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This presentation will focus on recent efforts to develop space and planetary sciences in Africa, particularly work on African impact structures and support for NASA space missions (New Horizons, Lucy) to explore asteroids through stellar occultation campaigns conducted in Senegal., Cette presentation s’intéressera aux récents efforts de développement des sciences de l’espace et des planètes en Afrique, et en particulier les travaux s’intéressants aux structures d’impacts africaines et au soutien des missions spatiales NASA (New Horizons, Lucy) d’exploration des astéroïdes par des campagnes d’occultation stellaire menées au Sénégal.

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During this PhD, we studied the "true" mineral perovskite CaTiO3, which is certainly not a major planetary constituent but which is structurally analogous to the main compound of the mantles of telluric planets of approximate formula MgSiO3. Thanks to the concept of chemical pressure, CaTiO3 presents the interest to have a behavior similar to that of MgSiO3 but at more moderate pressures. After two campaigns, one of static compression by diamond anvil cell and one of dynamic compression by laser shock, we have demonstrated the dissociation of CaTiO3 perovskite into a CaO + CaTi2O5 assembly. This type of dissociation, already proposed by a theoretical study of MgSiO3, could have a significant impact on the dynamics of silicate mantles of super-Earths. Our discovery could help to better understand a possible MgSi2O5 phase in planetary mantles.A second part of the thesis is based on the synthesis of materials by magnetron sputtering (PVD), elaborated in the form of complex successive layers in order to open the way to more precise dynamic experiments at ultra-high pressure on the materials of planetary mantles. Multilayer materials are currently not widespread in the fields of geophysics and planetology. The main interest of developing this method lies in the possibility to control with precision the architecture and the metrology of the samples, which in a near future will be used as starting products for static and dynamic compression experiments. Deposits have been made in the quaternary Mg-Fe-Si-O, the four main chemical elements of rocky planets. We were able to synthesize thin films of stoichiometric MgSiO3 (up to 7 μm thick) and of ~ Mg0.37Fe0.63SiO3 composition, both characterized by excellent homogeneity down to the nanoscale., Au cours de ce doctorat, nous avons étudié la pérovskite « vraie » CaTiO3, qui n'est certes pas un constituant planétaire majeur mais qui est structuralement analogue au composé principal des manteaux des planètes telluriques de formule approchée MgSiO3. Grâce au concept de pression chimique, CaTiO3 présente l'intérêt d'avoir un comportement analogue à celui de MgSiO3 mais à des pressions plus modérées. Après deux campagnes, une de compression statique par cellule à enclumes de diamants ainsi qu’une en compression dynamique par choc laser, nous avons mis en évidence la dissociation de la pérovskite de CaTiO3 en un assemblage CaO + CaTi2O5. Ce type de dissociation déjà proposé par l’étude théorique de MgSiO3 pourrait avoir un impact significatif sur la dynamique des manteaux silicatés de super-Terres et être mieux compris grâce au comportement de CaTiO3. Un second volet de la thèse repose sur la synthèse de matériaux par pulvérisation cathodique magnétron (PVD), élaborés sous forme de couches successives complexes afin d’ouvrir la voie vers des expériences dynamiques plus précises à ultra-haute pression sur les matériaux des manteaux planétaires. Les techniques de synthèses de matériaux multicouches sont aujourd’hui peu répandues dans le domaine de la géophysique et la planétologie. L’intérêt premier de développer cette méthode réside dans la possibilité de contrôler avec précision l’architecture et la métrologie des échantillons, produits de départ pour des expériences de compression tant statique que dynamique. Les dépôts ont été réalisés dans le quaternaire Mg-Fe-Si-O, c'est à dire les quatre éléments chimiques principaux des planètes telluriques. Nous avons été en mesure de synthétiser des couches minces de MgSiO3 stoechiométrique (jusqu’à 7 μm d’épaisseur) et de ~ Mg0,37Fe0,63SiO3, toutes deux caractérisées par une excellente homogénéité jusqu’à l’échelle nanométrique.

International audience

From summer 2023, the Rosalind Franklin rover of the ExoMars 2022 mission (ESA/ROSCOSMOS) will seek out past or present traces of life down to 2 m in the Martian subsurface with a drill, where collected samples could have been shielded from the harsh conditions of the surface. In order to give an insight into the structure and composition of the shallow subsurface prior to any drilling operations, and to provide clues on the geological context of the rover landing site, one of the 9 instruments onboard Rosalind Franklin is a Ground Penetrating Radar (GPR): WISDOM (Water Ice and Subsurface Deposits Observation on Mars). WISDOM will sound the first meters of the Martian shallow subsurface with a vertical resolution of a few cm. This thesis was dedicated to the assessment and implementation of new and sophisticated tools in the processing and interpretation chain of the WISDOM data, enhancing the quality and readability of future Martian observations.Data acquired by WISDOM consist in“radargrams”, displaying the amplitude of received signals (after reflection/scattering on subsurface structures) as a function of their time delays. Converting these time delays into distances requires the knowledge of the propagation speed of electromagnetic waves in the subsurface, which is linked to the dielectric permittivity of this subsurface. In the case of WISDOM, this property can be estimated from the surface echo intensity or from the shape of diffraction curves from scatter points buried in the subsurface. Since, unlike most GPR, WISDOM antennas are not directly on the ground, the latter method must account for the refraction of radar signals at the surface, which impacts the shape of the curves and thus the permittivity estimation. During this thesis, an automated tool of detection and characterization of diffraction curves was developed and validated, guarantying the display of radargrams as a function of distance.This thesis also focused on the enhancement of the vertical resolution (in range/depth) of WISDOM radargrams. The instrument operating on a large frequency bandwidth, a resolution of a few cm in the subsurface is already assured. A super-resolution technique based on the “Bandwidth Extrapolation” (BWE) was tested and implemented to the WISDOM data processing chain. This resulted in an improvement of the range resolution by a factor of 3. Such improvement has numerous positive implications on the interpretation of future WISDOM radargrams; echoes before impossible to separate can be now discriminated. Potential improvements of the BWE, exploiting for instance the polarimetric capabilities of WISDOM were also explored.Tools implemented during this thesis were systematically validated on both synthetic (analytical or simulated) and experimental data acquired on Earth with replicas of WISDOM instrument (in laboratory or natural environments). Two field campaigns were organised in the frame of this thesis (in the Desert of Atacama and at the Technical University of Dresden (TUD)), providing interesting datasets to validate the WISDOM processing and interpretation chains on, in preparation of future Martian operations., A partir de l’été 2023, le rover Rosalind Franklin de la mission ExoMars 2022 (ESA/ROSCOSMOS) recherchera à l’aide d’une foreuse de potentielles traces de vie, passées ou présentes, dans les 2 premiers mètres du sous-sol martien, là où les échantillons collectés pourraient avoir été protégés des conditions inhospitalières de la surface. Dans le but d’offrir un aperçu de la structure et de la composition de la proche sous-surface avant toute opération de forage et d’aider à reconstituer le contexte géologique du site d’atterrissage du rover, l’un des 9 instruments à bord de Rosalind Franklin est un radar à pénétration de sol (ou GPR pour Ground Penetrating Radar) : WISDOM (Water Ice and Subsurface Deposits Observation on Mars). WISDOM sondera les premiers mètres du sous-sol martien avec une résolution verticale centimétrique. Cette thèse a été dédiée à la mise en place d’une chaine de traitement et d’interprétation des données de WISDOM destinée à optimiser la qualité et lisibilité de ses futures observations sur Mars.Les données de WISDOM se présentent sous forme de « radargrammes » qui donnent l’amplitude des signaux reçus (après réflexion/diffusion sur des structures enfouies) en fonction de leur temps d’arrivée. La conversion de ces temps d’arrivée en distances requiert la connaissance de la vitesse de propagation des ondes électromagnétiques dans le sous-sol, qui elle-même est liée à la permittivité diélectrique du sol. Dans le cas de WISDOM, cette dernière peut être estimée à partir de l’intensité de l’écho de surface ou de la forme des courbes de diffraction provenant de réflecteurs ponctuels enfouis. Les antennes de WISDOM n’étant pas plaquées au sol (contrairement à celles de la majorité des GPR), cette seconde méthode d’estimation doit tenir compte de la réfraction des signaux du radar à la surface, qui a un impact sur la forme des courbes et donc l’estimation de la permittivité. Durant cette thèse, une chaîne automatique de détection et de caractérisation des courbes de diffraction tenant compte de la réfraction à la surface, a été développée et validée, garantissant la possibilité d’exprimer les radargrammes WISDOM en fonction de la distance.Cette thèse s’est aussi attachée à améliorer la résolution verticale (en distance/profondeur) des radargrammes de WISDOM. L’instrument opère sur une large bande de fréquences, ce qui lui assure déjà une résolution en distance de quelques cm dans le sous-sol. Une technique dite de super-résolution, fondée sur l’« Extrapolation de largeur de bande » (BWE), a été testée et implémentée dans la chaîne de traitement des données WISDOM. Il a été montré que cette technique permet d’améliorer la résolution en distance d’un facteur 3. Une telle amélioration de la résolution revêt un intérêt évident pour l’interprétation des futurs radargrammes WISDOM ; des échos avant impossible à séparer le sont à présent. De potentielles améliorations de la BWE, tirant par exemple partie des capacité polarimétriques de WISDOM, ont aussi été explorées.Les outils mis en place pendant cette thèse ont été systématique validés sur des données aussi bien synthétiques (analytiques ou numériques) qu’expérimentales acquises sur Terre avec des répliques de l’instrument (en laboratoire ou sur site naturel). Deux campagnes de mesures ont d’ailleurs été organisées durant cette thèse (dans le désert d’Atacama au Chili et à l’Université Technique de Dresden (TUD)), fournissant des observations sur lesquelles tester les chaînes de traitement et d’interprétation WISDOM pour préparer au mieux les futures opérations martiennes.

