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The Atmospheres and Orbital Dynamics of Hot Jupiters THE ATMOSPHERES AND ORBITAL DYNAMICS OF HOT JUPITERS Matthew Pryal Archbald, Pennsylvania B.S. Astronomy & Astrophysics, Penn State University, 2015 M.S. Astronomy, University of Virginia, 2017 A Dissertation Presented to the Graduate Faculty of the University of Virginia in Candidacy for the Degree of Doctor of Philosophy Department of Astronomy University of Virginia December 2020 Committee Members: Phillip L. Arras Zhi-Yun Li Tim Bastian Ajay B. Limaye c Copyright by Matthew Pryal All rights reserved December 18, 2020 To my family and friends. Whom without, I would have finished this thesis much, much earlier. iii Abstract The detection of the first exoplanets in the early 1990s brought along many questions about their characteristics, including on their atmospheric structure and the dynam- ics of their planetary systems. One of the most puzzling types of exoplanets were the so-called `hot Jupiters.' Hot Jupiters are Jupiter sized objects, orbiting very close to their host star, that absorb a large amount of radiation, making their atmospheres very hot. Their short orbital periods and hot, extended atmospheres are some of the many characteristics that make these objects unlike any planet in our Solar System. In this thesis, I present models of the electrical conductivity of the upper atmosphere of hot Jupiters as well as the migration of hypothetical moons orbiting hot Jupiters due to tidal friction effects. In Chapter1, I give an introduction and provide context to the research outlined in the thesis. Specifically, I give an overview of the detection of exoplanets and discuss HD 189733b, the hot Jupiter at the focus of my atmosphere model. I also introduce the interaction of a stellar wind with a planet's magnetosphere which is central to- wards setting the current that can run through the atmosphere, which is then affected by the atmosphere's electrical conductivity. Finally, I overview the dynamics of star- planet-moons systems and tidal friction as it relates to the hypothetical moons of hot Jupiters. In Chapter2, I detail the star-planet interaction between the charged particles of the stellar wind with a planetary magnetic field that set the current in the atmosphere. Importantly, the electrical conductivity of the atmosphere governs the rate at which the charged particles can flow and release energy into the atmosphere through col- lisions. I also review the formulas for electrical conductivity of an atmosphere and discuss the collision rates between charged particles and other species of the atmo- sphere which is then implemented into the HD 189733b atmosphere model in Chapter 3. In Chapter3, I present a hydrostatic model of the dayside upper atmosphere of hot Jupiter HD 189733b. With this model I compute its electrical conductivity and conductance, which determines the amount of energy that can be transferred to the atmosphere through Joule heating. I find that the conductance of hot Jupiters is much greater than the conductance of the Earth, and therefore Joule heating does not significantly impact the thermal structure of the atmosphere for Jupiter sized magnetic fields (B ∼ 10 G). Finally, in Chapter4, I examine the orbital migration of hypothetical moons of hot iv Jupiters. I find that, even in the case of synchronous rotation and circular orbits of the moon, gravitational perturbations from the star create a forced eccentricity in the moon that makes tidal friction never cease. This tidal friction then causes the inward migration of the moon towards the planet where it can be tidally disrupted. In the case of hot Jupiter systems, this inward migration is fast enough to explain the lack of large moons detected orbiting hot Jupiters. Additionally, I place an upper limit on the mass of moons that are able to survive this orbital migration effect within 5 Gyr, to be many orders of magnitude smaller than the mass of the Earth's moon. v Acknowledgements My love for Astronomy began in a ninth grade Earth and Space Science class, that I was warned by my older siblings was taught by a `crazy alien guy' { who I would later find out preferred to go by Mr. Durkin. Over the course of that class, I realized that Mr. Durkin's `craziness,' was actually child-like wonder and passion for a science that can be appreciated by anyone simply by looking up at the night sky. Unknown to him, Mr. Durkin's passion was passed to me, and over my years in Astronomy, I realized that I wanted to become that `crazy alien guy' for others. It is truly unbelievable to think how much Mr. Durkin's passion about Astronomy has impacted