Noam R. Izenberg^a, Rachel L. Klima^a, Scott L. Murchie^a, David T. Blewett^a, Gregory M. Holsclaw^b, William E. McClintock^b, Erick Malaret^c, Calogero Mauceri^c, Faith Vilas^d, Ann L. Sprague^e, Jörn Helbert^f, Deborah L. Domingue^d, James W. Head III^g, Timothy A. Goudge^g, Sean C. Solomon^h,i, Charles A. Hibbitts^a, M. Darby Dyar^j

^aPlanetary Exploration Group, The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
^bLaboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80303, USA
^cApplied Coherent Technology Corporation, Herndon, VA 20170, USA
^dPlanetary Science Institute, Tucson, AZ 85719, USA
^eLunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
^fInstitute of Planetary Research, Deutsches Zentrum für Luft und Raumfahrt, D-12489 Berlin, Germany
^gDepartment of Geological Sciences, Brown University, Providence, RI 02912, USA
^hDepartment of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA
ⁱLamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
^jDepartment of Astronomy, Mount Holyoke College, South Hadley, MA 01075, USA

The MESSENGER spacecraft’s Mercury Atmospheric and Surface Composition Spectrometer (MASCS) obtained more than 1.6 million reflectance spectra of Mercury’s surface from near-ultraviolet to near-infrared wavelengths during the first year of orbital operations. A global analysis of spectra in the wavelength range 300–1450 nm shows little regional variation in absolute reflectance or spectral slopes and a lack of mineralogically diagnostic absorptions. In particular, reflectance spectra show no clear evidence for an absorption band centered near 1 μm that would be associated with the presence of ferrous iron in silicates. There is, however, evidence for an ultraviolet absorption possibly consistent with a very low iron content (2–3 wt% FeO or less) in surface silicates and for the presence of small amounts of metallic iron or other opaque minerals in the form of nano- or micrometer-sized particles. These findings are consistent with MESSENGER X-ray and gamma-ray measurements of Mercury’s surface iron abundance. Although X-ray and gamma-ray observations indicate higher than expected quantities of sulfur on the surface, reflectance spectra show no absorption bands diagnostic of sulfide minerals. Whereas there is strong evidence of water ice in permanently shadowed craters near Mercury’s poles, MASCS spectra provide no evidence for hydroxylated materials near permanently shadowed craters.

Reference
Izenberg NR, Klima RL, Murchie SL, Blewett DT, Holsclaw GM, McClintock WE, Malaret E, Mauceri C, Vilas F, Sprague AL, Helbert J, Domingue DL, Head III JW, Goudge TA, Solomon SC, Hibbitts CA and Dyar MD (in press) The low-iron, reduced surface of Mercury as seen in spectral reflectance by MESSENGER. Icarus
[doi:10.1016/j.icarus.2013.10.023]
Copyright Elsevier

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