Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p23d..06h&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P23D-06
Mathematics
Logic
[5410] Planetary Sciences: Solid Surface Planets / Composition, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [5494] Planetary Sciences: Solid Surface Planets / Instruments And Techniques, [6235] Planetary Sciences: Solar System Objects / Mercury
Scientific paper
Reflectance spectroscopy at ultraviolet wavelengths is a valuable remote sensing tool for studying the chemical makeup of planetary surfaces. The MESSENGER spacecraft instrument payload includes the Mercury Atmospheric and Surface Composition Spectrometer (MASCS), which contains the Ultraviolet and Visible Spectrometer (UVVS), capable of acquiring point-reflectance spectra from the far to near ultraviolet (115-350 nm). The first disk-integrated reflectance spectrum of Mercury at middle-ultraviolet wavelengths (220-300 nm) was obtained by MASCS-UVVS during the first flyby of the planet on 14 January 2008. A comparison of this spectrum with the reflectance of the Moon obtained with the same instrument showed that an inflection, interpreted as a volume absorption due to an electronic charge-transfer between oxygen and a transition-metal cation, was present in the Mercury data but absent in the lunar spectrum. Given the intense space weathering environment at Mercury, it was expected that such volume absorptions might be obscured by even small amounts of nanophase metallic iron within vapor-deposited coatings. During the second Mercury flyby on 6 October 2008, several spatially resolved middle-ultraviolet spectra were acquired. These spectra were found to have spectral characteristics similar to those of the disk-integrated spectrum. However, it was not possible to discern subtle spectral variations because of the spatial-spectral coupling of the data. The UVVS operates as a scanning-grating monochromator. Consequently, during acquisition of a spectrum (obtained one wavelength at a time) the instrument field of view is carried across the planet’s surface by spacecraft motion. Therefore, variations in albedo, composition, maturity, topography, and shadowing all contribute to structure in the spectrum. During MESSENGER’s third flyby of Mercury on 29 September 2009, a specialized observing strategy was implemented. From multispectral images obtained during the previous encounters, a number of specific targets were selected on the basis of specific spectral and geologic properties. The selected targets include examples of relatively immature material exposed by impacts, the low-reflectance end-member color unit, and mantling deposits hypothesized to be pyroclastic in origin. The spacecraft actively tracked these targets (spatially fixing the field of view) while spectra were obtained by MASCS-UVVS. In this way, the spectral features can more closely be linked to composition and maturity.
Blewett Dave T.
Denevi Brett Wilcox
Domingue Donovan L.
Holsclaw Gregory M.
Izenberg Noam R.
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