Graduation Semester and Year

2009

Language

English

Document Type

Thesis

Degree Name

Master of Science in Physics

Department

Physics

First Advisor

Manfred Cuntz

Abstract

We provide a detailed statistical study of the ejection of Earth-mass planets from the habitable zones of the solar twins HD 20782 and HD 188015. These systems possess a giant planet that crosses into the stellar habitable zone, thus effectively thwarting the possibility of habitable Earth-mass planets. In the case of HD 188015, the orbit of the giant planet is essentially circular, whereas in the case of HD 20782, it is extremely elliptical. As starting positions for the giant planets, we consider both the apogee and perigee position, whereas the starting positions of the Earth-mass planets are widely varied. For the giant planets, we consider models based on their minimum masses as well as models where the masses are increased by 30%. Our simulations indicate a large range of statistical properties concerning the ejection of the Earth-mass planets from the stellar habitable zones. For example, it is found that the ejection times for the Earth-mass planet from the habitable zones of HD 20782 and HD 188015, originally placed at the center of the habitable zones, vary by a factor of ∼200 and ∼1500, respectively, depending on the starting position of the giant and Earth-mass planets. If the mass of the giant planet is increased by 30%, the variation in ejection time for HD 188015 increases to a factor of ∼6000. As a further application of this thesis, we also challenge the customary assumption that the entering of an Earth-mass planet into the Hill Radius (or multiples of the Hill Radius) of a giant planet is a valid is a valid criterion for its ejection from the star-planet system This assumption has been widely used in previous studies, especially those with an astrobiological focus. It has been found from our study that even though the Earth-mass planets are eventually ejected from the habitable zones of both star systems, the '“Hill Radius Criterion” is identified as invalid for the prediction of when the ejection is actually occurring.

Disciplines

Physical Sciences and Mathematics | Physics

Comments

Degree granted by The University of Texas at Arlington

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