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Vesta Surface Dark Material Deposits from Dawn Observations: A Working Hypothesis for Origin and Processes

McCord, T.B. and Combe, J-Ph. and Jaumann, R. and Palomba, E. and Reddy, V. and Blewett, D.T. and McSween, H.Y. and Williams, D.A. and Raymond, C.A. and Russell, C.T. and The Dawn, Team (2012) Vesta Surface Dark Material Deposits from Dawn Observations: A Working Hypothesis for Origin and Processes. In: 39th COSPAR Scientific Assembly. EGU 2012, 22.04-27.04.2012, Wien, Österreich.

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Abstract Observations from the Dawn spacecraft [1] revealed surface dark mate-rial deposits (DMD). Their geological context (small, well-defined and often associated with impact features) and basic compositional nature (pyroxene evidence everywhere but more subdued in DMD) is reported [2]. We synthe-size these reports and present a working hypothesis for explaining the origin of and processes affecting these DMD [3]. DMD are strongly influenced by impact mixing and gardening. Many DMD appear as chunks or layers out-cropping in crater walls, uncovered, broken and tossed about by the impact process. Some impacts have excavated DM and spread it as ejecta. There are also large regions of low-albedo surface material, often with indistinct boundaries, that appear to include DM [3]. These may be older and better mixed (DM into background material) than the smaller deposits, perhaps from a larger or more extensive event. We modeled VIR spectra of DMD to show that they all may represent intimate and/or macroscopic mixtures of only two endmember materials. Most or all regions on Vesta can be modeled as a linear mixture of a bright, pyroxene-rich soil and a darker material with varying reddish color [3]. The main hypotheses for DM origin, identified so far are: 1) low velocity infall from objects containing DM, 2) basalt flows, dikes or sills on/in Vesta that are disrupted and redistributed by impacts, and 3) impact melt from major cratering events. From the imagery, there is no conclusive evidence of basalt flows, and evidence of basaltic intrusions is equivocal. In addition, it is difficult to understand how a Vesta-like object could retain sufficient heat to create secondary melting and near-surface extrusion of lava late enough in Vesta’s evolution that the flows or major pieces of them would survive the impact history. On the other hand, there is morphological evidence of impact melt deposits that appear darker on Vesta. This would be expected, given the apparent active impact history of Vesta, which must have included some higher-velocity impactors. Infall origin for some material also seems probable. Surely, dark material from carbonaceous chondrite (CC) objects, especially from the outer parts of the asteroid belt and from comets, must strike Vesta’s surface and at lower-velocities than for, say, the Moon, resulting in preservation of major fractions of the impac-tor material. Further, the spectrum for the DMD endmember, derived above, is similar to that for CC material and for organic-rich material in the outer solar system in general. The infall explanation is also supported by certain howardite meteorites, breccias thought representative of the regolith of Vesta that contain clasts of carbonaceous chondrite material within a matrix of pyroxene-rich basaltic material [e.g., 4]. References: [1] Russell and Raymond, 2011, Space Sci. Rev., 163, pp. 3-23, DOI 10.1007/s11214-011-9836-2; [2] Jaumann et al.; Reddy et al; Palomba et al., 2012, LPSC 43, and in this session. [3] McCord et al., 2012, LPSC 43. [4] McSween et al., 2012, LPSC 43.

Item URL in elib:https://elib.dlr.de/80367/
Document Type:Conference or Workshop Item (UNSPECIFIED)
Title:Vesta Surface Dark Material Deposits from Dawn Observations: A Working Hypothesis for Origin and Processes
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
McCord, T.B.Bear Fight Institute, Winthrop WA, USAUNSPECIFIED
Combe, J-Ph.Bear Fight Institute, Winthrop WA, USAUNSPECIFIED
Jaumann, R. ralf.jaumann (at) dlr.deUNSPECIFIED
Palomba, E.Institute for Interplanetary Space Physics - INAF, Rome, ItalyUNSPECIFIED
Reddy, V.Max Planck Institute for Solar System Research , Katlenburg-Lindau, GermanyUNSPECIFIED
Blewett, D.T.Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USAUNSPECIFIED
McSween, H.Y.University of Tennessee, Knoxville, TN, USAUNSPECIFIED
Williams, D.A.Arizona State UniversityUNSPECIFIED
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:July 2012
Journal or Publication Title:39th COSPAR Scientific Assembly
Open Access:No
Gold Open Access:No
In ISI Web of Science:No
Keywords:Vesta, Dawn
Event Title:EGU 2012
Event Location:Wien, Österreich
Event Type:international Conference
Event Dates:22.04-27.04.2012
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: Aydin, Zeynep
Deposited On:09 Jan 2013 10:53
Last Modified:09 Jan 2013 10:53

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