At high spatial and spectral resolution, the 10-metre Keck and 3- metre NASA IRTF ground-based telescopes were used to observe Saturn and Jupiter, respectively. Pole-to-pole profiles of H[superscript +, subscript 3] emission were recorded along the planets’ respective noon meridians. The low latitude ionospheric H[superscript +, subscript 3] emission of these planets was thought to be broadly uniformly decreasing towards the equator, with the transition from bright emission at the poles produced by particle precipitation, to the weaker background glow elsewhere produced by sunlight. Instead, however, a pattern of intensity variability was detected at both Jupiter and Saturn. This pattern was found to be symmetric about the magnetic equator at Saturn, with peaks in H[superscript +, subscript 3] intensity magnetically mapping to gaps in Saturn’s rings. The transport of water ions from the gaps in Saturn’s rings to the planetary ionosphere, delivered via magnetic field lines, was used to explain this, as water ions cause an increased H[superscript +, subscript 3] density and therefore emission. In the same dataset, the temperature of Saturn’s H[superscript +, subscript 3] aurorae remained effectively constant, whilst the H[superscript +, subscript 3] column density and total emission varied greatly. The southern auroral oval was found to be significantly warmer than its northern counterpart, having average temperatures of 583 and 527 K, respectively. This asymmetry was attributed to an inverse relationship between ionospheric Joule and ion drag heating with magnetic field strength. Jupiter’s low latitude ionosphere also appears to vary significantly in H[superscript +, subscript 3] emission, but this time in longitude. This may be due to an inversely proportional relationship between magnetic field strength and particle precipitation. In summary, the planetary ionospheres of Saturn and Jupiter have been found to be globally subjected to space environment forcing. Whilst such forcing was well established for the auroral regions, we have here discovered that particle precipitation can dominate the low latitude ionospheres of the gas giants.

This thesis will examine the possibility of using information available from present day measured martian, terrestrial, meteoritic and solar noble gas abundances to help constrain models of planetary evolution. It is divided into four main sections. The first introductory section reviews the role of noble gases in the investigation of planetary sses and histories. It also summarises "a best current" solar system evolution and planetary accretion model.

No description available.

Of the myriad of insights into exoplanetary systems provided by the Kepler mission, one of the most intriguing new discoveries is that of a class of compact planetary systems which include Kepler-11, Kepler-32 and Kepler-90. In such systems, ensembles of several planets are found in very closely packed orbits (often within a few percent of an astronomical unit of one another). These systems present a challenge for traditional formation and migration scenarios, since these planets presumably formed at larger orbital radii before migrating inwards. In particular, it is difficult to understand how some planets in such systems could have migrated across strong mean-motion resonances without becoming trapped, and remaining relatively well-spaced. It is also difficult to explain how such systems remain dynamically cold, as resonant interactions tend to excite orbital eccentricity and lead to close encounters. I present a dynamical study of the formation of these systems, using an N-body method which incorporates a parametrized model of planet migration in a turbulent protoplanetary disc. The study explores a wide parameter space, and finds that under suitable conditions it is possible to form compact, close-packed planetary systems via traditional disc-driven migration, albeit with an over-abundance of mean-motion resonances. I then extend the study to include Jupiter-mass planets exterior to the compact systems, and find that the dynamical effect of these companions can significantly modify the resonant structure of the compact planets. Finally, I extend this work to two dimensional hydrodynamical simulations in an attempt to model type I migration self-consistently. In particular, I find that clearing of the disc by photoevaporation can halt migration of compact systems, and also discover that planet-disc interactions can - under the right conditions - break mean-motion resonances.

