐latitude field‐aligned currents observed during Cassini's F‐ring orbits (October 2016–April 2017). The overall ionospheric meridional current profiles in the northern and southern hemispheres, that is, the regions poleward and equatorward of the field‐aligned currents, differ most from the 2008 observations. We discuss these differences in terms of the seasonal change between data sets and local time (LT) differences, as the 2008 data cover the nightside while the F‐ring data cover the post‐dawn and dusk sectors in the northern and southern hemispheres, respectively. The F‐ring field‐aligned currents typically have a similar four current sheet structure to those in 2008. We investigate the properties of the current sheets and show that the field‐aligned currents in a hemisphere are modulated by that hemisphere's “planetary period oscillation” (PPO) systems. We separate the PPO‐independent and PPO‐related currents in both hemispheres using their opposite symmetry. The average PPO‐independent currents peak at ~1.5 MA/rad just equatorward of the open closed field line boundary, similar to the 2008 observations. However, the PPO‐related currents in both hemispheres are reduced by ~50% to ~0.4 MA/rad. This may be evidence of reduced PPO amplitudes, similar to the previously observed weaker equatorial oscillations at similar dayside LTs. We do not detect the PPO current systems' interhemispheric component, likely a result of the weaker PPO‐related currents and their closure within the magnetosphere. We also do not detect previously proposed lower latitude discrete field‐aligned currents that act to “turn off” the PPOs.

We newly analyze Cassini magnetic field data from the 2012/2013 Saturn northern spring interval of highly inclined orbits and compare them with similar data from late southern summer in 2008, thus providing unique information on the seasonality of the currents that couple momentum between Saturn's ionosphere and magnetosphere. Inferred meridional ionospheric currents in both cases consist of a steady component related to plasma subcorotation, together with the rotating current systems of the northern and southern planetary period oscillations (PPOs). Subcorotation currents during the two intervals show opposite north‐south polar region asymmetries, with strong equatorward currents flowing in the summer hemispheres but only weak currents flowing to within a few degrees of the open‐closed boundary (OCB) in the winter hemispheres, inferred due to weak polar ionospheric conductivities. Currents peak at ~1 MA rad−1 in both hemispheres just equatorward of the open‐closed boundary, associated with total downward polar currents ~6 MA, then fall across the narrow auroral upward current region to small values at subauroral latitudes. PPO‐related currents have a similar form in both summer and winter with principal upward and downward field‐aligned currents peaking at ~1.25 MA rad−1 being essentially collocated with the auroral upward current and approximately equal in strength. Though northern and southern PPO currents were approximately equal during both intervals, the currents in both hemispheres were dual modulated by both systems during 2012/2013, with approximately half the main current closing in the opposite ionosphere and half cross field in the magnetosphere, while only the northern hemisphere currents were similarly dual modulated in 2008.

We report about the derivation of visible (VIS) and infrared (IR) albedo maps and spectral indicators of Saturn's satellite Tethys from the complete Cassini-Visual and Infrared Mapping Spectrometer (VIMS) data set. The application of a photometric correction is necessary to remove illumination and viewing effects from the I/F spectra, to compute spectral albedo and to correctly associate spectral variations to changes in composition or physical properties of the surface. In this work we are adopting the photometric correction proposed by Shkuratov et al. (2011, https://doi.org/10.1016/j.pss.2011.06.011) to derive albedo maps of Tethys from disk-resolved Cassini-VIMS data. After having applied a similar methodology to Dione's data (Filacchione et al., 2018, https://doi.org/10.1002/2017GL076869), we present here the results achieved for Tethys: surface albedo maps and photometric parameters are computed at five visible (0.35, 0.44, 0.55, 0.70, and 0.95 μm) and five infrared (1.046, 1.540, 1.822, 2.050, and 2.200 μm) wavelengths and rendered in cylindrical projection with a 0.5° × 0.5° angular resolution in latitude and longitude, corresponding to a highest spatial resolution of 4.7 km/bin. The 0.35- to 0.55- and 0.55- to 0.95-μm spectral slopes and the water ice 2.050-μm band depth maps are computed after having applied the photometric correction, in order to trace the leading-trailing hemisphere dichotomy, to constrain the shape of the equatorial lens generated by the bombardment of high-energy magnetospheric electrons on the leading hemisphere, and to observe the stronger water ice band depth and reddening within the floors of Odysseus and Penelope impact craters.

