Dissertations / Theses on the topic 'Venus (Planet)'

The Pioneer Venus Orbiter Infrared Radiometer and Venera 15 Fourier Transform Spectrometer observations of thermal emission from Venus' middle atmosphere between 10°S and 50°N were used to determine global maps of temperature, cloud optical depth and water vapour abundance. The spectral regions observed include the strong 15 μtm carbon dioxide band and the 45 μm fundamental rotational water band. The main aim of this thesis is to reconcile the water vapour abundance results from these two sets of observations reported in previous studies. New radiative transfer and retrieval models have been developed for this purpose based on new correlated-k absorption tables calculated with up-to-date spectral line data. The H₂SO₄ cloud opacity and scattering properties have been recalculated from new refractive index data using Mie theory. For the first time these two sets of observations have been analysed using the same retrieval tools. From the Pioneer Venus Orbiter Infrared Radiometer observations we report a high abundance of water vapour in the early afternoon at the equatorial cloud-top region and a strong day-night variability in the cloud-top pressure. From the Venera 15 Fourier Transform Spectrometer observations we report medium local variability in water vapour abundance, with highest values in the near-equatorial region and slight decrease towards the polar region. It is found that serious constraints are placed on the validation of the retrievals by the lack of adequately accurate H₂SO₄ optical properties data in the shorter wavelengths and by the poor vertical resolution when sensing the complex but interesting cloud region which prohibits its rigorous modelling. The proposed European Space Agency Venus Express mission will carry a number of high resolution infrared and UV instruments that will shed new light to the interesting question of water vapour abundance in Venus' middle atmosphere.