my path in life { taking me from a four bedroom house in tiny Archbald, PA (at one time shared by 10 people!), to Penn State University, and Rome, on cross country trips, to the University of Virginia, and Hawaii and somehow to the stars and back. I urge everyone to embrace the passions in your life and share them with as many people as you can. You never know how much of an impact your passion can have on others. At each milestone I reach in my life, I can't help but think of all the little things that those in my life have taught me to get me to where I am. Grad school has admittedly been emotionally hard. The year 2020 has been especially stressful. But with everything I've been taught by family and close friends, we've been able to reach this finish line together. Thank you to my Mom and Dad for filling me with love and being proud of me every step of the way. For teaching me empathy, kindness, how to deal with sadness, and embrace my passions. Thanks, to my siblings Bridget, Sarah, Robbie, Lizzy, and Emma for teaching me how to be a family. To learn how to deal with anger (don't punch walls), to be more outgoing, to love unconditionally, and handle disagreements. One of the few good things about growing up, has been becoming closer to all of you each and every year and I can't wait for our relationships to continue to grow. Being the first person in my family to get a Ph.D., I can't help but think of my Grammie, Grampie, Grandma, and Grandpa. Thank you for creating a better life for all those around you and laying the groundwork for your loved ones to be able to dream big today. My thanks to my family could extend forever but since acknowledgements are supposed to be shorter than the thesis, I'll just say thank you to rest of my extended family for making my life as full as it can be. Thanks to my Brohana, my cohort, old Charlottesville friends, and the rest of those at UVA and in Charlottesville for making my time in grad school fun. Thanks for grilling and chilling, having tailgates, chatting around a fire, for going to Nelly's or Escaf´e,going to basketball games, playing poker, for Foxfield, and Raven banquets, for Festy and for everything else in between. Grad school would have been unbearable without all of you in it. Thank you to the Awesome Astronomy Enthusiasts of 2015 and everyone else at vi Penn State for teaching me that life's about 8 things and 8 things only. For being a bunch of nerds who embraced our shared weirdness, for really knowing how to have fun, and for always saying hi to me in the elevator. Integrity. Thank you to my NEPA friends for being a part of some of the most fundamental parts of my life and for effectively helping me grow up { although I wouldn't say we're there yet, and I'm not sure if we'll ever quite make it. Thanks to my thesis committee and thesis advisor Phil for making my research as great as it could be over the past 5.5 years. And to the rest of the UVA and Penn State Astronomy departments { thanks for your kindness and support along the way. And a special thanks to all those who I've had the pleasure of doing outreach with over the years. Especially to all the members of Dark Skies, Bright Kids, Astronomy on Tap - C'ville, those at the Science Museum of Virginia, and everyone else. You've helped make the journey worthwhile and I certainly would have been much crazier without you in my life. And last, but certainly not least (except in physical size) { thank you Molly for making one of the most stressful parts of my life, somehow the happiest. I was only able to get to this finish line because of your support these past few years. I eagerly await any stressful days ahead, as long as we're facing them together. Also, feather. With love, The other crazy alien guy Table of contents List of Figures xiv List of Tables xvi 1 Introduction1 1.1 Exoplanets.................................1 1.1.1 The Discovery of Exoplanets...................2 1.1.2 The Detection of Exoplanets...................3 1.1.3 Hot Jupiters............................9 1.2 The Upper Atmosphere of HD 189733b................. 11 1.2.1 Spectroscopic Observations of Exoplanet Atmospheres.... 12 1.2.2 Chemical Species in the Atmosphere of Hot Jupiters...... 13 1.2.3 Upper Atmosphere Models of Hot Jupiters........... 15 1.3 Planetary Magnetospheres and Ionospheres............... 16 1.3.1 Overview............................. 17 1.3.2 The Solar Wind and Magnetic Reconnection.......... 18 1.4 The Dynamics of Star-Planet-Moon Systems.............. 20 1.4.1 Introduction............................ 22 1.4.2 The Lack of Moons in the Inner Solar System........
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