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Ambient and cold-temperature infrared spectra and XRD patterns of ammoniated phyllosilicates and carbonaceous chondrite meteorites relevant to Ceres and other solar system bodies

Ehlmann, Bethany L. and Hodyss, Robert and Bristow, Thomas F. and Rossman, George R. and Ammannito, Eleonora and De Sanctis, M. Cristina and Raymond, Carol A. (2018) Ambient and cold-temperature infrared spectra and XRD patterns of ammoniated phyllosilicates and carbonaceous chondrite meteorites relevant to Ceres and other solar system bodies. Meteoritics and Planetary Science, 53 (9). pp. 1884-1901. ISSN 1086-9379. doi:10.1111/maps.13103.

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Mg‐phyllosilicate‐bearing, dark surface materials on the dwarf planet Ceres have NH_4‐bearing materials, indicated by a distinctive 3.06 μm absorption feature. To constrain the identity of the Ceres NH_4‐carrier phase(s), we ammoniated ground particulates of candidate materials to compare their spectral properties to infrared data acquired by Dawn's Visible and Infrared (VIR) imaging spectrometer. We treated Mg‐, Fe‐, and Al‐smectite clay minerals; Mg‐serpentines; Mg‐chlorite; and a suite of carbonaceous meteorites with NH_4‐acetate to exchange ammonium. Serpentines and chlorites showed no evidence for ammoniation, as expected due to their lack of exchangeable interlayer sites. Most smectites showed evidence for ammoniation by incorporation of NH_4^+ into their interlayers, resulting in the appearance of absorptions from 3.02 to 3.08 μm. Meteorite samples tested had weak absorptions between 3.0 and 3.1 μm but showed little clear evidence for enhancement upon ammoniation, likely due to the high proportion of serpentine and other minerals relative to expandable smectite phases or to NH_4^+ complexing with organics or other constituents. The wavelength position of the smectite NH4 absorption showed no variation between IR spectra acquired under dry‐air purge at 25 °C and under vacuum at 25 °C to −180 °C. Collectively, data from the smectite samples show that the precise center wavelength of the characteristic ~3.05 μm v_3 absorption in NH_4 is variable and is likely related to the degree of hydrogen bonding of NH_4‐H_2O complexes. Comparison with Dawn VIR spectra indicates that the hypothesis of Mg‐saponite as the ammonium carrier phase is the simplest explanation for observed data, and that Ceres dark materials may be like Cold Bokkeveld or Tagish Lake but with proportionally more Mg‐smectite.

Item Type:Article
Related URLs:
URLURL TypeDescription
Ehlmann, Bethany L.0000-0002-2745-3240
Hodyss, Robert0000-0002-6523-3660
Bristow, Thomas F.0000-0001-6725-0555
Rossman, George R.0000-0002-4571-6884
Ammannito, Eleonora0000-0001-6671-2690
De Sanctis, M. Cristina0000-0002-3463-4437
Raymond, Carol A.0000-0002-4213-8097
Additional Information:© 2018 The Authors. Meteoritics & Planetary Science published by Wiley Periodicals, Inc. on behalf of The Meteoritical Society (MET). This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. (Received 02 June 2017; revision accepted 12 March 2018) We appreciate the work of Stephanie Meursing in acquiring the XRD data. Thanks to Allan Treiman for providing the Griffith saponite, Mark Raven for providing the nontronites, Dave Rachford for providing the IMV saponite, and Christopher Herd for providing the Tagish Lake sample. Thanks to John Beckett for facilitating use of meteorites in the Caltech collection. Robert Hodyss gratefully acknowledges funding from the NASA Astrobiology Institute (Icy Worlds). Bethany Ehlmann thanks the Dawn project for welcoming her as an affiliate and partially supporting this work. Thanks to Janice Bishop, an anonymous reviewer, Hap McSween, and Tim Jull for comments that improved this manuscript.
Group:Astronomy Department, Division of Geological and Planetary Sciences
Funding AgencyGrant Number
Issue or Number:9
Record Number:CaltechAUTHORS:20180425-144715666
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Official Citation:Ehlmann, B. L., Hodyss, R. , Bristow, T. F., Rossman, G. R., Ammannito, E. , De Sanctis, M. C. and Raymond, C. A. (2018), Ambient and cold‐temperature infrared spectra and XRD patterns of ammoniated phyllosilicates and carbonaceous chondrite meteorites relevant to Ceres and other solar system bodies. Meteorit Planet Sci, 53: 1884-1901. doi:10.1111/maps.13103
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:86046
Deposited By: George Porter
Deposited On:25 Apr 2018 22:55
Last Modified:23 Nov 2022 19:11

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