In questo lavoro di tesi è descritta parte della ricerca svolta presso l’Istituto di Fisica dello Spazio Interplanetario (IFSI) e presso l’Istituto di Astrofisica Spaziale e Fisica Cosmica (IASF). Lo studio attuato riguarda l’analisi dei dati dello strumento Planetary Fourier Spectrometer (PFS) incluso nella missione ESA Mars Express (MEX) al pianeta Marte e del Visual and Infrared Thermal Imaging Spectrometer (VIRTIS) incluso nella missione ESA Venus Express (VEX) orbitante attorno al pianeta Venere. Venere e Marte appartengono ai cosiddetti pianeti con atmosfere dominate dalla CO2 e, sperimentando condizioni atmosferiche fra loro diverse, forniscono una possibilità unica di ottenere informazioni complete su questi tipi di atmosfera ed a stadi evolutivi diversi, inoltre le informazioni ottenute dallo studio dei pianeti terrestri risultano fondamentali per una maggiore comprensione dell’evoluzione climatica passata e futura del nostro pianeta, rappresentando essi in qualche modo un possibile stadio o un cammino alternativo della storia della Terra. Utilizzando i dati acquisiti dai due satelliti dell’ESA abbiamo investigato la composizione atmosferica di Marte e Venere poiché essa, su scala globale e regionale, influenza il clima del pianeta e la sua evoluzione e le informazioni ricavate sui gas presenti possono perciò essere utilizzate come traccianti della circolazione atmosferica, permettendo di comprendere le proprietà principali dei due pianeti ed in particolare la stabilità atmosferica e l’evoluzione a lungo termine. Il lavoro è stato concentrato su argomenti ancora affetti da incertezze nella nostra comprensione dei costituenti atmosferici diversi dall’ anidride carbonica, al fine di fornire indicazioni per studi futuri riguardanti l’aeronomia e i fenomeni di interazione con la superficie quali il vulcanismo e la correlata emissione di gas. Su questo obbiettivo abbiamo avuto la prima possibilità di effettuare uno studio intensivo del vapor d’acqua su Venere (gli studi precedenti sono stati eseguiti su regioni del pianeta limitate nel tempo e nello spazio), avendo l’acqua il ruolo di tracciante fondamentale nella comprensione dell’attuale bilancio energetico atmosferico Venusiano, con particolare riferimento allo strato globale di nubi che avvolge permanentemente il pianeta. Su Marte ci siamo invece dedicati allo studio degli isotopi stabili contenuti nel carbonio e nell’ossigeno (isotopi del CO2), offrendo informazioni sull’origine del pianeta e le sue relazioni con la Terra. L’utilizzo degli isotopi dell’ossigeno è particolarmente utile su Marte essendo questo abbondantemente presente sia nell’atmosfera che nella litosfera Marziana sottoforma del maggior costituente, l’anidride carbonica. Abbiamo inoltre eseguito uno studio sul monossido di carbonio (CO) su Marte di particolare importanza essendo esso il principale prodotto della fotolisi del CO2 e quindi direttamente correlato al problema della stabilità dell’atmosfera Marziana. La spettroscopia infrarossa e gli attuali spettrometri ad alta risoluzione, i due strumenti più efficaci di telerilevamento nel contesto delle osservazioni planetarie, sono stati utilizzati per ottenere le informazioni trasportate dalla radiazione che ha direttamente interagito con il pianeta. Per analizzare I dati abbiamo sviluppato alcuni codici che modellano le atmosfere dei due pianeti descrivono appropriatamente ciò che lo strumento misura al fine di ricavare dagli spettri le quantità richieste, quale la composizione atmosferica delle specie considerate. Il contenuto di vapor d’acqua nella mesosfera di Venere era già stato misurato in esperimenti da terra e dallo spazio, che hanno dato risultati simili di qulache ppm fino a poco più di 10. Un’interessante eccezione è stata il forte incremento fino a valori maggiori di 100 ppm riscontratosi nelle regioni equatoriali intorno a mezzogiorno, osservato da Pioneer Venus OIR (Schoefield et al., 1982; Irwin et al., 1997; Koukouli et al., 2005). Di conseguenza il nostro studio ha avuto il duplice obiettivo di misurare il contenuto d’acqua alla sommità delle nubi e ricercare la presenza dei “wet spots” osservati da Pioneer Venus. Come prodotto di passaggio abbiamo misurato anche l’altezza delle nubi. Con una risoluzione spaziale di circa 10 km alla superficie delle nubi abbiamo ricavato un valore di abbondanza di vapor d’acqua a basse latitudini in regioni subsolari di circa 6 ± 2 ppm, fornendo, l’alta risoluzione spaziale, una prima occasione di misurare le variazioni locali, risultate essere attorno al 20%, non eccedendo l’errore casuale delle misure. Il livello riscontrato di massima sensitività alle variazioni di contenuto d’acqua è situato a circa 68 km. I risultati di abbondanza del monossido di carbonio nell’atmosfera Marziana ottenuti dai dati PFS indicano un valor medio di circa 800 ppm per un dataset di osservazioni acquisite in un intervallo di latitudini pari a (- 60) ÷ (+ 60) gradi e in un intervallo di longitudini solari che comprende l’estate e l’inizio dell’autunno nell’emisfero settentrionale. Valori più alti, circa 900 ppm, sono stati riscontrati in osservazioni acquisite alla fine dell’inverno e l’inizio della primavera dell’emisfero nord. In conclusione abbiamo osservato un incremento di CO nell’inverno sud ed a latitudini subsolari in cui il flusso solare è maggiore e di conseguenza la fotolisi del CO2 più efficiente. E’ stata rinvenuta una crescita anche a bassi angoli di incidenza solare, attorno a mezzogiorno. I risultati sull’abbondanze isotopiche del CO2 consistono principalmente nell’identificazione di tutti gli isotopi nei dati PFS con una risoluzione spettrale mai raggiunta prima da strumenti nello spazio. Le abbondanze trovate dei principali isotopi, fuori dal centro della banda di maggiore assorbimento del CO2 centrata attorno a 667 cm–1 (LWC) e confermate dai risultati ottenuti dal canale a frequenze corte (SWC), suggeriscono valori simili ai valori terrestri con una media pesata di circa 0.91 ± 0.18.
