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1
Richardson, Derek C. "Planetesimal dynamics". Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309052.
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Barnes, Rory. "The dynamics of the initial planetesimal disk /". Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/5439.
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Armitage, Philip J., Josh A. Eisner y Jacob B. Simon. "PROMPT PLANETESIMAL FORMATION BEYOND THE SNOW LINE". IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621505.
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We develop a simple model to predict the radial distribution of planetesimal formation. The model is based on the observed growth of dust to millimeter-sized particles, which drift radially, pile-up, and form planetesimals where the stopping time and dust-to-gas ratio intersect the allowed region for streaming instability-induced gravitational collapse. Using an approximate analytic treatment, we first show that drifting particles define a track in metallicity-stopping time space whose only substantial dependence is on the disk's angular momentum transport efficiency. Prompt planetesimal formation is feasible for high particle accretion rates (relative to the gas, (M) over dot(p)/(M) over dot greater than or similar to 3 x 10(-2) for alpha = 10(-2)), which could only be sustained for a limited period of time. If it is possible, it would lead to the deposition of a broad and massive belt of planetesimals with a sharp outer edge. Numerically including turbulent diffusion and vapor condensation processes, we find that a modest enhancement of solids near the snow line occurs for centimeter-sized particles, but that this is largely immaterial for planetesimal formation. We note that radial drift couples planetesimal formation across radii in the disk, and suggest that considerations of planetesimal formation favor a model in which the initial deposition of material for giant planet cores occurs well beyond the snow line.
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Leinhardt, Zoë Malka. "Planetesimal evolution and the formation of terrestrial planets". College Park, Md. : University of Maryland, 2005. http://hdl.handle.net/1903/2359.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2005.Thesis research directed by: Astronomy. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Michikoshi, Shugo. "Theoretical study on planetesimal formation through gravitational instability". 京都大学 (Kyoto University), 2007. http://hdl.handle.net/2433/136768.
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Hughes, Anna. "Planetesimal growth through the accretion of small solids". Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/58965.
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The growth and migration of planetesimals in a young protoplanetary disk is fundamental to the planet formation process. However, in our modeling of early growth, there are a several processes that can inhibit smaller grains from growing to larger sizes, making growth beyond size scales of centimeters difficult. The observational data which are available ( e.g., relics from asteroids in our own solar system as well as gas lifetimes in other systems) suggest that early growth must be rapid. If a small number of 100-km-sized planetesimals do manage to form by some method such as streaming instability, then gas drag effects would enable such a body to efficiently accrete smaller solids from beyond its Hill sphere. This enhanced accretion cross-section, paired with dense
gas and large populations of small solids enables a planet to grow at much faster rates. As the planetesimals accrete pebbles, they experience an additional angular momentum exchange, which could cause slow inward drift and a consequent back-reaction on growth rates. We present self-consistent hydrodynamic simulations with direct particle integration and gas-drag coupling to estimate the rate of planetesimal growth due to pebble accretion. We explore a range of particle sizes and disk conditions using a wind tunnel simulation. We also perform numerical analyses of planetesimal growth and drift rates for a range of distances from the star. The results of our models indicate that rapid growth of planeteismals under our assumed model must be at orbital distances inwards of 1 AU, and that at such distances centimeter-sized pebbles
and larger are required for maximized accretion. We find that growth beyond 1 AU is possible under certain limited, optimized conditions.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Davison, Thomas M. "Numerical modelling of heat generation in porous planetesimal collisions". Thesis, Imperial College London, 2010. http://hdl.handle.net/10044/1/6333.
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An important unanswered question in planetary science is how planetesimals, the ~1–100 km solid precursors to asteroids and planets, were heated in the early Solar System. This thesis quantifies one possible heat source: planetesimal collisions. Recent work has predicted that collision velocities and planetesimal porosities were likely to have been higher than previously thought; this is likely to have significant implications on collision heating. The approach adopted in this research was to numerically model shock heating during planetesimal collisions. Simulations showed that an increase in porosity can significantly increase heating: in a 5 km s-1 collision between equal sized, non-porous planetesimals, no material was heated to the solidus, compared to two thirds of the mass of 50% porous planetesimals. Velocity also strongly influences heating: at 4 km s-1, an eighth of the mass of 50% porous planetesimals was heated to the solidus, compared to the entire mass at 6 km s-1. Further simulations quantified the influence on heating of the impactor-to-target mass ratio, the initial planetesimal temperature and the impact angle. A Monte Carlo model was developed to examine the cumulative heating caused by a population of impactors striking a parent body. In the majority of collisions the impactor was much smaller than the parent body, and only minor heating was possible. However, some larger or faster impactors were capable of causing significant heating without disrupting the parent body; these collisions could have heated up to 10% of the parent body to the solidus. To cause global heating, the collision must have catastrophically disrupted the parent body. The increase in specific internal energy from collisions was compared with the decay of short-lived radionuclides. In the first ~6 Ma, radioactive decay was the most important heat source. After ~10 Ma, the energy caused by collisions was likely to have overtaken radioactive decay as the dominant source.
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Simon, Jacob B., Philip J. Armitage, Andrew N. Youdin y Rixin Li. "Evidence for Universality in the Initial Planetesimal Mass Function". IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626045.
