University of South Florida Scholar Commons Graduate Theses and Dissertations Graduate School 2011 The Search for the Missing Mantles of Differentiated Asteroids: Evidence from Taxonomic A-class Asteroids and Olivine- Dominated Achondrite Meteorites Michael Peter Lucas University of South Florida, [email protected] Follow this and additional works at: https://scholarcommons.usf.edu/etd Part of the American Studies Commons, Geology Commons, and the Other Astrophysics and Astronomy Commons Scholar Commons Citation Lucas, Michael Peter, "The Search for the Missing Mantles of Differentiated Asteroids: Evidence from Taxonomic A-class Asteroids and Olivine-Dominated Achondrite Meteorites" (2011). Graduate Theses and Dissertations. https://scholarcommons.usf.edu/etd/3219 This Thesis is brought to you for free and open access by the Graduate School at Scholar Commons. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. The Search for the Missing Mantles of Differentiated Asteroids: Evidence from Taxonomic A-class Asteroids and Olivine-Dominated Achondrite Meteorites by Michael Peter Lucas A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Department of Geology College of Arts and Sciences University of South Florida Major Professor: Jeffrey Ryan, Ph.D. Matthew Pasek, Ph.D. Livio Tornabene, Ph.D. Date of Approval: July 8, 2011 Keywords: asteroids, taxonomic A-class, achondrite meteorite, pallasite, ureilite Copyright © 2011, Michael Peter Lucas DEDICATION I dedicate this thesis to the memory of my cousin, Kathryn “Kate” Pokorny. ACKNOWLEDGMENTS I would like to thank the following organizations for their support of this research; the Florida Space Grant Consortium for a Space Grant Fellowship, the Geological Society of America for a Graduate Student Research Grant, the USF Geology Alumni Society for a Richard A. Davis, Jr. Fellowship, the Antarctic Meteorite Working Group for supplying eight ureilite meteorite specimens, and Tenagra Observatories, Ltd. for providing telescope time. Second, I would like to thank Michael Fauerbach of Florida Gulf Coast University for fruitful collaborations over the years, Tom Beasley of the Florida Center for Analytical Electron Microscopy for assistance on the electron microprobe, Zachary Atlas for assistance on USF’s LA-ICP-MS instrument, and Ciprian “Cosmin” Stremtan for assistance with geochemical data processing. Lastly, I would like to thank the following friends and colleagues for their support; Meghan Lindsey for encouragement and friendship over the years, Mel Rodgers for friendship and occasionally housing a “hobo”, and Nathan Collins for becoming a true friend and colleague and for putting me up at his apartment so much during my second year of graduate school, I could not have done it without you. Finally, I would like to thank my committee members for being a positive influence in my life, my major professor – Jeffrey Ryan, and committee members Matthew Pasek and Livio Tornabene. TABLE OF CONTENTS List of Tables .................................................................................................................... iii List of Figures .................................................................................................................... iv Abstract .................................................................................................................... vi Introduction ......................................................................................................................1 Where Are All of the A-class Asteroids? ................................................................1 Background ......................................................................................................................5 Evolution of Asteroid Taxonomy ............................................................................5 Physical Properties of A-class Asteroids .................................................................7 Spectral Properties of A-class Asteroids................................................................11 Olivine-Dominated Achondrite Meteorites ...........................................................15 Main Group Pallasites ................................................................................16 Ureilites ......................................................................................................16 Brachinites .................................................................................................17 Meteoritic Parent-Body Linkages for A-class Objects ..........................................18 Analytical Methodology ....................................................................................................21 Photometric Telescopic Observations....................................................................21 Differential Photometry and Lightcurve Analysis .................................................24 Asteroid Lightcurve Inversion and Shape Modeling .............................................25 Meteorite Sample Acquisition and Preparation .....................................................26 Electron Probe Microanalysis (EPMA) .................................................................28 Laser Ablation Inductively Coupled Plasma Mass Spectrophotometry (LA-ICP-MS) .............................................................29 Results ....................................................................................................................34 Taxonomic Classification and Orbital Distribution of A-class Asteroids .............34 Asteroid Lightcurves ..............................................................................................39 Shape Model of 446 Aeternitas..............................................................................42 Pallasite and Ureilite Petrology .............................................................................44 Pallasites ....................................................................................................44 Ureilites ......................................................................................................47 Major Element Cosmochemistry ...........................................................................51 Trace Element Cosmochemistry ............................................................................59 i Discussion ....................................................................................................................66 Conclusions ....................................................................................................................71 References ....................................................................................................................73 Appendices ....................................................................................................................80 Appendix A: Glossary of Astronomical Terms ....................................................81 Appendix B: Standard Element Values for Three USGS Glass Rock Standards ....................................................................................................84 Appendix C: LA-ICP-MS Analysis of Three USGS Basalt Glass Standards ....................................................................................................85 ii LIST OF TABLES Table 1: Summary of large asteroid taxonomic surveys ............................................6 Table 2: Physical properties of seventeen recognized A-class asteroids .................10 Table 3: Meteorite statistics of unpaired olivine-dominated achondrites ................15 Table 4: Observational circumstances for six A-class asteroids ..............................23 Table 5: Observational circumstances for 446 Aeternitas .......................................26 Table 6: Pallasite and ureilite meteorites acquired for analysis ...............................28 Table 7: EPMA analysis of major elements for olivine and pyroxene grains .........30 Table 8: LA-ICP-MS analysis of trace elements for pallasite olivines ....................32 Table 9: LA-ICP-MS analysis of trace elements for ureilite silicates .....................33 Table 10: Orbital elements and taxonomic classification of A-class asteroids ..........36 Table 11: Rotational periods and amplitudes for five A-class asteroids ....................40 Table 12: Parameters for the derived shape model of 446 Aeternitas .......................42 Table B1: Standard trace element values for three USGS glass rock standards .........84 Table C1: LA-ICP-MS analysis of three USGS basalt glass standards ......................85 iii LIST OF FIGURES Figure 1: The distribution of 2940 asteroids based on rotational period versus diameter ............................................................................................9 Figure 2: Deconvolved near-IR spectra for forsteritic olivine and clinopyroxene .............................................................................................11 Figure 3: Distribution of proper orbital elements for 25 olivine-dominated asteroids .....................................................................................................37 Figure 4: Composite lightcurves for five A-class asteroids ......................................41 Figure 5: Shape model of 446 Aeternitas ..................................................................43