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. Issue 7 (12th July 2021)

• Record Type: Journal Article
• Authors: Bates, H. C.; Donaldson Hanna, K. L.; King, A. J.; Bowles, N. E.; Russell, S. S.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 7(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-07-12
• Subjects: asteroids -- aqueous alteration -- meteorites -- spectroscopy -- thermal alteration; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2021JE006827
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: 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 Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (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 midinfrared (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/H2 O 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 (e.g., ∼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. Plain Language Summary: Some asteroids show evidence for once being exposed to water, and these bodies are thought to have contributed water to the Earth early in its evolution. We can observe some of these asteroids in our Solar System today, and a number of space missions have visited some of them with the aim of trying to find out more about their composition and history. Two of these missions, Hayabusa2 and OSIRIS‐REx, have spectrometers, which can probe the surface mineralogy of the target asteroids. We can compare the data from these spectrometers to data we collect on Earth from meteorites, which we believe come from similar types of asteroids. In this study, we collected the spectra of meteorites which have undergone a variety of alteration and hence show a variety of compositions. We tried to tie features distinguishable in the spectra to the mineralogy, which we know well, so we have an example of what causes spectra to look a specific way. We can then look at Hayuabusa2 and OSIRIS‐REx spectra and see if they share any of the same features. That can give us an indication of what mineralogy may be present on the surfaces of their target asteroids. Key Points: Parameters related to varying degrees of aqueous and thermal alteration can be identified in near‐ and midinfrared spectra of meteorites Combining observations across multiple wavelength ranges provides the most robust mineralogical determinations Spectral parameters associated with mineralogy and processing can help interpret results from Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS‐REx) and Hayabusa2 observations