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Planetesimals may form from the gravitational collapse of dense particle clumps initiated by the streaming instability. We use simulations of aerodynamically coupled gas-particle mixtures to investigate whether the properties of planetesimals formed in this way depend upon the sizes of the particles that participate in the instability. Based on three high-resolution simulations that span a range of dimensionless stopping times 6 X 10(-3) <= tau <= 2, no statistically significant differences in the initial planetesimal mass function are found. The mass functions are fit by a power law, dN/dM(p) proportional to M-p(-p), with p = 1.5-1.7 and errors of Delta p approximate to 0.1. Comparing the particle density fields prior to collapse, we find that the high-wavenumber power spectra are similarly indistinguishable, though the large-scale geometry of structures induced via the streaming instability is significantly different between all three cases. We interpret the results as evidence for a near-universal slope to the mass function, arising from the small-scale structure of streaming-induced turbulence.
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Windmark, Fredrik [Verfasser] y Cornelis P. [Akademischer Betreuer] Dullemond. "Planetesimal formation by dust coagulation / Fredrik Windmark ; Betreuer: Cornelis P. Dullemond". Heidelberg : Universitätsbibliothek Heidelberg, 2013. http://d-nb.info/1177382938/34.
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Dittrich, Karsten [Verfasser] y Hubert [Akademischer Betreuer] Klahr. "Numerical Simulations of Planetesimal Formation in Protoplanetary Disks / Karsten Dittrich ; Betreuer: Hubert Klahr". Heidelberg : Universitätsbibliothek Heidelberg, 2013. http://d-nb.info/1177382873/34.
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Morrison, Sarah Jane y Sarah Jane Morrison. "The Dynamics and Implications of Gap Clearing via Planets in Planetesimal (Debris) Disks". Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625603.
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Exoplanets and debris disks are examples of solar systems other than our own. As the dusty reservoirs of colliding planetesimals, debris disks provide indicators of planetary system evolution on orbital distance scales beyond those probed by the most prolific exoplanet detection methods, and on timescales $\sim$10 Myr to 10 Gyr. The Solar System possesses both planets and small bodies, and through studying the gravitational interactions between both, we gain insight into the Solar System's past. As we enter the era of resolved observations of debris disks residing around other stars, I add to our theoretical understanding of the dynamical interactions between debris, planets, and combinations thereof. I quantify how single planets clear material in their vicinity and how long this process takes for the entire planetary mass regime. I use these relationships to assess the lowest mass planet that could clear a gap in observed debris disks over the system's lifetime. In the distant outer reaches of gaps in young debris systems, this minimum planet mass can exceed Neptune's.
To complement the discoveries of wide-orbit, massive, exoplanets by direct imaging surveys, I assess the dynamical stability of high mass multi-planet systems to estimate how many high mass planets could be packed into young, gapped debris disks. I compare these expectations to the planet detection rates of direct imaging surveys and find that high mass planets are not the primary culprits for forming gaps in young debris disk systems. As an alternative model for forming gaps in planetesimal disks with planets, I assess the efficacy of creating gaps with divergently migrating pairs of planets. I find that migrating planets could produce observed gaps and elude detection. Moreover, the inferred planet masses when neglecting migration for such gaps could be expected to be observable by direct imaging surveys for young, nearby systems. Wide gaps in young systems would likely still require more than two planets even with plantesimal-driven migration. These efforts begin to probe the types of potential planets carving gaps in disks of different evolutionary stages and at wide orbit separations on scales similar to our outer Solar System.
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Geretshauser, Ralf J. [Verfasser] y Roland [Akademischer Betreuer] Speith. "Simulation of Pre-Planetesimal Collisions with Smoothed Particle Hydrodynamics / Ralf J. Geretshauser ; Betreuer: Roland Speith". Tübingen : Universitätsbibliothek Tübingen, 2011. http://d-nb.info/1162699213/34.
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Railton, Anna Dorothy. "The structure and stability of vortices in astrophysical discs". Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/252700.
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This thesis finds that vortex instabilities are not necessarily a barrier to their potential as sites for planetesimal formation. It is challenging to build planetesimals from dust within the lifetime of a protoplanetary disc and before such bodies spiral into the central star. Collecting matter in vortices is a promising mechanism for planetesimal growth, but little is known about their stability under these conditions. We therefore aim to produce a more complete understanding of the stability of these objects. Previous work primarily focusses on 2D vortices with elliptical streamlines, which we generalise. We investigate how non?constant vorticity and density power law profiles affect stability by applying linear perturbations to equilibrium solutions. We find that non?elliptical streamlines are associated with a shearing flow inside the vortex. A ?saddle point instability? is seen for elliptical?streamline vortices with small aspect ratios and we also find that this is true in general. However, only higher aspect ratio vortices act as dust traps. For constant?density vortices with a concentrated vorticity source we find parametric instability bands at these aspect ratios. Models with a density excess show many narrow bands, though with less strongly growing modes than the constant?density solutions. This implies that dust particles attracted to a vortex core may well encounter parametric instabilities, but this does not necessarily prevent dust?trapping. We also study the stability and lifetime of vortex models with a 2D flow in three dimensions. Producing nearly?incompressible 3D models of columnar vortices, we find that weaker vortices persist for longer times in both stratified and unstratified shearing boxes, and stratification is destabilising. The long survival time for weak, elongated vortices makes it easier for processes to create and maintain the vortex. This means that vortices with a large enough aspect ratio have a good chance of surviving and trapping dust for sufficient time in order to build planetesimals.
