Linear Modeling of Spectra of Fine Particulate Materials: Implications for Compositional Analyses of Primitive Asteroids
Earth and Space Science 9:3 (2022)
Abstract:In this study, we applied a sum to one constraint weighted least squares (STO WLS) model to thermal infrared (TIR) spectra of a suite of primitive asteroid analogs spectrally and volumetrically dominated by fine particulates (<38 μm). Since coarse particulate emissivity spectra combine linearly, deriving compositions from these are fairly straightforward. Across the TIR it is not as straightforward for fine particulate emissivity spectra due to the nonlinear behavior that arises from volumetric scattering between particles when the particle size becomes comparable to the wavelength of light. Using a WLS model, mixed spectra may be deconvolved into areal percentages of each end member which we assume corresponds to their volume percentages. We used a spectral library of pure mineral spectra to model TIR spectra of a suite of physical mixtures and meteorites obtained under ambient (Earth-like) and simulated asteroid environment (SAE) conditions collected for the OSIRIS-REx team (Donaldson Hanna et al., 2021, https://doi.org/10.1029/2020JE006624). The STO WLS model underestimated the modal abundances of the dominant mineral phases by ∼25.0 ± 0.1% on average over the full spectral range and ∼22.0 ± 0.4% over a limited spectral range in all of the ambient and SAE physical mixture and meteorite spectra. Minor phases present in the mixtures and meteorites (abundances ≤5%) were typically not modeled. Also, phases not present in the mixtures were commonly selected (∼2 phases on average with an average abundance of ∼25.2 ± 1.9%) to get the best mathematical fit.
Tracing the earliest stages of hydrothermal alteration on the CM chondrite parent body
METEORITICS & PLANETARY SCIENCE 56:9 (2021) 1708-1728
A Spectral Investigation of Aqueously and Thermally Altered CM, CM-An, and CY Chondrites Under Simulated Asteroid Conditions for Comparison With OSIRIS-REx and Hayabusa2 Observations
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS 126:7 (2021) ARTN e2021JE006827
Christiansen Feature Map From the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment: Improved Corrections and Derived Mineralogy
Journal of Geophysical Research: Planets 126:6 (2021)
Abstract:Maps of plagioclase, olivine, and pyroxene at 1 km resolution are derived from a combination of data from the Diviner Lunar Radiometer on the Lunar Reconnaissance Orbiter and the Kaguya Multiband Imager. The Diviner instrument features three infrared bands designed to characterize a spectral feature of lunar soils that is sensitive to the average silica polymerization of the surface called the Christiansen Feature, which is directly sensitive to the presence of plagioclase, the dominant lunar silicate. Existing global mineral maps based on near-IR data largely infer the presence of plagioclase from the bright mineral’s effect on total reflectance, excepting in rare locations where the surface is nearly pure plagioclase and a weak feature in the plagioclase near-IR spectrum can be relied upon. By integrating both wavelength regions we produced more robust estimates of the abundance of the three dominant minerals. In the process of this work, we also improved the removal of space weathering effects from Christiansen Feature maps, and showed that silica rich compositional anomalies could be reliably detected by decorrelating Christiansen Feature and FeO maps. New silica-rich locations are reported as are the global abundances of the three major silicates.
Updates to the Oxford Space Environment Goniometer to measure visible wavelength bidirectional reflectance distribution functions in ambient conditions
Review of Scientific Instruments AIP Publishing 92:3 (2021) 034504