Computer Science
Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt........50b&link_type=abstract
Thesis (PhD). MASSACHUSETTS INSTITUTE OF TECHNOLOGY, Source DAI-B 61/01, p. 311, Jul 2000, pages.
Computer Science
49
Scientific paper
Visible wavelength spectra have been obtained for 1189 main-belt asteroids during the second phase of the Small Main-belt Asteroid Spectroscopic Survey. These telescopic measurements were made using charge-coupled device (CCD) detectors, allowing for the targeting of smaller asteroids. A majority of the asteroids sampled have estimated diameters of 30 km or less. The SMASSII survey provides the largest internally-consistent sample of asteroid spectra ever obtained, and reveals a greater range of spectral diversity among asteroids than has been previously shown. The larger sample size, greater spectral resolution, and greater photometric precision of the SMASSII survey, compared with the most extensive previous survey, provide a basis for developing a new ``feature-based'' taxonomic classification system for asteroids. This new taxonomy builds on the robust, large-scale structure of existing taxonomies, and relies on the presence or absence of specific spectral features to define new class boundaries. The SMASSII measurements reveal that many of the previous taxonomic classes that appeared to be distinctly separate, are instead spanned by a nearly continuous transition of spectral properties. This continuum may be evidence of sampling a more complete range of mineralogies. A subset of 465 SMASSII asteroids were specifically targeted to test the genetic reality of small dynamical ``families.'' These families likely result from the collisional disruption of larger parent asteroids, and are identified as clusters of objects having similar orbital parameters. The targeted region, encompassing the heliocentric distance range of 2.690 to 2.815 AU, contains 14 families that had been previously identified, based on numerous analyses of orbital distributions in this region of the main belt. A newly developed multivariate technique that analyzes the combination of spectral characteristics and orbital parameters reveals that all 14 of these previously proposed families are distinct from the ``background'' population of asteroids. This result implies that each of these families is likely to have been truly formed by a collisional event, providing strong evidence for an extensive collisional history within the asteroid belt. C- and S-type asteroids appear equally capable of forming families. Each family is found to be relatively homogeneous in its spectral characteristics, allowing the boundaries of the families, and potential interlopers, to be more precisely identified than was possible in previous dynamical analyses. The relative spectral homogeneity within each of these families provides little evidence for any to have been formed from a differentiated parent body. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139- 4307. Ph. 617-253-5668; Fax 617-253-1690.) (Abstract shortened by UMI.)
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