Thesis (PHD)--University of Montana, 2009. / Contents viewed on December 18, 2009. Title from author supplied metadata. Includes bibliographical references.

Thesis (M.S. in environmental science)--Washington State University, August 2009. / Title from PDF title page (viewed on Sept. 22, 2009). "School of Earth and Environmental Sciences." Includes bibliographical references (p. 92-97).

Not available / text

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 118-138).

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Our solar system is just one of billions in the Milky Way, situated about half way from the Galaxy's core to its edge, and nestled safely between a pair of spiral arms. Out of those billions of planets, ours is the only one that we know to support life. This begs two questions. First, is our location in the Galaxy especially suitable for life? Second, if we want to find other life out there, where should we focus our search? In this dissertation, I contribute answers to both questions by seeking to better understand the boundaries of the Milky Way's galactic habitable zone (GHZ), the place in the galaxy where habitable worlds are most likely to be found. We start in Chapter 2 by introducing a novel method for finding the average height of surface features on exoplanets, a characteristic that influences a planet's habitability but was heretofore unknowable. We use elevation data for the rocky bodies in our Solar System to simulate their transits in front of stars of different sizes. We provide a relationship between the scatter at the bottom of the resulting light curves and the so-called "bumpiness" of the transiting planet. In Chapter 3, we zoom out from planets to get a better understanding of the dynamical and chemical evolution of the Milky Way, which are both crucial for constraining the Galaxy's GHZ. We use the Extreme Deconvolution Gaussian Mixture Model to identify overdensities of stars in both velocity and action space, called moving groups and orbit groups, respectively. Velocities and actions are calculated using data from the early third data release of the Gaia mission. When we analyze the chemical abundance distributions of these moving and orbit groups with GALAH DR3 data, we find that using velocities alone to define moving groups, or even using velocities and actions together, yields an incomplete view of the underlying density distributions and their origins. Our chemical analysis also confirms expected chemical evolution trends in the Solar neighborhood. Next, we explore the effects of stellar motion and galactic dynamics on the habitability of planets in different regions of the Galaxy. In Chapter 4, we use Gaia DR2 data to calculate 3D galactocentric velocities for stars observed by the Kepler spacecraft. We compare the velocities of confirmed Kepler host stars to those of their non-host stellar twins and find that there's no relationship between stellar velocity and planet occurrence in the Solar neighborhood. In Chapter 5, we shift our attention to the Milky Way bulge, where stars are closer together and moving more quickly on more elliptical orbits than in the disk. We simulate the orbits of bulge stars and use a semi-analytical method to derive the rate of close stellar encounters. We find that roughly 8 in 10 bulge stars will come within 1000 AU of at least 1 other star every billion years. Half of these stars experience dozens of these encounters every gigayear. These encounters can have dramatic consequences for planets, and our findings strongly suggest that the Milky Way bulge is not the most suitable environment for life. In Chapter 6, I share an overview of the science communication and outreach work I've done while in graduate school and explain how it's so closely tied to my research on GHZs.

Thesis (Ph. D.)--University of California, San Diego, 2001. / Vita. Includes bibliographical references.

Thesis (LL.M.). / Written for the Institute of Air and Space Law. Title from title page of PDF (viewed 2008/12/04). Includes bibliographical references.

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2007. / Phillip Gibbs, Committee Member ; Rick Trebino, Committee Member ; Christoph Fahrni, Committee Member ; Donald Doyle, Committee Member ; Andreas Bommarius, Committee Chair.

