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A Probabilistic Approach to Determination of Ceres' Average Surface Composition From Dawn Visible‐Infrared Mapping Spectrometer and Gamma Ray and Neutron Detector Data
Author(s) -
Kurokawa H.,
Ehlmann B. L.,
De Sanctis M. C.,
Lapôtre M. G. A.,
Usui T.,
Stein N. T.,
Prettyman T. H.,
Raponi A.,
Ciarniello M.
Publication year - 2020
Publication title -
journal of geophysical research: planets
Language(s) - English
Resource type - Journals
eISSN - 2169-9100
pISSN - 2169-9097
DOI - 10.1029/2020je006606
Subject(s) - chondrite , meteorite , magnetite , radiative transfer , carbon fibers , analytical chemistry (journal) , mineral , atmospheric radiative transfer codes , mineralogy , chemistry , materials science , physics , astrobiology , environmental chemistry , optics , composite material , organic chemistry , composite number , metallurgy
The Visible‐Infrared Mapping Spectrometer (VIR) on board the Dawn spacecraft revealed that aqueous secondary minerals—Mg‐phyllosilicates, NH 4 ‐bearing phases, and Mg/Ca carbonates—are ubiquitous on Ceres. Ceres' low reflectance requires dark phases, which were assumed to be amorphous carbon and/or magnetite (∼80 wt.%). In contrast, the Gamma Ray and Neutron Detector (GRaND) constrained the abundances of C (8–14 wt.%) and Fe (15–17 wt.%). Here, we reconcile the VIR‐derived mineral composition with the GRaND‐derived elemental composition. First, we model mineral abundances from VIR data, including either meteorite‐derived insoluble organic matter (IOM), amorphous carbon, magnetite, or combination as the darkening agent and provide statistically rigorous error bars from a Bayesian algorithm combined with a radiative‐transfer model. Elemental abundances of C and Fe are much higher than is suggested by the GRaND observations for all models satisfying VIR data. We then show that radiative transfer modeling predicts higher reflectance from a carbonaceous chondrite of known composition than its measured reflectance. Consequently, our second models use multiple carbonaceous chondrite endmembers, allowing for the possibility that their specific textures or minerals other than carbon or magnetite act as darkening agents, including sulfides and tochilinite. Unmixing models with carbonaceous chondrites eliminate the discrepancy in elemental abundances of C and Fe. Ceres' average reflectance spectrum and elemental abundances are best reproduced by carbonaceous‐chondrite‐like materials (40–70 wt.%), IOM or amorphous carbon (10 wt.%), magnetite (3–8 wt.%), serpentine (10–25 wt.%), carbonates (4–12 wt.%), and NH 4 ‐bearing phyllosilicates (1–11 wt.%).