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Effects of Temperature, Particle Size, and Petrologic Type on VNIR Spectra of Ordinary Chondrite Meteorites

Presentation #204.04D in the session “Dust, Meteoroids, Meteors”.

Published onOct 03, 2021
Effects of Temperature, Particle Size, and Petrologic Type on VNIR Spectra of Ordinary Chondrite Meteorites

Laboratory infrared spectral analysis of well-characterized meteorite samples can be employed to more quantitatively analyze asteroid remote sensing data in conjunction with returned samples. Previous work has shown the individual effects of temperature and grain size on the visible and near-infrared (VNIR) spectra of silicate and meteorite powders. In this work, we have examined the combined effects of temperature, particle size, and petrologic type on VNIR spectra of ordinary chondrite meteorites. Six equilibrated (petrologic types 4-6) ordinary chondrite meteorite falls, spanning groups H, L, and LL, were prepared at four different size fractions (25-63 μm, 63-90 μm, 90-125 μm, and 125-250 μm) to capture the spectral diversity associated with asteroid regoliths dominated by various grain sizes. VNIR spectra of the ordinary chondrite material were measured under simulated asteroid surface conditions (defined as ~10-6 mbar, -100 °C chamber temperature, and low intensity illumination) at a series of temperatures chosen to mimic near-Earth asteroid surfaces. These reflectance spectra were collected in increments of 10 °C, over the range 10 °C to 100 °C. X-ray element maps of meteorite thick sections were used to calculate the exact mineral abundances for each meteorite, in order to characterize changes in spectral features due to variations in mineralogy. The resulting VNIR spectra show minimal variation in both major absorption bands due to a simulated near-Earth asteroid temperature regime. The spectral changes due to sample grain size are systematic, with the smallest and largest grain sizes having the highest reflectance. The more petrologically pristine samples from each ordinary chondrite group display relatively shallower band depths than their more petrologically altered counterparts (Figure 1a). The band depths shift to higher wavelengths as temperature, grain size, and petrologic type increase (Figure 1b). Spectral studies of meteorites combined with detailed petrologic analysis of the samples will greatly enhance interpretation of current and future planetary remote sensing data sets. This work continues an effort to develop a comprehensive spectral library of materials relevant to airless bodies and contemporaneous asteroid missions.

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