Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p43e..06i&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P43E-06
Mathematics
Logic
[5410] Planetary Sciences: Solid Surface Planets / Composition, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [6235] Planetary Sciences: Solar System Objects / Mercury
Scientific paper
Since entering orbit about Mercury in March 2011, the MESSENGER spacecraft has taken over 750,000 globally distributed surface reflectance spectra at wavelengths from the near ultraviolet (UV) to the near infrared (NIR) (320-1450 nm), with the Visible-Infrared Spectrometer (VIRS) channel of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS). Most geologic and geographic regions and units of the planet have been observed during the first Mercury solar day. We have generated an average disk-resolved spectrum of Mercury and average spectra for a number of spectral type examples and geologic units across the planet. From these data, we have derived a set of comparative parameters to aid in the discrimination and interpretation of spectral variations observed in the MASCS data. These include commonly used indicators such as albedo and NIR slope, as well as new parameters developed to quantify UV-visible spectral variations including spectral slope over 320-380 nm, relative difference between UV and NIR slopes, and inflection point and curvature in the UV. VIRS spectra of Mercury globally show a "red" slope; i.e., an increase in reflectance with wavelength, and lack clear absorption features near 1 mm typically associated with Fe2+-bearing silicates. The lack of this absorption feature, combined with X-Ray Spectrometer (XRS) data, supports a low-iron surface composition (2-3 wt% FeO) for Mercury. At UV and visible wavelengths, in contrast, features attributable to oxygen-metal charge transfer (e.g., a relatively steeper downturn in reflectance at wavelengths shorter than 400 nm) are associated with a variety of relatively young features possibly less affected by space weathering than elsewhere. These include crater rays, bright materials associated with "hollows" on materials exhumed from depth, and pyroclastic deposits. Fresh crater ejecta, rays, and material associated with hollows are brighter than average plains, less steeply sloped at NIR wavelengths, and much more steeply sloped in the near-UV. Candidate pyroclastic deposits in some crater interiors and surrounding rimless depressions appear brighter and more steeply sloped in the NIR but also exhibit a shallower slope into the UV. Other units and regions distinguished by color contrast and morphology as seen in Mercury Dual Imaging System (MDIS) image mosaics differ more subtly from the global average. For example, the northern hemisphere of Mercury has, on average both a slightly (3.5%) higher reflectance than the southern hemisphere and a somewhat redder slope into the NIR.
Blewett Dave T.
Domingue Donovan L.
Gillis-Davis Jeffery J.
Head James W.
Helbert Jérôme
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