Lightning is an important electrical phenomenon, known to exist in several Solar System planets. Amongst others, it carries information on convection and cloud formation, and may be important for pre-biotic chemistry. Exoplanets and brown dwarfs have been shown to host environments appropriate for the initiation of lightning discharges. In this PhD project, I aim to determine if lightning on exoplanets and brown dwarfs can be more energetic than it is known from Solar System planets, what are the most promising signatures to look for, and if these "exo-lightning" signatures can be detected from Earth. This thesis focuses on three major topics. First I discuss a lightning climatology study of Earth, Jupiter, Saturn, and Venus. I apply the obtained lightning statistics to extrasolar planets in order to give a first estimate on lightning occurrence on exoplanets and brown dwarfs. Next, I introduce a short study of potential lightning activity on the exoplanet HAT-P-11b, based on previous radio observations. Related to this, I discuss a first estimate of observability of lightning from close brown dwarfs, with the optical Danish Telescope. The final part of my project focuses on a lightning radio model, which is applied to study the energy and radio power released from lightning discharges in hot giant gas planetary and brown dwarf atmospheres. The released energy determines the observability of signatures, and the effect lightning has on the local atmosphere of the object. This work combines knowledge obtained from planetary and earth sciences and uses that to learn more about extrasolar systems. My main results show that lightning on exoplanets may be more energetic than in the Solar System, supporting the possibility of future observations and detection of lightning activity on an extrasolar body. My work provides the base for future radio, optical, and infrared search for "exo-lightning".

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IVETA PASTYŘÍKOVÁ: ORDER, PROGRESS, AND IDEAL GOVERNMENT IN CLAUDIAN'S EPIC DE RAPTU PROSERPINAE ABSTRACT The aim of the diploma thesis is to show how late Ancient poet Claudius Claudianus deals with the problem of ideal government in the mythological epic De Raptu Proserpinae, by which strategies he exhorts his reader to evaluate Jupiter's rule in the world of the poem and to compare it with the situation in the real world. The chosen method is the theory of fictional worlds. Firstly, the thesis outlines the relation between the fictional world of the epic and the real world, then, the attention is paid to the essential question of this fictional world, ideal government. The thesis presents the prefaces of the epic as entrances into the fictional world foreshadowing topics elaborated in the world of the poem, where the ruler Jupiter has a difficult task ahead of him: to harmonize progress with protection against chaos. The last chapter summarizes the author's strategies and compares the epic with Claudian's other poems.

Far-ultraviolet (FUV) spectral images of Jupiter's moon Europa were obtained by the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) on 20 occasions between the years 1999 and 2015. In this thesis these data are analyzed to look for Lyman-alpha emissions from a hydrogen corona. This hydrogen corona was recently discovered in absorption, also from HST Lyman-alpha images but with Europa in transit of Jupiter, and the aim of this study is to confirm the existence of the corona also in emission. Europa's thin atmosphere is dominated by molecular oxygen, mainly produced by radiolysis and sputtering of the icy surface. Atomic hydrogen, the main target for this study, is produced by sputtering from the surface and the dissociation of H2 and H2O. It quickly escapes the gravity of Europa. To study the hydrogen corona in the spectral STIS images the data need to be processed to remove the other Lyman-alpha contributions to the image. These other contributions include emissions from the geocorona, emissions from the interplanetary medium (IPM), dark current in the detector and sunlight reflected from the surface of Europa. To estimate the contribution to the image from the hydrogen corona, a basic model of the expected emissions from the corona is developed. By fitting this model to the processed STIS data values of the hydrogen density and the surface Lyman-alpha albedo of the moon are obtained. The results confirm the presence of a hydrogen corona, with varying densities between the different observations but generally about twice as large as the results from the previous study. The uncertainty for the results is however large and there is a clear correlation between hydrogen density and background level in the image, for which the reason is poorly understood. No hemispheric variability or connections to the true anomaly of the moon are found, but the hydrogen density seems to be increasing during the time of the observations. The results for the albedo is consistent with previous results, indicating a lower albedo on the leading than on the trailing hemisphere.