This work presents part of the efforts carried out in the Interplanetary Space Physics Institute (IFSI) and in the Cosmic Physics and Space Astrophysics Institute (IASF) of the Italian National Institute for Astrophysics (INAF) in the analysis of the data from the Planetary Fourier Spectrometer (PFS) experiment, included in the scientific payload of the ESA Mars Express (MEX) mission to Mars and the Visual and Infrared Thermal Imaging Spectrometer (VIRTIS) experiment, included in the ESA Venus Express (VEX) mission to Venus. Mars and Venus pertain to the planets with a “CO2 dominated” atmosphere and since they experiment different atmospheric conditions they provide an unique chance to obtain complete information on this atmospheric type at different evolutional stages; moreover, information obtained from the study of terrestrial planets are fundamental for the understanding of Earth past and future climate evolution, since other terrestrial planets represent in some sense a possible stage – or alternative path - of the Earth’s history. In particular, using the data acquired by the two ESA spacecraft we investigated the atmospheric composition of the two planets in order to give a contribute to the understanding of the main properties of Mars and Venus, since the composition of the atmosphere on global and regional scales influences the planetary climate and the evolution and the retrieved information can therefore be used to trace the atmospheric circulation, give constraints to the atmospheric stability and its long term evolution. For this task we had the first chance to perform an intensive study of water vapor on Venus, since the role of water as a trace constituent is key to illuminating the present-day Venus atmospheric energy balance, particularly with respect to the global cloud layers which permanently envelop the planet. On Mars we investigated the stable isotope record contained within carbon and oxygen (CO2 isotopes), to provide important constraints regarding the origin of the planet and its relationship to the Earth. Stable oxygen isotopes are particularly useful in the study of Mars because oxygen is abundantly present in both the Martian atmosphere and lithosphere, in particular in the main atmospheric constitute, carbon dioxide. We also investigated carbon monoxide (CO) on Mars, since it represents the main product of the CO2 photolysis and therefore is directly related to the problem of the stability of the Martian CO2 atmosphere. Infrared spectroscopy and present-day high resolution spectrometers, the most powerful remote sensing tools in the context of planetary observation, have been used to investigate the important information carried by the radiation which directly interacted with the planet. To analyze the data we developed some codes which model the two planets atmospheres and properly describe (simulate) what the instrument measures in order to retrieve from the spectra the required quantities, namely composition of the considered species. The water vapor abundance in the mesosphere of Venus has been already measured in a number of ground-based and spaceborn experiments. Various experiments gave approximately the same values from several ppm to a bit more than 10 ppm. An intriguing exception was the strong local enhancement up to 102 ppm soon after the subsolar point in the equatorial region observed by the Pioneer Venus OIR (Schoefield et al., 1982; Irwin et al., 1997; Koukouli et al., 2005). Thus our study had two main goals: to measure the water vapor abundance at the cloud tops with high spatial resolution, and to search for the wet spots observed by the Pioneer Venus. As a byproduct we measured the cloud top altitude. The Venus Express and VIRTIS observation strategy was particularly favorable for measurements at low latitudes around noon. Here the water vapor abundance near cloud top level at 2.5 μm was found to be 6 ± 2 ppm. Our best horizontal spatial resolution was about 10 km on the cloud “surface”, giving for the first time the chance with our high spatial resolution to measure local variations. Pixel-to pixel variations were within 20% and do not exceed random measurement error. Thus we did not observe any anomalously wet regions reported by the Pioneer Venus OIR experiment team. To be precise we have to note that the cloud top region in the far IR is located lower by several kilometers than that at 2.5 μm, and therefore we were sensitive to a higher level of atmosphere. The level of maximum sensitivity to the variations of water vapor is equal to 68 km, the corresponding cloud top altitude at 1.5 μm being equal to 75 ±1 km. Results show a CO mixing ratio with an average value of about 800 ppm from a first analyzed dataset observations acquired in a latitude range of approximately (- 60) ÷ (+ 60) degrees and in a solar longitude range which encompass the summer and the beginning of autumn in the northern hemisphere, therefore winter in the southern one (Ls range: 90° - 200°). Higher average values of about 900 ppm are found in the second dataset which comprises observations at the end of winter and beginning of spring in the north hemisphere (Ls range: 330° - 95°). In conclusion we find an increase in the Southern winter and at the latitudes of subsolar point where solar flux is higher and therefore CO2 photolysis is more efficient. In general seasonal features are more pronounced at equatorial latitudes and meridian profiles of the mixing ratio (for individual orbits) present seasonal shift of the maximum versus the sub solar point. We find an enhancement also at low incidence angles and at midday local time. Results on CO2 isotopes consisted primarily in the identification of all the CO2 isotopes in PFS data (LWC), with an instrumental spectral resolution never available before. The retrieved abundances of the main isotopes outside the center of the main CO2 absorption band at 667 cm–1 (LWC) performed from the analysis of the long wavelength channel of PFS spectrometer and confirmed by the short wavelength channel suggest results close to “terrestrial value” with a weighted-mean value which is equal to 0.91 ± 0.18.