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Schäfer, Urs [Verfasser]. "Turbulence and planetesimal formation induced by the streaming instability : Turbulenz und Planetesimalenstehung hervorgerufen durch die Streaming Instability / Urs Schäfer". Hamburg : Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky, 2020. http://d-nb.info/122113535X/34.
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Schreiber, Andreas [Verfasser] y Hubert [Akademischer Betreuer] Klahr. "Diffusion Limited Planetesimal Formation. Why asteroid and Kuiper-belt objects share a characteristic size / Andreas Schreiber ; Betreuer: Hubert Klahr". Heidelberg : Universitätsbibliothek Heidelberg, 2018. http://d-nb.info/1177252023/34.
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Lenz, Christian Tobias [Verfasser] y Hubert [Akademischer Betreuer] Klahr. "Semi-analytical Modeling of Planetesimal Formation. Implications for Planet Formation and the Solar Nebula / Christian Tobias Lenz ; Betreuer: Hubert Klahr". Heidelberg : Universitätsbibliothek Heidelberg, 2020. http://d-nb.info/1217539743/34.
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Syed, Bukhari Mohtashim Ahmad Verfasser] y Jürgen [Akademischer Betreuer] [Blum. "The role of pebble fragmentation in planetesimal formation during the gravitational collapse of a pebble cloud / Mohtashim Ahmad Syed Bukhari ; Betreuer: Jürgen Blum". Braunschweig : Technische Universität Braunschweig, 2018. http://d-nb.info/1175816175/34.
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Sousa, Rafael Ribeiro de. "A instabilidade na evolução dinâmica do sistema solar : considerações sobre o tempo de instabilidade e a formação dinâmica do cinturão de Kuiper /". Guaratinguetá, 2019. http://hdl.handle.net/11449/183463.
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Orientador: Ernesto Vieira NetoResumo: O estudo da formação e evolução do Sistema Solar é uma fonte de informação para entender sob quais condições a vida poderia surgir e evoluir. Nós apresentamos, nesta Tese de doutorado, um estudo numérico da fase final de acresção dos planetas gigantes do Sistema Solar durante e após a fase do disco de gás protoplanetário. Em nossas simulações, utilizamos um modelo recente e confiável para a formação de Urano e Netuno para esculpir as propriedades do disco trans-Netuniano original (Izidoro et al. , 2015a). Nós fizemos este estudo de uma maneira autoconsistente considerando os efeitos do gás e da evolução dos embriões planetários que formam Urano e Netuno por colisões gigantescas. Consideramos diferentes histórias de migração de Júpiter, devido a incerteza de como Júpiter migrou, durante a fase de gás. As nossas simulações permitiram obter pela primeira vez as propriedades orbitais do disco trans-Netuniano original. Então, calculamos o tempo de instabilidade dos planetas gigantes a partir de sistemas planetários que formam similares Urano e Netuno. Nossos resultados indicam fortemente que a instabilidade dos planetas gigantes acontecem cedo em até 500 milhões de anos e mais provável ainda ter acontecido em 136 milhões de anos após a dissipação do gás. Nós também realizamos simulações para discutir alguns efeitos dinâmicos que acontecem na região do cinturão de Kuiper. Estes efeitos acontecem quando Netuno esteve em alta excentricidade durante a instabilidade planetária. Para es... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: A study of the formation and evolution of the Solar System is a source of information for an understanding of what conditions life could arise and evolve. We present a numerical study of the final stage of accretion of the giant planets of the Solar System during and after the protoplanetary gas disc phase. In our simulations, we use a recent and reliable model for the formation of Uranus and Neptune to sculpt the properties of the original trans-Neptunian disk (Izidoro et al. , 2015a). We have done this study in a self-consistent way considering the effects of gas and the evolution of planetary embryos which form Uranus and Neptune by mutual giant collisions. We considered different Jupiter migration stories due to the uncertainty of how Jupiter’s migration was during the gas phase. Our simulations provide for the first time to obtain the orbital properties of the original trans-Neptunian disk. We then calculate the instability time of the giant planets from planetary systems which form similar Uranus and Neptune. Our results strongly indicate that the instability of the giant planets occurs early within 500 million years and even more likely to happen at 136 million years after gas dissipation. We also perform simulations to discuss some dynamical effects that happen in the Kuiper belt region. These effects happen when Neptune was in high eccentricity during planetary instability. For this problem, we use the simulations performed by Gomes et al. (2018) who investigated the... (Complete abstract click electronic access below)
Doutor
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Hull, Scott D. "Computational Modeling of Tungsten Metal-Silicate Partitioning in the Primordial Magma Oceans of 4-Vesta and Earth". The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1557199220613609.
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Hillier, Jonathan Karl. "The physical properties of outer solar system planetesimals". Thesis, University of Kent, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396916.
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Kirsh, David Robert. "Simulations of planet migration driven by the scattering of smaller bodies". Thesis, Kingston, Ont. : [s.n.], 2007. http://hdl.handle.net/1974/683.