Io is the innermost Galilean moon of Jupiter and is considered the most volcanically active body in our solar system. With the help of the Hubble Space Telescope’s (HST) on-board Space Telescope Imaging Spectrograph (STIS), far-ultraviolet (FUV) images of Io have been captured for the past 20 years. The final goal of this project is to study the sulphur dioxide (SO2) distribution and volcanic activity on Io in FUV data taken in 1997/98 and 2013/14. The method used concerns the conversion of spectral Lyman-α intensity to SO2 density using algorithms implemented in MATLAB. As a result the SO2 distribution and volcanic activity on Io were determined and compared between the data collections. We found that the SO2 was higher in the images from 1997/98 compared to 2013/2014.

In July 2031, a new chapter in the exploration of the Jovian system will begin with the arrival of the Jupiter Icy Moons Explorer (Juice) at Jupiter. Launched on April 14 2024 as part of ESA’s Cosmic Vision programme, the mission aims to study Jupiter and its icy Galilean moons Callisto, Europa, and Ganymede. Juice carries a whole suite of instruments for in-situ and remote ground observations, one of which is the Jovian plasma Dynamics and Composition analyser (JDC). As a part of the Particle Environment Package (PEP), the particle detector will measure the energy, mass, charge and arrival direction of ions and electrons in the Jovian magnetosphere. Spacecraft charging caused by interactions between the spacecraft and its surrounding plasma environment poses a significant problem for JDC because the electrostatic potential of the spacecraft accelerates/decelerates charged particles, resulting in distorted measurements, particularly for the lowest energy particles.  In this report, we show the results of spacecraft charging and instrument simulations performed in the Spacecraft Plasma Interaction System (SPIS) for the solar wind and Earth’s magnetosheath—two environments that Juice will encounter at the start of the cruise phase. We found that the conductive surfaces that cover the majority of the spacecraft become positively charged as a result of a large photoelectron current in both the solar wind and magnetosheath environments. We show that these surfaces are expected to reach potentials of 9 V in the solar wind and 4 V in the magnetosheath. The four radiators on Juice that are covered with dielectric paint and shaded by the sun shield become negatively charged in both simulated environments. The radiator potentials can be as low as -40 V in the solar wind and -100 V in the magnetosheath. We also conclude that due to blocking by the spacecraft main body, the ion population cannot be sampled in the solar wind unless a spacecraft roll is performed. Furthermore, due to the high ion f low energy, spacecraft charging will not influence JDC measurements in this environment.  In the magnetosheath, the ion population can be sampled by JDC, and we identified three distortion mechanisms: (1) repulsion by the main body, (2) attraction by two of the radiators, and (3) repulsion by the MAG boom. Of all the distortion modes, the one originating from a negatively charged (-67.8 V) radiator close to JDC is the strongest, affecting ions with energies above 80 eV. The least powerful but most prevalent mode is the repulsion of ions by the main body. Our results can be compared with future in-situ measurements to identify distortion mechanisms well ahead of the science phase in which the scientifically important measurements will be carried out.

Connaître en détail la structure interne d'un corps suppose une analyse sismique. La structure interne de Jupiter reste mal contrainte par les observations. Ce travail de these s'inscrit dans deux projets instrumentaux, conçus pour la sismologie jovienne : JOVIS, un projet de photométrie spatiale et SYMPA un interféromètre imageur multi-site. Le principe de JOVIS considère Jupiter tel un miroir réfléchissant la lumière solaire. Ce travail montre comment les nuages réagissent aux oscillations et présentent une amplification des variations relatives d'albédo d'un facteur 70. De telles variations sont mesurables depuis l'espace, par photométrie à haute précision. Le principe de SYMPA est la mesure du champ de vitesse, lié aux oscillations, par mesure du décalage Doppler. Trois campagnes ont été menées : les performances instrumentales sont conformes aux attentes et le dépouillement des données est en cours. Enfin, une méthode d'identification des modes d'oscillations dans un signal bruité a été développée.

