Forging Asteroid-Meteorite Relationships through Reflectance Spectroscopy by Thomas H. Burbine Jr. B.S. Physics Rensselaer Polytechnic Institute, 1988 M.S. Geology and Planetary Science University of Pittsburgh, 1991 SUBMITTED TO THE DEPARTMENT OF EARTH, ATMOSPHERIC, AND PLANETARY SCIENCES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN PLANETARY SCIENCES AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY FEBRUARY 2000 © 2000 Massachusetts Institute of Technology. All rights reserved. Signature of Author: Department of Earth, Atmospheric, and Planetary Sciences December 30, 1999 Certified by: Richard P. Binzel Professor of Earth, Atmospheric, and Planetary Sciences Thesis Supervisor Accepted by: Ronald G. Prinn MASSACHUSES INSTMUTE Professor of Earth, Atmospheric, and Planetary Sciences Department Head JA N 0 1 2000 ARCHIVES LIBRARIES I 3 Forging Asteroid-Meteorite Relationships through Reflectance Spectroscopy by Thomas H. Burbine Jr. Submitted to the Department of Earth, Atmospheric, and Planetary Sciences on December 30, 1999 in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Planetary Sciences ABSTRACT Near-infrared spectra (-0.90 to ~1.65 microns) were obtained for 196 main-belt and near-Earth asteroids to determine plausible meteorite parent bodies. These spectra, when coupled with previously obtained visible data, allow for a better determination of asteroid mineralogies. Over half of the observed objects have estimated diameters less than 20 k-m. Many important results were obtained concerning the compositional structure of the asteroid belt. A number of small objects near asteroid 4 Vesta were found to have near-infrared spectra similar to the eucrite and howardite meteorites, which are believed to be derived from Vesta. These asteroids appear almost certainly to be fragments of Vesta. Spectral variations between these objects are consistent with being primarily due to differences in particle size. These asteroids also tend to have stronger band depths with increasing ejection velocity from Vesta. Objects with distinctive olivine bands appear to provide definitive evidence that spectral alteration is occurring in the asteroid belt. These objects have similar band depths but appear significantly reddened relative to measured olivine samples due to their significantly higher reflectance values with increasing wavelengch. The only laboratory-simulated "weathering" process that reddens the spectra but does not significantly suppress the bands is alteration by laser irradiation, which is hoped to duplicate the effects of micrometeorite bombardment. A number of plausible main-belt parent bodies were identified. These include 19 Fortuna and the CM chondrites, Eos family members with the CO chondrites and 599 Luisa with the CV chondrites. 4 A significant fraction of S asteroids have spectral properties that range from similar to ordinary chondrites to much redder with weaker absorption bands. These objects tend to have spectra consistent with a mixture of ordinary chondrite material and metallic iron. However, other alteration processes cannot be ruled out. Asteroids with distinctive olivine bands are relatively rare. The available evidence is consistent with a scenario where, with the exception of Vesta, all differentiated bodies were either disrupted or had their mantles stripped very early in the age of the solar system. Olivine-rich metal-free fragments were then continually broken down until they almost all now fall below our current astronomical measurement limits. Thesis Supervisor: Richard P. Binzel Title: Professor of Earth, Atmospheric, and Planetary Sciences 5 This work is dedicated to my Mother, who never thought I would get into MIT, to my Father (1941-1995), who thought I would get in, and to Roger Burns (1937-1994), who got me into MIT. 6 Acknowledgements I would first like to thank my advisor Rick Binzel. He was the best advisor a person could ever have and a very good friend. He also designed the "asteroid" grism system for the Infrared Telescope Facility (IRTF) that was used to obtain the asteroid spectra in this thesis. I would also like to thank my first advisor, Roger Burns, who supported my initial research at MIT. There are so many questions that arose during this thesis that I wish I could have asked him. I would also like to thank Jim Elliot, Tim Grove and Carl6 Pieters for being on my thesis committee. My family supported (personally and financially) all my decisions that allowed me to go to MIT. Special thanks to my mother who did everything possible to help me. It is also a slightly sad time because every day I do wish that my father was still alive to see me graduate. I would also like to thank the Kamekas (LaLa and Art), who have been my friends for as long as I can remember. Numerous students, professors and staff at MIT have been very helpful during this project. Bobby Bus and Shui Xu supplied me with