AFRIKAANS: Die Antieke ruimtevaarder-teorie stel voor dat wesens uit die ruimte die Aarde in die antieke verlede besoek het. Hierdie wesens was betrokke by die vroeë geskiedenis van die planet. Hulle het bewoonbare toestande geskep asook menslike intelligensie deur 'n proses van genetiese ingenieurswese. Hul besoeke is opgeteken en deur mense oorgelewer in godsdienste, mitologieë en antieke legendes. Hul teenwoordigheid is ook nog waarneembaar in antieke fisiese oorblyfsels. Voorstanders van die Ruimtevaarderteorie bied dit aan as 'n wetenskaplike hipotese en as die "mees perfekte algemene noemer van alle tye" wat 'n moderne verklaring vir die oer-godsdiens bied. Afdeling A van die studie bied 'n oorsig oor die teorie en die bewyse wat daarvoor aangebied word. Daar word aangetoon dat, hoewel die meeste van die postulate nie deur die moderne wetenskap as "onsinnig" beskou word nie, dit nie oortuig as 'n werkbare wetenskaplike teorie nie. Omdat daar weinig verskille tussen die basiese onderneming van die wtenskap en die godsdiens bestaan (beide vertrek vanaf onbewysbare aannames om waargenome data te verklaar) word daar vermoed dat die Antieke ruimtevaarder-teorie eerder funksioneer op die vlak van religieusiteit. Hierdie tese word ondersoek in Afdeling B van die studie: Daar word voorgestel dat die Fenomenologiese metode van godsdienswetenskaplike ondersoek, wat poog om 'n fenomeen te verstaan nie soos dit manifesteer nie, maar op die dieper vlak van die funksie en betekenins daarvan, die mees paslike metode vir die ondersoek is. (p> Met gebruikmaking van die insigte van 'n Fenomenologiese benadering, word aangedui dat die Antieke ruimtevaarder-teorie funksioneer as 'n godsdienstige beweging met eienskappe van 'n kulte en 'n nieu-mitologie. Die aanvaarbaarheid van die teorie vir die vele volgelinge daarvan, en die gepaardgaande groei van die bcweging wat dit propageer, word verklaar uit 'n kombinasie van sosiologiese en psigologiese faktore wat aan die werk is in die moderne Westerse beskawing. Vanuit 'n fenomenologiese gesigspunt word gekonkludeer dat die Ruimtevaardcrteorie baie suksesvol op religieuse vlak is. Dit slaag daarin om die Bybel weer "geloofwaardig" te maak en skep weer 'n "kosmiese raamwerk" vir die betekenis van die menslike bestaan. Die teorie kan ook beskou word as 'n prysenswaardige poging tot die sintetisering van godsdiens en die modeme wetenskap vir die aanhangers daarvan, en om die geestelike behoeftes van mense in 'n verwarrende en verwarde wêreld aan te spreek. In 'n slotafdeling word die bevindinge van die studie teologies oorweeg en word die waarde daarvan vir die Chrislelike godsdiens aangetoon. ENGLISH: The Ancient astronaut theory proposes that beings from outer space came to Earth in the distant past. These beings were involved in the early history of the planet: They created habitable conditions and human intelligence by genetic engineering. Their visits were recorded and handed down by humans in their religions, mythologies and ancient legends. Their presence is also visible in ancient physical remains. Proponents present the Astronaut theory as a scientific hypothesis and as "the most perfect common denominator of all time", allowing a modem explanation for old-time religion: Section A of the study provides an overview of the theory and the evidence presented in support of it. It is shown that, although many of the postulates are being accepted by modem science as "not unreasonable", it is not convincing as a workable scientific theory. Since there is little difference between the basic enterprises of science and religion (both departing from unproven suppositions to explain perceived data) it is suspected that the Astronaut theory rather functions on a level of religiosity. This thesis is investigated in Section 8 of the study: It is proposed that the Phenomenological method of studying religion, which attempts to understand a phenomenon not in the way it manifests itself, but on the deeper level of its function and meaning, is the most appropriate for this investigation. Using the insights of a Phenomeno!ogical approach, it is shown that the Ancient astronaut theory functions as a religious movement with attributes of a cult and a new-mythology. The acceptability of the theory for its many followers and the resulting growth of the movement that proposes it, is explained from a combination of social and psychological factors at work in Western society. From a phenomenological point of view it is concluded that the Astronaut theory may be considered very successful on a religious level: It succeeds in making the Bible "respectable" again and it recreates a "cosmic framework" for the meaning of human existence. The theory may also be considered a praiseworthy attempt to synthesise religion and modem science for its supporters and to address the spiritual needs of man in a confusing and confused world. In a final section of the study, the results are being considered theologically and their value. being shown for Christianity. / Thesis (PhD (Science of Religion))--University of Pretoria, 2007. / Science of Religion and Missiology / unrestricted