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Morphology and dynamics of the Venus atmosphere at the cloud top level as observed by the Venus monitoring cameraMoissl, Richard January 2008 (has links)
Zugl.: Braunschweig, Techn. Univ., Diss., 2008
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Investigation of the Martian atmospheric water cycle by the OMEGA mapping spectrometer onboard Mars ExpressMaltagliati, Luca January 2008 (has links)
Zugl.: Braunschweig, Techn. Univ., Diss., 2008
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Ganymede's magnetosphere : unraveling the Ganymede-Jupiter interaction through combining multi-fluid simulations and observations /Paty, Carol S. January 2006 (has links)
Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 96-100).
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The Venus plasma environment a comparison of Venus express Aspera-4 measurements with 3D hybrid simulationsMartinecz, Cornelia January 2008 (has links)
Zugl.: Braunschweig, Techn. Univ., Diss., 2008
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Linking Super Earth Composition to Planet Formation HistoryAlessi, Matthew January 2016 (has links)
Super Earths are a class of exoplanets with masses between 1-10 M⊕. Comprising nearly 70 % of the discovered planet population, they are largest class of exoplanets known. Super Earths exhibit an interesting variety of compositions, as their densities imply that they range from dense, rocky planets to those with substantial amounts of water. This thesis aims to understand why super Earths form so frequently, and to connect the final compositions of super Earths to the regions where they form in protoplanetary disks. To do this, we combine a model that calculates the physical and chemical conditions within a protoplanetary disk with a core accretion model of planet formation. A key feature of our planet formation model is planet traps that act as barriers to rapid type-I migration. The traps we include in our model are the dead zone, which can be caused by cosmic ray or X-ray ionization, the ice line, and the heat transition. In disks with lifetimes > 4 Myr we find that planet formation in all traps results in Jovian planets. Typically, the X-ray dead zone and heat transition traps produce hot Jupiters orbiting near 0.05 AU while the cosmic ray dead zone and ice line traps produce Jupiters near 1 AU. Super Earths are found to form in disks with short lifetimes < 2 Myr that photoevaporate prior to planets undergoing runaway gas accretion. Additionally, we find that super Earth formation takes place in low-mass disks (< 0.05 M⊙), where planet formation timescales exceed disk lifetimes inferred through observations. The location of various traps throughout the disk play a key role in allowing super Earths to achieve a range of compositions. Super Earths forming in the ice line or heat transition accrete solids from cold regions of the disk, resulting in planets with large ice contents (up to 50 % by mass). Conversely, super Earths formed in the dead zone trap accrete solids from warm regions of the disk and are therefore composed of mostly rocky materials (less than 5 % ice by mass). / Thesis / Master of Science (MSc)
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Planet formation in self-gravitating discsGibbons, Peter George January 2013 (has links)
The work performed here studies particle dynamics in local two-dimensional simulations of self-gravitating accretion discs with a simple cooling law. It is well known that the structure which arises in the gaseous component of the disc due to a gravitational instability can have a significant effect on the evolution of dust particles. Previous results using global simulations indicate that spiral density waves are highly efficient at collecting dust particles, creating significant local over-densities which may be able to undergo gravitational collapse. This thesis expand on these findings, using a range of cooling times to mimic the conditions at a large range of radii within the disc. The PENCIL Code is used to solve the 2D local shearing sheet equations for gas on a fixed grid together with the equations of motion for solids coupled to the gas solely through aerodynamic drag force. The work contained here shows that spiral density waves can create significant enhancements in the surface density of solids, equivalent to 1-10cm sized particles in a disc following the profiles of Clarke (2009) around a solar mass star, causing it to reach concentrations several orders of magnitude larger than the particles mean surface density. These findings suggest that the density waves that arise due to gravitational instabilities in the early stages of star formation provide excellent sites for the formation of large, planetesimal-sized objects. These results are expanded on, with subsequent results introducing the effects of the particles self-gravity showing these concentrations of particles can gravitationally collapse, forming bound structures in the solid component of the disc.