Vénus, deuxième planète du système solaire, souvent appelée sœur de la Terre, car présentant des caractéristiques de taille et de masse similaires, est fort différente de notre planète. En effet, son atmosphère est beaucoup plus dense et dynamiquement active que celle de la Terre. Dans ce travail, nous nous concentrerons sur la région s'étendant de 70 km à 180~km d'altitude :la mésosphère et la basse thermosphère.

SOIR, acronyme de Solar Occultation in the InfraRed, est un instrument russo-franco-belge embarqué à bord de la mission Venus Express de l'Agence Spatiale Européenne. Il utilise un réseau à échelle comme élément diffractant. La plage de nombre d'onde mesurable par SOIR s'étend de 2200 cm-1 à 4400 cm-1, ou 4.3 µm à 2.2 µm en longueur d'onde. Les ordres de diffraction utiles varient de 101 à 194. Un filtre acousto-optique - AOTF - est utilisé comme passe-bande pour sélectionner les ordres de diffraction. La résolution de l'instrument varie de 0.13 à 0.24 cm-1.

Du fait d'un temps de développement raccourci, presque toutes les calibrations de l'instrument ont dû être réalisées en vol. Elles comprennent les calibrations relatives au réseau à échelle (angle exact de Blaze et fonction de Blaze), au détecteur (non-uniformité pixel à pixel, courbe de sensibilité spectrale, relation entre les pixels et les nombres d'onde, résolution de l'instrument, intervalle d'échantillonnage spectral, rapport signal sur bruit, background thermique) et à l'AOTF (relation entre la radio-fréquence d'excitation de l'AOTF et les nombres d'onde, fonction de transfert de l'AOTF). L'approche et la réalisation de ces différentes calibrations sont présentées dans le présent travail. Les caractéristiques de l'instrument y sont également décrites.

Un algorithme d'inversion spectrale a été développé pour le cas spécifique de SOIR. Tenant compte du mode de mesure, l'occultation solaire, la méthode de la pelure d'oignons a été implémentée dans un algorithme dit de l'Estimation Optimale. Cette méthode permet d'inverser l'ensemble des mesures spectrales en une fois, et également d'en tirer d'autres informations, comme l'amélioration de certaines caractéristiques instrumentales. Les paramètres qui sont ajustés au sein de l'algorithme sont la densité de la ou des espèces absorbant dans la région spectrale concernée, la température, les paramètres de la ligne de base, qui permettent de déterminer les caractéristiques des aérosols, le déplacement Doppler des raies qui trouve principalement son origine dans la vitesse de déplacement du satellite, et l'amélioration de certaines calibrations. Une étude de sensibilité des différents paramètres de l'algorithme est également présentée, ainsi qu'une évaluation des erreurs instrumentales systématiques.