Generative Adversarial Networks (GANs) hatten enorme Anwendungen in Computer Vision. Im Kontext der Weltraumforschung und der Erforschung der Planeten steht die Tür jedoch offen für große Fortschritte. Wir stellen Werkzeuge für den Umgang mit Planetendaten aus der Mission Chang'E-4 vor und präsentieren ein Framework für die Übertragung des neuronalen Stils unter Verwendung der Zykluskonsistenz aus gerenderten Bildern.Wir führen auch eine neue Echtzeit-Pipeline für Simultaneous Localization and Mapping (SLAM) und Visual Inertial Odometry (VIO) im Kontext von Planetenrovern ein. Wir nutzen vorherige Informationen über den Standort des Landers, um einen SLAM-Ansatz auf Objektebene vorzuschlagen, der die Pose und Form des Landers zusammen mit den Kameratrajektorien des Rovers optimiert. Als weiteren Verfeinerungsschritt schlagen wir vor, Interpolationstechniken zwischen benachbarten zeitlichen Abtastwerten zu verwenden. videlicet synthetisiert nicht vorhandene Bilder, um die Gesamtgenauigkeit des Systems zu verbessern.Die Experimente werden im Rahmen des Iris Lunar Rover durchgeführt, eines Nano-Rovers, der 2021 als Flaggschiff von Carnegie Mellon als erstem unbemannten Rover Amerikas auf dem Mond im Mondgelände eingesetzt wird., Generative Adversarial Networks (GANs) have had tremendous applications in Computer Vision. Yet, in the context of space science and planetary exploration the door is open for major advances. We introduce tools to handle planetary data from the mission Chang'E-4 and present a framework for Neural Style Transfer using Cycle-consistency from rendered images. We also introduce a new real-time pipeline for Simultaneous Localization and Mapping (SLAM) and Visual Inertial Odometry (VIO) in the context of planetary rovers. We leverage prior information of the location of the lander to propose an object-level SLAM approach that optimizes pose and shape of the lander together with camera trajectories of the rover. As a further refinement step, we propose to use techniques of interpolation between adjacent temporal samples; videlicet synthesizing non-existing images to improve the overall accuracy of the system.The experiments are conducted in the context of the Iris Lunar Rover, a nano-rover that will be deployed in lunar terrain in 2021 as the flagship of Carnegie Mellon, being the first unmanned rover of America to be on the Moon., Generative Adversarial Networks (GAN) ont eu d'énormes applications en vision par ordinateur. Pourtant, dans le contexte de la science spatiale et de l'exploration planétaire, la porte est ouverte à des avancées majeures. Nous introduisons des outils pour gérer les données planétaires de la mission Chang'E-4 et présentons un cadre pour le transfert de style neuronal utilisant la cohérence de cycle à partir d'images rendues. Nous introduisons également un nouveau pipeline en temps réel pour Simultaneous Localization and Mapping (SLAM) et Visual Inertial Odometry (VIO) dans le contexte des rovers planétaires. Nous exploitons les informations préalables sur l'emplacement de l'atterrisseur pour proposer une approche SLAM au niveau de l'objet qui optimise la pose et la forme de l'atterrisseur ainsi que les trajectoires de caméra du rover. Comme étape de raffinement supplémentaire, nous proposons d'utiliser des techniques d'interpolation entre échantillons temporels adjacents; videlicet synthétise des images inexistantes pour améliorer la précision globale du système. Les expériences sont menées dans le contexte de l'Iris Lunar Rover, un nano-rover qui sera déployé sur un terrain lunaire en 2021 en tant que vaisseau amiral de Carnegie Mellon, étant le premier rover sans pilote d'Amérique à être sur la Lune.

Generative Adversarial Networks (GANs) hatten enorme Anwendungen in Computer Vision. Im Kontext der Weltraumforschung und der Erforschung der Planeten steht die Tür jedoch offen für große Fortschritte. Wir stellen Werkzeuge für den Umgang mit Planetendaten aus der Mission Chang'E-4 vor und präsentieren ein Framework für die Übertragung des neuronalen Stils unter Verwendung der Zykluskonsistenz aus gerenderten Bildern.Wir führen auch eine neue Echtzeit-Pipeline für Simultaneous Localization and Mapping (SLAM) und Visual Inertial Odometry (VIO) im Kontext von Planetenrovern ein. Wir nutzen vorherige Informationen über den Standort des Landers, um einen SLAM-Ansatz auf Objektebene vorzuschlagen, der die Pose und Form des Landers zusammen mit den Kameratrajektorien des Rovers optimiert. Als weiteren Verfeinerungsschritt schlagen wir vor, Interpolationstechniken zwischen benachbarten zeitlichen Abtastwerten zu verwenden. videlicet synthetisiert nicht vorhandene Bilder, um die Gesamtgenauigkeit des Systems zu verbessern.Die Experimente werden im Rahmen des Iris Lunar Rover durchgeführt, eines Nano-Rovers, der 2021 als Flaggschiff von Carnegie Mellon als erstem unbemannten Rover Amerikas auf dem Mond im Mondgelände eingesetzt wird., Generative Adversarial Networks (GANs) have had tremendous applications in Computer Vision. Yet, in the context of space science and planetary exploration the door is open for major advances. We introduce tools to handle planetary data from the mission Chang'E-4 and present a framework for Neural Style Transfer using Cycle-consistency from rendered images. We also introduce a new real-time pipeline for Simultaneous Localization and Mapping (SLAM) and Visual Inertial Odometry (VIO) in the context of planetary rovers. We leverage prior information of the location of the lander to propose an object-level SLAM approach that optimizes pose and shape of the lander together with camera trajectories of the rover. As a further refinement step, we propose to use techniques of interpolation between adjacent temporal samples; videlicet synthesizing non-existing images to improve the overall accuracy of the system.The experiments are conducted in the context of the Iris Lunar Rover, a nano-rover that will be deployed in lunar terrain in 2021 as the flagship of Carnegie Mellon, being the first unmanned rover of America to be on the Moon., Generative Adversarial Networks (GAN) ont eu d'énormes applications en vision par ordinateur. Pourtant, dans le contexte de la science spatiale et de l'exploration planétaire, la porte est ouverte à des avancées majeures. Nous introduisons des outils pour gérer les données planétaires de la mission Chang'E-4 et présentons un cadre pour le transfert de style neuronal utilisant la cohérence de cycle à partir d'images rendues. Nous introduisons également un nouveau pipeline en temps réel pour Simultaneous Localization and Mapping (SLAM) et Visual Inertial Odometry (VIO) dans le contexte des rovers planétaires. Nous exploitons les informations préalables sur l'emplacement de l'atterrisseur pour proposer une approche SLAM au niveau de l'objet qui optimise la pose et la forme de l'atterrisseur ainsi que les trajectoires de caméra du rover. Comme étape de raffinement supplémentaire, nous proposons d'utiliser des techniques d'interpolation entre échantillons temporels adjacents; videlicet synthétise des images inexistantes pour améliorer la précision globale du système. Les expériences sont menées dans le contexte de l'Iris Lunar Rover, un nano-rover qui sera déployé sur un terrain lunaire en 2021 en tant que vaisseau amiral de Carnegie Mellon, étant le premier rover sans pilote d'Amérique à être sur la Lune.

This article proposes an explanation for High-Energy Atmospheric phenomena through the frames of Hypersphere World-Universe Model (WUM). In WUM, Terrestrial Gamma-Ray Flashes (TGFs) are, in fact, Gamma-Ray Bursts (GRBs). The spectra of TGFs at very high energies are explained by Dark Matter particles annihilation in Geocorona. Lightning initiation problem is solved by GRBs that slam into thunderclouds and carve a conductive path through a thunderstorm. We introduce Multiworld consisting of Macro-World, Large-World, Small-World, and Micro-World, characterized by suggested Gravitational, Extremely-Weak, Super-Weak, and Weak interaction respectively. We propose a new model of Ball Lightning formation based on the Dark Matter Core surrounded by electron-positron plasma in the Small-World.