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The application of Raman spectroscopy in support of the ExoMars 2020 missionBrolly, Connor January 2017 (has links)
The European Space Agency's ExoMars 2020 mission gives the astrobiology community the opportunity to scrutinise instrumentation, landing sites and proposed biosignatures in preparation for this mission. A miniaturised Raman spectrometer will be included as part of the payload instrumentation. The main focus of this work is to test the capabilities of this technique in support of this mission. The impact crater environment is one of the most valuable targets in search for life on Mars. One of the most well preserved craters on earth has evidence of microbial life in the post-impact hydrothermal deposits and the surface mineral crusts. Raman spectroscopy is able to identify more habitable forms of sulphate and detect photo-protective microbial pigments in the crusts. One of the building blocks of life is organic carbon. Raman spectroscopy will primarily be used to characterise organics, and as Mars has a limited atmosphere and lacks a global magnetic field, the surface of Mars is heavily oxidised. The effect that oxidation has on the Raman carbon signal is therefore important. Results show that hematite has an interfering band at the same frequency as the carbon D band, which could result in a misinterpretation of the carbon order, so caution must be taken. Oxidised iron could be a viable energy source of iron-reducing bacteria. One of the most common reduction morphologies in the geological record is the reduction spheroid. They are most likely formed by iron-reducing bacteria, and could be used as a biosignature on Mars. Results show that Raman spectroscopy is able to detect reduction spheroids by tracking the presence of hematite. Experimental work aiming to simulate the formation of a reduction spheroid was unsuccessful but shed light on the complexity of crystalline Fe(III) reduction. This work has highlighted the capabilities and limitations of Raman spectroscopy prior to the ExoMars mission.
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Rané fáze formování a vývoje planetárních systémů / Early phases of formation and evolution of planetary systemsChrenko, Ondřej January 2019 (has links)
We study orbital evolution of multiple Earth-mass protoplanets in their natal protoplanetary disk. Our aim is to explore the interplay between migration of protoplanets driven by the disk gravity, their growth by pebble accretion, and accretion heating which affects gas in their neighbourhood. Radiation hydrodynamic (RHD) simulations in 2D and 3D are used to model the problem. We find that the heating torque, i.e. the torque exerted by asymmetric hot underdense gas near accreting protoplanets, significantly changes the migration. Specifically, it excites orbital eccentricities of migrating protoplanets, thus preventing their capture in chains of mean-motion resonances. The protoplanets then undergo numerous close encounters and form giant planet cores by mutual collisions. Additionally, if inclinations also become excited, we describe a new mechanism that can form binary planets by means of consecutive two-body and three-body encounters, with the assistance of the disk gravity. Finally, our 3D RHD simulations reveal a complex distortion of the gas flow near an accreting protoplanet, driven by baroclinic perturbations and convection. For specific temperature-dependent opacities of the disk, an instability is triggered which redistributes gas around the protoplanet and leads to an oscillatory migration,...
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Modeling of forced planetary waves in the Mars atmosphereHollingsworth, Jeffery L. 05 June 1992 (has links)
Mariner 9 and Viking spacecraft observations during the 1970's have provided
evidence for planetary-scale wave-like disturbances in the Mars atmosphere. It has
been suggested that possible sources of the wave activity are dynamical instabilities
(e.g., barotropic and/or baroclinic instabilities). An other candidate source is forced,
quasi-stationary planetary waves. In connection with Mars' enormous relief, both
mechanical forcing and large-scale thermal contrasts due to spatially varying surface
thermal-inertia and albedo patterns should provide a strong source for planetary-wave
activity.
In this thesis, we attempt to model aspects of the observed wave activity, focusing
on forced planetary waves in the wintertime atmosphere of Mars. Our approach is
to apply two dynamical models: a linear primitive equations model and a quasi-linear
'wave, mean-flow' model. Both models have spherical geometry and represent deviations
from zonal symmetry in terms of Fourier modes. The former model permits
a separation of responses to different elements that make up the total forcing mechanism,
whereas the latter is used principally to investigate the role forced planetary
waves may play in the Mars polar warming phenomenon.
Basic states representing relatively 'non-dusty' and 'highly dusty' conditions
near winter solstice allow wavenumber-1 and -2 disturbances to propagate meridionally
and vertically into the winter jet. Higher wavenumbers are strongly vertically
trapped. Stationary waves in the northern and southern extratropics differ strongly
in amplitude, phase and horizontal wave pattern.
The possibility for near-resonant, long-period modes in Mars' winter atmosphere
is also examined. For several wave-amplitude measures and dissipation strengths,
dusty low-frequency responses are an order of magnitude larger than non-dusty ones.
Wave, mean-flow simulations using wavenumber-1 or -2 forcings indicate north
polar warmings can occur for the dusty basic states. The sensitivity (magnitude, location,
and time scale) of a simulated warming to the wave forcing and the dissipation
strength is investigated. / Graduation date: 1993
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A spatial analysis of gullies on Mars /Kincy, Leon. January 1900 (has links)
Thesis (M.A.Geo.)--Texas State University--San Marcos, 2009. / Vita. Reproduction permission applies to print copy: Blanket permission granted per author to reproduce. Includes bibliographical references (leaves 44-47).
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