EVIDENCE FOR A COMPOSITIONAL RELATIONSHIP BETWEEN ASTEROIDS AND METEORITES FROM INFRARED SPECTRAL REFLECTANCES Item Type text; Dissertation-Reproduction (electronic) Authors Feierberg, Michael Andrew Publisher The University of Arizona. Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 05/10/2021 16:29:15 Link to Item http://hdl.handle.net/10150/282081 INFORMATION TO USERS This was produced from a copy of a document sent to us for microfilming. While the most advanced technological means to photograph and reproduce this document have been used, the quality is heavily dependent upon the quality of the material submitted. 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ANN ARBOR, Ml 48106 8209705 Feierberg, Michael Andrew EVIDENCE FOR A COMPOSITIONAL RELATIONSHIP BETWEEN ASTEROIDS AND METEORITES FROM INFRARED SPECTRAL REFLECTANCES The University of Arizona PH.D. 1981 University Microfilms International 300 N. Zeeb Road, Ann Arbor, MI 48106 EVIDENCE FOR A COMPOSITIONAL RELATIONSHIP BETWEEN ASTEROIDS AND METEORITES FROM INFRARED SPECTRAL REFLECTANCES by Michael Andrew Feierberg A Dissertation Submitted to the Faculty of the DEPARTMENT OF PLANETARY SCIENCES In Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY In the Graduate College THE UNIVERSITY OF ARIZONA 198 1 THE UNIVERSITY OF ARIZONA GRADUATE COLLEGE As members of the Final Examination Committee, we certify that we have read the dissertation prepared by Michael Andrew Feierberg entitled Evidence for a compositional relationship between asteroids and meteorites from infrared spectral reflectances and recommend that it be accepted as fulfilling the dissertation requirement for the Degree of Doctor of Philosophy . w/M/fy Date / It. |\ Ski ta/tb/g f Date! I \ sf/J. /? % l-h '' ?/ !(?/<?( Date ~Zrj84L» |a. -ii-6) Date n .L/.&% J 3 / Date Final approval and acceptance of this dissertation is contingent upon the candidate's submission of the final copy of the dissertation to the Graduate College. I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fuxf*lling the dissertation requirement. Dissertation Director./ Date ' STATEMENT BY AUTHOR This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at the University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library. Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the copyright holder. SIGNED: ACKNOWLEDGEMENTS Dr. Harold P. Larson was the official advisor for all of the research contained in this dissertation. Portions of the research were done in collaboration with Drs. Clark R. Chapman, Michael J. Drake, and Larry A. Lebofsky. This research was supported by NASA grants NSG 7607 and NGR 03-002-332. TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS vi LIST OF TABLES viii ABSTRACT ix 1. THE METEORITE-ASTEROID CONNECTION 1 1.1 Introduction 1 1.2 Meteoritic Evidence 2 1.3 Astronomical Evidence 5 1.4 Interpretive Techniques 12 2. SPECTROSCOPIC EVIDENCE FOR UNDIFFERENTIATED S-TYPE ASTEROIDS 16 2.1 Introduction 2.2 Determinations of Silicate Compositions 20 2.3 The Diversity of S-type Asteroid Spectra 31 2.4 The Abundance of Metallic Iron 39 2.5 Discussion 44 3. SPECTROSCOPIC EVIDENCE FOR TWO ACHONDRITE PARENT BODIES 47 3.1 Introduction . 47 3.2 Compositional Analysis of New Infrared Spectra 49 3.3 Discussion 64 4. SPECTROSCOPIC EVIDENCE FOR AQUEOUS ALTERATION ON C-TYPE ASTEROIDS 72 4.1 Introduction 72 4.2 Spectral Reflectance Properties of CCMM Components 74 4.3 Compositional Analysis of Asteroid Spectral Reflectances 86 4.4 Discussion 95 5. CONCLUSIONS 98 5.1 Summary of Observational Results 98 5.2 Summary of Laboratory Calibrations 101 5.3 The Formation Locations of Asteroids and Meteorites 104 iv V TABLE OF CONTENTS—Continued Page 5.4 Implications for Other Areas of Planetary Science 108 5.5 Suggestions for Future Research HI APPENDIX A: OBSERVATIONAL TECHNIQUES 114 LIST OF REFERENCES 121 LIST OF