Decades of in-situ data measurement by missions focused on the study of the solar wind and its relation with the near-Earth environment allowed the study of the Sun-Earth coupling from a statistical point of view. Nevertheless, these studies are limited by the manual selection of the events of interest in the data that is still a subjective, fastidious and hardly reproducible task.Using machine learning algorithms, we elaborate automatic detection methods of events from in-situ data measurement. Whether they are applied to the detection of interplanetary coronal mass ejections, to the classification of the near-Earth regions or to the identification of magnetopause magnetic reconnection jets, the developed methods are more accurate than those based on manual, empirical thresholds. They are also adaptable from a mission to another provided the regions visited by the spacecraft are of the same nature. We show that the interpretation of the data by these methods is limited by the vision we have on the data and the events they measure.These methods pave the way for statistical studies of in-situ measured events with an important number of samples. Thereby, we use the classification of the different regions of the near-Earth environment to statistically study the position and shape of the magnetopause using the data of missions with equatorial (THEMIS, MMS, Double Star), polar (Cluster) and lunar (ARTEMIS) orbits. In addition to confirming the seasonal dependence, the azimuthal asymmetry and the influence of the solar wind dynamic pressure, we show that the clock angle of the interplanetary magnetic field modifies the shape of the magnetopause through the process of magnetic reconnection and lead a discussion on the nature of this boundary around the polar cusps. We combine the results of the study into an analytical model of the magnetopause position and shape that offers a more precise description of this boundary on the night side of the Earth magnetosphere., Les décennies d'accumulation de données provenant de missions explorant le vent solaire ainsi que l'environnement terrestre proche permettent l'étude de la relation Soleil-Terre de manière statistique. Ces études sont toutefois limitées par la sélection manuelle des événements d'intérêt dans les données qui reste une tâche fastidieuse, subjective et difficilement reproductible.En nous appuyant sur des outils d'apprentissage statistique, nous mettons au point des méthodes de détection automatique d'événements à partir de mesures de données in-situ. Qu'il s'agisse de détecter les éjections de masse coronale interplanétaires, de classifier les régions de l'environnement terrestre proche ou de détecter les jets de plasma issus de la reconnexion magnétique à la magnétopause, nos méthodes font moins d'erreurs que celles basées sur des seuils empiriques généralement utilisées pour sélectionner des événements. Elles sont de plus adaptables d'une mission à une autre pourvu que la nature des régions traversées par les sondes soient similaires. Nous montrons toutefois que l’interpretation des données par ces méthodes sont limitées par notre propre interprétation physique des données et des evenements qu’elles mesurent.Ces méthodes ouvrent la porte aux études statistiques d'événements mesurés in-situ à grand nombre d'échantillons.La classification des différentes régions de l'environnement terrestre proche nous permet par exemple d’étudier statistiquement la position et la forme adoptée par la magnétopause en s'appuyant sur les données de missions d'orbites equatoriales (THEMIS, MMS, Double Star), polaires (Cluster) et lunaires (ARTEMIS). En plus de confirmer l'influence saisonale, le rôle joué par la pression dynamique, et l'asymétrie azimutale, nous montrons que l'orientation azimuthale du champ magnétique interplanétaire modifie la forme de la magnétopause par le biais de la reconnexion magnétique et discutons de la nature de cette frontière au niveau des cornets polaires.L'étude résulte en la production d'un modèle analytique de la position de la magnétopause offrant une description plus précise de cette frontière du côté nuit de la magnétosphère terrestre.

Chemical processes of the dense CO2-atmosphere of Venus are determined by trace gases such as SO2, O3, H2O, CO, etc. Among these atmospheric components, a group of sulfur and oxygen compounds occupies a central position. The objective of this thesis is a study of sulfur dioxide and ozone at the night side of Venus' upper mesosphere that is related to altitudes from 85 to 110 km. Chemistry and dynamics of this altitude range is very active. The sulfuric chemical cycle in the mesosphere leads to a formation of the thick cloud deck at 47-70 km globally enshrouding the planet. Furthermore, it has not yet been determined exactly which chemical interactions are responsible for stabilizing the equilibrium in the chemical cycles of the atmosphere, and maintaining a high mixing ratio of CO2. The difficulty of evaluating the oxidizing capacity of the atmosphere, due to the lack of direct measurements of the amount of molecular oxygen, is one reason for this. However, indirect O2 estimations can be made based on derivatives of this molecule, and one of them is ozone. This gas is involved in reactions with species, probably mainly chlorinated compounds, leading to the general chemical cycles.The research is based on the data obtained from the first stellar occultation experiment released for Venus. It was performed by the UV channel of the SPICAV spectrometer onboard Venus Express orbiter working in 2006-2014. This is a powerful instrument to measure absorption of CO2, SO2 and O3 at the night side of Venus’ atmosphere above the cloud layer. This study also includes a detailed assessment of the accuracy of the spectral data processing methods used to retrieve vertical atmospheric gas concentration distributions. Mainly it concerns a separation of a stellar light from UV emission signal originated from different spread sources, which is a parasitic light for the stellar occultation data investigation. A significant influence of a calibration assignment of wavelength to a digital pixel number was obtained. The required accuracy was achieved by a determination of stellar lines position for a large set of stars' spectra measuring in each observational session. Thus, it allowed to establish a profile of the SO2 content from 85 km to 100 km mainly devoted to mid-latitudinal range. On average, it shows a stable mixing ratio with altitude. For this gas, a prevailed short-period variability has been confirmed. However, a weak possible increase of SO2 abundance with local time is noticed from the morning to the evening terminator at 90-95 km. After the discovery of the ozone layer on Venus made by Montmessin et al. (2011), the ozone content was confirmed in more than 100 occultation sessions. The current study also shows that the detected ozone values correspond to its maximum values rather than to the thick stable layer. These results are the first detailed vertical distribution of the SO2 and O3 content in the upper mesosphere on the night side, which opens up new possibilities for the theoretical description of processes occurring in the atmosphere of Venus., Les processus chimiques de l'atmosphère dense de CO2 de Vénus sont contrôlés par des gaz à traces tels que SO2, O3, H2O, CO, etc. Parmi ces composants atmosphériques, un groupe de composés soufrés et oxygènés occupe une place centrale.L'objectif de cette thèse concerne l'étude du dioxyde de soufre et de l'ozone présents du côté nuit de la haute mésosphère de Vénus entre 85 et 110 km d’altitude. La chimie et la dynamique sont très actives dans cette région et le cycle chimique du soufre dans cette région conduit à la formation de l’épaisse couche nuageuse entre 47 et 70 km d’altitude tout autour de la planète. En outre, on n'a pas encore déterminé exactement quelles interactions chimiques étaient responsables de l'équilibre sur le long terme du CO2. Une réelle difficulté subsiste en effet quant à notre capacité à évaluer la capacité d'oxydation de l'atmosphère vénusienne, du fait de l'absence de mesures directes de la quantité d'oxygène moléculaire. Cependant, des estimations indirectes de l'O2 peuvent être faites sur la base des dérivés de cette molécule, dont l'un en particulier est l'ozone. On s’attend à ce que l’ozone soit impliqué dans des réactions avec des espèces principalement chlorées très présentes sur Vénus.Mon travail de recherche est basé sur les données obtenues par le canal UV du spectromètre SPICAV à bord de l'orbiteur Venus Express qui a opéré entre 2006 et 2014. SPICAV est un instrument particulièrement bien adapté à la mesure de CO2, SO2 et O3 du côté nuit de l'atmosphère de Vénus au-dessus de la couche nuageuse. Mon étude comprend également une ré-évaluation détaillée de la précision des méthodes de traitement des données spectrales employées jusqu’alors pour déterminer les distributions verticales de la concentrations de gaz dans l'atmosphère. Il s'agit principalement d'une séparation entre la lumière d’une étoile utilisée pour la mesure et celle d’émissions UV provenant de différentes sources, que l’on considère comme parasitant l’interprétation des données obtenues lors des occultations stellaires. Une influence très forte de la calibration en longueur d'onde a pu être mise en évidence, et a abouti à une modification de la technique de calibration se basant sur la comparaison de la position des raies stellaires avec une base de données de référence. Ainsi, cela a permis d'établir des profils de SO2 de 85 km à 100 km principalement localisés dans les latitudes moyennes. Ces profils suggèrent que SO2 est uniformément mélangé dans cette gamme d’altitude et qu’il est soumis à une variabilité forte sur de faibles échelles de temps. Cependant, une faible augmentation a été constatée entre le matin et le soir dans les zones du terminateur vénusien et à une altitude de 90-95 km. Enfin, après la découverte de la couche d'ozone sur Vénus faite par Montmessin et al. (2011), la présence de l’ozone a pu être confirmée dans plus de 100 séances d'occultation. L'étude actuelle montre également que les valeurs d'ozone détecté correspondent à ses valeurs maximales plutôt qu'à l'épaisse couche stable que l’on trouve près du sommet des nuages. Ces résultats représentent la première base de données sur la distribution verticale détaillée de la teneur en SO2 et O3 dans la mésosphère supérieure du côté nuit, ce qui ouvre de nouvelles perspective pour la compréhension théorique des processus se produisant dans l'atmosphère de Vénus.

International audience

International audience; Introduction: The key scientific objectives of the ESA mission ExoMars2022 are searching for signs of past and/or present life on Mars and characterizing the subsurface geochemical environment as a function of depth. The Rosalind Franklyn rover [1] payload consists of a suite of nine instruments that will provide information about the geological and geochemical environment of the surface and subsurface of the selected landing site (i.e., Oxia Planum) [2]. Remote sensing measurements performed by OMEGA and CRISM suggest that the exposed rocks on the surface of Oxia Planum experienced an intense aqueous alteration [3]. The widespread presence of Fe/Mg-Al-phyllosilicates and, more generally, of silicates containing OH group confirms an interaction between water and mother rocks happened in the past geological history of the planet, which is a prerequisite favorable to the development of life. In this framework, we performed several laboratory spectroscopic measurements of clay minerals mixed with different organic compounds for determining whether the Ma_MISS (Mars Multispectral Imager for Subsurface Studies) instrument will be able to provide clues on the presence of organics in the Martian subsurface.

