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

1,2H. C Bates,2,3K. L. Donaldson Hanna,1A. J. King,2N. E. Bowles,1S. S. Russell
Journal of Geophysical Research, Planets (in Press) Link to Article [https://doi.org/10.1029/2021JE006827]
1Department of Earth Sciences, Natural History Museum, London, SW7 5BD UK
2Atmospheric, Oceanic and Planetary Physics, Oxford University, Oxford, OX1 3PU UK
3Department of Physics, University of Central Florida, Orlando, Florida, 32816 US
Published by arrangement with John Wiley & Sons

Volatile-rich asteroids are crucial to understanding the transport of water and organics to the terrestrial planet forming region in the early Solar System. Observations of two such asteroids by Hayabusa2 and OSIRIS-REx suggest a relationship between these bodies and CI, CM and CY chondrites. To confirm this, meteorite spectra need to be collected under appropriate conditions for comparison with asteroid observations. We report mid-infrared (MIR) emissivity spectra (5.5 – 50 µm) obtained under ambient and simulated asteroid environment conditions and near-infrared (NIR) reflectance spectra (2 ‒ 5 µm) of CM and CY chondrite fine-particulate (<35 µm) powders for which bulk mineralogy was determined using X-ray diffraction. Reflectance spectra show a 3 µm feature associated with -OH/H2O that shifts from shorter (∼2.72 µm) to longer (∼2.90 µm) wavelengths and develops a rounder shape and reduced band area with increasing thermal metamorphism. In the MIR, the transparency feature (TF) and features in the Si-O bending region (>15 µm) can be used to infer the relative degree of aqueous alteration, and to resolve the effects of aqueous and thermal alteration, when combined with NIR spectral parameters. The MIR spectra of metamorphosed CY chondrites are distinct from CM chondrite spectra, including a plateau around the Christiansen feature (∼8.00 – 12.50 µm) and features at longer wavelengths in the Si-O bending region (for example, ∼25.50 µm compared to ∼24.30 µm in the CM spectra). We additionally report potential implications of the spectra and parameters determined in this study for the results from Hayabusa2 and OSIRIS-REx.

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