This chapter presents a short overview of physical processes in a specific plasma region (a so-called plume) found by the Cassini orbiter in the vicinity of the icy moon Enceladus. In particular, we summarize highlights of scientific results which have been performed by German research groups in GFZ German Research Centre for Geosciences, Potsdam and Technical University of Braunschweig as part of the Special Priority Program “PlanetMag” of the Deutsche Forschungsgemeinschaft between 2013 and 2016. The highlights cover mostly those theoretical and numerical studies in which measurements of different Cassini instruments could be compared with theory or where the phenomenon has a diagnostic application. Dust charging, role of dust size distributions, and dust charge fluctuations are discussed. The findings are used for interpretations of the Cassini Plasma Spectrometer data and improve constraints on the dust characteristics. Then the main forces and dust dynamics are discussed in conditions relevant for the near-Enceladus environment. It is also examined how the charged dust can affect the plasma shielding length which is of importance for the reliable Cassini Langmuir probe measurements. Considering the dust grains as heavy negative ion species, the electric conductivity tensor is modified, whose elements are the key quantities for understanding the magnetic field perturbations registered by the Cassini Magnetometer during Enceladus flybys.

The purpose of this project is to investigate the spectral properties of turbulence in the magnetosheath of Saturn, using in-situ magnetic field measurements from the Cassini spacecraft. According to models of incompressible, turbulent fluids, the energy spectrum in the inertial range scales as the frequency to the power of -5/3, which has been observed in the near-Earth Solar wind but not in the Terrestrial magnetosheath unless close to the magnetopause. 120 time intervals for when Cassini is inside the magnetosheath are identified — 40 in each category of behind quasi-perpendicular bow shocks, behind quasi-parallel bow shocks, and inside the middle of the magnetosheath. The power spectral density is thereafter calculated for each interval, with logarithmic regressions performed at the MHD and sub-ion scales separated by the ion gyrofrequency. The results seem to indicate similar behaviour as in the magnetosheath of Earth, without significant difference between quasi-perpendicular and quasi-parallel cases except somewhat steeper exponents at the MHD scale for the former. These observations confirm the role of the bow shock in destroying the fully developed turbulence of the Solar wind, thus explaining the absence of the inertial range. Syftet med detta projekt är att undersöka de spektrala egenskaperna hos turbulens i Saturnus magnetoskikt, med in-situ-mätningar av magnetfältet från Cassini-rymdsonden. Enligt modeller av inkompressibla, turbulenta fluider, är energispektrumet i det intertiala omfånget proportionellt mot frekvensen upphöjd i -5/3, vilket har observerats i den jordnära Solvinden men inte i det jordiska magnetoskiktet förutom nära magnetopausen. 120 tidsintervall för när Cassini befinner sig inuti magnetoskiktet identifieras — 40 styck i kategorierna bakom kvasi-vinkelräta bogchockar, bakom kvasi-parallella bogchockar, och inuti mellersta delen av magnetoskiktet. Effektspektraltätheten beräknas därefter för varje intervall, med logaritmiska regressioner på MHD- och subjon-skalorna som separeras av jongyrofrekvensen. Resultaten verkar tyda på liknande beteende som i Jordens magnetoskikt, utan märkvärdig skillnad mellan kvasi-vinkelräta och kvasi-parallella fall förutom något brantare exponenter på MHD-skalan för de förnämnda. Dessa observationer bekräftar bogchokens roll i förstörandet av den fullt utvecklade turbulensen i Solvinden, därmed förklarande avsaknaden av det inertiala omfånget.