Dans l'ensemble des spectres enregistrés durant les 4 premières années de la mission, des profils verticaux de CO2, CO, H2O, HDO, SO2, H2SO4, HCl et HF ont été obtenus. Des valeurs limites de densité de OCS, H2CO, O3 et CH4 ont également été calculées.

Les résultats concernant le dioxyde de carbone sont développés dans le texte. Des profils verticaux de CO2 s'étendant de 70 km à 180 km d'altitude sont analysés en profondeur. Ils sont comparés aux profils dits hydrostatiques, et des hypothèses quant à la dynamique agissant au niveau des deux terminateurs de Vénus sont formulées.

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Venus, second planet of the solar system, is often seen as the sister planet of the Earth. In terms of size and mass, they are indeed very similar, but the Venus atmosphere is much thicker and active. The altitude region extending from 70 km to 180~km is studied in this thesis, namely the mesosphere and the lower thermosphere.

SOIR, which stands for Solar Occultation in the InfraRed, is a Russian / French / Belgian instrument flying on board of the Venus Express (VEX) spacecraft of the European Space Agency. The diffracting device of SOIR is an echelle grating. The wavenumber region studied ranges from 2200 cm-1 to 4400 cm-1, or 4.3 µm to 2.2 µm in wavelength. The diffraction orders used with SOIR vary from 101 to 194. To select the required echelle grating diffraction order, an Acousto-Optical Tunable Filter - AOTF - is located after the entrance slit of the instrument. The instrument resolution varies from 0.13 to 0.24 cm-1.

SOIR was developed in a very short time. Thus, virtually all the calibrations had to be made in-flight. These concern the echelle grating (exact Blaze angle computation, Blaze function), the detector (pixel-to-pixel non-uniformity, spectral sensitivity curve, pixel-to-wavenumber relationship, instrument resolution, spectral sampling interval, signal-to-noise ratio, thermal background) and the AOTF (wavenumber to AOTF frequency relation, AOTF transfer function). The procedure for and the computation of these calibrations are described in this work, as well as the instrument characteristics.

A spectral inversion algorithm was developed specifically for the SOIR measurement technique: the solar occultation. The onion peeling method is implemented using the Optimal Estimation Method. It allows the inversion of the spectral data in one go, and also the enhancement of some instrumental characteristics. The algorithm variables are the densities of the species absorbing in the diffraction order, the temperature of the atmosphere under study, the spectral background parameters, that allow the determination of the Venus aerosols characteristics, the Doppler shift (mainly linked to the shift induced by the satellite displacement), and the improvement of some instrumental calibrations. A sensitivity study on the algorithm parameters is also presented, and the instrumental systematic errors are investigated.

Vertical profiles of CO2, CO, H2O, HDO, SO2, H2SO4, HCl and HF are derived from the spectra measured during the first 4 mission years. Upper limits on OCS, H2CO, O3 and CH4 have also been calculated.

We focus on the carbon dioxide results in the present study. A selection of vertical profiles extending from 70 km to 180 km are analyzed in details. They are compared to the hydrostatic profiles, and propositions concerning the terminators' dynamics are formulated.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

Solar chimney power plant (SCPP) is a solar thermal energy conversion system which converts solar energy into thermal energy and indirectly to mechanical/electrical energy using air as the working fluid to drive a turbine-generator. The main challenge of SCPP is the plant’s low efficiency. This research focus on improving the SCPP collector’s efficiency through the use of underneath air-vents. The study revealed that the power output of the SCPP with air-vents improved by 60%.

