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An exhaustive parameter study involving 133 dynamic crystallization experiments was conducted, to investigate the validity of the planetary embryo bow shock model by testing whether the cooling rates predicted by this model are consistent with the most dominant chondrule texture, porphyritic. Results show that using coarse-grained precursors and heating durations ≤ 5 minutes at peak temperature, porphyritic textures can be reproduced at cooling rates ≤ 600 K/hr, rates consistent with planetary embryo bow shocks. Porphyritic textures were found to be commonly associated with skeletal growth, which compares favorably to features in natural chondrules from Queen Alexandra Range 97008 analyzed, which show similar skeletal features. It is concluded that the experimentally reproduced porphyritic textures are consistent with those of natural chondrules. This work shows heating duration is a major determinant of chondrule texture and the work further constrains this parameter by measuring the rate of chemical dissolution of relict grains. The results provide a robust, independent constraint that porphyritic chondrules were heated at their peak temperatures for ≤ 10 minutes. This is also consistent with heating by bow shocks. The planetary embryo bow shock model therefore remains a viable chondrule mechanism for the formation of the vast majority of chondrules, and the results presented here therefore strongly suggest that large planetary embryos were present and on eccentric orbits during the first few million years of the Solar System’s history.
ContributorsPerez, Alexandra Marie (Author) / Desch, Steven J (Thesis advisor) / Till, Christy B. (Committee member) / Schrader, Devin L (Committee member) / Arizona State University (Publisher)
Created2018
Description
Part I – I analyze a database of Smoothed Particle Hydrodynamics (SPH) simulations of collisions between planetary bodies and use the data to define semi-empirical models that reproduce remant masses. These models may be leveraged when detailed, time-dependent aspects of the collision are not paramount, but analytical intuition or a rapid solution is required, e.g. in ‘N-body simulations’. I find that the stratification of the planet is a non-negligible control on accretion efficiency. I also show that the absolute scale (total mass) of the collision may affect the accretion efficiency, with larger bodies more efficiently disrupting, as a function of gravitational binding energy. This is potentially due to impact velocities above the sound speed. The interplay of these dependencies implies that planet formation, depending on the dynamical environment, may be separated into stages marked by differentiation and the growth of planets more massive than the Moon.
Part II – I examine time-resolved neutron data from the Dynamic Albedo of Neutrons (DAN) instrument on the Mars Science Laboratory (MSL) Curiosity rover. I personally and independently developed a data analysis routine (described in the supplementary material in Chapter 2) that utilizes spectra from Monte Carlo N-Particle Transport models of the experiment and the Markov-chain Monte Carlo method to estimate bulk soil/rock properties. The method also identifies cross-correlation and degeneracies. I use data from two measurement campaigns that I targeted during remote operations at ASU. I find that alteration zones of a sandstone unit in Gale crater are markedly elevated in H content from the parent rock, consistent with the presence of amorphous silica. I posit that these deposits were formed by the most recent aqueous alteration events in the crater, since subsequent events would have produced matured forms of silica that were not observed. I also find that active dunes in Gale crater contain minimal water and I developed a Monte Carlo phase analysis routine to understand the amorphous materials in the dunes.
Part II – I examine time-resolved neutron data from the Dynamic Albedo of Neutrons (DAN) instrument on the Mars Science Laboratory (MSL) Curiosity rover. I personally and independently developed a data analysis routine (described in the supplementary material in Chapter 2) that utilizes spectra from Monte Carlo N-Particle Transport models of the experiment and the Markov-chain Monte Carlo method to estimate bulk soil/rock properties. The method also identifies cross-correlation and degeneracies. I use data from two measurement campaigns that I targeted during remote operations at ASU. I find that alteration zones of a sandstone unit in Gale crater are markedly elevated in H content from the parent rock, consistent with the presence of amorphous silica. I posit that these deposits were formed by the most recent aqueous alteration events in the crater, since subsequent events would have produced matured forms of silica that were not observed. I also find that active dunes in Gale crater contain minimal water and I developed a Monte Carlo phase analysis routine to understand the amorphous materials in the dunes.