International audience

Ariel, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, was adopted as the fourth medium-class mission in ESA's Cosmic Vision programme to be launched in 2029. During its 4-year mission, Ariel will study what exoplanets are made of, how they formed and how they evolve, by surveying a diverse sample of about 1000 extrasolar planets, simultaneously in visible and infrared wavelengths. It is the first mission dedicated to measuring the chemical composition and thermal structures of hundreds of transiting exoplanets, enabling planetary science far beyond the boundaries of the Solar System. The payload consists of an off-axis Cassegrain telescope (primary mirror 1100 mm x 730 mm ellipse) and two separate instruments (FGS and AIRS) covering simultaneously 0.5-7.8 micron spectral range. The satellite is best placed into an L2 orbit to maximise the thermal stability and the field of regard. The payload module is passively cooled via a series of V-Groove radiators; the detectors for the AIRS are the only items that require active cooling via an active Ne JT cooler. The Ariel payload is developed by a consortium of more than 50 institutes from 16 ESA countries, which include the UK, France, Italy, Belgium, Poland, Spain, Austria, Denmark, Ireland, Portugal, Czech Republic, Hungary, the Netherlands, Sweden, Norway, Estonia, and a NASA contribution., Comment: Ariel Definition Study Report, 147 pages. Reviewed by ESA Science Advisory Structure in November 2020. Original document available at: https://www.cosmos.esa.int/documents/1783156/3267291/Ariel_RedBook_Nov2020.pdf/

International audience

The SuperCam instrument [1,2] onboard Mars2020 disposes of a variety of active and passive techniques, including passive spectroscopy in the 0.40-0.85 (VIS) and 1.3 to 2.6 microns (IR, [3,4]) wavelength ranges. Since the landing on Mars of Perseverance in February 2021, Supercam has acquired numerous observations of its near and distant environment, exploring the geological and mineralogical context of Jezero crater. In addition, several measurements were devoted to probing the atmosphere surrounding the Perseverance rover. The technique of using sky spectra in passive mode, known as "passive sky", has already been demonstrated with ChemCam on the Mars Science Laboratory (MSL) rover [4]. SuperCam provides a superset of the ChemCam capabilities used in [4], and in particular adds a near-infrared component that includes absorption and scattering characteristics of key gases and aerosols/clouds. "Passive sky" measurements have typically been performed every other week to allow a consistent monitoring of the seasonal evolution of the main quantities (CO2, O2, H2O, CO, aerosols/clouds). Particular attention was given to joint measurements of O2 and CO, as they appear as key components of the Martian chemical cycle and have never been measured together at the same time on the surface of Mars. As the 2 m wavelength region is used for the first time at the surface of Mars, it enables the detection of CO (around 2.35 m). CO possesses a small absorption that has made it difficult to identify in SuperCam spectra so far. An overview of SuperCam's progress to date in its attempt to characterize the Martian atmosphere at Jezero will be presented. References : [1] Wiens, R.C., et al. , 2021. Space Sci Rev 217, 4, [2] Maurice, S., et al., 2021. Space Sci Rev 217, 47, [3] Royer, C., et al.., 2020. Review of Scientific Instruments 91, 063105, [4] Fouchet, T., et al., 2021, Icarus, submitted. [5] McConnochie T. H et al., 2018. Icarus 307, 294

On July 14th, 2015, NASA’s New Horizons spacecraft flew by Pluto, revealing a complex atmosphere and surface seen nowhere else in the Solar System. Pluto’s surface ices are composed of molecular nitrogen N2, methane CH4, and carbon monoxide CO. During Pluto’s elliptical orbit, these ices undergo a sublimation/condensation cycle resulting in a tenuous atmosphere (~11 µbar at the surface). This atmosphere is mostly composed of N2 and CH4, with ~500 ppm of CO. Subjected to extreme ultraviolet radiation and Lyman-α photons, it is the place of photochemical aerosol production, aerosols being solid particles in suspension in the atmosphere. The exact processes of formation of these aerosols are however not well constrained yet. These solid particles, whose chemical composition and optical properties are unknown, are observed up to more than 350 km of altitude in the atmosphere of Pluto. Numerical models have shown that the presence of these aerosols in the atmosphere could have an impact on the atmospheric chemistry and climate of Pluto. Moreover, it has been suggested that these aerosols sediment and constitute a source of organic matter on the surface of Pluto.During my Ph.D., I used an experimental approach to study the aerosols of Pluto, from their formation in the upper atmosphere to their evolution on the surface, through their interactions with the atmosphere. The formation of Pluto’s aerosols by photochemistry and their chemical composition are the subjects of the first and second part of this Ph.D. thesis (Chapter III and Chapter IV). The interaction of Pluto’s aerosols with solar radiation and the contribution of photochemical aerosols as a coloring agent on the surface of Pluto are the subjects of the third and fourth part of this Ph.D. thesis (Chapter V and Chapter VI).The experimental setup PAMPRE (Production of Aerosols in Microgravity by REactive Plasma), located at LATMOS, has been used to simulate the atmospheric chemistry of Pluto and to synthesize analogues of photochemical aerosols, usually called "tholins". Experiments have also been performed at GANIL, using the IGLIAS (Irradiation of astrophysical ices) experimental setup. By irradiating tholins with heavy ions, the objective was to simulate the ageing of organic matter on the surface of Pluto due to the charged particles constituting the galactic cosmic rays.Thanks to the physicochemical analyses carried out to characterize the chemical composition of Pluto-simulated atmosphere as well as that of the synthesized aerosol analogues, I was able to conclude to the importance of N2 and CO reactivity in the atmospheric chemistry of Pluto. The nitrogen constituting the molecules produced in the gas phase and ultimately incorporated in the solid particles is included not only in the form of terminal functional groups (amine, nitrile, isocyanide), but also in the form of nitrogen heterocycles (triazine, pyrazole, pyrazine, pyrrole). Regarding oxygen, only terminal oxygenated chemical functions (alcohol, carboxylic acid, carbonyl) were detected. These nitrogenous and/or oxygenated organic molecules are responsible for a strong absorption in the ultraviolet spectral range by Pluto aerosol analogues and a more moderate absorption in the visible and near-infrared. These results are consistent with spectral observations of Pluto’s surface and atmosphere by instruments onboard New Horizons. Finally, thanks to the experiments of irradiation of Pluto aerosol analogues by heavy ions, I was able to conclude that the surface of Pluto is processed by galactic cosmic ray irradiation, probably explaining the characteristic featureless spectra of the Cthulhu region., Le 14 Juillet 2015, la sonde New Horizons de la NASA a survolé Pluton, révélant une atmosphère et une surface complexes observées nulle part ailleurs dans le Système Solaire. La surface de Pluton est composée de glaces de diazote N2, de méthane CH4, et de monoxyde de carbone CO. Au cours de l’orbite elliptique de Pluton, ces glaces subissent un cycle de sublimation/condensation à l’origine d’une atmosphère ténue (~11 µbar à la surface). Cette atmosphère est majoritairement composée de N2 et CH4, avec ~500 ppm de CO. Soumise au rayonnement ultraviolet extrême et aux photons Lyman-α, elle est le siège de la production d’aérosols photochimiques, des particules solides en suspension dans l’atmosphère. Les processus exacts de formation de ces aérosols ne sont toutefois pas encore bien définis. Ces particules solides, dont la composition chimique et les propriétés optiques sont inconnues, sont observées jusqu’à plus de 350 km d’altitude dans l’atmosphère de Pluton. Des modèles numériques ont montré que la présence de ces aérosols dans l’atmosphère pouvait avoir un impact sur la chimie atmosphérique et le climat de Pluton. De plus, il a été suggéré que ces aérosols sédimentent et constituent une source de matière organique à la surface de Pluton.Dans le cadre de ma thèse, j’ai utilisé une approche expérimentale afin d’étudier les aérosols de Pluton, de leur formation dans la haute atmosphère à leur devenir en surface, en passant par leurs interactions avec l’atmosphère. La formation des aérosols de Pluton par photochimie et leur composition chimique sont les sujets de la première et de la deuxième partie de cette thèse de Doctorat (Chapitre III et Chapitre IV). L’interaction des aérosols de Pluton avec le rayonnement solaire et la contribution des aérosols photochimiques en tant qu’agent colorant à la surface de Pluton sont les sujets de la troisième et de la quatrième partie de cette thèse de Doctorat (Chapitre V et Chapitre VI).Le dispositif expérimental PAMPRE (Production d’Aérosols en Microgravité par Plasma REactif), situé au LATMOS, a été utilisé afin de simuler la chimie atmosphérique de Pluton et synthétiser des analogues d’aérosols photochimiques, communément appelés "tholins". Des expériences ont également été réalisées au GANIL, en utilisant le dispositif expérimental IGLIAS (Irradiation de GLaces d’Intérêt Astrophysique). En irradiant les tholins avec des ions lourds, l’objectif était de simuler le vieillissement de la matière organique à la surface de Pluton dû aux particules chargées constituant le rayonnement cosmique galactique.Grâce aux analyses physico-chimiques effectuées, tant pour caractériser la composition chimique de l’atmosphère simulée de Pluton que celle des analogues d’aérosols synthétisés, j’ai pu conclure à l’importance de la réactivité de N2 et CO dans la chimie atmosphérique de Pluton. L’azote constituant les molécules produites en phase gazeuse et incorporées ultimement dans les particules solides est inclus non seulement sous la forme de fonctions chimiques terminales (amine, nitrile, isonitrile), mais aussi sous la forme d’hétérocycles azotés (triazine, pyrazole, pyrazine, pyrrole). Quant à l’oxygène, seules des fonctions chimiques oxygénées terminales (alcool, acide carboxylique, carbonyle) ont été détectées. Ces molécules organiques azotées et/ou oxygénées sont responsables d’une forte absorption dans le domaine spectral ultraviolet par les analogues d’aérosols de Pluton et une absorption plus modérée dans le visible et l’infrarouge proche. Ces résultats sont cohérents avec les observations spectrales faites de la surface et de l’atmosphère de Pluton par les instruments à bord de la sonde New Horizons. Enfin, grâce aux expériences d’irradiation des analogues d’aérosols de Pluton par des ions lourds, j’ai pu conclure au vieillissement de la surface de Pluton par irradiation par le rayonnement cosmique galactique, expliquant probablement les spectres caractéristiques de la région Cthulhu.

