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Search for sulfates on the surface of Ceres
Author(s) -
Bu C.,
Rodriguez Lopez G.,
Dukes C. A.,
Ruesch O.,
McFadden L. A.,
Li J.Y.
Publication year - 2018
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/maps.13024
Subject(s) - chemistry , anhydrous , amorphous solid , analytical chemistry (journal) , absorption (acoustics) , infrared spectroscopy , mineralogy , absorption band , materials science , crystallography , optics , environmental chemistry , organic chemistry , physics , composite material
Abstract The formation of hydrated salts is an expected consequence of aqueous alteration of Main Belt objects, particularly for large, volatile‐rich protoplanets like Ceres. Sulfates, present on water‐bearing planetary bodies (e.g., Earth, Mars, and carbonaceous chondrite parent bodies) across the inner solar system, may contribute to Ceres’ UV and IR spectral signature along with phyllosilicates and carbonates. We investigate the presence and stability of hydrated sulfates under Ceres’ cryogenic, low‐pressure environment and the consequent spectral effects, using UV –Vis– IR reflectance spectroscopy. H 2 O loss begins instantaneously with vacuum exposure, measured by the attenuation of spectral water absorption bands, and a phase transition from crystalline to amorphous is observed for Mg SO 4 ·6H 2 O by X‐ray powder diffraction. Long‐term (>40 h), continuous exposure of Mg SO 4 · nH 2 O ( n = 0, 6, 7) to low pressure (10 −3 –10 −6 Torr) causes material decomposition and strong UV absorption below 0.5 μm. Our measurements suggest that Mg SO 4 ·6H 2 O grains (45–83 μm) dehydrate to 2% of the original 1.9 μm water band area over ~0.3 Ma at 200 K on Ceres and after ~42 Ma for 147 K. These rates, inferred from an Avrami dehydration model, preclude Mg SO 4 ·6H 2 O as a component of Ceres’ surface, although anhydrous and minimally hydrated sulfates may be present. A comparison between Ceres emissivity spectra and laboratory reflectance measurements over the infrared range (5–17 μm) suggests sulfates cannot be excluded from Ceres’ mineralogy.