Mid-infrared Spectroscopy of Meteorites and the Identification of Meteorite Parent Bodies, 15-R9830Printer Friendly Version
Inclusive Dates: 07/01/08 11/01/08
Background - Asteroids are remnants of the earliest materials that formed the planets, and they contain a record of processes key to understanding the formation of our solar system 4.6 billion years ago. Meteorites are pieces of asteroids on Earth that allow us to measure in detail many properties of their parent bodies. However, a fundamental problem exists in linking specific meteorites with parent bodies. To overcome this problem, scientists have made spectral measurement diagnostics of meteorites' mineralogies in the laboratory and compared those to spectra of asteroids. Unfortunately, interpretations of mid-infrared (approximately 5 to 50 µm) asteroid spectra have been hampered by inadequate spectral libraries of meteorites and analogue materials at appropriate particle sizes, as well as a lack of quantitative models with proven applicability to meteoritic/asteroidal materials. The objective of this project was to acquire new laboratory spectra of fine particulate (<65 µm) analog materials and demonstrate whether quantitative models for determining mineralogical composition and abundance from MIR spectra can be used successfully with spectra of meteorites, which contain unusual phases and which may not follow the linear mixing relations that are assumed in such models.
Approach - Mid-infrared emission spectra of a series of fine particulate minerals commonly found in meteorites were acquired in SwRI's spectroscopy laboratory. In the second task, positions of specific features observed in meteorite spectra collected by Salisbury et al. [Salisbury, J. W., et al., "Midinfrared (2.5-13.5 µm) Reflectance Spectra of Powdered Stony Meteorites," Icarus, 92, 280-297, 1991] were recorded and correlated with the meteorites' classifications and compositions in the literature. Finally, the third task tested the applicability of a linear "unmixing" algorithm to spectra of fine particulate meteorites for determining their modal mineralogies.
Accomplishments - The laboratory spectra collected represent the initiation of an effort to collect emissivity spectra of fine particulates that can be used for the quantitative analysis of mid-infrared spectra of meteorites and asteroids. The analysis of key meteorite spectral features demonstrated that in some cases features do not exhibit a consistent trend in position as a function of bulk composition, likely because weathering phases disrupt the trends. Although many classes of meteorites were successfully modeled using the linear mixing algorithms currently in use, carbonaceous chondrites were not always well modeled, probably because they include organic compounds that are not available in spectral libraries or because they mix nonlinearly. Some fine particulate meteorite spectra were not modeled well, likely because of a lack of fine particulate spectra in currently available spectral libraries used in the modeling.