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Constraints on Mercury’s surface composition from MESSENGER and ground-based spectroscopy

Warell, Johan and Sprague, Ann and Kozlowski, Richard and Rothery, David and Lewis, N and Helbert, Jörn and Cloutis, Ed (2010) Constraints on Mercury’s surface composition from MESSENGER and ground-based spectroscopy. Icarus: International Journal of Solar System Studies, 209 (1), pp. 138-163. Elsevier. DOI: 10.1016/j.icarus.2010.04.008.

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Abstract

The composition and chemistry of Mercury’s regolith has been calculated from MESSENGER MASCS 0.3-1.3 μm spectra from the first flyby, using an implementation of Hapke’s radiative transfer-based photometric model for light scattering in semi-transparent porous media, and a linear spectral mixing algorithm. We combine this investigation with linear spectral fitting results from mid-infrared spectra and compare derived oxide abundances with mercurian formation models and lunar samples. Hapke modeling results indicate a regolith that is optically dominated by finely comminuted particles with average area weighted grain size near 20 μm. Mercury shows lunar-style space weathering, with maturation-produced microphase iron present at ˜0.065 wt.% abundance, with only small variations between mature and immature sites, the amount of which is unable to explain Mercury’s low brightness relative to the Moon. The average modal mineralogies for the flyby 1 spectra derived from Hapke modeling are 35-70% Na-rich plagioclase or orthoclase, up to 30% Mg-rich clinopyroxene, <5% Mg-rich orthopyroxene, minute olivine, ˜20-45% low-Fe, low-Ti agglutinitic glass, and <10% of one or more lunar-like opaque minerals. Mercurian average oxide abundances derived from Hapke models and mid-infrared linear fitting include 40-50 wt.% SiO2, 10-35 wt.% Al2O3, 1-8 wt.% FeO, and <25 wt.% TiO2; the inferred rock type is basalt. Lunar-like opaques or glasses with high Fe and/or Ti abundances cannot on their own, or in combination, explain Mercury’s low brightness. The linear mixing results indicate the presence of clinopyroxenes that contain up to 21 wt.% MnO and the presence of a Mn-rich hedenbergite. Mn in M1 crystalline lattice sites of hedenbergite suppresses the strong 1 and 2 μm crystal field absorption bands and may thus act as a strong darkening agent on Mercury. Also, one or more of thermally darkened silicates, Fe-poor opaques and matured glasses, or Mercury-unique Ostwald-ripened microphase iron nickel may lower the albedo. A major part of the total microphase iron present in Mercury’s regolith is likely derived from FeO that is not intrinsic to the crust but has been subsequently delivered by exogenic sources.

Document Type:Article
Title:Constraints on Mercury’s surface composition from MESSENGER and ground-based spectroscopy
Authors:
AuthorsInstitution or Email of Authors
Warell, JohanDepartment of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden
Sprague, AnnLunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721-0091, USA
Kozlowski, RichardDepartment of Physics, Susquehanna University, 514 University Avenue, Selinsgrove, PA 17870, USA
Rothery, DavidDepartment of Earth and Environmental Sciences, The Open University, Milton Keynes MK7 6AA, UK
Lewis, NLunar and Planetary Laboratory, University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721-0091, USA
Helbert, Jörnjoern.helbert@dlr.de
Cloutis, EdDepartment of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, Manitoba, Canada
Date:September 2010
Journal or Publication Title:Icarus: International Journal of Solar System Studies
Refereed publication:Yes
In Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:209
DOI:10.1016/j.icarus.2010.04.008
Page Range:pp. 138-163
Publisher:Elsevier
Status:Published
Keywords:Merkur, Mineralogie
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 - Vorhaben BepiColombo
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Terahertz and Infrared Sensors
Deposited By: Dr.rer.nat. Jörn Helbert
Deposited On:09 Jan 2012 14:18
Last Modified:20 Mar 2013 19:44

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