International audience; Titan is one of the most promising bodies in the solar system from the astrobiological perspective in particular because of its large organic content in the atmosphere and on the surface. These chemical species evolve with time. We performed an analysis of spectra acquired by Cassini/CIRS at high resolution which cover the far-IR range from 10 to 1500 cm-1 since the beginning and until the last year of the Cassini mission in 2017 and describe the temperature and composition variations near Titan's poles and at the equator over almost two Titan seasons ([1-3]. By applying our radiative transfer code (ARTT) to CIRS data and to the 1980 Voyager 1 flyby values inferred from the re-analysis of the Infrared Radiometer Spectrometer (IRIS) spectra, as well as to the intervening ground-and space-based observations (such as with ISO), we study the stratospheric evolution over a Titanian year (V1 encounter Ls=9° was reached in mid-2010) [1,2]. CIRS nadir and limb spectral together show variations in temperature and chemical composition in the stratosphere during the Cassini mission, before and after the Northern Spring Equinox (NSE) and also during one Titan year. After the 2010 equinox we have thus reported on monitoring of Titan's stratosphere near the poles and in particular on the observed strong temperature decrease and compositional enhancement above Titan's southern polar latitudes since 2012 and until 2014 of several trace species, such as complex hydrocarbons and nitriles, which were previously observed only at high northern latitudes. This effect followed the transition of Titan's seasons from northern winter in 2002 to northern summer in 2017, while at that latter time the southern hemisphere was entering winter. Our data show a continued decrease of the abundances which we first reported to have started in 2015. The 2017 data we have acquired and analyzed here are important because they are the only ones recorded since 2014 close to the south pole in the far-infrared nadir mode at high resolution. A large temperature increase in the southern polar stratosphere (by 10-50 K in the 0.5 mbar-0.05 mbar pressure range) is found and a change in the temperature profile's shape. The 2017 observations also show a related significant decrease in most of the abundances which must have started sometime between 2014 and 2017 [3]. In our work, we show that the equatorial latitudes remain rather constant throughout the Cassini mission. We have thus shown that the south pole of Titan is now losing its strong enhancement, while the north pole also slowly continues its decrease in gaseous opacities. It would have been interesting to see when this might happen, but the Cassini mission ended in September 2017. Perhaps future ground-based measurements can pursue this investigation and monitor Titan's atmosphere to characterize the seasonal events. We have obtained thus significant results which set constraints on GCM and photochemical models.

The objective of this thesis is the analysis of extraterrestrial dust collected in Antarctica: chondritic Antarctic micrometeorites (AMMs) and ultracarbonaceous micrometeorites (UCAMMs). Models predict that 80% of the dust that falls to Earth is of cometary origin. AMMs share many characteristics with the cometary dust reported by the Stardust space mission, and the characteristics of UCAMMs suggest formation at very low temperatures, far from the early sun. Micrometeorites therefore offer an opportunity to understand the mechanisms of cometary dust formation. UCAMMs are mostly composed of an organic matrix containing small mineralogical assemblages. The large amount of organic matter (OM) present in UCAMMs allows its analysis without using the classical extraction methods used to extract insoluble organic matter (IOM) from meteorites. Analyses of the AMMs by Raman and infrared microspectroscopy indicate a polyaromatic OM with a high degree of disorder, with characteristics close to those of the cometary grains reported by the Stardust mission. The variability of the OM spectral parameters is however more important for hydrated chondritic AMMs than for those without phyllosilicates. The mid- and far-infrared spectra show that the non-hydrated AMMs contain pyroxene and olivine silicates and that the aqueous phases of the hydrated AMMs are mainly phyllosilicates. Infrared and Raman analyses of the UCAMMs show a relatively large amount of nitrogen in the organic matter, and the occasional presence of nitrile groups. Spatially resolved X-ray transmission microscopy (STXM-XANES) analyses of the OM show the presence of 3 organic phases of distinct compositions within the UCAMM OM. The nitrogen present in the UCAMMs is carried by only one of these three phases, which has N/C atomic ratios up to 0.2. The inorganic phases contained in the UCAMMs were analysed by transmission electron microscopy. They exist as isolated phases, or as small mineral assemblages in the organic matrix, or as aggregates of different minerals, often cemented by a silicon-rich matrix. A mineral with a texture similar to that of a phyllosilicate was observed in one of the UCAMMs analysed. The similarity between the organic matter of UCAMMs and that of cometary particles suggests that these objects were formed in the outer regions of the protoplanetary disk. The joint presence of high-temperature-forming minerals and hydrated minerals within this organic matter implies a transport mechanism from the inner to the outer regions of the protoplanetary disk. The observation of a potential phyllosilicate in UCAMMs also raises the question of the possibility of aqueous alteration directly on cometary surfaces. However, the presence of hydrated phases within cometary material could also result from the accretion of already altered grains on a previous parent body. Micrometeorites in general thus offer a unique tool for the study of the asteroid-comet continuum highlighted since the return of the Stardust mission samples, and for a better understanding of the relationships between the different objects of the young solar system and the space weathering mechanisms they have undergone., L’objectif de cette thèse est l'analyse de poussières extraterrestres collectées en Antarctique : les micrométéorites antarctiques chondritiques (AMMs) et les micrométéorites ultracarbonées (UCAMMs). Les modèles prédisent que 80% de la poussière qui tombe sur Terre est d'origine cométaire. Les AMMs partagent de nombreuses caractéristiques avec les poussières cométaires rapportées par la mission spatiale Stardust, et les caractéristiques des UCAMMs suggèrent une formation à très basse température, loin du soleil primitif. Les micrométéorites offrent donc une opportunité de comprendre les mécanismes de formation des poussières cométaires. Les UCAMMs sont majoritairement constituées d'une matrice organique contenant de petits assemblages minéralogiques. La grande quantité de matière organique (MO) présente dans les UCAMMs permet son analyse sans faire usage des méthodes d'extraction classiques utilisées pour extraire la matière organique insoluble (IOM) des météorites. L'analyse des AMMs par microspectroscopie Raman et infrarouge indique une MO polyaromatique présentant un fort degré de désordre, avec des caractéristiques proches de celles des grains cométaires rapportés par la mission Stardust. La variabilité des paramètres spectraux de la MO est cependant plus importante pour les AMMs chondritiques hydratées que dans celles ne contenant pas de phyllosilicates. Les spectres dans l'infrarouge moyen et lointain montrent que les AMMs non hydratées contiennent des silicates de type pyroxènes et olivines et que les phases aqueuses des AMMs hydratées sont principalement des phyllosilicates. Les analyses infrarouge et Raman sur les UCAMMs montrent une quantité relativement importante d'azote dans la matière organique, et la présence ponctuelle de groupements nitriles. Des analyses de la MO résolue spatialement par microscopie X en transmission (STXM-XANES) montrent la présence de 3 phases organiques de compositions distinctes au sein de la MO des UCAMMs. L'azote présent dans les UCAMMs n'est porté que par une de ces trois phases, qui présente des rapports atomiques N/C allant jusqu'à 0,2. Les phases inorganiques contenues dans les UCAMMs ont été analysées par microscopie électronique en transmission. Elles existent comme phases isolées, ou sous forme de petits assemblages minéraux dans la matrice organique, ou comme d’agrégats de différents minéraux, souvent cimenté par une matrice riche en silicium. Un minéral présentant une texture similaire à celle d'un phyllosilicate a été observé dans une des UCAMM analysées. La similarité entre la matière organique des UCAMMs et celle des particules cométaires suggère une formation de ces objets dans les régions externes du disque protoplanétaire. La présence conjointe de minéraux se formant à haute température et de minéraux hydratés au sein de cette matière organique implique un mécanisme de transport des régions internes vers les régions externes du disque protoplanétaire. L'observation d'un phyllosilicate potentiel dans les UCAMMs soulève aussi la question de la possibilité d'altération aqueuse directement sur les surfaces cométaires. Cependant, la présence de phase hydratées au sein de matériel cométaire pourrait également résulter de l'accrétion de grains déjà altérés sur un précédent corps parent. Les micrométéorites en général offrent donc un outil unique pour l'étude du continuum astéroïde-comète mis en évidence depuis le retour des échantillons de la mission Stardust, et pour mieux comprendre les relations entre les différents objets du système solaire jeune ainsi que les mécanismes d'altération qu'ils ont subis.