International audience; This chapter is intended to provide a concise overview of the state of knowledge regarding the temperature, clouds, and aerosols of the terrestrial bodies of our Solar System, namely Mars, Venus, and Titan. These bodies are the planetary objects that most resemble the Earth. The atmosphere of each body is described in terms of composition and vertical structure. We distinguish and compare the extent of the various atmospheric compartments that form the atmospheric column, from the troposphere up to the thermosphere. The temperature structure is then presented, and the main causes known for explaining its variations on each body are listed. The specific roles of waves, radiation, as well as convection in shaping temperature profiles are then discussed. In a second part, the particulate components of these atmospheres, clouds and aerosols, are described in terms of their physical properties (composition, optical properties) and of their variability in both space and time. Mars , Venus, and Titan exhibit a remarkable variety of clouds and aerosols. Our knowledge about them has made considerable progress thanks to the success of space missions during the last two decades, while in parallel theoretical models have improved to the point that three-dimensional Global Climate Models now include the detailed physics of clouds and aerosols. As a result, it is now widely recognized that particulates play a key role in forcing the climate and the evolution of these bodies.

We report about the derivation of visible (VIS) and infrared (IR) albedo maps and spectral indicators of Saturn's satellite Tethys from the complete Cassini‐Visual and Infrared Mapping Spectrometer (VIMS) data set. The application of a photometric correction is necessary to remove illumination and viewing effects from the I/F spectra, to compute spectral albedo and to correctly associate spectral variations to changes in composition or physical properties of the surface. In this work we are adopting the photometric correction proposed by Shkuratov et al. (2011, https://doi.org/10.1016/j.pss.2011.06.011) to derive albedo maps of Tethys from disk‐resolved Cassini‐VIMS data. After having applied a similar methodology to Dione's data (Filacchione et al., 2018, https://doi.org/10.1002/2017GL076869), we present here the results achieved for Tethys: surface albedo maps and photometric parameters are computed at five visible (0.35, 0.44, 0.55, 0.70, and 0.95 μm) and five infrared (1.046, 1.540, 1.822, 2.050, and 2.200 μm) wavelengths and rendered in cylindrical projection with a 0.5° × 0.5° angular resolution in latitude and longitude, corresponding to a highest spatial resolution of 4.7 km/bin. The 0.35‐ to 0.55‐ and 0.55‐ to 0.95‐μm spectral slopes and the water ice 2.050‐μm band depth maps are computed after having applied the photometric correction, in order to trace the leading‐trailing hemisphere dichotomy, to constrain the shape of the equatorial lens generated by the bombardment of high‐energy magnetospheric electrons on the leading hemisphere, and to observe the stronger water ice band depth and reddening within the floors of Odysseus and Penelope impact craters.

Purpose: To evaluate and investigate the distribution and repeatability of anterior corneal surface astigmatism measurements (axis and magnitude) using a novel corneal topographer. Methods: Anterior corneal surface astigmatism was investigated in a total of 195 eyes using a novel multicolored spot reflection topographer (Cassini; i-Optics). Two patient groups were studied, a younger-age group A and an older-age group B. Three consecutive acquisitions were obtained from each eye. The repeatability of measurement was assessed using Bland–Altman plot analysis and is reported as the coefficient of repeatability. Results: Group A (average age 34.3 years) had on average with-the-rule astigmatism, whereas the older-age group B (average age 72.3 years) had on average against-the-rule astigmatism. Average astigmatism magnitude measurement repeatability in group A was 0.4 diopters (D) and in group B 0.4 D. Average astigmatism axis measurement repeatability in group A was 5.4 degrees and in group B 5.5 degrees. The axis measurement repeatability improved with increasing magnitude of astigmatism: in the subgroups with astigmatism between 3.0 and 6.0 D, the axis repeatability was 1.4 degrees (group A) and 1.2 degrees (group B), whereas in the subgroups with astigmatism larger than 6.0 D, the repeatability was 1.1 and 0.6 degrees, respectively. Conclusions: This novel corneal topography device seems to offer high precision in reporting corneal astigmatism. This study reaffirms the established trend of a corneal astigmatism shift from an average “with-the-rule” to “against-the-rule” with aging.