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ABSTRACT Title of Dissertation: WATER IN THE EARLY SOLAR SYSTEM: INFRARED STUDIES OF AQUEOUSLY ALTERED AND MINIMALLY PROCESSED ASTEROIDS Margaret M. McAdam, Doctor of Philosophy, 2017. Dissertation directed by: Professor Jessica M. Sunshine, Department of Astronomy This thesis investigates connections between low albedo asteroids and carbonaceous chondrite meteorites using spectroscopy. Meteorites and asteroids preserve information about the early solar system including accretion processes and parent body processes active on asteroids at these early times. One process of interest is aqueous alteration. This is the chemical reaction between coaccreted water and silicates producing hydrated minerals. Some carbonaceous chondrites have experienced extensive interactions with water through this process. Since these meteorites and their parent bodies formed close to the beginning of the Solar System, these asteroids and meteorites may provide clues to the distribution, abundance and timing of water in the Solar nebula at these times. Chapter 2 of this thesis investigates the relationships between extensively aqueously altered meteorites and their visible, near and mid-infrared spectral features in a coordinated spectral-mineralogical study. Aqueous alteration is a parent body process where initially accreted anhydrous minerals are converted into hydrated minerals in the presence of coaccreted water. Using samples of meteorites with known bulk properties, it is possible to directly connect changes in mineralogy caused by aqueous alteration with spectral features. Spectral features in the mid-infrared are found to change continuously with increasing amount of hydrated minerals or degree of alteration. Building on this result, the degrees of alteration of asteroids are estimated in a survey of new asteroid data obtained from SOFIA and IRTF as well as archived the Spitzer Space Telescope data. 75 observations of 73 asteroids are analyzed and presented in Chapter 4. Asteroids with hydrated minerals are found throughout the main belt indicating that significant ice must have been present in the disk at the time of carbonaceous asteroid accretion. Finally, some carbonaceous chondrite meteorites preserve amorphous iron-bearing materials that formed through disequilibrium condensation in the disk. These materials are readily destroyed in parent body processes so their presence indicates the meteorite/asteroid has undergone minimal parent body processes since the time of accretion. Presented in Chapter 3 is the spectral signature of meteorites that preserve significant amorphous iron-bearing materials and the identification of an asteroid, (93) Minerva, that also appears to preserve these materials. WATER IN THE EARLY SOLAR SYSTEM: INFRARED STUDIES OF AQUEOUSLY ALTERED AND MINIMALLY PROCESSED ASTEROIDS by Margaret M. McAdam Dissertation submitted to the Faculty of the Graduate School of the University of Maryland, College Park, in partial fulfillment of the requirements for the degree of Doctorate of Philosophy in Astronomy 2017 Advisory Committee: Professor Jessica M. Sunshine, Chair Professor Kieren T. Howard Dr. Michael S. P. Kelley Professor Karen Prestegaard Professor Derek Richardson Professor Richard Walker © Copyright by Margaret M. McAdam 2017 Dedication In memory of Dr. Michael F. A’Hearn (1940-2017), a wonderful colleague and mentor. ii Acknowledgements I am grateful for the support and mentorship of my adviser, Jessica Sunshine as well as my committee members Derek Richardson and Michael Kelley. Thank you for your collaboration and the answers to my questions over the last six years. To Tim McCoy, Kieren Howard and Conel Alexander, thank you for the great scientific discussions, edits on my papers and guidance. I would also like to recognize the support and friendship of the Comet Group, especially Matthew Knight, Silvia Protopapa, Sam Crossley, and Carrie Holt. Thanks for all the chocolate! To Ron Ballouz, thanks for being a great officemate! I wish to also acknowledge all of the mentors, not yet mentioned, who have been instrumental to getting me where I am today. Starting with Dr. Bruce Gordon, my high school physics and astronomy teacher. You were the first person who taught me about planetary science and made me realize that I’m supposed to be a scientist. Thank you to Darby Dyar, Joanna Levine and Rachel Klima who were some of my incredible teachers at Mount Holyoke College. You taught me so much about astronomy in addition to being some of my most meaningful role models. To Karl Hibbitts, my very first boss, thank you for teaching me how to run a lab. Also thanks to Andy Rivkin. I really appreciate all the iii beers and friendship. Finally, thank you Cari Corrigan for teaching me about meteorites and being a really inspiring scientist. In addition to my mentors I wish to acknowledge the incredible network of scientists who I have the distinct privilege of calling friends. Thank you so much Erica Jawin, Rose Smith, Leah Cheek, Lauren Jozwiak, Hannah Susorney, and Sondy Springmann for the moral and scientific support. To my family, Hugh, John and Ester, and especially my parents Bud and Terrie, you guys inspire me every day to be passionate and work hard. Thank you for all of the love and support. To the Board Game Crew, all of my wonderful friends in DC and especially Aurora Coon, Rene Zelaya, Lauren Leffer, Rebecca Wener, Robert McCafferty, Chris Higgins, Jess Bell and Seth Puckett, thank you for all the laughs, deep conversations, dinner dates and little moments. Last, but certainly not least, I’d like to recognize the incredible support and love of Mark Oscar Larson. Thank you for everything. iv Table of Contents Dedication ........................................................................................................................... ii Acknowledgements ............................................................................................................ iii List of Tables ..................................................................................................................... xi List of Figures .................................................................................................................. xiii List of Abbreviations ..................................................................................................... xviii Chapter 1: Introduction ........................................................................................................1 1.1 Asteroids, Meteorites and their Importance .............................................................. 1 1.2 Carbonaceous Chondrites: Properties, Parent Body Processing and Naming Conventions .................................................................................................................... 4 1.2.1 Primary, Distinguishing Characteristics .............................................................4 1.2.2 Aqueous Alteration .............................................................................................6 1.2.3 Thermal Metamorphism ....................................................................................14 1.2.4 Meteorite Naming Conventions and Petrologic Types .....................................15 1.3 Description of Carbonaceous Chondrite Chemical Groups .................................... 17 1.3.1 Ivuna-like Chondrites........................................................................................18 1.3.2 Renazzo-like Chondrites ...................................................................................19 1.3.3 Mighei-like Chondrites .....................................................................................20 1.3.4 Ornans-like Chondrites .....................................................................................23 1.3.5 Vigarano-like Chondrites ..................................................................................24 1.3.6 Ungrouped Carbonaceous Chondrites ..............................................................24 1.4 Asteroids: Classification and Evidence for Water .................................................. 25 1.5 Spectroscopy: Remotely Determining Surface Properties. ..................................... 31 1.5.1 Visible and Near-infrared Spectroscopy ...........................................................32 1.5.2 Mid-infrared spectroscopy ................................................................................33 v 1.5.3 Spectroscopy of Carbonaceous chondrites and C-type asteroids .....................34 1.6 Summary Thesis Objectives ................................................................................... 34 Preface to Chapter 2 ...........................................................................................................39 Chapter 2: Aqueous Alteration on Asteroids: Linking the Mineralogy and Spectroscopy of CM and CI Chondrites .......................................................................................................41 Abstract ......................................................................................................................... 41 2.1 Introduction ............................................................................................................. 42 2.2 Background ............................................................................................................. 44 2.2.1 Mineralogical Changes Associated with Aqueous Alteration ..........................44 2.2.2 Mineralogy of the Meteorite Suite ....................................................................47
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