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Spectral reflectance “deconstruction” of the Murchison CM2 carbonaceous chondrite and implications for spectroscopic investigations of dark asteroids

Cloutis, Edward A. and Pietrasz, Valerie B. and Kiddell, Cain and Izawa, Matthew R. M. and Vernazza, Pierre and Burbine, Thomas H. and DeMeo, Francesca E. and Tait, Kimberly T. and Bell, James F., III and Mann, Paul and Applin, Daniel M. and Reddy, Vishnu (2018) Spectral reflectance “deconstruction” of the Murchison CM2 carbonaceous chondrite and implications for spectroscopic investigations of dark asteroids. Icarus, 305 . pp. 203-224. ISSN 0019-1035. http://resolver.caltech.edu/CaltechAUTHORS:20180205-095316304

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Abstract

Carbonaceous chondrites (CCs) are important materials for understanding the early evolution of the solar system and delivery of volatiles and organic material to the early Earth. Presumed CC-like asteroids are also the targets of two current sample return missions: OSIRIS-REx to asteroid Bennu and Hayabusa-2 to asteroid Ryugu, and the Dawn orbital mission at asteroid Ceres. To improve our ability to identify and characterize CM2 CC-type parent bodies, we have examined how factors such as particle size, particle packing, and viewing geometry affect reflectance spectra of the Murchison CM2 CC. The derived relationships have implications for disc-resolved examinations of dark asteroids and sampleability. It has been found that reflectance spectra of slabs are more blue-sloped (reflectance decreasing toward longer wavelengths as measured by the 1.8/0.6 µm reflectance ratio), and generally darker, than powdered sample spectra. Decreasing the maximum grain size of a powdered sample results in progressively brighter and more red-sloped spectra. Decreasing the average grain size of a powdered sample results in a decrease in diagnostic absorption band depths, and redder and brighter spectra. Decreasing porosity of powders and variations in surface texture result in spectral changes that may be different as a function of viewing geometry. Increasing thickness of loose dust on a denser powdered substrate leads to a decrease in absorption band depths. Changes in viewing geometry lead to different changes in spectral metrics depending on whether the spectra are acquired in backscatter or forward-scatter geometries. In backscattered geometry, increasing phase angle leads to an initial increase and then decrease in spectral slope, and a general decrease in visible region reflectance and absorption band depths, and frequent decreases in absorption band minima positions. In forward scattering geometry, increasing phase angle leads to small non-systematic changes in spectral slope, and general decreases in visible region reflectance, and absorption band depths. The highest albedos and larger band depths are generally seen in the lowest phase angle backscattering geometry spectra. The reddest spectra are generally seen in the lowest phase angle backscatter geometry spectra. For the same phase angle, spectra acquired in forward scatter geometry are generally redder and darker and have shallower absorption bands than those acquired in backscatter geometry. Overall, backscatter geometry-acquired spectra are flatter, brighter, and have deeper 0.7 µm region absorption band depths than forward scatter geometry-acquired spectra. It was also found that the 0.7, 0.9, and 1.1 µm absorption bands in Murchison spectra, which are attributable to various Fe electronic processes, are ubiquitous and can be used to recognize CM2 chondrites regardless of the physical properties of the meteorite and viewing geometry.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.icarus.2018.01.015DOIArticle
https://www.sciencedirect.com/science/article/pii/S0019103517306711PublisherArticle
ORCID:
AuthorORCID
Bell, James F., III0000-0002-2006-4074
Additional Information:© 2018 Elsevier Inc. Received 18 September 2017, Revised 5 January 2018, Accepted 10 January 2018, Available online 4 February 2018. The University of Winnipeg's HOSERLab was established with funding from the Canada Foundation for Innovation, the Manitoba Research Innovations Fund and the Canadian Space Agency, whose support is gratefully acknowledged. This study was supported by research grants from NSERC, the Canadian Space Agency, the Hatch foundation, and the University of Winnipeg. Thanks to Ian Nicklin, and Brendt Hyde at the Royal Ontario Museum for providing the Murchison sample at the heart of this study. Support for this work was also provided by the Remote, In Situ, and Synchrotron Studies for Science and Exploration (RIS4E) node of NASA's Solar System Exploration Research Virtual Institute.
Funders:
Funding AgencyGrant Number
Canada Foundation for InnovationUNSPECIFIED
Manitoba Research Innovations FundUNSPECIFIED
Canadian Space Agency (CSA)UNSPECIFIED
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Hatch FoundationUNSPECIFIED
University of WinnipegUNSPECIFIED
NASAUNSPECIFIED
Subject Keywords:Meteorites; Spectroscopy; Regoliths
Record Number:CaltechAUTHORS:20180205-095316304
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180205-095316304
Official Citation:Edward A. Cloutis, Valerie B. Pietrasz, Cain Kiddell, Matthew R.M. Izawa, Pierre Vernazza, Thomas H. Burbine, Francesca DeMeo, Kimberly T. Tait, James F. Bell III, Paul Mann, Daniel M. Applin, Vishnu Reddy, Spectral reflectance “deconstruction” of the Murchison CM2 carbonaceous chondrite and implications for spectroscopic investigations of dark asteroids, Icarus, Volume 305, 1 May 2018, Pages 203-224, ISSN 0019-1035, https://doi.org/10.1016/j.icarus.2018.01.015. (https://www.sciencedirect.com/science/article/pii/S0019103517306711)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84673
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:05 Feb 2018 21:04
Last Modified:05 Feb 2018 21:04

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