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Drążkowska, Joanna [Verfasser] y Cornelis P. [Akademischer Betreuer] Dullemond. "From Dust to Planetesimals / Joanna Drazkowska ; Betreuer: Cornelis P. Dullemond". Heidelberg : Universitätsbibliothek Heidelberg, 2014. http://d-nb.info/1180301374/34.
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Krause, Maya [Verfasser] y Jürgen [Akademischer Betreuer] Blum. "Wärmeleitfähigkeit von Planetesimalen / Maya Krause ; Betreuer: Jürgen Blum". Braunschweig : Technische Universität Braunschweig, 2019. http://d-nb.info/1175387428/34.
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Mommert, Michael [Verfasser]. "Remnant Planetesimals and their Collisional Fragments : Physical Characterization from Thermal–Infrared Observations / Michael Mommert". Berlin : Freie Universität Berlin, 2013. http://d-nb.info/1042186081/34.
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Panichi, Federico. "La migrazione planetaria in un disco di planetesimi: Risultati analitici e numerici". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5675/.
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Thébault, Philippe. "Les processus d'accretion dans un disque de planetesimaux perturbe par un proto-jupiter". Paris 7, 1997. http://www.theses.fr/1997PA077302.
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Nous avons etudie l'influence de la presence precoce d'un proto-jupiter sur le processus de formation d'embryons planetaires par accretion mutuelle de petits planetesimaux. Nous nous sommes principalement interesses a l'effet couple des perturbations gravitationnelles du proto-jupiter et des collisions entre planetoides. Un modele numerique a ete developpe pour suivre l'evolution d'un disque tridimensionnel de particules test subissant des collisions inelastiques mutuelles et dont les orbites sont perturbees par un proto-jupiter. Nos simulations ont mis en evidence un phenomene de diffusion collisionnelle, par lequel les fortes perturbations des zones resonantes se propagent vers l'interieur du disque. En quelques 10#5 ans, toute l'energie resonante a ete ainsi redistribuee sur une zone plus large, ou les vitesses relatives entre les corps sont tres elevees et ralentissent le processus d'accretion. Si le proto-jupiter est peu massif (formation de la planete geante par accretion d'un noyau solide), la zone perturbee est assez reduite. En revanche, si la masse du perturbateur est proche de sa valeur actuelle (formation rapide par collapse gravitationnel), la diffusion collisionnelle peut fortement freiner l'accretion sur toute la region s'etendant au dela de 1,7 u. A. , ou les plus gros objets formes ne depassent pas 100 a 200 km de rayon. Ces resultats pourraient expliquer certaines caracteristiques de la structure actuelle du systeme solaire interne, notamment la frontiere entre les planetes telluriques et la ceinture d'asteroides, ainsi que la taille typique de ces derniers. D'autres points sont plus difficile a expliquer, par exemple la presence de gros asteroides pres des resonances. Le debat sur la presence precoce d'un proto-jupiter massif est donc encore ouvert. Dans un futur proche, l'etude du mecanisme de diffusion collisionnelle sera etendue a d'autres cas astrophysiques, en particulier aux systemes planetaires extra-solaires recemment decouverts.
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Simon, Jacob B., Philip J. Armitage, Rixin Li y Andrew N. Youdin. "THE MASS AND SIZE DISTRIBUTION OF PLANETESIMALS FORMED BY THE STREAMING INSTABILITY. I. THE ROLE OF SELF-GRAVITY". IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/621219.
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We study the formation of planetesimals in protoplanetary disks from the gravitational collapse of solid over-densities generated via the streaming instability. To carry out these studies, we implement and test a particle-mesh self-gravity module for the ATHENA code that enables the simulation of aerodynamically coupled systems of gas and collisionless self-gravitating solid particles. Upon employment of our algorithm to planetesimal formation simulations, we find that (when a direct comparison is possible) the ATHENA simulations yield predicted planetesimal properties that agree well with those found in prior work using different numerical techniques. In particular, the gravitational collapse of streaming-initiated clumps leads to an initial planetesimal mass function that is well-represented by a power law, dN / dM(p) proportional to M-p(-p), with p similar or equal to 1.6 +/- 0.1, which equates to a differential size distribution of dN / dR(p) proportional to R-p(-q), with q similar or equal to 2.8 +/- 0.1. We find no significant trends with resolution from a convergence study of up to 512(3) grid zones and N-par approximate to 1.5 x 10(8) particles. Likewise, the power-law slope appears indifferent to changes in the relative strength of self-gravity and tidal shear, and to the time when (for reasons of numerical economy) self-gravity is turned on, though the strength of these claims is limited by small number statistics. For a typically assumed radial distribution of minimum mass solar nebula solids (assumed here to have dimensionless stopping time tau = 0.3), our results support the hypothesis that bodies on the scale of large asteroids or Kuiper Belt Objects could have formed as the high-mass tail of a primordial planetesimal population.
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Crowley, John. "On the Dynamics of Plate Tectonics: Multiple Solutions, the Influence of Water, and Thermal Evolution". Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10435.
