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Optical Space Weathering on Vesta: Radiative-transfer Models and Dawn Observations

Blewett, D. and Denevi, B. and LeCorre, Lucille and Reddy, V. and Schröder, S.E. and Pieters, C. and Tosi, F. and Zambon, F. and Desanctis, M.C. and Ammannito, E. and Roatsch, Thomas and Raymond, C.A. and Russell, C.T. (2015) Optical Space Weathering on Vesta: Radiative-transfer Models and Dawn Observations. Icarus: International Journal of Solar System Studies. Elsevier. DOI: http://dx.doi.org/ 10.1016/j.icarus.2015.10.012 ISSN 0019-1035

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Abstract

Exposure to ion and micrometeoroid bombardment in the space environment causes physical and chemical changes in the surface of an airless planetary body. These changes, called space weathering, can strongly influence a surface's optical characteristics, and hence 2 complicate interpretation of composition from reflectance spectroscopy. Prior work using data from the Dawn spacecraft (Pieters et al., 2012) found that accumulation of nanophase metallic iron (npFe0), which is a key space-weathering product on the Moon, does not appear to be important on Vesta, and instead regolith evolution is dominated by mixing with carbonaceous chondrite (CC) material delivered by impacts. In order to gain further insight into the nature of space weathering on Vesta, we constructed model reflectance spectra using Hapke's radiative-transfer theory and used them as an aid to understanding multispectral observations obtained by Dawn's Framing Cameras (FC). The model spectra, for a howardite mineral assemblage, include both the effects of npFe0 and that of a mixed CC component. We found that a plot of the 438-nm/555-nm ratio vs. the 555-nm reflectance for the model spectra helps to separate the effects of lunar-style space weathering (LSSW) from those of CC-mixing. We then constructed ratio-reflectance pixel scatterplots using FC images for four areas of contrasting composition: a eucritic area at Vibidia crater, a diogenitic area near Antonia crater, olivine-bearing material within Bellicia crater, and a light mantle unit (referred to as an "orange patch" in some previous studies, based on steep spectral slope in the visible) northeast of Oppia crater. In these four cases the observed spectral trends are those expected from CC-mixing, with no evidence for weathering dominated by production of npFe0. In order to survey a wider range of surfaces, we also defined a spectral parameter that is a function of the change in 438-nm/555-nm ratio and the 555-nm reflectance between fresh and mature surfaces, permitting the spectral change to be classified as LSSW-like or CC-mixing-like. When applied to 21 fresh and mature FC spectral pairs, it was found that none have changes consistent with LSSW. We discuss Vesta's lack of LSSW in relation to the possible agents of space weathering, the effects of physical and compositional differences among asteroid surfaces, and the possible role of magnetic shielding from the solar wind.

Item URL in elib:https://elib.dlr.de/98836/
Document Type:Article
Additional Information:Bisher nur online erschienen.
Title:Optical Space Weathering on Vesta: Radiative-transfer Models and Dawn Observations
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Blewett, D.Johns Hopkins University Applied Physics Laboratory 11100 Johns Hopkins Rd. Laurel, MD 20723-6099, USAUNSPECIFIED
Denevi, B.Johns Hopkins University Applied Physics Laboratory 11100 Johns Hopkins Rd. Laurel, MD 20723-6099, USAUNSPECIFIED
LeCorre, LucillePSI, TucsonUNSPECIFIED
Reddy, V.Department of Space Studies, University of North Dakota, Grand Forks, ND 58202, USAUNSPECIFIED
Schröder, S.E.stefanus.schroeder (at) dlr.deUNSPECIFIED
Pieters, C.Brown University, Providence, RI, USAUNSPECIFIED
Tosi, F.INAF-IASF Istituto di Astrofisica Spaziale e Fisica Cosmica, Roma ItalyUNSPECIFIED
Zambon, F.INAF-IAPS, Via del Fosso del Cavaliere 100, I-00133 Rome, ItalyUNSPECIFIED
Desanctis, M.C.INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica, Roma, ItalyUNSPECIFIED
Ammannito, E.UCLAUNSPECIFIED
Roatsch, Thomasthomas.roatsch (at) dlr.deUNSPECIFIED
Raymond, C.A.Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109-8099, USAUNSPECIFIED
Russell, C.T.Institute of Geophysics, University of California, Los Angeles, Los Angeles, CA 90095UNSPECIFIED
Date:2015
Journal or Publication Title:Icarus: International Journal of Solar System Studies
Refereed publication:Yes
Open Access:No
In DOAJ:No
In SCOPUS:Yes
In ISI Web of Science:Yes
DOI :http://dx.doi.org/ 10.1016/j.icarus.2015.10.012
Publisher:Elsevier
ISSN:0019-1035
Status:Published
Keywords:Vesta, Space weathering
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Space Science and Exploration
DLR - Research area:Raumfahrt
DLR - Program:R EW - Erforschung des Weltraums
DLR - Research theme (Project):R - Projekt DAWN
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Planetary Geology
Deposited By: Roatsch, Dr.rer.nat. Thomas
Deposited On:17 Nov 2015 13:42
Last Modified:10 Jan 2019 15:47

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