Europa is a Jupiter’s moon covered with a water-ice layer, hiding a global liquid water ocean approximately 100 km thick. Europa’s interior is heated by the tidal forces induced by Jupiter, that provide enough energy to maintain a vigorous geological activity on this moon. Europa’s surface is very young, with an age estimated around 70-90 Ma, which demonstrates a recent resurfacing of the moon. Various geological features have been identified at Europa’s surface, and some of them, like the smooth plains, domes and chaos might indicate the presence of sub-surface reservoirs of liquid water or brines (cryomagma). In this thesis, we propose a cryovolcanic eruption model from a cryomagma reservoir stored in the ice crust. The overpressure generated during the cryomagma freezing could be high enough to fracture the ice crust and let the cryolava rise toward the surface and spread on it. This predictive model allows us to know the duration of an eruption, and the total cryolava volume erupted as a function of the reservoir depth in the ice crust. It also allows us to calculate the pressure in the reservoir and the fluid velocity in the fracture during the eruption. We investigated the influence of the cryomagma composition and the ice crust rheology on the possibility of an eruption. We finally modeled the deformation of a reservoir stored in a viscoelastic ice crust. A few images taken by the Galileo spacecraft during the 1990’s show quasi-circular smooth features, that may be interpreted as cryolava flows. We wanted to use these images to constrain our eruption model by measuring the volume of these objects. To do this, we generated digital elevation models (DEMs) of these images thank to the photoclinometry technique. We used the AMES StereoPipeline (ASP) tool, provided by the NASA. We estimated the uncertainties on the DEMs produced by the ASP by doing a sensitivity study of this tool. We also measured the volume of four smooth plains and deduced the size of reservoir needed to generate these thanks to our eruption model. Two missions, JUICE (ESA) and Europa Clipper (NASA) will be launch in the next years and should provide new insights on Europa’s sub-surface. In this context, this thesis could help to select the zones the more likely to show biosignatures. The smooth plains studied in this thesis might be linking the interior and the surface of the Europa, which could present a great interest for the future exploration of this moon., Europe est une lune de Jupiter couverte de glace d’eau, et abritant un océan interne global d’eau liquide d’une centaine de kilomètres d’épaisseur. L’intérieur d’Europe est réchauffé par les forces de marées induites par la présence de Jupiter, qui fournissent une quantité d’énergie suffisante à maintenir une activité géologique vigoureuse sur ce satellite. La surface d’Europe est très jeune avec un âge estimé à 70-90 Ma, ce qui démontre son ressurfaçage récent. De nombreuses structures géologiques ont été identifiées à la surface d’Europe, et certaines comme les plaines lisses, les dômes ou les dépôts sombres pourraient indiquer la présence de réservoirs d’eau liquide ou de saumures (cryomagma) stockés dans la couche de glace. Nous proposons dans cette thèse un modèle d’éruption cryovolcanique depuis un réservoir de cryomagma contenu dans la couche de glaces. Le moteur de l’éruption est la surpression générée dans le réservoir par le gel du cryomagma, qui peut être suffisante pour entrainer la fracturation de la couche de glaces sus-jacente et laisser les cryolaves se répandre en surface. Ce modèle prédictif permet de connaître les caractéristiques d’une éruption telles que sa durée et le volume de cryolave émis en surface en fonction de la profondeur du réservoir. Il permet aussi d’évaluer la pression dans le réservoir et la vitesse du fluide s’en échappant au court de l’éruption. Nous avons testé l’influence de la composition du cryomagma et de la rhéologie de la couche de glace sur la faisabilité d’une éruption. Nous avons notamment modélisé la déformation d’un réservoir contenu dans une couche de glace viscoélastique. Quelques images d’Europe prises par la sonde Galileo dans les années 1990 montrent des structures lisses quasi-circulaires que nous interprétons comme de possibles écoulements de cryolaves à la surface. Nous avons souhaité utiliser le volume de ces objets afin de contraindre notre modèle d’éruption. Pour ce faire, nous avons généré des modèles numériques de terrain (MNT) de ces images grâce à la photoclinométrie, et plus particulièrement avec l’AMES StereoPipeline (ASP) fourni par la NASA. Nous avons porté une attention particulière à l’estimation des incertitudes sur les MNT en menant une étude de sensibilité de l’ASP. Nous avons pu mesurer le volume de quatre plaines lisses, et en déduire la taille des réservoirs de cryomagma requis pour les créer lors d’éruptions. Les missions JUICE (ESA) et Europa Clipper (NASA) devraient partir dans les prochaines années et permettront une étude plus poussée de la surface d’Europe. Cette thèse a pour vocation d’aider à la sélection des zones les plus susceptibles de présenter des bio-signatures en vue de ces missions. Les plaines lisses étudiées dans cette thèse peuvent possiblement représenter des zones d’échange d’eau liquide entre la surface et la sub-surface d’Europe, et sont donc d’un grand intérêt pour l’exploration future de cette lune.

We outline a flagship-class mission concept focused on studying Titan as a global system, with particular emphasis on the polar regions. Investigating Titan from the unique standpoint of a polar orbit would enable comprehensive global maps to uncover the physics and chemistry of the atmosphere, and the topography and geophysical environment of the surface and subsurface. The mission includes two key elements: (1) an orbiter spacecraft, which also acts as a data relay, and (2) one or more small probes to directly investigate Titan's seas and make the first direct measurements of their liquid composition and physical environment. The orbiter would carry a sophisticated remote sensing payload, including a novel topographic lidar, a long-wavelength surface-penetrating radar, a sub-millimeter sounder for winds and for mesospheric/thermospheric composition, and a camera and near-infrared spectrometer. An instrument suite to analyze particles and fields would include a mass spectrometer to focus on the interactions between Titan's escaping upper atmosphere and the solar wind and Saturnian magnetosphere. The orbiter would enter a stable polar orbit around 1500 to 1800 km, from which vantage point it would make global maps of the atmosphere and surface. One or more probes, released from the orbiter, would investigate Titan's seas in situ, including possible differences in composition between higher and lower latitude seas, as well as the atmosphere during the parachute descent. The number of probes, as well as the instrument complement on the orbiter and probe, remain to be finalized during a mission study that we recommend to NASA as part of the NRC Decadal Survey for Planetary Science now underway, with the goal of an overall mission cost in the "small flagship" category of ~$2 bn. International partnerships, similar to Cassini-Huygens, may also be included for consideration., 13 pages, white paper submitted to the NRC Decadal Survey for Planetary Science and Astrobiology

International audience

Flux transfer events (FTEs) are transient phenomena frequently observed at the Earth's magnetopause. Their usual interpretation is a flux rope moving away from the reconnection region. However, the Magnetospheric Multiscale Mission revealed that magnetic reconnection sometimes occurs inside these structures, questioning their flux rope configuration. Here we investigate 229 FTE‐type structures and find reconnection signatures inside 19% of them. We analyze their large‐scale magnetic topology using electron heat flux and find that it is significantly different across the FTE reconnecting current sheets, demonstrating that they are constituted of two magnetically disconnected structures. We also find that the interplanetary magnetic field (IMF) associated with reconnecting FTEs presents a strong By component. We discuss several formation mechanisms to explain these observations. In particular, the maximum magnetic shear model predicts that for large IMF By, two spatially distinct X lines coexist at the magnetopause. They can generate separate magnetic flux tubes that may become interlaced.

International audience; The Cassini Langmuir Probe (LP) data acquired in the ionosphere of Titan are re-analysed to finely study the electron behaviour in the birthplace of Titan's aerosols (900-1200 km). The detailed analysis of the complete Cassini LP dataset below 1200 km (57 flybys) shows the systematic detection of 2 to 4 electron populations, with reproducible characteristics depending on altitude and solar illumination. Their densities and temperatures are deduced from the Orbital Motion Limited theory. Statistical correlations with other quantities measured by Cassini are investigated. We finally discuss the origins of the detected populations, one being possibly emitted by aerosols.

International audience; During the early stages of a protoplanetary disk, it is expected that the temperatures reached in the disk will lead to total or partial vaporization of dust, followed by condensation upon cooling. Similarly, chondrule forming events or giant impacts followed by magma oceans can also produce partial evaporation. Thus, moderately volatile elements can be mobilized during these thermal events, thereby leading to characteristic isotope signatures that can be used to decipher the conditions of elemental fractionation. Indeed, the magnitude of isotope fractionation of moderately volatile elements is directly modulated by the partial pressure of the element of interest. Thus, the isotope fractionation pattern for a given level of elemental depletion can be used to infer the 2 pressure conditions during condensation or evaporation, thus providing strong constraints on astrophysical settings. The observations made on moderately volatile elements or on some major elements such as Mg, Si, or Fe isotopes demonstrate that the isotope signature is most generally more subdued than that of vacuum evaporation producing the maximum isotope fractionation. Thus, experimental studies showing the existence of kinetic isotope fractionation associated with evaporation experiments are not sufficient to interpret cosmochemical data. In this study, we show that the evaporation or condensation coefficients may play a key role in controlling isotope fractionation. The possible role of composition and temperature on the values of evaporation/condensation coefficients are emphasized. Similarly, the role of diffusion in the gas phase leading to a back reaction of condensation during evaporation (or vice-versa) is addressed. In addition, we demonstrate that a new expression linking elemental depletion and isotope fractionation needs to be used in the case of evaporation or condensation in a closed system. Specifically, for condensation in a closed system, one needs to take into account the effect of decreasing oversaturation to model isotope fractionation. We also explored the effect of having a population of grains rather than a single grain on isotope fractionation associated with evaporation on the isotope trajectories. Last, the case of evaporation with multiple species produces a situation where the isotope fractionation pattern is modified. Overall, this study demonstrates a wealth of behaviors in isotope tracers associated with volatile loss that needs to be carefully investigated to fully exploit the information carried by them.