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An analytic boundary layer model for thermal convection with a finite-strength plate and depth-dependent viscosity is developed. The model includes a specific energy balance for the lithosphere and accounts for coupling between the plate and underlying mantle. Multiple solutions are possible with three solution branches representing three distinct modes of thermal convection. One branch corresponds to the classic boundary layer solution for active lid plate tectonics while two new branches represent solutions for sluggish lid convection. The model is compared to numerical simulations with highly temperature dependent viscosity and is able to predict both the type of convection (active, sluggish, or stagnant lid) as well as the presence of single and multiple solution regimes. The existence of multiple solutions suggests that the mode of planetary convection may be history dependent. The dependence of mantle viscosity on temperature and water concentration is found to introduce a strong dynamic feedback with plate tectonics. A dimensionless parameter is defined to quantitatively evaluate the relative strength of this feedback and demonstrates that water and heat transport may be equally important in controlling present-day platemantle dynamics for the Earth. A simple parameterized evolution model illustrates the feedback and agrees well with our analytic results. This suggests that a simple relationship may exist between the rate of change of water concentration and the rate of change of temperature in the mantle. This study concludes by investigating the possibility of a magnetic field dynamo in early solar system planetesimals. The thermal evolution of planetesimals is modeled by considering melting, core formation, and the onset of mantle convection and then employing thermal boundary layer theory for stagnant lid convection (if possible) to determine the cooling rate of the body. We assess the presence, strength and duration of a dynamo for a range of planetesimal sizes and other parameters. We find that a minimum radius of O(500) km is required for a thermally driven dynamo of duration O(10) My. The dependence of the results on model parameters is made explicit through the derivation of an analytic solution.Earth and Planetary Sciences
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Meisner, Thorsten [Verfasser], Gerhard [Akademischer Betreuer] Wurm y Jürgen [Akademischer Betreuer] Blum. "Experimentelle Untersuchungen zum Wachstum von Planetesimalen in protoplanetaren Scheiben / Thorsten Meisner. Gutachter: Jürgen Blum. Betreuer: Gerhard Wurm". Duisburg, 2014. http://d-nb.info/1060631881/34.
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Schwinger, Sabrina Verfasser], Sumit [Gutachter] Chakraborty y Thomas [Gutachter] [Müller. "Chemical zoning in pristine objects of chondrites as archive of the thermal and redox history in the early solar nebula and planetesimals / Sabrina Schwinger ; Gutachter: Sumit Chakraborty, Thomas Müller". Bochum : Ruhr-Universität Bochum, 2016. http://d-nb.info/1114679747/34.
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Schwinger, Sabrina [Verfasser], Sumit Gutachter] Chakraborty y Thomas [Gutachter] [Müller. "Chemical zoning in pristine objects of chondrites as archive of the thermal and redox history in the early solar nebula and planetesimals / Sabrina Schwinger ; Gutachter: Sumit Chakraborty, Thomas Müller". Bochum : Ruhr-Universität Bochum, 2016. http://d-nb.info/1114679747/34.
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Augereau, Jean-Charles. "Evolution des disques planétaires : observations, modélisation et perspectives instrumentales". Université Joseph Fourier (Grenoble), 2000. http://www.theses.fr/2000GRE10194.
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Les disques de poussieres et de gaz autour des etoiles rejoignant la sequence principale sont les sites de formation des planetes extrasolaires dont l'existence s'est vu confirmee recemment. Cette these aborde l'etude de la poussiere des environnements circumstellaires. Elle associe des observations spatiales a haute resolution angulaire, la modelisation des proprietes physico-chimiques des poussieres et leur comportement optique, la modelisation des disques optiquement fins et la dynamique des planetesimaux a l'origine des grains observes autour des etoiles agees. Les images obtenues avec le telescope spatial hubble revelent deux nouveaux disques circumstellaires autour des etoiles hd 141569 et hd 100546, parfois classees dans la categorie des etoiles de herbig. Bien que les systemes presentent des ages proches (10 millions d'annees), les morphologies tres differentes des disques mettent en evidence la difficulte pour elaborer un scenario unique d'evolution des systemes protoplanetaires. L'anneau fin de poussieres autour de hr 4796 a, une etoile d'age similaire aux precedentes, est marginalement resolu depuis le sol. La modelisation complete de ce disque permet de reproduire l'ensemble des observations disponibles. Ces resultats impliquent la presence de planetesimaux, a un age aussi peu avance, pour repeupler le disque en poussieres poreuses et essentiellement amorphes qui sont soufflees par la pression de radiation. Une modelisation dynamique du prototypique disque autour de pictoris est proposee. Associee a une description realiste du comportement optique des grains, cette approche reproduit les caracteristiques generales du disque ainsi que des asymetries plus fines en supposant la presence d'une planete dans un disque de planetesimaux et en tenant compte des effets differentiels de la pression de radiation sur les grains. Enfin, le modele de disques que j'ai developpe est exploite dans le but d'optimiser l'utilisation des nouveaux instruments.
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Marino, Estay Sebastián. "Exocomets at large orbital radii and their inward transport in debris discs". Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/283617.
