Date of Award

Spring 5-29-2020

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Physics

Advisor

Neil Comins

Second Committee Member

Thomas Stone

Third Committee Member

Robert Meulenberg

Additional Committee Members

Christopher Spalding

Abstract

Among the many exciting and thought-provoking discoveries facilitated by the Kepler telescope, one of the most puzzling is the very large proportion of systems with only a single transiting planet in them, relative to the number of systems with multiple transiting planets. Given that most of these multis are close together and have low mutual inclinations, and that planetary systems tend to form in such a configuration, the next logical step is to guess that at least some of the singles are part of multi-planet systems with large mutual inclinations between planets, excited by some other object’s gravitational perturbations. A number of such mechanisms have been put forth as explanations for the excess of singles, but our currently limited knowledge of planetary systems prevents any one mechanism from being identified as the most probable cause. One mechanism involves a young, tilted, oblate star that forces its closest-in planets to precess about its spin axis, rotating them out of alignment with each other as its oblateness decays. Still relatively new territory in planetary science, the stellar oblateness mechanism has only been explored thus far for specific Kepler systems; its effects on generic systems as different planetary variables are tuned is not well understood. In addition, while it has been put forth as a possible source for the abundance of single-transit systems, we do not know whether the stellar oblateness mechanism creates singles from multis frequently enough to reproduce that high single/multi ratio. To address this issue, I perform a suite of N-body simulations on Kepler-like systems, evolved under the influence of a star with different tilts and spin periods. I observe the final average mutual inclinations of the surviving systems, as well as the conditions under which they go unstable, and the maximum number of transiting planets observable at the end of evolution. Recent data analysis has shown that the closest-in exoplanet pairs are also the most highly mutually inclined; I demonstrate that this is a natural outcome of evolution around an oblate, tilted star. I have further found that multi-planet systems in this scenario most often come out of it with all of their planets on fairly coplanar orbits, or with very few of their planets remaining, dynamically excited to the point where only one of the few surviving planets can be observed to transit at a time. Thus, I conclude that Kepler singles are almost always truly single, sometimes with one or two hidden neighbors, very rarely more. In addition, truly single post-instability planets tend to “relax” onto lower-inclination orbits, somewhat erasing their star’s initial obliquity. This implies that modern measurements of misalignment in Kepler singles likely underrepresent the true distribution of initial stellar obliquities in the universe.

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