International audience; Introduction: UltraCarbonaceous Antarctic Mi-croMeteorites (UCAMMs) are interplanetary dust particles that exhibit large concentrations of organic matter with high N concentrations and extreme D/H ratios [1-4]. The mineralogy, the elemental and isotopic composition of UCAMMs indicate that they most likely originate from the cometary reservoir [1, 2, 5]. Most UCAMMs exhibit large variations on D/H, 15 N/ 14 N and 13 C/ 12 C ratios at the micron or sub-micron scale. These isotopic fractionations are carried by the organic matter and their origin is still an open question. We showed that the precursors of UCAMMs can be formed by irradiation with high energy ions of N-rich ice mixtures with hydrocarbons, a process likely to take place at the surface of icy bodies orbiting beyond a nitrogen snow line and irradiated by galactic cosmic rays [2, 6]. Recent experimental simulations showed that the irradiation itself does not induce large D fractionation, but that the refractory organic residue resulting from irradiation of isotopically heterogeneous ice mixtures can exhibit large D/H spatial variation at the micron scale [7]. We performed a new series of experiments on D, 15 N and 13 C labelled ices to study the transmission of the isotopic labelled ice layers to the irradiation-induced residue. Material and method: Irradiation experiments of ices were conducted with the low-energy beam (Irrsud, 0.5-1 MeV/n) at GANIL (Caen, France). We used the IGLIAS experimental setup [8] which allows to deposit and irradiate complex ice films mixtures on substrate windows held at temperatures ranging from 8K to 300K (Figure 1). The evolution of the ices during the irradiation was monitored in situ with a Brucker Vertex 70v Fourier transform infrared (FTIR) spectrometer. The gas mixtures deposited are controlled with a Quadrupole Mass Spectrometer (QMS). We followed the same protocol as described in [7]. We first irradiated a mixture of ices made of two equally thick layers of 14 N2-CH4 (90:10) of about 5 µm each surrounding a thin layer of isotopically labeled (in D, 13 C and 15 N) ice with a thickness of about 0.2 µm. The ice films were formed by gas injections on ZnSe windows at 8K. The thickness of the central isotopically labeled ice layer was estimated from the volume of gases injected (i.e. 2% of the total thickness). The overall thickness of the ice sandwiches (11 µm) were

International audience; The search for organic molecules at the surface of Mars is a key objective in astrobiology, given that many organic compounds are possible biosignatures and their presence is of interest with regard to the habitability of Mars. Current environmental conditions at the martian surface are harsh and affect the stability of organic molecules. For this reason, and because current and future Mars rovers collect samples from the upper surface layer, it is important to assess the fate of organic molecules under the conditions at the martian surface. Here, we present an experimental study of the evolution of uracil when exposed to UV radiation, pressure, and temperature conditions representative of the surface of Mars. Uracil was selected because it is a nucleobase that composes RNA, and it has been detected in interplanetary bodies that could be the exogenous source of this molecule by meteoritic delivery to the surface of Mars. Our results show that the experimental quantum efficiency of photodecomposition of uracil is 0.16 ± 0.14 molecule/photon. Although these results suggest that uracil is quickly photodegraded when directly exposed to UV light on Mars, such exposure produces dimers that are more stable over time than the monomer. The identified dimers could be targets of interest for current and future Mars space missions.

International audience; Natural emissions of whistler-mode electromagnetic waves, especially chorus and hiss, can influence the dynamics of the Van Allen radiation belts via quasi-linear or nonlinear wave particle interactions. They can play a role in complex processes of the energy transfer between different electron populations. To separate temporal and spatial variations of their characteristics, measurements at different points in space are necessary. We show initial results of measurements of the Cluster space fleet during the period of close separations between Cluster 3 and Cluster 4 from September to December 2018. As the separations of these spacecraft decrease down to 3 km in the equatorial source region of chorus we can perform systematic phase measurements of nonlinear wave packets of chorus. The embedded fine structure of sub-packets is particularly interesting in this context because their spatio-temporal scales have been shown to be much shorter compared to scales of the chorus wave packets. We use detailed waveform measurements of the WBD instruments onboard Cluster 3 and Cluster 4 close to the equator, with Cluster 1 and/or Cluster 2 located at much larger separations at higher latitudes. These detailed measurements are put in the context of overall wave propagation and polarization patterns by multi-component data of the STAFF-SA instruments onboard all the 4 Cluster spacecraft, with the FGM instruments used to define the magnetic field-aligned coordinate system and to normalize the measured frequencies by the electron cyclotron frequency.

International audience; Using a novel approach, we reanalyzed data acquired by the GCMS instrument aboard Huygens during its descent to Titan. We were able to retrieve concentration of several key volatile species in Titan's troposphere and their vertical profiles.

International audience; The discovery of haze in Pluto's atmosphere on July 14 th , 2015, has raised lots of questions. To help understand the data provided by the New Horizons spacecraft, Pluto's aerosols analogues were synthetized and their chemical composition was determined by high-resolution mass spectrometry (Orbitrap technique).

International audience; Pluto's fly-by by the New Horizons spacecraft in July 2015 has revealed a dark reddish equatorial region (informally named Cthulhu). The non-icy material constituting the terrains of this region may have been formed from the sedimentation of aerosols [1,2]. Here, we investigate this hypothesis through the interpretation of the data collected by the visible imager (MVIC) and the near-infrared spectrometer (LEISA). Analogs (tholins) of Pluto's aerosols were synthesized in conditions that mimic Pluto's high atmosphere, and their optical properties were determined and used in Hapke models. We show that some of these tholins fit the reflectance level fairly well in the near-infrared, but don't match the shape of the red visible slope. In addition, several tholin bands are absent in LEISA observations, which might be due to a highly porous crust (formed from ice/tholin sublimation or microgravity), or to GCR irradiation. The first is our preferred interpretation.

International audience; Introduction: Asteroids are super-kilometer-sized bodies formed by gravitational instability in turbulent regions of the protoplanetary disk. Hydrated C-type asteroids −the most common bodies in the main asteroid belt experienced subsequent heating due to heat released by the decay of 26 Al. However, quantitative estimation of their thermal histories has not yet been possible, leading to considerable uncertainty on the physical characteristics of early-formed primitive rocky bodies. Aqueously-formed carbonaceous chondritic minerals such as carbonates represent direct snapshots of the asteroidal fluids and can in theory be used to decipher their thermal evolution. However, determining carbonate precipitation temperatures requires knowing the O-isotopic compositions of their parent fluids , which itself requires to know the carbonate precipitation temperatures, leading to a seemingly endless problem. Here we report in situ O-isotopic analyses of Ca-carbonates and propose a new isotopic alteration model that reconciles petrographic observations and formation temperatures of CM carbonates. Methods: Detailed observations of calcite grains in polished sections of the CM2 Murchison and Mukundpura were made using a scanning electron microscope (SEM) JEOL JSM-6510 equipped with an Energy Dispersive X-ray (EDX) Genesis detector. Their oxygen isotopic compositions were determined using a CAMECA ims 1280 HR2 ion microprobe at CRPG (Nancy, France). Results: Only calcite grains surrounded by serpentine (hereafter T1 calcite) were found in the two polished sections of Murchison. O-isotopic measurements show that Murchison's T1 calcites have δ 18 O values between 25.5 and 41.5‰, δ 17 O values between 14.5 and 23.5‰ and Δ 17 O values between-1.1 and 1.8‰ (n = 24). In contrary, two types of carbonates were found in the polished section of Mukundpura: (i) T1 calcite grains and (ii) polycrystalline grains of calcite containing Fe-Ni sulfide inclusions (hereafter T2 calcite). O-isotopic analyses on Mukundpura's Ca-carbonates reveal that (i) T1 calcites have δ 18 O values between 27.4 and 38.2‰, δ 17 O values between 13.3 and 18.5‰ and Δ 17 O values between-1.4 and-0.2‰ (n = 8), whereas (ii) T2 calcites have δ 18 O values between 12.4 and 18.6‰, δ 17 O values between 4.2 and 7.3‰ and Δ 17 O values between-4 and-0.9‰ (n = 13). Discussion: Our data define a mass-independent trend that is similar, within errors, from those commonly reported in different CM chondrites [1-3]. In first approximation, this trend suggest that the O-isotopic compositions of CM carbonates is essentially controlled by variable degrees of isotopic exchanges between 16 O-rich anhydrous silicates and a 17-18 O-rich fluid [4]. However, when considering only T1 calcites, their O-isotopic compositions define a distinct trend that is indistinguishable, within errors, from the TFL (i.e., average Δ 17 O =-0.4 ± 1.0). Conversely , T2 calcites exhibit clustered δ 17 O-δ 18 O values with average Δ 17 O of-2.6 ± 1.0, which artificially generate the aforementioned mass-independent trend. This demonstrates that petrographic observations of carbonates are essential for understanding the O-isotopic evolution of asteroidal fluids and the constraints they bear. Direct estimations of the O-isotopic composition of asteroidal alteration fluids was possible thanks to CO 2 clumped-isotope thermometry (Δ 47 , [5]). Based on measurements performed on the T1 calcite-dominated CM chon-drites Murchison and Murray, this led to alteration fluids ranging from δ 18 O = 2 ‰ and Δ 17 O =-0.55 ‰ to δ 18 O = 6.8 ‰ and Δ 17 O =-0.49 ‰. As these fluids experienced oxygen isotopic exchanges with the anhydrous CM chondrite protolith (δ 18 O =-3.8 ‰, δ 17 O =-6.5 ‰; [6]), they define two trends that delimit the possible O-isotopic compositions of the alteration fluids. Considering these extreme trends, the precipitation temperatures of each calcite and serpentine can be calculated according their respective isotopic fractionation factor α. Our isotopic approach allows a formation sequence of CM secondary phases to be proposed, characterized by a temperature increase from T1 calcites < serpentines < T2 calcites. This implies that fluid circulation in CM parent body-(ies) occurs during a prograde evolution of the temperature, where T1 calcites formed first at T = 0-30 °C, followed by the precipitation of (Fe,S)-rich serpentine and tochilinite at T = 30-100°C and then T2 calcites at T = 110-140°C.