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Planetary systems are not only composed of planets, but also of km-sized rocky and icy bodies that are confined within belts similar to the Asteroid and Kuiper belt in the Solar System. Mutual collisions within these belts grind down solids producing dust and giving rise to debris discs. Primitive asteroids and comets likely played a major role in the emergence of life on Earth through their delivery of volatiles early in the lifetime of our planet. Cometary impacts, therefore, could be a necessary condition for the emergence of life in exoplanets and the study of debris discs essential to determine the ubiquity of such phenomenon. Moreover, exocometary discs provide a unique window into the origins and outer regions of planetary systems as comets do within our Solar System. Initially, in Chapter 1 I present an overview of the study of exoplanetary systems, focusing on debris discs. I discuss the basics of planet formation, its connection with debris discs, and how these evolve and interact with planets. I also describe how we observe these discs and probe their volatile component that is locked inside exocomets, and some evidence supporting the idea of exocomets venturing into the inner regions of planetary systems. Then, in Chapters 2, 3, 4 and 5 I present new ALMA observations of the systems HD 181327, η Corvi, the multiplanet system 61 Vir and HD 107146, which host debris discs. In the first two, I highlight the derivation of the density structure of their discs and the detection of volatiles being released by exocomets; while in the third and fourth I compare the observations with simulations, which I use to set constraints on the underlying planetesimal distribution and mass and orbital distance of unseen planets. Finally, in Chapter 6 I present result obtained from N-body simulations to study the process of inward transport of comets by a multiplanetary system and how these can deliver material to inner planets and explain the frequently observed exozodiacal dust. To conclude, in Chapter 7 I summarise the results and conclusions of this dissertation and discuss ongoing and future work.
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Néri, Adrien. "Etude de la différenciation métal-silicates dans les petits corps du système solaire : une approche pluridisciplinaire". Thesis, Toulouse 3, 2019. http://www.theses.fr/2019TOU30184.
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De nombreux petits corps du système solaire ont connu la différenciation métal-silicate. Ce processus a provoqué la séparation du métal et du silicate, et peut avoir entraîné la formation d'un noyau métallique. Cette thèse porte sur la compréhension des processus physiques à l'origine de cette différenciation et de leurs conséquences sur les matériaux trouvés dans l'enregistrement météoritique. Afin de proposer des modèles les plus pertinents possibles, une approche conjointe expérimentale et de modélisation a été menée. Un système expérimental à trois phases a été conçu pour être représentatif d'échantillons naturels en cours de différenciation, et analysé à l'aide de techniques électroniques et de microtomographie 3D par rayons X. La différenciation métal-silicate se produit principalement par percolation d'un réseau métallique interconnecté. Cependant, une extraction importante des liquides silicatés est nécessaire pour permettre la formation d'un tel réseau. La différenciation est restée partielle dans les achondrites primitives à cause d'une accrétion tardive et des faibles tailles de grain des silicates, ce qui n'a pas permis une fusion complète des phases riches en fer ou encore une extraction efficace des produits de fusion. Les corps accrétés plus tôt qui ont connu un stade d'océan de magma sont sujets à une différenciation totale. Les modèles suggèrent qu'une fraction significative des silicates ne fond pas (correspondant au seuil rhéologique), empêchant les particules métalliques de sédimenter. A la fin de la phase d'océan de magma, la compaction et l'extraction efficace des produits de fusion favorisent la différenciation et la formation des météorites de fer, des achondrites et des pallasitesMany early-accreted small bodies of the Solar System experienced metal-silicate differentiation. This process caused the metal and silicate to separate and may have led to the formation of a metallic core. This PhD focused on understanding the physical processes that drove this differentiation and their consequences on the materials found in the meteoritic record. In order to provide the most plausible models, a joint experimental and modeling approach was used. A three-phase experimental system was designed to be representative of natural samples undergoing differentiation and analyzed using computed 3D X-ray microtomography and electronic techniques. Metal-silicate differentiation mostly occurs though the percolation of an interconnected metallic network. However, significant extraction of the silicate melt is required to allow the formation of such a network. Differentiation remained partial in primitive achondrites due to late accretion and low silicate grain sizes that did not allow complete melting of the iron-rich phases or efficient melt extraction. Complete differentiation occurs for bodies accreted earlier that experienced a magma ocean stage. Models suggest that a significant fraction of the silicates does not melt (corresponding to the rheological threshold), preventing the metal particles from settling. At the end of the magma ocean phase, compaction and efficient extraction of the melts favors differentiation and the formation of achondrites (pallasites, stony and iron meteorites)
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Raney, Robert 1987. "Fluid Migration During Ice/Rock Planetesimal Differentiation". Thesis, 2012. http://hdl.handle.net/1969.1/148317.
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Much speculation on extraterrestrial life has focused on finding environments where water is present. Heating of smaller icy bodies may create and sustain a possible liquid layer below the surface. If liquid water was sustained for geologically significant times (> 108 years) within the ubiquitous small bodies in the outer solar system, the opportunities for development of simple life are much greater. The lifetime of the liquid water layer will depend on several factors, including the rate of rock/water reaction, which will depend on the rate at which water can be segregated from a melting ice/rock core. For the liquid water phase to migrate toward the surface, the denser rock phase must compact. The primary question that this thesis will answer is how fast melt water can segregate from the core of an ice-rich planetesimal.