Volcanism has been a crucial planetary process in the evolution of Venus, shaping the surface and contributing to the formation of the atmosphere and clouds. Some of the key outstanding questions are whether or not volcanism is active today, and what range of volcanic styles have occurred in the past or may occur in the future. This project uses three methods of investigating these questions. Firstly, computer modelling is used to simulate volcanic processes under Venusian conditions using a steady-state, isothermal, homogeneous flow model. It was found that the addition of CO2 to an H2O-driven eruption reduces the H2O requirement for explosive activity, and that eruptions possible on Venus may be detectable in Venus Express data. Next, radar datasets from both Venus and Earth were investigated with the aim of assessing relationships between differing volcanic deposits on Venus and their likely mode of formation, and using trends in the Earth radar data to inform us of what the Venus observations may be telling us. It was found that, in some cases, regional-scale radar observations may be useful in identifying deposit types, but the data used in the study were insufficient to define a globally applicable deposit identification scheme, pending further study. Finally, mapping and spatial analysis of volcanic features and rifts was performed to evaluate the nature of the interaction of volcanism within the global tectonic environment. Spatial relationships are consistent with aspects of the directional model of Venus' evolution, favouring a shift from globally dispersed, relatively small-scale, volcanism spread randomly across the planetary surface towards a gradually more rift-focused distribution indicative of a corresponding shift in global tectonic regime. These various strands are brought together here in order to contribute to our further understanding of volcanism as a fundamental Venusian planetary process.

Near-Earth Objects (NEOs), a group of small interplanetary objects whose orbits around the Sun approach the Earth's orbit to within 45 million km (~0.3 Astronomical Units), have the possibility to impact with the Earth. Such a hazard could potentially cause major damage and result in many casualties depending on impact location and impactor composition and energy. Unique to this type of natural hazard is the possibility of advance warning and the ability to reduce or remove the NEO threat through mitigation such as deflection and evacuation. This work investigates the human vulnerability in the form of human injuries and fatalities expected from an NEO impact on Earth along with the ability to evacuate. New models have been developed to predict the potential human loss from six individual land impact hazards, using historical data about earthquakes and large explosions, models regarding roof collapse and casualties due to ignition exposure and the uncertainty in the data available. Models have also been developed that mimic human travel behaviour during an evacuation. These models were based on survey data regarding human behaviour during evacuations from hurricanes in the US along with models that estimate local road network capacity and flow-time. The development of a decision support toolbox, the Near Earth Object Mitigation Support System (NEOMiSS) supports this research. NEOMiSS is a collection of tools that individually and in collaboration provide useful information to decision-makers regarding human vulnerability (i.e. the number of human injuries and fatalities), ability to evacuate, physical impact effects and uncertainties in models, input data and risk corridor knowledge. This enables decision-makers to gain a better knowledge about the potential consequences of their decisions. A number of case studies were investigated using NEOMiSS. These illustrate how the impact location and impactor energy can result in very different outcomes with regards to human vulnerability. They also illustrate how local road networks and the location of local settlements along with the evacuation strategy affect the ability to perform a successful evacuation. The success of such an evacuation will influence the human vulnerability by reducing the number of expected casualties.

No description available.

Internal gravity waves are a common feature of stratified fluids. They facilitate transport of momentum and energy – thus influencing the evolution of the fluid. There is a large body of research addressing the behaviour of gravity waves in the terrestrial atmosphere. This thesis builds and extends the research to giant planets – in particular to close-in extrasolar giant planets and the solar system giant planet, Jupiter. Because the atmospheres of close-in giant planets are expected to be strongly stratified, knowledge of the behaviour of gravity waves in such atmospheres is especially important. Close-in giant planets are thought to have their rotations and orbital period 1:1 synchronised, i.e., they are “tidally locked”. Such planets do not exist in the Solar System. However, many are known from observations of extrasolar systems. Their synchronisation means that they have a permanent day-side and night-side leading to interesting atmospheric dynamics. Modelling these circulations with global circulation models (GCMs) and comparing these models with observations is an active research area. However, many GCMs filter some or all gravity waves removing their effects. This thesis addresses this by explicitly looking at the effects gravity waves can have on the circulation. It is shown that gravity waves provide a mechanism for accelerating, decelerating, and heating the flow. Further, horizontally propagating gravity waves are shown to provide a possible means for coupling the day- and night-sides of tidally locked planets. As well as affecting the dynamics of the atmosphere, gravity wave behaviour is affected by the dynamics of the atmosphere. Therefore, gravity waves can be used to explore atmospheric properties. In this thesis gravity waves observed in Jupiter’s atmosphere, by the Galileo probe, are used to identify features of Jupiter’s atmosphere such as the altitude of the turbopause and the vertical profile of zonal winds at the probe entry site.

