An infrared reflectance study of water in outer belt asteroids: Clues to composition and origin.
AuthorJones, Thomas David.
AdvisorLewis, John S.
MetadataShow full item record
PublisherThe University of Arizona.
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.
AbstractThis study consisted of a comprehensive laboratory and telescopic investigation of H₂O distribution among the low-albedo, outer belt asteroids (2.5-5.2 AU). The water distribution was determined by surveying asteroids for the 3-μm molecular H₂O and structural OH ion absorption, the spectral signature of meteorite and asteroid hydrated silicates. Survey results were interpreted using the mid-infrared (2.5-25 μm) reflectance spectra of 16 carbonaceous chondrites and other likely asteroidal materials. The 19 asteroids observed in this program, augmented by earlier reflectance data, yielded 3-μm band depth measurements that reflect the present outer belt H₂O distribution. Of the 32 C-class asteroids in this sample, 66% have hydrated silicate surfaces, indicating a mild aqueous alteration episode early in solar system history. Strictly speaking, the C class is thus not a primitive asteroid group, but the anhydrous objects appear little altered, as do the P and D asteroid classes beyond 3.5 AU. In addition to this pronounced difference in hydration state among the outer belt classes, the C region shows a gradual decline in hydrated silicate abundance from 2.5 to 3.5 AU. This trend, coupled with the apparently anhydrous P and D surfaces, is consistent with an original outer belt asteroid composition of anhydrous silicates, water ice, and complex organic material. Early solar wind induction heating of proto-asteroids declined in intensity with heliocentric distance, and produced the observed radial decrease in hydrated silicate abundance. The mild thermal processing of the outer belt is a continuation of the intense heating and differentiation episode that occurred sunward of 2.5 AU, and both events support the induction heating mechanism. The larger outer belt inventory of volatile-rich objects may have been a significant contributor to the atmospheres of the terrestrial planets.
Degree ProgramPlanetary Sciences