Les étoiles de type solaire génèrent un champ magnétique dans leur enveloppe convective grâce à l'effet dynamo. De l'énergie magnétique est injectée dans leur atmosphère étendue, la couronne, qui est chauffée à quelques millions de Kelvin. Le gradient de pression entre la base de la couronne et le milieu interstellaire produit alors un vent de particules chargées responsable du freinage rotationnel de l'étoile sur la séquence principale. Après une première partie introduisant les concepts fondamentaux de la magnétohydrodynamique stellaire, cette thèse se consacre à l'influence du vent magnétisé sur la rotation stellaire et la couronne. À l'aide d'un ensemble de 60 simulations MHD axisymétriques, nous quantifions en premier lieu l'influence de la topologie magnétique sur le freinage. Nous démontrons l'efficacité d'une nouvelle formulation de freinage qui permet de prendre en compte des topologies arbitrairement complexes grâce au flux ouvert magnétique. Nous proposons ensuite une méthode pour estimer le flux ouvert des étoiles de type solaire à partir de modèles analytiques de reconstruction coronale, qui permettent l'utilisation de cette formulation dans les modèles d'évolution rotationnelle. Enfin, à l'aide de simulations entièrement tridimensionnelles contraintes par des champs magnétiques observés, nous étudions l'évolution des propriétés du vent avec l'âge des étoiles. En modélisant l'évolution de la température et de la densité coronale en fonction du taux de rotation de l'étoile, nous retrouvons les prescriptions usuelles des modèles d'évolution rotationnelle. Les simulations 3D permettent également d'accéder à la structure complexe de la couronne organisée en régions ouvertes et fermées. Nous démontrons également que, pour les étoiles jeunes, la distribution de vitesse du vent est trimodale du fait de l'effet magnéto-centrifuge et de l'expansion superradiale des lignes de champ magnétique.La troisième partie de cette thèse aborde les interactions magnétiques étoile-planète sous deux aspects. Tout d'abord, lorsque la planète est proche, un couplage magnétique permet un échange de moment cinétique entre les deux corps. Nos travaux quantifient pour la première fois ces couples magnétiques en fonction des paramètres stellaires et des paramètres orbitaux de la planète, grâce à des simulations MHD 2D et 3D. Ce couple apparaît comme un facteur non négligeable de la migration de Jupiter chauds vers leur étoile hôte. Puis, dans le cas d'une planète plus lointaine, nous nous intéressons aux émissions radios créées dans les magnétosphères planétaires à travers l'exemple de Mercure, ouvrant la voie à la détection et à la caractérisation de magnétosphères exoplanétaires
Solar-like stars are believed to generate magnetic fields in their convective envelope through dynamo processes. Magnetic energy is injected in their extended atmosphere, the corona, which is heated up to few million Kelvin. The outward pressure gradient drives a magnetized stellar wind that induces a rotational braking on the star.We first focus on the consequences of this magnetized outflow on stellar rotation. Thanks to 2.5D MHD wind simulations, we quantify the influence of complex topologies of the magnetic field on the efficiency of the braking. We derive a general formulation that accounts for arbitrary complex magnetic topologies using the open magnetic flux. We propose a way to estimate the open magnetic flux for solar-like stars thanks to semi-analytical models, in order to use our formulation in rotational evolution models. We then use 3D simulations constrained by spectropolarimetric maps to study the evolution of stellar winds with age. Our simulations, thanks to prescriptions on the evolution of the coronal base density and temperature, are in good agreement with empirical rotational models. Moreover, we unravel the complex structure of realistic coronae made of dead zones and open regions. We also demonstrate that young and fast rotating stars have a trimodal wind speed distribution due to the magneto-centrifugal effect and superradial flux tube expansion.The last part of this thesis discusses the interaction of stellar winds with planets. We demonstrate that close-in planets, such as hot Jupiters, experience star-planet magnetic interactions that have a significant influence on their migration time scale toward the star. We then quantify the radio emission due to energy transfer between the stellar (or solar) wind and electrons of the planetary magnetospheres through the example of Mercury. This study is a first step toward the characterization of exoplanetary magnetospheres

