Constraints on the surface composition of Trojan asteroidsfrom near infrared (0.8-4.0 μm) spectroscopy and spectral modeling

Persistent Link:
http://hdl.handle.net/10150/280170
Title:
Constraints on the surface composition of Trojan asteroidsfrom near infrared (0.8-4.0 μm) spectroscopy and spectral modeling
Author:
Emery, Joshua P.
Issue Date:
2002
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.
Abstract:
The present surface composition of primitive objects provides clues to understanding the conditions under which the solar system formed. Characterization of the inner solar nebula progresses rapidly due to remote studies of asteroid and planetary surfaces as well as laboratory analyses of meteorites and lunar samples. Because of their atypical orbital position at 5.2 AU, the Trojan asteroids hold the potential to help resolve several problems in planetary science, including conditions in the early solar nebula. The study presented herein was undertaken in order to uncover the nature of these poorly understood asteroids. Near-infrared reflectance spectra are presented over the wavelength range 0.8-4.0 μm. These observations nearly double the number of published 0.8-2.5 μm spectra of Trojans and provide the first systematic study of the L-band (2.8-4.0 μm) region for these distant asteroids. The spectra do not contain any definitive absorption features characteristic of surface composition (e.g. H₂O, organics, silicates) as seen on main-belt asteroids and several Centaur and Kuiper Belt objects. These data are combined with previously published data to construct spectra covering the visible and near-IR (0.3-4.0 μm) for as many objects as possible. The composite spectra are analyzed quantitatively using the formulation for scattering in a particulate medium developed by Hapke. Under this rigorous examination, it is found to be unlikely that the red spectral slope is a result of organics on the surfaces, due mainly to the lack of absorptions in the L-band. These surfaces are compatible with mixtures of anhydrous silicates and carbonaceous material. Upper limits are placed on the amount of water ice and hydrated silicates present on the surfaces. Similar analysis is performed for several other groups of dark solar system objects. Comparison of these results with those for Trojan asteroids indicates that it is likely that the Trojans formed in the solar nebula near 5 AU. If this is true, then the determination that the red slope is probably not due to organic material does not fit with the generally accepted view of trends of composition with heliocentric distance. Implications and possible alternative explanations are discussed.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Physics, Astronomy and Astrophysics.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Planetary Sciences
Degree Grantor:
University of Arizona
Advisor:
Brown, Robert H.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleConstraints on the surface composition of Trojan asteroidsfrom near infrared (0.8-4.0 μm) spectroscopy and spectral modelingen_US
dc.creatorEmery, Joshua P.en_US
dc.contributor.authorEmery, Joshua P.en_US
dc.date.issued2002en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © 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.en_US
dc.description.abstractThe present surface composition of primitive objects provides clues to understanding the conditions under which the solar system formed. Characterization of the inner solar nebula progresses rapidly due to remote studies of asteroid and planetary surfaces as well as laboratory analyses of meteorites and lunar samples. Because of their atypical orbital position at 5.2 AU, the Trojan asteroids hold the potential to help resolve several problems in planetary science, including conditions in the early solar nebula. The study presented herein was undertaken in order to uncover the nature of these poorly understood asteroids. Near-infrared reflectance spectra are presented over the wavelength range 0.8-4.0 μm. These observations nearly double the number of published 0.8-2.5 μm spectra of Trojans and provide the first systematic study of the L-band (2.8-4.0 μm) region for these distant asteroids. The spectra do not contain any definitive absorption features characteristic of surface composition (e.g. H₂O, organics, silicates) as seen on main-belt asteroids and several Centaur and Kuiper Belt objects. These data are combined with previously published data to construct spectra covering the visible and near-IR (0.3-4.0 μm) for as many objects as possible. The composite spectra are analyzed quantitatively using the formulation for scattering in a particulate medium developed by Hapke. Under this rigorous examination, it is found to be unlikely that the red spectral slope is a result of organics on the surfaces, due mainly to the lack of absorptions in the L-band. These surfaces are compatible with mixtures of anhydrous silicates and carbonaceous material. Upper limits are placed on the amount of water ice and hydrated silicates present on the surfaces. Similar analysis is performed for several other groups of dark solar system objects. Comparison of these results with those for Trojan asteroids indicates that it is likely that the Trojans formed in the solar nebula near 5 AU. If this is true, then the determination that the red slope is probably not due to organic material does not fit with the generally accepted view of trends of composition with heliocentric distance. Implications and possible alternative explanations are discussed.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectPhysics, Astronomy and Astrophysics.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplinePlanetary Sciencesen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorBrown, Robert H.en_US
dc.identifier.proquest3073216en_US
dc.identifier.bibrecord.b43428046en_US
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