To answer this question we treat the core as two phase flow problem: a compacting viscous “solid” (ice/rock mixture) and a segregating liquid (melt water). The model developed here is based on the approach derived to study a different partially molten solid: in the viscously deforming partially molten upper mantle. We model a planetesimal core that initially a uniform equal mixture of solid ice and rock. We assume chondritic levels of radiogenic heating as the only heat source, and numerically solve for the evolution of solid and melt velocities and the distribution of melt fraction (“porosity”) during the first few million years after accretion. From a suite of numerical models, we have determined that the meltwater is segregated out of the core as fast as it is created, except in the case of very fast melting times (0.75 My vs. 0.62 My), and small ore radius (~25 to 150 km, depending on the viscosity of the ice/rock mixture in the solid core). In these latter cases, segregation is slower than migration and a high water fraction develops in the core. Heat released by water-rock reactions (not included in this model) will tend to drive up melting rates in all cases, which may favor this latter endmember.
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Glaschke, Patrick [Verfasser]. "Studying the formation of protoplanets : a new hybrid code for planetesimal dynamics / presented by Patrick Glaschke". 2006. http://d-nb.info/979968135/34.
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"Chronology of Planetesimal Differentiation Based on the Timing of Achondrite Formation in the Early Solar System". Doctoral diss., 2020. http://hdl.handle.net/2286/R.I.57177.
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abstract: During the early Solar System many physiochemical processes were taking place that would shape the formation and evolution of rocky bodies. Growth of these rocky objects was rapid, with some growing to sizes of 10s – 1000s km (“planetesimals”) in the first few million years. Because these objects formed early, they contained sufficient 26Al (an isotope of Al with a short half-life of ~705,000 yrs) to heat the interiors to melting temperatures, resulting in the formation of the first igneous rocks in nascent Solar System. Depending on the size and time of accretion, some bodies experienced high degrees of melting (with some having global magma oceans) while others experienced lower degrees of partial melting, and yet others did not experience any melting at all. These varying degrees of heating and melting processes on early-formed planetesimals produced a variety of achondritic meteorite types. These achondrites have bulk compositions ranging from ultramafic to basaltic, with some rare types having more highly “evolved” (i.e., high-SiO2) compositions. Determining the detailed chronology of their formation with fine time resolution is key for understanding the earliest stages of planet formation, and there are high resolution chronometers that are ideally suited for this application. Three such chronometers (i.e., the 26Al-26Mg, 53Mn-53Cr, and 207Pb-206Pb chronometers) are the focus of this work. Based on investigations of these chronometers in several achondritic meteorites, the implications for the formation and evolution of planetesimals in the early Solar System will be discussed.Dissertation/Thesis
Doctoral Dissertation Geological Sciences 2020
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Fraser, Wesley Christopher. "The Kuiper belt size distribution: constraints on accretion". Thesis, 2008. http://hdl.handle.net/1828/2552.
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The Kuiper belt is a population of planetesimals outside the orbit of Neptune. The high inclinations and eccentricities exhibited by many belt members, and its very low mass (M 0.1M) present an enigma to planetesimal accretion scenarios: the high relative encounter velocities (vrei 1 km s-1), and infrequent collisions of the largest members make the growth of Pluto-sized bodies impossible over the age of the Solar system. Accretion in the early stages of planet-building must have been in a more dense environment allowing large objects to grow before growth was halted.
The current Kuiper belt population is the left-over relic of accretion, which has undergone collisional re-shaping since the epoch of accretion. The shape of the size distribution can provide constraint on the accretion timescale, the primordial Kuiper belt mass, and the collisional processing the belt has undergone. Thus, a measure of the size distribution provides one of the primary constraint on models which attempt to explain the formation of the Kuiper belt.
We have performed a large-scale ecliptic Kuiper belt survey, with an aerial cov¬erage of 3.3 square degrees to a limiting magnitude m(R) 27. From these ob¬servations, we have discovered more than 100 new Kuiper belt objects. Using this survey we have provided the best measurement of the Kuiper belt luminosity function to-date, from which we have inferred the size distribution. We have found that the size distribution is well described by a power-law for large objects with a steep slope q1 = 4.8, that breaks, or rolls over to a shallower power-law with slope q2 = 2 at ob¬ject diameter ~ 60 km. The steep large object slope is indicative of a short accretion phase, lasting no more than a few 100 Myr. The large break diameter demonstrates that the Kuiper belt has undergone substantial collisional processing.
We have developed a collisional evolution model which we have used to study the effects of planetesimal bombardment and disruption on the size distribution. We have found that, in the current Kuiper belt, little to no evolution is occurring, or has occurred for the observable Kuiper belt. We conclude that the large break diameter cannot be produced in the current environment over the age of the Solar system. A period of intense collisional evolution in a much more dense, and hence, more massive belt is required. These findings are consistent with accretion models; the typical finding is that growth of the largest Kuiper belt objects over the age of the Solar system requires a much more massive belt than currently observed. These results point to a history in which an initially much more massive Kuiper belt underwent a short period of quiescent accretion producing Pluto size bodies.
Some event then occurred, which dynamically excited the planetesimals, producing an erosive environment which effectively halted planet growth and rapidly depleted the majority of the primordial mass. The remnant of this depletion is the Kuiper belt we observe today.
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"The Effect of Bulk Composition on the Sulfur Content of Cores". Master's thesis, 2020. http://hdl.handle.net/2286/R.I.57332.