Il y a quelques quatre milliards et demi d’années, l’effondrement d’une région dense d’un nuage moléculaire a donné naissance à une étoile (notre Soleil) entourée d'un disque composé de poussières et de gaz. L’étude des premiers solides du disque et de leurs rapports D/H a révélé un enrichissement important en deutérium comparé au réservoir principal, l’étoile en formation. L’irradiation ionisante par l’étoile pourrait avoir joué un rôle important dans l’évolution de cette matière finement divisée. Au cours de cette thèse, une étude expérimentale des effets des irradiations ionisantes sur le fractionnement isotopique de l’hydrogène a été menée sur des d’analogues de poussières du disque. L’irradiation d’analogues de matière organique insoluble (MOI) a montré un enrichissement significatif en deutérium en fonction de l’énergie déposée. L’ensemble des modifications structurales, chimiques et isotopiques sont corrélées et suivent une même loi cinétique du premier ordre. La présence de plateaux isotopiques pour les doses maximales et les facteurs de fractionnement intramoléculaires associés suggèrent que l’irradiation ionisante pourrait être à l’origine de la signature isotopique de la MOI de la chondrite primitive Orgueil, à partir d’un précurseur possédant une signature terrestre.L’irradiation d’analogues de silicates hydratés a montré un enrichissement en deutérium dépendant de la dose mais cependant moins élevé que pour la MOI. Ces résultats vont dans le sens d’une évolution découplée entre une matière organique très riche en deutérium et des silicates hydratés très proches de la signature terrestre, observations reportées pour l’ensemble des chondrites carbonées. / About four and a half billions years ago, the collapse of a dense region of an interstellar cloud resulted in the formation of a young star (our Sun), surrounded by a disk of gas and dust. The study of the first solids in the protoplanetary disk has revealed a large variability of the hydrogen isotopic signature. This signature is highly enriched in D compared to the main reservoir, the newly formed star. In this context, ionizing irradiations could act as a powerful mechanism to transform the dust in the disk. In this thesis, an experimental study of the effects of ionizing irradiation on the hydrogen isotopic fractionation has been carried out, on dust H-bearing analogues. The ionizing irradiation of insoluble organic matter (IOM) has shown significant deuterium enrichment as a function of the deposited energy. The structural, chemical and isotopic evolutions are correlated and can be fairly described using a first-order rate law formalism. Plateau values, corresponding to the maximum bulk isotopic composition, allow a direct determination of the intramolecular fractionation factors. These fractionation factors point out the ionizing irradiation as a possible mechanism to explain the isotopic signature of the IOM of the Orgueil primitive chondrite, from an organic precursor with a terrestrial isotopic signature. The ionizing irradiation of hydrated silicates has revealed a limited deuterium enrichment compared to the IOM. These results are consistent with isotopic measurements made in carbonaceous chondrites. In these objects, the IOM is highly enriched in deuterium compared to the hydrated silicates, with an isotopic signature close to the terrestrial oceans value.

Free-floating planets (FFPs) are very difficult to observe directly since they are isolated and intrinsically faint. The gravitational microlensing effect is now major method to observe FFPs, but observing low-mass FFPs is still difficult due to their short duration. We compute simulations for FFP microlensing observations down to Earth-mass using the numerical Besancon Galactic model created by Robin et al. (2012a). These are the first detailed simulation of FFP microlensing using a population synthesis Galactic model incorporating a 3D extinction model, and we also take full account of finite source effects. Firstly, we simulate the microlensing event rate and spatial distribution using three different modes, and for each mode three FFP lens masses (Jupiter, Neptune, and Earth). For the target area of (l, b) =(1, -1.75) which corresponds to the centre of the proposed Euclid ExELS field, our simulations result in 184-920 Jupiter-mass FFPs during the 5 year Euclid mission depending on simulation assumptions. For the Earth-mass FFPs, the rate range is 9-49 FFPs assuming 100% detection efficiency. Next, we compute the rate of parallax detection using a 3D model of the observers. We consider parallax detection by Euclid and WFIRST-AFTA, and by Euclid and LSST. We found that 52 Jupiter-mass FFPs will be detected by a parallax between Euclid and WFIRST-AFTA for two 30-day continuous period around equinoxes if they observe simultaneously. The rate falls to 4 parallax events for Earth-mass FFPs. The parallax detection between Euclid and LSST would be affected by the observation time on the Earth, but it could provide 20 Jupiter-mass FFPs down to 1.4 Earth-mass FFPs.