Mineralogical analysis of the Oppia quadrangle of asteroid (4) Vesta: Evidence for occurrence of moderate-reflectance hydrated minerals

Journal
Date Issued
2015
Author(s)
•
•
Combe, J. -Ph.
•
•
•
Ammannito, E.
•
•
Hoffmann, M.
•
Nathues, A.
•
Garry, W. B.
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Blewett, D. T.
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Pieters, C. M.
•
•
Stephan, K.
•
McFadden, L. A.
•
McSween, H. Y.
•
Russell, C. T.
•
Raymond, C. A.
DOI
Description
Acknowledgments This work was supported by the Italian Space Agency (ASI), ASI-INAF Contract I/004/12/0. The authors thank the Dawn Science, Operation and Instrument Teams for a successful Dawn at Vesta mission. D.T. Blewett received support from the NASA Dawn at Vesta Participating Scientist program. The VIR instrument was developed under the leadership of INAF, Italys National Institute for Astrophysics, Rome. The instrument was built by SELEX-Galileo, Florence, Italy. We thank Jennifer Scully and Sharon Uy for their assistance in revising the manuscript. Dawn datasets are publicly available at the Planetary Data System Small Bodies Node ( http://pdssbn.astro.umd.edu/ ).
Abstract
Quadrangle Av-10 ‘Oppia’ is one of five quadrangles that cover the equatorial region of asteroid (4) Vesta. This quadrangle is notable for the broad, spectrally distinct ejecta that extend south of the Oppia crater. These ejecta exhibit the steepest (‘reddest’) visible spectral slope observed across the asteroid and have distinct color properties as seen in multispectral composite images. Compared to previous works that focused on the composition and nature of unusual (‘orange’) ejecta found on Vesta, here we take into account a broader area that includes several features of interest, with an emphasis on mineralogy as inferred from data obtained by Dawn’s Visible InfraRed mapping spectrometer (VIR). Our analysis shows that the older northern and northeastern part of Av-10 is dominated by howardite-like material, while the younger southwestern part, including Oppia and its ejecta blanket, has a markedly eucritic mineral- ogy. The association of the mineralogical information with the geologic and topographic contexts allows for the establishment of relationships between the age of the main formations observed in this quadran- gle and their composition. A major point of interest in the Oppia quadrangle is the spectral signature of hydrous material seen at the local scale. This material can be mapped by using high-resolution VIR data, combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features. Hydrated mineral phases studied previously on Vesta gener- ally correlate with low-albedo material delivered by carbonaceous asteroids. However, our analysis shows that the strongest OH signature in Av-10 is found in a unit west of Oppia, previously mapped as ‘light mantle material’ and showing moderate reflectance and a red visible slope. With the available data we cannot yet assess the presence of water in this material. However, we offer a possible explanation for its origin.
Volume
259
Start page
129
Uri
Url
Issn Identifier
0019-1035
Ads BibCode
2015Icar..259..129T
Rights
open.access
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