ContributorsGabriel, Travis Saint James (Author) / Asphaug, Erik I (Thesis advisor) / Hardgrove, Craig (Thesis advisor) / Sharp, Thomas (Committee member) / Zolotov, Mikhail (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2019
Description
Planets are generally believed to form in protoplanetary disks within a few million years (Myr) to several hundred Myr. But planetary embryos or protoplanets likely exist before disk gas dissipates (in three to ten Myr), capturing H2 -rich primary atmospheres from the nebula. Exploring these primordial atmospheres of planets provides a pathway to understanding the origins and the diversity of planets in the solar system and beyond. In this dissertation, I studied the primary atmospheres by modeling their formation, their impacts on planet formation, and determining methods to characterize them on exoplanets.
First, I numerically investigated the flow structures and dynamics of the primary atmospheres accreted on Earth-sized planets with eccentric orbits. Such planets can generate atmosphere-stripping bow shocks, as their relative velocities to the gas are generally supersonic. The atmospheres are three to four orders of magnitude less massive than those of planets with circular orbits. Hydrodynamic simulations also revealed large-scale recycling gas flow in the post-shock regions. This study provides important insights into the impacts of migration and scattering on primary atmospheres.
Second, I looked into how the presence of the primary atmosphere affects the trajectories of chondrule precursors passing through a planetary bow shock. To determine what magnetic fields chondrules were exposed to as they cooled below their Curie points, I computed the gas properties and magnetic diffusion rates in the bow shock region of a planet with and without the primary atmosphere. I concluded that, if melted in planetary bow shocks, most chondrules were cooled in the far downstream and they probably recorded the background nebular field.
Last, I studied the characterization of cloudy primary atmospheres on exoplanets using a Bayesian retrieval approach. I focused on obtaining bulk cloud properties and the impact of clouds on constraining various atmospheric properties through transmission spectroscopy using the James Webb Space Telescope (JWST). Most key atmospheric and cloud inferences can be well constrained in the wavelength range (0.6 – 11 µ m) but there are different optimal wavelengths for constraining atmosphere or cloud parameters. Other results including degeneracies among cloud parameters can also serve as a guideline for future observers.
First, I numerically investigated the flow structures and dynamics of the primary atmospheres accreted on Earth-sized planets with eccentric orbits. Such planets can generate atmosphere-stripping bow shocks, as their relative velocities to the gas are generally supersonic. The atmospheres are three to four orders of magnitude less massive than those of planets with circular orbits. Hydrodynamic simulations also revealed large-scale recycling gas flow in the post-shock regions. This study provides important insights into the impacts of migration and scattering on primary atmospheres.
Second, I looked into how the presence of the primary atmosphere affects the trajectories of chondrule precursors passing through a planetary bow shock. To determine what magnetic fields chondrules were exposed to as they cooled below their Curie points, I computed the gas properties and magnetic diffusion rates in the bow shock region of a planet with and without the primary atmosphere. I concluded that, if melted in planetary bow shocks, most chondrules were cooled in the far downstream and they probably recorded the background nebular field.
Last, I studied the characterization of cloudy primary atmospheres on exoplanets using a Bayesian retrieval approach. I focused on obtaining bulk cloud properties and the impact of clouds on constraining various atmospheric properties through transmission spectroscopy using the James Webb Space Telescope (JWST). Most key atmospheric and cloud inferences can be well constrained in the wavelength range (0.6 – 11 µ m) but there are different optimal wavelengths for constraining atmosphere or cloud parameters. Other results including degeneracies among cloud parameters can also serve as a guideline for future observers.
ContributorsMai, Chuhong (Author) / Desch, Steven SD (Thesis advisor) / Line, Michael ML (Committee member) / Patience, Jennifer JP (Committee member) / Li, Mingming ML (Committee member) / Shkolnik, Evgenya ES (Committee member) / Arizona State University (Publisher)
Created2020