ILLUSTRATIONS 1. A schematic view of the formation of meteorite parent bodies 2 2. Composite spectral data for three representative asteroids 10 3. Cross-sections of idealized meteorite parent bodies 19 4. The spectral reflectance of eleven S-type asteroids 21 5. Analysis of silicate compositions for three representative S-type asteroids 23 6. A plot of the composition-dependent spectral parameters of S-type asteroids 26 7. S-type spectral groups seen in 0.3-1.1 ym spectrophotometry 34 8. The effect of metallic iron on the reflectance of silicates 41 9. The spectral reflectances of 4 Vesta and two meteoritic analogs 51 10. The spectral reflectance of 349 Dembowska and two meteoritic analogs 52 11. Analysis of silicate compositions for Vesta and Dembowska 53 12. A plot of band positions for Vesta, Dembowska, and their meteoritic analogs 55 13. Time-resolved spectra of 4 Vesta 59 14. An attempt to simulate the infrared spectrum of Dembowksa 63 15. Dehydration of minerals under asteroidal conditions 77 vi vii LIST OF ILLUSTRATIONS—Continued Figure ^a9e 16. A simulation of the spectral reflectance of CCMM 80 17. The effect of low-albedo opaque minerals on the reflectance of silicates 83 18. The spectral reflectances of three low-albedo asteroids.. 87 19. A plot of 3 pm band depth versus 2.2 pm albedo for asteroids and laboratory samples 90 LIST OF TABLES Table Pa9e 1. Asteroids observed in this study.... ® 2. S-type spectral groups 32 3. Comparison of asteroid and meteorite compositions 65 4. Spectroscopic evidence for aqueous alteration products... 96 5. Summary of observational results 99 6. Summary of laboratory calibrations 102 7. List of comparison stars ^ 8. Comparison of spectroscopic and photonetric data vfit ABSTRACT High-resolution Fourier spectra in the 0.9-2.5 ym region were measured for sixteen asteroids. These data were combined with 0.3-1.1 um spectrophotometry and 3.0-3.5 urn narrowband photometry for compositional analysis. Comparison spectra of meteorites and terrestrial minerals were measured in the laboratory, some under simulated asteroidal conditions of pressure and temperature. Spectra of eleven representative S-type asteroids show a range of olivine/pyroxene ratios overlapping those of ordinary and carbonaceous chondrites, but not approaching those of common differentiated meteorite types. The reddening in the asteroid spectra implies the presence of metallic iron, but if the metal is finely divided its abundance could be low. S-type asteroids have spectra most consistent with undifferentiated compositions, and some of them, especially 8 Flora, could be ordinary chondrite parent bodies. 4 Vesta and 349 Dembowska are unusual asteroids which have spectra resembling those of achondritic meteorites. Vesta has a pyroxene-feldspar mineralogy intermediate in composition between eucrites and howardites. If shergottite-like basalts are present, they must be in low abundance. Dembowska has an olivine-pyroxene mineralogy similar in some ways to ordinary chondrites, but there is considerable ix X evidence that it is actually a fragment of the mantle of a differentiated Vesta-like parent body. The most diagnostic spectral feature seen on three low-albedo asteroids is the 3 ym band due to water of hydration, 1 Ceres must consist mostly of a low-iron clay mineral with some hydrated salts. 2 Pallas has a low abundance of hydrated minerals relative to Ceres, with the bulk of its composition being anhydrous iron-free silicates. 324 Bamberga probably contains clay minerals, but its spectrum is dominated by abundant magnetite. These and other C-type asteroids have surface compositions consistent with massive aqueous alteration of primary carbonaceous chondrite minerals. These results all indicate that the compositions of main belt asteroids are more closely related to the compositions of meteorites than was previously believed.