Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 23 for “"Planetesimals"”.
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Magnetic Properties of Iron Meteorites and Their Parent Bodies
… solar system. Similar to Earth, some of these “planetesimals” underwent differentiation into a metallic core and a silicate mantle, and powered magnetic fields by the motion of their liquid cores via dynamo effect. Although most planetesimals no longer exist, records of their magnetic fields are …
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The origin and evolution of Transneptunian binaries
… producing these transneptunian binaries, where planetesimals and binaries form directly from the gravitational collapse of a pebble cloud. Merging collisions and conservation of angular momentum naturally lead to the formation of similar mass binary objects, and strongly prefers the formation of …
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A matter of life and death: the formation and destruction of planetary bodies
… research (Chapter 2) deals with the formation of planetesimals - a plausible starting point for planet formation. I develop a new theory that relates the formation of these planetesimals to the spinning motion around their own axis. Specifically, I show that a general mechanism exists, whereby …
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The influence of planetary and stellar companions on debris discs
… stars are known to host debris discs composed of planetesimals and the dust produced in their collisions. The structures of these discs can be constrained through spectral energy distribution (SED) modelling or direct imaging of the dust. Gravitational perturbations in a system containing planets …
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High-resolution studies of exoplanetesimal belt formation and evolution
… the protoplanetary system: planets, and belts of planetesimals (km-sized rocky and icy bodies). Planetesimals within belts readily collide and produce detectable levels of dust and gas, known as debris discs, around 20% of main sequence stars. Despite the ubiquity of planets and planetesimal belt …
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The structure and stability of vortices in astrophysical discs
… 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 …
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The effect of bombardment of small bodies on the evolution of atmospheres of terrestrial bodies
… smaller objects, such as asteroids, comets and planetesimals left over after terrestrial planet formation are evidenced by crater observations, and are an inevitable outcome of dynamical simulations of planet and moon formation. These impacts deliver mass and energy, and are capable of altering …
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GENETICS, AGES, AND CHEMICAL COMPOSITIONS OF IRON METEORITES
… siderophile element chemical characteristics of planetesimals. Iron meteorite parent bodies from the CC reservoir typically have smaller relative cores and a greater proportion of the Fe content in the mantle, consistent with the CC reservoir being a more oxidized environment, such as the outer …
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Late accretion to the early Earth and rocky exoplanets
… were characterised by the violent collisions of planetesimals, asteroids and comets -- by-products of the primary stage of planet formation -- with the nascent planet. It is thought these impacts, delivering vast sums of energy, may have transformed surface environments -- melting Earth's …
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Planetesimal and Protoplanet Dynamics in a Turbulent Protoplanetary Disk
… disk subject to magneto-rotational instability, planetesimals and protoplanets undergo diffusive radial migration as well as changes of other orbital properties. The magnitude of the effect on particle orbits has important consequences for planet formation scenarios. To accurately measure the …
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Probing planetary system histories via observations, experiments, and modelling of circumstellar gas and dust
… that become part of nascent planets and planetesimals. Debris disks, the name for circumstellar material after the protoplanetary disk dissipates, are remnants of earlier processes and carry clues to the formation conditions and evolutionary pathways of mature systems. In this thesis, I …
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THE CONCENTRATION OF HYDROGEN IN INCOMPLETELY AND WHOLLY MELTED TERRESTRIAL BUILDING BLOCKS
… carbonaceous chondrites. Similarly, all melted planetesimals are commonly assumed to be anhydrous. However, recent analyses of enstatite chondrites (ECs), which are formed in the inner solar system and are the closest match to the nucleosynthetic isotopic composition of the bulk Earth, suggest …
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Hydrocode modeling of oblique impacts into terrestrial planets
… picture of the impact process for differentiated planetesimals possessing iron cores with radius = 100 km that impact into magma oceans. The impact process strips away the silicate mantle of the planetesimal and then stretches the iron core, dispersing the liquid iron into a much larger volume of …
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Streaming Instabilities in Class 0/I Disks
… drift of pebbles inhibit the growth of grains to planetesimals. To overcome these barriers, effective localized dust clumping on a short enough time scale is required. One promising solution to this problem is the streaming instability. Streaming instability is only triggered with a large enough …
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Partial Melting on FeO-Rich Asteroids: Insights to the First Stage of Planetary Differentiation
The melting of planetesimals was a widespread geologic phenomenon taking place in the early inner solar system. Petrologic and geochemical evidence shows that this melting frequently resulted in full differentiation of planetary bodies into a core, mantle, and crust. The extent of this early …
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Dust disks around hot white dwarfs and central stars of planetary nebulae
… with the origin as collisionally disrupted planetesimals. The dust disks around CSPNs with near-IR excesses are likely optically thick, and possibly descended from binary post-AGB stars. The Helix Nebula's CSPN is also associated with a hard X-ray point source, whose origin is not known. We …
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CREATING TEST MECHANISMS FOR SILICON SUBSTRATE BASED (SSB) DEVICES FOR USE IN FAR-IR TO MILLIMETER ASTROPHYSICAL SPECTROSCOPY
… via winds or outflows, and composition of planetesimals that shape terrestrial and gas-giant cores. Chapter III, ‘EoR-Spec’, answers the question of which components to use to adjust the FPI spectroscopy instrument. For the EoR-Spec instrument, the Si-based mirrors/filters will be used for …
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The origin and evolution of warm exozodiacal dust
… of warm habitable zone dust and cold belts of planetesimals similar to the Solar System’s Kuiper belt. Given this correlation and the short lifetime of dust grains close to the star, it is probable that exozodiacal dust originates further out in the planetary system and is transported inwards. …
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Planetesimal Belts in Misaligned Wide Stellar Binaries
… companion on a misaligned wide orbit perturbs planetesimals to high eccentricities. First, in order to explain the mys- terious light-curve of KIC 8462852, one component of a wide binary star system in the Kepler field with deep, irregular and aperiodic dips in its light-curve, a Monte Carlo …
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Tiny Space Magnets: X-ray Microscopy and Nanopaleomagnetism of Meteoritic Metal
… solar system and the formation and evolution of planetesimals. One of the few direct observations of internal geophysical processes within planetary bodies is the presence or absence of a dynamo-driven magnetic field. These observations provide essential constraints on the degree of …
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