all their asteroid spectra from their Small Main-Belt Asteroid Spectroscopic Survey (SMASS). Sam Bowring and Mark Schmitz allowed me the use of their clean room to prepare meteorite samples. The staff at the Lindgren Library, especially Anne, Gareth, Kathy and Joe, were very helpful in my numerous searches for journals and books. The administrative assistants (Allison and Ginny) helped me considerably in travel arrangements. Courses taught by Professors Rick Binzel, Sam Bowring, Jim Elliot, Fred Frey and Tim Grove were invaluable for giving me the scientific background to work on this thesis. Many different agencies and people supported this project. NASA supplied the grant money that supported me and this research. The Meteorite Working Group loaned me numerous American Antarctic samples and the National Institute of Polar Research loaned me some Japanese ones. Joe Boesenberg at the American Museum of Natural History also loaned a number of meteorite samples. Reflectance spectra were run at the RELAB facility at Brown University by Taki Hiroi and at the Planetary Geosciences/HIGP (Hawaii Institute of Geophysics and Planetology) spectrometer facility at the University of Hawai'i by John Hinrichs and Anders Meibom. Taki also supplied me with numerous unpublished spectra. Compositional analyses of the Antarctic samples were done by Paul Buchanan at the Instrumental Neutron Activation Analysis Laboratory at Johnson Space Center using the Cameca SX-100 electron microprobe at the NASA Johnson Space Center. Paul also supplied the Macibini sample for spectral analysis. The IRTF approved our group's requests for a significant amount of observing time for SMASSIR (SMASS in the near-infrared). Mike Hicks and Dave Rabinowitz supplied me with 7 broad-band visible data for 7889 1994 LX. Mike Gaffey supplied me with his spectra of 6 Hebe and 349 Dembowska. A lot of lucky events occurred on my path to and through MIT. I met Mike Gaffey, who got me interested in asteroids, after seeing his picture in a RPI (Rensselaer Polytechnic Institute) newsletter. I picked the University of Pittsburgh as my first graduate school because of its late application deadline. Bruce Hapke allowed me to work on my own project for my Masters' thesis analyzing Jeff Bell's 52-color survey. When I wanted to leave Pittsburgh, Brian Marsden hired me part-time at the Center for Astrophysics in Cambridge to put labels on envelopes when his student worker went off mountain-climbing. Dale Graessle then gave me a full-time job there working on AXAF (Advanced X-Ray Astronomical Facility) so I could have enough money to eat and pay te rent. Roger Bums was able to then get me into MIT even though my undergraduate grades were rather low. I luckily picked Ashdown House to live, where I made almost all my friends at MIT. Tim McCoy gave me a reason to leave by helping to get me a postdoc at the Smithsonian Institution in Washington, D.C. I have made too many friends here to count. I always get into trouble when I rank people, but my three best friends here were Kevin O'Brien, Benjie Sun and Fyllio Katsavounidou. I will remember hanging out with Kevin in the Ashdown lobby, driving a9 around Boston with Benjie on his little adventures and going to concerts with Fyllio. Each of them in their own ways have made a considerable difference to my life here at MIT. I need to list the other good friends that I have made here. Some of these people I have lost touch with, but they were all good friends at one time. They include Ronak Bhatt, Brian Bowers, Juan Bruno, Emy Chen, Doug Crawford, Mario De Caro, Jenny Farver, Jennifer Han, Jennifer Healey, Jesse Hong, Rob Jagnow, Judy Kim, Dhaya Lakshminarayanan, Tom Lee, Francois Le Sellier, Bill Liteplo, Kathy Liu, Christina Manclatou, John Matz, Chi Nguyen, Lynn Qu, Vandana Sareen, Chris Spohr, Andy Tsai, Neda Vukmirovic, Rada Vukmirovic, Pat Walton, Ben Williams, Richard "Mouser" Williams, Rebecca Xiong, Lee Yang and Ruilin Zhao. I have also made numerous friends at conferences with many of them helping considerably with my thesis. These people include Tomoko Arai, Erik Asphaug, Dave Blewett, Paul Buchanan, John Hinrichs, Taki Hiroi, Dante Lauretta, Tim McCoy, Anders Meibom, Ljuba Moroz, Andy Rivkin, Jessica Sunshine and Kees Welten. Paul suggested extensive revisions for the chapter on the Vesta family. Clark Chapman, Mike Gaffey, Faith Vilas and John Wasson reviewed published papers that were incorporated into this thesis. John needs to be especially thanked for suggesting the name "Battered to Bits" for the grinding down of mantle material in the main belt. Alberto Cellino, Don Davis and Paolo Farinella were very helpful in answering specific questions that I had during this study. 8 I would like to thank everybody who I met at Ashdown House, who made my time here so enjoyable. I would especially like to thank Beth and Vernon Ingram, who do so much for the dorm.