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abstract: This study explores how bulk composition and oxygen fugacity (fO2) affect the partitioning of sulfur between the molten mantle and core of an early planetesimal. The model can be used to determine the range of potential sulfur concentrations in the asteroid (16) Psyche, which is the target of the National Aeronautics and Space Administration/Arizona State University Psyche Mission. This mission will be our visit to an M-type asteroid, thought to be dominantly metallic.
The model looks at how oxygen fugacity (fO2), bulk composition, temperature, and pressure affect sulfur partitioning in planetesimals using experimentally derived equations from previous studies. In this model, the bulk chemistry and oxygen fugacity of the parent body is controlled by changing the starting material, using ordinary chondrites (H, L, LL) and carbonaceous chondrites (CM, CI, CO, CK, CV). The temperature of the planetesimal is changed from 1523 K to 1873 K, the silicate mobilization and total melting temperatures, respectively; and pressure from 0.1 to 20 GPa, the core mantle boundary pressures of Vesta and Mars, respectively.
The final sulfur content of a differentiated planetesimal core is strongly dependent on the bulk composition of the original parent body. In all modeled cores, the sulfur content is above 5 weight percent sulfur; this is the point at which the least amount of other light elements is needed to form an immiscible sulfide liquid in a molten core. Early planetesimal cores likely formed an immiscible sulfide liquid, a eutectic sulfide liquid, or potentially were composed of mostly troilite, FeS.Dissertation/Thesis
Masters Thesis Geological Sciences 2020
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Shannon, Andrew. "Growth of Planetesimals and the Formation of Debris Disks". Thesis, 2012. http://hdl.handle.net/1807/32886.
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At the edge of the Solar System lies the Kuiper Belt, a ring of leftover planetesimals from the era of planet formation. Collisions between the Kuiper Belt Objects produce dust grains, which absorb and re-radiate stellar radiation. The total amount of stellar radiation so absorbed is perhaps one part in ten million. Analogous to this, Sun-like stars at Sun-like ages commonly have dusty debris disks, which absorb and re-radiate as much as one part in ten thousand of the stellar radiation. We set out to understand this difference. In chapter 1, we outline the relevant observations and give a feel for the relevant physics. In chapter 2, we turn to the extrasolar debris disks. Using disks spanning a wide range of ages, we construct a pseudo-evolution sequence for extrasolar debris disks. We apply a straightforward collision model to this sequence, and find that the brightest disks are a hundred to a thousand times as massive as the Kuiper Belt, which causes the difference in dust luminosity. Current theoretical models of planetesimal growth predict very low efficiency in making large planetesimals, such that the Kuiper Belt should be the typical outcome of Minimum Mass Solar Nebula type disks. These models cannot produce the massive disks we find around other stars. We revisit these models in chapter 3, to understand the origin of this low efficiency. We confirm that these models, which begin with kilometer sized planetesimals, cannot produce the observed extrasolar debris disks. Instead, we propose an alternate model where most mass begins in centimeter sized grains, with some kilometer sized seed planetesimals. In this model, collisional cooling amongst the centimeter grains produces a new growth mode. We show in chapter 4 that this can produce the Kuiper Belt from a belt not much more massive than the Kuiper Belt today. We follow in chapter 5 by showing that this model can also produce the massive planetesimal populations needed to produce extrasolar debris disks.
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Santamaría, Pablo J. "Un código de árbol para la dinámica de planetesimales". Tesis, 2004. http://hdl.handle.net/10915/1975.
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La tesis se divide en cinco capítulos:
El capítulo 1 describe la teoría básica de los integradores simplécticos, las limitaciones que éstos sufren en situaciones de encuentros entre partículas, y como puede construirse un integrador que pueda resolver tales situaciones manteniendo a la vez la propiedad simpléctica.
El capítulo 2 plantea y construye un esquema computacionalmente eficiente para la evaluación de la interacción gravitatoria de un sistema formado por muchos cuerpos que será implementado en el algoritmo híbrido.
El capítulo 3 muestra un procedimiento eficiente para determinar los vecinos próximos y encuentros en base a la estructura presentada en el capítulo 2.
El capítulo 4 describe la determinación de órbitas centrales y encuentros binarios, proporcionando esta última la componente no simpléctica del algoritmo híbrido.
El capítulo 5 muestra los detalles prácticos de la implementación computacional del algoritmo híbrido y analiza el desempeño del mismo en una serie de experimentos numéricos sobre un problema típico de la dinámica de planetesimales.
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Paraskov, Georgi [Verfasser]. "The influence of high speed collisions and gas flow on the formation of planetesimals / vorgelegt von Georgi Paraskov". 2006. http://d-nb.info/990505634/34.
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城野, 信一 y Sin-iti Sirono. "A unified model of the thermal history of icy planetesimals : Evolution of their temperature, chemical composition and mechanical properties". Thesis, 1998. http://hdl.handle.net/2237/10119.
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Ghosh, Amitabha. "Thermal evolution of planetesimals and protoplanets in the terrestrial planet region code optimization and implementation on a distributed grid using netsolve /". 2003. http://etd.utk.edu/2003/GhoshAmitabha.pdf.
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Thesis (M.S.)--University of Tennessee, Knoxville, 2003.Title from title page screen (viewed Sep. 18, 2003). Thesis advisor: Jack Dongarra. Document formatted into pages (ix, 73 p. : ill. (some col.)). Vita. Includes bibliographical references (p. 39-48).