International audience; The sub µm-scale characterization of secondary phases in a compound Ca and Al rich inclusion (CAI) suggests that some of these phases were formed in the nebular gas before the coagulation of the proto-CAIs.

We analyse images of comet C/1858 L1 (Donati) in the sky of Paris published in books by Amédée Guillemin and Camille Flammarion., Nous poursuivons ici nos analyses des gravures de la comète C/1858 L1 (Donati) représentée dans le ciel de Paris. Nous avions commenté la gravure parue dans Les Comètes de Guillemin (1875), la figurant au-dessus de la Conciergerie et en avions souligné les inexactitudes. Nous nous intéressons ici à une autre représentation parue dans Le Ciel (édition de 1877) du même Guillemin, la montrant cette fois-ci au-dessus de la cathédrale Notre-Dame, ainsi qu'à des illustrations parues dans des ouvrages de Flammarion. Ici encore, l'exactitude scientifique a été abandonnée pour des raisons esthétiques.

International audience; The ExoMars Trace Gas Orbiter (TGO), a mission by ESA and Roscosmos, was launched in March 2016 and reached its final, near-circular 400 km orbit around Mars in March, 2018. On board TGO, the Atmospheric Chemistry Suite (ACS) is a set of three spectrometers including a thermal-infrared channel, TIRVIM. This Fourier-transform spectrometer covers the range 600-6000 cm-1 (1.7-17μm) with a spectral resolution of 1.2 cm-1. We focus here on nadir observations in the range 600-1300 cm-1, which covers absorption by CO2 (centered at 667 cm-1), water ice clouds (centered at 820 cm-1) and dust (centered at 1100 cm-1). The advantage of the TIRVIM data set over previous instruments comes from the TGO orbit, which is not sun-synchronous and was designed to sample a complete daily cycle every 55 days. Hence, TIRVIM has the capacity to uniquely study both the diurnal and seasonal variability of the thermal structure, dust and ice cloud opacity. We have developed a radiative transfer model coupled to a retrieval algorithm that exploits TIRVIM spectra to simultaneously retrieve vertical profiles of the temperature from 5 to 45 km, surface temperature, and integrated optical depth of dust and water ice clouds. This algorithm was tested and validated against synthetic observations generated under various conditions (local time, seasons, latitude, aerosol load, ...). We have then applied this algorithm to the first 45 days of TIRVIM data acquired in March-April, 2018. The retrieved temperature profiles have been validated against thousands of co-located measurements acquired by the Mars Climate Sounder around 3am and 3pm, a limb-viewing radiometer onboard Mars Reconnaissance Orbiter. The agreement between the two data sets is very satisfactory. In particular, the amplitude of the diurnal thermal tide as seen by MCS is very well captured by TIRVIM at pressures greater than 10 Pa. However, TIRVIM underestimates it in the range 1-10 Pa, which is due to a much poorer vertical resolution in this region (as expected from a nadir-viewing sounder). We will present these results with an emphasis on the diurnal cycle of the atmospheric temperature and the aerosols load, along with comparisons with predictions from the LMD Mars GCM. Analysis of TIRVIM data acquired during the dust storm in June-July 2018 is in progress and will also be presented. Acknowledgements: The ACS experiment is led by IKI in Moscow. We acknowledge support by CNES and Roscosmos.

During my thesis, I numerically simulated the dynamical behaviour of dust and small grains around stars, applied to two ranges of stellar distance : debris disks and exozodis.Concerning debris disks, I focused on the fast moving arch-like structures observed over 15 years inside the disk of AU Mic. Supposing that they all come from a single parent body and that the dust composing the arches have the same dynamics, I showed that the parent body must be closer-in than the planetesimal belt (, Mon travail de thèse a porté sur la simulation numérique du comportement dynamique de poussières et de petits corps autour d’étoiles, appliqué à deux grands domaines de localisation : les disques de débris et les exozodis.Concernant les disques de débris, je me suis plus particulièrement intéressé aux arches mouvantes observées sur une période de 15 ans au sein du disque d’AU Mic. En supposant qu’elles proviennent toutes d’un corps parent unique et que les grains composant les arches ont la même dynamique que les arches elles-mêmes, j’ai montré que le corps parent doit être plus interne que la ceinture de planétésimaux (

International audience; New 3-μm spectral analyses of primitive outer main-belt asteroids are placed in the context of the current thermal and dynamical theories.

International audience; Quantification of the influence of collisional erosion during accretion on the budget of lithophile and refractory elements such as Sm and Nd.

Accepted for publication in Astronomy & Astrophysics; We present the analysis of ≈100 molecular maps of the coma of comet 67P/Churyumov-Gerasimenko obtained with the MIRO submillimeter radio telescope on board the Rosetta spacecraft. From the mapping of spectral lines of H 16 2 O, H 18 2 O, H 17 2 O, CH 3 OH, NH 3 and CO, and some fixed nadir pointings, we retrieved the outgassing pattern and total production rate for these species. The analysis covers the period from July 2014, inbound to perihelion, to June 2016, outbound, and heliocentric distances r h =1.24 to 3.65 AU. A steep evolution of the outgassing rates with heliocentric distance is observed, typically in r −6 h , with significant differences between molecules (e.g. steeper variation for H 2 O post perihelion than for methanol). As a consequence the abundances relative to water in the coma vary. The CH 3 OH and CO abundances increase after perihelion while the NH 3 abundance peaks around perihelion and decreases after. Outgassing patterns have been modeled as 2-D Gaussian "jets". The width of these jets is maximum around the equinoxes when the bulk of the outgassing is located near the equator. From July 2014 to Feb. 2015 the outgassing is mostly restricted to a narrower jet (Full Width at Half Maximum, FWHM ≈80 •) originating from high northern latitudes, while around perihelion most of the gaseous production comes from the southernmost regions (−80±5 • cometocentric latitude) forming a 100-130 • (FWHM) wide fan. We find a peak production of water of 0.8 × 10 28 molec. s −1 , 2.5 times smaller than measured by the ROSINA experiment, and put an upper limit to a 50% additional production that could come from the sublimation of icy grains. We estimate the total loss of ices during this perihelion passage to 4.18 ± 0.18 × 10 9 kg. We derive a dust-togas ratio in the lost material of 0.7 to 2.3 (including all sources of errors), based on the nucleus mass loss of 10.5 ± 3.4 × 10 9 kg estimated by the RSI experiment. We also obtain an estimate of the H 18 2 O/H 17 2 O ratio of 5.6 ± 0.8.

International audience; Planet–planet scattering is the leading mechanism to explain the broad eccentricity distribution of observed giant exoplanets. Here we study the orbital stability of primordial giant planet moons in this scenario. We use N-body simulations including realistic oblateness and evolving spin evolution for the giant planets. We find that the vast majority ( 80%–90% across all our simulations) of orbital parameter space for moons is destabilized. There is a strong radial dependence, as moons beyond 0.1 R Hill are systematically removed. Closer-in moons on Galilean-moon-like orbits (

The full range of 50 initial, Moon-orbit-forced superharmonic resonance periods is detected in the 1969-1977 time-series of all 12474 consecutive 0.02 Hz moonquakes from the Apollo Program catalog. The resonance is found forcing the strongest-energy (highest-fidelity) part of the 10 hours–100 days (27.78–0.115741 μHz) long-periodic band at 99–67% confidence as well as below. Resonance signatures of the Moon’s other four long tidal periods – synodic, anomalistic, nodical, and tropical – were also identified but not as separate drivers of body resonance. The spectra were computed using a least-squares spectral analysis method that enabled separation of the signal driver and noise signatures of all lunar tides, as well as extraction of the exact sequence of resonant subperiods affecting the solid Moon. Thus lunar seismotectonics is forced by the Moon’s orbital period as the disruptive phase that introduces nonlinearity into lunar vibration, giving rise to superharmonic resonance and probably the so-called free librations as well. The earlier computation of the Earth superharmonic resonance and this computation of the Moon superharmonic resonance constitute conclusive proof of the universality of body mechanical resonance in astronomical bodies, as well as of the driving role of geophysics as a catalyst of life.

International audience; Interstellar objects present a unique opportunity to sample material from another solar system. We need to be prepared for the next discoveries.

International audience; We performed 40 keV He+ and Ar+ ion irradiation of carbonaceous chondrites as a simulation of solar wind irradiation of carbonaceous asteroids. We determined which spectral features are more sensitive to the effects of space weathering.

The heavy elements are synthetized in black holes and expelled thanks to local supercriticities inside. These black hole eruptions produce pieces of heavy atoms catching with them some of the black hole, a wrapping event around that black hole produces the star (in case there is enough mass for sustained fission), planet / moon and nuclear fission is together with fusion the motor of stars. This is demonstrated through many levers. Gravitational waves are constituted by waves of neutrons, when they impact the ground they may trigger underground nuclear blasts, that produce magma caves (explaining volcano swarms). Black holes erupting from the inside of the stars produce hyper variations in the regime of brightness (eruptive variables for instance), and in planets or moons, effusive volcanism, as well as supercavitating bolides (fireballs such as the one causing the event of the Tunguska in 1908). The strike of gravitational waves may be powerful enough, in a rare case, to blast all nuclear plants working in continent-wide regions. Things such as the ridge on Iapetus, the “actinide boost” in stars, “earthquake lights” and the "crown of stars in the sky" (in religious texts) and can be explained thanks to this model.