Les développements techniques récents en radioastronomie au sol ont permis l'émergence de nombreux nouveaux projets. LOFAR (le "LOw Frequency ARray") est un interféromètre de réseaux phasés comptant parmi ces nouveaux radiotélescopes géants. Son architecture distribuée à travers l'Europe comprend plusieurs milliers d'éléments regroupés en "stations". Il permet d'étudier l'Univers dans la fenêtre radio ~20-250 MHz, inexplorée avec une très haute sensibilité et de très hautes résolutions angulaire, temporelle et spectrale. La station LOFAR de Nançay a permis à la communauté française de participer aux projets scientifiques "clefs" de LOFAR. Elle a également suscité un développement instrumental original visant à augmenter significativement les performances de LOFAR aux basses fréquences (≤80 MHz) en formant un nouveau réseau géant d'antennes sensibles: la "Super Station LOFAR" (LSS). Le premier volet de cette thèse présente les études de conception et de réalisation d'un démonstrateur pour la LSS à trois échelles: l'antenne élémentaire, le "mini-réseau" d'une vingtaine d'antennes et la distribution globale de 96 mini-réseaux à Nançay. Ce projet est conçu pour être totalement compatible avec le réseau LOFAR et étendre ses performances (en particulier pour ses objectifs (exo)planétaires), et pour constituer un nouvel instrument sensible et autonome à Nançay. Le second volet porte sur le développement d'un mode d'imagerie planétaire avec l'interféromètre LOFAR et son application à l'étude du rayonnement synchrotron des ceintures de radiation de Jupiter. Ce mode a rendu possible la formation des toutes premières images planétaires résolues dans la bande 127 - 172 MHz.

The primary importance of trajectory reconstruction is to assess the accuracy of pre-flight predictions of the entry trajectory. While numerous entry systems have flown, often these systems are not adequately instrumented or the flight team not adequately funded to perform the statistical engineering reconstruction required to quantify performance and feed-forward lessons learned into future missions. As such, entry system performance and reliability levels remain unsubstantiated and improvement in aerothermodynamic and flight dynamics modeling remains data poor. The comparison is done in an effort to quantitatively and qualitatively compare Kalman filtering methods of reconstructing trajectories and atmospheric conditions from entry systems flight data. The first Kalman filter used is the extended Kalman filter. Extended Kalman filtering has been used extensively in trajectory reconstruction both for orbiting spacecraft and for planetary probes. The second Kalman filter is the unscented Kalman filter. Additionally, a technique for using collocation to reconstruct trajectories is formulated, and collocation's usefulness for trajectory simulation is demonstrated for entry, descent, and landing trajectories using a method developed here to deterministically find the state variables of the trajectory without nonlinear programming. Such an approach could allow one to utilize the same collocation trajectory design tools for the subsequent reconstruction.

La détection et la caractérisation d'exoplanètes apparaissent clairement comme des thèmes centraux de l'observation astronomique pour les années à venir. Les projets spatiaux ou au sol sont nombreux (HARPS, CoRoT, Kepler, JWST, SPHERE...), mais les études théoriques visant à l'analyse et à la compréhension des données recueillies et à venir sont nécessaires. Durant cette thèse j'ai étudié divers processus physiques affectant la structure interne et l'évolution des planètes géantes, aussi bien au sein, qu'à l'extérieur de notre système solaire. J'ai notamment modélisé en détail: -L'impact de l'irradiation intense émise par l'étoile sur l'atmosphère d'une planète à faible distance orbitale, et l'effet induit sur l'évolution interne de cette planète. -Le couplage par dissipation de marée de l'évolution orbitale et thermique d'une planète interagissant avec sa proche étoile parente. -L'effet de la déformation due aux marées sur les paramètres observables d'une planète en transit grâce au suivi photométrique de son passage devant l'étoile. -L'incidence sur la structure et l'évolution d'une diminution de l'efficacité du transport de chaleur par convection due à un gradient d'éléments lourd dans l'enveloppe gazeuse d'une planète géante, conduisant au phénomène de convection double-diffusive. A travers l'étude des ces divers processus, j'ai développé différents modèles analytiques et codes numériques qui sont à la fois flexibles et robustes, et qui permettent maintenant d'étudier certaines propriétés des nouveaux objets substellaires détectés à mesure qu'ils sont découverts.