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Brucite and carbonate assemblages from altered olivine-rich materials on Ceres


The dwarf planet Ceres is the largest object in the asteroid belt, and is generally thought to be a differentiated body composed primarily of silicate materials and water ice1,2. Some remotely observed features, however, indicate that Ceres may instead have a composition more similar to that of the most common types of carbonaceous meteorite3,4,5,6,7. In particular, Ceres has been shown to have a distinct infrared absorption feature centred at a wavelength of 3.06 μm that is superimposed on a broader absorption from 2.8 to 3.7 μm (refs 58), which suggests the presence of OH- or H2O-bearing phases. The specific mineral composition of Ceres and its relationship to known meteorite mineral assemblages, however, remains uncertain. Here we show that the spectral features of Ceres can be attributed to the presence of the hydroxide brucite, magnesium carbonates and serpentines, a mineralogy consistent with the aqueous alteration of olivine-rich materials. We therefore suggest that the thermal and aqueous alteration history of Ceres is different from that recorded by carbonaceous meteorites, and that samples from Ceres are not represented in existing meteorite collections.

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Figure 1: Linear mixing model results for the near-infrared reflectance spectrum of Ceres.
Figure 2: Linear mixing model results for the mid-infrared reflectance spectrum of Ceres.
Figure 3: Reflectance spectra of representative C1 and C2 carbonaceous chondrites.


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This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. We also acknowledge support from RELAB at Brown University, the NASA Planetary Astronomy Program and the Infrared Telescope Facility, which is operated by the University of Hawaii under Cooperative Agreement no. NCC 5-538 with the NASA Planetary Astronomy Program.

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R.E.M. was responsible for writing most of the text and the spectral modelling. A.S.R. contributed to the text, acquired and provided the near-infrared spectrum of Ceres and assisted with interpretation of the results.

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Correspondence to Ralph E. Milliken.

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Milliken, R., Rivkin, A. Brucite and carbonate assemblages from altered olivine-rich materials on Ceres. Nature Geosci 2, 258–261 (2009).

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