Bien qu’elles ne disposent pas de muscles, les plantes ont réussi à développer un nombre remarquable de mécanismes permettant de créer des mouvements rapides, du repliement rapide des feuilles de mimosa pudica à la dispersion de graines par explosion. Parmi ces exemples spectaculaires qui ont depuis longtemps fasciné les scientifiques, la plante carnivore dionée, dont les feuilles se referment en une fraction de secondes pour capturer des insectes, fait figure de paradigme. Récemment, nous avons montré que ce mouvement met en jeu une instabilité de flambage élastique, due à la forme de coque mince des feuilles du piège. Cependant, l’origine microscopique du mouvement qui permet à la plante de franchir le seuil d’instabilité et de changer activement sa courbure reste méconnue. Dans cette thèse nous étudions ce mouvement actif en utilisant un dispositif micro-fluidique, la sonde de pression, qui donne accès directement aux paramètres élastiques et hydrodynamiques à l’échelle de la cellule (pression osmotique, perméabilité cellulaire, élasticité de la paroi, ...). Nos résultats remettent en question le rôle des flux d’eau d’origine osmotique souvent mis en avant pour expliquer la fermeture active du piège de la dionée. De plus, nous développons un dispositif de micro indentation original utilisant un rhéomètre, pour mesurer la réponse locale des tissus et les propriétés mécaniques des épidermes interne et externe. Nous mesurons une signature claire du mouvement actif de la dionée, et fournissons ainsi de nouveaux arguments pour discuter le mécanisme de fermeture, et plus généralement les mouvements rapides dans les plantes
Although they lack muscle, plants have evolved a remarkable range of mechanisms to create rapid motion, from the rapid folding of sensitive plants to seed dispersal. Of these spectacular examples that have long fascinated scientists, the carnivorous plant Venus flytrap, whose leaves snap together in a fraction of second to capture insects, has long been a paradigm for study. Recently, we have shown that this motion involves a snap-buckling instability due to the shell-like geometry of the leaves of the trap. However, the origin of the movement that allows the plant to cross the instability threshold and actively bend remains largely unknown. In this study, we investigate this active motion using a micro-fluidic pressure probe that gives direct hydraulic and mechanical measurements at the cellular level (osmotic pressure, cell membrane permeability, cell wall elasticity). Our results challenge the role of osmotically-driven water flows usually put forward to explain Venus flytrap’s active closure. Moreover, we developp a micro-indentation original setup using a rheometer, to measure the local tissue response and mechanical properties of the lower and upper epidermis. Then, we detect a clear signature of the active movement in the Venus Flytrap, and thus provide new arguments to discuss this mechanism, and more generally the movements in plants

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".

5 Abstract This study is dedicated to evaluating the potential for a novel pathway of abiotic synthesis of phosphine (PH3) from phosphorus trioxide (P4O6) by a photocatalytic mechanism on aerosols. The mechanism might explain the recent possible detection of phosphine on Venus. This scenario has recently been suggested theoretically by our team based on an analogy with methane production form carbon dioxide on acidic photochemically-active surfaces of materials, which may account for a possible source of methane on Mars. Methane, just like phosphine, was suggested as an indicator of life on terrestrial planets, including Mars. The theoretical testing of photochemical phosphine generation suggests that even if this gas is present in the atmosphere of Venus it cannot be considered as an indicator of life until the suggested mechanism is excluded theoretically, or by experimental results, or direct evidence of life on Venus. This thesis will be followed by preparation of sophisticated experiments and intensive laboratory research addressing this. Furthermore, the role of nitrous oxide as another false positive biosignature was evaluated in this study. The presence of nitrous oxide can also be explained by processes other than biological, particularly on early planets. This study specifically demonstrates the...